Insidious hazards – Fatigue, creep and brittle fracture

ANSYS simulation of a fatigue analysis of a high pressure heat exchanger subject to thermal transients

Cyclic fatigue is a hazard to any component subject to cyclic thermal and/or pressure loadings. Qualification for cyclic loading is performed using the guidelines of ASME Section III Subsection NB-3222.4 which provides the methodology (Miner’s rule) to compute the cumulative damage factor for components subject to a large number of dissimilar cyclic loadings.

Creep is a concern in pressure vessels operating at elevated temperatures such as liquid sodium reactors. The service life of creep-constrained designs is, of necessity, limited by the amount of permissible creep. The ASME code provides a methodology for computing cumulative creep that the Company has used in certain applications.

Long term settlement of a soil foundation under load is an example of ambient temperature creep. Our methodology for subgrade settlement has been approved by NRC.

Brittle fracture is a concern in thick walled pressure vessels and weldments subjected to thermal or mechanical shock loadings. The ASME Code contains restrictions and required testing to qualify materials for applications vulnerable to brittle fracture.