Improvement of Weld Characteristics by Variation in Welding Processes and Parameters in Joining of Thick Wall 304LN Stainless Steel Pipe

Abstract

Various properties of weld joints of 25 mm thick wall 325 mm O.D, 304LN austenitic stainless steel pipe prepared by using different welding process and conventional V-groove as per AWS specification have been compared. The welding was carried out by commonly used shielded metal arc welding (SMAW), gas metal arc welding (GMAW) and pulsed current gas metal arc welding (P-GMAW) processes. In P-GMAW process the influence of pulse parameters have been studied by considering their summarized influence defined by a dimensionless hypothetical factor fϭ[(I b /I p )f · t b ] where, t b ϭ[(1/f )Ϫt p ]. The characteristics of weld joints with respect to their metallurgical, mechanical, corrosion and fracture mechanics properties as well as residual stresses have been studied and compared. Welding of thick wall stainless steel pipe by P-GMAW process significantly improves the tensile properties, reduces the inclusion and porosity content, increases initiation fracture toughness and lowers residual stresses of weld joint in comparison to those observed of SMA and GMA weld joints. The influence of f on properties of P-GMA weld joints is primarily attributed to the reduction in severity of weld thermal cycle and refinement of microstructure of weld deposit.KEY WORDS: austenitic stainless steel; SMAW; GMAW; P-GMAW; pulse parameters; residual stresses; inter granular corrosion; microstructure; mechanical properties; fracture toughness. stainless steel requiring multipass weld deposition.In view of the above an effort has been made in the present investigation to carry out a comparative study on the characteristics of conventional V-groove welds of 304LN SS pipe prepared by using shielded metal arc (SMA), GMAW and P-GMAW processes. The P-GMA weld joints have been further compared by considering the influence of pulse parameters in reference to variation in f. The characteristics of weld joint have been analysed primarily with respect to the distribution of longitudinal and transverse residual stresses at the top and root of the weld joints and the microstructure of the weld and HAZ. In order to understand their utility the weld joints are also briefly characterised by studying their mechanical, fracture mechanics and corrosion properties. Experimentation Welding of PipesThe welding of 25 mm thick wall and 325 mm outer diameter AISI 304LN stainless steel pipe has been carried out using GTAW autogenously and in consecutive two root passes followed by filling passes using SMA, GMA and P-GMA welding processes at conventional V-groove confirming the ASME Section IX of Boiler and Pressure Vessel Code. Schematic diagram of the weld groove as well as the consumable root insert used of matching composition with filler metal have been shown in Figs. 1(a) and 1(b) respectively. The multipass welding was performed by using appropriately designed welding procedure specifications (WPS) resulting in a practically sound weld with respect to lack of fusion. The welding was carried out in 1GR position by holding the pipes in a rotating table with t...

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