Slow Strain Rate Testing Technique Research Articles

Investigating Microstructural and Microchemical Effect of Aging on Cu-rich Phase of 304HCu SS Exposed to Chloride Environment by Slow Strain Rate Testing Technique

Investigating Microstructural and Microchemical Effect of Aging on Cu-rich Phase of 304HCu SS Exposed to Chloride Environment by Slow Strain Rate Testing Technique

SCC susceptibility of chromized type 409 stainless steel in alkaline chloride solutions at ambient temperature and pressure

Biomass hydrothermal liquefaction (HTL) is operated in a harsh reaction medium that contains hot pressurized water, inorganic acidic or basic catalyst, and inorganic/organic corrosive components released during the conversion. Candidate alloys for this application require suitable resistance to both corrosion and stress corrosion cracking (SCC) to withstand the HTL process conditions (250°C–374°C and 4–22 MPa). Ferritic iron-chromium (Fe-Cr) steels are more prone to corrosion but less susceptible to SCC compared to austenitic iron-chromium-nickel (Fe-Cr-Ni) steels. Chromizing can significantly reduce corrosion of Type 409 stainless steel (Fe-11Cr) in a simulated aqueous HTL solution. The objective of this study is to determine the SCC susceptibility of chromized Type 409 stainless steel, relative to the bare (non-chromized) case. The slow strain rate testing (SSRT) technique was used for this purpose. For simplicity of experimentation, SSRT was conducted using simulated HTL water containing 800 ppm potassium chloride (KCl), 1 M potassium carbonate (K2CO3), and 10 wt% acetic acid at ambient temperature and pressure. Complementary potentiodynamic polarization measurements and surface analysis by X-ray photoelectron spectroscopy (XPS) were also made to help interpret the SSRT results. The SSRT results show no significant difference in SCC susceptibility, regardless of the starting surface. Thus, chromizing, while significantly reducing the corrosion of Type 409 stainless steel, does not adversely affect SCC susceptibility, at least under the conditions tested.

Sulfide stress cracking inhibition of a supermartensitic stainless steel by using an imidazol obtained from palm oil

PurposeThis paper aims to use an imidazole-based n-ionic Gemini surfactant derived from palm oil to inhibit the sulfide stress corrosion cracking of a supermartensitic stainless steel.Design/methodology/approachThe slow strain rate testing technique, hydrogen permeation tests and potentiodynamic polarization curves have been used.FindingsAddition of the inhibitor below the critical micelle concentration (CMC) decreased the corrosion current density (icorr), but not enough to avoid embrittlement due to the entry of hydrogen into the steel. Instead, the addition of the inhibitor close to the CMC decreased the icorr, suppressed the entry of hydrogen and inhibited the sulfide stress cracking of steel. Finally, the addition of inhibitor above the CMC led to a slight increase of icorr and promoted localized corrosion, however, the sulfide stress cracking of steel was inhibited.Originality/valueA green sulfide stress corrosion cracking inhibitor of a supermartensitic stainless steel has been obtained.

Effect of AC interference on the stress corrosion cracking susceptibility of X65 steel under cathodic protection

The influence of alternating current (AC) on the stress corrosion cracking (SCC) susceptibility of X65 steel under cathodic protection (CP) was studied by slow strain rate testing (SSRT) and electrochemical techniques. The X65 steel exhibits an increase in SCC susceptibility and brittle morphology with increasing AC current density and CP potential. The effect of AC interference on the SCC susceptibility is more pronounced at −0.77 VSCE than −1.12 VSCE. The imposed AC signals at −0.77 VSCE decrease elongation, percentage reduction in area and produce a ductile to brittle transition in the fracture morphology, mainly controlled by an anodic dissolution mechanism. At −1.12 VSCE, AC interference enhances the kinetics of the cathodic reactions producing higher hydrogen concentration on the steel surface, that leads to hydrogen assisted cracking. Pitting corrosion was observed under CP potential and AC interference. The pitting severity in terms of size and depth, increases with increasing AC current density, especially at −1.12 VSCE. The maximum pit depth of 90 µm was found at the CP potential of −1.12 VSCE and 90 A/m2 AC (3 V rms). Microcracking and crack evolution from the pits were also observed.

