Environmentally assisted cracking and hydrogen diffusion in traditional and high-strength pipeline steels

Abstract

This article deals with the risk of environmentally assisted cracking of steel structures that are kept under cathodic protection (CP). The experimental results collected on both hydrogen diffusion and hydrogen embrittlement (HE) of high-strength low-alloy (HSLA) steels under CP are discussed. Hydrogen diffusion was evaluated by permeation experiments and a scanning photoelectrochemical current technique, as a function of microstructure orientation, on both loaded and unloaded specimens. HE tests were carried out under constant load, slow strain rate (SSR tests), and slow bending conditions. Tests were also carried out on several grades of HSLA steel having different microstructures. The results confirm that HE in artificial seawater under CP can occur in steel with tensile yield strength in the range of 400–660 MPa only in the presence of high cathodic polarization and continuous plastically straining conditions. HE susceptibility increased with increasing applied cathodic polarization and with decreasing strain rate. HE susceptibility of the rolled steels at relatively high strain rate (10-4 to 10-5 s-1) increased with the hydrogen diffusion coefficient. Similar results were observed in terms of the HE contribution to corrosion fatigue crack growth rate. High-temperature-tempered martensitic steels showed a lower HE susceptibility.

Hydrogen Embrittlement and Diffusion in High Strength Low Alloyed Steels with Different Microstructures

“…This critical potential is related to the cracking initiation, and especially to the adsorbed hydrogen concentration, but not to the hydrogen diffusion coefficient into the steel. The differences evidenced by the martensitic steels were attributed to their heat treatment, especially to the size and distribution of carbides in their microstructure [21,54] . Figure 5 reports the normalized RA as a function of the potential during the SSR tests at strain rate 10 -5 s -1 .…”

“…The diffusivities are correlated to the hydrogen embrittlement susceptibility evaluated by means of slow strain rate tests. The results are compared to literature data and previous results [21,[44][45][46][47][48] .…”

“…HE risks, either microbiologically produced or due to CP, have also been considered in the ISO 19902:2007 standard in which it is specified that HE susceptibility increases with the yield strength for steels with a specified minimum yield strength (SMYS) values in the range of 460-500 MPa. However, field experience has demonstrated that thermomechanically controlled processed steels with SMYS values between 450 and 480 MPa are not susceptible to HE [21] .…”

“…In the absence of microstructural alterations few cases were observed, and only in buried pipelines subject to slow plastic deformations [27][28][29] or mechanical damage and landslides [30] . Corrosion-Fatigue (CF) can occur on sea lines as a result of the combined action of cyclic stress and corrosive environment [21,[31][32][33] . In this regard, there are numerous laboratory studies reported by different authors on HE on pipeline steels [1,[34][35][36][37][38][39][40][41][42][43] .…”

Effect of Hot Mill Scale on Hydrogen Embrittlement of High Strength Steels for Pre-Stressed Concrete Structures

“…Susceptibility depends on composition, microstructures, and mechanical properties of the steels [10][11][12].…”