ORNL-TM-2712.txt

ORNL-TM-2712

Contract No. W-T405-eng-26

Reactor Division

FEASIBILITY STUDY OF REMOTE CUTTING AND WELDING
FOR NUCLEAR PLANT MAINTENANCE

Peter P. Holz

 

- LEGAL NOTICE

This Teport was prepared ag an account of Government spomsored work. Neither the United
States, nor the Commission, nor any persan acting on behalf of the Commission:

A, MaKes any warranty or reprcsn.nuticn.pxpr.:sued or implied, with reapect @ the acou-
racy, complieteness, oF usefulness of the fnfurmation contained io this report, or vhat the use
of any information, apparatus, methed, or process dlsclosed In this report may not infringe
privately owned rights; or

B. Assumes any liabilities with respect to the use «of, or for damagea resulting from the
use of any {aformatian, apparatus, method, OF Process disclosed in this report.

Au used in the above, ‘‘persen acting on bepalf of the Commission" includes any em-
ployee or cantractor of the Commission, ar ampiovee ol such contractor, o the extent that
guch employee or rontractor of the Commission, or ¢mployee of such contraclor prepires,
disseminates, T provides access to, any information pursaant o his employment oT contract
with the Cemmissgion, or his employment with such contracior,

 

 

 

 

e ————————

NOVEMBER 1969

OAK RIDGE NATIONAL LABORATORY
Oak Ridge, Tennessee
cperated by
UNION CARBIDE CORPORATION
for the
U.S. ATOMIC ENERGY COMMISSION

DISTRLI TN o D

LT UNLTMOTED

 
1ii

CONTENTS

ABSTRACT .
ACKNOWLEDGMENTS .

SECTION A
1. MAINTENANCE PHILOSOPHY .
1.1 Introduction .
1.2 Approaches to Maintenance.
l.2.1 Some Examples of Maintenance Methods.
1.3 Remote Maintenance Considerations.
1.3.1 Eguipment Location for Maintenance.
l.3.2 Mechanical Joint Consideraticns .
1.3.3 Welded Joint Closure Considerations .
2. HISTORY OF REMOTE WELDING .
2.1 Background .
2.2 The Pennsylvania Advanced Reactor Program.
2.3 The Atomics International Program.
2.4 State of the Art Survey .
2.5 Survey Findings-
2.6 Continued Need for Remote Welding Development.

3. THE SELECTION OF A SYSTEM TO BE DEVELOPED FOR
REMOTE MAINTENANCE. C e e e e e e e

3.1 "Orbital-Vehicle'" System Advantages.
3.2 Future System Expansion and Modification Plans .
3.2.1 Development of Additional Modules .

3.2.2 Alternate Carriage for Seal-Weld Capability .

3.2.35 Development of Special Features for
Nuclear System Applications .
SECTION B
4. PRESENT PROGRAM STATUS.
4.1 General.

L.2 ORNL's Prototype Automated Remote Cutting and
Welding System for 6 and 8-in. Pipes . .

L.2.1 Carriage.
4.2.2 Universal Machining Head.

-~ O O OV O W W

Moot e
H P O O O O

-
)

15
15
15
15

16

17
17

L7
18
18
iv

L.2.3 Universal Welding Heuad.
L.2.4 Welding Programmer and Control Unit
L.2.5 Power Supply.

L.2.6 Equipment Modifications for Remote Work .

MACHINING STUDIES .

5.1
5.2
5.3
5.4
D5

General.

Equipment Evaluation .

Tooling.

Machining Feeds and Speeds . . . . . . . . . . <

Machining Techniques for Slitting and Beveling Pipes;
Pipe End Preparation Requirements for Welding.

WELDING STUDIES .

6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9

General.

Preweld Joint Cleaning .

Joint Fitup Tolerance.

Inert Shield Gas

Electrode Configuration.
Automatic Arc Voltage Control.
Pre-Weld Positioning .

Root Pass.

Fill Passes.

6.10 Repair Welding .
SPECTAL ORBITAL EQUIPMENT MAINTENANCE REQUIREMENTS.

T.1

7.2
7-3
7.4
7.5

Carriage

7.1.L Drive Rollers .
T.1.2 1Idlers.
Electrical Items .
Milling Head .
Welding Head

General.

SECTION C

PROGRAM PROPOSAL: DEVELOPMENT OF REMOTE CUTTING, WELDING
AND INSPECTION EQUIPMENT FOR REACTOR SYSTEM MAINTENANCE .

8.1

Overall Requirements for Remote Cut/Weld Maintenance

18
25
25
28
28
28
30
30
31

L6
8.2 A Long-Range, Three-Phase Development Program for
Pipe and Vessel Maintenance. e e e

8.2.1 Phase I, The General Program.
8.2.2 Phase II, The Pipe Joint Program.
8.2.3 Phase III, The Vessel Closure Program .

bt

& & 4
FEASIBILITY STUDY OF REMOTE CUTTING AND WELDING
FOR NUCLEFAR PLANT MAINTENANCE

Peter P. Holz

ABSTRACT

When reactors and related systems require maintenance
and repairs on highly radicactive components, there is an
ilmportant need for remotely controlled equipment to remove
and replace parts of the nuclear systems. Remote cutting
and welding can be valuable technigues for component replace-
ment as well as for sealing flanges and vessel closures.
Welding offers very attractive advantages: Jjoints can be
made leaktight, joint configurations require less cell space
than flanged Jjoints; and the locations of joints can be
changed comparatively easily, if necessary.

In seeking equipment which could be adapted to remotely
controlled operation for reactor maintenance, ORNL selected
the Air Force "orbital vehicle" cut-and-weld system as
currently being most promising for further development to
meet nuclear system requirements. The concept of an orbital
vehicle equipment system for automated pipe work originated
in 1964 at the Rocket Propulsion Laboratory of the Air Force
Systems Command at Edwards Air Force Base. The development
of this system was performed in conjunction with North American
Rockwell Corporation, Los Angeles Division, who designed,
built and tested initial models. ORNL has started to modify
and adapt the orbital design for completely remote work
applications.

The orbital system includes a carriage, interchangeable
modules for machining or tungsten-arc welding, a weld programmer,
and a conventional power supply. The working unit is quite
compact, about 4 in. thick in radial dimension x 10 1/2 in.
long, designed to be clamped around a pipe.

To date, we have completed the detailed drawings for
fabrication of the prototype orbital system and have procured
all the components for initial non-nuclear tests of the
equipment. We have demonstrated the following operations
by remote control methods that were generally satisfactory:
clamping of the carriage on the pipe, cutting and beveling
with one orbital head, changing heads, and performing filler
pass welding opergtions. We noted that nearly perfect pipe
Joint preparation and alignment were required to achieve
acceptable root pass welding without the addition of weld
inserts. These requirements wesre the most difficult to
meet with the orbital equipment, and root pass welding gave
the most trouble. However, an alternate method of root pass
welding gave good results when joining surfaces were machined
to provide extra metal on one inside pipe edge and were given
a fusion welding without filler wire on the root pass. These
weldments showed full penetration and excellent, even bead
shape all the way around the pipe. In all cases, the subse-
quent filler passes were made easily and were of good quality.
Since welding variables such as travel speed, current, wire
feed rate, arc voltage, and arc control voltage all affect
weld quality, it was cbserved during the tests that weld
defects could often be detected as they occurred by noting
the pips on recorder chart traces.

The report describes factors involved in radioactive
system maintenance, summarizes some previous work on remote
maintenance development, and explains how the automated
orbital cutting and welding machinery system may overcome
problems that have been encountered in nuclear repair work.
Progress of the feasibility study to date is summarized,
including descriptions of the prototype equipment and the
results of machining and welding tests. The report describes
additional requirements for development to provide fully
remote operations and controls and proposes a long range
program for development of a complete remote maintenance
system for radicactive system equipment replacement by
cutting and welding.

 

ACKNOWLEDGMENTS

The author acknowledges with thanks the excellent cooperation and
assistance of the Permanent Tube Joint Technology Section of the Air
Force Rocket Propulsion lLaboratory, Alr Force Systems Command, Edwards,
California. The project engineer, Captain John L. Feldman, USAF, and
his staff, particularly Mr. Edward H. Stein and Lt. Albert B. Spencer,
USAF, all have done an outstanding job in supplying requested technical
information and data. C. Bruce Deering of the AEC's Oak Ridge Operations
Site Office provided liaison between AEC and the Air Force. Carl M.
Smith, Jr., gave invaluable day to day assistance with equipment design,
development, shakedown and checkout, and William A. Bird and Robert L.
Moore gave important help with trouble-shocting and refining of the
electronics and instrumentation. E. L. Armstrong, W. F. Cartwright,

T. Ray Housley, Dunlap Scott, G. M. Slaughter, Irving Spiewak, T. K.
Walters, and L. C. Williams provided valuable guidance and support.
Special thanks glso to W. E. Thompson for his assistance in editing
this report, and to others, unlisted for brevity, who contributed in
many ways .
SECTION A

1. MAINTENANCE PHILOSOPHY
1.1 Introduction

In the design, development, and testing of molten salt reactors at
the Ozk Ridge National Laboratory, the need for remote welding equipment
was encountered. However, the development of reactor designs which in-
clude provisions for maintenance by remote welding logically reguires
that a welding process be proven feasible before the design studies are
completed. Similarly, the capabllity for remote welding must be fully
developed before a large reactor is designed con the basis of maintenance
methods which require remote welding. The potential of remote welding
for saving time in replacing reactor system components and for producing
more reliable joints and seals was recognized, and feasibility studies
of remote welding were started as part of the Molten Salt Reactor Program.
From discussions of remote maintenance with the designers, builders, and
operators of other reactors, it has become clear that the special welding
equipment and techniques that have been devised on many occasions for
specific repalr or replacement Jobs are not generally applicable. There
is strong interest in a portable, remotely controlled welding system
that would be generally applicable in reactor maintenance and repair
work. A reliable, automated system to produce high-quality welds, even
without remote controls, would be welcomed by the reactor builders, who
report considerable difficulty in obtaining qualified welders and in
achieving acceptable weld quality on field work at the construction site.
Use of automated systmes for construction welding would also give confi-
dence and experience which would help the application of remotely control-
led units in maintenance and repair work.

The problems of maintenance and repair on reactor systems after
operation has built up the radiation levels are important and widespread--
no reactor is immune. The need for remote welding equipment has been
recognized by reactor designers, builders and operators; but, to date
there is no remote welder that can be used for general pipe and seal
welding applications, although special purpose devices have been em-
ployed for some reactor maintenance Jjobs.

Automatic welding equipment is being used today for many appli-
cations. Some of the automatic welding methods and equipment seem
well suited to development for remote welding. In particular, an auto-
mated pipe-welding apparatus developed by North American Aviation for
the Air Force showed promise for remote control applications in nuclear
reactor systems.

