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Code Case N 822 for Pin Brazing Non-Structural Attachment
Tabs for Buried Pipe Cathodic Protection
Quimica General (Universidad Privada del Norte)
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Proceedings of the ASME 2018
Pressure Vessels and Piping Conference
PVP2018
July 15-20, 2018, Prague, Czech Republic
PVP2018-84897
CODE CASE N-822 FOR PIN BRAZING NON-STRUCTURAL ATTACHMENT TABS
FOR BURIED PIPE CATHODIC PROTECTION
Steven L. McCracken and Nick Mohr
EPRI, Welding and Repair Technology Center
Charlotte, North Carolina, USA
ABSTRACT
Cathodic protection (CP) is one of the primary methods
to protect buried piping and pressure components from
corrosion and is a critical element in asset management of
buried piping at nuclear power plants. Implementation of
cathodic protection requires non-structural attachments to the
buried piping for electrical leads and connections. The
method of attaching copper-copper alloy CP leads to carbon
steel piping and components using traditional arc welding
processes can be difficult and time consuming. A two-step
process is frequently used where a carbon steel weld tab is
first welded to the pipe or component by a traditional arc
welding process. The copper-copper alloy CP lead is then
joined to the carbon steel weld tab by the exothermic welding
process.
An alternative to this cumbersome two-step process is pin
brazing which is an automatic brazing process that uses
electric current resistance to heat the interface between a pin
capsule and the component. An arc between the pin capsule
and the outside surface of the electrical connector is then used
to melt the capsule or pin that contains the brazing filler metal.
The process is similar to stud welding in that the brazing pin
is loaded into an automatic pistol and the brazement is made
when the trigger is pulled. ASME Section XI Code Case N882 delineates rules and requirements for application of pin
brazing on Class 2 and 3 pressure boundary components. This
paper provides the background and description of the pin
brazing process with a summary of the technical basis for
Case N-882.
The attachment of the sacrificial anode or direct current
system electrical connection to components is difficult with
traditional arc welding processes such as shielded metal arc
welding (SMAW). Typically, a piece of carbon steel “weld
tab” is welded (e.g. SMAW) to the system and a secondary
process is used to join the electrical connector to the weld tab.
Pin brazing is a proposed alternative joining process where
the electrical connection is brazed directly to the carbon steel
component eliminating the need for a weld tab. Pin brazing is
similar to stud welding in that the brazing pin is loaded into
an automatic pistol and the brazement is made when the
trigger is depressed. The pin brazing process is relatively fast
and simple with minimal components required. This process
is currently not included within American Society of
Mechanical Engineers (ASME) Section III or XI nuclear
power codes although it is frequently used in other industries.
ASME Section IX codified pin brazing in Code Case 2866
[2].
Code Case 2866 provides requirements for qualification
of procedures and operators, but current wording in ASME
Section XI does not provide specific guidance for using pin
brazing to attach temporary or permanent nonstructural
attachments to ASME Class 2 or 3 components. To address
this gap new Case N-882 was developed to provide
requirements for pin brazing nonstructural electrical
connections specifically for applications such as cathodic
protection and grounding for Class 2 and 3 moderate energy
components.
CODE CASE N-882 GENERAL REQUIREMENTS
Draft Code Case N-882 is applicable for attaching copper
or copper alloy nonstructural temporary and permanent
electrical connections to Class 2 and 3 carbon steel
components (P-No. 101 for brazing and P-No. 1 for welding),
and is an alternative to IWA-4440 Welding and Brazing
Qualifications [3, 4]. General requirements of the case include
the maximum operating temperature not exceeding 200°F
(95°C) and operating pressure exceeding 275 psig (1.9 MPa).
The removal of temporary attachments is in accordance with
NC-4435(b) or ND-4435(b). Lastly, cleanliness requirements
are imposed such that brazing is done on a clean dry surface
and protected from detrimental environmental conditions.
BACKGROUND
One of the primary methods in which buried piping and
tanks are protected against the deleterious effects of corrosion
is by using cathodic protection. Cathodic protection is applied
as a system through impressed currents or passive means by
instigating protection through galvanic coupling of a
sacrificial anode. These systems are expected (based on
design) to have shorter life spans than what power plants are
experiencing, especially as plants seek license and subsequent
license renewals. Resulting from this is a need for power plant
personnel to review site conditions and existing CP systems
to determine the feasibility and benefit of installing and/or
upgrading CP systems [1].
1
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Process Description
Pin brazing is a relatively simple process as detailed in
the seven steps outlined below.
