表面亀裂開口変位による大径鋼管の脆性破壊発生特性の評価

概要

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The brittle fracture initiation from the surface crack in the large diameter pipe subjected to inner pressure is treated from the practical point of view. The crack opening stretch model is applied to the surface crack and the ligament of the crack is subjected for the crack closure force. The hydrostatic tests are carried out for two kinds of pipes. One is a heavy wall and large diameter pipe, API 5 L X70 grade, 940mm in outer diameter and 39.2mm in wall thickness. Another is a relatively thin wall and small diameter pipe. API 5 L X 65 grade, 508mm in outer diameter and 12.7mm in wall thickness. The test pipes have various notches, which are machined by electrical discharge. And the crack closure force is experimentally determined from the notch tip COD, which is directly measured by the clip gage installed on the center of the notch tip, by use of the Dugdale Model with regard to the bulging factor for the pipes. Consequently crack tip COD of the surface crack center is calculated by the proposed crack opening stretch model. And corresponding to the defect size, the required fracture toughness to prevent the brittle fracture initiation from the surface crack of the pipes subjected to inner pressure is estimated.
社団法人日本船舶海洋工学会の論文