In all reactor systems maintenance must be performed by some method
whenever the need arises. If it could be accomplished with reliability
at reasonable cost, completely remote maintenance would be preferred,
because, it reduces personnel radiation exposures and simplifies the
problems of decontamination prior to undertaking the maintenance opera-
tions. Remote welding offers great promise for general application in
that almost any part of a reactor system which might fail can be cut out
and replaced if equipment is availuble for remote cutting and rewelding.

With first-of-a-kind reactors, i1t 1s necessary to test the designs
using mock-ups of the more complicated systems and components. If, at
this stage, the ability to perform remote maintenance can be tested on
the mock-ups, the final design can ve demonstrated to be functionally
sound and capable of being maintained. The satisfactory performance of
remote handling devices and techniques can be proved in mock-up tests,
giving increased confidence in thelir reliability and providing training
in maintenance techniques which will reduce downtime.

It is recognized that provisions for remote control removal and re-
placement of all components of a reactor system would be prohibitively
expensive. In practice, therefore, the degree of ease provided to accom-
plish remote maintenance depends upon the anticipated frequency of main-
tenance on each component. A reactor vesel designed for a 30-year
maintenance-free life will hopefully require no remote maintenance equip-
ment. Punps, valves, cold traps and other items which fail or need main-
tenance more frequently may justify rather elaborate remote control
devices to speed up and make more reliable the operations of maintenance
and replacement. If portable remote welding equipment can be proved
workable, even already-built reactors not designed for remote maintenance
may receive many of the benefits.

In October 1968, a draft of the "Code for Inservice Inspection of
Nuclear Reactor Coolant Systems” was developed under the sponsorship of
the American Society of Mechanical Engineers and the AEC. The Committee
which prepured the draft of the Code noted that "recognition was given
to the problems of examining radiocmctive areas where human access is im-
possible, and provisions are incorporated in the Code for the examination
of such areas by remote means which are not yet fully developed.” The
Code clearly shows that welds are considered to be of prime importance
amont the areas requiring inspection. The general need for remote cutting
and welding equipment which can repair flaws disclosed by the inspections
is given emphasis by the criteria speiled out in the Code.

1.2 Approaches to Maintenance

Components which failed or developed trouble after radioactivity
levels had built up have been repaired in many reactors. The methods
employed in making repairs have invariably been make-shift in terms of
equipment, techniques and procedures because standard equipment for re-
mote maintenance is not available. There seem to have been two general
approaches to reactor system maintenance: Where possible, flooding with
water has been used to provide radiation shielding while still allowing
visibility and mobility. In other cases portable or temporary shields,
usually lead, have been employed to protect workers who must enter
radiation fields. The methods have been combined at times.
1.2.1 Some Examples of Maintenance Methods

 

The Gas-Cooled Reactor Experiment in Idaho was floocded with water
and repaired by divers working underwater to break and remake flange
Jjoints in replacing sections of two cooling water lines. Two divers
worked 112 hours in making the repairs. No welding was involved.
Radiation exposures were about 400 to 600 mr for the workers' bodies
and about 50% more for their hands .}

Divers were also used in making repairs to the core support plate
and the fuel channels of the Big Rock Point boiling water reactor. This
work involved bolting pieces in place and not welding. Later, repair
work on the thermal shield of the same reactor was performed underwater
with long~handled tools and television viewing. At this time, the radia-
tion levels had increased, during additional reactor operation, to the
point where the use of divers again could not be considered. The under-
water maintenance operations involved some machining work and included
seal welding of all nuts and keepers.2’®

The Dresden-1 boiling water reactor experienced a number of cracks
in welds which were repaired by direct work from behind a lead shield
with a lead pipe to protect the worker's hand and arm. By having just
a small hole in the lead pipe to allow movement of the welding head,
workers were protected as much as possible during their working time
inside the radiation zone. Even so, more than 50 welders had to be
called upon so that no person would have to work in the radiation field
long enough to receive an overexposure to radiation.*’®

On the BONUS boiling water, nuclear superheat reactor, Oak Ridge
supplied a welder to work on the superheater steam piping. With some
water shielding and a lead box for the worker, welds were made directly
on the tubes.®

The boiling water reactor of the Oyster Creek Nuclear Power Plant
was found to have cracks in field welds on the tubes for the control rod
drives.’ Fortunately the cracks were discovered before the reactor had
been operated. Nevertheless a one-year delay resulted from the time re-
quired to diagnose the problem and its extent and to prepare to make the
necessary repairs, even though remote control operations were not neces-
sary. Similar cracks have been found, also before operations started,
in the boiling water reactors for the Nine-Mile Point Power Plant of
Niagara Mohawk and the Tarapur Nuclear Power Station in India. Had these
cracks not been discovered before operations started, the job of fixing
them would have involved long shut-downs.

For work on the calandria of the Sodium Graphite Reactor, Atomics
International developed a remotely controlled cutting and welding system.
Bench tests were promising for specialized welding on the SGR calandris,
which the remote welder was specifically designed to fit; however, the
reactor project was terminated and the equipment was never used in a
radiation field.®
A remote welder was rented from Atomics International to make weld
repairs on the tube-~to-tube sheet welds of the steam generator of the
Fermi sodium-cooled, fast reactor. This machine was used to make 1200
welds, taking 45 sec per tube.9’°

The Dounreay Fast Reactor developed a small leak in a sodium coolant
outlet pipe near the reactor vessel. The reactor was down for one year
to locate and repair the leak.'! The cutting of the leaking section was
done directly using a lead shield, but a special remote welding gadget
was designed and built for rewelding the pipe.lg:13 Welders received
their three months' radiation exposure limit in six hours' working time.
Problems were encountered in cbtaining skilled welders to do the job.

The Hallam sodium-graphite reactor used an automated remotely con-
trolled welder inside a hot cell to seal weld the containers for spent
fuel elements. Manipulators are used to operate the remote welding
apparatus.t®

1.3 Remote Maintenance Considerations

In general, radiocactive reactor system components are interconnected
with large pipes which must be disconnected and rejoined when components
are replaced. Also large vessel access openings must be opened for in-
spection and replacement of internals and then resealed. Flanges with
mechanical seals and remote welding are two possible methods of rejoining
pipe or closing vessel openings. Some of the considerations which affect
the choice of the approcach are given below. More detailed discussions on
weld Jjoint maintenance are included in Section B.

1.3.1 Equipment Location for Maintenance

 

To be best suited for remote maintenance, reactor components and
piping should be physically located so as to permit access from above
for removal and replacement operations. This, however, imposes rather
severe restrictions on layout since it virtually eliminates stacking of
equipment within a cell. Therefore, if cell space savings from stacking
of components are to be achieved, consideration must be given tQ the pre-
dicted frequency of maintenance on any specific assembly of piring and
components so that the most frequently worked-on assemblies will be placed
in the most readily accessible locations. The designer thus provides
unrestricted overhead access on a first priority basis for the components
needing maintenance on a regularly scheduled basis, and then provides
access for anticipated "trouble area' work. When this has been done,
remote methods can be employed most effectively to reduce the cost and
increase the reliability of maintenance operations.

1.3.2 Mechanical Joint Considerations

 

a. All reactor system Joints must be leak-tight to prevent the
outleakage of coolant and radioactivity or the in-leakage of
external gases which might contaminate the contained fluid.
Furthermore, scme of the reactor coolants become very corrosive
when exposed to atmospheric oxygen or moisture. An inert gas
buffer between the gas or liguid in the pipes and the atmosphere
is sometimes employed, at slightly higher pressure, to assure
that mechanical joints are effectively leak tight. Since this
seal is so important for the integrity of the system, the equip-
ment which maintains the overpressure must be extra reliable.

Any mechanical seal requires large forces to keep the sealing
surfaces in contact during all excursions of system tempera-
ture and pressure. As an example, the so0lid metal seals which
use rings in grooves require a certain minimum force to main-
tain the seal. Additional strength is needed to resist the
axial and bending stresses transmitted through the pipe. There
are acceptable clamping and bolting methods for providing this
strength where the Jjoint is not subjected to large thermal
stresses which deform the ring seal, or to high temperatures
which might anneal the clamps. Unfortunately, the higher
temperatures (1000 to 1500°F) of advanced reactor systems make
satisfactory bolting or clamping a difficult problem.

In high-radiation fields, the flanged joints must be operated

and maintained by remote means. There are problems of operating
bolts or bulky clamps by remote control, of removing the component
without damaging the joint, inspecting and cleaning the precision
seal surfaces, installing the polished ring undamaged, instal-
ling the new component, aligning the joint, remaking the clamp,
and leak checking the seal. Some of these problems would be
encountered in remote welding, also. When a mechanical Jjoint
leaks, the maintenance crew has a choice of repair by tightening
the joint or by replacing the ring with one plated with a soft
metal such as gold.

For replacement by welding or by flanged connections, all joints
connecting the component into the system must be in proper align-
ment before bolting or clamping. Warpage during the thermal
cycling that occurs in any plant may require awkward placement

of the Jjoint and a complicated installation sequence as the new

" component is brought into the final position. The changes in

previously established locations will require careful measure-
ment by remote means to determine the exact location of the in-
cell joint so that adjustments can be made to align the new
component. A mechanical joint does not permit much margin for
error in alignment and fitting after the component is in the
cell, whereas with a welded joint, in-cell machining of mating
surfaces could be used to correct certain misalignments.

1.3.3 Welded Joint Closure Considerations

8.

In joining pipes, welding can be used either to provide a full
strength, full penetration welded joint, or to provide a seal
around a gasketed flange joint. Most full-strength weld

closures require multi-pass welds which are difficult to make.
Yet these all-welded joints, to be leaktight, must be metal-
lurgically sound. dJoint alignment, purge gas, weld arc, and
weld metal feed variables will affect bead shapes and weld
quality. These variables are discussed in more detall in
Section B.

b. Numercus problems that are associated with the inspection of
welds are not encountered or are less severe with flanged
Joints. It is an accepted fact that welds must be thoroughly
and properly inspected to assure joint integrity. Nuclear
plant weld quality requirements exceed the specifications for
conventional steam power plants. Weld inspection techniques
must work in high radiation backgrounds which make normal
radiography impossible. Inspection equipment manipulations
must be controllable from remote locations and viewing is
possible only by indirect means. Inspecting with magnetic
fields, or charged particle beams, generally is unsuitable
to nuclear plant materials and/or conditions. Ultrasonic
inspection has shown promise, although much more must be done
to adapt ultrasonic techniques to remote work. The Pacific
Northwest Laboratory has proposed an ultrasconic inspection
development program for the FFTF. Another ultrasonic lnspec-
tion development program is bteing sponsored by industry
through the Ediscon Electric Institute, and is being conducted
under subcontract at the Southwest Research Institute, Houston,
Texas.>®

c. Preweld Jjoint preparation required for remote welding involves
accurate, axially square precutting of the Jjoint, matching of
the respective inside and outside diameters along with pre-
cision alignment of the pipe stub to be welded, and possible
rebeveling to obtain acceptable alignment of mating Jjoint
members. It is imperative that a thorough cleaning of the
pipe interior at the Jjoint area precede all work, and that
utmost care be taken to completely remove all weld preparation
cuttings which might damage pumps, valves, etc., 1f allowed to
remgin in the system and circulate with the fluid. Wire brushing
and solvent cleaning may also be required to prepare the weld
areas,.

d. Repairs to faulty reweld joints are equally difficult. The
previously described inspection and cleaning requirements
apply to rewelding also.

