©September 2015, Society of Naval Architects & Marine Engineers. Used with permission for information and discussion purposes (author rights). May not be reprinted or transmitted.

Of Smut, Magic Backing Bars, and Hybridization:

Lessons Learned in Government-Industry Cooperation to

Develop Nickel-Aluminum Bronze (NAB) Main

Propulsion Shaft Repair Procedures

N. Andrew Greig, (V) Welding Manager, Steel America

Nickel-Aluminum bronze (NAB) (UNS 63000) main propulsion shafts are employed in AVENGER

Class minesweepers due to the alloy’s strength, corrosion resistance, and low ferromagnetic

signature. The US Navy sought additional sources of sustaining the Fleet with refurbished shafts

using weld repair processes followed by Post-weld Temper Annealing (PWTA) heat treatment to

mitigate dealloying corrosion. This paper describes the high level of technical cooperation and

information sharing among Navy, shaft repair facility, and supplier metallurgists and engineers

needed to successfully develop, test, and qualify three essential weld repair processes and

supporting inspection and PWTA procedures for NAB shafts.

KEY WORDS: Propulsion Shaft; Repair

Welding; Nickel-Aluminum Bronze (NAB);

Dealloying corrosion; Post-weld Temper Anneal; Weld Procedure Specifications (WPSs); Performance

Qualification Records (PQRs)

INTRODUCTION Main propulsion shafts for AVENGER Class

minesweepers (also known as MCMs) are fabricated

from Nickel-Aluminum Bronze (NAB) Alloy C63000,

primarily because this alloy is non-ferromagnetic, and

also because of its strength (100 ksi UTS) and

corrosion resistance in seawater. Fourteen MCMs

were built beginning in the mid-1980s and 11 remain

in service. During major overhauls, the US Navy

(specifically NSWC-PD Code 932 Mr. Scott Coble)

observed cracking and corrosion of MCM shafts

particularly in way of the seal journal on the stern tube

shafts. Shaft repair welding procedures – specifically

including a shop-specific Weld Procedure

Specification (WPS) WP-31 for weld metal buildup

using the gas metal arc welding (GMAW) process

mechanized via weld lathe approved by the local

Naval Sea Systems Command (NAVSEA)

representative on September 7, 2010 - did NOT

include a Post-weld Temper Annealing (PWTA) step

rendering weld-repaired NAB shafts susceptible to

dealloying corrosion.

MIL-STD-2195A is the Navy Test Method for

detecting dealloying corrosion using silver nitrate.

Dealloying corrosion is defined therein as “…a

seawater corrosion phenomenon in which one

constituent of certain …nickel-aluminum bronze

alloys is selectively attacked, often with no visible

evidence on the surface…(but which) may extend to a

depth below the surface…significantly reducing the

strength and ductility of the component.” Where

dealloying corrosion is detected, repair is affected by

removing it completely by machining and restoring

shaft thickness and diameter by weld metal build-up.

Dealloying corrosion on in-service shafts was

confirmed using this procedure in April 2015 on shafts

extracted from GUARDIAN.

The Navy invited the Shaft Repair Facility (hereafter

SRF or we) to develop comprehensive inspection,

weld repair, and heat treating procedures to repair and

restore MCM NAB propulsion shafts. This paper

describes lessons learned during NAB shaft weld

repair procedure testing and development, and

acknowledges the Government-Industry team efforts

required to successfully develop such procedures.

Figure 1. MCM shafts as received for repair (note bow

in shaft on the left)

APPROACH

MIL-STD-2195 describes standard practices for repair

welding, weld cladding, straightening, and cold rolling

of naval main propulsion shafting. This standard

covers only steel alloy shafts. Nonetheless, Navy

representatives stated this standard be reflected in any

weld procedure development and qualification effort,

specifically as regards qualification of major shaft

repair welding by groove weld testing, rather than by

testing weld metal build-up as SRF had done in 2010.

Further, weld mechanical tests should be performed

following PWTA.

Shaft repair typically involves

A mechanized weld metal build-up process

whereby a spiral bead is deposited on a rotating

shaft with a torch traveler that advances the

width of one weld metal build-up bead per

revolution, and

At least one manual or semiautomatic welding

process for spot repair of the weld metal build-

up, bolt hole repair, or filling keyways.

