Stress intensity factors for fatigue analysis of weld toe cracks in a girth-welded pipe

• A methodology to study weld toe magnification factors in welded pipes is proposed.
• Based on J-integral evaluation by the finite element method for girth-welded pipes.
• Empirical equations to predict Mk-factors developed by curve-fitting results.
• Prediction of fatigue crack growth in pipes using derived SIFs and Mk-factors.

This paper addresses the lack of three-dimensional stress intensity factor solutions for small to large surface cracks located at the weld toe region of welded pipes. A methodology was developed to model and calculate the stress intensity factors and weld toe magnification factors for semi-elliptical surface cracks in a circumferentially welded pipe. Three-dimensional finite element models were developed for a wide range of surface crack geometries. The stress intensity factors for surface cracks in a plain pipe were benchmarked with reported results and showed good agreement to within 2.6%. Stress intensity factors and weld toe magnification factors solutions were determined for weld toe surface cracks located at a circumferentially welded pipe. The weld toe semi-elliptical surface cracks geometries vary from small crack depth-to-thickness (a/ta/t) ratios of 0.05 to large crack depth-to-thickness (a/ta/t) ratio of 0.5. Three semi-elliptical surface crack shape aspect ratios (a/ca/c) were modelled for values of 1.0, 0.5 and 0.25. The stress intensity factor and weld toe magnification factors solutions are reported in this paper for a wide range of semi-elliptical surface crack geometries with crack depth-to-thickness ratios (a/ta/t) from 0.05 to 0.5 and crack shape aspect ratios (a/ca/c) from 0.25 to 1.0 subject to pipe wall tension and bending loading. The stress intensity factor and weld toe magnification factors solutions are used for fatigue crack growth prediction assessment of weld toe surface cracks propagating in a circumferentially welded pipe.