EFFECTS OF OFF-CENTERED CRACKS AND RESTRAINT OF INDUCED BENDING CAUSED BY PRESSURE ON THE CRACK-OPENING-AREA ANALYSIS OF PIPES

Current models for the crack-opening-area analysis of pipes with circu mferential through-wall cracks are based on various idealizations or a ssumptions which are often necessary to simplify the mathematical form ulation and numerical calculation. This paper focuses on the validity of two such assumptions that involve off-centered cracks and the restr aint of induced bending caused by pressure, and quantifies their effec ts on the crack-opening area analysis of pipes. Finite element and/or simple estimation methods were employed to compute the center-crack-op ening displacement and crack-opening shape for a through-wall-cracked pipe, considering off-centered cracks and the restraint of induced ben ding caused by pressure. The results of the analyses show that, for bo th cases, the crack-opening area can be reduced significantly. For pip es with off-centered cracks, the crack-opening area can be evaluated f rom analyses of symmetrically centered cracks and assuming elliptical profile. For pipes with complete restraint of the induced bending caus ed by pressure, the reduction in crack-opening area depends on the cra ck size. When the crack size is small, the restraint effects can be ig nored. However, when the crack size is large, the restrained crack ope ning can be significantly smaller than the unrestrained crack opening, depending on the length of pipe involved; hence, it may be important for the crack-opening-area and leak-rate analyses.