Tensile Strain Capacity Equations for Strain-Based Design of Welded Pipelines

Abstract

Various industry efforts are underway to improve or develop new methods to address the design of pipelines in harsh arctic or seismically active regions. Reliable characterization of tensile strain capacity of welded pipelines is a key issue in development of strain-based design methodologies. Recently, improved FEA-based approaches for prediction of tensile strain capacity have been developed. However, these FEA-based approaches require complex, computationally intensive modeling and analyses. Parametric studies can provide an approach towards developing practical, efficient methods for strain capacity prediction. This paper presents closed-form, simplified strain capacity equations developed through a large-scale 3D FEA-based parametric study for welded pipelines. A non-dimensional parameter is presented to relate the influence of flaw and pipe geometry parameters to tensile strain capacity. The required input parameters, their limits of applicability and simplified equations for tensile strain capacity are presented. The equations are validated through a comprehensive full-scale test program to measure the strain capacity of pressurized pipelines spanning a range of pipe grades, thickness, weld overmatch and misalignment levels. It is shown that the current simplified equations can be used for appropriate specification of weld and pipe materials properties, design concept selection and the design of full-scale tests for strain-based design qualification. The equations can also provide the basis for codified strain-based design engineering critical assessment procedures for welded pipelines.

Engineering critical assessment for a sandwich pipe field joint

“…taking into account the effect of biaxial loading, yield stress mismatch and misalignment. Using largescale 3D FEA-based parametric studies, in (Kibey et al, 2010) closed-form strain capacity equations were derived, which were then utilised for strain based design ECA procedures for welded pipelines.…”

“…In response to the geometric limitations of the stress intensity factor and reference stress solutions as documented for pipe joint types in recommended practice standards, finite element fracture mechanics methods have been long utilised to capture the stress state for different combinations of (Arun et al, 2014, Kibey et al, 2010, Bell et al, 1985. In addition, it is used to confirm the validity and hence conservatism of analytical procedures (Bjerke et al, 2011).…”

Investigation of strain measurements in (curved) wide plate specimens using digital image correlation and finite element analysis

“…Note that some LVDTs exceed the assumed potential area of uniform strain (0 mm \ z 45°\ 100 mm). Longer LVDTs have also been considered since they produce signals with a lower relative measurement error, due to the denominator GL 0 in equation (2). In the absence of other considerations, they are therefore preferred over smaller LVDTs.…”

“…This is reflected in the absence of residual stresses in numerical analyses that led to different existing strain capacity prediction equations, e.g. Kibey et al 2 and Østby.…”

“…For pipelines that have to withstand global plastic deformations, a widely validated and standardized procedure for the assessment of girth weld flaws is inexistent 1,2 and an extensive testing program remains essential for the qualification of pipe and weld design. Typically involved is the curved wide plate (CWP) tension test, which can be described as an intermediatescale tensile test on an unflattened sample of a pipeline section containing a girth weld (Figure 1(a)).…”