Step 1 – Connecting Equipment, and Cleaning Base
Material
Initial equipment setup entails connecting the battery
pack in the power unit, attaching the grounding lead to the
workpiece and power supply, and attaching the automated pin
brazing gun lead to the power supply. The base material is
also cleaned at this time to bright metal removing any scale,
oil, dirt, moisture, or debris.
Step 2 – Setting the Ferrule
The ceramic ferrule is inserted into the end of the pin
brazing gun as shown in Figure 2. The ceramic ferrule has
multiple purposes in the pin brazing process. The ferrule
concentrates heat, keeps molten filler metal directed in the
braze region, and provides arc shielding. In this model the
ferrule also provides the correct standoff from the work when
a cable lug is properly placed. The system will not initiate the
brazing process without the ceramic ferrule unless the user
willfully bypasses the safety feature. Ceramic ferrules are
single use and must be replaced after each use [5].
The qualification requirements of procedures and brazing
machine operators are the same as Case 2866 except for minor
clarifications. The qualification requirements include brazing
10 pin brazements with the same equipment, connector, pin
capsule, and position that will be done in the field. Each
brazement is then bent at least 45 degrees and is acceptable if
there is no more than 50% visible separation or fracture after
bending. The test is acceptable if all 10 brazements meet these
acceptance criteria. Brazing machine operators are qualified
with acceptable procedure qualification under the essential
variables of QB-351.2. Alternatively, each brazing machine
operator shall successfully pin braze 5 samples meeting the
acceptance criteria for the brazing procedure qualification.
The Brazing Procedure Specification (BPS) is required to
include at a minimum: base metal P-No., position(s) qualified,
equipment description, connector type (size, shape, material),
and brazing material (capsule type).
PROCESS AND EQUIPMENT DESCRIPTION
Equipment Description
Typical equipment associated with pin brazing consists
of a battery-operated power source, automatically timed
brazing gun, ceramic ferrule, brazing pin, cable lug, and
grounding lead as shown in Figure 1. Note that the equipment
pictured is the Easybond unit by BAC® Corrosion Control
(BAC®). There are several other pin brazing equipment
manufacturers but they all have the same general
characteristics (i.e. power source is battery operated (36V
DC), similar consumables, and use an automatically timed
brazing gun).
Figure 2: Ceramic ferrule loaded into the pin brazing gun
Step 3 – Loading the Pin Brazing Capsule
The pin brazing capsule is loaded into the pin brazing gun
and is automatically set via a spring-loaded mechanism. The
pin brazing capsule is comprised of various parts and alloys
that provide the flux, filler metal, and stops the brazing
process (e.g. fuse wire) [6]. The loaded pin brazing capsule
and a description of the various parts are shown in Figure 3.
It should be noted that pin capsules come with or without fuse
wires depending on the pin brazing gun and system. A pin
brazing system that electronically controls the brazing time
does not come with a fuse wire.
Figure 1: Typical pin brazing equipment A) power supply, B)
brazing pin with fuse wire, ceramic ferrule, cable lug (from left
to right), C) pin braze gun, and D) magnetic grounding cable
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4. Arc is extinguished when the circuit is mechanically
opened (via a fuse wire) or electronically shut off and the
brazing pin is pushed into the molten pool of brazing filler
metal
5. Brazer maintains pressure for 2 to 4 seconds after the
arc is extinguished
Pictures of pin brazing when the arc has been initiated
and after the arc is extinguished are shown in Figure 5. The
total brazing time is approximately 6 to 10 seconds.
Figure 3: Pin brazing capsule loaded into the pin brazing gun
(left) and capsule description [3] (right)
Step 4 – Seating the Connector
The selected connector is properly placed with the pin
brazing capsule through the center as shown in Figure 4. Note
that a downward force was not applied on the pin brazing gun
in Figure 4 purposely to show the pin brazing capsule in the
center of the cable lug. The brazing process would not initiate
unless the downward force was applied to properly seat the
ferrule against the lug surface. A cable lug is shown, but there
are multiple sizes and types of connectors.
Figure 5: Pin brazing once arc has been initiated (left) and
after the arc has been extinguished via fuse wire (right)
Step 6 – Detaching the Pin Brazing Capsule Shank
The pin brazing capsule shank left after the brazing
process has been completed is designed for removal and is
easily broken off the lug via a mild hammer blow. A picture
containing a pin brazement with and without the shank
removed is provided in Figure 6.
Figure 4: Cable lug installed before commencement of
brazing
Step 5 – Brazing
Once the proper setup has been completed the pin brazing
process is initiated and automatically controlled when the
trigger is depressed. The only tasks the brazer must perform
are to keep the trigger depressed, and maintain constant
pressure on the gun during brazing for 2 to 4 seconds after the
arc is extinguished. The pin braze process sequence is
described as follows [5, 7]:
1. Trigger is depressed.
2. Resistance of current between the pin brazing
capsule head and base metal melts the silver capsule.
