Hydrogen induced cracking of X80 pipeline steel

The hydrogen-induced cracking （HIC） behavior of X80 pipeline steel was studied by means of electrochemical charging, hydrogen permeation tests, tension test, and scanning electron microscopy （SEM）. The experimental results indicate that the increase of charging time and charging current density or the decrease of the solution pH value leads to an increase of the hydrogen content in X80 steel, which plays a key role in the initiation and propagation of HIC. It is found that the majority of macro-inclusions within the as-used X80 steel do not constitute a direct threat to HIC except aluminum oxides, which directly or indirectly lead to HIC. The hydrogen trap density at room temperature is estimated to be pretty high, and this is an essential reason why the steel is sensitive to HIC. After hydrogen charging, the elongation loss rate and area reduction of X80 steel decline obviously, taking a noticeable sign of hydrogen-induced plasticity damages. It is demonstrated that the losses of these plastic parameters have a linear relation to the fracture size due to hydrogen.

Relationship between Critical Hydrogen Concentration and Applied Stress for Hydrogen Induced Cracking in 0.2 wt—%C Annealed Plain Steel

1.IntroductionSo far there are few people who studythe relationship between the criticalhydrogen concentration and the stress forhvdrogen induced cracking (CCHIC)quantitatively.Several researchers have cal-culated the CCHIC of steels under no stressby means of H permeation method,but no

INFLUENCE OF GRAIN SIZE ON STRENGTH AND HYDROGEN INDUCED CRACKING OF DUPLEX STAINLESS STEELS

The relation between grain size and strength of the duplex stainless steels and influence of grain size on properties of hydrogen induced cracking in these steels have been investigated. The Hall-Petch relation between grain size and strength of the steels is also followed.The susceptibility to hydrogen induced cracking of the steels increases with increasing grain size.

(Ⅰ+Ⅱ)MIXED MODE HYDROGEN INDUCED CRACKING

Hydrogen induced cracking(HIC)of 0.3% C,1% Cr,1% Mn,1% Si high strength steel has been studied under simple mode Ⅰ,mode Ⅱ and(Ⅰ+Ⅱ)mixed mode loading conditions.Af- ter being hydrogen-charged in IN H_2SO_4 solution,the material behaved hydrogen embrittlement in all the cases studied.The threshold K_(ⅡH)/K_(ⅡX) of HIC under mode Ⅱ load- ing was 0.27,which was nearly the same as that K(ⅠH)/K_(ⅠX)=0.29 under mode Ⅰ loading. While the thresholds of-HIC under(Ⅰ+Ⅱ)mixed mode loading were 0.36,0.41 and 0.37 cor- responding to the K_Ⅱ/K_Ⅰ ratio of 0.27,0.4 and O.81.The results show that simple mode Ⅰ or mode Ⅱ loading is more susceptible to hydrogen embrittlement than(Ⅰ+Ⅱ)mixed mode. For explaining the experimental results,the effects of triaxial stress as well as plastic deformation ahead of crack tip has been discussed.

Stress Oriented Hydrogen Induced Cracking of Linepipe Steel

The stress oriented hydrogen induced cracking (SOHIC) is a typical hydrogen embrittlement phenomenon occurring in the linepipe steels exposed to sour environment containing H 2 S gas.However,even recently,the cracking mechanism of SOHIC has not been clarified because of lacking in the empirical data on the actual failure mode of SOHIC cracking.The factors affecting SOHIC are discussed in terms of metallurgy of high strength linepipe steel and hydrogen electrochemistry.The cracking mechanisms of SOHIC are examined by comparing them with the empirical failure mode of SOHIC which is developed by observation of the actual fracture sites of the hydrogen induced blister cracking (HIBC) and secondary cracks.Finally,the correlation between SOHIC and HIC is discussed.