Deposition of weld metal build-up as spiral beads is

required by MIL-STD-2191 to balance circumferential

weld distortion. For steel shafts, the groove specified

for qualifying major weld repair welding is a

compound angle V-groove approximately 2-inches

deep. Otherwise, MIL-STD-2191 references Naval

Sea Systems Command (NAVSEA) Technical

Publication S9074-AR-GIB-010/248 (TP248) for

developing welding procedures and for performance

qualification testing and records.

To assist contractors develop Weld Procedure

Specifications (WPSs) and Performance Qualification

Records (PQRs) in a standard format checked against

TP248 and the applicable fabrication specification, the

Navy sponsored development of an on-line WPS/PQR

software program called NavWeld. However, MIL-

STD-2195 is not one of the fabrication standards

embedded in Navweld software. Working around this

limitation was required. NAVSEA Technical

Publication S9074-AR-GIB-010/278 (TP278),

“Requirements for Fabrication, Welding and

Inspection…and Repair of Machinery….” was cited as

the fabrication specification, but weld test

configurations adapted from MIL-STD-2195 were

used. Specifically, the weld type selected was “single

V pipe weld with (infinite) backing” to match a

plausible category of TP278 weld preparation. This

“hybridized” required manual manipulation of the

software to produce WPSs and PQRs in the desired

format, but still access the code-checking features of

the software.

“Special procedures” as defined in TP248 require

NAVSEA approval. While the Mechanized GMAW

(Mech GMAW) process did not meet this category, the

SRF agreed to submit the procedure (designated WP-

31) and qualification test records to NAVSEA

headquarters for approval via its local representative

because 1) the procedure is mechanized and 2) though

qualified in accordance with TP278 machinery repairs,

the procedure is intended for shaft repair.

Accordingly, NAB shaft weld procedure

qualification plans were submitted to Navy

warrant holders for review and comment. The

test plan included:

1. Acquiring a 10-inch diameter NAB round bar

simulating an MCM shaft

2. Machining circumferential V-grooves grooves

per MIL-STD-2195 Figure 3, except the depth of

the groove would be 3/8-inch rather than 2-

inches for Mech GMAW major repairs and also

for a manual GTAW minor repairs.

3. Preliminary Nondestructive Evaluation (NDE)

of the welds to identify and correct any defects

4. PWTA

5. Final NDE

6. Destructive mechanical testing of each weld by

two transverse tensile tests and three side bend

tests as required by TP248.

The mock shaft was sized to accommodate two Mech

GMAW welds and two GTAW welds made by two

different welders to 1) have sufficient weld diameter

to extract tensile test specimens capturing most of the

depth of the weld, 2) qualify at least two welders per

procedure and 3) double chances of at least one weld

being satisfactory for PQR testing following PWTA.

Navy comments regarding increasing Mech GMAW

weld groove depth to at least ¾-inch and other

configuration and testing comments were

incorporated.

Fig. 2. Weld test assembly for qualifying Mechanized

GMAW seen with ¾-inch x 45° circumferential weld

groove in 10-inch OD solid NAB partially filled

DISCUSSION AND LESSONS LEARNED

Literature and Specification Review

Past experience and weld consumable technical data

sheets provided ample guidance on weld process

electrical parameters, shielding gases, and

characteristics of the base metal. The literature also

provided guidance on the appropriate PWTA

temperature and effects of PWTA on microstructure

(especially Li, 2012 and Anantapong, 2014).

However, there was little guidance on heating cooling

rate controls or time at temperature limits. Our

experience with post-weld stress relief (PWHT) was

based on MIL-STD-2191 practices developed for

steel, which typically requires the time at temperature

be determined by the thickness rule: 1 hour per inch

of thickness, 1 hour minimum with slow heating rate

and cooling rate controls provided by settings on

power sources for induction heating systems. This

was the process identified in our initial test plan.

Richard Vonderau acting as consultant to the local

NAVSEA representative advised cooling “as quickly

as possible without causing distortion” because NAB

exhibits “a ductility dip in the 800-500°F range.”

Reflecting this advice, initial weld test specimens were

subjected to the 1250°F PWTA using the thickness

rule for time at temperature, no limits on ramp up

heating, but with slow cooling with insulation to

1000°F followed by removing the insulation to

accelerate cooling rate in ambient air.

