doi: 10.1111/j.1460-2695.2011.01589.x Assessing the accuracy of fatigue life in surface-cracked straight pipes S. SAXENA Advanced Materials and Processes Research Institute (AMPRI), Bhopal 462026, India Received in final form 14 March 2011 ABSTRACT The demonstration of leak before brake (LBB) based on fracture mechanics requires information on the initial size of a defect, initiation of crack growth from the inherent defect and subsequent crack growth rates. In the present paper the prediction methodolo- gies have been tested for three different full scale pipes geometry experimentally tested data. The prediction accuracy of two SIF solutions available in the literature has also been judged. The effect of fatigue crack closure and corrections needed in the numerical prediction methodology using FEM have also been included. The results showed that the FEM could fairly predict the fatigue crack initiation and crack growth life of full-scale piping components having a constant depth crack profile. Keywords crack growth; cracked pipes; fatigue loading; finite element analysis; stress intensity factor. INTRODUCTION Failure of piping components under normal operating conditions well below the allowable stress given by codes can often be due to flaws. Crack-like defects could de- velop at the manufacturing/installation stage or it could develop as a result of continued operation, with cyclic loading and material deterioration being the two major causes for defect initiation and propagation. 1 This neces- sitates detailed flaw evaluation of different piping compo- nents such as straight pipes, elbow and branch tees. In the primary heat transporting system of power plants, piping components are subjected to high stresses due to temper- ature fluctuations, vibration, etc. Based on the results of investigations of failures conducted by Nishida and his co-operating researchers, failures are generally caused di- rectly or indirectly by fatigue. 2 Such failures show that conventional stress analysis is not sufficient to guarantee component integrity under operational condition. Design criteria for the prevention of fatigue failure have evolved from the concept of almost infinite life to the present- day fail-safe design philosophy. Therefore, fail-safe design criteria such as leak-before-break (LBB) based on frac- ture mechanics concepts are being adopted. An impor- tant consideration in this methodology is the selection of materials with high fracture toughness. This design crite- rion requires the demonstration of integrity of the piping Correspondence: S. Saxena. E-mail: san_bpl@yahoo.com system by showing that unstable crack growth will not oc- cur before a crack penetrates the wall thickness, nor will it occur for a through-wall leakage size flaw. The demon- stration of LBB design criteria requires information on the size of initial defects, initiation of crack from the in- herent defect and subsequent propagation rate of the initi- ated crack till the crack penetrates the wall thickness under fatigue loading. Thereafter, the crack will grow in the cir- cumferential direction under cyclic loading till the accept- able leakage size flaw yields the detectable leakage rate. 3 Therefore, various tests are required for the determina- tion of fatigue crack initiation, fatigue crack growth and fracture resistance behaviour of the components. Simulta- neously, efforts are also required to improve and simplify the prediction procedure with increasing the reliability of these prediction procedures. This requires continu- ous efforts of numerical prediction of components fatigue behaviour and its validation with experimentally tested component data of crack initiation and crack growth be- haviour. The work will be useful to improve the remaining life of the components used in older nuclear power plants and also to assess its remaining life for the further continu- ous use. Piping components fatigue behaviour is generally evaluated by conducting experiments and its prediction using available numerical techniques. Fatigue crack initiation has been studied in the past us- ing notched small specimens by evaluating local stress or strain at the notch tip considering the stress or strain concentration, equivalent energy density method and c  2011 Blackwell Publishing Ltd. Fatigue Fract Engng Mater Struct 34, 1003–1011 1003 Fatigue & Fracture of Engineering Materials & Structures