**TFTR D&D PROJECT**

**FINAL EXAMINATION AND TESTING**

**OF THE TFTR TF-COILS**

December 18, 2002

Irving J. Zatz

![](media/image1.jpeg){width="6.0in" height="4.506944444444445in"}

TABLE OF CONTENTS

1\. INTRODUCTION

2\. TF COIL DESIGN AND MANUFACTURING OVERVIEW

3\. THE EXAMINATION AND TEST PROGRAM

3a. IN THE TFTR TEST CELL

3b. COIL BUNDLE DISASSEMBLY AND TEST SPECIMEN PREPARATION

3c. TESTING PERFORMED IN THE PPPL MATERIALS TEST LAB (MTL)

3d. TESTING PERFORMED OUTSIDE OF PPPL

4\. SUMMARY AND CONCLUSIONS

5\. ACKNOWLEDGEMENTS

6\. REFERENCES

APPENDIX A -- RAW AND TABULATED DATA FROM MTL TESTING

APPENDIX B -- FINAL METALLURGICAL REPORT FROM CITY TESTING AND

> RESEARCH LABORATORIES

**[1. INTRODUCTION]{.underline}**

In operation for nearly 15 years, TFTR was not only a fusion science
milestone, but a milestone of achievement in engineering as well. The
TFTR D&D program provided a rare opportunity to examine machine
components that had been exposed to a unique performance environment of
greater than 100,000 mechanical and thermal load cycles. In particular,
the possible examination of the TFTR Toroidal Field (TF) coils, which
met then exceeded the 5.2 Tesla magnetic field machine specification,
could supply the answers to many questions that have been asked and
debated since the coils were originally designed and built. A test
program conducted in parallel with the D&D effort was the chance to look
inside and examine, in detail, the TFTR TF coils for the first time
since they were delivered encased to PPPL. The results from such a
program would provide data and insight that would not only benefit PPPL
and the fusion community, but the broader scientific community as well.

A test program was proposed that would set aside a number of selected
sections from the twenty TFTR TF coils as they were removed during D&D.
These sections would be cut from the coils in several different areas
including the nose, back leg, water fitting and lead block regions,
concentrating on those known areas whose performance was questioned
during TFTR operations.

The approved test program included documented visual inspections and
photography during all phases of disassembly and testing. Physical
examinations of the coils were performed to determine consistency of
coil manufacturing techniques, including status of the potting compound,
quality of turn-to-turn epoxy impregnation and bonding, and
determination of the cause of coolant leaks during operation. Selected
chemical and metallurgical analyses were conducted to determine if the
composition of the materials have altered and to identify unknown
materials. Multiple mechanical test samples in various orientations were
cut from several magnet and case locations to check for consistency and
range of material properties.

With the exception of the chemical and metallurgical analyses, this test
program was performed entirely at PPPL.

**[2. TF COIL DESIGN AND MANUFACTURING OVERVIEW]{.underline}**

Each of the twenty TFTR TF coil assemblies was comprised of a copper
alloy magnet enclosed in a four segment bolted Nitronic 33 stainless
steel case. The case was necessary to provide stiffness and strength to
withstand the loads produced by 73.3 kA of current in the magnet, which
generated a maximum toroidal field of 5.2 Tesla. This field resulted in
a net centering force of 6.1 million pounds and an overturning moment of
105 million inch-pounds in each magnet. Due to the exceptional overall
performance of the TF coils, these design levels were exceeded late in
the TFTR program. Specifically, the 44-turn, spiral wound, two-pancake
magnet was made of a variation of CDA 104 silver-bearing OFHC copper
alloy, extruded and drawn to a minimum yield strength of 32 ksi
\[Reference 1\]. Turn thickness varied in three groups from 0.552-inch
to 0.677-inch to balance temperature gradients in the coil. The coil
insulation system was comprised of the following \[Reference 2\]:

-   Turn-to-turn insulation made up of multiple half-lapped layers of
    0.007-inch thick glass fiber tape

-   Barrier strips and glass filler insulation between pancakes

-   Ground wrap insulation

-   Potting compound inserted after the coil was installed in the case -
    inner case surfaces were treated with a parting agent (mold release)
    to prevent bonding of the potting compound to the case

The case bolt material was Inconel 718. As a historical footnote, the
TFTR coil case was originally designed to be made from titanium alloy
with these Inconel bolts. For a variety of reasons, late in the design
stages of TFTR, the case material was switched to Nitronic 33 stainless
steel, which has higher elastic modulus but lower strength than
titanium. This design change was made because it produced a more
favorable distribution of load within the coil. The high strength
Inconel bolts bearing on the lower strength Nitronic case material may
have resulted in local yielding of the case and could have been a
contributing cause to the bolt loosening incident which temporarily
hampered TFTR operations in the early 1990\'s.

**[3. THE EXAMINATION AND TEST PROGRAM]{.underline}**

**[3a. IN THE TFTR TEST CELL]{.underline}**

A baseline examination and test program was outlined \[Reference 3\]
with the expectation that variations could occur as conditions
warranted. When dealing with structures as large and complex as TFTR
components, coupled with the requirements and schedule of the D&D
program, flexibility becomes critical. As initially planned, sections of
TF Coils #3 and #18 would be set aside to be used to prepare samples for
a variety of mechanical, metallurgical and visual tests. These two coils
were specifically targeted because they had been the sources of some of
the most nagging coolant leaks during TFTR operations. Over the years,
TF #3 had developed leaks at several of the fourteen water fittings at
the base of the coil. Numerous well-documented attempts \[examples
References 4 & 5\] were made to resolve these leaks, but none had been
completely successful, ultimately leading to the substitution of
Fluorinert (with a high electrical resistivity) for the de-ionized water
as the TF coil coolant.

It has long been suspected that the water fitting material that was
brazed to the OFHC copper TF conductors may not have been oxygen free
copper, resulting in potential hydrogen embrittlement which could lead
to cracking and leaking in the water fitting regions.

A chronic leak developed in the lead block region of TF #18 that was
speculated to have originated in the lead spur joint within the body of
the coil. This leak could not be rectified despite numerous in situ
inspections and attempted remedies \[example Reference 6\].

