Proposed Revision to ASME B31.1 Para. 102.2.4 Allowance for Variation From Normal Operation

Abstract The ASME B31.1-2024 Power Piping Code (Code) para. 102.2.4 [1] provides an allowance regarding operating above the design temperature and internal pressure for short time periods. The concept of allowing occasional operation for short periods of time at higher than the design pressure or temperature has been in the Code since 1967. The 1967 Code para. 102.2.4 limitations were based on engineering judgment that can now be quantitatively evaluated for the additional creep life consumption. The Code states that the pressure or temperature or both may exceed the design values if the computed circumferential pressure stress does not exceed the maximum allowable stress from Mandatory Appendix A for the coincident temperature by: (A) 15% if the event duration occurs for no more than 8 hours at any one time and not more than 800 hours per year, or (B) 20% if the event duration occurs for no more than 1 hour at any one time and not more than 80 hours per year. In 2019 it was estimated that using para. 102.2.4 Allowance A or B for 11 materials operating in the creep range over 10 operating years resulted in increased creep life consumption in the range of 0.0% to 6.4% [2]. The proposed revision to para. 102.2.4 in this study will align the increased creep life consumption for the same 11 materials to a similar range of 1% to 6%. This study provides a technical basis for a possible revision to para. 102.2.4 considering the additional creep life consumption for 11 materials operating in the creep range. The materials considered in this paper are: 1. Low carbon steel 2. 1.25Cr 0.5Mo 3. 2.25Cr 1Mo 4. 9Cr 1 Mo V 5. Type 304 SS 6. Type 316 SS 7. Type 316L SS 8. Type 321 SS 9. Type 321H SS 10. Type 347 SS, and 11. Type 347H SS If operated within the limits of proposed Equation 1 for 10 years (80,000 operating hours), the methodology resulted in an estimated range of 1% to 6% increased creep life consumption compared to the piping system operating at the design temperature and design pressure during the 10 years. In addition, the proposed methodology may be used to evaluate operations slightly above the design temperature and design pressure during each year.