Ethanolic Media Effect on the Susceptibility to Stress Corrosion Cracking in an X-70 Microalloyed Steel with Different Aging Treatments

The objective of this research was to evaluate the stress corrosion cracking (SCC) of X-70 micro-alloyed steel in contact with bio-ethanol and E-50 gasohol. Environmental factors, including water (1%, 3% and 5%) and NaCl (10 mg/L and 32 mg/L), as well as two aging treatments were studied. Experimental values were obtained by the Slow Strain Rate Test (SSRT) technique, X-ray fluorescence (XRF), and tensile test according to the information reported in the literature. The results of the SSRT for the SCC determination showed that this steel in these conditions did not show evidence of SCC, which was attributed to the formation of an oxide (Fe2O3) not soluble in ethanol. The oxide layer acts as a protector preventing the formation of pitting, one of the main causes of cracks initiation in SCC.

Studies on the Susceptibility of Modified 9Cr-1Mo Steel to Stress Corrosion Cracking in Sodium Hydroxide Using Slow Strain Rate Testing Technique

Round tensile specimens of modified 9Cr-1Mo steel were subjected to slow strain rate tests in 1-4 M sodium hydroxide (NaOH) solutions at 473 K to evaluate their susceptibility to caustic stress corrosion cracking (CSCC). The results obtained in NaOH solutions were compared with specimen tested in de-mineralized (DM) water. Secondary stress corrosion cracks were observed in all specimens tested in 1-4 M NaOH, the number of secondary cracks increased with increase in concentration up to 3 M. Tensile test data showed that ductility (%TE) decreased with increasing concentration of NaOH up to 3 M and nearly remained the same for 4 M NaOH. Time to failure was highest for specimen exposed in DM water and decreased with increasing concentration up to 3 M and remained constant thereafter. Crack velocity showed a trend of increasing velocity with increasing concentration of caustic media up to 3 M and remained same for 4 M NaOH. Laser Raman spectroscopic (LRS) analysis confirmed dissolution of protective magnetite and accelerated corrosion on the specimens exposed to 1-4 M NaOH solutions, leading to the formation of a number of oxides and oxyhydroxides. Fractographic studies showed typical surface oxide cracking with decohesions in all specimens. The studies showed that P91 steel is susceptible to CSCC in the concentrations from 1 to 4 M NaOH solutions at 473 K at a strain rate of 10−6 s−1. The evidence for dissolution of magnetite and the presence of decohesions indicated an important role for hydrogen in caustic cracking of P91 steel.

Composition design of 7XXX aluminum alloys optimizing stress corrosion cracking resistance using machine learning

In this paper, three different strategies based on machine learning methods were applied to Al-Zn-Mg-Cu series alloy composition design with the targeted property of stress corrosion cracking (SCC) resistance. By comparing the results of the strategies, it was discovered that the performance of the efficient global optimization (EGO) method was better than that of response surface optimization method, and much better than that of Random method, among which the Al-6.05Zn-1.46Mg-1.32Cu-0.13Zr-0.02Ti-0.50Y-0.23Ce (named EGO alloy) alloy had the best stress corrosion cracking resistance. The slow strain rate test (SSRT) technique was carried out to compare the EGO alloy with the traditional 7N01 alloy. It indicated that the ISCC of the new EGO alloy was lower than that of traditional 7N01 alloy for both single and double aging treatment. With the XRD, SEM and EDS analysis, it was found the rare earth elements formed Al8Cu4(Y, Ce) and quadrilateral phase Al20Ti2(Y, Ce) in the EGO alloy.

