Prediction for plastic collapse stresses for pipes with inner and outer circumferential flaws

内外周方向欠陥を有する管の塑性崩壊応力の推定

長谷川 邦夫; Li, Y. ; Mare, V.*; Lacroix, V.*

Hasegawa, Kunio; Li, Y.; Mare, V.*; Lacroix, V.*

周方向の表面欠陥を有する管の曲げによる塑性崩壊応力はASME Code Section X Appendix C-5320の式により推定される。この式は、管の内外表面欠陥に適用される。著者らは欠陥部分の管の平均半径を考慮し、内外表面欠陥を有する管の塑性崩壊応力式を導いた。その結果、外表面欠陥を有する管の塑性崩壊応力はAppendix Cの式から得られる応力より小さく、内表面欠陥の応力はAppendix Cの応力より大きいことを見出した。

Appendix C-5320 of ASME Code Section XI provides a formula of bending stress at the plastic collapse, where the formula is applicable for both inner and outer surface flaws. Authors considered the separated pipe mean radii at the flawed ligament and at the un-flawed ligament and formulas of plastic collapse stresses for each inner and outer flawed pipe were obtained. It is found that the collapse stress for inner flawed pipe is slightly higher than that calculated by Appendix C-5320 formula, and the collapse stress for outer flawed pipe is slightly lower than that by Appendix C-5320 formula. The collapse stresses derived from the three formulas are almost the same in most instances. For less common case where the flaw angle and depth are very large for thick wall pipes, the differences among the three collapse stresses become large.