REFERENCES
Divers Repair GCRE Vessel, Nucleonics, p. T8, May 1961.

J. I. Riesland and E. A. Gustafscn (GE - San Jose), Work Performed
on Fuel Channels and the Core Support Plate at Big Rock Point
Nuclear Power Plant, Conference on Reactor Operating Experience,
July 28-29, 1965, Supplement to Vol. 8, Transactions of the
American Nuclear Society, 1965.
10.

11.

12.

13.

1k,

15.

L. M. Hausler and R. L. Hauter (Consumers Power), In-Vessel
Modifications of Irradiated Reactor Internals at Big Rock Point,
Conference on Reactor Operating Experience, July 28-29, 1965,
Supplement to Vol. 8, Transactions of the American Nuclear Society,

1965.

R. H. Holyoak (Commonwealth Edison) The 1967 In-Service Inspection
of Dresden 1 Nuclear Power Plant, Transactions of the American
Nuclear Society, Vol. 10, p. 635, November 1967.

Clifford Zitek, Personal communication during a visit to ORNL, 1968.

Everett Rogers (Osk Ridge Y-12 Plant) Personal communication;
Rogers did the welding for the BONUS repairs, 1968.

United States Atomic Energy Commission Licensing Docket No. 50-219,
Amendment 35, Final Report on Reactor Vessel Repair Program, March 1968.

L. Newcomb, Calandria Remote Maintenance Tool Development, Atomics
International Report NAA-SR-11202, April 1966.

J. F. McCarthy, Compilation of Current Technical Experience at the
Enrico Fermi Atomic Power Plant, Monthly Report No. 7 to the U. S.
Atomic Energy Commission, February 1967.

L. T. Bogarty, Modular Steam Generator Fabrication, Atomics Inter-
national Report NAA-SR-11739, February 1966.

Dounreay Developments: Good progress on PFR; DFR is back at full
power, Nuclear Engineering, p. 633, August 1968.

Memo to Myron B. Kratzer, Assistant General Manager International
Activities, U. S. AEC, from Carl R. Malmstrom, AEC Scientific Re-
presentative, U. S. Embassy, London, England; Trip Report to Dounreay,
February 20, 1968.

R. R. Matthews and K. J. Henry, Dounreay Experimental Reactor
Establishment, TRG Report 185L4R, Nuclear Engineering, Vol. 13,
No. 149, pp. 8L0-844, October 1968.

S. Berger et al., Six Element Irradiated Fuel Shipping Cask, Atomics
International Report NAA-SR-12547, Appendix 10, pages 310-319,
November 1967.

Grady Whitman, Welding Research Council, Pressure Vessel Research
Committee, Personal communication, September 1968.
2. HISTORY OF REMOTE WELDING
2.1 Background

Attempts to develop autcomated remote welding systems for use in
nuclear work have been pursued, off and on, for more than ten years.
Most of the efforts, including some at ORNL, were on a small scale.
Limited findings from the earliest remote welding work formed the
background for the Pennsylvania Advanced Reactor (PAR) maintenance
welding development program.

2.2 The Pennsylvania Advanced Reactor Program

The Pennsylvania Advanced Reactor (PAR) was planned in the mid
1950's to use a circulating aqueous slurry fuel pressurized to 1000
psi. The high-pressure system required extra care in fabrication to
avoid leaks and also placed a premium on being able to repair leaks
that developed. It was recognized that circulating fuel would increase
the radiation levels in the reactor system areas and would make com-
pletely remote maintenance a necessity.

In planning the PAR,16 Westinghouse specified remote welding as
the mandatory method for performing maintenance on the reactor plant.
Although certain phases of the development program were completed,
the PAR proJject was terminated before the remote welding technigues
were ever demonstrated in an operating reactor system. A tube-plugging
procedure had been devised to use remote welding in maintaining the
system generator; the plug was to be inserted into the tube and welded
to the tube sheet. A flange on the plug provided the metal for the
weld and alsc covered the leak path between the tube and tube sheet.

The tungsten-arc welding process was selected by the PAR group for
remotely butt welding joints in the fixed piping. To¢ simplify equipment,
it was decided that each remote welding head would be designed to fit no
more than two pipe sizes. A contract had been negotiated with a manu-
facturer of welding equipment to improve an existing machine to permit
continuous rotation welding with 100 percent arc time, with automatic
and complete control, and with completely dependable weld guality. A
prototype model of the machine with fully automatic controls showed
promise in bench tests, but it was not equipped for remote work. Also,
the machine needed further development to be sufficiently reliable for
remote maintenance work.

2.3 The Atomics International Program

During the 1960's, Atomics Internaticnal, now a Division of North
American Rockwell Corporation, developed and perfected a number of auto-
mated welding systems. Some were remctely controlled for work in con-
nection with AEC's sodium-cooled reactors; others were automated, but
not remotely controlled, for space program reguirements and for the
shop fabrication of heat exchangers and tubing systems for civilian
power reactors. While much of their work was concentrated on production
11

welding operations in shop fabrication, AI also developed advanced
remote welding technology for specific applications, such as internal
tube welding for steam generator fabrication, deep-hole welding for
work on the calandria of the sodium-~graphite reactor, and seal welding
the containers for nuclear fuel canning.

Internal welding equipment makes tube-to-tube-sheet welds and also
tube-to-tube welds, with the welding head located inside the tube. AIl's
automatically programmed system was developed for fabrication of high-
temperature, high-pressure modular steam generator Joints for the Sodium
Component Test Installation. It did not operate by remote control.'®

Deep-hole welding equipment was developed as an extension of internal
welding technology to permit remote removal and replacement of process
tube and associated graphite log assemblies from the Sodium Graphite
Reactor Calandria Core. Blind cutting and TIG rewelding were accomplished
by remote control equipment reaching as far as 40 ft through a b-in.-
inside-diameter tube.®

The seal welding of spent fuel in cans was performed in a manipu-
lator cell at Hallam.'*

2.4 State of the Art Survey

Seeking information on remote maintenance equipment and techniques
that might be applicable to molten salt reactors, ORNL conducted a
survey early in 1968 to determine the state of the art. Emphasis was
placed on remote welding, which was considered to be of greatest interest
for molten salt reactor systems. OSpecific inquiries were made about all
development and applications of remotely operated, automated equipment
for reactor system maintenance and repairs. Equipment and techniques
for cutting{ beveling, welding and testing weld quality were particularly
sought out. 7 Ve specifically loocked for a utility machine that would
do cutting, beveling and welding with one set up.

2.5 Burvey Findings

The survey disclosed a few specially designed, automated welding
assemblies which were remotely controlled by manipulators. Argonne
Naticnal Laboratory has performed welding on the complex experimental
equipment inside a hot cell in this way; at Hallam, Nebraska, Atomics
International has a manipulator cell equipped for making seal welds on
containers for spent fuel elements; Aerojet Corporation at Azusa,
California, used a similar setup for canning radioisotope sources.
The Electric Boat Company at Groton, Connecticut, and the Liquid
Carbonics Company of Chicago, both Divisions of General Dynamics,
developed an automated welding system for use on shop fabrication
work, without remocte controls. In the production of components for
submarines, welding is being done increasingly by the automated
welding systems (TIG, with weld inserts for root pass). The Nav
claims time and dollar savings along with superior weld quality.>”

It was pointed out by a number of the people interviewed that, at
i2

present, no one markets automated welding machinery for field use,
although there are many applications where automated equipment would
be most valuable.

The following comments from Mr. Richard H. Freyburg, Assistant
Manager of Operations for Consolidated Edison Company of New York,
point ocut some of the reasons why reactor builders have keen interest
in automated welding equipment, even without remote controls:

"Industry can not take trained nuclear welders from site
to site for reactor construction because union restrictions
usually permit only one company welder for every 12 welders
supplied by the local union. The training program for nuclear
welders is tedious; we're lucky to get 60% of the new men
qualified. Many of those passing the nuclear welding qualifi-
cation tests are not well suited for constructicn work in other
respects. If we had reliable, relatively simple, automated
machinery for beveling and welding, we could train welders
faster to operate the automated equipment and the quality of
the welds would be better, with fewer rejections. In fact,
automated beveling and welding machines, on construction, could
be worked around the clock. We could even afford to put on an
extra man to permit coffee breaks for the operators and still
be well ahead. Furthermore, if our people gain confidence in
the automated machinery during construction of the reactor,
they will be glad to pay the price later for a more expensive,
remotely operated machine for reactor maintenance work. My
most urgent need is for a reliable, automated welder that
reduces rejections on construction field work . "+8

Maintenance and associated program and control equipment for auto-
mated welding have not yet been simplified and made rugged to the point
where such systems economically challenge manual welding for field work.
Our survey, however, revealed two automated systems which, with modi-
fications, might be useful for remote nuclear work. One is an "orbital
vehicle combination cut, bevel, weld carriage concept' developed and
tested by North American Aviation, Los Angeles, a Division of North
American Rockwell Corporation, under Air Force Contract; the other is
a combination of either Wachs (E. H. Wachs Company, Wheeling, Illinois)
or Fein (Prescott Tool Company, West Boylston, Massachusetts) pipe
cutters for cutting, plus specially automated Dyna-Surge APW Series
Systems (Liquid Carbonic Division, General Dynamics Corporation, Chicago,
Tllinois) for welding. The Dyna-Surge system technology originated at
the Electric Boat Division of the General Dynamics Corporation and was
uged for their production welding in submarine work. Dyna-Surge weld
head assemblies employ a stationary cylindrical track, clamped around
the pipe, with a geared rotating part on which the electrode holder is
mounted. Torch support and travel components are similar to equipment
marketed by AB ASEA SVETSMASKINER, the Stockholm, Sweden manufacturer
fcr special European automated weld machinery, or by Clarke, Chapman
& Co., Ltd. of England. Wachs and Fein pipe cutters are commongly used
in coal mining operations, in fabricating gas plant equipment, 1n
13

marine salvage work, and in production pre-weld pipe end shaping. A
still experimental automatic welding machine for large size overland
transmission piping only is being built by CRC-CROSE, Inc. of Houston,
Texas, and 1s now being tried out in a full scale field test on a
Coastal States Gas Producing Company pipeline in the Southwest .1®

2.6 Continued Need for Remote Welding Development

There were two full-fledged remote welding development programs
primarily associated with reactor projects, the PAR and the SGR, which
were discontinued before remote welding equipment was fully developed.
Other devices for remote welding have been built and used to perform
specific jobs in making repairs to reactor systems.

