It has been nearly a quarter of a cen-tury since researchers first conceivedof combining a conventional welding

arc with a laser beam in a hybrid process( Refs. 1, 2), but only recently has laser-gas metal arc (GMA) hybrid weldingbegun to be utilized in industrial applica-tions. Now, hybrid laser-GMA welding isfast making the transition from laboratoryto production, in industries as diverse asshipbuilding to automobile manufactur-ing. Recent work investigating the poten-tial benefit of applying this technology toa shipyard pipe shop suggests that signifi-cant cost savings may be realized. This

paper presents ongoing efforts to studyand evaluate hybrid welding, and to esti-mate potential cost savings that may berealized in a shipyard pipe welding shop.

Hybrid Laser-GMA Welding

Laser beam welding (LBW) offers highwelding speed and deep penetration com-pared to conventional arc-based joiningprocesses. With recent advances in com-mercial laser technology, laser supplierscan now deliver dramatically higher powersystems in a much smaller package with atenfold increase in energy efficiency com-

pared to just a few years ago, all at signif-icantly reduced cost. Unfortunately, dueto the small spot size typically utilized inL BW, it has had limited success in certainwelding applications due to an inability toaccommodate gaps and mismatch typi-cally found in industry. Consequently,laser beam welding requires high preci-sion during edge preparation and setup,an added cost during manufacturing op-erations. Additionally, the focused energyof the laser beam results in a narrow heataffected zone (HAZ) characterized byhigh cooling rates that can result in a lossof ductility with certain materials.

JUNE 200666

Joining Pipe with the HybridLaser-GMAW Process:

Weld Test Resultsand Cost Analysis

EDWARD W. REUTZEL and DARLENE A. MIKESIC are with The Applied Research Laboratory, The Pennsylvania State University, StateCollege, Pa. MICHAEL J. SULLIVAN is with General Dynamics NASSCO, San Diego, Calif.

BY EDWARD W. REUTZEL, MICHAEL J. SULLIVAN, AND DARLENE A. MIKESIC

If a successful hybrid

system is implemented, it

is estimated a pipe shop

could save $500,000 in

production costs

annuallyFig. 1 — View of the conventional pipe welding process at Gen-eral Dynamics NASSCO.

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67WELDING JOURNAL

In contrast, conventional GMAW of-fers the ability to easily bridge gaps in thejoint because of the diffuse heat sourceand the introduction of filler metal to theprocess. The composition of the filler ma-terials can be customized to produce im-proved material properties. The addi-tional heat generated by the process re-sults in reduced cooling rates, which canlead to improved ductility. However, thenature of the process prevents deep pen-etration welds. As a result, joining thicksections often require multiple weldpasses.

In certain applications, these short-comings can be overcome by marrying theL BW and GMAW processes. Not only isthis helpful in accommodating gaps andreducing weld head positioner tolerancerequirements while maintaining deeppenetration (Ref. 3), but it has also beenshown to enable operation at even greaterwelding speeds and to provide an im-proved weld microstructure upon cooling(Ref. 4). Additionally, the combination ofL BW and GMAW may significantly re-duce overall weld time in thick sectionsby joining in a single pass what would re-quire multiple passes using conventionaltechniques, which can lead to the addedbenefit of reduced thermal-mechanicaldistortion. For these reasons, shipyards inthe U.S. are showing growing interest inhybrid laser-GMA welding technology.

Hybrid Laser-GMA for Joining Pipe

Welding of pipe represents a signifi-cant cost in the construction of tankersand other ships. Though much welding ofpipe must occur on board the ship, asmuch pipe as possible is rolled in the pipeshop and manually welded in the down-hand position. Figure 1 illustrates a cur-

rent joining technique employed at Gen-eral Dynamics NASSCO. In the figure,the pipe is fixtured to a rotary positionerthat rotates the pipe beneath the arc weldtorch. The weld head is manually manip-ulated by the operator.

