The concerns about Fitness-For-Service (FFS) assessment technique for pressure equipments with local metal loss have been growing from some characteristic damages, for example, many examples of the corrosion under insulation (CUI) of pressure equipment, have been reported from petroleum and petrochemical industries. FFS assessment procedure for the pressure equipments for metal loss has been validated by the results of various burst tests and FEM simulations for internal pressure loads.
There has, however, been little study to validate FFS assessment for pressure equipments subjected to seismic load. This paper suggests an FFS assessment procedure for pressure equipments with local metal loss subjected to both internal pressure and seismic loading. To ensure consistency to High Pressure Gas Law in Japan, allowable stress is based on the Japanese seismic design code. Developed stress on local metal loss from both internal pressure and seismic load is evaluated in accordance with API 579/ASME FFS-1.
The authors have verified safety margin and reliability of this method to toward to practical application. In order to verify, some cyclic bending load testings and finite element analysis were implemented under the conditions of ambient temperature and 300 degree C. The results of these validations show that the safety margins against low cycle fatigue are the range of 2.6 to 4.6. In addition, the test results at 300 degree C showed higher safety margin than that in ambient temperature.