Pipeline Welding - African Fusion Magazine - March 2011

Cover storyBy using a Bugo Piper-Bug with solid wire STT for the root and gas-shielded FCAW forthe fill passes, 30 joints per day can typically be achieved.Inverters also enable the move into thewhole range of wire welding processes,GMAW and FCAW, in particular. “Weoffer a whole range of suitcase feeders that support all of the GMAW andFCAW processes. For pipe GMAWwelding, they are designed with ahigh/low switch to allow the welderto switch to lower current parameterson-the-fly to adjust for the transitionfrom the vertical down to the overheadposition at 8 o’clock and 4 o’clock.This allows the welder to go all the wayaround the pipe without having to stopbecause the weld metal is falling out.This is typical of a feature born out ofa long engagement with the needs ofpipeline welders,” he confirms.The newest inverter-based pipewelding initiative is the development ofSurface Tension Transfer (STT ) technology. “The traditional way of doingpipe welding is to put in a stick root,which gives a concave weld bead with‘wagon tracks’ on either side caused byundercut at the fusion boundary. Thenyou do a hot pass, with the sole purpose of digging out the wagon tracksthat have been created during rootwelding. This procedure has an inherent risk of quality problems becauseone is putting in defects and then, ifthe welder is skilful enough, diggingthem out again. The STT processcompletely eliminates the undercutting problem and therefore the risk.There are no wagon tracks to dig outand therefore no need for a hot pass.“The use of STT has always beenjustified based on a productivity argument, but there is also a huge qualityadvantage,” Nagle points out. “It’s nowa very, very reliable process, which canusually be coupled with CO2 shielding18gas to give spectacular penetration.STT controls the arc so well that theCO2 becomes much easier to use andspatter is significantly reduced,” headds. The first STT welding machineswere stand-alone machines but Lincolnhas now adopted a modular approachat a much lower cost. “STT can now beadded to our new Power Wave S350simply by adding an optional bolt-onmodule. The latest technology also hasa much better inverter, upgraded from40 to 120 kHz.”Lincoln’s monitoring and recording features, built into all of its PowerWave inverter solutions, are alsohelpful in the drive to enhance pipewelding quality.“True Energy, for example, can helpcontractors to track and record the trueheat input of every weld, which helpswith quality assurance. Also, WeldScore data monitoring gives a full datarecord of the welding parameters andan instant pass/fail indication immediately after each weld is completed.This is a very useful feature for anyweld-critical application,” believesNagle. “If a welder remains betweenthe preset parameters of a good weld,then the procedure used for that weldis deemed acceptable, but if not, thedeviation is highlighted and noted asa possible problem,” he explains. Thistool provides greater traceability andconfidence in making quality welds.“Clearly it doesn’t replace the normalquality acceptance criteria, but ratheradds another indicator for inspectorsand engineers looking for potentialproblems”Turning his attention to Lincoln’sconsumable range, Nagle says thatthe consumable business has changedconsiderably over its 80 years of pipeline welding applications. “Now, highstrength steels are the norm, toughnessrequirements are high and so diffusible hydrogen is a critical issue. Also,because of the need for traceabilityand quality assurance, you need certificates for every consumable used toweld any part of a pipeline. We havetherefore designed a whole range ofwelding consumables to cater for thecurrent needs of the pipeline industry.”One common feature of Lincoln’sPipeliner consumable range is thepackaging: “All consumables are protected in hermetically sealed packagesfor example, sealed pails for fluxes andflux cored consumables, sealed cansfor stick electrodes and vacuum sealedfoil bags for solid GMAW wires. It’s allabout making the packaging robustbecause we know the consumableswill be used for critical applications insome of the harshest environments inthe world, the slopes of Siberia or theforests of the Congo. We know thatproduction requirements demand themost stringent adherence to quality,and any lack of consistency cannotbe tolerated,” says Nagle. A materialtest report is therefore issued for everylot of consumables – stick electrodes,shielded and self-shielded flux coredwires, and solid GMAW wires.“The Pipeliner consumable rangeis a large family of products,” saysNagle. It begins with the original cellulosic range, Pipeliner 6P , 7P and8P . “With diffusible hydrogen of 40ml/100g, these are not low hydrogenproduct, though,” he points out.The low hydrogen range of mildsteel and low-alloy stick electrodesincludes the Pipeliner 16P,17P and18P, for X60 and X70 pipe and forthe new X80 and X90 pipe materials, Pipeliner LH-D80, LH-D90 andLH-D100. All of these are low hydrogen electrodes and come withCharpy V-notch test certificates downto -29 C.For GMAW, Lincoln offers thePipeliner 70S-G, 80S-G and the80Ni1 with root pass capability onThe STT process completely eliminatesundercut. The root thickness is also large(5,6 mm), which eliminates burn throughon next weld pass.AFRICAN FUSION — MARCH 2011