Although TF coils #3 and #18 were targeted for mechanical and
metallurgical testing, each of the other eighteen TF coils were visually
inspected for any anomalies that could provide useful data. The usual
D&D procedure was to remove each of the ten two-coil and vacuum vessel
segments from the TFTR pedestal (Figure 1) following diamond wire
cutting (Figure 2), then disengage each of the coils from the vacuum
vessel segment on a specially designed stand fixture (Figure 3). As each
cased TF coil was removed from the stand, it was placed on the table of
a Marvel band saw located in the TFTR Test Cell (Figure 4). Since an
individual TF coil was considered too large for transport to the Nevada
Test Site for final disposal, each coil was cut into two segments at its
mid-plane. From a test program perspective, this was an enormous benefit
because it permitted the close visual examination of the four faces of
the mid-plane cross section of every coil. These observations provided
the first ever glimpses of the quality and consistency of the
Westinghouse manufactured coils. Figure 5, showing the TF #3 nose
section as it was removed from the Marvel saw, is typical of what was
found in these cross sections. Note that the cooling channels are filled
with residual copper slivers from the sawing process. Also,
discolorations on the metal surfaces are the striations from the cut,
while the color variation in the insulation is the effect of the light
on the various strips and layers of material rather than any
inconsistency in manufacturing.

Upon closer visual inspection, the coil bundles appeared to be in
outstanding condition, showing virtually no observable signs of wear or
fatigue. Epoxy and potting compound penetration appeared to be uniformly
excellent throughout. No visible voids could be found. It was hard to
imagine that a structure this complex could have endured over 100,000
mechanical and thermal load cycles and looked so pristine. When the case
components were removed from the coil bundles, concerns about the
deterioration of the potting compound on the exterior faces of the coil
bundles proved to be unfounded. It had been suspected that with years of
load cycling, coil movement within the case could have gradually cracked
and ground the potting compound into small pieces or even dust. In fact,
in every coil examined, the potting compound was not only found to be
intact, but retained an almost Teflon-like quality (Figure 6) enabling
the coil to glide in a nearly frictionless manner within the coil case
during operations. When the case pieces were first unbolted, these
segments, each weighing hundreds of pounds, could be readily slid along
the coil\'s potting compound surface with relative ease (Figure 7). The
only signs of wear were superficial cracks along the potting compound
surface (Figures 8 & 9). There was no spalling. Black marks found on the
surface of the potting compound was determined to be residue of the
parting agent (mold release) used to prevent the potting compound from
bonding with the case during original impregnation. The same black
markings were found on the case pieces as well.

These visual inspections of every TF coil cross section found that the
coils were built and assembled with remarkable consistency and quality.
The extruded cooling channels were clear and clean. Turn transition
regions were smooth and consistent (Figure 10). No evidence of any
turn-to-turn shorts, burn marks or contact could be found. There were
only two observable geometric anomalies. Occasionally, the turns within
a 22-turn pancake would not be in perfect alignment and would vary by up
to 3 mm (Figures 11 & 12). Also seen in these figures is that the
turn-to-turn insulation layer thickness normally varied within a range
of twenty percent of the 0.05-inch design thickness, but in no instance
was any metal-to-metal contact observed.

As indicated previously, the baseline test program would take samples
from TF coils #3 and #18. Accordingly, these coils were to be cut
differently, in accordance with the layouts shown on Figures 13 & 14,
respectively \[Reference 7\]. Three two-to-three-foot long segments
would be taken from each of these coils (Figure 15). Segments from the
mid-plane inner and outer legs of these two coils would be set aside. TF
#3\'s third segment would be the water-fitting region while TF #18\'s
third segment would be from the lead block region. Six cuts on the
Marvel saw were required for each of these coils instead of the usual
bisecting two cuts for the other TF coils (Figure 16).

The D&D staff working in the TFTR Test Cell were alerted to observe the
TF coils for anything that seemed different or unusual. They observed
and reported that TF coil #8 was different. Up to TF #8, which was cut
after TF's #3 & 18, each cut of a TF coil on the Marvel saw averaged 5
to 6 hours. This included cutting through the entire coil and case cross
section. Early on, cuts were taking even longer because cutting through
the Inconel 718 case bolts added a significant amount of time.
Recognizing the bolt issue led to a policy of removing all bolts along a
cut line in order to expedite the process. The first cut of TF #8 took
approximately one hour. Close examination of the cutting procedure
indicated that the saw band speed was slower, but the usual procedure
had been followed otherwise. Given the unusual circumstances, it was
decided that a small section of the TF #8 nose was to be set aside for
material testing (Figure 17). The second cut to remove this segment took
longer than one hour, but with the slower band speed, still took far
less than the average 6 to 8 hours. All TF coil cuts from that point
forward were made at the slower band speed and the average cut time
dropped to 2.5 to 4 hours each, but none came anywhere near the one hour
it took for the first TF #8 cut. This anomalous event justified the
closer examination that followed for TF #8. Saw blade quality was
another possible variable that may have influenced the cut time.
Normally, a new saw blade was used for every TF coil cut made during the
D&D program. It was possible that the blade used for the first TF #8 cut
was of exceptional durability and sharpness. Regardless, TF #8 was to be
part of the material test program along with the segments cut from TF #3
and #18.

In all, seven TFTR TF coil sections were set aside for physical and
metallurgical testing, the aforementioned six sections from TF #3 and
#18, and the nose section from TF #8. The cases of the three nose
sections (TF #3, 8, 18) and two back leg sections (TF #3 and 18) were
disassembled in the TFTR Test Cell. While on a pallet and properly
supported with slings, each of these five sections had its case bolts
removed. The four Nitronic case sections (inner ring, outer ring, and
two sidewalls) were saved, along with the bolts and shims for each
section (Figure 18). All parts were cataloged and retained for further
inspection and testing. Coil and case segments were decontaminated and
measured by HP for activation. Following decontamination, activation
levels in the disassembled sections were measured as follows:

Copper 1.5 +/- 0.5 mrem/hr - contact

0.5 +/- 0.2 mrem/hr - @ 30 cm

Nitronic 33 2.8 +/- 0.5 mrem/hr - contact

1.2 +/- 0.3 mrem/hr - @ 30 cm

> Insulation Measured with copper, but activation should be less than
> copper

Once this process was complete, the pallet for each coil segment was
transported to the Rad Waste building. The other two cased coil segments
(water fittings on TF #3 (Figure 19) and lead block on TF #18 (Figure
20)) were sent intact to the Rad Waste building. Due to the various
protrusions from the sidewalls of these segments, their disassembly
would be a more delicate operation involving removal of external
insulation and potting material with a router first. This work was to be
done in the Rad Waste building where the work could be performed with
fewer distractions. The level of activity and premium placed on
available floor space in the TFTR Test Cell made it impractical to
attempt this effort there. The Nitronic case sections surrounding the TF
#3 water fitting section (Figures 21 & 22) and the TF #18 lead block
section (Figure 23), were successfully disassembled in the Rad Waste
building shortly thereafter. All disassembled case segments were kept on
individual pallets along with their corresponding coil sections in the
Rad Waste building until individual pieces were required for test
specimen preparation in the RESA building machine shop. In this way, a
minimum of activated material would be outside of the Rad Waste facility
at any given time.