3. Arc is initiated between the outside surface of
connector and pin braze capsule, bringing filler metal up to
melting temperature and heating connector.
Figure 6: As-brazed copper lug with pin braze capsule shank
(top) and completed pin brazement with shank removed
(bottom)
Step 7 – Clean Soot Off Lug and Base Material
The last step is removing the soot with a wire brush or
other suitable method.
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MECHANICAL AND METALLURGICAL TESTING
PERFORMED BY EPRI
Multiple pin brazements were made by the Electric
Power Research Institute (EPRI) to evaluate the pin brazing
process and to demonstrate qualification requirements
proposed in Case 2866 (Case 2866 was not yet approved at
the time of EPRI testing). This EPRI demonstration provides
the data needed to support Section IX Case 2866 and Section
XI Case N-882 while also providing multiple specimens for
destructive evaluation.
Pin brazing specimens were made with ASTM A-36
carbon steel base material (P-No. 101 for brazing and P-No.
1 for welding) using the pin brazing equipment and
consumables discussed in the previous section of this paper.
The qualification entailed pin brazing 10 cable lugs
consecutively as shown in Figure 7. The 10 cable lugs were
then bent approximately 45 degrees via a hammer and
visually inspected to determine if there was visible separation
greater than the allowable 50% between the lug and plate. All
10 of the pin brazes passed this visual acceptance criteria.
Two of the lugs were then bent an additional 45 degrees in
two incremental steps: 1) additional 20 degrees and 2)
additional 25 degrees. These two lugs were visually inspected
at both steps and found to have slightly more visible
separation when bent past the required 45 degrees but still
much less than the 50% allowable separation, and overall
showing a sound brazed connection. The required 45 degrees
bend test for the 10 cable lugs and the additional bending of
two cable lugs are shown in Figure 8.
A metallurgical plan was developed to further investigate
three pin brazements. The pin brazement heat-affected-zone
(HAZ), using the prescribed pin braze qualification process,
was compared to the HAZ of a shielded metal arc weld
(SMAW) single bead-on-plate specimen. The SMAW process
was selected because it is commonly used to join the weld tab
to the pressure boundary component for CP and ground
connections. The selected analysis plan is detailed in Table 1
and the specimen cut plan is shown in Figure 9. A photograph
of a pin brazement after mounting and polishing is shown in
Figure 9 for familiarization to the expected cross section
shape and appearance.
Table 1: Analysis plan for pin brazement and bead-on-plate
specimens
Specimen
Cross
Section
Location
Macro
Exam
Microhardness
Mapping
Composition
(EDS)
1
Medial
X
X
X
2
Lateral
X
X
-
3
Medial
X
-
-
Bead-onplate (BOP)
Lateral
X
X
-
Figure 9: Cut plan for specimen removal (left and top right)
and representative cross sections of a pin brazement taken
from an earlier preliminary EPRI study (bottom right)
Material Descriptions
The base material selected was approximately 0.75 inch
(19 mm) thick ASTM A-36 carbon steel plate with nominal
composition of (0.18% C, 0.83% Mn, 0.14% Ni, 0.1% Ni,
0.05% Mo) with a carbon equivalent value (CEV) of 0.37,
using the International Institute of Welding (IIW) formula.
The chemical composition of the cable lug was identified
in BAC® technical datasheet as annealed copper [11]. The pin
shank and filler metal (pin) was stated in the datasheet to be
brass and Silver Alloy AGA Silco 610 respectively. Searches
on the internet for further information regarding AGA Silco
610 yielded no results. Therefore, energy dispersive x-ray
analysis (EDS) via scanning electron microscope (SEM) was
used to interrogate various regions of Specimen 1 after
microhardness mapping was completed. Figure 10 shows six
areas that were selected for composition analysis.
Figure 7: Completed qualification coupon in the as-brazed
condition prior to bend testing
Figure 8: Qualification coupon after bending all pins
approximately 45 degrees and two pins roughly an additional
45 degrees (left) and the qualification coupon after bending all
pins approximately 45 degrees (right)
4
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Table 2: Chemical composition of 6 areas identified in Figure
10 and BAg-36 braze metal
Chemical Composition (wt. %)
Figure 10: Composition locations investigated with EDS
The EDS analyses corroborated the copper connector and
brass pin shank composition listed in the technical datasheet
by BAC®. The copper connector appears to be a relatively
high purity copper (Areas 1 and 4) and this was expected due
to the high conductivity of pure copper. The exact
composition or material specification for the brass shank
(Area 2) cannot be deduced from this analysis but certainly
there is sufficient zinc additions to be classified as a brass
alloy. Traces of lead were found in Area 2 which may be an
intentional addition to the pin capsule shank, although it
should be mentioned that these measurements had high
percentage of error.
