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Strain Rate of Pipe Elbow at Seismic Event and Its Effect on Dynamic Strain Aging

[+] Author Affiliations
Hiroe Kobayashi

Ishikawajima-Harima Heavy Industries Company, Ltd., Yokohama, Japan

Yoshio Urabe

Mitsubishi Heavy Industries, Ltd., Hyogo, Japan

Yasuhide Asada

Thermal and Nuclear Power Engineering Society, Tokyo, Japan

Paper No. PVP2005-71443, pp. 371-378; 8 pages
doi:10.1115/PVP2005-71443
From:
  • ASME 2005 Pressure Vessels and Piping Conference
  • Volume 1: Codes and Standards
  • Denver, Colorado, USA, July 17–21, 2005
  • Conference Sponsors: Pressure Vessels and Piping Division
  • ISBN: 0-7918-4186-3 | eISBN: 0-7918-3763-7
  • Copyright © 2005 by ASME

abstract

NRC expressed their refusal of revised seismic stress criteria for piping systems of the ASME Section III, 2001 Edition at their proposed rule making by 10CFR50.55a. One of technical bases of their refusal is “Dynamic strain aging of carbon steel at high strain rate caused by earthquake and at high temperature condition of nuclear power operation”. This paper presents that the effect of dynamic strain aging at the allowable stress limit is practically negligible small even if the seismic allowable stress for nuclear piping increases up to 150% at ASME Section III 2001 and 2003 Edition from 3.0Sm (ASME Section III 1995 Edition). This seismic stress limit revision was achieved by using the B′2 that is equal to 2/3 B2 instead of B2 stress index in Equation of ASME Section III NB-3656 at seismic stress evaluation. At first, maximum elastic-plastic strain of pipe elbow was calculated at various stress level up to revised allowable stress limits by using the elastic-plastic FEM which was verified by the comparison with experimental results. Obtained strain was converted to strain rate by introducing the dominant frequency of piping system at seismic events. Secondary, data of relationship of strain rate and yield to tensile stress ratio for various type of carbon steel was collected. The yield to tensile stress ratio at very low strain rate was compared with that at strain rate of seismic event. The value of yield to tensile stress ratio at strain rate of seismic event was also evaluated. Finally, effect of maximum strain rate at seismic event under revised stress limit condition was discussed by evaluating the change of the yield to tensile stress ratio at low and seismic event condition and the value of the yield to tensile stress ratio at seismic event. From this discussion, dynamic strain aging would not occur in carbon steel piping at seismic event and high temperature condition under revised stress limit condition.

Copyright © 2005 by ASME
Topics: Pipes , Earthquakes

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