The TF #3 water fitting coil section was originally cut in the TFTR Test
Cell to ensure that the fourteen water fittings would remain intact.
Some of the fitting protrusions had been cut off during diamond wire
cutting, but all of the braze joints and portions of the outside tubes
needed for the metallurgical investigation were still intact.
Ultimately, this coil section was disassembled turn by turn in the RESA
building so that individual water fittings could be subjected to the
necessary testing.

The TF #18 lead block segment was originally cut in the TFTR Test Cell
to preserve both the lead block protruding from the side of the coil as
well as the lead spur located within the coil body. Over the years, the
lead spur had been identified as the prime candidate for the origin of
the chronic leak in TF #18 (Figure 24). While still in the Rad Waste
building, the lead area was borescoped from several locations, but the
results were inconclusive regarding the origin of the leak. It was
originally planned to disassemble this coil section so that the lead
block/spur turn could be investigated in detail, however, resources
became limited and this exercise could not be completed. The TF #18 lead
block coil section remains in the Rad Waste building awaiting the
possibility of conducting this investigation at some point in the
future.

![](media/image2.jpeg){width="6.0in" height="4.506944444444445in"}

Figure 1 - Removal of a TFTR two-coil segment from the pedestal

![](media/image3.jpeg){width="3.373611111111111in"
height="4.506944444444445in"}

Figure 2 - Diamond wire cutting of TFTR

![](media/image4.jpeg){width="6.0in" height="4.506944444444445in"}

Figure 3 - Two TF coil segment on stand fixture

![](media/image5.jpeg){width="6.0in" height="4.506944444444445in"}

Figure 4 - Marvel band saw preparing to cut TF #3 nose section

![](media/image6.jpeg){width="6.0in" height="4.506944444444445in"}

Figure 5 - TF #3 nose section following saw cut

![](media/image7.jpeg){width="6.0in" height="4.506944444444445in"}

Figure 6 - TF #3 nose section bundle with potting compound intact

![](media/image8.jpeg){width="3.373611111111111in"
height="4.506944444444445in"}

Figure 7 - Inner and outer ring case sections on TF #3 back leg coil
bundle

![](media/image9.jpeg){width="5.7in" height="4.559722222222222in"}

Figure 8 - Minor cracking in TF #18 nose section potting compound

![](media/image10.jpeg){width="5.6in" height="4.479861111111111in"}

Figure 9 - Minor cracking in TF #18 back leg section potting compound

![](media/image11.jpeg){width="6.0in" height="4.506944444444445in"}

Figure 10 - Close up view of turn transition in back leg of TF #3

![](media/image12.jpeg){width="5.6in" height="4.479861111111111in"}

Figure 11 - Slight turn-to-turn misalignment

![](media/image13.jpeg){width="5.1in" height="4.5in"}

Figure 12 - Slight turn-to-turn misalignment

![](media/image14.jpeg){width="5.997916666666667in"
height="7.938194444444444in"}

Figure 13 - Cut plan to extract three test sections from TF #3
\[Reference 6\]

![](media/image15.jpeg){width="5.997222222222222in"
height="7.863888888888889in"}

Figure 14 - Cut plan to extract three test sections from TF #18
\[Reference 6\]

![](media/image16.jpeg){width="6.0in" height="4.506944444444445in"}

Figure 15 - Encased TF #3 back leg section prior to disassembly

![](media/image17.jpeg){width="6.0in" height="4.506944444444445in"}

Figure 16 - Cutting the TF #3 back leg test section on the Marvel band
saw

![](media/image18.jpeg){width="5.7in" height="4.559722222222222in"}

Figure 17 - TF #8 nose section

![](media/image19.jpeg){width="6.0in" height="4.506944444444445in"}

Figure 18 - Bolts and shims following TF #3 back leg coil case section
disassembly

![](media/image20.jpeg){width="5.551388888888889in"
height="4.440972222222222in"}

Figure 19 - TF #3 water fitting coil section

![](media/image21.jpeg){width="5.551388888888889in"
height="4.440972222222222in"}

Figure 20 - TF #18 lead block coil section

![](media/image22.jpeg){width="5.551388888888889in"
height="4.440972222222222in"}

Figure 21 - Disassembled TF #3 water fitting coil section

![](media/image23.jpeg){width="5.551388888888889in"
height="4.440972222222222in"}

Figure 22 - Close up of TF #3 water fittings with partial removal of
insulation

![](media/image24.jpeg){width="5.85in" height="3.9in"}

Figure 23 - Close up of TF #18 lead block

![](media/image25.jpeg){width="5.9944444444444445in"
height="7.709027777777778in"}

Figure 24 - Schematic of a Typical Lead Block and Lead Spur Reg

**[3b. COIL BUNDLE DISASSEMBLY AND TEST SPECIMEN
PREPARATION]{.underline}**

Once a Radiological Controlled Area (RCA) was set up by Health Physics
(HP) in the RESA building to use as a holding area, individual coil and
case pieces were transported from the Rad Waste building on an as needed
basis. RCA\'s were set up around machines to be used for cutting and
milling test specimens.

Mechanical testing of the OFHC copper from the coil bundles and the
Nitronic 33 from the coil cases were comprised primarily of two ASTM
standard tests - ASTM E8 ("Standard Methods of Tension Testing of
Mechanical Materials") and ASTM E23 ("Standard Methods for Notched Bar
Impact Testing of Metallic Materials") \[Reference 8\]. Conformance with
the ASTM E8 tension testing would require precision cut 'dog bone' type
specimens (Figure 25). Similarly, precision cut Charpy impact (notched
bar) specimens (Figure 26) would be required for the ATSM E23 tests. All
specimens were prepared by PPPL's machine shop in the RESA building.