Two areas (Areas 3 and 5) were investigated to gain
further information about the brazing filler metal used in the
pin brazing capsule. This could be difficult because the arc
between the top of the lug and the pin may have caused some
level of dilution among the filler metal and pin capsule shank.
Thus, the true composition of the filler metal is thought to be
higher in silver content while lower in copper and zinc.
Brazing filler metal composition ranges found in ASME
Section II Part C, SFA-5.8 were reviewed to determine if a
known brazing filler metal overlapped the compositions
found in Areas 3 and 5 [8]. No potential classification matches
were found during review of SFA-5.8.
The transition from pin brazement to the base metal was
explored in Area 6 using 7 spots starting from the brazement
moving towards the carbon steel base metal. It should be
noted that very distinct compositions are determined because
the small spot size can minimize averaging that are found
when using line/area scans. The transition found nothing of
significance to report. Spot 5 was removed from the table
because the spectral analysis was found, after processing, to
include carbon peaks. Carbon is difficult to detect accurately
with the EDS system used, distorting the results, and should
have been removed. It was observed that Spot 4 composition
close to the interface but sufficiently away from carbon steel
gave a composition close to BAg-36 filler metal. The average
of the specification ranges for BAg-36 was taken by ASME
Section II Part C, SFA-5.8 is included in Table 2 for
convenience [8]. However, it is not known if the Spot 4
measurement is representative of the bulk filler composition
or an Ag rich phase which coincidently aligns with BAg-36
composition ranges.
Location
Cu
Zn
Pb
Ag
Fe
Sn
Mn
C
Area 1
100.00
-
-
-
-
-
-
-
Area 2
59.33
40.10 0.57*
-
-
-
-
-
Area 3
53.25
26.36 0.29* 20.11
-
-
-
-
Area 4
100.00
-
-
-
-
-
-
-
Area 5
56.87
20.27
-
22.85
-
-
-
-
Area 6
-
Spot 1
65.28
26.31
-
8.41
-
-
-
-
Spot 2
64.34
26.63
-
9.04
-
-
-
-
Spot 3
59.36
26.33
2.42
11.02
0.86*
-
-
-
Spot 4
29.16
21.79 0.57* 43.77 0.57*
4.14
-
-
Spot 5
-
-
-
-
-
-
-
-
Spot 6
-
-
-
-
99.07
-
0.93
-
Spot 7
-
-
-
-
98.67
-
1.31
-
BAg-36+
27.00
25.00
-
45.00
-
3.00
-
-
* Error greater than 10%, +Average of range provided in SFA-5.8 [5]
Macro Examination
The three pin braze specimens were cross sectioned per
the cut plan in Table 1, polished, and examined at 5X
magnification. The un-etched cross sections are presented in
Figure 11 with etched cross sections of Specimens 1 and 2
included in following Microhardness Testing subsection. The
macrographs revealed some areas of porosity and small
regions where the filler metal did not join to the shank or base
metal. These observations were primarily seen in Specimen 1
(note that the large tear on the left side is a result of sectioning
via the band saw and not a result of bend testing). Specimen
3 also showed a line along the shank that did not appear
completely joined to the connector. However, even with
excessive bending beyond 45 degrees, Specimen 3 only had
minor separation as can be seen on the left side of the
macrograph in Figure 11. Specimen 2 was cut in a different
orientation (laterally) compared to Specimens 1 and 3, but
showed similar discontinuities such as porosity. For all
samples the filler metal interface between the pin brazement
and the carbon steel plate was difficult to resolve at all
locations. It did appear that a good bond was achieved, as no
large areas of separation were seen during bending, but
identifying the filler metal between the two was challenging
in some cases.
It was observed that Specimen 1 and 3 had several
intergranular microcracks all less than 0.004 inch (0.10 mm)
located under the pin brazement penetrating the carbon steel.
5
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This is thought to be minor instances of copper penetration
into the carbon steel, although a full analysis of the
microcracks was not completed. The largest microcrack was
found in Specimen 1 and pictures of the crack are presented
in Figure 12.
Literature was found that documents copper penetration
into carbon steel base materials. It was mentioned that copper
penetration in carbon steels was found to be shallower than
compared to low alloy steels [9]. BAC® literature [5] also
alludes to this phenomenon where it states:
“When working with steel pipelines, in accordance with
BS4515:1996, the fusion line of the braze should not be
more than 1 mm below the pipe surface. Intergranular
copper penetration of the pipe material should not
exceed 0.5mm beyond the fusion line when a microsection is examined at a magnification not exceeding
x50.”
