Research of main gas pipeline (steels X65, X60, 17G1S) susceptibility to stress corrosion cracking, hydrogen uptake and ST 37-2 steel fatigue testing

Abstract

According to the data from the slow strain rate stress corrosion cracking test, two histograms were constructed that shows an increase in the susceptibility of metals to stress corrosion and hydrogen charging due to the rise in temperature (+ 25°C to +50°C). Consequently, susceptibility to stress corrosion increased from 0.85 to 0.87 for steel X65 and rose to 0.9 for steel X60, respectively. The same trend was observed for hydrogen charging (from + 25°C to + 50°C, the hydrogen charging increased from 1 to 2 (mol · H)/(n) for steel X65 and from 1.2 to 3.5 (mol · H)/(n) – for steel X60). In the second study, for the low-cycle fatigue under varying strain conditions, V-shaped shear specimens of ST 37-2 steel were used. It shows that grain-boundary steel has a crack width of 1.3 µm, whereas steel with an initial and cellular structure - 0.34 and 0.42 µm. Comparing the data obtained from Severgazprom, a histogram of the dependence of corrosion-stressed defects in the pipeline segments in front of the compressor station was constructed. The sections of the 115 km of the underground gas pipeline infrastructure were surveyed. In case of steel grade 17G1S, the diameter of the pipes ranged from 1020 mm to 1420 mm. Graphs were constructed for the dependence of the density of corrosive destruction in winter or summer seasons. The range of temperatures during operation of main gas pipelines was from 60°C to 25°C in summer and from 30°C to −30°C -in winter.