At NASSCO, the steel pipe ranges inthickness from 0.237 to 0.50 in. (6.0–12.7mm), corresponding to 4-in. SCH-40through 30-in. SCH-XS pipe. For thethicker sections, producing an adequatejoint requires the execution of multipleweld passes, with up to five passes re-quired for thicker sections. Typical travelspeed for these welds is 5–10 in./min(0.13–0.25 m/min). Figure 2 shows a crosssection of a typical multipass weld to join0.50-in. (12.7-mm) -thick pipe.

N ASSCO desired a cost-effective al-ternative welding technology that can joinpipe in a single pass. Details of the exper-iments and cost analysis developed to sup-port this effort follow.

Development of Hybrid Laser-GMA Welding Process

Experimental Objective

A series of experiments were con-ducted at the Applied Research La b o r a-tory, Pennsylvania State University (ARLPenn State) to investigate the effects ofvarying joint design and hybrid laser-GMA welding process parameters onweld characteristics. Specifically, the ef-fect of changing bevel angle and landheight on the fusion zone geometry wereinvestigated, as well as the effects of travelspeed and laser-to-GMA welding heads p a c i n g1. A portion of the hybrid weldedjoints were subjected to mechanical andradiological tests. Finally, practical as-pects of hybrid welding, such as weldingover tack welds, overlap of weld start and

stop (required for circumferential pipewelds), and root opening tolerance werealso investigated.

Experimental Plan

A series of hybrid welds were per-formed using a combination of a Tr u m p fHLD4506 diode-pumped 4.5-kWN d : YAG laser and a Lincoln Po w e r Wa v e455 STT GMAW power supply operatedin constant voltage mode. Figure 3 showsthe setup used to conduct the experimentsat ARL Penn State. It should be notedthat fully integrated hybrid welding headsare available from a variety of commer-cial vendors, but were not used for thisproject since the ability to easily and ac-curately modify processing conditions(such as separation distances and anglesof the two processes) were of particularimportance in this evaluation.

The welds were performed on mildsteel butt joints (A36) using 70S-6 fillermetal at a diameter of 0.045 in. (1.1 mm).In general, Ar-10% CO2 shield gas wassupplied through the GMAW weldinghead, though at larger laser-to-GMAWhead separations an additional gas nozzledirected N2 gas at the laser keyhole forplasma suppression and supplementalshielding. Experiments were performed

Fig. 2 — Cross section of conventional multipass pipe weld with0.50-in. (12.7-mm) thickness.

Fig. 3 — Experimental setup used to run experiments at ARLPenn State.

1. Note that “hybrid” welding can be defined indifferent ways. Throughout this paper, hybrid ismeant to refer to a laser beam weld and GMAweld taking place simultaneously in close prox-i m i t y. It has been noted in the literature that hy-brid often refers to laser beam and GMAW wireimpinging on the part within 0–2 mm (0.0–0.08in.). In many of our experiments, the laser beamled the GMAW wire by 10 mm (0.39 in.) or more.It was suggested that “tandem welding” may be abetter way to refer to welds that use this spacing.Though we have chosen not to use this terminol-ogy in this paper, it is a noteworthy distinction.

JUNE 200668

on a variety of butt joint configurations toinvestigate potential effects of variationsin bevel angle and land height (Table 1and Fig. 4). Figure 5 shows representativecross sections of welds made by the GMA,laser, and hybrid processes that were per-formed as part of the testing. The weldsare shown side-by-side for comparison.

The schematic in Fig. 6 illustrates theconfiguration of the laser and GMAWwelding head. In all experiments, the laserfocus spot at the bottom of the joint, andthe contact-tip-to-workpiece-distance

(CTWD), measured from the bottom ofthe joint as shown, were held constant andthe laser-to-GMAW head spacing was var-ied to observe its effect on process robust-ness, fusion zone geometry, and weldquality. Both laser-leading and GMA-leading configurations were investigated.