The EPRI test specimens had most instances of copper
penetration below 0.002 inch (0.05 mm) with the largest at
0.004 inch (0.10 mm), well below 0.02 inch (0.50 mm).
Another paper was located that discusses copper penetration
for thermite welding. It was thought to be relevant to this
discussion even though the article is specific to thermite
welding. In a Nuclear Engineering and Design article [10] the
following is reported:
“In the microscopic examination the cross sections of
all samples processed under different conditions were
examined with an optical microscope. From
microscopic examination of joints following remarks
can be made: The copper and steel were formed
intermediate layer, which contains the penetrated
copper. The thickness of this layer is from 10 to 20 μm.
In some places, just below the steel surface, martensite
microstructure occurs due to rapid cooling. Just below
the surface of the base material, an increased grain size
can be found. In the martensite microstructure
microcracks were observed. Their length was up to 0.12
mm. The microcracks were filled with copper. In the
samples without martensite microstructure microcracks
were not detected.”
The authors of that article conclude that reducing
formation of martensite via preheat could suppress the
initiation of microcracks during thermite welding. They also
did a cursory review of the influence of microcracks on the
static strength and found only minor reduction in strength
[10]. There are distinct difference between thermite welding
and pin brazing. First is the fact that pin brazing does not have
a fusion zone (what the authors call the intermediate layer).
Second, there was not a distinct microstructure defining
where copper penetration is found or is not found. Specimen
2 showed no indication of copper penetration although it had
similar microstructure to Specimens 1 and 3. This could
suggest that instances of copper penetration may tend to form
in a location with surface irregularities due to preparation or
cleaning.
Instances of copper penetration were found in 2 out 4 pin
braze specimens cross sectioned (including the initial
evaluation specimen). It is concluded that the small size and
limited number of these microcracks while being contained
under the pin brazement render the microcracks of little
consequence. They are not expected to be detrimental to the
intended function of the piping/components or the connector.
However, this may not be true for materials more susceptible
to deeper copper penetration (e.g. low alloy steels and
austenitic stainless steels), and these conditions would require
further evaluation. The use of a preplaced brazing ribbon with
high silver content such as BAg-7 or BAg-8 could be used to
buffer the high copper content at the carbon steel interface.
The use of the preplaced brazing ribbon may eliminate copper
penetration, but has yet to be tested by EPRI at this time.
Figure 11: Macrographs at 5X magnification for Specimen 1
(top), Specimen 2 (middle), and Specimen 3 (bottom)
Figure 12: Specimen 1 micro crack identified via a circle (top),
same microcrack magnified to 100X by optical microscope
(bottom left), and same microcrack magnified to 1000X by
SEM (bottom right)
6
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Microhardness Testing
Microhardness mapping was completed on Specimens 1
and 2 using a Vickers indenter and a load of 500 grams (HV
500 gf) with grid spacing of 0.01 inch (0.25 mm) in the X and
Y directions. A weld bead was made using SMAW on the
same qualification material to provide a comparison between
Specimen 1, Specimen 2, and a bead-on-plate heat affected
zone. The weld bead was made using 1/8-inch diameter
E7018 electrode at ambient temperature which is consistent
with filler metal that would be used to attach the weld tab in
the field. The microhardness data was then used to develop a
color map for each using Origin® software version 9.1. Each
cross section along with the corresponding color map is
presented in Figure 13, 14, and 15 (color map hardness scale
is the same for each figure). The cross sections were etched
using Nital solution. It should be noted that some areas of the
carbon steel cross section became over-etched attempting to
reveal more of the pin brazement microstructure and regions.
Specimens 1 and 2 each have five additional measurements in
the unaffected base metal to determine the average hardness
for the bulk material.
Analysis of the hardness maps showed that the HAZ
associated with pin brazements are roughly three times
shallower than the bead-on-plate specimen. Another
difference is the highest hardness areas are centrally located
under the pin brazement at the surface of the carbon steel. The
area of highest hardness (identified with shades of red)
reaches a depth of 0.016 inch (0.40 mm). This contrasts with
the weld where the high hardness follows the fusion zone
down into carbon steel and reaches a depth of roughly 0.083
inch (2.10 mm). A white dotted line was placed on each color
map at a depth of 0.039 inch (1.00 mm) for reference among
the three color maps.
for Specimen 1, 2, and the bead-on-plate were 171.5, 179.8,
and 195.5 HV 500 gf respectively. As expected, the brazing
and SMAW bead-on-plate weld caused higher hardness in the
weld HAZ, with the bead-on-plate specimen exhibiting the
highest hardness. The peak hardness in the bead-on-plate
specimen was 349 HV 500 gf while Specimen 2 had the
highest pin brazement peak of 319 HV 500 gf. Lastly, the
histograms in Figure 16 show the SMAW bead-on-plate had
a larger percentage in the right tail correlating to larger areas
of higher hardness. Therefore, the pin brazing process
demonstrates a shallow and more localized region of
increased microhardness when compared to an SMAW weld
that is representative of the weld process typically used to
attach a carbon steel tab.
