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Tensile and fracture tests were performed on nickel-based alloy clad pipelines girth welds using customised rigs to elevate the temperature. Fracture tests were performed using single edged notched bend (SENB) and single edged notched tension (SENT) specimens, both with notch depth ratio of 0.2. The tensile test results showed reduction in strength at elevated temperatures for base metal, weld metal and clad metal while the fracture resistance reduced by up to 0.6 times depending on the notch location and the specimen geometry. The SENT specimens exhibited a higher fracture resistance than the SENB specimens, with an increase by about 1.3 times. [ABSTRACT FROM AUTHOR]

Finite element method was used to document the effects of temperature, environment, crack location and weld strength mis-match on the fracture capacity of modern pipeline girth welds. The results demonstrated a marginal reduction (>0.83 times) in the crack driving force for pipelines operating in a sour environment or at elevated temperatures or for cracks located in the weld centerline than at the fusion line. The crack driving force is lower for under-matching than over-matching welds. Furthermore, the numerical method was compared with analytical method as per BS7910 and the results showed that the latter was more conservative for deeper cracks ( a / t > 0.4). [ABSTRACT FROM AUTHOR]

Tensile and fracture specimens (pre-charged with H 2 S) were tested in solution using customised rigs. When comparing with uncharged specimens, the tensile test results showed significant reduction in ductility for base and weld metal. The fracture resistance test results showed similar reduction of ∼0.3 times in base and weld metals and heat affected zone. There was noticeable increase in yield and tensile strength in both base and weld metals, due to the effect of hydrogen. When using partially coated specimens, higher fracture resistance was obtained, with reduction of ∼0.4 times only. This was mainly contributed by crack tip hydrogen and less so by the bulk hydrogen. [ABSTRACT FROM AUTHOR]

A theoretical model is developed to investigate the fracture behavior for an elliptical inhomogeneity embedded in an elastic-plastic matrix. It contains an arbitrarily oriented crack under a uniform stress field at infinity. In the model, the generalized Irwin approach is applied for plastic zone correction for crack-tip yielding. The distributed dislocation technique is utilized to formulate the present problem. The effective stress intensity factors, the plastic zone size and the crack tip opening displacement are evaluated by solving the formulated singular integral equations. The solution takes into account the plastic zone size at the crack tips and thus could provide accurate stress intensity factors and crack tip opening displacements for the assessment of crack growth. In the numerical examples, the case under a y -direction uniaxial tension is considered. The effects of the ellipse's aspect ratio, the shear moduli ratio and the normalized crack-inhomogeneity distance are investigated. The results show that the shapes of the inhomogeneity and the material combinations have significant influences. Crack propagation may be hindered if the inhomogeneity is close to circular or a hole and the crack inclination angle is close to 90°. [ABSTRACT FROM AUTHOR]