It is important to note that the importance of following the ASTM
standards is to give the tests credibility and validity for the purposes
of publishing results and comparing with data available in the
literature. The ASTM is the recognized international testing standard
reference.

Data obtained from the tension test can provide the yield, ultimate,
modulus of elasticity, reduction of area, and elongation of a material.
The impact test provides a standardized value of impact energy to
failure that can give insight into the relative ductility and fracture
characteristics of a material.

It was readily apparent that the sidewalls would be best suited for
cutting the test coupons based on the geometry of the four coil case
pieces for each disassembled coil segment (inner ring, outer ring and
two sidewalls). The principle reason for this decision was that every
dimension of the inner and outer ring pieces was at least several
inches. A great deal of machining would be necessary to cut test coupons
from these thick pieces. On the other hand, the sidewall thickness
varies roughly from 0.75 inches to 1.5 inches (Figure 27). It is worth
noting that Nitronic 33 is so difficult to machine that one machinist at
first thought that he was cutting an Inconel alloy. Machining the
sidewall plates into the necessary tension and impact test articles
would greatly simplify the preparation process saving a substantial
amount of time and manpower.

Furthermore, it was decided that the most efficient way to machine the
required 'dog bone' shaped tension specimens was with the water jet
cutter because of the difficulty of machining Nitronic 33 (even in the
thinner sidewall plates) with a conventional blade saw. Charpy impact
test specimens, however, were still prepared by more conventional
methods because of their simpler geometry and smaller size.

A minimum of three tension and three Charpy specimens were cut in each
of two perpendicular directions from the sidewall plates of the three TF
coils that were set aside (#3, 8, and 18). Specimens were cut oriented
along the two principal plate directions -- TFTR's poloidal direction
and minor radial direction. Depending on the procedures that were used
to build the coil case sidewalls, the material properties might be
affected by plate orientation. The testing would determine this.

While the Nitronic 33 material from the sidewall plates was readily
accessible but difficult to machine, the OFHC copper was exactly
opposite. Working with the 44-turn bonded copper bundles was fairly
cumbersome and time consuming. Machining the copper was relatively easy
once it could be extracted. First, the two 22-turn pancakes had to be
separated from each other. This was usually accomplished by setting the
overall bundle in a sling to orient it for a single saw cut in the RESA
building. Once to two pancakes were separated, the next task was to
separate the 22-turns in each of the pancakes from each other. This
required the removal of the potting compound and overwrap materials from
the pancakes, to be followed by the turn-to-turn separation of the
copper. Several randomly selected turns of copper were chosen beforehand
to be extracted for cutting into the tension and Charpy test coupons.
Figure 28 shows a typical turn of copper with portions of insulation
tape still attached to the turn. Each one of these selected turns would
then be cut in such a way as to yield three coupons in both the axial
and transverse directions for impact testing (six impact test coupons
from each selected turn). Figure 29 shows a typical Charpy coupon prior
to machining. This was accompanied by cutting three tension coupons
(Figure 30) from each selected turn along the axial (poloidal) direction
of the turn. Acceptable tension specimens in the transverse direction
were not possible because of the presence of the extruded cooling
channel in the turn. Figure 31 shows the leftover turn following the
cutting of all necessary coupons from it.

The process of separating the copper tuns from their pancakes furnished
extremely valuable information about the turn-to-turn bond strength
between the copper and epoxy. This bond strength was one of the most
debated issues during the days of TFTR operations because it led to the
calculated TF coil stiffness and strength. This ultimately determined
the limits for coil currents and magnetic fields. The question was could
the coil bundle be assumed to be fully bonded resulting in a composite
cross section of maximum stiffness, or was there any turn-to-turn
delamination resulting in a lower stiffness cross section where only
friction kept adjacent turns from sliding relative to each other? To be
conservative, analytical models of TFTR assumed some degree of
delamination.

The visual inspection of the coil bundles, as seen in prior figures and
close-up in Figure 32, gave every appearance that the coil was fully
bonded because of the pristine condition of the copper, insulation
material and epoxy. There were frequent instances during actual
turn-to-turn separation where the turns were indeed well bonded and were
extremely difficult to pry apart. But there were also instances where
the pancake turns separated with significantly less effort. In fact, in
some instances, the turns separated with hardly any effort with the
epoxy bonded to only one copper turn. In other cases, the epoxy and
insulation apparently failed to bond to either adjacent turn. The copper
turns gave every appearance of proper pre-treatment and the integrity of
the epoxy and glass tape layer was observed, yet turn-to-turn bonding
either never occurred or did not persevere satisfactorily possibly
because the pre-treatment was not properly applied or was not an
effective process. For example, in Figure 33 the glass fiber tape, which
should be bonded to the copper via epoxy, can be seen to be
substantially delaminated from the turn. In a more extreme example,
Figure 34 is a sleeve of bonded glass fiber tape where the copper turn
simply slid out. Figure 35 is an instance where the entire ground wrap
insulation of a coil bundle 'popped' off the bundle with only minimal
effort during turn separation. These observations of variable
turn-to-turn and insulation delamination in the TF coil bundles is
direct evidence that the structural assumption of a perfectly bonded and
integral composite coil would have been unconservative, thereby
justifying the design limits originally set during machine operations.
Accordingly, the need to perform elaborate shear testing at this time to
determine the turn-to-turn bond strength was considered moot because
even where bonding occurred, the bond strength was inconsistent.

Another important observation made while the TF coil bundles were being
separated was that several turns had visibly detectable brazed joints
where the lengths of extruded copper were spliced to form the wound
coil. Every inspected joint had a flawless appearance with no evidence
of any wear or residual defect. Test specimens were taken from several
of these braze joint regions.

Once the selected turns to be used for mechanical testing were extracted
from the bundles, the test coupons were cut and machined into the ASTM
specimens ready for testing. It was during this process that the
machinists observed and reported that the degree of difficulty in
machining and milling the copper varied from specimen to specimen. Some
coupons cut more easily than others, indicating a softer, lower strength
copper. Upon further inspection, it was found that the copper was softer
in the immediate vicinity of the brazed joints. High temperatures
encountered during the brazing process had locally annealed the copper,
which gradually hardened as one moved away from the joints, as expected.
The extent of this annealing would be determined by the mechanical
tests.

