Effect of Post-Weld Heat Treatment on the Corrosion Resistance of Stainless Steel Welds in Chemical Processing Equipment

This study examines the effect of post-weld heat treatment (PWHT) on the corrosion resistance of Type 316L austenitic stainless steel welds used in chemical processing equipment at facilities in Lagos and Ogun States, South West Nigeria. Sensitisation of stainless steel welds due to chromium carbide precipitation at grain boundaries is a known mechanism of intergranular corrosion and stress corrosion cracking susceptibility, and PWHT is applied to restore corrosion resistance. Weld specimens are produced by GTAW using matching 316L filler and subjected to PWHT at 1050, 1100, and 1150 degrees Celsius with rapid water quenching (solution annealing), as well as a stabilisation treatment at 900 degrees Celsius. Samples are also tested in the as-welded condition as a reference. Corrosion resistance is evaluated by the double loop electrochemical potentiokinetic reactivation (DL-EPR) test for sensitisation degree quantification, immersion testing in boiling 65 percent nitric acid (Huey test per ASTM A262), and potentiodynamic polarisation in 3.5 percent NaCl. Microstructural characterisation by SEM-EDX and EBSD is performed to assess grain boundary chromium distribution. Findings demonstrate that solution annealing at 1100 degrees Celsius eliminates sensitisation measurable by DL-EPR, reduces corrosion rate in the Huey test by 85 percent relative to the as-welded condition, and fully restores passive behaviour in NaCl solution. Keywords: post-weld heat treatment, stainless steel, corrosion, sensitisation, chemical processing.