Real-time radioscopic inspection of insulated piping systems : Galbraith, J.M.; Allen, W.T.; Coleman, K.L.; Alreja, V.J. Insight, Vol. 37, No. 6, pp. 417–420 (Jun. 1995)

Abstract

Corrosion of pipelines is commonplace in many industries. Methods exist that can be used to calculate the overall integrity of damaged piping if the depth and configuration of the corroded areas are known (1) . By determining the depth and dimension of pitting, and knowing the design parameters of a given system, one can calculate the maximum pressure that a corroded pipe can contain. Severe localised corrosion in multiphase oil transportation piping within major Alaskan oil fields led to development of extensive programmes that have been used for over a decade to inspect hundreds of miles of piping to locate pitting and determine the integrity of corroded lines. The initial programmes developed in the first year of piping inspection utilised ultrasonic wall thickness testing. Ultrasonic testing can generally be performed even if only one surface of the component is accessible; however stripping of the insulation is required where this type of inspection is used. Therefore, the ultrasonic inspection was slow, restricted to short sections of piping, and costly. A less expensive alternative was developed using manual radiography. This eliminated the need to remove insulation, yet it was still slow and so only short sections of pipe could be examined. Although extreme value statistics indicated that inspection of short sections of pipe would locate the most severe pitting with a high probability, this proved not to be the case. To assure that the most severe area of pitting was located and the integrity of the corroded piping accurately determined, a technique was needed that could be used to examine economically long sections of piping. This need provided the impetus to develop real-time radioscopy as a field tool. In the early 1980s, stationary real-time radioscopic units were available, but translating these systems into one that could function reliably in the harsh field environment encountered in northern Alaska took a number of years. A working real-time radioscopic system began field inspection of piping in 1987. Over the past eight years, over 1,750,000 feet (533 km) of piping have been inspected with this technique, and continuing evolution has produced dependable, versatile equipment. These developments and the future capabilities of the real-time radioscopic inspection system are discussed.