Research on the fatigue properties of sub‐heat‐affected zones in X80 pipe

Abstract

Pipeline transmission is an essential means of oil and gas transportation, but its safety is threatened by fatigue fracture that generally occurs in the heat-affected zone (HAZ) adjacent to welded joints of the pipeline. Therefore, it is important to determine the fatigue properties of HAZ. In this work, the microstructure and mechanical properties in the HAZ of a X80 pipe were accurately simulated by thermal simulation. The fatigue life and crack growth rate of typical sub-HAZ were tested. The results showed that fine grain HAZ exhibited the lowest strength and fatigue life. In contrast, coarse grain HAZ had the highest strength, but its fatigue life was lower than that of the intercritical HAZ. The microstructure of each sub-HAZ and the effect of this structure on fatigue properties were analysed and discussed in detail. The results provide insight into the effects of microstructure and mechanical properties on the service safety of pipeline transportation.

Crack propagation through weld and heat affected zone

“…Crack propagation tests on different heat affected zones, that is, coarse grained, fine grained, which resembled single pass welds and reheated coarse grained heat affected zones resembling multi-pass welds along with the base metal itself were carried out in Kim et al 1 and results showed that the crack growth rate was fastest in the reheated coarse grained HAZ, whereas the base metal showed the best fatigue crack resistance. Also, the crack propagation rate in fine grained HAZ was slower than in the coarse grained HAZ, which was also found in Qiu et al 2 and Tsay et al 3 In Xu et al 4 it was found that the fine grained HAZ had a lower fatigue life than the course grained HAZ.…”

Influence of welding HAZ microstructure on low-temperature impact fracture behaviour in C–Mn shipbuilding steel

“…The heat input of the thermal cycles was 45 kJ cm -1 , mimicking the practical production condition. The peak temperatures at different distances from the weld metal were calculated according to the previous studies [16]. The welding heat cycle processes and the heating and cooling parameters are provided in Figure 2 and Table 2.…”

A frequency‐domain approach for damage detection in welded structures

“…However, as is well‐known, the fatigue strength of a welded component in presence of multiaxial cyclic loading is significantly lower than that of an unwelded one (even if the components are made of the same material) 2 . In particular, the factors causing the above strength reduction 3–5 are residual stresses, 6–9 thermal distortions, 10 defects caused by partial penetration, 11 and material microstructural imperfections 12 …”

“…2 In particular, the factors causing the above strength reduction [3][4][5] are residual stresses, [6][7][8][9] thermal distortions, 10 defects caused by partial penetration, 11 and material microstructural imperfections. 12 Moreover, complex time variable load histories applied to welded components result in severe stress/ strain gradients at the weld toes/roots leading to fatigue damage near such critical regions.…”