There was one additional observation made during the dismantling of the
outer leg coil bundles. A thin strip of copper, approximately one
millimeter thick and approximately one inch wide, was found embedded
between the outerwrap and potting compound of each coil bundle centered
between the pancakes (Figures 36 & 37). This strip of copper is the
ground plane electrode that electrically connected the coil's ground
plane to the case.

![](media/image26.jpeg){width="5.998611111111111in"
height="3.0229166666666667in"}

Figure 25 - Typical \'dog bone\' tension specimen

![](media/image27.jpeg){width="5.998611111111111in"
height="3.129861111111111in"}

Figure 26 - Typical Charpy V-notch impact specimen

![](media/image28.jpeg){width="6.0in" height="4.506944444444445in"}

Figure 27 - Profile view of back leg sidewall case plates

![](media/image29.jpeg){width="6.0in" height="4.0in"}

Figure 28 - Typical copper turn (with insulation tape) following bundle
separation

![](media/image30.jpeg){width="6.0in" height="4.013888888888889in"}

Figure 29 - Typical Charpy coupon cut from copper turn prior to
machining

![](media/image31.jpeg){width="6.0in" height="4.053472222222222in"}

Figure 30 - Typical tension coupons shown in various stages of machining
prior to \'dog bone\' milling

![](media/image32.jpeg){width="6.0in" height="4.093055555555556in"}

Figure 31 - Leftover turn following cutting of 6 Charpy and 3 tension
coupons

![](media/image33.jpeg){width="5.7in" height="4.559722222222222in"}

Figure 32 - Extreme close up of insulation where tape layers can be
distinguished

![](media/image34.jpeg){width="6.0in" height="4.190277777777778in"}

Figure 33 - Bonded tape delaminated from copper turn

![](media/image35.jpeg){width="6.0in" height="3.879861111111111in"}

Figure 34 - Sleeve of bonded glass fiber tape where copper turn slid out

![](media/image36.jpeg){width="6.0in" height="4.0in"}

Figure 35 - Large section of ground wrap insulation which easily
separated from the coil bundle

![](media/image37.jpeg){width="5.448611111111111in"
height="4.367361111111111in"}

Figure 36 - Copper strip separated from the outerwrap and potting
compound

![](media/image38.jpeg){width="3.0in" height="4.5in"}

Figure 37 - Copper strip separated from the outerwrap and potting
compound

**[3c. TESTING PERFORMED IN THE PPPL MATERIALS TEST LAB]{.underline}**

In order to prepare for the in-house mechanical testing of the tension
and impact specimens being cut in the machine shop, it was necessary to
calibrate the test machines that were going to be used. The selected
'dog bone' tension specimens conforming with the ASTM standards would
fit the available grips and load carrying capacity of PPPL's 100-kip MTS
servo-hydraulic testing machine (Figure 38). The Charpy impact (notched
bar) mechanical tests would be done with PPPL's Tinius-Olson 300 ft-lb
testing machine (Figure 39).

Due to the arrival of a new braze furnace in mid-2002, the MTS test
machine had to be moved to a new position in the Materials Test Lab
(MTL). When this is coupled with the fact that the MTS and Tinius-Olson
machines had been dormant for some time, machine re-calibration became
essential to the integrity of the mechanical tests. Accordingly, these
machines were re-certified to meet the ASTM testing standards. Prior to
the start of actual testing, several sample tests were conducted to
verify machine performance.

Upon receipt of the final test specimens from the machine shop, each
article was carefully measured to certify that it met ASTM's tight
geometric tolerances. This process did identify several specimens that
did not meet those standards. Whenever possible, those specimens were
re-machined and milled so that they could be used in the test program.

Over a period of several weeks, the tension and impact testing of the
copper and Nitronic samples was conducted in the MTL. The testing
program was successfully completed without complication. A summary
discussion of the test program results follows. The complete set of raw
and tabulated test data can be found in Appendix A.

The CDA 104 OFHC copper used to fabricate the TFTR TF coils was extruded
and drawn to a specification of a minimum 32 ksi yield stress and a
minimum 35 ksi ultimate stress. Per the copper standards \[Reference
9\], these values correspond to slightly less than a half-hard tempered
OFHC copper. An overwhelming majority of the copper tension samples
corroborated these specifications. The yield stress values from the
tests ranged between 32.5-41.7 ksi with a mean value of approximately 34
ksi. The ultimate stresses ranged between 35.9-42.9 ksi with an
approximate mean value of 36.4 ksi. Other material properties were
consistent with the standards as well. The testing results for
elongation ranged between 20-39 percent while reduction of area ranged
from 80-86 percent. Figure 40 is a close-up view of the failure surfaces
of a typical copper tension specimen that clearly shows the necked down
reduction of area. All of these results either met or exceeded the
specifications established for the TFTR conductor material.

As was discussed previously, an observation made during the disassembly
and machining of the copper was that some of the tension specimens
straddled the brazed joints that spliced the long lengths of copper
windings together \[Reference 10\]. The braze process was expected to
anneal the surrounding copper, but the brazed joints were intentionally
staggered by design to avoid a concentration of annealed copper in the
windings. The braze joints themselves were designed to be stronger than
the local copper implying that the failures in the relevant tension
specimens would be in the copper and not the joints. With one exception,
these specimens all failed in the copper. The mean yield stress for this
group of specimens was 13.8 ksi and the mean ultimate stress was 30.5
ksi. These values correspond with reference values for copper that is
almost fully annealed. Similar consistency with reference values was
exhibited for elongations of approximately 50 percent and reduction of
areas of over 80 percent. Figure 41 compares two tension samples - one
hardened and the other almost fully annealed. The most obvious
difference between them is that the ductility in the annealed specimen
(with the brazed V-joint clearly visible) grew nearly an inch longer in
the tension test prior to failure. The one specimen that did fail in the
braze joint showed far less ductility by yielding at 13.8 ksi, but
failing at only 26.6 ksi. Elongation was 25 percent, half the annealed
values, while the reduction in area was also lower at 76.5 percent.

There were a few intermediary tension test results observed for some of
the specimens. They gave test results that fell between half-hard and
annealed copper. Although a brazed joint was not physically located in
the sample, it was concluded that these specimens were softened by being
in the vicinity of a brazed joint and had been affected by heating due
to the high thermal conductivity of the copper.