For a number of years, ORNL has used an automated, remotely
controlled welding apparatus inside a hot cell to seal radioisotope
source containers. In this case the containers are small, the job
is repetitive, and the remote welding equipment does not have to be
moved about within the cell. In general practice, reactor fuel
elements are seal welded in thin-walled containers before being placed
in the shielded carrier when they are to be shipped off site. This
seal weld 1is usually made by remotely controlied equipment in a hot
cell. Other remote welding operations have been performed at various
times and places using equipment specially adapted for the specific
Job. The state of the art seems to be that automated welding equip-
ment has been developed to a point where it is possible to adapt com-
mercially avallable equipment to the performance of specific - and, to
date, fairly simple - remote welding Jjobs.

Although automated welding is being used increasingly in shops
for a variety of applications, there are no present applications of
automated welding to nuclear reactor system components being welded
in the field. In the shop production of components for the nuclear
power systems of submarines, automated welding is being increasingly
used. Weld insert rings are used to fusion weld Naval Jjoint root
passes. The Navy reports savings in time and cost over manual welding,
and claims superior weld quality, also.

Needs for remote welding equipment have become more widespread
and actual gpplications of equipment for performing specific remote
welding jobs have become more numerous. To date, however, no one has
perfected a generally useful remote welding system, It is instructive
to consider why the equipment has not been developed to date, even
though attempts have been made, and to evaluate the prospects for
success 1f another attempt is made. The following factors seem impor-
tant:

1. Limited funding forced previous developers to resort to
crude control and programming equipment and to limit their
mechanical designs to oversimplified hardware items.
6.

17.

18.

19.

1h

2. Welding and programmed control apparatus of the past lacked
pulsed-arc and arc length regulation, integrated digital
functional controls and sclid state devices for instant
response actuation. Today's remote control capabilities
are much more sophisticated and adaptable to meeting welding
guality specifications.

3. Miniaturized components and automated welding hardware were
not available for application in the previously attempted
remote welding systems. Welding equipment systems that have
been developed recently for the National Aeronautics and
Space Administration and for advanced aircraft applications
are much superior to those that were available in the earlier
attempts to adapt equipment for remotely controlled welding
operations.

REFERENCES

Vol. IV, Peansylvania Advanced Reactor Project, Layout and Main-
tenance, Parts 1 and 2, WCAP 1104 and 1105; Westinghouse Electric
Corporation and Pennsylvania Power and Light Company, March 1959.

Memo from P. P. Holz to Distribution, A Preliminary Survey of
Remote Cutting and Welding Techniques Under Development in the
United States, MSR-68-4k4, February 20, 1968.

Richard H. Freyburg, Assistant Manager of Operations, Consolidated
Edison Company of New York, Personal communication by telephone,
October 1, 1968.

Wall Street Journal, July 8-69 issue, Page 23, Column 4, Para-
graph 5.
15

3. THE SELECTION OF A SYSTEM TO BE DEVELOPED FOR REMOTE MAINTENANCE
3.1 "Orbital-Vehicle" System Advantages

The Air Force's orbital vehicle machinery developed by North
American-Rockwell for pipe Jjoint-replacement maintenance offers a
number of advantages for cutting and rewelding nuclear piping. A
single, compact carriage propels interchangeable heads for cutting
or welding. This single setup for all phases of repair work simpli-
fies the indexing on the spot to be cut and welded and assures re-
petitive precision tool alignment. Equipment setup time savings also
result, especlally where weldment repairs might be required.

The tungsten inert gas (TIG) welding process which had been used
by the Air Force in their work with orbital machinery was also chosen
for initial tests at ORNL because it offers most promise of meeting
nuclear weld requirements. This process has several inherent charac-
teristics that are especially suitable for remote fixed-position
welding. TIG welding is a low inertia process and is relatively slow,
which makes it much easier to control and monitor for high integrity
welds. The amount of molten metal at any time is relatively small,
creating a quick-freezing puddle with sufficient surface tension to
counteract gravity. The process thus works equally well whether the
weld is going up-hill, down-hill or horizontally. The arc length of
the non-consumable electrode can be maintained more easily than that
of a consumable electrode. There is no flux or slag associated with
the process to require special interpass cleaning, although brushing
to remove the light oxide film is desirable. Filler wire is fed
directly intc the weld puddle. The metal does not have to be trans-
ferred into a molten state across an electric arc, an operation that
sometimes results in spatter and uneven bead formations. A system
with integral wire feed has the capability to complete a weld of
thicker section than can be made by autogenous welding. It alsc is
more likely to provide satisfactory crack-free weld metal of good
composition, grain size and porosity. TIG equipment can be made
compact and portable.

3.2 Future System Expansion and Modification Plans
The overall development program for an automated cut-and-weld
reactor maintenance gsystem is divided into two parts; a system feasi-
bility study and development phase, and future system expansions and

modifications along the lines described below.

3.2.1 Development of Additional Modules

 

The ability to change modules on the orbital vehicle carriage
suggests that development and application of additional, interchangeable
modular insert packages might be the easiest way of accomplishing
additional functions. Since welding operations require strict clean-
liness control and it is important to keep chips and dirt out of the
process system, a clean-up module or attachment may be needed. Welding
requires that oxide and dye penetrant test films be removed from bead
surfaces before making additional weld filler passes. A modular head
could be developed to apply solvent cleaners and to drive a rotary
wire brush for physically cleaning the weld. We plan to also develop
additional modular heads for a welding inspection package, complete
with TV camera, dial indicators, penetrant inspection devices, etc.

3.2.2 Alternate Carriage for Seal-Weld Capability

Present machinery is designed for work on piping only, with the
capability of preparing Jjoints for butt-welding, and of performing
the welds. Investigations have been started to determine whether the
existing modules along with the programmer can be used for seal welding
applications. Such a system may include a substitute carriage to "walk"
about a set of indexed mating contoured seal lips. Motor propulsion
equipment for this alternate seal-joint carriage should be compatible
with the orbital vehicle carriage drive so that it can be operated with
the same controls and instrumentation. An alternate approach under
consideration for vessel seal-weld closures is based on a free-swinging
carriage operated from a radius linkage at the centerline of the opening.

3.2.3 Development of Special Features for Nuclear System Applications

A number of additional design modifications will be necessary in
adapting the present Air Force machinery to provide better instagllation
and operation capablilities for nuclear applications. These modifications
will involve changes to positicning and handling attachments so that all
of the equipment can be installed and operated from any available over-
head access.

The Air Force design was modified somewhat before being used to
fabricate a prototype unit for the ORNL feasibility studies. The ORNL
prototype, like the Air Force equipment, utilizes readily-machinable,
light-weight materials, generally aluminum. Reactor maintenance appli-
cations will require equipment which is rugged, is able to be decontami-
nated and repaired, if necessary, while being kept inside a hot cell,
and is resistant to radiation and high temperatures. It should be
possible to incorporate materials and to develop design modifications
which will adapt the system to nuclear work without reducing the proven
effectiveness of the overall system design or operations. For initial
tests with the prototype, significant savings in time and money were
achieved by using units that incorporate standard industrial components
and materials. This approach will be ccntinued through most of the
development program. The more costly units, incorporating special
materials for ease of decontamination and for resistance to radiation
and to high temperatures, will only be built after present tests have
shown complete suitability and performance of the design. For future
machinery systems we contemplate relocating some electronic control
components from their present module stations to the programmer, and
possibly replacing some of the electrical sensing and control equipment
in the module with fluidic systems to minimize radiation damage problems.
17

SECTION B

4. PRESENT PROGRAM STATUS
4.1 General

ORNL representatives visited the North American Aviation Los
Angeles, California Division of North American Rockwell Corporation
and the Rocket Propulsion Laboratory, U.S. Air Force Systems Command,
Edwards Air Force Base, California during March 1968. At that time
North American Rockwell, as Air Force contractor, had already fabri-
cated two prototype orbital vehicle machines for cutting and welding
1- to 3-in. and 3- to 6-in. diameter tubing. Performance testing had
Jjust been started. Designs had also been completed by NAR for units
to handle larger diameter pipes; 6- to 9-in., 9- to 12-in., and 1l2-
to 16-in.

Arrangements were made for the Atomic Energy Commission to receive
Air Force contractor design data. Design drawings for the 6- to 9-in.
diameter orbital vehicle machinery were supplied to the AEC during
April and May 1968. The Commission, in turn, relayed the information
to ORNL. After detailed review, ORNL redesigned equipment to include
provisions for remote installation and operation capabilities, and
prepared detailed drawings and specifications for the commercial
purchase of mechanical assemblies. Fabrication of the prototype unit
for testing at ORNL began in August 1968 and was completed during
February 1969. To save time and initial costs, arrangements were
made to borrow a spare Alr Force programmer to control the operation
of the equipment for a limited evaluation period. A replacement pro-
grammer is being fabricated by ORNL and will be completed by September

1969.

The initial ORNL development efforts started in March 1969 and
were directed toward establishing the feasibility of using remotely
operated machinery that will cut, bevel, and either seal or strength-
weld joints and piping for nuclear applications. Initial cutting and
welding studies and tests closely followed current USAF rocket system
welding technology developments.

Detailed discussions on early development findings at ORNL are
reported on in the following chapters on pipe machining and welding
studies. The development work to date shows that it is feasible to
use automated orbital machinery for remote cutting and welding.

4.2 ORNL's Prototype Automated Remote Cutting and Welding
System for 6 and 8-in. Pipes

The Air Force has orbital carriages for the following cutside
diameter ranges; 3 to 6 in., 6 to 9 in., 9 to 12 in., and 12 to 16 in.
We selected the 6- to 9-in. carriage for work with 6- and 8-in. pipes.
All listed carriages use the same interchangeable machining and welding
heads.
18

The automated remote cutting and welding machinery package includes
the following components shown in Fig. 1, 2, and 3: carriage, machining
head, welding head, weld programmer, and welding power supply. The
functions performed by these components and brief equipment summations
are described in the following paragraphs.

