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SAW (SUBMERGED ARC WELDING) TEMPERBEAD TECHNIQUES FOR ROTOR JOURNAL REPAIR

Michael J. Jirinec, PMP Robert E. Kilroy Jr. ALSTOM Power Inc. 1200 Willis Rd. Richmond, Virginia 23237

Gang (Joe) Zhou, Ph.D ALSTOM Power Inc. 1119 Riverfront Parkway Chattanooga, TN 37402

William F. Newell Jr., PE IWE EUROWELD LTD. 255 Rolling Hills Road Mooresville, NC 28117

James W. Hales Specialty Welding & Machining Inc. 9304 Birchwood Pike Harrison, TN 37341

Presented at the:

EPRI 7th International Welding and Repair Technology Conference for Power Plants June 21 – 23, 2006 Ponte Vedra Beach, Florida

Printed by ALSTOM Power Inc., Turbine & Generator Repairs Engineering, Richmond, VA

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SAW Temperbead Techniques for Rotor Journal Repair

Michael J. Jirinec, PMP ALSTOM POWER, Inc.

1200 Willis Road Richmond, VA 23237

Robert E. Kilroy, Jr.

ALSTOM POWER, Inc. 1200 Willis Road

Richmond, VA 23237

Gang (Joe) Zhou, Ph.D. ALSTOM POWER, Inc. 1119 Riverfront Pkwy.

Chattanooga, TN 37402

William, F. Newell, Jr., PE, IWE EUROWELD, LTD.

255 Rolling Hills Road Mooresville, NC 28117

James W. Hales

Specialty Welding & Machining, Inc. 9304 Birchwood Pike Harrison, TN 37341

Abstract Controlled deposition techniques, oftentimes called temperbead welding, have long been used in the nuclear, shipbuilding, fossil, pulp & paper, steel, and petrochemical industries as an alternative to achieving satisfactory material properties without applying post weld heat treatment. Both ASME and the NBIC include provisions in the code body for controlled deposition procedure development and application. Use of similar methodologies for steam turbine and generator rotor repair have been limited in the past to GTAW machine applications. Deposition rates associated with GTAW machine deposits using .035 or .045” diameter wires are characteristically low. The acceptance of controlled deposition welding has long been established in other industries. A natural progression for expanding use of this approach includes qualification and application of high deposition rate welding processes. This paper describes the development, testing and qualification of controlled deposition submerged arc welding for applications involving the repair of selected steam turbine and generator rotor journal alloys without post weld heat treatment.

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Introduction The power generation industry has long been a proponent of alternative welding techniques to improve weldment performance, reduce repair cycle time and or a combination of both. One activity that adds considerable time to any weld repair operation is post weld heat treatment (PWHT). Traditional thinking and most codes require PWHT for many alloys, particularly low alloy steels and weldments. It is only by exception and by qualification and implementation of special welding procedures that PWHT elimination is permitted. Both ASME and the National Board (NBIC) have included requirements for qualification and testing of controlled deposition (temperbead) welding procedures. Temperbead welding and conventional welding with post weld heat treatment are similar in implementation. With the exception of potentially higher residual stresses, results for temperbead techniques on the base metal heat-affected zone (HAZ) are equal to if not superior to the welds made with full post weld heat treatment. Welding residual stresses will be a function of the component geometry, alloys involved and weld thickness/dimensions. Temperbead welding involves the deposition of weld beads in a particular pattern using specific parameters to temper the previous beads and heat-affected-zone(s) (HAZ), In the case of turbine or generator rotor repair, eliminating PWHT can result in savings of approximately 2-4 days of critical path time, depending upon component size. The purpose of this evaluation was to develop and verify welding parameters to permit rotor shaft restoration by welding on selected alloys without the need for post weld heat treatment. Controlled deposition welding techniques were utilized to produce adequately tempered weld beads and base metal heat-affected zones. The submerged arc welding process and normal shop practice were used to ensure that the technique would be applicable for either shop or field repair work.

