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Fracture resistance is an important material property and characterized by a J-integral resistance curve (J-R curve) or a crack-tip opening displacement (CTOD) resistance curve. ASTM standard specimens with deep cracks are subject to bending dominant forces, leading to high crack-tip constraint conditions and conservative fracture resistance curves. Actual cracks occurring in line pipes and welds are often shallow ones dominated by tensile forces, resulting in low constraint conditions. Shallow cracks have been shown to generate elevated fracture resistance curves in comparison to standard deep-crack results. To reduce the over-conservatism of standard resistance curves and to produce more realistic toughness properties to meet the needs of strain-based design approaches for pipelines, different procedures and technologies have been developed over the years to determine the low-constraint fracture resistance curves by use of the single edge-notched tension (SENT) specimens. This includes the multiple specimen method developed and standardized by DNV for J-R curve testing, the single specimen method developed by CanMet for J-R and CTOD-R curve testing, and the single-specimen method developed by ExxonMobil for CTOD-R curve testing. This paper delivers a technical review of existing fracture test methods using SENT specimens, and discusses the advantages and limitations of each method.

This article presents the results of an experimental study of the effects of heat input and temperature on the crack-tip opening displacement (CTOD) in the coarse-grained heat-affected zones (CG HAZs) that are generally considered to be the weakest sections of fusion welded structures. The study focuses primarily on the fracture mechanisms in CG HAZs in submerged-arc-welds (SAWs) between A707 steel base metal. The first section of the article explores the effects of heat input on the fracture toughness (CTOD) of the CG HAZs. Following a description of the microstructures in HAZs and inclusions in the CG HAZs, the article summarizes the effects of heat input (1.2, 1.8, and 2.6 MJ/ m) on the CTOD. The underlying fracture mechanisms are elucidated via detailed scanning electron microscopy (SEM) analysis. The results of multiple CTOD tests at 4.4 ЊC (in the transition temperature regime) are analyzed within a statistical framework. The measured distributions of CTOD data are shown to be well described by Weibull statistics. The second section of the article focuses on the effects of temperature on the CTOD. The study of fracture in the lower-shelf and transition-temperature regimes indicates that the ductile-to-brittle transition occurs between Ϫ10 and 23 ЊC. Fracture initiation in both the lower-shelf and transition-temperature regimes is shown to occur by ductile tearing, prior to a transition to cleavage fracture. The dimple size variations in the stable tearing regime are shown to be well described by Weibull statistics. The implications of the results are discussed for analysis of CG HAZ fracture.