PWTA Lessons Learned TP248 declares the PWHT temperature an essential

variable, but is silent with regard to time at

temperature. However, the code checking feature of

NavWeld referenced §6.4.5 of TP278 which

establishes a PWTA time at temperature requirement

of 6 hours for ANY weld on an NAB surface exposed

to seawater. There is no guidance regarding cooling

rate control to avoid the ductility dip described by

Vonderau. TP278 suggests air cooling for NAB

castings. American Bureau of Shipping (ABS) Part 2

Supplementary Requirements for Naval Vessels,

Chapter 13 Materials for Machinery, Boilers, Pressure

Vessels and Pipes, Section 14 Nickel-Aluminum

Bronze Castings (Febraury 14, 2014) rules for PWTA

of NAB recommends cooling “as rapidly as possible”

after the end of 6 hours. This guidance appears most

accurate given Fuller reporting a brittle microstructure

forms below 800°C (1472°F) which can be avoided by

rapid cooling at about 1K°/s (1.8F°/s). Fuller makes

no mention of a ductility dip at 427°F (800°F). (Fuller,

2007) Similarly, Anantapong showed the beneficial

effects of annealing at 675°C (1250°F) followed by air

cooling on dissolving an intergranular phase

constituent (β´) known to promote corrosion and

exhibit high hardness (more brittle), however is silent

about the deleterious effects of slow cooling.

(Anantapong (2014) pg. 236). The literature agrees

the annealing heat treatment results in the most

corrosion-resistant microstructure accompanied by

lower tensile strength but higher ductility than as-cast

or hot extruded NAB base materials or weldments of

those base materials.

Based on bend and transverse tensile testing of

weldments in plate, 10-inch rounds and in transverse

“plate” cut from the 10-inch round; no significant

difference in mechanical properties could be discerned

with respect to time at temperature or cooling rate.

Data are not reported here because the effort was not

intended as a statistical study. The time at temperature

requirement in TP278 was unknown to SRF until after

testing started. So procedure qualification weldments

were subjected to time at temperatures at 2, 3 and 6

hours depending on thickness based on past

experience rather than the TP248 “6 hours no matter

what” requirement. Any failures in preliminary

testing were due to test specimen design errors, welder

workmanship errors or machining errors (all discussed

below) as opposed to any bulk property changes

resulting from PWTA time at temperature or cooling

rate.

Fig 3. Round Mech GMAW test weld and 3/8-inch

GTAW plate after PWTA

Lessons learned regarding PWTA of NAB are:

“Hybridizing” Navy fabrication requirements

requires effort, but can be done to achieve the

best possible product for the Navy. NavWeld

procedure development, qualified range reports

and code checking features were highly useful in

this regard. Use of “dummy data” to generate

draft WPS/PQRs can identify process or

parameter changes before initiating qualification

welding.

NAB is an unusual propulsion shaft material

with a very specific PWTA requirement which

had to be “discovered.” While Navy and

industry experts were responsive to most

contractor questions by email, contractors

dealing with unusual materials or “special

welds” should consider meeting with Navy and

weld consumable experts to devise special weld

procedure qualification projects.

TP248 should be revised to provide PWTA

cooling rate guidance similar to ABS rules.

Nondestructive Evaluation (NDE) Lessons

Learned Radiography (RT) was impractical because of the size

and thickness of the 10-inch round specimen. ¾-inch

NAB plate was procured to allow welders employ

semiautomatic GMAW parameters and techniques

similar to the Mech GMAW procedures which would

be employed on the long-lead 10-inch round mock

shaft. These “practice welds” were radiographically

examined. The first welder’s plate passed RT and

subsequent bend and tensile tests. Rejectable

interbead Lack of Fusion (LOF) was detected in the

start and stop ends of a second welder’s plate.

Interestingly, bend tests cut in the center of the second

welder’s test plate where RT indicated no LOF still

failed at the location RT had detected rejectable LOF

at the ends.

SRF desired some form of preliminary volumetric

weld testing to identify any poor qualification welds

prior to absorbing the expense of PWTA and loss of

rather expensive base material. Shear wave UT is

impractical for the curved surface of the solid mock

shaft. SRF’s Level III inspection contractor,

InspecTesting, proposed developing a compression

wave ultrasonic test (UT) procedure in exchange for

SRF providing a NAB calibration block. SRF

fabricated the block out of the center of one of the test

rounds after being split down the axis. Machining ten

1/8-inch diameter holes was difficult and time

consuming: NAB has high conductivity and thermal

expansion properties which causes it to close back

over the drill bit as it cools. The local NAVSEA

representative allowed InspecTesting to use a

calibration block with partial rather than through-

holes.

