Japanese Code for Assessment Procedure for Crack-like Flaws in Pressure Equipment

There are numerous instances in which in-service flaws due to various kinds of damage and deterioration are found in equipment as a result of in-service inspections. The proper evaluation of such flaws is extremely important. Fitness-for-Service (FFS) codes, such as ASME B&PV Code Sec. XI and JSME S NA1 for nuclear power generation facilities and BS 7910 and API-RP579 for general industrial facilities, are available. In light of such circumstances, the High Pressure Institute of Japan (HPI) has prescribed its code “Assessment procedure for crack-like flaws in pressure equipment” for conducting quantitative safety evaluations of flaws detected in common industrial pressure components such as pressure vessels, piping, storage tanks, and so on designed and fabricated in accordance with Japanese codes and regulations such as JIS B8265 and High Pressure Gas Safety Law. The FFS code consists of Level 1 assessment (whereby assessment can be conducted without extensive knowledge of fracture mechanics) and Level 2 assessment (which enables more detailed fracture mechanics analyses and is currently being studied). The allowable flaw size is specified in accordance with the plate thickness. The required impact absorbed energies based on material strength, whether or not PWHT has been done and the orientation of the flaw in relation to the weld seam, are also specified. An approximated equation of stress intensity factor for an embedded flaw near the surface has been derived. The re-characterization procedure for assessing an embedded flaw has been clarified. The flaw can be judged to be acceptable if its size is less than that of an allowable flaw and the equipment is to be used at temperatures exceeding the temperature (MAT) at which the material absorbed energy meets the required impact absorbed energy.