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©September 2015, Society of Naval Architects & Marine Engineers. Used with permission for information and discussion purpo...
Figure 1. MCM shafts as received for repair (note bow
in shaft on the left)
APPROACH
MIL-STD-2195 describes standard pract...
inches for Mech GMAW major repairs and also
for a manual GTAW minor repairs.
3. Preliminary Nondestructive Evaluation (NDE...
the annealing heat treatment results in the most
corrosion-resistant microstructure accompanied by
lower tensile strength ...
However, compression wave UT exhibited limitations.
First, the density and large grain size of NAB
attenuates the sound wa...
Mechanical testing of NAB weld coupon lessons
learned are:
 Take full advantage of AWS B4.0 minimum
requirements for roun...
Navy and industry professionals were consulted and
forthcoming regarding these phenomenon. The local
NAVSEA representative...
 Observe maximum interpass temperature limits.
ANALYSIS OF PQR TEST RESULTS
All circumferential or linear welds passing
p...
Fig. 8. Element analysis report depictions of semi-tensile specimen showing (a) SEM micrograph (15X) revealing
(welder wor...
REFERENCES
NAVSEA Technical Publication S9074-AR-GIB-
010/278, “Requirements for Fabrication, Welding and
Inspection…and R...
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NAB Lessons Learned Paper Greig 2015

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NAB Lessons Learned Paper Greig 2015

  1. 1. ©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.
  2. 2. 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-
  3. 3. 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
  4. 4. 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.
  5. 5. 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.
  6. 6. 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)
  7. 7. 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.
  8. 8.  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.
  9. 9. 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)
  10. 10. 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) ________________________________________________ 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.

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