Scale Effects: Correlation of Fatigue Capacity for Full-Scale Pipes and Samll-Scale Specimens

Increasing a component’s size is known to have detrimental effect on the fatigue performance. To account for this, reduction factors are given in several design codes. Away from plate products, there is no general consistency between the various correction procedures. The main causes of the scale effects can be divided into three phenomenon: Statistical effects (probability for defects that initiate cracks), technological effects (differences in material and production procedures for large and small components), and stress gradient effects (scaling differences for stress level for (small) cracks). In this paper the main factors influencing the scale effect is reviewed and correction rules are discussed. Fatigue data for 30” and ID6” pipes with girth welds are analysed and compared with medium sized sector specimens cut out from pipes. Also effects of weld quality and pipe alignment (hi/lo and angular distortion) in this context are discussed. On this basis, recommendations for applying the scale correction procedures for welded pipes are proposed.