Effect of Microstructure on Hydrogen Induced Cracking Behavior of a High Deformability Pipeline Steel

The hydrogen induced cracking （HIC） behavior of a high deformability pipeline steel was investigated with three different dual-phase microstructures, ferrite and bainite （F＋B）, ferrite and martensite/austenite islands （F＋M/A） and ferrite and martensite （F＋M）, respectively. The HIC test was conducted in hydrogen sulfide （H2S）-saturated solution. The results showed that the steels with F＋B and F＋M/A dual-phase microstructures had both higher deformability and better HIC resistance, whereas the harder martensite phase in F＋M microstructure was responsible for the worst HIC resistance. The band-like hard phase in dual-phase mi- crostructure was believed to lead to increasing susceptibility to HIC.

Relationship between microstructure and hydrogen induced cracking behavior in a low alloy pipeline steel

Hydrogen induced cracking（HIC） behaviors of a high strength pipeline steel with three different microstructures, granular bainite ＆ lath bainite（GB ＋ LB）, granular bainite ＆ acicular ferrite（GB ＋ AF）, and quasi-polygonal ferrite（QF）, were studied by using corrosion experiment based on standard NACE TM0284. The HIC experiment was conducted in hydrogen sulfide（H_2S）-saturated solution. The experimental results show that the steel with GB ＋ AF and QF microstructure present excellent corrosion resistance to HIC, whereas the phases of bainite lath and martensite/austenite in LB ＋ GB microstructure are responsible for poor corrosion resistance. Compared with ferrite phase, the bainite microstructure exhibits higher strength and crack susceptibility of HIC. The AF ＋ GB microstructure is believed to have the best combination of mechanical properties and resistance to HIC among the designed steels.

TEM Study on Hydrogen-Induced Cracking of Fe_3Al Alloy

Hydrogen-induced cracking (HIC) of Fe3Al alloy was studied by in situ transmission electron microscope (TEM). Electron transparent specimens were mounted onto a constant displacement device. Stress was applied to the specimen by using a bolt through the device. The results showed that hydrogen enhanced the dislocation emission and motion in Fe3Al alloy. A dislocation free zone (DFZ) was formed following the dislocation emission. Microcrack initiated in the DFZ or at the main crack tip when the emission reached a critical extension. Hydrogen played an important role in the process of brittle fracture of Fe3Al alloy.

Hydrogen-induced Cracking of Weld Metal of Austenitic Stainless Steels

For 308L and 347L weld metals of austenitc stainless steels (ASS), hydrogen induced cracking (HIC) occurred during dynamically charging under constant load. The threshold stress intensity for HIC, Km, decreased linearly with the logarithm of the concentration of diffusible hydrogen C0 in the weld metals and the rolled plate of type 304L ASS, i.e., KIH=85.2-10.71nC0 (308L), KIH=76.1-9.31n C0(347L), and KIH=91.7-10.11nC0(304L). The fracture mode for HIC in the three type of ASS changed from ductile to brittle with the decrease in the applied stress intensity KI or/and the increase in C0. The boundary line between ductile and brittle fracture surfaces was KI-54+25exp(-C0/153)=0.

Fractal Dimensions of Hydrogen Induced Brittle Fracture of Titanium Aluminide

The relationship between the stress intensity factor K_1~* required for brittle crack initiation and propa- gation and the fractal dimension D_F of the fracture surface was derived,i.e, InK_1~*=(1/2)In2γE'+(1/2)In(d_f/L_0)(1-D_F) The real surface energy can be calculated based on the measured linear relation of the InK_1~* vs D_F, The equation is not only suitable for the overload fracture but also for the delayed fracture,e.g. hydrogen induced cracking (HIC) and stress corrosion cracking (SCC).The experiment results showed that the hydrogen induced delayed cracking occurred in the Ti-24AI-11 Nb alloy during dy- namic charging,and the threshold stress intensity factor was very low,i.e..K_(IH)/K_(IC)= 0.43.The ex- perimental relationship between the stress intensity factor K_1~* and D_F was consistent with the theo- retical equation.