Influence of Scandium Addition on Stress Corrosion Cracking Susceptibility of Al-Zn-Mg Alloy in Different Corrosive Environments

Stress corrosion cracking (SCC) susceptibilities of Al-Zn-Mg alloys without and with Scandium addition were evaluated in 3.5% NaCl solution at different pH and different strain rate, using slow strain rate test technique. The results indicate that Sc addition reduces grain size and width of precipitation free zones, and transforms grain boundary precipitates from continuous distribution into interrupted distribution by inhibiting recrystallization. In solution at pH 1, pH 3 and pH 7, Sc addition reduces the degree of localized corrosion of alloy surface and SCC susceptibility of Al-Zn-Mg alloy. However, in solution at pH 10 and pH 12, grain refinement significantly promotes the diffusion of hydrogen atoms into matrix, thus Sc addition increases SCC susceptibility of Al-Zn-Mg alloy. Under different strain rate conditions, Sc addition can all reduce SCC susceptibility of Al-Zn-Mg alloy in solution at pH 1, pH 3 and pH 7, and can all increase SCC susceptibility of Al-Zn-Mg alloy in solution at pH 10 and pH 12. As a result, Sc modified Al-Zn-Mg alloy in practical applications should be avoided in alkaline environments.

Effect of Cooling Rate on SCC Susceptibility of β-Processed Ti–6Al–4V Alloy in 0.6M NaCl Solution

The effects of cooling rate on the stress corrosion cracking (SCC) susceptibility of β-processed Ti–6Al–4V (Ti64) alloy, including BA/S specimen with furnace cooling and BQ/S specimen with water quenching, were investigated in 0.6M NaCl solution under various applied potentials using a slow strain rate test technique. It was found that the SCC susceptibility of β-processed Ti64 alloy in aqueous NaCl solution decreased with fast cooling rate, which was particularly substantial under an anodic applied potential. The micrographic and fractographic analyses suggested that the enhancement with fast cooling rate was related to the random orientation of acicular α platelets in BQ/S specimen. Based on the experimental results, the effect of cooling rate on the SCC behavior of β-processed Ti64 alloy in aqueous NaCl solution was discussed.

Stress corrosion cracking susceptibility of thermally-aged Type 310S stainless steels in supercritical water

The effect of thermal ageing on the stress corrosion cracking (SCC) susceptibility of Type 310S stainless steel in supercritical water (coolant for a supercritical water cooled reactor design concept) was evaluated. SCC was evaluated using the slow strain rate testing technique, straining samples to 10% in a flowing autoclave test facility using 25 MPa SCW at 500 °C with 20 ppm dissolved oxygen. The localized deformation model for SCC initiation and a void-assisted film-cleavage model for SCC propagation can be used to explain the SCC susceptibility exhibited by the thermally-aged Type 310S stainless steel in supercritical water.

Comparison of SCC Behavior of 304L Stainless Steels With and Without Boron Addition in Acidic Chloride Environment

The stress corrosion cracking (SCC) behavior of 304L B4 grade borated stainless steel (SS) as well as 304L SS was investigated by constant load and slow strain rate testing (SSRT) techniques. The microstructure, pitting, and SCC behavior of borated SS in the as-received, sensitized, and solution-annealed conditions were analyzed. Potentiodynamic anodic polarization and double loop electrochemical potentiokinetic reactivation (DLEPR) experiments were carried out to find out pitting corrosion resistance and degree of sensitization (DOS). The number of boride particles (composed of Cr, Fe, and B) were highest for the specimen solution annealed at 1423 K/2 h. Solution-annealing treatment at 1423 K/4 h was found to be beneficial in improving the corrosion resistance of borated 304L SS. Although the borated 304L SS exhibited a higher DOS, it showed improved pitting corrosion resistance compared to 304L SS. Constant load experiments revealed the time to failure to be the highest for the specimen solution annealed at 1423 K/4 h. SCC susceptibility index (Iscc) values obtained from SSRT tests were lower for solution-annealed borated 304L SS compared to the as-received and sensitized conditions. The improved SCC resistance of borated 304L SS was attributed not only to the solution-annealing treatment but also the higher stacking fault energy (SFE) value compared to 304L SS.

