Recent advances in curved wide plate testing and implications for strain-based design

The wide plate test has been used for about a half century to assess the structural significance of weld defects. Early work mostly utilized plate specimens, but within the last 20 years the curved wide plate test (CWPT) has become popular for pipeline girth weld testing. Even more recently, the CWPT has been used to measure girth weld strain capacity for strain-based design applications. Considering that the wide plate test was not originally intended for assessment of structures loaded well into the plastic regime, it is appropriate to consider improvements and new approaches that may be applicable to high strain applications. This paper presents recent CWPT results on X80, X100, and X120 girth welds. A non-contact photographic measuring system was used to quantify surface strains. Finite element analysis (FEA) was used to optimize specimen geometry by increasing specimen length-to-width ratio which suppresses premature strain localization in the pipe body. This is particularly useful for testing high strength steels. Unloading compliance in combination with FEA was used to assess crack growth. Compliance transfer functions were developed and tearing resistance was quantified using the CWPT. It was found that tearing can initiate at low levels (similar to 0.5%) of plastic strain. Welds with high tearing resistance are useful for strain based design applications.