L.2,1 Carriage

The carriage provides a rigid, stable platform on which the
machining head and the welding head can be mounted, indexed, and
operated. Figure 4 shows the carriage with the welding head. The
carriage supplies a drive mechanism to rotate the platform around the
pipe circumference at preset, reproducible speeds, with controls to
maintain the platform surface at a constant distance from the pipe
surface so that the milling cutter depth and arc length controls will
perform properly. The platform will maintain its lateral position
with respect to the pipe Jjoint while rotating about the pipe, so that
when modules are changed from cutting, beveling and welding, the align-
ment will already be correct. The carriage geared actuator arm
assemblies clamp securely to the pipe; its drive rollers agre loaded
by special torsion bars to maintain controlled roller clamping pressure
and to compensate for pipe ovalty within commercial specifications.
Carriage design permits all listed tasks to be accomplished within a
4L 1/2-in. radial clearance.

The carriage structure consists of two side pieces which provide
a platform for the welding and machining heads, and two end supports.
These supports contain the water, inert gas and electrical power con-
nections and switches; the front support also contalns the clamping
device, namely worm gears which position the idle rollers through a
slider crank linkage. The carriage rotates via a direct drive system
from motors mounted at the two hinge points of the actuating arms
within the rollers. The vulcanized high temperature, abrasion-
resistant viton coating provides the necessary roller traction.

L.2.2 Universal Machining Head

 

The machining head shown in Fig. 5, can be mounted on the carriage
to cut pipe or tubing, mill the tube ends square, and bevel the edges
to the desired configuration for welding. The machining head includes
an outer housing, a Triac, speed-regulated, 1/4-hp air-cooled electric
drive motor of the type produced for hand drills, plus the drive motor
housing and cutter assemblies. Two-axis manual cutter adjustment is
avallable. Several types c¢f cutter blades can be installed as needed.

4L.2.3 Universal Welding Head

The welding head, Fig. 6, can be mounted on the carriage in place
of the machining head after the cutting and beveling operations have
been completed. The welding head is designed with adjustable vertical
and horizontal slides to locate the electrode accurately with respect
to the cut and beveled edges of the weld joint. Filler wire will be
   

 

 

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25

fed automatically at the desired rate to the weld Jjoint from a spool
which stores enough wire for multiple filler weld passes. The welding
head will provide an inert welding gas to the torch cup, will provide
power and cooling water flow to the torch head, and will oscillate the
welding electrode acrcoss the seam. It will also provide integral
switches for test operating the wire feed jog, the osciliator, and inert
gas flow.

L.2.4 Welding Programmer and Control Unit

A pendant-housed start-stop control unit and the console-welding
programmer contain the measurement recorders and control devices that
provide for automated welding. The programmer, shown in Figs. 7 and 8,
is designed to control and/or sequence each of the following weld
variables or functions; welding current vs. time, maximum welding
current, welding current pulse amperes and pulse time, current upslope
time, weld time, current downslope time, welding voltage, welding tool
speed and start and stop time, wire feed speed and start and stop time,
arc voltage control voltage, and oscillator freguency.

The welding current and the carriage (tool) drive circuits are
respectively servo-controlled. The wire feed rate can be adjusted to
maintain constant electrode/weld puddle distances by using a feedback
system to monitor the arc voltage and compare it to a preset, pre-
determined value, and, as required, generate a correction signal.
Changes in the arc gap are reflected as changes in arc voltage and
these changes generate a correction signal which changes the filler
wire speed to build up or to decrease the weld puddle to maintain a
preset arc gap. The wire feed system also includes a transistorized
motor control servo system to quantitatively regulate filler deposits
in response to a tachometer feedback signal. Pipe ovalty corrections
are regulated by a mechanical cam device which rides the pipe and
spring loads the weld head within the carriage to tend to maintain a
constant tool/workpiece spacing.

Lighted buttons are provided for function indication and/or
selection. Indicating meters are incorporated for tool and wire feed
speed, arc voltage, and weld current. The unit is designed to provide
signals which can be used with commercially-available recorders to
provide permanent records. At present we use a multi-channel Sanborn
150 Recorder. The Air Force programmer, Fig. 7 also includes provisions
for punched card input to provide automatic capability for program setup.
This feature is especially desirable for production work. For the time
being, however, primarily for economy reasons, we are not using punch
card techniques in our replacement programmer.

L.2.5 Power Supply

Most commercially-available welding power supply units are compatible
with the programmer control circuitry and can be employed as power sources.
We utilize a Lincoln Model TIG 300/300 welder with minor circuit modifi-
cations. Inductive transient supressors and a transistorized reactor
 

 

 

 

 

 

 

 

 

 

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28

control amplifier shown in Fig. 9 have been added to the welders'
regcetor control circuits. Welder controls for gas and water solenoid
valve relays are transferred to the programmer.

L.2.6 Equipment Modifications for Remote Work

ORNL's 6- to 9-in.-diameter carriage and the welding and milling
insert heads incorporate a number of changes and modifications to similar
Air Force equipment. Our machinery includes actuateors, lifting and
positioning lugs designed for remote tooling and handling. We have
also eliminated from the original Air Force weld head two disconnects
in the welding power supply line and the water and gas lines. Our
cables are integral with the torch and route directly from the torch
holder through a grommet insert in the adjacent carriage front panel.
Stray RF currents and potential water leaks are eliminated. Our directly
coupled torch also permits completely independent weld head (in, or out
of cell) checkout and replacement. The separate power and control leads
at opposite ends of the carriage work well in remote installation.
Separated cords do not tangle while rotating the carriage to loop cables
prior to cutting or welding, or during actual work operations. We have
also added a Lossy-Line Absorptive Filter RF Suppressor to provide
increased protection of wiring and components connecting to the electrode.
OQur wire feeder exit trough is oxide coated to eliminate arcing and
fusing. Its trough pivot device is altered to permit more flexibility
and to provide a lock-in feature to center tracking. A similar hori-
zontal travel locking device was added to the cutter head to prevent
lateral carriage motion while cutting. Our cutter tool feed actuator
includes ratchet depth set control.

5. MACHINING STUDIES
5.1 QGeneral

Considerable time was spent to check and generally confirm Air
Force machining data and to develop cutting and milling techniques for
stainless steel and Inconel piping. We noted that cutting criteria
applicable for 300 series stainless steel pipes do not apply for Inconel
work. Available Inconel pipe was chosen to approach Hastelloy N material
characteristics. We were able to prepare beveled pipe Joints.

Cutter trials started in late February 1969. Major performance
tests held during March and April included saw tracking studies and
runout determinations and machining studies on (in order) 304 stainless
steel, 347 stainless steel and Inconel piping. We tested 1/16 in. and
3/32 in. thick high speed steel and Circoloy alloy slitting saws and high
speed steel single and double bevel cutters. We varied cutter speeds,
cutter feeds, and carriage travel rates to determine programmed operating
combinations for acceptable tool performance and pipe surface finish.
Test efforts also served to evaluate our equipment, and to develop
acceptable machining techniques for both slitting and beveling pipe to
prepare desired pipe end configurations for welding. We noted parti-
cularly that pipe wall thickness variations, even within the allowed
 

 

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30

code limits for commercial piping, greatly complicate the joint
machining requirements for dependable weld joint geometries.

5.2 Equipment Evaluation

The machining head appears to have capability to cut pipe, trim
ends square, and to prepare end bevels. Little difficulty is encountered
in machining stainless materials; problems, however, arise in cutting
Inconel because of its work-hardening tendencies.

All ORNL machining tests were performed on horizontal piping.
Slitting saws and double bevel cutters track true within approx.
.003 in. Single bevel cutters tend to walk out of, and away from the
cut, especially on the harder Inconel pipe. Cutter drive motor power
and speed control capabilities appear adequate. The carriage and
machining head will withstand loading and vibrations caused by the
milling cutters with proper travel speed and tool feed selection.
Improvements, however, are required to provide a stronger and more
positive cutter depth control and to give more stable longitudinal
adjustments. A ratchet-controlled worm gear depth control is contem-
plated for more precise feed capability. A locking clamp already
installed to the longitudinal adjustment appears to adequately prevent
axial cutter shifts.

The cutter drive motor and its speed reduction gear train work
well. We have observed no signs of motor overheating during performance
tests, even during severe milling operations. The 110 V ac motor is
rated at about 5 amps; 2.5-amp readings were the highest noted in test
operations. Motor speed control appears adequate, for speeds ranging
from gbout 30 rpm to about 120 rpm. Observations to date indicate the
carriage drive may be the limiting factor on cutting capability. We
have observed roller slippage on the pipe, and at times have tripped
the drive roller circuit breaker protection. Cutter feed and carriage
speed adjustment changes, however, restored operations. During a
recent maintenance period to revulcanize the roller viton friction
surfaces we found a broken shear pin on one of the two carriage drivers.
We do not know when this pin sheared, or for how long we may have
operated with but a single carriage drive roller. (The other motor
cperated satisfactorily, but slipped within its concentric cannister
housing. Available indicator signals registered proper dual motor
operation but not the effect of the sheared pin.) Therefore, we are
uncertain how much the cutting performance may be limited by the
carriage drive system. However, we were able to make the machine work
even with only one motor actually driving its roller.

5.3 Tooling

We have cut with high speed steel and Circoloy alloy slitting saws
and milling cutters. The alloyed tool teeth appear to stay sharper
longer, possibly by as much as a factor of one and a half. Early
results from Inconel machining experimentation indicate that the
cutting edges of all cutter teeth must be genercusly relieved to
31

provide ample clearance for chip fallout. Free falling chips minimize
work hardening tendencies for Inconel pipe. It 1s also quite important
that all teeth of a cutter engage the work during the cutting. Off the
shelf commercial cutters used to date appear to cut with usually only
about a fourth of their teeth. Improved cutting was noted when cutters
were regound locally to precision specifications; almost seventy-five
percent tooth engagement can be attained. We further noted the impor-
tance of tool travel and cutter speed adjustments for Inconel pipe work.
Available machine shop machining data do not apply to the orbital cutting
assembly because it does not have the driving power of shop machines.
Also, dry machining is specified for nuclear system maintenance because
coolants might contaminate the nuclear system. Therefore the tool
travel, cutting speeds and tool feed rates must be much lower than
usual shop practice.

The table on the following page shows the number of inches of cut
a blade can be expected to make before it must be resharpened. The
table also shows how deep the blade would cut in traveling the indicated
number of inches around a 6-in.-diameter pipe, taking a 30-mil or a
12-mil cut, as indicated. The short cutter life experienced in test
operations means that blades will have to be replaced frequently. We
plan to test carbide cutter blades in hopes that they will last longer.

5.4 Machining Feeds and Speeds

Efficient cutting requires the thickest possible chip per cutting
tooth, but may have to be compromised somewhat to obtain reascnable
cutter life and proper surface finish. This is particularly true in
the case of high-nickel steels where the base material tends to work
harden with the result that chip removal is inadequate or incomplete.