Results for the Charpy V-notch impact tests ranged from 137-156 ft-lbs
of energy absorbed for the hardened copper and ranged from 66-119 ft-lbs
for the annealed copper. This means that the impact resistance of the
hardened copper is greater than that for the annealed copper and should
be evident upon viewing the tested samples. Figure 42 shows three Charpy
specimens - an untested Charpy specimen, a hardened test sample and an
annealed test sample (from left to right). The major difference visible
in this figure is that the break in the annealed sample runs much deeper
than the hardened sample, indicative of the hardened sample\'s ability
to absorb more impact energy. Figure 43 is a close-up view of the break
faces. The annealed sample (on the right) has a larger, cleaner and
smoother fracture surface, indicative of lower impact resistance than
the hardened specimen, which has a more pronounced hourglass shape and
more striated fracture surface.

Every Charpy sample was also used for Rockwell hardness measurements.
The hardened copper samples ranged from B30 to B54, which compares
favorably to the literature. Rockwell hardness measurements for the
annealed copper, however, were more erratic ranging from B19 to B73. The
literature also has inconsistent hardness data for annealed copper.

In all of the copper tests performed, the only variable that affected
the data was the degree of annealing. The test results did not show any
significant deviation as a function of either directionality (in the
Charpy samples) or coil origin. TF #8 (the one-hour cut) results overlay
closely with results from TF #3 and TF #18 pointing to an excellent
consistency in the copper material and the processes used to manufacture
the coils.

The Nitronic 33 (Armco 18-3 Mn Stainless Steel, ASTM Grade XM-29, UNS
S24000) material test program went smoothly, as well. Reference minimum
values for yield and ultimate stresses are 55 ksi and 100 ksi,
respectively \[Reference 11\]. Test results for yield stress ranged from
55.1-62.6 ksi with a mean value of 59 ksi. Ultimate stress ranged from
95.6-104 ksi with a mean value of 101.5 ksi. Note that two specimens
failed at less than the specified minimum of 100 ksi ultimate stress,
but all specimens exceeded the minimum yield spec. Although the Nitronic
tension tests were performed on sets of orthogonal specimens cut from
the sidewalls, all results indicate isotropic behavior. Elongation
values ranged from 49-62 percent compared with 40 percent minimum in the
literature. Reduction of area ranged from 55-59 percent compared with 50
percent minimum in the literature. Figure 44 shows the break faces of a
typical failed tension specimen. In the literature, Rockwell hardness
values indicate ranges from B96 to a maximum B-scale value of 100. The
test samples consistently reached the B100 mark, so measurements were
taken on the next level C-scale from C5 to C16.

Charpy V-notch impact results in the literature vary from 232-300+
ft-lbs at room temperature for Nitronic 33. The first few Nitronic
Charpy tests conducted at room temperature were consistently greater
than 290 ft-lbs. Since the Tinius-Olson impact test machine is a 300
ft-lb device, accurate performance and results could not be assured
under these conditions. It was decided to test the majority of the
samples at liquid nitrogen (77K). The literature indicates a minimum 30
ft-lb impact strength for Nitronic 33 at 77K. Test results ranged from
34-51 ft-lbs, exceeding the established minimum for impact strength.
These results can be extrapolated and coupled with the few tests
performed at room temperature resulting in a conclusion that all Charpy
specimens met the minimum established impact resistance requirements.
Charpy tests results were isotropic. Figure 45 compares Charpy specimens
at room temperature (left) and LN2 (right). Lower temperature makes the
metal more brittle, thereby reducing its impact resistance. Due to its
ductility, the room temperature sample readily absorbed 300 ft-lbs of
energy, while the LN2 sample broke at approximately 40 ft-lbs. Figure 46
compares the fracture faces of these two samples. The room temperature
sample (left) has a rough, striated face indicative of high impact
resistance. The LN2 sample (right) has a smooth, clean fracture surface
with slight shear lips at the edges, which is normal.

The Nitronic 33 material yielded very consistent test results that, with
very few exceptions, exceeded the minimum program specifications. All
measured properties were isotropic and uniform from coil case to coil
case. As with the copper, nothing in the test results distinguished the
TF #8 samples from the TF #3 and 18 samples. This virtually assures that
the anomalous TF #8 cut was due to the cutting procedure itself rather
than the materials.

![](media/image39.jpeg){width="5.551388888888889in"
height="4.440972222222222in"}

Figure 38 - 100-Kip MTS Servo-Hydraulic Test Machine

![](media/image40.jpeg){width="5.551388888888889in"
height="4.440972222222222in"}

Figure 39 - Tinius-Olson 300 Foot-Pound Impact Machine

![](media/image41.jpeg){width="5.747916666666667in"
height="4.353472222222222in"}

Figure 40 - Typical Failure Surface of Copper Tensile Specimen

![](media/image42.jpeg){width="5.750694444444444in"
height="4.600694444444445in"}

Figure 41 - Comparison of Hardened vs. Annealed Copper Tension Specimens

![](media/image43.jpeg){width="5.448611111111111in"
height="4.3590277777777775in"}

Figure 42 - Copper Charpy Specimens - Untested, Hardened, Annealed (from
left)

![](media/image44.jpeg){width="5.5in" height="4.559722222222222in"}

Figure 43 - Copper Charpy Impact Fracture Faces - Hardened (left) vs.
Annealed

![](media/image45.jpeg){width="5.7in" height="4.559722222222222in"}

Figure 44 - Typical Failure Surface of Nitronic 33 Tensile Specimen

![](media/image46.jpeg){width="5.5in" height="4.509722222222222in"}

Figure 45 - Nitronic Charpy Impact Test Speciems - Room Temperature
(left) vs. LN2

![](media/image47.jpeg){width="5.7in" height="4.559722222222222in"}

Figure 46 - Nitronic 33 Charpy Impact Fracture Faces - R.T. (left) vs.
LN2

**[3d. TESTING PERFORMED OUTSIDE OF PPPL]{.underline}**

During TFTR operations, when TF coil coolant leaks were observed at the
water fittings, numerous attempts were made to locate, explain and
repair those leaks. Among the techniques employed were borescoping,
flushing with solvents and resealing with various compounds.
Nevertheless, some of these leaks could not be resolved or repaired
adequately resulting in the use of Fluorinert as the conductor coolant.
The ability to perform actual metallurgical analyses on these leaking
fittings was obviously limited during TFTR operations to in-situ,
non-destructive testing.

