Use of API 579-1/ASME FFS-1 Limit-Load Criteria for Establishing Load Limits for Pressure Vessel Internals Available to Purchase

The 2007 edition of ASME Boiler & Pressure Vessel Code Section VIII Division 2 and the 2007 edition of Fitness-For-Service API 579-1/ASME FFS-1 provide the option to use the limit-load method to assess protection against plastic collapse for components of pressurized process equipment. Per the methodology presented therein, the allowable load on a component is established by applying design factors to the elastic-perfectly plastic limit-load such that the onset of gross plastic deformation (plastic collapse) will not occur. Typically, the design limitations of pressure vessel internal components have been assessed through closed form solutions with conservative assumptions. It has been found that the maximum pressure delta across vessel internals established through closed form solutions can become limiting in determination of time between equipment shutdowns. This paper will outline a practical example of industry applied use of the limit-load method to qualify extended limits on mechanical loads applied to pressure vessel internals.