However, compression wave UT exhibited limitations.

First, the density and large grain size of NAB

attenuates the sound wave much more than steels

requiring operation at a lower frequency than steel.

Lower frequency UT often must be performed at a

40% of screen reject level to avoid noise and excessive

false positives, which is acceptable for MIL-STD-271

Class 2 acceptance criteria for machinery repair.

However, TP248 requires volumetric inspection to

meet Class 1 acceptance levels meaning a 20% of

screen reject level. Furthermore, compression wave

UT could miss defects oriented parallel to the sound

wave. Therefore compression wave UT was only used

for screening finished welds where RT was

impracticable. RT was accomplished as final post-

PWTA inspection of mock shaft weldments after

weldments were sectioned for mechanical tests. Plate

weldments were RT’d both pre- and post-PWTA.

After initial welding and sectioning the 10”OD x 33”

long test round, UT rejected one welder’s Mech

GMAW weldment and both GTAW circumferential

groove weldments. One Mech GMAW weld exhibited

about 2 circumferential inches of lack of fusion and

several other regions of non-relevant indications. We

elected to repair this joint by machining a 1/4-inch

deep 360° groove centered at the location of the .22-

inch deep rejectable indication. The repair was

accomplished in early December 2015 and the test

specimen, now cut down to a 10-inch long x 10-inch

diameter piece, was subjected to PWTA at 1250°F for

six hours as required by TP278, slow cooling (rather

than blanket cooling to avoid weld distortion) to

1000°F followed by blanket cooling (in lieu of air

cooling as planned due to operator error). “Plate” and

backing bar 3/8” thick was cut from section drops for

new GTAW tests. Similarly, ¾” plate was salvages

from round sections to produce material for additional

semiautomatic GMAW testing in the horizontal

position.

The specimen passed final UT following PWTA and

was sectioned for transverse tensile and bend tests.

One ¾x2x10 transverse test block was rejected due to

machining error. Two others passed RT prior to final

machining.

Mechanical Testing Lessons Learned TP248 requires a minimum of two tensile tests and

three bend tests per weldment for each position tested.

The first tests were performed on the GMAW

“practice plate” fabricated in the flat position. The test

joint was a type B1V.1 joint, single V groove with a

3/8-inch backing bar. Backing bars were removed

after PWTA and final RT and full ¾-inch weld

thickness transverse tensile specimens were removed.

Actual tensile strengths for both the base plate and for

the MIL-CuNiAl weld consumable exceeded 100ksi.

Regrettably, this exceeded capacity of the tensile test

machine as the first tensile test specimen failed in the

base metal in the chuck. The cross section of the

second specimen was reduced to accommodate the

machine and passed, but was not reported because the

method of reducing cross section violated AWS B4.0

methodology. Given the limited amount of test plate

remaining, a ½-inch round transverse tensile specimen

could was machined, tested, and passed.

Another lesson learned was to use a mandrel size

appropriate to the material for guided bend tests.

Vonderau recommended use of the roller bend test

device of AWS B4.0 for this test, but no vendor in the

area had such a device; they all used plunger mandrels

and dies for guided bend tests. Initial tests were

performed using mandrel and dies for steel causing

some inadvertent failures. Use of mandrels sized per

AWS B4.0 resulted in all further bend tests meeting

specification requirements. Surface finish also is

critical to successful and accurate mechanical testing

of NAB weldments. The relatively low ductility, high

strength, and large grain size exacerbate the crack-

starter effect of any surface flaws, nicks, or sharp

edges on a test specimen.

Fig 4. Representative NAB bend test and semi-tensile

test specimens as machined

For transverse tensile specimens removed from welds

in the mock shaft, specimen blocks were visually

examined, often PT examined, RT’d, and split into two

thinner halves to accommodate capacity of the tensile

test machine as allowed per AWS B4.0. That is in this

case for a ¾-inch groove weld, a single transverse

tensile test representing the full thickness of the weld

from face to root consisted of two approximately 3/8”

thick transverse tensile test specimens.

Mechanical testing of NAB weld coupon lessons

learned are:

Take full advantage of AWS B4.0 minimum

requirements for rounding edges and surface

finish.

Visually inspect samples before testing; reject or

rework any exhibiting nicks, scratches or sharp

edges in the test zone (generally 1-inch either

side of the center of the weld or transverse weld

tests and bend tests) and PT the tests zone to

reveal invisible pinholes.

