Hydrogen sulphide stress corrosion cracking of weld overlays for desulfurization reactors

Abstract

Weld overlays of austenitic stainless steels on 2.25 Cr-Mo steel were made by the shielded metal are welding process. Single layer weld overlays (SLWO) of 3 mm thick were made by using either E309 (A-type specimen) or E347 (B-type specimen) electrodes and double layer weld overlays (DLWO) were made by depositing 1 mm of E309 and then 2 mm of E347 on the steel (C-type specimen). Constant extension rate tensile (CERT) tests were performed to investigate the fracture characteristics of the weld overlay specimens in air and in H2S solution. Cracks were initiated at the fusion boundaries between the stainless steel deposit and 2.25 Cr-Mo steel substrate, and then propagated normally to loading direction into the steel substrate and stainless steel deposit. This procedure was repeated for all types of specimens in the as-welded condition. The results revealed the untempered narrow diluted zone (DZ) and hear-affected zone (HAZ) were susceptible to hydrogen embrittlement (HE). However, the high susceptibility of the HAZ to HE could be reduced significantly in all specimens by tempering at 690 degrees C for one hour. The susceptibility to cracks in the DZ was lower for the A-type specimens than the B-type and C-type specimens. C-type specimens had the declined tensile strength, which could be attributed to the extensive dilution in the first layer deposit, resulting in a high susceptibility to HE. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.