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 origins of fatigue crack growth, which may cause serious failure of the whole structure. An analysis of crack growth and penetration behaviour from these defects may therefore be one of the most important subjects on the reliability of the LBB (leak before break) design philosophy. However, studies on fatigue crack growth and COD (crack opening displacement) behaviour in a complex through-wall crack are relatively rare. To that purpose, a series of fatigue tests has been carried out at room temperature on carbon steel pipe which has an inner surface crack. Before crack penetration, leak-life, fatigue crack growth behaviour, e.g. aspect ratios and da/dN versus Delta K were evaluated successfully by using a proposed plate model. After crack penetration, a new formula to evaluate K is proposed. For the complex crack created after through-wall penetration, fatigue life and fatigue crack growth behaviour were evaluated quantitatively by using the new formula and the model proposed in this study.