Sulfide stress corrosion cracking and hydrogen induced cracking of A216-WCC wellhead flow control valve body

• SEM observations were performed on the surface and the cross-sectional plane of the fracture to detect the failure mode.
• The control valve body failed due to combination of SSC and HIC cracking in wet H2S environment.
• According to HIC and SSC laboratory tests the best alternative for the valve body alloy is A217-WC9 steel.
• Anodic polarization curves clearly shows a considerable improvement in pitting resistance.

The wellhead flow control valve bodies which are the focal point of this failure case study were installed in some of the upstream facilities of Khangiran's sour gas wells. These valve bodies have been operating satisfactorily for 3 years in wet H2S environment before some pits and cracks were detected in all of them during the periodical technical inspections. One failed valve body was investigated by chemical and microstructural analytical techniques to find out the failure cause and provide preventive measures. The valve body alloy was A216-WCC cast carbon steel. During investigation many cracks were observed on the inner surface of the valve body grown from the surface pits. The results indicate that flow control valve body failed due to combination of hydrogen induced corrosion cracking (HICC) and sulfide stress corrosion cracking (SSCC). According to HIC and SSC laboratory tests and also with regard to cost of engineering materials, it was evident that the best alternative for the valve body alloy is A217-WC9 cast Cr–Mo steel.