Stress Corrosion Cracking of SA-543 High-Strength Steel in All-Volatile Treatment Boiler Feed Water

Susceptibility of SA-543 steel, its welds (with and without stress relief treatment), and the heat-affected zone (HAZ) to stress corrosion cracking (SCC) was investigated in de-aerated and aerated boiler feed water subjected to the all-volatile treatment (AVT-BFW), and distilled water at 275 °C using the slow strain rate testing (SSRT) technique. The SSRT specimens were tested at three extension rates (3.50 × 10−6, 9.00 × 10−6, and 7.50 × 10−5 mm/s) using a novel SCC testing rig capable of testing at high temperatures and pressures. There are no significant differences in the time-to-failure among the four tested specimens. The elongation of the specimens at the time of failure is in the range of 10-23%. The reduction of the cross-sectional area of the failed specimens is large (45-77%) and the absence of any signs of intergranular propagation in fractured specimens, determined by scanning electron microscopy, indicates that the failure is due to mechanical load and not due to SCC. Dissolved oxygen does not affect the susceptibility of the specimens to SCC, which could be due to the inhibition effect of the test solution. SA-543 steel as the base metal, its welds (with and without stress relief treatment), and the HAZ are suitable for use in hot AVT-BFW and distilled water.

Through-thickness inhomogeneity of localized corrosion in 7050-T7451 Al alloy thick plate

The through-thickness corrosion inhomogeneity of 7050-T7451 Al alloy thick plate was studied using immersion tests, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), slow strain rate testing (SSRT) technique combined with optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the through-thickness corrosion resistance is ranked in the order of T/2>surface>T/4. And the 75 mm-thick 7050 alloy plate presents better corrosion resistance than the 35 mm-thick plate. The results are discussed in terms of the combined effect of recrystallization and cooling rate in quenching. Alloy with lower volume fraction of recrystallization and smaller grain aspect ratio displays better corrosion resistance. The lower corrosion resistance caused by the slower cooling rate results from the higher coverage rate of grain boundary precipitates and larger width of precipitate free zone.

Stress Corrosion Cracking Behaviour of Flux Bounded TIG Welded AA2219 T87 Aluminum Alloy in 3.5 Weight Percent NaCl Solution

Limitation in penetration depth is a concern in conventional TIG welding. To improve penetration capability of TIG process, Flux Bounded TIG (FBTIG) has been developed. Stress corrosion cracking (SCC) behavior of FBTIG welds of aluminum alloy AA 2219 T87 is evaluated in 3.5 weight percent NaCl solution using Slow Strain Rate Test technique (SSRT) as per ASTM G129. SCC index defined as the ratio of the elongation of tensile tested specimen in NaCl to that of air is taken as a measure of the susceptibility to cracking. Based on the SCC index, it is concluded that the SCC resistance of FBTIG joints are good and comparable to that of conventional TIG welds.

Influence of Aging Treatments on Alterations of Microstructural Features and Stress Corrosion Cracking Behavior of an Al-Zn-Mg Alloy

