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The Combined Effects of Stress Concentration and Tensile Stresses from Autofrettage on the Life of Pressure Vessels

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Technical Report

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US Army Benet Labs Watervliet United States

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Thick walled pressure vessels are often hydraulically or mechanically overstrained in order to impart favorable near bore residual compressive hoop stresses in an attempt to enhance fatigue life. As a result of imparting these favorable near bore compressive stresses, self-compensating tensile residual stresses result, which in some case can be detrimental. In the early stages of development of each system, multiple full size vessels are hydraulically fatigue tested and a safe life is determined. Recent developments have pushed these vessels into longer years of service. In some cases, this has caused unanticipated field issues and resulted in field service lives that are less than the original safe lives. These service issues have several common threads which link them together including tensile residual stresses from autofrettage, outside diameter stress concentration effects including features designed into the vessel as well as unanticipated effects from inadequate material quality, and long term effects from corrosion and pitting. This paper will present several case studies which will identify the cause of the reduced lives and propose corrective action.

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