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Research Papers: Materials and Fabrication

Creep Life Evaluations of ASME B31.1 Allowance for Variation From Normal Operation

[+] Author and Article Information
Marvin J. Cohn

Mem. ASME
Intertek AIM,
601 W. California Avenue,
Sunnyvale, CA 94086-4831
e-mail: marvin.cohn@intertek.com

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received July 2, 2015; final manuscript received October 1, 2015; published online April 28, 2016. Assoc. Editor: Marina Ruggles-Wrenn.

J. Pressure Vessel Technol 138(4), 041405 (Apr 28, 2016) (4 pages) Paper No: PVT-15-1146; doi: 10.1115/1.4031747 History: Received July 02, 2015; Revised October 01, 2015

The ASME B31.1-2012 Power Piping Code (Code) paras. 102.2.4, 102.3.3, and 104.8.2 provide an allowance regarding operating above the design temperature and internal pressure for short time periods. This study is a quantitative evaluation of the permitted increased life consumption associated with the 2012 Code operating allowances for piping materials operating in the creep range. Three base metal materials are considered in this paper—ASTM A335 Grades P11, P22, and P91. Results of this evaluation could be used to improve the ASME B31.1 Code, including a technical basis for a recommended revision. The para. 102.2.4 allowables were evaluated: (A) 15% stress increase for 10% of the operating hours and (B) 20% stress increase for 1% of the operating hours. It was determined that these allowances increased the base metal creep rupture life consumption of Grade P11 material up to 8%, Grade P22 material up to 14%, and Grade P91 material up to 25%. Allowance A results in permitting significantly more creep life consumption than Allowance B. An evaluation was performed to realign the increased creep life consumption of Allowance B to be approximately equivalent to the increased creep life consumption of Allowance A. If Allowance B event duration is increased from 80 hrs per year to 400 hrs per year (from 1% to 5% of the operating hours per year), Allowance B increased the creep life consumption which is slightly less than Allowance A life consumption for Grades P11, P22, and P91 materials. Main steam (MS) and hot reheat (HRH) piping system typical operating temperatures and stresses were evaluated for these variation allowances. This study revealed that Grade P22 base metal creep damage is slightly more sensitive to stress than Grade P11 material creep rupture damage, and Grade P91 base metal creep damage is substantially more sensitive to stress than Grade P22 material creep rupture damage.

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References

ASME, 2012, “ ASME B31.1-2012 Edition, Power Piping,” ASME Code for Pressure Piping, B31, An American National Standard, American Society of Mechanical Engineers, New York.
API 579-1/ASME FFS-1, 2009, June 2007 and 2009 Errata, Fitness for Service, Table F.31, 2nd ed., American Petroleum Institute, Washington, DC, p. F-92, F-93.
API STD 530, 2003, Calculation of Heater-Tube Thickness in Petroleum Refineries, 5th ed., American Petroleum Institute, Washington, DC.
NRIM, 1994, Data Sheets on the Elevated-Temperature Properties of Normalized and Tempered 1-1/4 Cr-1/2 Mo-Si Steel Plates and Pressure Vessels (SCMV 3 NT) (NRIM Creep Data Sheet No. 21B), National Research Institute for Metals, Tokyo, Japan.
NRIM, 1997, Data Sheets on the Elevated-Temperature Properties of Normalized and Tempered 2-1/4Cr-1Mo Steel Plates for Boilers and Pressure Vessels (SCMV 4 NT) (NRIM Creep Data Sheet No. 11B), National Research Institute for Metals, Tokyo, Japan.
NRIM, 1996, Data Sheets on the Elevated–Temperature Properties of 9Cr-1Mo-V-Nb Steel Tubes for Boilers and Heat Exchangers (ASME SA-213/SA-213M Grade T91) and 9Cr-1Mo-V-Nb Steel Plates for Boilers and Pressure Vessels (ASME SA-387/SA-387M Grade 91), (NRIM Creep Rupture Sheet 43), National Research Institute for Metals, Tokyo, Japan.

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