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Specimens from nickel-based clad pipeline girth welds were tested in H 2 S solution. The results of the fatigue crack growth rate curve at higher Δ K values were about 4 times higher than the in-air values. The rate at 180 °C was generally higher than the in-air data for flaw assessments found in the British Standard BS7910 by a factor of up to 3 times. From the analyses of the diffusible hydrogen, the backing steel of such pipelines are predominantly protected from the sour environment by the corrosion-resistant alloy clad layer. The results from this study are relevant for desktop Engineering Critical Assessment of girth welds of such pipelines. [ABSTRACT FROM AUTHOR]

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]