Temperbead Welding Conventional welding using the gas tungsten arc (GTA), manual shielded metal arc (SMAW), submerged arc (SAW) or flux cored arc (FCAW) process produces a HAZ in the base metal and between weld beads and layers. It is this HAZ that metallurgical and welding engineers around the world pay particular attention to determining the suitability of the weldment for service. The authors (1,2) have first hand experience with the use and qualification of temperbead procedures for ASME Section III component repair using ASME Code Case N-432, for the qualification and repair of the Indian Point Unit 2 Steam Generator Girth Welds, as well as various other temperbead qualifications for carbon and low alloy steels, using the SMAW, Machine GTAW, GMAW and FCAW94) processes. In addition, the authors have been directly and indirectly involved with the development of the Electric Power Research Institute (EPRI) SMAW temperbead applications for P11 and P22 piping for Ravenswood Unit 3 HRH piping manifold (2). The writers (5) are also familiar with the use of temperbead welding for the repair of HP and IP steam turbines,

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and have now taken their combined expertise to a new level involving the development of temperbead techniques using the high deposition submerged arc welding process. Temperbead or controlled deposition welding involves the judicious placement of the first layer weld beads with controlled deposition and bead step over, followed by a controlled second layer using modified deposition parameters compared to the first layer deposit. A schematic representation of the temperature profile for a single weld bead is shown in Figure 1. Following with a modified or controlled deposition layer technique, the temperature profile and microstructure of the heat-affected-zone (HAZ) are altered in relation to the single bead deposit. It is important to deposit the first layer in such a manner that penetration is uniform and scalloping form bead-to-bead is minimized. This approach is also required for the second and subsequent layer plus particular attention must be paid to the parameters to avoid penetrating through previously deposited weld beads/layers. Further, success is achieved with this controlled deposition technique via it’s ability to force grain refinement and in particular, the refinement of the course-grained (HAZ), thereby improving the microstructure and the mechanical properties of the weldment. These results enable achievement of specific property results, precluding the need for high temperature post weld heat treatment, with equal to of better mechanical properties.

Figure 1 - Represents a typical heat-affected zone transition temperature points as they relate to the iron-carbon phase diagram.

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PHASE I Development Base material selected for the test program was 2 ¼ Cr-1Mo plate (SA-387, Grade 22, Class 2) because of its similarity to certain turbine and generator rotor shafts requiring repair. Welding wire used was NiCrMo1 (AWS A5.23, ~EM2) plus a neutral submerged arc flux. Based on the previous experience with the temper-bead technique and submerged-arc welding process, three key technical issues were identified in development of SAW temper-bead technique:

1. Shape of individual bead: The large depth-to-width aspect ratio inherent to SAW beads creates a severely scalloped fusion line profile that prevents uniform grain refinement and tempering of the base metal HAZ by the second layer of weld metal. It was proposed that the program’s initial effort be focused on adjusting the welding current, voltage, traveling speed, and wire-feed speed to reduce the depth-to-width aspect ratio of the SAW beads and thereby minimize levels of the scalloping along the fusion line.

2. Bead-To-Bead Position: This was another key factor to control the fusion line

profile. It was recommended that the minimum bead overlap must be at least 50%, which was achieved by controlling the step-over distance.

3. Heat Input Ratio: The heat input ratio between the 1st and 2nd layers is the key

factor to control the level of grain refinement and tempering. It was specified that this ratio should be increased, significantly over that typically used for GTAW machine qualifications.

All welding trials and parameter development were conducted at Specialty Welding & Machining, Inc., Harrison, TN. Metallographic examination, determination of grain refinement and mechanical test results were obtained from the Alstom Material Technology Center (MTC), Chattanooga, TN(6). Welding engineering and project management oversight were provided by Alstom and Euroweld. This was to ensure a successful transition from the laboratory to the repair shop inclusive of field applications. Various current, travel speeds and bead overlap trials were conducted on expendable material to evaluate and determine the technique that initially produced favorable tempering and heat-affected zone (HAZ) grain refinement as shown in Figure 2.

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Figure 2 - Example of technique trials to establish a point from which to adjust welding parameters to maximize grain refinement yet offer a methodology that

could be duplicated in the shop on a consistent basis.

