关键词: 合于使用评价, 裂纹类缺陷, 超高压容器, 设计, 疲劳分析

Abstract: Fitness-for-service (FFS) assessment is usually used to evaluate the residual strength or residual life of in-service pressure vessels with defects; for ultra-high pressure vessels, due to the high stress level in the shell and the relatively poor plasticity reservation of the material, any small defects or artificial damages on the inner wall are hidden dangers for fatigue failure. Hence fatigue failure is one of the failure modes that must be taken into consideration in the design of ultrahigh pressure vessels. If the ultra-high pressure vessels cannot fail in the mode of leakage before burst, the number of design cycles should be calculated according to the method of fracture mechanics. Therefore, the FFS assessment method should be introduced in the design stage to determine the allowable final crack depth. The FFS assessment method of API 579 has become one of the most widely used methods in the evaluation of pressure vessels with crack-like flaws. The crack-like flaws of ultra-high pressure vessels can be evaluated with level 2, including 12 steps. Finally, based on the failure assessment diagram (FAD), it can be determined whether or not a given crack and operating conditions are acceptable.

Key words: fitness-for-service assessment, crack defects, ultra-high pressure vessel, design, fatigue analysis