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Explanation of ASME UT in Lieu of Radiography Fracture Mechanics SME Section VIII Div.2 Alternative Acceptance Criteria/Code Case 2235-10

This paper is to clarify the sometimes misunderstood acceptance criteria of fracture mechanics using UT in Lieu of Radiography ASME Sec VIII requirements. First off let us address some key differences in the characterization of an indication and what ultimately decides Acceptance or Rejection of said indication. The ASME alternative acceptance criteria’s broken down into tables called aspect ratios which will be further reviewed in later sections. When using these aspect ratio tables the first decision is based on the riteria is the flaw surface (a) or subsurface (2a). This determination plays a large part in the criticality to which the indication will be evaluated. When compared to the common workmanship acceptance criteria such ASME Sec VIII Div.1 App.12 a Lack of Fusion or even subsurface crack would be rejectable regardless of any amplitude or length. With fracture mechanics this is not true since all flaws to this acceptance criteria are viewed as planar in geometry the deciding factor for the indication accept/reject rating is based on the flaw height and length, and proximity to the closest pressure retaining surface. Note although the criteria is written to use a 20% of DAC ( Distance Amplitude Curve ) for investigative threshold when using amplitude based techniques the acceptance criteria is not amplitude based.

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