Once initial trials were concluded and a preliminary procedure determined, test plates were prepared and preheat applied that was consistent with that applied in the shop, typically 450F. (Figure 3) Consensus on the results with the Alstom Materials Technology Center (MTC) to ensure adequate grain refinement was a requirement and was reached. Trial samples were polished, etched and examined for level of grain refinement by the MTC.

Figure 3 - Test Set-up using a submerged arc welding system, side beam and an induction heating system for preheat.

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Figures 4,5 and 6 illustrate the typical sequence for depositing multiple layer weld test trials. Ten (10) test weldments with varying parameters were required to achieve what was considered to be an acceptable level of grain refinement in the base metal heat-affected zone (HAZ). Key factors included: a) shape of the individual weld beads to reduce the depth-to-width aspect ratio, b) control of step-over to reduce scalloping at the fusion line, and c) determining the necessary heat input to maximize grain refinement and tempering. Nine (9) different test parameters including heat input, wire diameter, travel speed, step-over, and even oscillation of the welding torch were examined. Hardness measurements and traditional metallography using optical means were used for evaluating grain refinement and related tempering. A tenth and final test culminated previous trials and was the satisfactory result of all information gained from previous tests.

PHASE II Development Once final parameters were determined, additional test trials were conducted to produce a weld build-up block to check mechanical properties. This included tensile strength, toughness (Charpy-V), hardness and metallography to verify that the parameters could be duplicated and to ensure the status of the base metal HAZ and deposited weld metal. In addition, a transition geometry test block, to simulate a rotor that had defective material that had to be removed by machining and then required weld build-up to re-establish dimensions, was completed. Tempering the base material at the notch that was created at the bottom of the transition area during machining was of primary interest.

Figure 4 - 1st layer Figure 5 - 1st & 2nd layer Figure 6 - 2nd & 3rd layer

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Discussion & Results Ten controlled deposition (temperbead) plus two special verification weldments were made in the course of the evaluation, as well as many interim trials to test the effect of varying selected parameters. Many significant adjustments were made with each additional test coupon. Early attempts to empirically establish heat input/penetration parameters did not yield satisfactory results(7-12). It was initially speculated that a 40 to 50% difference between the 1st and 2nd layer heat input would produce an acceptable result. This was not the case, and higher heat inputs were required to effect tempering.

Metallography Metallographic examination of the test coupons confirmed that the final welding parameters were repeatable, with the refinement level of the base metal coarse-grained HAZ (CGHAZ) consistently exceeding 90%. Metallography of the SAW weldments are illustrated in Figures 7 through 10. The fusion line profile was uniform through the entire weldment (Figure 7). In comparison with the single-layer zone (Figure 8), the base metal CGHAZ was almost completely refined by the second layer using the parameters developed in the evaluation. ( Figures 9 and 10).

Figure 7 .Example of the Temper-Bead Weldment Coupons with the Final Welding Parameters. Note That This Coupon Included the Single Layer Zone, Two-Layer

Temper-Bead Zone, and Four-Layer Temper-Bead Zone. (Ref. 6)

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05117-N Nital Etch Single Layer Zone

05118-N Single Layer Zone Nital Etch

Figure 8 - Typical Features of the HAZ Microstructure in the Single-Layer Zone and

Illustrating the un-tempered CGHAZ. (Ref. 6)

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05117-O Nital Etch Two Layer Zone

05118-O Two Layer Zone Nital Etch

Figure 9 - Typical Features of the HAZ Microstructure in the Two-Layer Zone and

Exhibiting >90% Refinement of the CGHAZ of the 1st Layer. (Ref. 6)

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05117-P Nital Etch Four Layer Zone

05118-P Four Layer Zone Nital Etch

Figure 10 - Typical Features of the HAZ Microstructure in the Four-Layer Zone and

Exhibiting >90% Refinement of the CGHAZ of the 1st Layer. (Ref. 6)

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Hardness Testing Representative measurements across the test weldments exhibited a significant reduction in the hardness of the base metal CGHAZ and FGHAZ resulting from grain refinement and tempering effect from the controlled deposition welding. Table 1.

