Circumferential inner fatigue crack growth and penetration behaviour in pipe subjected to a bending moment

Surface defects in most pipe components under cyclic stress tend to be orig ins of fatigue crack growth, which may cause serious failure of the whole s tructure. An analysis of crack growth and penetration behaviour from these defects may therefore be one of the most important subjects on the reliabil ity of the LBB (leak before break) design philosophy. However, studies on f atigue crack growth and COD (crack opening displacement) behaviour in a com plex through-wall crack are relatively rare. To that purpose, a series of f atigue tests has been carried out at room temperature on carbon steel pipe which has an inner surface crack. Before crack penetration, leak-life, fati gue crack growth behaviour, e.g. aspect ratios and da/dN versus Delta K wer e evaluated successfully by using a proposed plate model. After crack penet ration, a new formula to evaluate K is proposed. For the complex crack crea ted after through-wall penetration, fatigue life and fatigue crack growth b ehaviour were evaluated quantitatively by using the new formula and the mod el proposed in this study.