Use maximum mandrel/roller diameter as

allowed by AWS B4.0 for the material being

tested.

Choose test facilities having capacity for full-

thickness weld tests and roller guided bend tests.

Weld Process Lessons Learned

Materials, parameters and process controls for welding

NAB are published by welding consumable suppliers

and are well known. However, SRF discovered some

unusual characteristics welding NAB.

Practice welds performed in summer 2014 without

preheat by two different welders were both clean

exhibiting good fusion during in-process inspections.

The NAVSEA Authorized Representative, the Mid-

Atlantic Regional Maintenance and Repair Center

(MARMC) QA Code 132.1, Mr. Phillip DeSiano

agreed to allow testing of the practice plates to qualify

semi-automatic GMAW despite not being invited to

witness root pass welding. However, a LOF defect

apparently limited to one of over twenty stringer beads

by one welder in one plate which, despite passing RT

in the center of the plate, caused bend test failure. LOF

suggested improving technique to better achieve

interbead and sidewall fusion during Mechanized

GMAW welding. Because Mech GMAW test welding

was done in colder winter months, 125°F preheat was

employed. The mock shaft was chucked into a lathe

with a Lincoln TC-3 beam rider holding a straight gas-

cooled torch attached to a Lincoln PowerWave S455

and Lincoln 10M wire feeder/controller. The weld

parameters (wire feed speed, voltage) were set to the

same values proven in the semiautomatic GMAW

trials. Similarly, the rotational lathe speed was set to

approximate the arc travel speed established in

semiautomatic trials. Welds were deposited as

individual stringer beads in a groove so the TC-3

motivator was switched off and translated manually

between each pass.

Two phenomenon appeared that had not been seen in

semiautomatic GMAW welds: 1) After the root and

hot passes were deposited, subsequent passes

exhibited black smut deposited on the weld bead and

sidewalls; 2) One sidewall exhibited intermittent LOF.

The black smut was easily removed by rotary wire

brush. Each deposited bead, especially in the regions

of LOF, were cleaned further and blended by grinding.

However, the intermittent side wall LOF appeared in

the same regions every time a new stringer was

deposited on the lathe chuck side of the groove.

Fig. 5. In-process Mech GMAW weld exhibiting (a) smut deposits and (b) intermittent, localized Lack of Fusion

(LOF)

Navy and industry professionals were consulted and

forthcoming regarding these phenomenon. The local

NAVSEA representative, Mr. Philip DeSiano,

forwarded information suggesting the smut was the

aluminum constituent of both the NAB base metal and

weld filler metal condensing from the plasma of the

arc. White confirms this observation noting smut is

common for GMAW of aluminum alloys because

“…as the filler wire passes through the arc and melts,

some of it reaches the vaporization temperature and

condenses on the cooler base metal …not adequately

protected by shielding gas.” (White, May 2015) Smut

also was observed on another semiautomatic GMAW

PQR test plate. In performing subsequent welds,

including a repair weld on the test piece (discussed

above), the senior welder noted increasing set voltage

appeared to reduce smut deposition, particularly on the

weld bead as deposited.

Between practice and qualification the principle

change was ambient temperature and preheat. Higher

heat was thought needed to promote fusion, but may

have contributed to smut production and, possibly,

LOF if a dielectric oxide was formed by improper

torch heating. For example, the backing bar for

GTAW test plate in the vertical position exhibited no

fusion whatsoever. This “magic backing bar” acted

more like a ceramic backing bar than a metal

consumable backing bar. This made the backing bar

easy to remove and a little buffing was all the

mechanical cleaning needed on the root weld side of

the test plate. The GTAW PQR plate passed all non-

destructive tests and mechanical tests.

Fig. 6. “Magic backing bar” exhibiting no root pass fusion

No detailed chemical analysis of the backing bar was

attempted to determine if the LOF was due to residual

surface contamination. This hypothesis is unlikely

given the uniformity of root pass LOF. Further,

attachment tack welds made without preheat exhibited

acceptable fusion. Surveillance during welding did

reveal the oxy-acetylene torch used for preheat often

was directed into the weld preparation in violation of

workmanship practice requiring torch heating no

nearer than 3-inches either side of the weld

preparation. A dielectric oxide may have formed on

the backing bar resisting fusion, though the sides of the

weld preparation were not similarly affected.

Grinding between passes may have removed fusion-

resistant oxide layers formed by preheating.