Experimental Results

A large number of processing param-eters are available to affect the joiningprocess when the LBW and GMAW

processes are combined. Results of someexperiments to investigate these complexrelationships are presented below.

Effects of Laser-to-GMAW Head Spacingand Travel Speed

In a typical set of experiments, bothl a s e r - t o - G M AW head spacing and travelspeed were varied to observe the effect onfusion zone geometry — Fig. 7. In this casethe thickness, land height, and includedjoint angle are 10 mm (0.39 in.), 3 mm(0.12 in.), and 12 deg, respectively. Astravel speed is increased, the wire feedspeed (WFS) is increased proportionallyto maintain constant weld bead cross-sectional area, and voltage is varied ac-cordingly. It has been widely reported thata synergistic effect occurs when the twoprocesses are spaced near one another;however, as spacing is increased with thistype of beveled butt joint, additional ob-servations can be made.

For 20 in./min (0.5 m/min) travelspeed, at both 2- and 4-mm (0.08- and0.16-in.) spacing it appears that full pen-etration has been achieved and full mix-ing of the filler and base metals through-out the fusion zone has occurred. How-ever, as is evident in the cross sections,significant backside melt-through waspresent in both cases resulting in unac-ceptable weld quality. A slight increase inspacing led to incomplete penetration,and there appear to be two separate so-lidification events as evidenced by the twodistinct fusion zones.

As travel speed increases with closespacing, it appears that the reduced heatinput per unit length prevents full pene-

Table 1 — Evaluated Joint Geometries

Thickness Lan Height Included Bevel Angle

0.25 in. 0.0 in. N/A(6.4 mm) (0.0 mm)0.39 in. 0.12 in. 12 deg(10.0 mm) (3.0 mm)0.39 in. 0.20 in. 20 deg(10.0 mm) (5.0 mm)0.39 in. 0.20 in. 40 deg(10.0 mm) (5.0 mm)0.39 in. 0.20 in. 60 deg(10.0 mm) (5.0 mm)0.50 in. 0.35 in. 90 deg(12.7 mm) (8.8 mm)

Fig. 4 — Joint configurations employed in this work.

Fig. 5 — Three welds, 0.50-in. (12.7-mm) thick ASTM A-36/ABS Grade A steel plate, buttjoint with 0.35-in. (8.8 mm) land and beveled with a 90-deg included angle and with an1⁄8-in. (3.2-mm) chamfer at the root.

Fig. 6 — Sketch shows the hybrid configu-ration and the definition of laser-to-GMAWhead spacing (note that the GMAW gas noz-zle is modified to prevent clipping of thelaser beam).

20° incl.40° incl. 60° incl.

90° incl.12° incl.

0.394 inch[10.0 mm]0.394 inch[10.0 mm]

0.394 inch[10.0 mm]

0.197 inch[5.0 mm]

0.197 inch[5.0 mm]

0.197 inch[5.0 mm]

0.345 inch[8.8 mm]

0.394 inch[10.0 mm]

0.394 inch[10.0 mm]

0.500 inch[12.7 mm]

0.118 inch[3.0 mm]

69WELDING JOURNAL

tration. However, as laser-to-GMAWhead spacing is increased to 16 mm (0.63in.), complete joint penetration is ob-served to occur at much higher speeds.This seems to indicate that at higherspeeds and greater laser-to-GMAW headspacing, the laser beam does not interactwith the arc nor the material introducedby the GMAW process. In a separate ex-periment, autogenous laser weldsachieved full penetration at both 30 and40 in./min travel speed with no melting ofthe bevel side walls. Data at 20 in./mintravel speed was not available; however,at 15 in./min full penetration was notachieved, seemingly due to melting of thebevel sidewalls, which absorbed energyand filled the joint with material.

