REAL-TIME RADIOSCOPIC INSPECTION OF INSULATED PIPING SYSTEMS

Corrosion of pipelines is commonplace in many industries. Methods exis t that can be used to calculate the overall integrity of damaged pipin g if the depth and configuration of the corroded areas are known((1)). By determining the depth and dimenston of pitting, and knowing the de sign parameters of a given system, one can calculate the maximum press ure that a corroded pipe can contain. Severe localised corrosion in mu ltiphase 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 d etermine the integrity of corroded lines. The initial programmes devel oped in the first year of piping inspection utilised ultrasonic wall t hickness testing. Ultrasonic testing can generally be performed even i f only one surface of the component is accessible; however stripping o f the insulation is required where this type of inspection is used. Th erefore, the ultrasonic inspection was slow, restricted to short secti ons of piping, and costly. A less expensive alternative was developed using manual radiography. This eliminated the need to remove insulatio n yet it was still slow and so only short sections of pipe could be ex amined Although extreme value statistics indicated that inspection of short sections of pipe would locate the most severe pitting with a hig h probability, this proved nos 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 t he impetus to develop real-time radioscopy as a field tool. In the ear ly 1980s, stationary real-time radioscopic units were available, but t ranslating these systems into one that could function reliably in the harsh field environment encountered in northern Alaska took a number o f years. A working real-time radioscopic system began field inspection of piping in 1987. Over the past eight years, over 1,750,000 feet (53 3 km) of piping have been inspected with this technique, and continuin g evolution has produced dependable, versatile equipment. These develo pments and the future capabilities of the real-time radioscopic inspec tion system are discussed.