Two metallurgical evaluations \[References 12 & 13\] were performed on
water fittings and copper specimen samples available from sources like
one of the spare TF coils (e.g., the 250 coil). Since the required
technology to do this work was unavailable at PPPL, outside contractors
were used. These tests were conducted for the purpose of doing
metallograpic and micrographic analyses of grain sizes and any defects
in the samples. This information would then be utilized in an
evaluation, including failure analysis, of the specimens. One particular
mode of copper deterioration that would contribute to possible cracking
and leaking in the fittings is hydrogen embrittlement. Ordinarily, using
oxygen free copper, such as the OFHC CDA 104 used for the TFTR TF coil
bodies, is sufficient to avoid hydrogen embrittlement. But in 1992, one
vendor \[Reference 12\] reported finding evidence that it did, indeed,
exist in the test samples provided and that the copper oxidation leading
to embrittlement may have inadvertently occurred somehow during the
fabrication process. It was also noted that with hydrogen embrittlement,
defect growth is a progressive condition, meaning that once oxidized
copper is present, the embrittlement could continue gradually with time.
Higher temperatures would likely accelerate embrittlement. Ultimately, a
microscopic defect will manifest itself as a crack leading to a
potential leak.

The other metallurgical evaluation performed in 1995 \[Reference 13\],
however, found no evidence of hydrogen embrittlement or abnormal grain
growth in the water fitting samples it received and tested.

With the TF #3 water fitting section set aside as part of the D&D
project (Figures 19, 21, 22), actual leaking fittings could finally be
extracted and subjected to a rigorous metallurgical evaluation and
analysis. To be consistent, both vendors that conducted the prior work
were contacted about regarding the opportunity to do the follow-up work
on the TF #3 fittings. Unfortunately, one vendor (Structure Probe)
declined due to their policy of not handling activated materials. The
other vendor (City Testing and Research Laboratories) was prepared to
examine these fittings.

There are fourteen water fittings on each TF coil numbered 1 through 7
then 10 through 16. Figure 47 is a schematic that shows the locations of
these fittings. It was decided that the vendor would do a metallurgical
examination on three selected fittings -- numbers 3, 13 and 14 from TF
#3. Prior to this metallurgical work, these three fittings had the
following history:

-   Water fitting 3 had an unresolved leak. No defect had been found.

-   Water fitting 13 was known to have cracks in the vicinity of the
    brazed joint connecting the water fitting outer tube to the main
    body of the coil (Figures 48 & 49). Attempts had been made to patch
    these cracks in-situ, but that effort was never completely
    successful.

-   Water fitting 14 was never known to have a leak and was to serve as
    a reference for the metallurgical tests.

In the RESA building machine shop, the TF #3 water fitting coil section
was carefully dismantled and cut to preserve the water fittings for
these tests. A typical extracted water fitting cut from TF #3 is shown
in Figure 50. As planned, fittings 3, 13 and 14 were sent to the City
Testing and Research Laboratory for evaluation. The primary questions
asked over the years which had to be answered were whether any hydrogen
embrittlement had occurred in these fittings which might have caused the
known cracking and to identify the material composition of the brazed
outer water fitting tube. During TF coil construction, the coil windings
themselves were clearly specified as OFHC copper, but the copper alloy
for outer fitting tubes had not been formally designated. If, in fact,
these tubes were made from an oxygen bearing copper alloy, that would
have been the likely source of hydrogen embrittlement, if any was found.

City Testing and Research Laboratories completed its metallurgical
evaluation of the submitted fittings. Each fitting was examined in
several key locations. Their findings are documented in Appendix B
\[Reference 14\]. The principal findings and conclusions in Reference 14
are as follows:

-   The outer water fitting tubes are made of OFHC copper.

-   No hydrogen embrittlement was found in any of the water fitting
    samples tested.

-   \"There is no evidence of any unusual microstructural indication or
    any abnormal grain growth\" in any of the samples.

-   Cracks and their resulting leaks in fitting 13 are not related to
    the brazed joints.

-   The cracks in fitting 13 \"appear to have been caused by a thin wall
    during manufacture of the assembly (i.e., cavity not centered
    between section walls)\". There is no evidence of fatigue or crack
    propagation. The cracks are indicative of a non-ductile type
    failure.

-   Fittings 3 and 14 did not show any evidence of cracking. The
    reported leak at fitting 3 does not appear to originate in the
    fitting area.

It was upon the return of these cup-up tested water fittings that the
probable cause of many of TFTR\'s water fitting leaks became apparent.
Figure 51 is a view of the fitting 13 crosswise cooling channel linking
the external water fitting to the extruded cooling channel in the body
of the winding. Not only is this crosswise channel severely deformed,
but the channel itself is not centered within the thickness of the turn,
leaving a very thin wall of copper. In this case, the deformation in the
cooling channel has resulted in a thru-crack in the turn. This
deformation was almost certainly caused during the manufacturing
process. The sequence of brazing the fitting in the copper plate
probably annealed the local copper in the crosswise channel. As one
moves away from the braze area, the copper transitions back to hard (32
ksi yield) copper. The copper plate is then wound into the coil turn,
and buckling in the annealed crosswise channel can easily occur as the
metal acts like a hinge.

The other two tested fittings also had this same buckled phenomenon,
however, the crosswise cooling channel was centered better in those
turns, avoiding a thin-walled thru-crack. It is not hard to imagine that
out of the 280 water fittings on the TFTR TF coils, several others may
have had leaks where the annealed copper crosswise channel was not
properly centered in the turn.

![](media/image48.jpeg){width="6.0in" height="8.3in"}

Figure 47 - Schematic of the Locations and Numbering of TF Coil Water
Fittings

![](media/image49.jpeg){width="5.995833333333334in"
height="3.870833333333333in"}

Figure 48 - Typical TF Coil Water Fitting Detail

![](media/image50.jpeg){width="5.998611111111111in"
height="7.866666666666666in"}

Figure 49 - Schematic Detailing TF #3 Water Fitting Crack Observations

![](media/image51.jpeg){width="6.0in" height="4.097222222222222in"}

Figure 50 - Extracted Water Fitting Section From TF #3 For Metallurgical
Examination

![](media/image52.jpeg){width="6.0in" height="4.055555555555555in"}

Figure 51 - TF #3 - Fitting 13 - Deformed Crosswise Cooling Channel

**[4. SUMMARY AND CONCLUSIONS]{.underline}**

As part of the TFTR D&D project, an extensive examination and test
program has been conducted on the TF coils while the machine was being
dismantled. Coils were subjected to visual, photographic, physical,
mechanical and metallurgical inspection and testing.