It is believed the reason for these ob-servations is that at near spacing, the laserbeam must penetrate the base metal aswell as the additional molten material pro-vided by the welding wire (which tends toflow slightly ahead of the wire). In thiscase, at slow travel speeds the combinedprocess provides enough heat to result infull joint penetration, albeit accompaniedby backside melt-through and unaccept-able weld quality. As the spacing is in-creased to 10 mm (0.39 in.), the laser leadsthe GMAW weld pool by enough distancesuch that the laser beam irradiates thesubstrate directly, i.e., it no longer has topenetrate the molten weld pool (fed bythe GMAW wire) that is filling the joint.This is illustrated in Fig. 8. It is noted thatapplication of higher power laser systems

may result in different operationalregimes and trends at this thickness.

Other Observations

In addition to investigating the affectsof laser-to-welding head spacing vs. travelspeed, several other parameter interac-tions were studied. It was demonstratedthat at these conditions with close spac-ing, the weld is very intolerant to smallvariations in travel speed, i.e. a 10%change in speed can result in either cata-strophic blow-through or incomplete pen-etration. Experiments with larger sepa-ration, up to 16 mm (0.63 in.), perhapsmore appropriately termed a tandemrather than hybrid weld, indicate thatwhile interactions directly between thelaser and arc are eliminated, the laser key-hole can provide full penetration of theland, and the added heat provided by theleading laser appears to help ensure com-plete sidewall fusion in narrow grooves.Additionally, experiments reveal that,given appropriate control of process pa-rameters, hybrid laser-GMA welding canprovide adequate penetration in practi-cal aspects of pipe welding, such as weld-ing through tack welds and weld overlap( Ref. 5).

Testing of Hybrid Laser-GMAWelded Joints

Through experimentation, a set of hy-brid laser-GMAW processing conditions

was found for welding 0.50-in. (12.7-mm)-thick A36 steel that produced a visually ac-ceptable weld. The weld produced full pen-etration, desirable reinforcement on the topand bottom surfaces, and demonstrated anability to compensate for some degree ofweld joint misalignment — Fig. 9.

Several of these welded samples weresent to a certified lab to undergo reduced-section tensile and bend testing (both faceand root) according to ASME Section IXof the Pressure Vessel Code — Fig. 10. Alltensile and bend tests passed. In all ten-sile tests, the failures occurred outside theweld heat-affected zone, indicating ac-ceptable mechanical properties.

The welds were also subjected to radi-ographic testing in accordance withASME Section IX — Fig. 11. Though themajority of the weld is porosity free, these

Fig. 8 — Illustrates how close spacing may cause the laser beam to inter-act with the GMAW pool, while increased spacing permits laser to directlyirradiate the bottom of the joint.

Fig. 7 — Macroscopic cross-sections illustrate effects oflaser-to-GMAW head spacing and travel speed on fusionzone geometry.

Fig. 9 — Hybrid welds used for mechanicaland radiographic testing. Parameters are0.5-in. (12.7-mm) -thick plate, 0.345 in. (8.8mm) land, 90 deg included angle, 16 mm(0.63 in.) spacing, 10 in./min (0.25 m/min)travel speed, 200 in./min (5.1 m/min) wirefeed speed.

JUNE 200670

tests revealed a small degree of porositynear the beginning and end of the weld.Laser beam keyhole instability may be thecause. Ongoing investigations are beingundertaken to determine the cause of thisporosity and to eliminate it.

Based on the results of these tests, it islikely that with additional process opti-mization, porosity will be eliminated andhybrid welding can soon be successfullyqualified for use in steel pipe welding inthicknesses up to 0.50 in. (12.7 mm).

Cost Analysis

To help determine potential savings inconverting from conventional joiningprocesses to a single-pass hybrid weld, adetailed study was undertaken to assesscurrent practice in the shipyard (Ref. 6).A time study was conducted to determinethe time spent on each of the various op-erations used to join two pipes. A sampleof the results for a P-2 open root joint overa range of pipe diameters is shown in Fig.12. It was determined that for the P-2 jointthe total process time is 102 min for 4-in.pipe, and up to 270 min for 30-in. pipe.The multipass conventional weld portionof the process contributes significantly tothis time.

