High Deposition Pulse Current GMAW Can Change Current Scenario of Thick Wall Pipe Welding

Abstract

The high deposition pulse current gas metal arc welding (P-GMAW) with multiple drop transfer per pulse has been used to weld thick wall austenitic stainless steel pipe. Welding of the pipe was also carried by the commonly used shielded metal arc welding (SMAW) and conventional gas metal arc welding (GMAW) processes and compared. Utility of the P-GMAW to facilitate narrow gap welding of the thick wall pipe by appropriate control of pulse parameters has been discussed in reference to produce superior quality weld. The superiority of weld quality has been justified through the microstructure, mechanical properties, residual stresses and fracture mechanics properties of weld joints. Basic characteristics of the P-GMAW process changing the scenario of thick wall pipe welding have been closely studied with respect to its arc characteristics and behaviour of metal transfer. A precise control of the process in order to achieve desired thermal, mechanical and microstructural effects in the narrow gap welding has been achieved by regulation of summarised influence of pulse parameters, mean current (Im) and arc voltage. The summarised influence of pulse parameters is defined by a hypothetically defined dimensionless factor φ = [(Ib/Ip) f.tb] where, the Ib, Ip, f and tb are the base current, peak current, pulse frequency and pulse off (base) time respectively.

Assembling of thick-section HSLA steel with one seam per layer multi-pass PC-GMA welding producing superior quality

“…Thus, it is expected that MP-OSPL-ENG centrally laid narrow groove weld joint may develop relatively lower residual stresses as compared to that in MP-MSPL-CG weld joint. It may be noted that the residual stresses developed in multi-pass multi-seam per layer commonly used narrow gap PC-GMA weld joint are in the order of 300 MPa [24,25] which is clearly higher than the shrinkage stress (254 MPa) of weld joint prepared by using MP-OSPL-ENG weld deposition technique under relatively lower I m of 240 A. This observation further confirms the above statement.…”

Challenges in Application of Pulse Current Gas Metal Arc Welding Process for Preparation of Weld Joint with Superior Quality

“…Out of several modes of metal transfer of GMAW process, the spray mode of metal transfer offers better ease of operation primarily due to dominating electromagnetic force resulting in projected transfer of the droplet. In GMAW process utilizing continuous current, depending upon filler wire material, filler wire size and shielding environment, spray transfer can be achieved only at significantly higher welding current above transition level, which increases heat input to the weld [4,47]. This, increase in heat input consequently enhances temperature of the weld pool and adversely affects quality of the weld joint in the form of its mechanical and metallurgical properties through its influence on weld thermal cycle, weld isotherm and geometry of the weld bead.…”