Failure analysis of carbon steel pipes used for underground condensate pipeline in the power station

• The failure cause is SCC induced by Cl− and residual stress in welding seam.
• Corrosion products of the fracture surface contain Cl and S in the failed pipe.
• There was residual tensile stress in welding seam.
• Crack type of welding seam was typical branch type SCC.

In this paper, the cause of failure of an ASTM A53 Grade B carbon steel pipe was investigated. The investigated ASTM A53 Grade B pipe was used for a condensate pipeline and was found to be cracked after six months in service. The failed parts were investigated by means of stereoscopic microscope, optical microscope, scanning electron microscope equipped with energy dispersive X-ray spectroscopy micro-analysis, spark emission spectrometer, tension tester and Vickers hardness tester, in order to identify the failure causes and to suggest preventive solutions. A specially instrumented indentation tester was used for the measurement of residual stress on welding seam. The study shows that failure was mainly due to stress corrosion cracking caused by chloride and tensile residual stress on the welding seam due to insufficient heat input or low compression, etc during welding processing.