Based on this data, successful imple-mentation of a single-pass hybrid weld canbe expected to result in dramatic savings

in time and money, as well as a reductionin welding wire consumption, hazardousfume emissions, and reduced total heatinput for decreased distortion. Ad d i t i o n-ally, reducing the number of weld startsand stops and the total linear weld lengthprovides fewer opportunities for defects.Comparing the fusion zones of hybrid andconventional welds, shown in Fig. 13, em-phasizes these savings.

To evaluate cost effectiveness of thehybrid laser-GMAW process, time andmaterial savings were calculated using thebest available data. The analysis indicatesthat, for the same quantity of pipe welds,hybrid welding would require less than600 man-hours annually vs. nearly 8500man-hours annually using conventionalmultiple weld pass methods. The result-ant annual savings are estimated to be$286,000 based on industry standardrates. An additional cost saving that wasconsidered is the reduction in filler ma-terial consumption. The change in weldvolume for GMAW / F C AW butt jointweld designs compared to these nonopti-mized hybrid weld joint designs decreasedwelding wire consumption from morethan 46,000 lb to less than 7000 lb, and isestimated to save $218,000 annually. An-other factor that is considered is the dailyconsumable costs for such items as gasshielding cups and contact tips. Otherconsumables have been estimated at 10%

of the yearly material costs. Re d u c t i o n sin weld fume emissions that are haz-ardous to workers and harmful to the en-vironment are not considered, but are ex-pected to be significant.

Summary

Experiments were conducted thatdemonstrated the ability of existing com-mercially available hybrid welding tech-nology to weld up to 0.50-in. (12.7-mm)-thick ASTM A-36/ABS Grade A steelplate (similar in chemistry to A-53 pipematerial) in a single pass. A portion of thewelds were subjected to nondestructiveradiographic testing (RT) and tensile andbend testing in accordance with SectionIX of the ASME Pressure Vessel Code. Notall welds passed the RT test due to poros-ity near the start and end of the weld; how-ever, it is believed that further process op-timization will enable weld porosity to beeliminated. All welds passed tensile andbend tests, with all tensile failures occur-ring in the base material. Additional on-going development of laser-GMAW isproviding insight into the process that willaid in transitioning the technology into in-dustrial applications.

Detailed time studies over an 11 weekperiod at an actual pipe shop coupled withthe welding data gathered during the proj-ect indicate that annual cost savings couldbe significant. Based on average industryrates, it is estimated that shipyards havethe potential to generate more than$500,000 in annual operational cost sav-ings should they implement a hybrid-GMA pipe welding system.

Other Applications for Hybrid Laser-GMA Welding

This investigation represents just one ofmany efforts worldwide to use high powerlaser-GMA hybrid welding for joining of

Fig. 10 — Mechanical testing of hybrid weld in 0.5-in.-thick mild steel indicated adequate mechanical properties.

Fig. 11 — Radiographic testing of hybrid weld in 0.50-in. (12.7-mm) -thick mild steel revealsa small amount of porosity confined to regions near the end of the weld.

thick sections in industrial applications.In 1999, Meyer Werft shipyard in Pa-

penburg, Germany, began investigatingthe potential to use high-power CO2 laser-GMA welding for joining operations ontheir prefabricated deck panels and side-walls. After a comprehensive test pro-gram, high-power laser-GMA hybridwelding was implemented in 2002 to jointhick sections (Ref. 7). Around this sametime, the domestic energy pipeline indus-try commissioned studies of hybrid laser-G M AW for pipeline girth welding (Re f .8). This has been complemented by otherpipeline investigations from researchgroups at Cranfield University, the Uni-versity of Cambridge, TWI Ltd, the Bre-men Institut für Angewandte Strahltech-nik (BIAS), and others. The U.S. Navy isalso taking interest, with ongoing investi-gations conducted at ARL Penn State andelsewhere to apply hybrid welding in anumber of applications, such as reducingdistortion in thin steel construction (Re f .9). Recent efforts are directed at devel-oping hybrid welding of the tee sectionsthat serve as safety line tracks on sub-marines, and are soon expected to obtainU.S. Navy approval.

