Volume Loss, A New Parameter In Assessment Of Remaining Strength Of Pitting Corroded Steel Pipes
Proceedings Publication Date
Mojtaba Mokhtari
Mojtaba Mokhtari, Robert E. Melchers
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Failure of steel pipelines caused by pitting corrosion is a major concern in maintaining the integrity of steel pipeline systems. Regardless of service interruption and major loss of product, many incidents and more serious accidents involving death and injury related to flammable fluid pipeline failures demonstrate the importance of maintaining steel pipeline integrity. For pipelines suffering pitting corrosion, the remaining strength of pipes can be estimated by application of a number of methodologies. Semi-empirical models, also known as burst capacity models, are the most common approach to assessing the remaining strength of a pitting corroded pipe. These conventional burst capacity models can be excessively conservative or present considerable scatter in their predictions for many practical cases of corroded pipelines, particularly those that have developed deep pits of complex topology. Ideally for these cases a more advanced assessment approach is desirable. This is considered in the present study, aimed at producing an accurate and stable burst capacity model. The procedure described herein considers the volume loss caused by pitting corrosion as a key parameter to estimate the burst capacity of a pipe under high pressure. A number (nine) of full scale burst capacity tests of steel pipes with complex isolated pits were conducted, followed by advanced finite element simulations. This was done to evaluate the precision of the presented modified semi-empirical model and also to compare it with other well-known burst capacity models. The finite element models were found to be validated against the experimental data. The modified model resulted in very high accuracy and stability in its prediction of burst pressures of the steel pipes considered in the present study. With further validation work on-going, it is expected that, in a near future, the new model will be available to the pipeline industry for assisting in maintaining steel pipeline integrity.

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