Cracks in close proximity may interact and lead to leaks or ruptures at pressures well below the predicted failure pressures of the individual cracks. Several industry organizations and standards, including CEPA, ASME, API, and British Standards provide guidance on the treatment of potentially interacting cracks. This guidance tends to be very conservative. This paper is a study of crack interaction, including a discussion of industry guidance, a critical review of failure pressure models, and a review of results of laboratory hydro-testing of pipe sections containing either in-service flaws or simulated flaws. In some cases the industry guidance and current failure pressure models provide inconsistent predictions, and this leads to uncertainty in the assessments used in routine crack management programs. The results of the hydro-testing are discussed in the context of both types of predictions. Understanding and predicting these interactions is important in maintaining an effective and efficient crack management program. The paper is aimed at engineers involved in integrity assessments and integrity management system process improvement.
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