Cover storyProductivity gains (deposition rate operating factor) for different pipeline weldingprocesses.The use of Lincoln’s true DC generatorswith its Pipeliner range of SMAWelectrodes remains the most appropriatepipe welding solutions in many places ofthe world.X100 steel and Charpy V-notch valuesof between 68 and 95 J at -50 C.These wires are all designed to givea good back bead shape when usingLincoln’s STT process.“The self-shielded flux-cored wires,Pipeliner NR-207s and 208s, areoften the simplest wire solution. Designed for vertical-down fill passes, theprocess is continuous and therefore offers productivity advantages over stickelectrodes,” says Nagle. “There is nostub loss, no gas shielding is requiredand these wires can be used to weldpipe grades of up to X80.”Completing the consumable rangeare the gas shielded flux-cored wires,the Pipeliner G70M, G80M andthe new 81M, These are suitable forvertical-up fill passes using Argon/CO2 shielding gas mixtures. They offerimproved toughness and strengths ofup to that of X100 pipe. “But to usethem you will need shielding gas and,in the field, a tent for protection againstwind,” Nagle suggests.driving contractors towards automation. Internationally, there is also a lackof skilled pipeline welders.Nagle describes two basic approaches to mechanisation on pipelinecontracts. “There are some weldingservices contractors, like CRC-Evans orSerimax, who will not only supply thenecessary pipe-welding equipment, butthey will also take responsibility for thewelding itself,” he says.Using narrow groove GMAW witha relatively expensive bevelled weldpreparation, a welding services subcontractor with high expertise andexpensive mechanised systems cantypically produce 100 to 150 jointsper day on 36-inch pipe. “This is anexpensive, high-risk, high reward scenario,” Nagle advises.But by using a lower cost solution,Bug-O Piper-Bug, for example, withSTT for root welding and fill passesusing gas shielded FCAW, 30 joints perday can typically be achieved. “Thisis a much simpler automation optionand much more suitable for Africa.It’s a medium risk, medium rewardalternative to full scale automation,”he suggests.“There are going to be a lot ofopportunities for pipeline contractorsall over the African continent,” Naglepredicts. “The people who offer the solutions best suited to the environment,be they simple, robust and reliable ormechanised, effective and productive,are going to be chosen as partners,”he says.“We believe that Lincoln Electrichas, more than anybody else, the experience and the solutions to meet thedemands of pipeline welding anywherein the world,” he concludes.The move towards automationProductivity in pipeline welding is allabout achieving a high number of quality joints per day. Deposition rate andthe arc-on time (operating factors) ofdifferent processes are key drivers ofproductivity. Continuous productivityimprovements are essential becauseof ever tighter project schedules andbudgets and an abundance of plannedprojects. Higher quality requirements,the need to reduce repair rates, smallerallowable defects and the need for consistent weld properties are all factorsAFRICAN FUSION — MARCH 2011Lincoln’s VRTEX 360 virtual welding solution is an ideal tool for training and qualifyingpipe welders in this scarce skill.19

STT controls the arc so well that the CO 2 becomes much easier to use and spatter is significantly reduced,” he adds. The first STT welding machines were stand-alone machines but Lincoln has now adopted a modular approach at a much lower cost. “STT can now be added to our new Power Wave S350 simply by adding an optional bolt-on module.