Figure 14: Pin braze Specimen 2 hardness map (HV 500 gf)
Figure 13: Pin braze Specimen 1 hardness map (HV 500 gf)
Descriptive statistics were performed for Specimens 1, 2,
and the bead-on-plate with the results summarized in Table 3
and histograms with cumulative probability plots provided in
Figure 16. The unaffected base metal was found to have an
average microhardness of 136.7 HV 500 gf while the averages
Figure 15: Bead-on-plate hardness map (HV 500 gf)
7
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Table 3: Microhardness statistics
Measure
-ments
Min
.
Max.
Mean
Median
STD
10
129
144
136.7
135.5
5.2
Spec. 1
490
129
279
171.5
163
29.5
Spec. 2
525
132
319
179.8
166
38.7
BOP
850
136
349
195.5
169
46.3
Specimen
Base Metal
Robustness Testing of the Pin Brazing Process
Robustness testing was conducted after completing the
qualification testing using the same ASTM A-36 test plate.
The objective of robustness testing was to determine how
sensitive the pin brazing process was to a number of variables
and when intentionally performed incorrectly. An initial test
matrix was developed and can be seen in Figure 17. A builtin safety feature automatically ends the brazing cycle
prematurely when a cable lug or a ceramic ferrule are not used
together. Both conditions were validated and the cycle did not
melt the pin capsule leaving those locations available for a
second round of testing. The second round of testing included
not depressing the trigger through the whole brazing cycle,
and overriding the built-in safety feature so brazing would
commence without a ceramic ferrule. Note that proper safety
precautions were taken during testing without the ceramic
ferrule to shield operator and spectators from molten filler and
arc flash.
The results from the robustness testing determined that
overall the pin brazing process can produce acceptable
brazements under most conditions. The off-angle pin brazing
seen in Figure 18 was thought to be one of the most likely
situations encountered in the field and had acceptable results.
Pin brazing with lower downward pressure, over mild mill
scale and soot, and with a shortened trigger depression all
resulted in an acceptable brazement after bend tests.
Attempting to pin braze without either a cable lug or a ceramic
ferrule resulted in the fuse almost immediately being broken,
ending the brazing process. In both cases, the safety feature
engaged as expected with arc initiation noticed on the base
metal for the test without the cable lug. Pictures of the tests
without the ceramic ferrule or cable lug are found in Figure
19. When attempting to override the safety feature
(attempting to trick the system into thinking that both a cable
lug and ferrule are present) the process quickly blew a fuse as
well leaving a small mark on the base metal. The last test
condition was brazing over full mill scale which represents
attempting to braze without cleaning the base metal. This
condition also resulted in an obvious failure visually and the
connection fell off when attempting to remove the capsule
shank. Pictures of brazing over mild mill scale and soot, and
full mill scale are found in Figure 20.
The resultant test plate with all conditions identified via
a text box and a summary table can be found in Figure 20 and
Table 4 respectively. A green text box represents conditions
that passed Case 2866 and draft N-882 code case acceptance
criterion with a red text box indicating a failed condition.
Hardness (HV 500 gf)
# of
Figure 16: Hardness histogram and cumulative probability of
Specimen 1 (Top), Specimen 2 (middle), and Bead on Plate
(bottom)
8
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Figure 21: Results of robustness testing after bending
approximately 45 degrees with green boxes representing test
that passed qualification requirements and red boxes
representing those that failed
Figure 17: Initial test matrix for robustness testing
Table 4: Summary of tests and results of robustness testing
Figure 18: Off angle test before (left) and after brazing (right)
Test Condition
Description of Results
Results
Brazing gun held offangle
Acceptable after bending
Pass
Brazing gun with low
pressure applied
Acceptable after bending
Pass
Pin braze without
cable lug
Safety feature engaged, fuse
blown before brazing could
begin
Fail
Pin braze without
ferrule
Safety feature engaged, fuse
blown before brazing could
begin
Fail
Pin braze without
ferrule (Safety feature
overridden)
Brazing initiated but fuse was
blown quickly after trigger
(did not join)
Fail
Pin braze over mild
scale and soot
Braze was erratic with
significantly more separation
was observed
Pass
Pin braze over full
scale
Did not join to the plate and
broke off easily
Fail
Pin braze with trigger
depressed shorter
than directed
Acceptable after bending
(more separation than typical
pin brazement)
Pass
Pin Brazing with Water Backing
A comment received on the ASME Standards Committee
XI first consideration ballot of Case 2866 regarded the
effectiveness of pin brazing for water backed applications.
