Some observations on fatigue crack initiation and growth in carbon steel elbows

Piping components such as tees and elbows used in the primary heat transpor t system of power plants undergo stress fluctuations due to operational and extreme loading conditions. Crack initiation and through-thickness lives o f piping components are of primary concern in the justification of Leak Bef ore Break methodology for the design of piping components. Two full-scale c arbon steel (SA333 Gr6) elbows of 406 mm outer diameter were tested under c onstant amplitude cyclic loading. Crack initiation and crack growth were mo nitored using NDT equipment. The fatigue tests on the two elbows show that the inner surface of the elbows at the crown points is the vulnerable locat ion for the occurrence of fatigue cracks. It was also observed that more th an one crack grows simultaneously at the crown point of the elbows.