LOOP is a concept to evaluate corroded or damaged pipelines based on detailed data from UT-pigging. The procedure of LOOP delivers a 3D-model generated from the data of a commercial in-line inspection tools (ultrasonic, magnetic flux). This makes it possible to use the full functionalities of the relevant finite element software like evaluation of wall-thinning (LOOP 1) and fracture mechanics analysis to evaluate cracks in the wall (LOOP 2). In this paper is given the basic ideas of the LOOP concept, where the main focus is directed to the LOOP 1 assessment procedure.
Based on a real example of a corroded pipeline is demonstrated the assessment procedure, which is based on an elastic-plastic analysis of a real inner contour of the corroded surface transferred in the finite element geometry model. The unique element is that the surface data of the UT-pigging is used directly to generate the geometry model in the FE-software ANSYS. The assessment procedure is validated by a burst pressure test of a corroded pipeline. The result of the burst pressure test is compared with the calculated limit load from an elastic-plastic analysis based on measured material properties.
Additionally, the assessment procedure is compared with the results of a limit load analysis based on DIN EN 13445-3 and with the results of the standard assessment procedure. At the end the assessment procedure is compared with the procedure given in API 579-1 standard.