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A Suggestion of Improvement Plan for ASME Sec. III Requirements Through the Construction Experience of Korea Standard Nuclear Power Plants: Hydrostatic Test Pressure and PWHT Temperature of P-No.4 Materials

[+] Author Affiliations
Sanghoon Lee, Youngho Son, Jaehoon Lee, Woosung Kim

Korea Institute of Machinery and Materials, Kyungnam, South Korea

Seogchan Yoon

Korea Electric Association, Seoul, South Korea

Paper No. PVP2007-26433, pp. 635-642; 8 pages
doi:10.1115/PVP2007-26433
From:
  • ASME 2007 Pressure Vessels and Piping Conference
  • Volume 1: Codes and Standards
  • San Antonio, Texas, USA, July 22–26, 2007
  • Conference Sponsors: Pressure Vessels and Piping Division
  • ISBN: 0-7918-4279-7 | eISBN: 0-7918-3804-8
  • Copyright © 2007 by ASME

abstract

The minimum hydrostatic test pressure for class 2 and 3 components has been reduced from 1.5 to 1.25 times the Design Pressure in ASME B&PV Sec. III, Division 1 since 1999 addenda. If these requirements are applied to the system hydrostatic test as they are, the minimum hydrostatic test pressure of components and system becomes identical. Therefore it may happen that the test pressure imposed on components installed at low locations in the system exceeds the maximum permissible pressure due to the static head during the system hydrostatic test. PWHT temperature requirements for P-No.4 materials in various Construction Codes, such as ASME B31.1, Sec. I and Sec. VIII, except Sec. III have been unified and the minimum PWHT temperature became 649°C (120°F) since 2004 edition. When considering the mechanical properties of the weld, the minimum PWHT temperature of 593°C or that of P No. 4 materials in Sec. III is too low to reduce hardness and to increase toughness. When PWHT is performed on dissimilar material joints (e.g., between P-No.1 or P-No. 3 and P-No. 4) at 649°C (1200°F) in accordance with Sec. VIII etc., it is possible that the strength of the lower P-No. materials is decreased below the design strength because the PWHT temperature will exceed the tempering temperature of the lower P-No. materials. In this study, the cases of system hydrostatic test in UC-3, 4 units and Steam Generator Nozzle to feedwater pipe joint in Korea Standard Nuclear Power Plants (e.g., UC-3, 4 units, YK-3, 4 units and YK-5, 6 units) were reviewed and analyzed. And then problems of two cases were presented. It is suggested that the minimum system hydrostatic test pressure in Sec. III NC, ND should be decreased by the reduction rate of test pressure for components and the minimum PWHT temperature for P No. 4 materials in Sec. III should be 630°C (1166°F).

Copyright © 2007 by ASME

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