The role of a stressed state in the formation of stress-corrosion flaws in pipelines

Abstract

In recent years, as a result of performance of intensive in-tube flaw detection, the integrity and reliable operation of trunk pipelines have been achieved. However, because of an unpredictable development of such tube flaws as stress corrosion, the probability of occurrence of emergencies in pipelines substantially increases. An analysis of the stressed state in pipelines exposed to their main load—the operating pressure—and various types of additional forces is presented. As a result, it is shown that the obtained direction, value, and location of the effective maximum stresses in the tube wall fully correspond to the pattern of statistical formation of stress-corrosion flaws in pipelines. It can be concluded from the data of this study that the standardized tube-strength margin is insufficient; during tube operation, this circumstance may lead to the formation of stresses at the level of the metal yield stress and initiation and growth of stress-corrosion cracks.