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Our presentation will describe and compare the usual failure assessing methods against static pressure load, like ASME B31 G, RStrength, DNV, TÜV NORD method. We compare the methods among each other and to the results of real burst tests.
However, this simple assessment of the indications against static pressure load is only a small part within the scope of a pipeline assessment over a future period.
In the scope of the assessment it is necessary to consider the detection and sizing capability of the inspection tools, especially the differences between the ndt-methods MFL und UT. In many cases the assignment of the TÜV starts with the assistance of the pipeline owner with the selection of the best inspection tool for his special pipeline.
The first step of the assessment is a meaningful verification and qualification of the inspection data. Therefore in most cases a significant number of indications have to be checked at the pipeline.
The following assessment of the inspection data considers the deviation established during the qualification of the inspection data mentioned above. Among others the type of the failure, the position, the pipeline surrounding, the possible corrosion influence, the effectiveness of the cathodic protection and possible dynamic pressure load will be considered.
The assessment covers three failure mechanisms: 1. Failure due to static pressure load; 2. Failure due to dynamic pressure load; 3. Failure due to leakage. Under consideration of individual corrosion rates, for each pipeline section, these three criteria were projected into the future.
Concerning the static and dynamic pressure load, the results are safety factors or the probability of failure for each indication over the time. The leakage assessment provides the projected remaining wall thickness for each indication over the time. The significant indications were marked.
In the final assessment TÜV NORD provides suggestions for checking or repairing of significant indication as well as suggestions for optimizations to ensure the proper condition of the pipeline in the future. Future actions will be established under consideration whether or when another inspection run is intended.
After the check or repair of relevant indications the verification of the inspection will be updated und a re-assessment of the indications will be conducted. After a re-assessment, the TÜV-Nord report will be updated and provides detailed information concerning the present and future integrity and safety of the pipeline.