The commenter asked if the greater heat sink of a water
backed component would have a deleterious effect on the
process to join the connector. A water backed condition was
considered bounded by the plate thickness was selected for
pin brazement testing and since no preheat was applied.
However, to evaluate a water back condition more directly
remnant from robustness testing was used to perform pin
brazing with water back conditions. The water backing was
simulated using a pan filled with water that encroached up to
approximately half of the plate thickness. Pictures of the test
setup is shown in Figure 22.
Three pin brazements were made after the test plate was
positioned in the trough for approximately 15 minutes.
Figure 19: Pin brazing without a cable lug (top), without a
ceramic ferrule (bottom left), and the result of brazing without
ceramic ferrule (bottom right)
Figure 20: Pin brazing over full mill scale (left) and pin brazing
over mild mill scale and soot from previous brazement (right)
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Temperature readings of the water and plate were taken before
and after brazing using a single digital thermometer. For the
first test, the measurements for the water and plate were not
taken at the same durations after the initial temperature
readings. The water temperature was measured fairly quickly
after pin brazing for Specimen 1-WB, but was found to have
minimal increase. For the remaining two brazements the plate
temperature was monitored more closely after completion of
brazing. It was observed that temperature decreases rapidly
after brazing had been completed. A table of temperature
readings for all specimens are found in Table 5. Note that the
digital thermometer appeared to perform better in the water
due to a greater surface area of the probe being exposed to the
media being measured whereas a smaller surface area could
contact the plate. This is assumed to be the reason for the
temperature differences between the initial water and plate
temperatures. Water measurements were taken next to the
plate near the brazement and plate measurements taken
approximately a half inch next to the completed brazements.
The completed brazements are seen in Figure 23.
The three completed pin brazements were removed from
water backing and bent approximately 45 degrees
representing the requirements of Case 2866 and draft Case N882. All pin brazements were found to meet the acceptance
requirements of both cases. They were then bent an additional
45 degrees to determine if there was good correlation between
the water backed samples and those done during the
qualification testing. Pictures of the initial 45 degrees bend
and the 90 degrees bend are found in Figure 24. All bend test
samples (with and without water backing) had similar results
with minor amounts of separation that would be acceptable in
accordance with the cases. In conclusion, testing shows there
is good correlation between pin brazements made with and
without water backing.
Figure 22: Water backed testing setup (top and bottom left)
and water level relative to test plate (top and bottom right)
Figure 23: Pictures of the first pin brazement before brazing
(top left), three completed pin brazement with capsule shanks
still attached (top right), top view of pin brazements with
capsule shanks removed (bottom left), and side view of pin
brazements without shanks removed (bottom right)
Table 5: Temperature readings taken during water backed pin
brazing
Specimen
1-WB
2-WB
3-WB
Time
(sec.)
Water
Temperature
°F (°C)
Plate
Temperature
°F (°C)
Initial
5
15
25
Initial
5
15
25
Initial
5
15
30
70.7 (21.5)
74.5 (23.6)
70.7 (21.5)
71.9 (22.2)
71.4 (21.9)
71.2 (21.8)
73.0 (22.8)
93.5 (34.2)
85.5 (29.7)
74.8 (23.8)
125.0 (51.7)
90.0 (32.2)
Figure 24: Pin brazements bent approximately 45 degrees
(left) and pin brazements bent an additional 45 degrees (right)
78.9 (26.1)
130.0 (54.4)
105.0 (40.6)
-
STATUS OF CASE N-882
Standard Committee XI approved Code Case N-882 on
March 29, 2018 by a vote of 28 approved, 0 disapproved, and
0 abstaining (Ballot 18-657). The case was approved for
publication by the ASME Board of Nuclear Codes and
Standards (BNCS) on April 18, 2018 (Ballot 18-987) [3].
10
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SUMMARY AND CONCLUSIONS
The pin brazing process was found to produce multiple
brazements all able to withstand aggressive bending while
maintaining an acceptable bond. Ten pin brazements were
evaluated and passed proposed qualification requirements of
bending to 45 degrees with no visible separation greater than
50%. In fact, two pin brazements were bent an additional 45
degrees and only showed minor separation from the ASTM
A-36 qualification plate. The pin brazing copper lug, shank,
and filler metal composition were evaluated using EDS and
found to be copper, brass alloy, and an Ag-Cu-Zn-Sn alloy
respectively. Although the EDS analysis is not used for
ascertaining definitive chemical composition, it could
corroborate information found in BAC® technical datasheet.