We selected Air Force recommended cutting speeds between 70 and
80 surface feet per minute for stainless steels and chose 50 feet per
minute for Inconel in order to achieve reasonable cutter life. The
cutting speeds correspond to approximately 100 and 62.5 revolutions
per minute for our 3 inch diameter alloy steel slitting saws. Test
verified feed per tooth selections compatible with tool strength and
rigidity were .00l in. for stainless work, and about .0005 in. for
Inconel. We chose respective travel speeds of 3 1/4 in./min. and
1 in./min. for the 32 tooth saws based on the formula

TRAVERSING SPEED (in./min.)

FEED per TOOTH (mils) = f——roerm GUPTER x SPEED (rpm)

Our feed per tooth rates are low when compared to rates in standard
machine shop work, but are still creditable considering our small sized
and low powered equipment. The depths of cut depend on available horse-
power and cutter shapes, and on the sharpness of the cutters, as they

in turn affect the power required at the cutter motor spindle. We re-
peatedly cut .030 in. deep into stainless, and .0l15 in. into Inconel.

We anticipate deeper cutting capability with the "all carbide cutters”
now on order. -
Table 1.

Expected Life of Cutter Blades

 

Description

Blade Lifetime

 

In Stainless Steel

In Inconel

 

 

 

Saw Tooth Speed 70 to 80 ft/min 50 ft/min
Carriage Speed 3 1/4 in./min 1l in./min
Feed Per Tooth 001 in. .0005 in.
Inches of Total Depth Inches of Total Depth
cut, average of* cut, 6-inch cut, average of cut,
depth 30 wmils. pipe wall. depth 12 mils. 6-inch
inches inches inches pipe wall.
inches.
1/16-in.-thick slitting saw,
3 in. dia., 32 teeth
nigh speed steel 530 3/
1/16-in.-thick slitting saw,
3 in. dia., 32 teeth
Circoloy alloyx 800 1 1/8 730 7/16
3/32-in.-thick slitting saw,
3 in. dia., 32 teeth
high speed steel 430 5/8
3/32—in.—thick slitting saw,
3 in. dia., 32 teeth
Circoloy alloy* 650 7/8 600 11/32
70° included double angle mill
2 3/4 in. dia., 20 teeth, 1/2 in. wide
high speed steel L70 11/16 L20 1/k

 

*
Trade name for Circular Tool Company (Providence, R.I.) special high-speed steel alloyed blades of
high carbon, medium chrome, high vanadium, high tungsten and medium cobalt composition.

A
33

5.5 Machining Techniques for Slitting and Beveling Pipes; Pipe End
Preparation Requirements for Welding

An important feature desired for pipe weld joints is a perfect
match for adjoining pipe ends. Pipe inside walls must align and must
be concentric. Regardless of the geometry of a selected joint, whether
it is V-bevel, J-bevel, or butt, precision fitup and mating geometrical
concentricity will be required, along with square-cut ends and s uniform
gap, or complete contact, of the Jjoint ends.

ASME Materials Specifications, Section Two, Boiler Code for Piping
permit various diametrical and wall thickness dimensional variations.
Section SB 167 for Nickel-Chrome Alloy Pipe, as an example, permits an
allowable eccentricity of pipe inside and outside diameter up to ten
percent of the nominal wall thickness. Comparable SA 106 Steel Pipe
Specs allow for 12 1/2 rercent thickness variations below nominal pipe
wall thickness. Diameters for large pilping may vary as much as 1/8 in.
All commercial pipe is governed by these specifications. Our experience
indicates that piping dimensions vary at least as much as, or slightly
more than the allowable tolerances.

Figure 10 illustrates problems encountered when we cut commercial
piping for a J-bevel weld joint with our orbital equipment. The carriage
rollers ride the pipe outside surface, which then becomes the reference
surface for the cutter. For simplicity, Fig. 10 shows the end view
eccentricity about only one centerline. In practice, one encounters
eccentricities in several planes. The two elevations shown represent
matched and mismatched joint alignment. Mismatching destroys mating
inside diameter surface contact and prohibits proper root pass weld
penetration. To achieve matched and aligned joint surfaces requires
sensors and controls which will properly regulate the root pass weld
variables (weld current, -speed, -wire feed, and -arc voltage) to
adjust for variations of the joint. To date we have no sensing means
which will automatically adjust the programmed weld variables for non-
uniform geometries of the weld joint.

Figure 11 illustrates how a remedial cut can be taken to approach
uniform wall thickness for pipe weld joints. This requires that the
operator obtain accurate dimensional information from his initial
slicing cut so that he can properly position and feed the cutter for
subsequent machining. A wax impression of the pipe end contour could
be used for remote work applications. If the pipe is contaminated and
then contaminates the impression device, duplicate non-contaminated
replicas can be made in hot cells or glove boxes via a recast plaster
of paris process. This technique of remote replication has been used
successfully in working with very highly radicactive materials.

Figure 12 shows one way of field matching a pipe end with a pipe
stub previously welded onto a replacement component. For reactor
maintenance, replacement items such as pumps, heat exchangers, etc.,
are all jig prefabricated. A blank end stub of slightly heavier
schedule pipe, to gain a smaller inside diameter for subsequent fitup
machining, could be field ground to an impression replica of the pipe end.
34

A machining technique has been developed for remotely preparing
J-bevel pipe ends for welding. Figure 13 schematically represents
an in-cell maintenance cutting procedure which tends to compensate
for the variations in pipe wall thickness which, under the ASME Code,
can be as much as 12 1/2%.

1. Step 1l: Make a light cut around the pipe with a thick
slitting saw and inspect for true tool tracking. Continue
slitting to the predetermined depth which will leave a land
surface for the root weld.

2. Step 2: On the cutter shaft, mount a hardened steel thrust
washer and a single-angle milling cutter so that the washer
will ride in the slit made by the saw and will gulde the
bevel cutter.

3. ©Step 3: After making the bevel cut, insert a thin slitting
sawblade and cut through the wall.

4. Make a wax impression of the cut joint. Make a plaster of
paris non-contaminated replica.

5. Machine to a constant land wall thickness at the joint by
cutting metal from segments of the land surface where
measurements of the replica indicate it is too thick.

6. Make a second replication of the joint for use in out-of-
cell machining on the stub end of a replacement component
to make 1t fit the pipe inside the cell.

7. Use information from the replica to set programmer weld
current curves so that they will compensate for variations
in the arc gap caused by out-of-roundness or by the machining
to give constant land wall thickness.

All of our machining operations must be accomplished in the
standard "milling up" mode of operation where the cutter tooth in
contact with the pipe is moving in the same direction as the carriage.
We lack rigidity for reverse, or "climb mill" cutting. Our torsion
bar clamping action on the carriage roller does not give enough
friction contact for climb cutting.

6. WELDING STUDIES
6.1 General

Orbital TIG welding operations on plpe require precise weld joint
machining to obtain concentric pipe inside diameters and matched pipe
wall thicknesses as well as near-perfect alignment of the respective
two joint members. Failure to meet these requirements results in root
welds that are undercut, lack full penetration, or that have too much
penetration, resulting in excessive convexity. Fill-pass weld criteria
A_—,

ORNL DWG. 69-11837

 

2

ATCHED LIAIND THICKN—>T

 

 

 

 

—N—
v

 

 

 

 

 

 

 

 

 

 

 

 

    

-

 

-
%

NN

SECTION END  VIEW SECTION
MATCHED ALIGNMENT MISMATCHED AL|GNMENT

 

 

 

 

 

 

 

/s
//,

 

fi__M

 

 

 

 

 

|

 

 

 

Fig. 10. Orbital Cutter (Riding Pipe 0.D.). Typical "As Cut" Pipe Joints.

Gt
ORNL DWG. 69-11838

 
 

) cormecTive ot

]

 

 

 

 

 

 

THICKNESS

 

 

- = LAND

 

 

MODIFIED END VIEW MODIFIED SECTION

Fig. 11. Orbital Cutter (Tiding Pipe 0.D.). Corrective Joint Cutting Plan.

 

9t
 

ORNL DWG. 69-11839

 

 

 

\'\ N o

 

   
  

   
    

= FIELD GRIND
TEMPLATE

 

 

 

To AT CONTOUR

 

 

 

R AT IR T T — = =
mEEE LATSTI AT ——— N
e - T

 

 

 

 

 

REPLACEMENT COMPONENT X- HEAVY PIPESTU

 

Fig. 12. Modified Final Joint Preparation.

LE
ORNL DWG. 69-11840

 

 

 

 

 

 

 

 

 

 

 

— = PIPE WALL = —

  

/ |

/

4

///j

STEP | STEP 2 STEP3
SCRIBE BEVEL
GROOVE BeVEL CUT THROUGHCUT
THICK SAWBLADE
THRUST WASHER THIN SAWBLADE

GUIDED ANGLE MILL

Fig. 13. Pipe Joint - Machining Sequence.

QL
39

do not appear to be guite so critical, though we note a dependence of
successive welds on prior weld passes. It is quite simple to lay good
fillers over gecod root welds, or over good prior filler welds. It is
difficult to perform remedial tasks over poor substrates. All these
observations are based upon our recent work, which has generally in-
volved extra-heavy 6-in.-diameter, 347 stainless steel pipe prepared
with V- or J-bevel joints, and always fitted up without joint gap,

and without weld inserts. Remote work on nuclear systems cannot use
gap Jjoints or the common weld insert rings.

Test operations with the orbital welding equipment were started
during late February 1969. The first tests consisted of simply
placing weld beads around the exterior surface of the pipe. Subse-
quently, V- and J~bevel pipe-joint root and filler pass weld tests
were tried. We had hoped that acceptable root pass weldments could
be obtained without having to do the precision machining that is re-
quired for close alignment and fitting of mating surfaces. However,
the test welds showed that preparing the surfaces for precision
matching and alignment is important in achieving quality welds.

Because it is time consuming and difficult to do precision
machining by remote control, we plan to experiment with joints in
which one preapplies weldwire filler metal to one of the two joint
ends prior to placing the pipe inside the cell. This type of joint
preparation permits plain fusion root pass welding, and requires no
other filler wire additions. It should also greatly reduce the require-
ments for precision joint matching and alignment. Several highly
successful root pass welds have just been performed by a similar
method in which the pipe ends were machined to include an integral
flat washer on one of the two mating J-joint sections. This washer
permitted the root pass weld to be a single fusion weld which, in the
tests exhibited excellent bead shape and full weld penetration.