7xxx series Al-Zn-Mg-(Cu) alloys have higher strength in their peak-aged (T6) states compared with other age-hardenable aluminum alloys; however, the maximum strength peak-aged state is more susceptible to stress corrosion cracking (SCC) which leads to catastrophic failure. The over-aged (T7) temper with 10-15% lower strength has higher resistance to SCC requiring oversized structural aerospace component applications. The medium-strength AA7017 Al-Zn-Mg weldable alloy without Cu is also prone to SCC under certain environmental conditions. In the present investigation, the SCC behaviors of an AA7017 Al-Zn-Mg alloys of different tempers have been assessed. Specific aging schedules have been adapted to an AA7017 alloy to produce various tempers, e.g., under-, peak-(T6), over-(T7), and highly over-aged tempers. Artificial aging behavior of the AA7017 alloy has been characterized by hardness, electrical conductivity measurements, x-ray diffraction, differential scanning calorimetry, and electrochemical studies. Slow strain rate test technique was used to assess the SCC behaviors of the AA7017 alloys of under-, T6, T7, and highly over-aged tempers in 3.5 wt.% NaCl solution at free corrosion potential (FCP) and at applied anodic potential, as well. Results revealed that the AA7017 alloy tempers are not susceptible to SCC in 3.5 wt.% NaCl solution at FCP, but severely damaging to SCC at applied anodic potentials. Microstructural features, showing a non-recrystallized grain structure and the presence of discrete, widely spaced, not-interconnected η precipitates at the grain boundaries, are the contributive factors by virtue of which the alloy tempers at FCP did not exhibit SCC. However, the applied anodic potential resulted in rapid metal dissolution from the grain boundary region and led to SCC. The local anodic dissolution (LAD) is believed to be the associated SCC mechanism.

Effect of Nitrogen Content on the Tensile and Stress Corrosion Cracking Behavior of AISI Type 316LN Stainless Steels

This paper deals with the effect of nitrogen on the tensile and stress corrosion cracking (SCC) behavior of type 316LN stainless steel. Yield stress (YS) and ultimate tensile stress (UTS) increased while the ductility [% total elongation (% TE)] decreased with increasing nitrogen content. Evaluation by conventional assessment parameters, such as ratios of UTS, % TE and SCC susceptibility index, derived by SCC testing using the slow strain rate testing (SSRT) technique indicated an improvement in SCC resistance on increasing the nitrogen content. However, crack growth rates, calculated from ratios of fracture stress from the SSRT tests in liquid paraffin and boiling 45 % magnesium chloride in SSRT tests, and the constant load tests at loads corresponding to 20 % YS in boiling 45 % magnesium chloride conclusively established that the SCC resistance of type 316LN stainless steel decreased with increasing nitrogen content.

Anisotropy of localized corrosion in 7050–T7451 Al alloy thick plate

The corrosion anisotropy of 7050–T7451 Al alloy thick plate in NaCl solution was investigated by immersion tests, slow strain rate testing (SSRT) technique, potentiodynamic and anode polarization measurements, optical microscropy (OM) and scanning electron microscopy (SEM) observations. The results show that the thick plate exhibits severe corrosion anisotropy due to the microstructure anisotropy. The observations of immersion surfaces together with the analysis of polarization curves reveal that the differences of the corrosion morphologies on various sections in this material are mainly related to the area fraction of the remnant second phase, and higher area fraction displays worst corrosion resistance. The stress corrosion cracking (SCC) susceptibility of different directions relative to the rolling direction is assessed by SSRT technique, ranked in the order: S direction >L direction >T direction. The result show that the smaller the grain aspect ratio, the better the corrosion resistance to SCC.

Effect of Heat Treatment on the Stress Corrosion Cracking Susceptibility of a Dual-Phase Steel

The stress corrosion cracking (SCC) susceptibility of a microalloyed steel under different heat treatments in 3.5% sodium chloride (NaCl) solution with different pH values (3, 7, and 12) using the slow strain rate testing (SSRT) technique has been evaluated. Heat treatments include the as-received condition (with a martensitic/perlitic microstructure), a quenched from 750°C condition (producing a dual-phase microstructure consisting of martensite/ferrite), and a quenched from 950°C condition (producing an almost pure martensitic microstructure). The as-received and quenched from 950°C conditions were highly susceptible to SCC whereas the steel with the dual-phase microstructure was only mildly susceptible. A direct correlationship was found between the corrosion rate and the SCC susceptibility. The SCC mechanism seems to be hydrogen embrittlement.

