STP918: Preventing Fracture By Inspection and Analysis

    Selz, A
    Vice presidents, O'Donnell & Associates, Inc., Pittsburgh, PA

    Peterson, DB
    Vice presidents, O'Donnell & Associates, Inc., Pittsburgh, PA

    Pages: 15    Published: Jan 1986


    Abstract

    A problem in operating pressure components under cyclic loading conditions is establishing an in-service inspection frequency to assure continued operability without threat of catastrophic failure. For some extremely high pressure components, this has been done on a rational basis by (1) establishing the regions of highest stress, usually thread roots or other local stress raisers in a high stress field, (2) establishing the minimum-size reliably observable crack-like defect, using proven inspection means, such as magnetic particle or eddy current testing, and (3) determining the number of design cycles this minimum observable crack needs to grow to critical size, using Paris law or analogous crack propagation relations, and then dividing the resulting number of cycles by a factor of at least three. This factor of three is based on retaining cyclic margin to failure, even if a given defect is below perceptible size at initial inspection and is missed during the next inspection. A factor of four would accommodate two consecutive failures to observe a defect. Methods have been also developed which permit modification of the inspection interval if the operating logs show the imposition of a distribution of operating cycles other than the design cycles upon the component.

    The methods described were originally developed and applied to predicting safe life and establishing inspection intervals for a hypervelocity wind tunnel. They have since been applied to commercial pressure vessels and for recertification of pressure vessels for the National Aeronautics and Space Administration.

    Keywords:

    crack propagation, fatigue, fracture, high pressure, inspection, isostatic press, pressure vessel


    Paper ID: STP19334S

    Committee/Subcommittee: E08.08

    DOI: 10.1520/STP19334S


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