HIC Resistance Research Articles

Effect of Nb on the Hydrogen-induced Cracking of X80 Pipeline Steel

Nb is a key alloying element added into X80 pipeline steel, and it can enhance mechanical properties by refining grains and introducing precipitates. However, HIC resistance is also one of the most significant performances for pipeline steel served in H2S environment. An all-inclusive recognition of the response of niobium to HIC refusal is important for the appropriate design of the Nb addition amount, the rolling and cooling parameters, and protective techniques to obtain excellent mechanical properties, including strength and ductility and HIC refusal. So in the paper, many test methods, such as EBSD, SEM, and HIC, were adopted to research the response of niobium addition on resistance of hydrogen-induced cracking performance of X80. As the increase in Nb content, grain size decreased and had the strongest trapping hydrogen atom ability. Besides, the percentage of low-angle grain boundaries went up, and more precipitates greatly raised the amount of irreversible hydrogen pitfalls. Nb could greatly promote the HIC resistance, inhibiting crack initiation, and propagation.

Hydrogen Induced Cracking of API X52 and X60 Sour Service Steels Subjected to Pre-Strain under Prolonged H2S Exposure

The effect of plastic deformation on API X52 and X60 sour service steels on hydrogen induced cracking was studied. Plastic deformation was performed with a tensile pre-strain with the percentage variation of strain. The HIC test was carried out with a duration of 168 hours of hydrogen charging to investigate the cracking behavior. After hydrogen charging, the cross sections of both steels were observed to find out hydrogen cracks. Ultrasonic testing was carried out on the specimen surface to see the distribution of laminated cracks. The hydrogen crack surface was observed using SEM. The results showed that the values of CSR, CLR and CTR increased with increasing percentage of pre-strain. Ultrasonic testing showed that the area influenced by HIC increased with increasing percentage of pre-strain. The susceptibility of API X52SS and X60SS to HIC increases with increasing percent of pre-strain. API Steel X52SS has better HIC resistance than X60SS on high pre-strain.

Features of Technology for Pipe Steel Modification with Calcium and Cerium with Specification for Resistance to H2S-MEDIA

Among many factors influencing steel resistance to hydrogen induced cracking, the sulfur content in the metal and steel modification technology with calcium are of particular importance. In assessing the impact of process parameters on HIC resistance many authors do not consider their effect on production process efficiency and other quality indicators. The combined effect of calcium and rare earth metals on hot-rolled steel quality is described (with respect to steel HIC resistance, and contamination of metal by nonmetallic inclusions) in this paper. Formation of nonmetallic inclusions containing calcium and rare earth metals is described, and nonmetallic inclusions in the metal with different versions of modification are analyzed. The optimum amount of calcium and cerium required for obtaining stable results for HIC resistance in low-carbon micro-alloyed steels while retaining good rolled steel surface quality is determined.

Effect on properties of HIC resistance vessel steel of quenching and tempering heat treatment

The effect on strength properties, microstructure and HIC of heat treatment of normalizing rolling, normalizing and quenching & tempering was analysed. The following conclusions can be drawn: The strengths of samples of normalizing rolling and normalizing range 459MPa~470MPa. However the strengths of quenching and tempering samples range 539MPa~614MPa. And the strengths of quenching and tempering samples decrease with the tempering temperature rising. The Max. CLR is around 14% of normalizing rolling samples but 4% of normalizing samples. However no cracks was observed on the quenching and tempering samples. The cracks originate on center of samples’ thickness direction and propagate along pearlite bands. However the HICs have a low occurrence rates on the quarter of samples without origination that only exist on thickness center of samples. The quenching and tempering microstructure can prevent the propagation of the originated HIC, which improves the HIC resistance properties of vessel steel.

Role of cold rolled followed by annealing on improvement of hydrogen induced cracking resistance in pipeline steel

Abstract In this study, we investigated the effect of cold rolled followed by annealing on hydrogen induced cracking susceptibility in an API X60 pipeline steel. To this, we carried out cold rolling on X60 steel up to 20%, 50% and 90% in thickness reduction to change the microstructure and texture of steel. Then, we annealed all specimens at 850 °C for 90 s. We studied all tested specimens by electron backscatter and X-ray diffraction techniques. EBSD results showed that the grain refinement process was properly done via cold rolling and annealing treatments in tested specimens. However, the dislocation density was high for all tested steels. Moreover, electrochemical hydrogen charging experiment on tested steels proved that all specimens were still highly susceptible to hydrogen induced cracking. Therefore, we increased the annealing temperature and its duration of the 90% cold rolled specimen (the specimen with finest grains) up to 950 °C for 5 min. Interestingly, there was no HIC crack on this steel after hydrogen charging experiment. EBSD measurements on this steel showed strong textures of {100}//ND and {111}//ND. As a result, such strong textures, low Kernel Average Misorientation data, a high proportion of recovered grains and coincidence site lattice boundaries were recognized as the most important reasons for the highest HIC resistance in the mentioned steel.

Optimization of Electric Resistance Welding Conditions in Small Diameter X60 Pipes for HIC Resistance

The optimization of electric resistance welding conditions has been investigated in order to improve the resistance to hydrogen induced cracking at bondline in API 5L X60 line pipes from center-slit coils. It was found that the elongated (Si, Mn, Al) rich oxide inclusions at bondline provided a preferential site for HIC, but no evidence on the center segregation effects was found. Design of experimental (DOE) method was used to find out the optimum ERW condition in the viewpoint of the minimization of defects ratio at bondline. The optimum ERW condition suggested by DOE successfully led to an excellent HIC resistance at bondline. Furthermore, it was observed that there was no relation between segregation and HIC resistance at bondline.

Effect of the thermo-mechanical control process on the properties of high-strength low alloy steel.

The effect of the Thermo-Mechanical Control Process (TMCP) on the properties o f high-strength low alloy steel has been examined and the following results have been obtained.The addition of niobium or titanium, especially the combination of niobium and boron is effective for TMCP. Low-temperature toughness of TMCP plate is not significantly influenced by the cooling conditions, but is mainly determined by the controlled-rolling (CR) conditions. TMCP alters the microstructure from ferrite-pearlite to fine-grained ferrite-bainite and consequently increases the strength without a loss in low-temperature toughness, compared with CR process.The advantages of TMCP plate are a decrease in the carbon equivalent, improvement of HIC resistance and an increase in the impact energy.