Environmental Assisted Cracking Behavior of Sigmatized Super Duplex Stainless Steel in Oilfield Production Brine

The slow strain rate test (SSRT) technique was used to investigate the stress corrosion cracking (SCC) susceptibility of sigmatized super duplex stainless steel (SDSS) grade UNS S32760, exposed to a simulated oilfield brine containing carbon dioxide/hydrogen sulfide (CO2/H2S) at 80°C. The sigma phase was precipitated by heat treatment (HT) at 850°C for various durations (0 to 12 min). Results show that low levels (less than 2%) of sigma have no profound impact on the mechanical and corrosion properties of SDSS. However, at higher levels (greater than 2%) of sigma phase, there is severe loss in ductility and increased corrosion rate. Fractographic observations using scanning electron microscopy (SEM) show that the fracture mode shifts from ductile to transgranular cracking with increasing levels of sigma phase. Electron-backscattered diffraction (EBSD) results show that crack nucleation occurs in the sigma grains. The cracking mechanism involves brittle fracture of sigma phase and slip-assisted anodic diss...

STRESS CORROSION CRACKING BEHAVIOR AND MECHANISM OF X65 AND X80 PIPELINE STEELS IN HIGH pH SOLUTION

X80 pipeline steel is a low carbon, micro–alloyed high–grade steel and a fairly new steel used as pipeline material in worldwide. The material has the huge potential to be used widely for building the oil/gas transmission pipelines in the 21st century because of its high intensity and high toughness. X80 steel has been adopted on the second west–east gas transmission pipeline project in China. Whereas, there is a issue, stress corrosion cracking (SCC) is more likely to occur on X80 pipeline steel, because of its high strength and fine microstructure, it will be a vital threat to safe operation of buried oil/gas pipelines. However, the related research about SCC behavior of X80 pipeline steel in high pH carbonate/bicarbonate solution is rarely reported at present. Comparing with X65 pipeline steel, X80 steel has higher strength and finer microstructure, because of these differences, it may have some certain influence on the SCC behavior of X80 steel, and even change the mechanism of high pH SCC. Consequently, it is necessary to study the SCC behavior and mechanism of X80 steel in high pH solution. In this work, the SCC behavior and mechanism of X65 and X80 pipeline steels in high pH concentrated carbonate/bicarbonate solution are investigated by slow strain rate testing (SSRT), electrochemical test and surface analysis technique. The results show that the cracking mode of X65 pipeline steel in carbonate/bicarbonate solution is intergranular SCC (IGSCC). While the mixed cracking mode of X80 pipeline steel in high pH solution is that the crack is intergranular in the early stage of the crack propagation, and transgranular SCC (TGSCC) in the later stage, which is mainly * 6r=$/= *v 51131001 B6r!n^B oQ*v 2012AA040105 :5 X^=#* : 2013–06–08, X^6 #* : 2013–09–07 B z : 0 m, y, 1985 ~?, !Q? DOI: 10.3724/SP.J.1037.2013.00315 j 12 / le : X65 A X80 /$ pH +U%bdI F(U2 f^C 1591 transgranular. The cracking mode of X80 steel is associated with the microstructure and high strength of the steel. The key reason for TGSCC occurring of X80 steel is that the decrease of pH value of the crack tip during the crack propagation process. The SCC mechanism of X65 steel in high pH carbonate/bicarbonate solution is anodic dissolution (AD) mechanism. While the SCC mechanism of X80 steel in high pH solution is mixed controlled by both AD and hydrogen embrittlement (HE) mechanisms, and the HE mechanism may play a significant role in the deep crack propagation at the later stage. The high strength X80 steel consisted of fine acicular ferrite and granular bainite has a higher susceptibility to SCC in high pH solution, comparing with low strength X65 steel composed of ferrite and pearlite.