Focusing on strain-based design conditions, mismatched strength properties of the girth weld or the HAZ areas can cause local strain concentration. To evaluate the behavior of such heterogeneous welds under fully contained yielding conditions, this paper investigates the influence of different weld configurations and (yield and tensile) strength mismatch conditions on the strain distribution and constitutive behavior of the weld metal in a cross weld specimen. This investigation is merely based on finite element simulations complemented with some example data of strain field measurements. The results indicate that the current widely used yield strength mismatch concept is not sufficient to evaluate the strain capacity of a defect-free weldment.
In the past, most of the pipelines have been designed within a stress-based context. This resulted in a safe construction as the critical load was merely determined by the maximum stress, e.g. due to internal pressure, and was not allowed to exceed a fraction of the specified minimum yield strength. However, the increasing demand for fossil fuels requires to access natural gas and oil reserves located in more challenging, harsh environments (e.g. permafrost, landslides, …). Possible large deformations imposed on the pipelines by the environment, contrast the fundamentals of a stress controlled loading condition. Therefore, a traditional stress-based design can no longer assure pipeline integrity. A more relevant approach, the so-called strain-based design, assesses pipeline integrity under displacement (strain) controlled loading conditions and is therefore more suitable for assessing pipelines subjected to large deformations. It is widely acknowledged that weld metal strength overmatch is beneficial in a strain-based design context since it shields possible defects from plastic strain by locking the plasticity in the weaker base metal (Wang, Liu et al. 2006; Denys, Hertelé et al. 2010; Kibey, Wang et al. 2010; Macia, Kibey et al. 2010).