Effect of crystallographic orientation on crack growth behaviour of HSLA steel

In this work,the crack growth behaviours of high strength low alloy(HSLA)steel E690 with three crystallographic orientations(the rolling direction,normal direction,and transverse direction)were investigated and compared from the view of the mechano-electrochemical ef-fect at the crack tip.The results show that the crack growth of the HSLA steel is controlled by the corrosion fracture at the crack tip.The vari-ation of crystallographic orientation in E690 steel plate has no influence on the crack tip electrochemical reaction and crack growth mechanism,but changes the crack growth rate.When the stress loading direction is parallel to the rolling direction and the fracture layer is parallel to the transverse-normal plane,the crack growth rate is the slowest with a value of 0.0185 mm·h^(-1).When the load direction and the fracture layer are parallel to the normal direction and the rolling-transverse plane,respectively,the crack growth rate is the highest with a value of 0.0309 mm·h^(-1).This phenomenon is ascribed to the different microstructural and mechanical properties in the rolling direction,normal direction,and transverse direction of E690 steel plate.

Sulfide Stress Cracking Assessment of Carbon Steel Welding with High Content of H<SUB>2</SUB>S and CO<SUB>2</SUB>at High Temperature: A Case Study

In the oil and gas industry, it has been established that for pipelines fabricated with carbon steels, their limitation is related to H2S and CO2 environments, which is 7 to 10 psia of partial pressure of CO2. Therefore, in carbon steel cracking is shown, after 7 or 10 psia of partial pressure of CO2. The experimental work was performed under static conditions in autoclaves within a pH of 3 to 3.8;partial pressures of 16 - 96 psi for H2S and 15 - 53 psi for CO2, in the temperature range of 25°C - 150°C. It was observed that the average yielding stress used in Sulfide Stress Cracking (SSC) tests decreases with temperature increment. Hydrogen Induced Cracking (HIC) evaluations showed that X52 steel, under conditions, was not susceptible to HIC. Results of SSC did not show indications of cracking after exposure to sour solutions, except for the specimen exposed to high H2S and CO2 content (96 psi of H2S and 53 psi of CO2 of the partial pressure) and high temperature (150°C). Microcracks located between the upper and lower weld beads were also observed. However, the highest average corrosion rate was 0.27 mm/year (10.6 mpy), which occurred in samples exposed to 96 psi of H2S and 53 psi of CO2 at 150°C. Likewise, the highest localized corrosion (severe pitting attack) was obtained at the same environment with a corrosion rate of 4.2 mm/year (167 mpy). The oil and gas industry could use carbon steels pipelines in partial pressure higher than 10 psia.

MECHANISM OF HYDROGEN FACILICATED CLEAVAGE IN TITANUM ALUMINIDE

Both hydrogen induced cracking and overload crack initiated at same characteristic distance, r~*,within the plastic zone along the slip line when the plastic zone developed to a critical ex- tent.For the overload crack. K_(IC)=αr~*^(1/2)[σ_F^((n+1)/2n)/σ_(ys)^((1-n)/2n)],σ_F=σ_0+g[2μbσ_(th)/π~2L(1-v)]^(1/2) For the hydrogen induced cracking: K_(IH)=αr~*^(1/2)[σ_F(H)^((n+1)/2n)/σ_(ys)(H)^((1-n)/2n)], σ_F(H)={σ_0(H)+g[2μbσ_(th)(H)/π~2L(1-v)]^(1/2)}/k Hydrogen pomoting the dislocation multiplication and motion would result in σ_0(H)<σ_0, k>1,Therefore,hydrogen promoting the cleavage fracture in titanum aluminide can be due to that hydrogen facilitates the local plastic deformation,which results in σ_F(H)<σ_F and then K_(IH)<K_(IC).

INTERPHASE STRESS CORROSION CRACKING OF ALLOY Ti－24Al－11Nb IN METHANOL SOLUTION

For alloy Ti-24Al-11Nb,stress corrosion cracking(SCC) in methanol solution and hydrogen induced cracking(HIC) during dynamic charging at room temperature have been studied.Experiment has shown that the normalised threshold stress intensities of SCC failure for various microstructures are KISCC/KC =0.53 0.69 and the threshold value for SCC arresting KISCC/ KIC=0.61-0.79.The threshold values of HIC during dynamic charging are close to that of SCC,but da/dt or fracture time of HIC is one to three orders of magnitude smaller or longer than that of SCC,respectively.The.fracture surface for HIC is also different from that for SCC.For the Ti-24Al-Nb alloy-methanol systein,a kind of inierphase SCC has been found For the microstructures resulting from furnace cooling,SCC initiated and propagated preferentially along theα2/βinterphase boundaries,displaying the microstructure on the fracture surface of SCC.However,there is no interphase SCC for the microstructure resulting from air cooling.

