Stress Intensity Factor Solutions for Surface Cracks in a Cylinder in HPIS Z101 Level 2

The High Pressure Institute of Japan published the first edition of Fitness for Service assessment procedure, HPIS Z101, in 2001. The current assessment procedure contained only Level 1 version, in which the structural integrity of flawed pressure vessels and piping systems is evaluated using Charpy absorbed energy and allowable flaw size. Z101 is currently revised and updated including the addition of Level 2 version. In the Level 2 assessment procedure, the structural integrity of flawed pressure vessels and piping systems is going to be evaluated by means of a two parameter method. The two parameter method requires evaluation of fracture ratio Kr and a ratio of applied load and yield load Lr, respectively. Kr is calculated as a ratio of stress intensity factor to fracture toughness and Lr is calculated as a ratio of reference stress to yield stress. Z101 Level 2 assessment procedure, therefore, should provide stress intensity factor (SIF) solutions and reference stress solutions. This paper describes SIF solutions that are going to be adopted in Z101 Level 2 assessment procedure. SIF values of semi-elliptical cracks in a cylinder were calculated using existing FFS codes such as API579 and R6, and these values were compared. It was found by the comparison that the two codes gave almost the same SIF when the ratio of crack depth and thickness a⁄t is equal to or greater than 0. 2 but gave different SIF when a⁄t is equal to 0. Since SIF values at a⁄t=0 calculated by R6 showed good agreement with those by Z101 Level 1 solutions, R6 solutions for semi-elliptical cracks in a cylinder were adopted as the SIF solutions in Z101 Level2. For extended axial cracks and fully circumferential cracks in cylinder, API579 and R6 gave almost the same SIF values. Since API579 provides SIF solutions for broad range of inner radius to thickness ratio, API579 solutions for extended axial cracks and fully circumferential cracks in cylinder were adopted as the SIF solutions in Z101 Level2.