Proper Quality control (QC) plays a vital role during manufacturing of Oil and Gas facilities new equipment. Improper QC does occur sometimes resulting in sub-standard products, which may be silent for years till the right conditions are in place and then contributes to major failures. These non-conformances during manufacturing may lead to accelerated corrosion induced failures, which in turn lead to unscheduled shutdowns, production loss, environmental contamination, as well as health and safety hazards. This study highlights the premature failures of three motor operated valves (MOV) of various sizes, made of duplex stainless steel, which were operating in effluent water service in a crude oil gathering facility. These valves were in operation for only three years and consisted of: (1) a 16 inch (0.41 m) diameter Gate Valve installed at the suction line of effluent water feed pump; (2) a 10 inch (0.25 m) diameter Gate Valve installed at the suction line of effluent water feed pump, and (3) a 36 inch (0.91 m) diameter Gate Valve installed at the discharge header of pump. The failure investigation revealed that, in all three cases, the valve materials were subjected to improper heat treatment during the component production stage, resulting in substandard quality of the materials and consequent poor corrosion resistance.
Duplex Stainless Steels (DSS) are most sought after alloys when dealing chloride environments due to the fact that they are less susceptible to Stress Corrosion Cracking (SCC). Duplex stainless steels are more economical in welding (Since 50% ferrite is allowed) and fabrication (since its yield strength is quite high compared to most other engineering alloys This is particularly alarming while casting and/or welding of these alloys. The intermetallics are detrimental to DSS since they impair the corrosion resistance of DSS quite drastically.