At the moment we still lack essential information to suitably
program the pipe root pass weld {with filler wire addition) for pipes
in the horizontal plane. We have found no easy solution to the problem
of sensing the weld puddle behavior as it relates to consistent full
weld penetration. ©Such a sensing capability would permit automatic
control and would make it possible to do remote welding with far less
critical specifications for prior joint preparation. We have, however,
recently coupled a Sanborn 150 Recorder to our weld programmer to study
simultaneous data printouts of the inter-related weld functions (weld
current, - travel speed, -wire feed rate, -arc voltage, and -arc
voltage control). We have Jjust begun to learn how to select and
introduce proper weld programs for controlled high quality welding.
There appears to be an excellent chance that we will soon be able to
develop joint preparation, fitup, and weld criteria for consistent
reactor quality welding.

We observed manual TIG welding operations in an attempt to study
Just how a welder actually manipulates his feed wire relative to his
weld puddle. Slight pulsing of the wire advance motions were noted,
Lo

with speed adjustments to maintain the wire at the weld puddle's
lower edge. For the present we lack built-in programmer wire feed
pulse capability. We do, however, have the capability for weld cur-
rent pulsing with up to 50 amperes peak to peak pulse amplitudes at
either L0 or 60 pulses per minute. However, these pulses do not give
the puddle stability observed in manual welding. An improvised method
of wire feed pulsing was tested and appeared to give improved puddle
stability, better arc tie-in to the Joint walls, and uniform bead
periphery. A Wavetek wave function generator provided 3 cycles per
second pulsing with 50% on and off times. Additional trials will be
scheduled with refined circuitry.

6.2 Preweld Joint Cleaning

Stored metals will form external oxide coatings. These oxides
are refractory. Excess power (weld current) is required to obtain
initial weld penetration when metal surfaces are oxide coated, and
this often results in weld porosity due to hydration of the oxide.
Once penetration has been achieved, new problems arise. One encounters
difficulties with weld puddle control, especially in or near overhead
weld positions. Weld deposits are uneven with balling tendencies and
vold inclusions.

Routine cleaning procedures of stainless steel wire brushing to
cut oxide coatings and wiping with solvent to remove surface dirt and
grease traces are necessary for all welds with the present orbital
equipment. Additional draw filing, or grinding, may be required for
filler passes to remove sharp notches or protrusions to obtain smocoth,
blended surfaces.

6.3 Joint Fitup Tolerance

Joint mismatch has already been listed as g cause for poor root
pass welds in horizontal pipe lines. Mismatch is most critical in
the overhead or 6 o'clock pipe position. Here a slight mismatch of
adjacent inner diameter pipe jcint lips, commonly referred to as mating
land surfaces, causes the weld to pull out, or suck back metal due to
gravity conditions. We concluded that it will be necessary to match
pipe bottom quadrants most precisely for best weld results, since mis-
fit conditions can be tclerated to a greater degree in the top quadrant
surfaces. Pipe joint mating surfaces should preferably make physical
contact on fitup for radiocactive system remote maintenance welding.
Purge gas losses are minimized with contacting surfaces, and filler
metal additions are reduced, also.

6.4 Inert Shield Gas

There is a difference in ionization potential of inert gases which
affect the heat input to the weld zone. Helium requires only about 60%
of the welding current required for an equivalent weld with argon shield
gas. Different arc plasma shapes result. Argon spreads the welding
heat; helium concentrates heat. Air Force experimentation indicated
L1

that wide argon plasmas give best results for work with stainless
welding. All ORNL work has been done with argon shielding gas. We
have also used argon gas to purge pipe interiors, usually with a 20 cfh
gas purge flow.

6.5 Electrode Configuration

Air Force experimentation indicated that better welds can be
obtalned by tapering the torch electrode tungsten to a 60° included
angle. Electrode configuration influences the arc spread pattern.
The tendency of an arc to spread to an adjacent area causes the weld
nugget to fuse only intermittently to the joint sidewalls, resulting
in lack of fusion and an uneven, knotty-rope appearing surface on the
weld bead. It is practically impossible to lay subsequent acceptable
fill passes over such defective surfaces; one must resort to corrective
interpass machining and blending prior to proceeding with further
welding. We tentatively standardized on a 60° included electrode
angle for our stainless welding work.

6.6 Automatic Arc Voltage Control

It is necessary to control both the torch-to-pipe distance and
the torch electrode-to-weld puddle distance to maintain a constant
arc length and & constant arc voltage with a selected inert welding
gas. The orbital system weld head is spring loaded within the carriage.
A cam follower rides the pipe's perimeter and actuates a spring to
perpendicularly vary the weld head to work-piece spacing and continu-
ously compensate for ovalty or local flat spots in the piping. North
American Rockwell also devised an electronic arc voltage control (AVC)
system to maintain constant electrode-to-weld puddle spacing. The
Air Force programmer built by Rockweel includes a feedback system which
monitors the arc voltage, compares it to a predetermined value, and,
as required, generates a correction signal to adjust the wire feed rate.
The AVC system thus actually senses or observes changes in the arc gap
as changes in arc voltage to increase or decrease the filler wire speed
to deposit larger or smaller weld puddles to maintain preset gap.

The angle of the tip of the electrode determines where the arc
will initiate. Arc emission can occur from any spot of the heated
electrode's tapered emitting surface. Weld bead shape can be some-
what varied by changing electrode tip angles. Precision, caution
and care are required even with AVC regulation to confine the arc
emission direction to keep from bumping into pipe joint sidewalls
or weld puddles. Additional precautions are necessary to prevent
contacting the electrode with the filler wire during the overlap
portion of the weld. The wire feed motor cutoff point must be pro-
grammed to stop in the initial downslope portion of the weld current.
Lo

6.7 Pre-Weld Positioning

Pipe ends to be Jjoined by welding must be rigidly held in position
during welding to prevent weld heat-induced pipe movement at the joint
due to expansion and contraction forces. Pipes may be clamped or fusion
tack welded prior to the root pass.

We plan to use mechanical clilamps for remote maintenance welding,
as machine tack welding presents additional problems: after tacking,
pipe Joint groove surfaces of the tack must be machined to a thin,
blended buildup; surfaces must then be wire brushed and solvent cleaned;
machine tack welding must also be confined to the upper half of the
pipe to prevent undercutting at the end of the tackweld.

6.8 Root Pass

The ideal root-weld pass requires the shortest possible arc length
without "sticking" and with additions of as much filler wire as possible
for crack sensitive metals. For pipe in horizontal runs weld passes
should start in the overhead portion of a Joint to take utmost advantage
of the chilling effects of cold pipes. Pipe Jjoint lands should ideally
be uniform in thickness and in width. The angle for wire entry and the
exit location of the wire feeder guide tube relative to the weld puddle
are critical. Experimentation to date has followed.the listed Air Force
recommended settings:

For stainless steel welding: Root Pass Arc Length = 1/16 in.

Filler Wire Rate, approx. 10 in./min.
with .045-in. wire

Tool Drive (carriage) Travel Speed, approx.
4 in./min.

Pipe Joint Lands, approx. 1/16 in. wide x
1/16 in. high

Wire Feeder Entry Angle 25 to 30° above
the tangent pcecint with pipe surface,
1/4 in. away from the electrode, with
the wire dragging the groove directly
below the electrode.

AVC set at 8 1/2 to 9 volts with argon
purge gas

Start Position approx. 9 o'clock

Some indications of root pass weld quality can be observed from
programmer voltmeter and wire feed rate meter readings. Both meters
indicate any variations in arc length. The weld bead is not penetra-
ting the pipe Jjoint if voltage readings hold steady but wire feed
43

rates register only below selected rates. Usually a small increase

in welding current will remedy this situation. If, however, the wire
feeder motor builds up tc the set rate, and voltage continues to climb,
poor welding also results, and the cycle should be stopped at once.
The problem will usually be an excessive joint gap formation with too
much pushthrough in the upper quadrants of the pipe, filler wire bound
up within the wire feeder drive and not feeding into the weld, or
excessive puddle fluidity in pipe vertical positions causing puddle
flow away from the electrode tip.

6.9 Fill Passes

Satisfactory weld fill passes do not appear to present great
problems. The second weld pass, or first fill pass, requires some
special care to properly add filler wire and cbtain weld buildup
without affecting the root pass drop-through. Heat input selections
for this and subsequent passes require only fusion to the previous
pass and to the Joint sidewalls. Oscillation of the weld torch
assists to assure fusion into the sidewall. Current pulsing tends
to maintain a stable weld puddle.

Few programmer input changes are required for initial fill passes,
except to add torch oscillation and to halve the wire feeder exit to
pipe surface entry angle. Final fill passes can be made with increased
weld power, wider oscillation, and faster wire feeds. An 11 o'clock
first filler pass start position generally helps to balance partial
distortion of the pipe created by the root pass.

6.10 Repair Welding

The orbital welding system can also be employed to repalr some
weld defects. Two common defects are intermittent lack of fusion
along the sidewalls of a joint, and cold, balled, ropey-like deposits
along a weld Jjoint sidewall. Resultant defective surfaces then pre-
vent subsequent weld pass puddles from wetting and flowing smoothly.
Weld beads exhibit areas of lack of fusion and void inclusions.

Placing the electrode Jjust ahead of the poorly fused area and
manually starting a new weld pass without filler wire additions or
oscillation will generally remelt and, fuse the weld. Pinholes can
also be repaired in a similar manner with the torch located directly
over the pinhole prior to a delayed electrode "start-fire."

A procedure to fill local weld areas which have been purposely
ground out to remove weld defects is to place the carriage about 1/2
in. in front of the area to be filled, set a short arc gap of 1/32 in.,
and initiate a weld cycle. The AVC wire feed control will start to
add wire as soon as the arc gap increases once the carriage traverses
the recessed area. The wire feeder motor will again shut off on the
far side of the depressed area to permit manual weld downsloping.
Ly

T. SPECIAL ORBITAL EQUIPMENT MAINTENANCE REQUIREMENTS

Orbital equipment used for maintenance of reactor systems may
become contaminated. In such cases, repairs to the orbital equipment,
or component replacement operations may have to be performed in shielded
hot cells. Viton-rubber-coated roller surfaces may require periodic
interchange; motors, cutters, torches, etc., may have to be replaced.
Equipment maintenance procedures are listed for major equipment in-cell
components which might be subjected to contamination. Work experience
to date suggests a number of modifications which could be made to the
orbital equipment to provide better access for repairs to be performed
by remote control inside a hot cell and to reduce the time required
for maintenance of the orbital equipment. The changes indicated on
the basis of experience to date are described in the following para-
graphs.

7.1 Carriage

T7.1.1 Drive Rollers - Minor changes to the wire trough of each carriage
arm and provisions for an externally accessible,
flat, Winchester type connector in respective
motor circuits would permit faster interchange
for spare roller assemblies. The removal of
two roller end plugs and two roller end cap
screws and opening the electrical connector
frees the drivers.

