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The inspection of onshore and offshore pipeline is mostly performed based on given constant intervals. By using a risk based approach the inspection frequency can be adapted to the current status and the potential failure consequence of the specific pipeline.
This paper describes some of the major aspects of the methodology developed to estimate the risk to onshore & offshore pipelines. Based on a risk assessment an optimised inspection strategy can be developed. The determination of the risk includes the identification of the different failure modes, the probability of failure and the potential consequences. The interaction of different failure modes is also considered. Finally, the base line risk, current risk and future risk can be estimated.
The paper presents the results of a general risk assessment of 80 aged onshore & offshore pipelines. Although only basic data has been available this was sufficient to work out reliable results within a semi-quantitative approach. Depending on varying wall thickness, diameter, etc. a pipeline was divided in different segments. The assessment reveals different governing threats and failure modes, like ageing, free span or corrosion. In a final step the results of the risk assessment are used for the optimisation of the inspection intervals within the proposed risk based inspection framework.