Fitness of service assessment of a pressure vessel with crack-like flaws

• Main Authors: Lin-ya Wang, 王鈴雅
• Other Authors: Chen-hua Wang
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/82273277900717056519

碩士 === 國立高雄第一科技大學 === 環境與安全衛生工程所 === 96 === For all kind of reasons, flaws may happen and are mostly difficult to detect during the life span of a piece of process equipment.When flaws are found upon a pressure vessel, people would take it for granted and anticipate that flaws be not just inspected but also assessed. In fact, plants do have scheduled plan for non-destructive testing equipment, but a majority of plants lack of the capability to assess flaws other than general metal loss to the vessel wall. Furthermore, there are de facto standards for designing pressure vessels, but rarely do we see a widely recognized technical standards regarding aging equipment with defects or flaws on vessel wall. Crack analysis is extremely sophisticated due to the fact that yielding occurs at the crack tip while other portion remains elastic.Literature reviews show that for smaller cracks, linear elastic fracture mechanics (LEFM) is most often utilized for modeling and simulating the stress field around the crack surface and the crack tip. However, only planner cracks of simple geometry can be computed, which is far from practical at for for plant use. In addition, the mechanics problems become much cumbersome for special locations such as the weld and discontinuities. All these make the stress analysis of a crack almost impossible. Fitness for service (FFS) receives growing attention lately in Japan, Europe, and the United States.What FFS provides is a standardized approach toward assessment of the remaining strength and thus the acceptance for continual service.Based on LEFM, a plant can evaluate a crack, and make decision on whether the equipment has enough strength for further use. In this thesis, several case studies were utilized for comparing results among the fitness for service, LEFM, and numerical methods.Results from FFS are quite closed to those from using the finite element method. Also, a computer program for level 1 and level 2 was written to test out the feasibility of web-based analysis and diagnosis environment.