Effect of H2S Corrosion on the Fracture Toughness of the X80 Pipeline Steel Welded Joint

Abstract

To analyze the causes and mechanisms affecting the fracture toughness of X80 pipeline steel welded joints against H2S, the fracture toughness of different zones of X80 pipeline steel welded joints in both air and saturated H2S solution was investigated. The fracture toughness of welded joints degraded significantly in the saturated H2S solution, where the crack tip opening displacement (CTOD) characteristic value in the coarse grain heat-affected zone (CGHAZ) and weld metal (WM) was only 8% and 12% of that in air, respectively. However, the sub-critical grain heat-affected zone (SCHAZ) showed better resistance to H2S corrosion, with the CTOD characteristic value reaching 42% of that in air. The resistance of the welded joint to H2S corrosion was sensitive to microstructures. The grain boundary ferrite (GBF) presented in WM, and the angle of grain boundary orientation in CGHAZ was not conducive to hindering crack propagation. Moreover, the formation of the resultant hydrogen cracks owing to the H2S corrosion also reduced the fracture toughness of the welded joint.

Improvement of the Mechanical Characteristics, Hydrogen Crack Resistance and Durability of Turbine Rotor Steels Welded Joints

“…In comparison to similar H-free samples, the H-charged samples presented lower fracture toughness. For samples, with notches located at the base metal, stir zone and heat-affected zone metal, the average Critical Crack Tip Opening Displacement decreased from 0.96 to 0.25 mm, from 0.48 to 0.43 mm and from 0.22 to 0.08 mm, respectively [42]. At the working temperature (450 • C), the effect of hydrogen is negligible (Table 4).…”

“…All of this also negatively affects the performance of machine parts under cyclic and static loads during long-term operation. Uneven grain sizes, the sizes and distribution of reinforcing phases, local thermal stresses and other defects cause the significant sensitivity of various structural elements of welded joints to the action of hydrogen [41][42][43][44][45][46]. Even the simulation of the soldering regime with the short-term (15 min) heating of KhN43MBTYu and 05Cr19Ni55 alloys to 1473 K leads to an increase in grain size and the concentration of large grain boundary Uneven grain sizes, the sizes and distribution of reinforcing phases, local thermal stresses and other defects cause the significant sensitivity of various structural elements of welded joints to the action of hydrogen [41][42][43][44][45][46].…”

“…Uneven grain sizes, the sizes and distribution of reinforcing phases, local thermal stresses and other defects cause the significant sensitivity of various structural elements of welded joints to the action of hydrogen [41][42][43][44][45][46]. Even the simulation of the soldering regime with the short-term (15 min) heating of KhN43MBTYu and 05Cr19Ni55 alloys to 1473 K leads to an increase in grain size and the concentration of large grain boundary Uneven grain sizes, the sizes and distribution of reinforcing phases, local thermal stresses and other defects cause the significant sensitivity of various structural elements of welded joints to the action of hydrogen [41][42][43][44][45][46]. Even the simulation of the soldering regime with the short-term (15 min) heating of KhN43MBTYu and 05Cr19Ni55 alloys to 1473 K leads to an increase in grain size and the concentration of large grain boundary intermetallic precipitates, which significantly enhances the hydrogen embrittlement of materials [47,48].…”

“…Important characteristics of critical structures, including steam and hydrogen turbine rotors, are the parameters of crack resistance , which are also significantly reduced by hydrogen [41,42,[46][47][48][53][54][55][56] with a pressure up to 10 MPa. Given the variety of factors that determine the properties of welded elements in hydrogen-containing environments, to assess their performance requires the experimental determination of a set of physical and mechanical properties of a particular joint [119][120][121][122][123][124][125], especially for the structural elements of the hydrogen energy buffer (electrolizers, fuel cells, hydrogen storage and grid distribution), with the intention of utilizing hydrogen and the accompanied phenomenon of their hydrogen degradation during long-term service.…”

“…At short-term stretching at room temperature, its effect is manifested in a significant reduction in the relative elongation δ, the relative transverse narrowing ψ and the critical stress intensity factor (K Ic ) of steels and, especially, welded joints. The viscosity of the fracture, which is characteristic of many welds, deteriorates significantly (by 40-50%) [41,42].…”