Sulfide Stress Cracking of Offshore Gas Injection Header: A Case Study

Abstract

The gas produced from an oil field is used to inject into the well for enhanced recovery of oil and gas. The injected gas flows through a pipeline called a header to individual wells for gas injection. One such 6” gas injection header at an offshore process complex experienced a leakage during operation just after 2 years of service. The operating pressure of the pipeline was normal, and there was no process disturbance at the time of the failure. There was no localized corrosion and thinning of the header. The material of construction of the header sample was reported to be ASTM A106 Gr B specification. Laboratory investigations revealed that the material did not conform to ASTM A106 Grade B standard. In the present case, the H₂S partial pressure was 0.09 psi; this comes under sulfide stress cracking (SSC) region 2 as per ISO 15156-2:2015; therefore, the environment is prone to SSC. During metallography and SEM analysis, cracks filled with corrosion product typical of SSC were observed which propagated intergranularly. Zigzag cracks typical of hydrogen-induced cracking that branched out from the main SSC crack were also observed. As the metal was too brittle in nature, the gas injection header cracked at many sites. When the crack grew to the extent that the pipe could not withstand the operating pressure anymore, it failed in a brittle manner and the header was shattered into pieces.