周方向表面亀裂を有する管の塑性崩壊強度に及ぼす亀裂面に作用する圧力の影響評価

抄録

The Rules on fitness-for-Service of Japan Society of Mechanical Engineers (the rules on FFS) sets up the limit load evaluation method based on the plastic collapse strength as one of the fracture evaluation methods for pipes with circumferential flaws. However, since it is an evaluation method that is not limited to the position in the thickness direction of the flaw, the internal pressure acting on the flaw surface is not taken into consideration even when the flaw is on the inner surface of the pipe. In the pipes that constitute the pressure boundary, the impact of internal pressure on plastic collapse strength is negligible excepting for cases of inner surface flaws. The limit load evaluation methods that take into account the effect of the internal pressure acting on the flaw surface are derived, and compared the plastic collapse load with and without considering the internal pressure acting on the flaw surface. When the flaw is shallow and the angle is small, the plastic collapse load is almost the same even if the internal pressure acting on the flaw surface is taken into consideration. However, when the flaw is deep and the angle is large, the plastic collapse load decreases due to the internal pressure acting on the flaw surface. Especially when the internal pressure is high, the effect is large. In the rules on FFS, the flaw depth is limited by a regulatory requirement when the flaw angle exceeds 60 degrees, so the effect of the pressure acting on the flaw surface on the plastic collapse strength is small. However, if this flaw depth limitation is to be abolished in the future, to change the evaluation formula for plastic collapse strength will be proposed so as to take into account the effect of pressure acting on the flaw surface.