Influence of Microstructures on Polarization Resistance and Hydrogen-Induced Cracking of a Micro-Alloyed Steel Submitted to Different Cooling Rates

The effect of different microstructures on the polarization resistance (Rp) and the hydrogen-induced cracking (HIC) of a micro-alloyed steel austenitized and submitted to different cooling rates was studied.Samples 19.1 x 6 x 2 mm,containing the whole thickness of the plate were extracted from a 20 mm plate and heat treated on a quenching dilatometer,were submitted to Rp and HIC corrosion tests.Both Rp and HIC tests followed as close as possible ASTM G59 and NACE standard TM0284-2003,in this case,modified only with regard to the size of the samples.Steel samples transformed from austenite by a slow cooling (cooling rate of 0.5℃.s-1) showed higher susceptibility to hydrogen-induced cracking,with large cracks in the middle of the sample propagating along segregation bands,corresponding to the centerline of the plate thickness.For cooling rates of 10℃.s-1,only small cracks were found in the matrix and micro cracks nucleated at non-metallic inclusions.For higher cooling rates (40℃.s-1) very few small cracks were detected,linked to non-metallic inclusions.This result suggests that structures formed by polygonal structures and segregation bands (were eutectoid microconstituents predominate) have higher susceptibility to HIC.Structures predominantly formed by acicular ferrite make it difficult to propagate the cracks among non-oriented and interlaced acicular ferrite crystals.Smaller segregation bands containing eutectoid products also help inhibit cracking and crack propagation;segregation bands can function as pipelines for hydrogen diffusion and offer a path of stress concentration for the propagation of cracks,frequently associated to non-metallic inclusions.Polarization resistance essays performed on the steel in theas received condition,prior to any heat treatment,showed larger differences between the regions of the plate,with a considerably lower Rp in the centerline.The austenitization heat treatments followed by cooling rates of 0.5 e 10℃.s-1 made more uniform the corrosion resistance along the thickness of the plate.The effects of heat treatments on the corrosion resistance are probably related to the microconstituent formed,allied to the chemical homogenization of the impurities concentrated on the centerline of the plate.

The Behavior of Rare Earths in Steel

This review paper outlines recent progress in the application of rare earth metals (RE) in steel to improve the mechanical properties of steel. It includes: the physical chemistry of RE in steel; comparison of the application of RE and Ca in steel; the ways of adding RE into steel and nozzle blockage; the solid solubi- lity limit of RE in Fe and the amount of RE soluble in steel; the segregation of RE on grain boundaries of steel and its reaction with other elements; the effect of RE on the structure and mechanical properties of steels; the reaction of RE with H in steel.

Hydrogen trapping and electrochemical corrosion behavior of V–N microalloyed X80 pipeline steels consisting of acicular ferrite and polygonal ferrite

Hydrogen trapping behavior of V–N microalloyed X80 pipeline steels was studied by means of hydrogen permeation and hydrogen induced cracking(HIC)tests.In addition,the electrochemical performance of the steels in 3.5 wt.%NaCl solution was investigated.Results indicated that the microstructure of experimental steels mainly consisted of acicular ferrite and polygonal ferrite(PF).When the fraction of PF was 9.1%and 30.4%,hydrogen effective diffusion coefficient was 1.624×10^(−6) and 3.121×10^(−6) cm^(2)/s,respectively.The pipeline steels were not susceptible to HIC.Numerous potential hydrogen traps distributed in homogeneous dispersion were conducive to high HIC resistance.With increasing the fraction of PF from 9.1%to 30.4%,the corrosion current density increased from 5.39×10^(−6) to 9.49×10^(−6) A cm^(−2),the corrosion potential decreased from−0.48 to−0.57 V,and the charge transfer resistance decreased from 2301 to 2068Ωcm^(2),respectively.Increased fraction of PF was disadvantageous for corrosion resistance because of galvanic corrosion.