Piping and pressure vessel nozzle flange leaks contribute to the loss of containment, health, safety, and environmental (HSE) issues in the petrochemical industry. This paper discusses a project to mitigate flange leaks through a non-intrusive nondestructive (NDE) technique by early detection and quantification of flange face corrosion. A case study of two amine units from a US gas plant is presented. Process leaks had occurred on piping and nozzle flanges due to CO2 corrosion and erosion of raised-face sealing surfaces. Several corroded flanges were removed and submitted for a study of advanced N DE detection and sizing techniques capable of in-service inspection prior to a scheduled plant maintenance shutdown. If possible, the NDE techniques were to use standard NDE test equipment and conventionally trained NDE technicians. During phase I of the project, a specialized manual ultrasonic shear wave (UT-SW) procedure was developed and used for the initial on-stream inspection. In phase II, an ultrasonic imaging technique was developed using an automated ultrasonic imaging system (AUT) and a special miniature scanner that rides on the outside diameter of the flange hub. After some successful field trials, both phase I and phase II test methods expanded to other petrochemical applications such as inspection of HF-Alky refinery pipe flanges, H2S, and other services where flange damage may occur. Other flange designs, such as ring type joints (RTJ’s) were also added to the project. After 18 months of use, the UT techniques were released to interested petrochemical companies within the American Petroleum Institute (API) and the Petroleum Environmental Research Forum (PERF) industry consortium. The techniques were also given to professional NDE training companies in the US and UK in order to promote its HSE benefits across the industry. As of this writing, 12 inspection companies have trained ultrasonic technicians on the manual technique.
Key Words: Flange corrosion, non-destructive testing, ultrasonic examination, CO2 corrosion, HF-Alky corrosion