Mechanical degradation of API X65 pipeline steel by exposure to hydrogen gas

Abstract

Hydrogen-induced degradations have generally been investigated through the ex situ testing of cathodically hydrogen-charged specimens. However, the cathodic charging cannot realize damage accumulation by gaseous hydrogen in transportation pipelines. Thus, we designed an ampule specimen which enables an in situ tensile test containing gaseous hydrogen. Ampule specimens made of API (American Petroleum Institute) X65 pipeline steel showed significant reductions of 3.4 % and 4.1 %, respectively, in their ultimate tensile strength and fracture strain after exposure to 20 MPa of hydrogen gas. The resulting fracture surface showed quasi-cleavage perpendicular to the loading direction and a fracture thickness close to the initial wall thickness, significantly different from the complex dimples and highly reduced fracture thickness by shear deformations in nitrogen gas and air environments.

Effect of gaseous hydrogen charging on the tensile properties of standard and medium Mn X70 pipeline steels

“…This observation is consistent with the contribution of hydrogen cracking to fracture at a lower stress compared to testing in the absence of hydrogen. The NTB sample showed the maximum embrittlement index, consistent with the results of three-point bend (TPB) testing reported in Hejazi et al 27 Although there are reports of tensile testing in the presence of gaseous hydrogen of X65 steel at the room temperature, 28 stainless steel at −20 to −250°C 31 and medium carbon steel at room temperature, 32 tensile testing of X70 steel under hydrogen at elevated temperatures (50 and 100°C) has not previously been reported. Since pipelines located in the desert environment are subject to deformation at low strain rates and can reach 50°C and over, the current work constitutes an attempt to simulate this service condition.…”

“…These observations indicate that the hydrogen-charged specimen tested at 100°C undergoes lower elongation before fracture than the argon-charged specimen at 25°C. These are consistent with results of Lee et al, 28 who conducted the same tensile test on X65 hollow cylindrical samples with hydrogen or nitrogen inside. They also found brittle fracture surface with almost no necking under hydrogen charging.…”

“…These are consistent with results of Lee et al ., 28 who conducted the same tensile test on X65 hollow cylindrical samples with hydrogen or nitrogen inside. They also found brittle fracture surface with almost no necking under hydrogen charging.…”

“…Although there are reports of tensile testing in the presence of gaseous hydrogen of X65 steel at room temperature [28], stainless steel at -20 to -250˚C [31] and medium carbon steel at room temperature [32], tensile testing of X70 steel under hydrogen at elevated temperatures (50 and 100˚C) has not previously been reported. Since pipelines located in desert environment are subject to deformation at low strain rates and can reach 50˚C and over, the current work constitutes an attempt to simulate this service condition.…”

Influence of Hydrogenation on Residual Stresses of Pipeline Steel Welded Joints

“…Perhaps the plastic deformation produced around these defects favored nucleation and propagation of internal and surface cracks, which contributed to the embrittlement of steel. This behavior is consistent with the literature, since many authors have reported the influence of hydrogen in the reduction in ductility and strength of steel [24][25][26][27] . Figure 9 shows the SEM micrographs of the fracture surfaces of the base metal (BM) test specimens, in asreceived (AR) condition.…”