Weld process lessons learned suggest employing the

same cleaning materials and workmanship methods as

would be employed for welding aluminum, which

include:

Fastidious weld preparation and interpass

cleaning.

Proper torch preheating techniques (neutral flame,

preheat outside the weld groove).

Adjust parameters within WPS limits to minimize

smut.

Proper weld technique, specifically with regard to

shortening the contact tube-to-work distance,

optimizing gas flow rate and nozzle size for the

weld joint and position, nozzle cleanliness, and

push angle.

Observe maximum interpass temperature limits.

ANALYSIS OF PQR TEST RESULTS All circumferential or linear welds passing

preliminary and final UT/RT and other surface

nondestructive examination, met TP248 mechanical

testing standards with one exception. The weld face

half of one set of transverse tensile specimens in the

Mech GMAW weld broke 2.8% below the minimum

required ultimate tensile strength (UTS) requirement

for MIL-CuNiAl weld wire. Specifically, while all

other specimens exceeded the 100 ksi minimum UTS

requirement for the base material, this one specimen

exhibited a tensile strength of 82.6 ksi which is less

than the minimum requirement specified in MIL-E-

2376/3A of 85 ksi for the weld metal. This weld filler

metal specification requires all weld metal tensile

testing in the as-welded state whereas testing of this

weldment was performed after PWTA. However,

when averaged with its companion semi-tensile

coupon per AWS B4.0, UTS for the pair of thin tensile

test coupons representing a single transverse tensile

test was 94ksi, exceeding the minimum required for

the weld metal.

At least one reviewer interpreted TP248 as requiring

EACH tensile test meeting the minimum ultimate

tensile strength of the weaker of either the base metal

or the weld metal notwithstanding the averaging

method of AWS B4.0. Regrettably, sectioning of the

original test piece for destructive evaluation,

fabrication of UT calibration standards, and for other

weld tests left no piece large enough to conduct repeat

tensile tests or to weld another mechanized GMAW

PQR.

The fracture surface was examined by two other Navy

reviewers. All agreed failure likely was initiated at a

small region of LOF (undetected by either UT or RT).

A less probable failure mechanism posited the failure

initiated in a slightly embrittled Heat Affected Zone

(HAZ) opposite the weld face side of the specimen.

One Navy reviewer recommended seeking NAVSEA

approval notwithstanding the failure of one semi-

tensile coupon because testing indicated the procedure

was valid and the “failure” likely was due to a lapse in

welder workmanship.

Fig. 7. Semi-tensile specimen that exhibited less than 85Ksi UTS (4) after testing and (b) exposing fracture surface

exhibiting LOF undetected by pre-test radiography (RT)

However, other reviewers sought more detailed

metallurgical analysis of the 1 of 4 semi-tensile

coupon exhibiting tensile strength under 100ksi.

Element Materials Technology (Element) was

contracted to examine the fracture surfaces and

identify the failure mechanism. Scanning Electron

Microscope (SEM) examination revealed a high level

(15-20%) of porosity in the weld metal and LOF with

base metal along one side of the groove. Some intra-

bead shrink-back LOF also was detected. While the

location of side wall LOF matches the location of (as

yet unexplained) LOF observed during initial welding,

the extent of porosity and LOF was surprising given

the test blank passed RT. In contrast, metallurgical

examination of a transverse section of the weld

revealed neither side wall LOF on the opposite side

nor interbead LOF.

Fig. 8. Element analysis report depictions of semi-tensile specimen showing (a) SEM micrograph (15X) revealing

(welder workmanship) defects such as gas holes and LOF and (b) metallographic transverse specimen through LOF

revealing fracture initiation point in base metal and perfect interbead fusion and soundness

Element concluded the tensile test fracture initiated in

the base metal and then ran up the fusion line

weakened by the porosity and LOF. The LOF and

porosity observed only on this side wall completely

account for this semi-specimen failing 17-20% below

the average UTS of the other pair of tensile tests, and

for all other tensile tests conducted on test plates made

with GTAW and semiautomatic GMAW. Again,

neither RT nor UT detected this region of porosity and

given the other tensile test location and four bend test

passed mechanical testing, the porosity and base metal

fusion line LOF observed was restricted to just this

region of the original weld, either because of

residual contamination after solvent cleaning of

the groove,

formation of a non-wetting oxide despite in-

process mechanical cleaning between passes by

rotary wire brush and grinding wheel,

or perhaps due to a puff of air disturbing the

shielding gas.

