scope:

Part 1: Effect of Loading and Stress-Strain Curve on Stress Intensification Factors

Part 2: Investigation of Criteria Where Piping Pystem Analysis is Not Required by ASME Piping Codes B31.1 and B31.3

Stress Intensification Factors (SIFs) were first used in the design of piping systems in 1955 when they were incorporated into the B31 Piping Code. These SIFs were based on a series of fatigue tests on various piping components performed by Markl and George. The tests that were performed utilized cantilever bending loading.

Later testing, which was based on 4-point bending loading, yielded different results than predicted based on Markl's work. This suggested that the results were dependent upon the method of loading.

The objective of PART1 is to investigate the impact of the method of loading on the resultant SIF. Specifically the ratio of the SIF based on cantilever loading to that based on four-point loading is studied. Both low cycle and high cycle failures are investigated. The study indicates that the cantilever method is conservative particularly in the low cycle regime.

B31.1 and other piping Codes provide criteria, which if satisfied, exempt a piping system from the requirement for detailed or rigorous piping system flexibility analysis. This criteria applies to piping systems in which the piping is of uniform size, has only two anchors and no intermediate restraints, and less than 7000 operating cycles. The criteria are specified as equations that are a function of nominal dimensions, displacements, movements to be absorbed, etc. PART 2 investigates the background of the criteria, the various criteria equations, the associated "warnings" and the accuracy of the criteria equations