Radiographic evaluation of corrosion and deposits in pipelines: results of an IAEA co-ordinated research programme

The principle of wall thickness measurement and monitoring of corrosion and deposits by means of film-based tangential projection radiography is known since decades. Nevertheless, there are no international standards and guidelines available. The International Atomic Energy Agency has organized a co-ordinated research programme bringing together participants from twelve member states to study the state of the art. The general scope of the project covered radiographic inspection of corrosion and deposits in steel pipes (diameter >150mm) corroded on the outer or inner surfaces with or without insulation. Two inspection methods have been investigated: 1. tangential radiographic projection technique (TRT) and 2. double wall inspection technique (DWT). The application ranges of both methods were studied depending on pipe diameter, wall thickness, radiation source (X-ray, Ir-192 and Co-60 were used) and screen/film combination. Diagrams for application limits using TRT have been designed and verified by the participating countries. All measurements have been performed on special designed test pieces and also industrial pipes. Corrosion measurements based on DWT are more sophisticated and use effective attenuation coefficients to calculate wall thickness changes from density differences shown on the film. The values of effective attenuation coefficients, established for Ir-192 and Co-60, are stable and independent in a wide range on pipe diameter and insulation. Guidelines were developed and tested in the twelve different countries to determine the reliability of this technology. A testing procedure approved by the project partners has been released and shall be submitted as standard proposal. (orig.)