Incident Case Study of Baseline Pigging During In-Line Inspections for Corrosion Resistant Alloy Clad Pipelines

Abstract

This paper describes an incident that occurred during the baseline inspections of pre-commissioning activities performed on a 20-in. metallurgically bonded corrosion resistant alloy (CRA) clad pipeline of an approximate length equal to 2.7 km. The inspection tool, deployed as part of the baseline inspections before the startup of the pipeline, was damaged in the CRA clad pipeline. This damage occurred despite extensive computer simulations, carried out before the inspection, which indicated that the tool, an ultrasonic (UT) pig, was able to traverse the length of the pipe without major issues. The application of the pressure surges was successful in dislodging the UT pig; however, as a direct consequence, the UT pig crashed into the pig receiver and sustained significant damage. The sealing pigs that were trailing behind the UT pig also collided with the rear of the UT pig, and it was at this junction that all further data transmission was ceased. A metal swarf was discovered upon inspection of the UT pig after retrieval, indicating that the inner wall of the pipeline also sustained damage. An analysis of the swarf indicated that it comprised solely of the CRA alloy that was metallurgically bonded to the inner wall of the carbon steel pipe. It was concluded that, due to the anticorrosive nature of the CRA material and high-quality control standards upheld during the manufacture of CRA pipes, the baseline in-line and routine inspections were unnecessary and can be detrimental if the inspection tool becomes impacted, thereby compromising the containment of the CRA layer.