Fatigue Crack Growth Behavior in Pipes and Elbows of Carbon Steel and Stainless Steel Materials

Abstract

Abstract The objective of the present study is to understand the fatigue crack growth behavior and validate analytical procedures for austenitic stainless steel and carbon steel pipes, pipe welds and elbows. The study involved fatigue tests on actual components and specimens. The Paris law has been used for the prediction of fatigue crack growth life. Paris constants have been determined for pipe (base), pipe weld and pipe elbow materials by using Compact Tension (CT)/Three Point Bend (TPB) specimens machined from the actual pipe, pipe weld and pipe elbow. Analyses have been carried out to predict the fatigue crack growth life of these piping components having part through cracks on the outer surface. In the analyses, Stress Intensity Factor ( K ) has been evaluated through two different schemes. The first scheme considers the ‘ K’ evaluations at two points of the crack front i.e. maximum crack depth and crack tip end at the outer surface. The second scheme accounts for the area averaged root mean square stress intensity factor (KRMS) at deepest and surface points. In order to validate the analytical procedure/results, experiments have been carried out on full scale pipes, pipe welds with part through circumferential crack. The tests have also been conducted on the full scale carbon steel elbows having part-through circumferential notch at intrados location and axial notch at crown location on the outer surface. Fatigue crack growth life evaluated using both schemes have been compared with experimental results. Use of stress intensity factor (KRMS) evaluated using second scheme gives better fatigue crack growth life prediction compared to that of first scheme.