Fatigue and fracture studies on carbon and stainless steel pipe welds and elbows
Experimental investigations were carried out on 168 mm and 324 mm outer diameter pipes and elbows made of SA 333 Gr. 6 carbon steel and Type 304LN stainless steel used in power plant industry to demonstrate the Leak-Before-Break (LBB) design criterion. Fatigue crack growth studies were carried out on pipes with circumferential outer surface notch at base metal, weld metal and heat affected zone under cyclic loading in air and water environments, vibration loading, and combined torsion and bending in air environment and elbows with circumferential outer surface notch, axial notch and without notch in air environment under in-plane bending moment. Beach mark loading technique was introduced during fatigue tests to validate the crack depth measurement using ACPD technique. Number of cycles for crack initiation, fatigue crack propagation and fatigue life (through-wall crack) were observed under various loading and environmental conditions for straight pipes and elbows.