Visual and photographic inspection has confirmed the consistently good
quality in the manufacture and performance of the twenty TF coils.
Initially, no defects, other than very minor geometric anomalies, could
be found in the coil sections as they were cut in the TFTR Test Cell.
Once the selected coil sections from TF #3 and 18 were completely
disassembled, a few defects emerged that indicated an inconsistent and
less than perfect bonding of the copper windings to each other. However,
these occasional lapses did not appear to significantly affect the
integrity of these complex assemblies.

Mechanical testing revealed that the material properties of the OFHC
copper and the Nitronic 33 stainless steel case met or exceeded the
original design specifications in virtually every sample tested. Tensile
yield and ultimate stresses, as well as other properties, generally fell
into a narrow range and showed no signs of deterioration as a result of
either repeated cyclic mechanical and thermal loads or activation
incurred during TFTR operations. Local annealing of the copper windings
in the vicinity of spliced braze joints were expected and examined as
well. The pattern of measured copper strengths showed no sign of hard
copper softening or soft copper hardening, which, if it occurred, would
be indicative of turn-to-turn slipping and redistribution of load.
Although the turn-to-turn bonding of the copper windings were found to
vary, enough bearing and friction load was present during operations to
negate these irregularities, prevent any measurable slip, and result in
the coils performing at design levels.

One coil, TF #8, which cut with greater ease than the other nineteen
coils in the TFTR Test Cell was also subjected to comprehensive testing,
but the results and observations were consistent with TF #3 and 18.

Three water fittings from TF #3 were sent to a vendor for metallurgical
testing. Two of these fittings had a history of leaking. Although
hydrogen embrittlement was suspected as the cause of these leaks, the
results indicated that none had occurred. When these fittings were
completely cut-up and examined, it was evident that the crosswise
cooling channels had routinely buckled and deformed as part of the
original manufacturing process. If a channel was not centered in the
turn thickness, the resulting thinner wall would form thru-cracks due to
the local annealing of the copper in the braze area and the forces of
winding the coils.

A leak suspected at the lead spur of TF #18 could not be resolved
through borescope inspection but can still be examined in more detail at
some point in the future. Other less critical but important tests that
can be considered for future evaluation are the testing of the Inconel
case bolts and shear testing of the turn-to-turn copper epoxy bond
strength which appears to have a broad span based on the work done to
date. In order to accommodate the possibility that there may be an
opportunity for follow-up testing, a variety of TF coil samples,
including the TF #18 spur region, have been stored in the Rad Waste
building.

TFTR\'s success can be attributed, in large part, to the well designed
and constructed TF coils, whose overall quality has been confirmed by
this test program.

**[5. ACKNOWLEDGEMENTS]{.underline}**

This work was supported by the US DOE under Contract No.
DE-AC02-76-CH03073.

A project of this scope and magnitude could never have been completed
without the cooperation and dedicated efforts of many individuals. The
author would like to express special thanks to the following people
whose support was essential to the successful completion of this work:
Mike Williams, Erik Perry, Jim Chrzanowski, Mike Viola and Steve Kemp
for their guidance and administrative assistance; Keith Rule in the Rad
Waste Building; Bob Hitchner from Health Physics; Bill Zimmer and Bob
Clark in the Machine Shop; and grateful appreciation to Steve Jurczynski
in the Materials Test Lab for his countless hours of effort performing
the actual mechanical tests and data reduction.

**[6. REFERENCES]{.underline}**

1\. Heilbrunn, W., \"Fabrication Aspects of Toroidal Field Coils Fot the
Tokamak Fusion Test Reactor\", Eighth Symposium on Engineering Problems
of Fusion Research, San Francisco, CA, November 1979.

2\. Smith, G. E. and Punchard, W. B. F., \"TFTR Toroidal Field Coil
Design\", Seventh Symposium on Engineering Problems of Fusion Research,
Knoxville, TN, October 1977.

3\. Zatz, I. J., \"Proposal For the Final Examination and Testing of the
TFTR TF Coils\", PPPL D&D Proposal, 2 October 2000.

4\. Meighan, T., \"TF Coil Fitting Modification Procedure For Leak
Test\", PPPL TFTR Repair Procedure RP-TOK-040, 19 May 1995.

5\. Chrzanowski, J., \"Minutes of TF #3 Repair Meeting\", PPPL Memo
OPR-7333, 20 September 1995.

6\. Hubrig, J.G., \"Preparation For TF Coil Cooling Line Leak Repair\",
PPPL TFTR Repair Procedure RP-TOK-010, 13 April 1989.

7\. Chrzanowski, J., \"Dissection of TF Coils for Engineering
Examination and Analysis\", PPPL TFTR D&D Procedure D-D&D-IP-2680, 5
October 2001.

8\. American Society For Testing and Materials, \"Annual Book of ASTM
Standards - Section 3 - Volume 03.01\", Philadelphia, PA, 1986.

9\. AMAX Copper, Inc., \"OFHC Brand Copper - A Survey of Properties and
Applications\", New York, NY, 1974.

10\. Tobias, J. B., \"Brazing of Large Section Water-Cooled Copper
Conductor On TFTR\", Eighth Symposium on Engineering Problems of Fusion
Research, San Francisco, CA, November 1979.

11\. Armco, Inc., \"Armco Nitronic 33 Stainless Steel - Product Data
Bulletin No. S-79\", 1986.

12\. Structure Probe Technical Report #54051, \"Metallurgical Failure
Analysis Research Investigation of Copper Fittings Using Metallography,
Scanning Electron Microscopy and Energy Dispersive X-Ray Spectroscopy
Techniques\", Metuchen, NJ, 28 May 1992.

13\. City Testing and Research Laboratories, Inc. Report S-91770,
\"Metallurgical Analysis Per S.O.W. Copper Alloy Coil Section - Slice
From Coil No. 250\", Rahway, NJ, 29 August 1995.

14\. City Testing and Research Laboratories, Inc. Report S-104730, \"
Metallurgical Analysis Per S.O.W. - Three Copper Alloy Coil Sections -
TFTR TF Coil No. 3\", Rahway, NJ, 27 November 2002.