Engineering approach for circumferential flaws in girth weld pipes subjected to bending load Marcelo Paredes a, * , Claudio Ruggieri b a Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, USA b Department of Naval Architecture and Ocean Engineering, University of Sao Paulo, Av. Prof. Mello Moraes 2231, Sao Paulo, SP 05508-030, Brazil article info Article history: Received 18 May 2014 Received in revised form 9 September 2014 Accepted 16 September 2014 Available online 23 September 2014 Keywords: Girth weld pipes EPRI methodology Weld strength mismatch J integral CTOD abstract The current investigation pursues extending the applicability of fully plastic solutions for J-integral and crack-tip opening displacement (CTOD), originally cataloged in a series of handbooks (also known as EPRI handbooks), in defective girth weld pipes subjected to bending load for a wide range of surface crack dimensions and weld strength mismatch levels. The suitability of the given set of solutions in this work is constrained by a certain number of parameters that are derived from the coupled effect of weld strength mismatch and configurational effects upon near-tip stress-strain fields in heterogeneous media. These results reveal a weak dependence of coupled effect of weld strength mismatch and weld groove size upon crack driving force, when the ratio of the mismatch between weld and base normalizing stresses is considered moderate (1.3), whereby the proposed estimation method becomes essentially valid for failure assessment procedures and fitness-for service (FFS) evaluations. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction The flaw acceptance criteria for girth weld pipes are derived from the Engineering Critical Assessment (ECA) procedures. They represent a critical step into design and safety operation of piping systems, including nuclear power plants, oil and gas transmission pipelines and marine risers. However, common failures in pipeline infrastructure result primarily from crack-like surface flaws (either internal or external flaws) that often occur in the weld metal and heat affected zone (HAZ) [1e3]. A major concern in integrity as- sessments of circumferential flaws in field girth weld pipes is the high level of axial stress present in the crack, even if the internal pressure is relatively low. The most common loading condition comes from soil and ground movements, severe thermal gradients or exhaustive service rate, and installation-induced forces. Struc- tural components falling into this category are deep water steel catenary risers that are installed by the reeling method. This method allows pipe welding and inspection to be conducted at onshore facilities [4,5]. Then, the welded pipe is coiled around on an onboard large reeling drum and subsequently, it is transported to the exploration area where, is unreeled, straightened, and finally it is deployed to the sea floor. While faster and more cost effective, the reeling method induces large bending loads and high tensile forces into the pipeline with potential impact on stable crack propagation of undetected flaws at girth welds. To increase the fracture resistance of the welded region many codes and current fabrication practices (see Refs. [6e8] for illustrative examples) require the use of weldments with weld metal strength higher than the base plate strength. This condition is referred to as over- matched and aims to diminish the risk of structural failure caused by an undetected weld defect. While, the large plastic deformation developed around the crack-tip is transferred from the welded region to the base metal, the fracture resistance of the component will increase because of lack of surface defects. However, while the overmatch practice has been used in many structural applications effectively, the level of mismatch between the weld metal and base plate material may affect the relationship between remotely applied loading and the crack-tip driving forces. Fitness-for-service (FFS) assessment procedures for pipes and cylinders with circumferentially-oriented cracks subjected to large bending deformation rely heavily on the accuracy of computing the J-integral and the crack-tip opening displacement (CTOD) [9]. The fundamental work of Kumar et al. [10] introduces a J estimation procedure for selected crack geometries based on fully-plastic so- lutions [11], which later became widely known as the EPRI meth- odology. The original work was extended by Zahoor [12] to include additional geometries for circumferentially and axially cracked pipes under tensile and bending loads which, nevertheless, remain * Corresponding author. E-mail addresses: lmparedes53042@gmail.com, lparedes@mit.edu (M. Paredes). Contents lists available at ScienceDirect International Journal of Pressure Vessels and Piping journal homepage: www.elsevier.com/locate/ijpvp http://dx.doi.org/10.1016/j.ijpvp.2014.09.003 0308-0161/© 2014 Elsevier Ltd. All rights reserved. International Journal of Pressure Vessels and Piping 125 (2015) 49e65