Alternate Welding Processes for In-Service Welding

016485282009Final ReportPDFTech Report5637C.FRDTRS56-03-T-0010Alternatives analysisCrackingElectric arc weldingHydrogenPipelinesState of the practiceWeld strengthWeldsWeldingResearch HubWeldingConstructionMaintenance and PreservationPipelinesUnited StatesBMT Fleet Technology LimitedBegg, DarrenBMT Fleet Technology LimitedUnited States. Dept. of Transportation. Pipeline and Hazardous Materials Safety AdministrationUS Transportation CollectionThe primary objective of this project is to define parameters and conditions associated with each advanced welding process that can preclude hydrogen cracking and burn-through in a reproducible manner. A significant, process dependent, in-service welding concern that can be addressed by modern power sources is the reliable control of heat input and weld size that are often difficult to maintain in all position welding. To increase in-service welding productivity, improve welder safety and assure weld integrity, alternative arc welding processes and other recent technological developments were evaluated. These were: (1) Self-shielded flux cored arc welding (SS-FCAW); (2) Gas metal arc welding with Controlled Dip Transfer Technology, (Miller Electric's Regulated Metal Discharge (RMD)); (3) Pulsed Gas Metal Arc Welding (PGMAW) using state-of-the-art power sources with closed loop feedback control; (4) Gas Shielded Flux Cored Arc Welding (GS-FCAW); and (5) Pulsed Metal Cored Arc Welding (PMCAW). Each of these semi-automatic processes has the potential to be used with mechanical tracking devices, and thus remove the variability in weld deposition and thus improve the safety and integrity of in-service welding. To assess if the alternative processes/variations do indeed offer some or all of the expected advantages, the alternative processes were subjected to mutual head to head experimental comparisons, as well as with the current practice, viz., shielded metal arc welding using low hydrogen electrodes. The comparison or performance trials focused on the prevention of hydrogen cracking, burn-through, and weld flaws. The evaluations were performed on instrumented pipe of both low and high strength pipe with a range of heat sink conditions, including static air and water backing, thus representing the extremes of expected in-service heat sink conditions that could be encountered during welding on thin wall live pipelines