Effect of Line Pipe Steel Microstructure on Susceptibility to Sulfide Stress Cracking

Abstract

The purpose of this experiment was to evaluate the effect of microstructure on sulfide stress cracking (SSC) properties of line pipe steel. Different kinds of microstructures, with chemical compositions identical to one steel heat, were produced by various thermomechanically controlled processes (TMCP). Coarse ferrite-pearlite, fine ferrite-pearlite, ferrite-acicular ferrite, and ferrite-bainite microstructures were investigated with respect to corrosion properties, hydrogen diffusion, and SSC behavior. SSC was evaluated using a constant elongation rate test (CERT) in a NACE TM0177 solution (5% sodium chloride [NaCl] + 0.5% acetic acid [CH3COOH], saturated with hydrogen sulfide [H2S]). The corrosion properties of steels were evaluated by potentiodynamic and linear polarization methods. Hydrogen diffusion through steel matrix was measured by an electrochemical method using a Devanathan-Stachurski cell. The effect of microstructure on cracking behavior also was investigated with respect to crack nucleation and propagation processes. Test results showed that ferrite-acicular ferrite microstructure had the highest resistance to SSC, whereas ferrite-bainitic and coarse ferritie-pearlitic microstructures had the lowest resistance. The high susceptibility to SSC inferritie-bainitic and coarse ferritic-pearlitic microstructures resulted from crack nucleation on hard phases such as grain boundary cementite in coarse ferritie-pearlitic microstructures and martensite/retained austenite (M/A) island in bainitic phases. Hard phase cementite at grain boundaries or M/A constituent in bainitic phases acted as crack nucleation sites and could be cracked easily under external stress; consequently, the susceptibility of steel to SSC increased. Metallurgical parameters including matrix structure and defects such as grain boundary carbides and inter-lath M/A constituents were more critical parameters for controlling SSC than the hydrogen diffusion rate.

Effect of microstructure and composition on hydrogen permeation in X70 pipeline steels

“…On the other hand, the results obtained from the present study are comparable to those reported Koh et al [30] for pipeline steels having ferrite-pearlite microstructures.…”

“…In the past few decades, several investigations have dealt with the influence of various parameters on diffusion in pipeline steels [14,[25][26][27][28][29][30][31][32][33][34][35]. Table 1 summarises diffusion coefficients and other parameters obtained, for pipeline steels, by different authors along with other related information such as the solutions employed, exit side coating and method used for calculating the diffusion coefficient.…”

“…Kim et al [29] investigated the effect of environmental factors such as H 2 S partial pressures and pH values on the permeation of hydrogen in high strength low alloy (HSLA) steels and found that reversible trapping was affected by H 2 S rather than pH. The effect of precipitates was investigated by Koh et al [30] who reported that diffusion of hydrogen was related to the volume fraction of carbonitride precipitates rather than the ferrite microstructure. Huang et al [13] studied the ability of microstructures and inclusions to trap hydrogen in three different X120 steels having similar amounts of Ti,Nb(C,N) precipitates and found that irreversible hydrogen trapping efficiency increases with the volume fraction of non-metallic inclusions such as Al 2 O 3 and MnS.…”

Corrosion Evaluation of SAW Welded API 5L X-80 Joints in H2S-Containing Solution

“…It is well known that H 2 S originating from different processes in the oil and gas industry can accelerate the anodic and cathodic reactions of the corrosion process: iron dissolution and hydrogen evolution reaction, respectively [1][2][3][4][5][6][7][8][9][10] . Studies focusing on improving the resistance of pipeline steels to H 2 S corrosion to avoid failures during oil and gas transport have been reported [9][10][11][12][13][14] . In Brazil, the manufacture and use of high-strength low-alloy steel pipelines have been implemented in recent decades; these pipelines are nationally produced using thermomechanical controlled processing (TMCP) without accelerated cooling and fabricated using the UOE process (pressing a U-shaped pipe between two semi-circular dies to form an O-shaped pipe, then welding the pipe closed and circumferentially expanding it to obtain a highly circular shape) for the conduction of liquid and gaseous hydrocarbons.…”

Determination of Hydrogen Diffusion Parameters of Ferritic Steel from Electrochemical Permeation Measurement under Tensile Loads

“…The high-strength ferritic steels used in the petrochemical industry suffer frequently from hydrogen assisted cracking (HAC) problem when they are used in a sour environment containing H 2 S. [1][2][3] Atomic hydrogens which result from the reduction of H + ions dissociated from H 2 S become the hydrogen molecule by the recombination reaction (H + H → H 2 ). Since H 2 S dissolved in aqueous environment suppresses this recombination reaction, the hydrogen atoms are easily adsorbed on the steel surface and diffuse into the steel matrix.…”