Though certainly not a comprehensivelist of thick-section hybrid welding activi-ties, they add to the evidence gathered inthe present development effort in under-lining the potential that industry and gov-ernment see for this technology to gener-ate substantial economic benefit. Contin-uing rapid improvements in high-powerlaser technology, and associated reduc-tions in cost and size, will only serve tohasten the widespread industrial accept-ance of high-power hybrid laser-GMAwelding.

Acknowledgments

The authors gratefully acknowledge

and thank Jay Tressler, Ed Good, Ro bCrue, and Amish Shah of the ARL- P S ULaser Processing Division, who all con-tributed substantially to generating thedata used in this study. Additional thanksgo to Richard Martukanitz, Shawn Kelly,and James McDermott for many enlight-ening technical discussions. Finally, ac-knowledgement is given to the GeneralDynamics NASSCO for providing guid-ance, support, and several of the imagesused herein.

This material is based upon work sup-ported by the National Shipbuilding Re-search Program, SP-7 Welding Commit-tee and by the Office of Naval Re s e a r c hthrough the Center for National Ship-building Technology (CNST) under Con-tract No. N00014-03-C-0413, SubcontractNo. 2005-352. CNST is administered byATI, Charleston, S.C. Any opinions, find-ings, conclusions, or recommendations ex-pressed in this material are those of theauthors and do not necessarily reflectviews of the Office of Naval Research orthe Naval Sea Systems Command.

References

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2. Steen, W. M. 1980. Arc augmentedlaser processing of materials. J. Appl. Phys.51 (11): 5636–5641.

3. Engstrom, H., Nilsson, K., and Flink-feldt, J. 2001. Laser hybrid welding of highstrength steels. Proc. ICALEO 2001, Jack-sonville, Fla., Paper No.303, LIA.

4. Walz, C., Seefeld, T., and Sepold, G.2001. Process stability and design of seamgeometry during hybrid welding. P r o c .ICALEO 2001, Jacksonville, Fla., Pa p e rNo. 305, LIA.

5. Reutzel, E. W., Kelly, S. M., Tressler,J. F., and Martukanitz, R. P. 2005. Exper-

imental analysis of practical aspects of hy-brid welding of thick sections. Proc. ICA-LEO 2005, Miami, Fla., Paper No. 306,LIA.

6. Reutzel, E. W., Mikesic, D. A.,Tressler, J. F., Crue, R. A., Gwinn, E. A.,and Sullivan, M. J. 2005. Laser Pipe Weld-ing: Technology Evaluation and CostAnalysis, ARL Penn State, Technical Re-port No. 04-014 (available atwww.nsrp.org).

7. Müller, R., and Koczera, S. 2003.Shipyard uses laser-GMAW hybrid weld-ing to achieve one-sided welding. The Fa b r i c a t o r (available at w w w. t h e f a b-rictaor.com).

8. Holdren, D. 2002. Feasibility ofN d : YAG laser and hybrid laser/arc weld-ing processes for pipeline girth weldingapplications. Pipeline Research CouncilInternational, Inc., Catalog No. L51934.

9. Kelly, S. M., Martukanitz, R. P. ,Michaleris, P., Bugarewicz, M., Huang, T.D., and Kvidahl, L. 2006. Low heat inputwelding for thin steel fabrication. J o u r n a lof Ship Production, in press.

71WELDING JOURNAL

Fig. 12 — Plot of process times for entire conventional pipe join-ing process for P-2 open root joint.

Fig. 13 — Macrosections comparing fusion zone of single-pass hybridweld of 0.50-in. (12.7-mm) -thick plate vs. a multipass conventionalweld.

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