T.1.2 Idlers - Idler replacement presently requires the somewhat
tedious disassembly of electrical connectors, the
carriage rear frame and side walls, and the link
pins. For maintenance to be performed inside a hot
cell some simplifications are possible, especially
with use of modified right angle electrical connector
replacements. We recommend Jjigged holddown devices
for all hot cell idler interchange operations to
maintain the highly critical centerline alignment of
the Jjackscrews with the torsion bar gear and the
torque arm gear.

7.2 Blectrical Itews

Access is avallable for all component electrical wiring and acces-
sory items by simply removing cover plates. More extensive use of
miniature connectors might be desirable for electrical system parts
which might require maintenance during developmental test periods.

7.3 Milling Head

Hot cell jigs will be required to support the milling head for
cutter replacement. The cutter is replaced by removing the bolt
holding it toc the output shaft. Washers are employed to hold the
cutter tightly.
L5

Improvements are necessary for more precise depth of cut adjust-
ments and for the horizontal cutter placement adjustment. Precision
worm gear replacements are contemplated for existing miter gears. We
also plan to add an airline connection through the rear carriage panel
to modify cutter motor forced cooling and to keep chips generated
during cutting from entering gear drives, the motor, and the positioning
ad justments.

No problems are expected for routine cutter motor servicing in-
volving backplate, control panel and cutter removal. Motor brushes
can be replaced by simply moving the motor partially out of the housing.
The gear train connecting the motor to the output shaft 1Ls servicable
by disassembling the motor canister.

For our next model, cutter motor speed control circuitry will be
eliminated from the head and transferred to the programmer.

7-4 Welding Head

Periodic cleaning of the weld head is important to prevent high-
frequency arcing. The weld head is disassembled by first removing the
wire feed spool. The torch, oscillator, and wire feed mechanism slide
off the vertical guilde as a unit after the removal of the vertical
adjustment knob. The common mounting block is removed by unscrewing
the horizontal guide pins and the setscrew on the horizontal adjust-
ment shaft. The wire feed is disconnected from the torch and oscil-
lator by removing two screws. The feed pressure-adjusting screw
should be removed to inspect bearing races between rotating disks.

Special, simple remote tooling will be required to replace
threaded torch assemblies, or to interchange electrodes.

Jigs are recommended to support the weld head for hot cell
maintenance work. We plan weld head design change improvements for
our next model's oscillator adjustment cam to the 1id latch device,
and to the horizontal and vertical torch movement gear trains.
Present items do not work well with remote tooling. We also plan to
transfer the present "touchdown" light, which indicates electrode
contact with the work on setup, from the welding head to the programmer.

7.5 General

In the future we also hope to incorporate brighter directional
lighting for both the milling and weld heads, to possibly enlarge the
viewport openings, and to alter the front panel of the carriage to
permit improved viewing for hot cell and operational setups and
possibly for monitoring use in actual reactor repair use.

We are also investigating fluidic sensing and control devices
for remotely setting and controlling oscillator operation. This
would reduce costs, gain reliability, improve weld head rigidity and
compactness and eliminate maintenance time requirements to place long
handled tools into the cell to alter the present electro-mechanical
oscillator's amplitude settings required for successive fill passes.
SECTION C

8. PROGRAM PROPOSAL: DEVELOPMENT OF REMOTE CUTTING, WELDING AND
INSPECTION EQUIPMENT FOR REACTOR SYSTEM MAINTENANCE

8.1 Overall Requirements for Remote Cut/Weld Maintenance

The question of how maintenance will be accomplished is one which
must be answered at the time a reactor system is being designed in
order that appropriate provisions for maintenance will be included
in the design. TIn considering the design of a Molten Salt Breeder
Reactor, ORNL has explored the reported experience in the whole field
of reactor maintenance problems and methods of making repairs. The
advantages of welded joints in nuclear systemsare generally recognized,
but there is no suitable equipment for performing remote cutting and
welding operations in the ways reactor system maintenance would re-
quire. However, there are some new types of equipment which show
promise for radiocactive system applications after further development
of remote controls and other special features for work in high radiation
areas.

The orbital cutting and welding equipment developed for the Air
Force and adapted for remote handling and operation by ORNL demonstrated
good performance in tests of a prototype unit, and thus gave support
to the formation of a new philosophy for maintaining piping systems
and vessel closures in radiocactive systems. The new maintenance
philosophy is to rely on the use of remote cutting and welding equip-
ment to remove from the nuclear system any component which fails and
to install a replacement. This provides a great deal more flexibility
and relisability than a piping system in which flanged Jjoints must be
opened and resealed by remote control. Remote cutting and welding
would provide for all maintenance on the piping system and on seal
welding the flanged openings in vessels. For maintenance of the
electrical, instrumentation and other systems, long-handled tools or
special remote control devices would be used in the manner already
demonstrated in the MSRE and other reactors.

The orbital equipment will require further modifications and
additions to meet the special needs of remote maintenance operations
on pipes and vessels, so that, for example, the equipment can be
positioned at the work site by remote control, without being able to
see directly what is being done. The Air Force cutting and welding
equipment has semi-remote controls for the cutting and welding opera-
ticns and these will require additional special features for fully
remote control.

Work on radiocactive systems not only requires remote controls
for all operations, but alsc requires that the maintenance equipment
be fabricated of materials that resist the damaging effects of radia-
tion and withstand high temperatures and the corrosive action of
decontamination chemicals. The performance of remote maintenance
b7

operations will require special attachments for viewing, measuring,
and sensing from a shielded work area and for performing inspection
operations by remote contrcl. This will necessitate the development
of highly specialized apparatus plus new techniques and procedures
for examination, measurement and inspection. Remotely controlled
methods for accurately positioning and aligning large pipes must be
developed in order to be able to do high quality welding on pipe
Joints. There are many interrelated and difficult problems for which
solutions are not now available. The development programs described
below are proposed to provide the needed equipment and techniques for
remotely controlled, autcmated cutting and welding on highly radio-
active piping and compconents of nuclear systems.

The remote maintenance equipment development program will first
be concerned with completion of the testing and evaluation of the
Air Force orbital equipment with special emphasis on improved cutting
capability for extra hard materials such as alloys with high nickel
content, and the development of proper techniques for acceptable root
pass welding. OSuccessful completion of the testing and evaluation
program should give assurance that the broader, long range development
program can produce a fully autcmated and remotely controlled system
which will meet the rigid quality requirements for maintenance on
nuclear systems.

8.2 A Long-Range, Three-Phase Development Program for Pipe and Vessel
Maintenance

The long range program encompasses three phases: general investi-
gations of welding requirements and remotely controlled equipment for
welding, an extended pipe-joint program, and a vessel closure program.
It is proposed that the study of general remote welding problems and
the development of equipment to handle the specific problems of
reactor pipe Jjoints and vessel closures should be pursued concurrently.
Remote welding equipment modifications can be developed, studied, and
tested at the same time general studies are in progress, with refine-
ments from the general studies being added as they become available.

8.2.1 Phase I, The General Program

 

Major investigations under the general program are the basic
studies of factors that determine the quality of welded joints in
various metals, the studies of different welding techniques and
controls needed to assure that weld quality criteria are met, the
determination of materials and components that will withstand the
effects of radiation, temperature, and of chemical decontamination
treatments, the improvement of welding controls and programming appa-
ratus, the development of equipment and techniques for remote-control
alignment of components, and the determination of environmental and
cleanliness criteria. For the applied phase of the general programn,
mockup work is planned to evaluate various new or modified types of
equipment and remote controls, especially the pipe positioning and
movement schemes designed to achieve acceptable pipe Joint alignment
prior to welding.
L8

It is also recommended that the welding metallurgy of irradiated
materials be investigated. It 1s important to know whether neutron
irradiated pipe metal shows radiaticn effects which will affect welding
and whether minute cracking will occur in heat-affected weld zones.

At present, only limited data are available from tests conducted at
ORNL.>=° Attempts to weld small corrosion samples removed from the MSRE
gave effective welds in only 70% of the cases;21 however, further
testing indicated that better cleaning of the metal surfaces to remove
salt residues prior to welding would solve the problem. Test specimens
should be obtained from actual irradiated sections of reactor pipe in
which the combined effects of neutron irradiation and thermal cycling
are present. The Navy, has informally expressed interest in studying
the welds in highly irradiated sections of nuclear submarine pipe
systems. Valuable data and maintenance experience might be obtained,
in cooperation with the Navy, by using the remotely controlled cutting
and welding equipment to cut out and replace test sections of the ship-
board nuclear system piping so that the removed sections could be
subjected to detailed study of the old welds and of new welds made on
the irradiated metal.

8.2.2 Phase II, The Pipe Joint Program

 

The continuation of the pipe joint program will require development,
and testing of prototype carriages for the larger pipe sizes, design,
development, and testing of second generation cutting and welding
heads, and the establishment of specific techniques, methods and equip-
ment for cutting and welding various metals. It is also planned to use
the findings of the environmental study and the materials and components
study, carried out under the general program to upgrade the materials
and components of the pipe joint maintenance machinery to withstand the
effects of radiation, temperature, and of decontamination treatments in
actual nuclear applications.

8.2.3 Phase III, The Vessel Closure Program

 

A dual approach is suggested for the development of equipment for
cutting and welding of seals on the manhole-type openings in large
vessels in reactor systems. The initial cutting, beveling and welding
work will be performed using various commercially available components
adapted for remote control. Performance appraisals from these tests
will permit the development of modifications to overcome the problems
that are encountered and after further tests, the final component
specifications will be established for industry to supply complete
equipment systems for further testing on vessel closure maintenance.
Another part of the program will be concerned with application of
orbital vehicle machinery to the special problem of seal welding on
lips installed around manhole covers. The pipe welding development
program will determine the applicability of the modular insert carriage
scheme for remote maintenance work. After obtaining satisfactory per-
formance on pipe welds, the welding equipment could be mounted on
special carriages designed to suit the manhole cover geometries. These
carriages should utilize the same cut, bevel, weld and inspection
49

inserts and operate from the same programmer as the pipe welder.

Great time savings and sizeable dollar savings can result from applying
such a system directly to seal welding. Spare part problems and inven-
tories are also minimized. The final procurement of the components
selected to suit the needs of a nuclear environment will incorporate
the most promising apparatus, materials and components indicated by

the development and testing activities.

REFERENCES

20. Molten Salt Program Semiannual Report for the Period ending
February 28, 1966, ORNL Report No. ORNL-3936, p. 117, 1966.

21. Molten Salt Reactor Experiment Monthly Report for August 1968,
ORNL Report No. MSR-68-123, p. 19, 1968.
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23

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erry

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Giambusso, AEC-Washington

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Roth, AEC-ORO
AEC-DRDT
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AFRPL (RPRPD/Capt. F. M. Cassidy)
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