Table 1 - Hardness of Temper-Bead Weldment (Ref. 6)

Hardness - HV (HRC/HRB)

Single-Layer Zone Two-Layer Zone Location

Average Range Average Range

Weld Deposit 271 HV (26 HRC)

259-279 HV (24-27 HRC)

263 HV (24 HRC)

253-269 HV (23-25 HRC)

Base Metal CGHAZ

359 HV (36 HRC)

254-365 HV (36-37 HRC)

302 HV (30 HRC)

299-308 HV (30-31 HRC)

Base Metal FGHAZ

316 HV (32 HRC)

304-323 HV (30-32 HRC)

253 HV (22 HRC)

236-277 (97 HRB-27

HRC)

Base Metal 206 HV (93 HRB)

201-210 HV (92-93 HRB)

197 HV (91 HRB)

193-203 HV (90-92 HRB)

The hardness of the base metal coarse-grained HAZ has been significantly reduced through the effect of the refinement and tempering of the 2nd layer.

Tensile Testing Tensile specimens (two, 0.252” diameter) were removed from the build-up trial. One specimen was composed entirely of weld metal, with its long axis oriented parallel to the welding direction. The other specimen (a cross-weld) was oriented perpendicular to the fusion line and consisted of base metal, HAZ, and weld metal. Results of the tensile testing are provided in Table 2. Also note that weldment properties satisfied the requirements for ASME SA-387, Grade 22 material. The cross-weld tensile specimen ruptured in the sub-critical HAZ, as shown in Figure 11.

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Table 2 - Tensile Testing (Ref. 6)

Tensile Testing

Material & Location Tensile

Strength (ksi)

Yield Strength

(ksi)

Elongation (%)

Reduction In Area

(%) ASME Spec.

SA-387, Grade 22, Class 2

75 - 100 45 18 (min) 40 (min)

Weld Metal Specimen 99.3 81.7 32 73

Cross-Weld Specimen* 91.0 --- 18 54

* Cross- weld specimen ruptured in the sub-critical HAZ.

05117-S Nital Etch Tensile Sample

Figure 11 -Tensile Specimen Removed from ARTB-10BU Weldment

Coupon Showing the Rupture Location in the Sub-critical HAZ. (Ref. 6)

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Bend Tests Six bend test specimens were removed from the build-up trial. All bend test specimens were taken across the weld, with three bends in a direction parallel to the weld direction and three bends transverse to the weld direction. Bend tests were conducted in such a way that the refined HAZ was under the most tension, and all bend specimens were subjected to greater than 20% strain. Figure 12 shows each type of bend specimen after testing. Examination of the bend specimens after testing exhibited no signs of cracking or tearing but did show that the maximum strain occurred in the sub-critical HAZ, as anticipated.

Bend Specimen Parallel to Welding Direction

Bend Specimen Transverse to Welding Direction

Figure 12 - Typical Bend Test Results from ARTB-10BU. Bending was conducted to ensure that maximum strain occurred in the sub-critical

HAZ. (Ref. 6)

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Toughness Testing Toughness testing (Charpy V-notch) was conducted in both the refined HAZ and the base metal at ambient temperature. Five specimens were tested in each location. For the refined HAZ specimens, the notch was located in the base metal HAZ adjacent to the fusion line after each specimen had been properly etched to reveal the macrostructure of the weldment. The results of the toughness testing are documented in Table 3. Results of from the refined HAZ were better than the unaffected base metal.

Table 3 - Toughness Testing Results (Ref. 6)

Summary of Toughness Tests (Charpy V-Notch) (SAW Temper Bead)

Temperature

(°F) Refined HAZ

(ft-lb) Base Metal

(ft-lb) Specimen Size

72 60 40 Standard 72 40 36 Standard 72 64 38 Standard 72 57 40 Standard 72 55 50 Standard

Average Value 55 41 --- Results of the final weldment coupons clearly show that the SAW controlled deposition (temper-bead) technique developed in this evaluation satisfied both metallurgical and mechanical requirements established by ALSTOM. The weld deposit and base metal HAZ exhibit properties that meet and exceed the original base material. The parameters developed in this evaluation were ready to transfer to the ALSTOM Richmond Workshop for actual component mock-up testing.

