Computer modelling of the computed radiographic inspection of wall loss flaws in pipes for image simulation and POD prediction

Within the oil and gas industry, there is increasing use of computed radiography (CR) for the in-service inspection of pipes for wall loss flaws such as corrosion and erosion. Within the HOIS joint industry programme, a major project is underway to develop a recommended practice for this application of CR. This is being underpinned by the development of a computer model for CR image simulation and prediction of probability of detection (POD). The overall approach follows that developed previously for the POD modelling of the ultrasonic corrosion mapping technique.

The CR model described in this paper differs from others developed elsewhere in that it has a relatively simple physical/mathematical basis, and does not require special interfaces to 3-D CAD packages. This allows the model to run in only a few minutes on a typical current PC. The results from the model are compared with those from an experimental POD trial. Results are also given from a sensitivity study to identify and quantify the main parameters which influence POD under different inspection conditions.