Failure analysis of a welded impeller in coke oven gas environment

In this study, a centrifugal impeller made of FV520B martensitic precipitation hardening stainless steel failed after 12 months service in coke oven gas environment. An increase in vibration was recorded prior to the breakdown. Analysis revealed that fracture initiated at the welded joints and the main failure mechanism was sulfide stress corrosion cracking (SSC). Efforts were made to assess the cracking susceptibility of base metal and weld metal. Results indicated that welded joints experienced lower fracture toughness and higher susceptibility to SSC cracking. This paper brings out the details of investigation and suggests remedial measures to improve performance of this welded impeller under aggressive environment.