PHASE III Development This phase of the development utilized a spare DFLP rotor fabricated from ASTM A 470 Class 7 material. The development parameters from phase I & II were implemented on this rotor after completion of a weld prep to simulate a typical journal repair. Journal repairs would be utilized to reestablish rotor geometry or to repair damaged journals from operational incidents as shown in Figure 13.

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Figure 13 – Damaged generator rotor journals that would

typically be repaired via this temperbead process. The weld-prepped area was welding using the parameters previously established by metallographic and mechanical testing. The deposition sequence followed the parameters for the first four layers, before switching over to standard weld build-up parameters to finish the deposit to accommodate test sample removal. The actual journal rotor build-up is shown in Figure 14. The test coupons were machined from the repair weld in three ring sections—identified in Figure 15 as the left section, center section, and right section—and submitted to the MTC for metallurgical examination. It should be noted that the left-most bead in the first layer of the weld deposit was intentionally left unrefined and un-tempered for comparison purposes. Metallographic specimens were removed from each ring section to permit a detailed evaluation of the condition of their macrostructure and microstructure. As illustrated in Figures 16 through 19, the SAW temper-bead technique developed in the laboratory was completely repeatable on the actual journal, with the grain refinement level of the base metal coarse-grained HAZ (CGHAZ) consistently exceeding 90%. For comparison purposes, the unrefined base metal HAZ produced by the deposition of a single weld bead is shown in Figure 17. As recorded in Table 4, hardness measurements across the weldments revealed a significant reduction in the hardness of the base metal CGHAZ as the result of the grain refinement and tempering effect. In order to determine the mechanical properties of journal test weld, six 0.252” tensile specimens were removed from the weld. Two specimens were removed from unaffected base metal, two were extracted from the weld deposits with their long axis oriented parallel to the welding direction, and two were cross weld specimens taken perpendicular to the fusion boundary so as to include the base metal, HAZ, and weld metal. The results of the tensile testing are recorded in Table 5, where it may be seen that the SAW

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temper-bead weldment properties satisfied the requirements for A 470, Class 7 material. It should be noted that the two cross weld specimens ruptured in the weld deposit zone. Charpy V-notch testing was conducted on the refined HAZ, the weld metal, and the base metal at ambient temperature. Five specimens were tested in each location. For the specimens in the refined HAZ, the notch was placed in the base metal HAZ adjacent to the fusion line after each specimen had been properly etched to reveal the macrostructure of the temper-bead weldment. The results of the Charpy testing are documented in Table 6. As can be seen, the impact toughness of the refined HAZ was better than that of the unaffected base metal, while the weld deposit revealed the maximum average toughness. In summary, the evaluation results of journal test weld demonstrated that the SAW temper-bead technique developed at the MTC in cooperation with Specialty Welding and Euro Weld could be successfully used to weld repair a journal. Both the metallurgical condition and mechanical properties of the simulated weld repair satisfied the requirements established by ALSTOM.

Figure 14 – Journal Test weld on DFLP rotor.

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Figure 15A – Ring samples removed from the journal weld

temperbead qualification test.

Figure 15B – Ring samples removed from the journal weld

temperbead qualification test.

Left

Section

Right

Section

Center

Section

Center Section

Left

Section

Right Section

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Figure 16 – Cross-section of left hand weld deposit.

Figure 17 – Left hand edge bead showing un-refined section

for comparison purposes only.

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Figure 18 - Un-Refined CGHAZ At The Left Toe Of Left Section

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Figure 19 - Typical Example Of Refined CGHAZ Of Left Section (>90% Refinement)

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Table 4. Hardness of Journal Temper-Bead Weldment

Hardness - HV (HRC/HRB)

Unrefined CGHAZ Region Typical Temper-Bead Region Location

Average Range Average Range

Weld Deposit 225 HV (96 HRB)

224-226 HV (96-96 HRB)

229 HV (97 HRB)

229-231 HV (96-97 HRB)

Base Metal CGHAZ

396 HV (40 HRC)

389-401 HV (40-41 HRC)

358 HV (36 HRC)

355-361 HV (36-37 HRC)

Base Metal FGHAZ

313 HV (31 HRC)

310-316 HV (31-32 HRC)

313 HV (31 HRC)

310-317 HV (31-32 HRC)

Base Metal (A 470 Class 7)

270 HV (26 HRC)

268-274 HV (25-26 HRC)

274 HV (26 HRC)

272-2275 HV (26-26 HRB)

It is evident that the hardness of the base metal coarse-grained HAZ has been significantly reduced through the effect of the refinement and tempering of the second layer.

