Abstract

The rules of ASME B&PV Section VIII Code provide (i) allowable tensile stress at elevated temperatures based on time duration of 100,000 hours; (ii) external pressure charts which do not account for reduction of buckling strength due to creep under short or long-term loads. For short term operating conditions for which component design governed by an allowable tensile stress based on long term (100,000 hours) creep properties is unrealistically conservative and may be non-conservative in the case of very long load durations (> 100,000 hours). At elevated temperatures, the allowable compressive stress depends on magnitude of load and duration. The newly released code cases, Case 2951 ‘Alternative Approach for Operating Conditions (Including Occasional Loads) in the Time-Dependent Regime’ and Case 2964 ‘Allowable Compressive Stress in the Time-Dependent Regime’ provide procedures for elevated temperature design of pressure vessels considering load durations. In this paper, for successful implementation of these code cases, the key variables are reviewed and the inherent assumptions made in the development of these code cases are highlighted. Also, the code cases are applied for design of typical pressure vessel components and the results are compared with other relevant procedures which consider load duration into account.

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