Evaluation Of Flange Face Corrosion Using Phased Array Ultrasonic Testing (Paut) In Process Industry

Crevice corrosion [3] is a well-known damage mechanism in Oil and Gas facilities and is caused by a concentration of corrosive substances within a confined space. The crevice between two adjoining flanges is the ideal environment for initiation of crevice corrosion. Because of the concentration of these corrosive substances in a localized area, rate of corrosion gets accelerated. When flanges are used in very corrosive environments such as sea water, acid service and H2S concentrated drain piping the flange face is particularly susceptible. Corrosion of the sealing area can cause loss of containment and therefore have the potential to cause a release of product with potentially catastrophic consequence. Phased Array Ultrasonic testing technology [6], was recently introduced by specialized inspection companies, the technology can be used to identify the flange face gasket seating surface condition and extent of corrosion in all types of Carbon Steel flanges (weld neck raised face and ring groove) in the Piping and Pressure vessels while in service and without the need to separate the flange joint. The PAUT technology can be described as a semi-quantitative technique to measure the metal wastage (Crevice corrosion, erosion etc.,) at the flange faces gasket seating area. Defect dimensions are measured in C-Scan image (plan view) and POD [2] (Probability of detection) is up to 90%. The PAUT technology was validated in the current research by two ways one is by break opening few bolted in-service flanges and also by the use of flanges with artificial defects/flaws and compare them with inspection findings. This research paper is discussing the results for the use of PAUT technology in a large scale inspection survey of the process industries. The paper will discuss results, results validation, technology strength point and limitations. The same is seen as valuable information for all oil and gas operators worldwide.