Hardness Reduction in SA-335 P11 Welds by GTAW Using Controlled Interpass Temperature and the Temper Bead Technique without Post Weld Heat Treatment

Regulations governing welding in the oil and gas industry mandate post-weld heat treatment (PWHT) for all welded joints, regardless of pipe wall thickness. The maximum permissible hardness is limited to 248 HV to prevent cracking. However, PWHT is time-consuming, energy-intensive, and costly. This study investigates the use of interpass temperature control and the temper bead welding technique as alternative methods for reducing weld hardness without PWHT. SA-335 Grade P11 low alloy steel pipes were welded using the GTAW process with ER80S-B2 filler metal and 99.99% argon gas. A preheat temperature of 250 °C was applied in all conditions. Four experimental groups were investigated: (1) PWHT at 650 °C for 1 hour, (2) low interpass temperature at 250 °C, (3) high interpass temperature at 600 °C, and (4) temper bead welding with 17 overlapping beads. The first three groups used 7 beads for comparison. Weld quality was assessed using VT, PT, and RT. Hardness testing served as the primary evaluation method, followed by tensile, bend, macrostructural, and microstructural analysis. Hardness results showed that the PWHT and high interpass groups remained below 248 HV, with the temper bead group achieving the lowest weld metal hardness (215.5 HV). The low interpass group exceeded the limit (up to 256.3 HV). All specimens failed in the base metal during tensile testing, with average strengths ranging from 498.3 MPa (PWHT) to 526.3 MPa (temper bead). No critical defects were found in bend tests. Microstructural comparison revealed that temper bead welding produced finer and more uniform grains, contributing to lower hardness and improved thermal softening in the HAZ.