Table 5. Tensile Testing of Journal Temper-Bead Weldment

Tensile Testing

Material & Location Tensile Strength

(ksi)

Yield Strength

(ksi)

Elongation (%)

Reduction In Area (%)

122.1 106.6 22.0 64.6 Base Metal Specimen

122.4 106.9 20.0 62.5

93.0 80.4 29.0 75.4 Weld Metal Specimen

93.0 79.5 31.0 77.1

98.4 --- --- --- Cross Weld Specimen*

100.1 --- --- ---

* Cross weld specimens ruptured in the weld deposit.

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Table 6 - Charpy V-Notch Testing of Journal Temper-Bead Weldment

Summary of Charpy V-Notch Tests (SAW Temper Bead On Journal)

Temperature (°F)

Refined HAZ (ft-lb)

Base Metal* (ft-lb)

Weld Deposit (ft-lb) Specimen Size

72 137 148 146 Standard 72 158 149 154 Standard

72 148 149 171 Standard

72 172 146 166 Standard

72 158 147 183 Standard

Average Value 155 148 164 Standard

* Base Metal: A 470 Class 7 Journal.

Summary Temperbead weld procedure qualifications with the use of the submerged arc welding process have yielded successful results in both laboratory and on actual shop welded rotor journals. Filler metal selection of NiCrMo1 was utilized for the initial development with excellent success. Development of a 2.5 NiCrMo and a 3.5 NiCrMo filler metals using the same technical approach have also been developed. The metallographic examinations of all test samples showed grain refinement of >90%, with excellent mechanical properties. This technique has the capability to reduce outage duration on the order of 5-7 days compared with the GTAW temperbead technique.

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References

1) Burkhalter, S.M., Mark, J.T. and Jirinec, M.J. - "A Case Study of Nuclear Plant Steam Generator Repair Using Temperbead and Full Postweld Heat Treatment Techniques " North American Welding Research Conference, Columbus, Ohio, Oct. 1994.

2) Gunther, Louis A. – “Temperbead Repair Welding of a P-4 Hot Reheat Piping

System Manifold”, Welding Research Council Conference, New Orleans, LA March 2002

3) US Patent 5,914,055 - Rotor Repair System and Technique

4) P-4 & P-5 FCAW on P11 & P22

5) Zhou, Joe G., “Development of SAW Temper-Bead Technique”, LN-05D244,

MTC-05-360, 01 November 2005.

6) “Welding & Brazing Qualifications”, Section IX, QW-290 & QW-462.12, ASME Boiler and Pressure Vessel Code, 2004 Edition.

7) Jackson, C. E., “The Science of Arc Welding, Adams Lecture 1959”, WRC, Supplement to the Welding Journal, June 1960.

8) Jackson, C.E. and Shrubsall, A.E.; “Control of Penetration and Melting Ratio with Welding Technique”, Welding Journal, April 1953.

9) Shultz, B.L. and Jackson, C.E.; “Influence of Weld Bead Area on weld Metal Mechanical Properties”, Welding Journal, January 1973.

10) Wilson, J.L., Claussen, G.E. and Jackson, C.E.; “The Effect of I2R Heating on Electrode Melting Rate”, Union Carbide - Linde, 52-510.

11) Newell, Jr.,W.F.,“Composition and Product Form Effects on Strip Cladding Deposition Rates”, 1997 AWS Show, Los Angeles, California, April 1997.

12) Zhou, Joe G., “Evaluation of Journal Test Weld #1 Reference: SAW Temper-

Bead” - LN-05D244 MTC-06-034