The pin brazing filler metal composition could not be
definitively determined, but was found to align closely with
BAg-36 filler metal. Note that both Case 2866 and N-882
require the same materials (connector and pin) that were used
during the qualification process be used in production. The
pin brazements were also examined via macrographs and
found to contain some level of porosity and areas where there
did not appear to be complete coalescence. This was not found
to hamper the bond nor is it expected to lessen the
effectiveness of the cathodic protection system. Copper
penetration into the carbon steel was also found during macro
examination in two specimens with the largest microcrack
penetrating to 0.004 inch (0.10 mm). Most observed
microcracks were on the order of 0.002 inch (0.05 mm) or
smaller. Literature searches determined that copper
penetration for carbon steel and for pin brazements is not
uncommon with these material combinations. All
microcracks were found to be contained under the pin
brazement and due to the small size, limited amount, and
intended function of the connectors (i.e. non-structural) they
are expected to have no significance.
The areas of higher hardness in the HAZ of pin
brazements were determined to penetrate no more than 0.039
inch (1.0 mm) with the area of highest hardness contained
centrally under the pin brazement. A weld bead-on-plate HAZ
was used as comparison to the pin brazements and it was
deeper penetrating and resulted in higher peak hardness.
Thus, pin brazing can develop elevated hardness in the HAZ
but it was found to be of smaller magnitude (depth and
hardness) compared to a weld made using SMAW.
The pin brazing process is purposely developed for
installing cathodic protection connectors and does so quickly
with reproducible results. Additionally, the process
potentially has significant benefits to utilities in regards to
time and cost savings by using a single step to attach cathodic
protection connectors. The portability and reproducibility of
pin brazing makes it ideal for applications such as buried
piping which usually extend a great distance away from the
plant. This evaluation of the pin brazing process found
nothing to suggest the pin brazing process should not be used
for cathodic protection applications. It is recommended that
the pin brazing process be considered for attaching electrical
connectors on carbon steels (P-No. 101 for brazing, limited to
materials with a P-No. 1 for welding) via Code Case N-882
for Class 2 and 3 applications. Using the pin brazing process
on base materials other than P-No. 101 would require further
study.
ACKNOWLEDGMENTS
The authors would like to recognize Robert (Dana)
Couch, EPRI Principal Technical Leader – Welding and
Repair Technology Center, for his expertise, guidance during
testing and development of Section IX case 2866 which much
of the basis for the Section XI case is based upon. Dylan
Cimock, EPRI Technical Leader – Plant Technology, for his
expertise and input during testing and development of Section
IX case 2866. Ben Sutton, EPRI Technical Leader – Welding
and Repair Technology Center for his assistance with the EDS
work associated with the Pin Brazing specimens.
REFERENCES
[1] Evaluation for Installing or Upgrading Cathodic
Protection Systems: A Guide for Cathodic
Protection for Buried Piping and Tanks. EPRI,
Palo Alto, CA: 2015. 3002005067
[2] Case 2866, Pin Brazing, Approved September 30,
2016, ASME Record No.: 15-1762
[3] ASME Record No.: 17-1715, BPV SC-XI, Section
XI Code Case N-882 for Pin Brazing
[4] ASME Boiler and Pressure Vessel Code, ASME
Section XI, Rules for Inservice Inspection of
Nuclear Power Plant Components
[5] Glenn Symington. “Pin Brazing- A metallurgically
safe method of making electrical connections to
pipelines and other metallic structures, which are
to be cathodically protected or electrically
earthed”, BAC Corrosion Control Ltd.
[6] Website: http://www.pin-brazing.com/
[7] Website: http://www.stanleyhydraulics.com/produ
cts/pin-brazing-safebonding
[8] ASME Boiler and Pressure Vessel Code, Section
II-C, Specifications for Welding Rods, Electrodes,
and Filler Metals 2015 Edition, American Society
of Mechanical Engineers, New York, NY.
[9] W. F. Savage, E. F. Nippes, AND R. P. Stanton,
“lntergranular Attack of Steel by Molten Copper”,
American Welding Society Welding Journal,
January 1978, pg 9-s to 16-s
[10] M. Suban, S. Bozic, A. Zajec, R. Cvelbar, B.
Bundara. “Crack Analysis in Thermite Welding of
Cathodic Protection”, Nuclear Engineering and
Design 246, 2012, pg. 123 -127
[11] BAC© Corrosion Control, “Pin Brazing –
Easybond Unit”, Technical Datasheet 5.1-2
11
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