Fracture Toughness Requirements for ASME Section VIII Vessels for Temperatures Colder Than 77K

Abstract

Earlier research work conducted at MIT and NIST indicated that CVN specimens with an initial temperature at or near 4K (−452°F) actually fracture at temperatures significantly above 4K due to adiabatic heating. As a result of this work, ASTM E-23 test method on CVN testing was revised to incorporate a restriction that CVN tests are valid only at 77K (−320°F) and warmer. ASME requested PVRC to assess the above CVN issue and provide an appropriate recommendation for the Code change or for a further Code change, if needed for vessels with MDMT colder than 77K. PVRC formed a Task Group under the Committee on Failure Modes. The TG undertook a program which included a review of the existing data and an experimental program to develop new KIcJ data at 4K and 77K and CVN data at 77K. In the experimental program, a total of four 1-in-thick weldments were prepared from SA 240, Type 304 stainless steel plate using the SMAW process and E316L-15 electrodes. The electrodes purchased permitted the preparation of the weldments with four progressively higher levels of ferrite. The PVRC data and existing data were utilized in developing the recommendations to ASME. The recommendations are: use CVN tests (with 316L S.S. weld filler metal with FN⩽5) at 77K with increased acceptance criterion of 21 mils lateral expansion; for welds not meeting the foregoing requirements, use ASTM E1820 JIc tests at MDMT and the acceptance criterion for KIcJ has been set at 120 ksi√in. This paper presents the test data, analysis and technical basis for the PVRC recommendations to ASME.