Given all other regions of the weld, including the

repair weld, appeared perfectly fused and sound, and

because all other mechanical tests (3 semi-tensile tests

and 4 bend tests) met or exceeded TP248 requirements

validates the assertion the fusion line origin of the

failure was due to workmanship error(s). The Navy

approved the Mech GMAW process on August 5,

2015.

SUMMARY AND RESULTS A Norfolk-based integrated Shaft Repair Facility

(SRF) developed and tested three Nickel-Aluminum

Bronze (NAB) weld procedures to affect repair of

MCM Class minesweeper main propulsion shafts.

NAB rarely is used in this application so extraordinary

effort was required with extraordinary cooperation

among the SRF, welding suppliers, inspection and test

contractors and Navy warrant holders to test and

validate welding, Post-weld Temper Annealing

(PWTA), and inspection procedures over a one year

period. Despite having to “hybridize” requirements

from two different fabrication standards and one weld

procedure requirements standard, NavWeld

WPS/PQR software made available by the Navy

proved essential to developing procedure and test

documentation in a standard format easily understood

by all participants. Fabrication and analysis of test

welds showed special attention to welder

workmanship akin to that employed to weld aluminum

alloys is required to successfully weld NAB especially

with regard to joint cleanliness, interpass cleaning and

welder technique.

ACKNOWLEDGEMENTS Success of this effort was achieved through technical

interchange, cooperation and effort of the following:

Steel America (Russell Gray, Chris Chapman and its

Management, welders, machinists, and inspectors);

Welding Consultants/Contractors (Rich Vonderau,

AECOM; Paul Beck, Arcet; Kyle Drummer, Lincoln

Electric and Les Scott, Arcos); Inspection/Test

Contractors (Mary Turner & Randy Billiter,

InspecTesting and Bill Hong, Element) and Navy (Phil

DeSiano and Melissa Taylor, MARMC; Matt Sinfield,

NSWC-CD; Nicole Elia and Jeremy Gephardt,

NSWC-PD; and Katheryn Wong, NAVSEA 05P2)

REFERENCES

NAVSEA Technical Publication S9074-AR-GIB-

010/278, “Requirements for Fabrication, Welding and

Inspection…and Repair of Machinery….”

NAVSEA Technical Publication S9074-AR-GIB-

010/248, “Requirements for Welding and Brazing

Procedure and Performance Qualification”

MIL-STD-2191 with ACN 1, “Standard Practice:

Repair Welding, Weld Cladding, Straightening, and

Cold Rolling or (stet) Main Propulsion Shafting”

MIL-E-23765/3A, “Military Specification, Electrodes

and Rods- Welding, Bare, Solid, Copper Alloy”

J.A. Wharton, R.C. Barik, G. Kear, R.J.K. Wood, K.R.

Stokes, F.C. Walsh, “The corrosion of nickel–

aluminium (stet) bronze in seawater,” Corrosion

Science 47 (2005) 3336–3367.

Li, H., Grudgings, D., Larkin, N. P., Norrish, J.,

Callaghan, M. & Kuzmikova, L. (2012). Optimization

of welding parameters for repairing NiAl bronze

components. Materials Science Forum, 706-709 2980-

2985.

M.D. Fuller, S. Swaminathan, A.P. Zhilyaev, T.R.

McNelley (2007). Microstructural transformations

and mechanical properties of cast NiAl bronze: Effects

of fusion welding and friction stir processing.

Materials Science and Engineering A 463 (2007) 128–

137.

J. Anantapong, S. Suranuntchai, A. Manonukul, V.

Uthaisangsuk, "Investigation of Nickel Aluminum

Bronze Alloy under Hot Compression Test",

Advanced Materials Research, Vols 931-932, pp. 365-

369, May. 2014

White, Galen, “Best Practices for Welding

Aluminum,” Practical Welding Today® Vol. 763,

May/June 2015 (published at TheFabricator.com)

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N. Andrew Greig has been the Welding Manager for Steel America- the fabrication and shaft repair divisions of

Colonna’s Shipyard, Inc. - since 2011 following 25 years as a materials integration consultant to NAVSEA and

other service branches. He received a bachelor’s degree in Metallurgy from Penn State, a master’s degree in

Finance from the Virginia Commonwealth University, and a Certificate from the Bettis Reactor Engineering School.