Non-destructive Evaluation of Corrosion Under Insulation in Oil and Gas Pipelines Using Gamma and X-ray Linear Profilers Using Monte Carlo Method

A substantial volume of oil and gas pipelines, particularly in petrochemical industries, are insulated with various materials. In many cases, a small opening or leak can allow water and other corrosive liquids to penetrate, leading to corrosion under insulation (CUI). This type of corrosion is not detectable through conventional methods over the insulation. With the usual methods of non-destructive inspection, such as visual and ultrasonic tests, it is not possible due to the lack of access to the metal of the pipeline. One of the most effective non-destructive methods for this purpose is the use of radiographic profiling devices. In this paper, using the Monte Carlo method, the common X-ray spectra for this technique at 70 keV and 90 keV were simulated. Industrial radioisotopes used, including Ir-192 and Co-60, were considered as sources. The pipeline phantoms implemented were made of 6mm thick carbon steel and 24mm thick polyethylene insulation. Artificial corrosion with a depth of 3mm was created on the pipeline wall. A single-energy linear detector made of CsI(Tl) with a thickness of 5mm and a pixel pitch of 1.6mm was implemented in the code, and the spatial signal was recorded on it. The transport of X-ray and gamma photons for the used sources was visually recorded for 20,000 photons, and the signal recorded on the detector, along with the accumulated energy in each detector pixel, was measured. The results indicate the suitable performance of the implemented system in locating and detecting CUI defects.A substantial volume of oil and gas pipelines, particularly in petrochemical industries, are insulated with various materials. In many cases, a small opening or leak can allow water and other corrosive liquids to penetrate, leading to corrosion under insulation (CUI). This type of corrosion is not detectable through conventional methods over the insulation. With the usual methods of non-destructive inspection, such as visual and ultrasonic tests, it is not possible due to the lack of access to the metal of the pipeline. One of the most effective non-destructive methods for this purpose is the use of radiographic profiling devices. In this paper, using the Monte Carlo method, the common X-ray spectra for this technique at 70 keV and 90 keV were simulated. Industrial radioisotopes used, including Ir-192 and Co-60, were considered as sources. The pipeline phantoms implemented were made of 6mm thick carbon steel and 24mm thick polyethylene insulation. Artificial corrosion with a depth of 3mm was created on the pipeline wall. A single-energy linear detector made of CsI(Tl) with a thickness of 5mm and a pixel pitch of 1.6mm was implemented in the code, and the spatial signal was recorded on it. The transport of X-ray and gamma photons for the used sources was visually recorded for 20,000 photons, and the signal recorded on the detector, along with the accumulated energy in each detector pixel, was measured. The results indicate the suitable performance of the implemented system in locating and detecting CUI defects.