B-2123.1 Service Limits A and B(a) For Class 1, MC, and CS components and for Class 2 vessels designed to NC-3200, Service Limits A and B are provided in order to evaluate the effect of system operating loads on the fatigue life of the component. For a fatigue analysis the loads applicable to the component being considered should be described in terms of quantities that the designer may use [NB-3222.4(e)]. The variation with respect to time of pressure, temperature, flow rate, etc., as well as the number of times these changes occur in the life of the component, is needed. In this regard, a service cycle is defined in NB-3213.15 as: . . . the initiation and establishment of new conditions followed by a return to the conditions which prevailed at the beginning of the cycle. Thus, as an example, the conditions associated with plant startup do not constitute a service cycle. Startup and shutdown together constitute a service cycle, and if there are n1 start-ups in the Design Specification, there should be the same number of shutdowns

Service Limit C. Service Limit C is provided in order to evaluate the effect of plant operating loads on the structural integrity of a component for situations which are not anticipated to occur for a sufficient number of times to affect fatigue life and for which large deformations in 202 areas of structural discontinuities are not objectionable. Since the occurrence of stress associated with this Limit may result in removal of the component from service for inspection or repair, the Owner should review the selection of this Limit for compatibility with established system safety criteria. Refer to NB-3113(b) and NH-3113.5 for the limit of number of cycles. B-2123.3

Service Limit D. Service Limit D is provided in order to evaluate the effect of plant operating loads on the structural integrity of a component for situations in which gross general deformations, loss of dimensional stability, and damage requiring repair, excluding loss of pressure retaining function, are not objectionable. Since the occurrence of stress associated with this Limit may require removal of the component from service, the Owner should review the selection of this Limit for compatibility with established system safety criteria.