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Stress corrosion cracking (SCC) susceptibility of austenitic EN 1.4301 (AISI 304, UNS S30400) stainless steel was studied as a function of electrode potential at T = 190°C in 15 g/kg NaOH + 150 g/kg Na2S containing caustic environment simulating heavy black liquors (HBL) of the pulp industry. Severe cracking was detected at the corrosion potential and at the cathodic potential of −0.11 VMo/MoS2 reference electrode. On the other hand, at anodic potentials of 0.03 VMo/MoS2 to 0.3 V Mo/MoS2 no cracking was observed. Thus, SCC of EN 1.4301 steel can potentially be mitigated in HBL environment by applying anodic protection. At the corrosion potential, selective dissolution of Fe and slight localized enrichment of Ni and Cr, as well as Na, S, and O, was observed. At anodic potentials, Fe was selectively dissolved and marked enrichment of both Ni and Cr, as well as Na, S, and O, took place in the corrosion product. The simultaneous enrichment of Ni and Cr in the corrosion product film was concluded to be the precondition to prevent SCC.

The resistance of commercial duplex stainless steels (DSS) UNS S32205 and UNS S32101 to corrosion and stress corrosion cracking (SCC) has been studied using immersion tests and slow strain rate tests (SSRT) in hot alkaline-sulfide solution, with and without chloride ions, at 170°C. Weight-loss coupons of austenitic, superferritic, and DSS alloys were used to study the influence of alloy composition. SCC susceptibility of UNS S32205 and S32101 was evaluated in 150 g/L sodium hydroxide (NaOH, 3.75 M) and 50 g/L sodium sulfide (Na2S, 0.64 M) with 0 to 100 g/L sodium chloride (NaCl, 0 to 1.7 M) at 170°C, using SSRT at an initial strain rate of 2 × 10−6 s−1. The results indicate that there is a complex relationship among the chloride concentration, alkalinity, and percent sulfidity of the solution and behavior of the stainless steels. Corrosion resistance of the ferrite phase of DSS was superior to the austenite phase in chloride-containing solutions, which had an important role in SCC initiation. Crack initiation in the austenite phase and at austenite-ferrite phase boundaries of DSS was enhanced by the presence of chlorides. These findings demonstrate that chloride ions have an important role in the corrosion and SCC susceptibility of DSS in hot alkaline-sulfide solutions.

The cracking of composite tube systems based on Type 304L stainless steel (SS) (UNS S30403) in the lower-furnace section of kraft recovery boilers continues to be a serious problem. One remedial approach used by pulp mills involves replacing the conventional system based on Type 304L SS with alternative composite tube systems based on Alloys 825 (UNS N08825) and 625 (UNS N06625). U-bend stress corrosion cracking (SCC) tests were conducted on these alloys in a sodium sulfide hydrate-sodium hydroxide (Na2S·xH2ONaOH) molten salt mixture at 180°C (simulated wash-water environment) to help rationalize the observed service performance and to help assist with the selection of the more resistant composite tube system. Attention was given to studying relative SCC resistance of those three alloys in relevant metallurgical conditions, which include mill-annealed, sensitized, cold-worked, and solution-annealed conditions. It was concluded that Type 304L SS is susceptible to cracking even with an ideal micros...

Austenitic stainless steels (SS) are known to be susceptible to caustic stress corrosion cracking (SCC) at temperatures higher than ∼121°C. However, when sulfides are present in caustic so...

The hydrogenation inhibitive effect of sodium sulfide (Na2S) on Ti-6% Al-4% V alloy (UNS R56400) in aqueous sulfuric acid solution (H2SO4[aq]) was investigated qualitatively and quantitatively using optical microscopy, x-ray diffraction (XRD), and glow-discharge spectrometry (GDS). Introduction of Na2S into the electrolyte resulted in an obvious inhibitive effect of hydrogen absorption on as-received (covered with a thin thermal oxide film < 0.5 μm) and abraded specimens (free of thermal oxide film) irrespective of applied current density and operating period. The contrary effect of Na2S on Ti-6% Al-4% V alloy vs ferrous alloys could have resulted from the fact that molecular hydrogen sulfide (H2S), which adsorbed on the titanium surface as on the iron surface, facilitated formation of a thin layer of E titanium hydride (TiH2). TiH2 effectively retarded ingress of hydrogen.

Phase constitution of the iron (Fe)-aluminum (Al) alloy layer and corrosion behavior of the welding zone of Al-coated steel in saturated hydrogen sulfide (H2S) solution were studied using a metalloscope, scanning electron microscope, and x-ray diffractometer. H2S was generated by reacting sulfuric acid (H2SO4) solution and saturated sodium sulfide (Na2S) solution. The Fe-Al alloy layer was composed mainly of δ-Fe(Al) solid solution, Fe3Al, and FeAl. There were no brittle FeAl2, Fe2Al5, or FeAl3 phases in the Fe-Al alloy layer. Pitting attack occurred in the Fe-Al alloy layer in the heat-affected zone (HAZ), while electrochemical attack was concentrated in the fusion zone.

Mild steel samples were studied by chronoamperometry in sodium sulfide (Na2S) aqueous solution. Pit nucleation and growth also were monitored by optical microscopy. The influence of variables such as temperature, polarization potential, surface roughness, the presence of electrochemically generated oxide layers, and the simultaneous presence of potassium hydroxide (KOH) was studied. The influence of each parameter on pit shape and growth was reviewed. Different reactions and competitive processes were proposed based on the experimental results.

The resistance of commercial austenitic, ferritic, and duplex alloys to stress corrosion cracking in a 5% NaOH-2% Na2S-2% Na2CO3-0.2% Na2SO4-0.1 % NaCl solution at 150° has been studied by...

The stress corrosion cracking (SCC) of 90/10 Cu-Ni alloy in sulfide solutions is not reported in the literature. The SCC behavior of the alloy was studied in dilute and concentrated Na2S solutions at room temperature. The alloy was found to be susceptible to SCC under slow strain rate conditions in the concentrated (0.1 to 1 M) sulfide solutions, but not in the dilute (0.002 to 0.03 M) solutions. On the basis of electrochemical data and EPMA analysis of the metal/film interface of the cracked samples, the mechanism of cracking can possibly be attributed to a dealloying (selective dissolution) phenomenon where the copper matrix but not the solute Ni is selectively removed.

The constant potential intermediate strain rate technique (ISRT) was used to evaluate the stress corrosion cracking (SCC) susceptibility of yellow brass in sodium sulfate and sodium sulfit...

Stress-corrosion cracking experiments have been performed on a high-strength carbon steel exposed to acidified sodium chloride solution poisoned with sodium sulfide. The electrochemical potential of the specimen was monitored during the experiment, and this paper reports the observed electrochemical noise. The analysis was performed using both the maximum entropy method and the discrete Fourier transform. A consistent noise behavior was observed throughout the experiment, with the only perturbation of any significance being associated with major transients that occurred when the specimen actually failed. The average noise power measured over a period of the same order as the duration of the transients has been found to be an effective method of detecting them, but it is expected that this will be much more difficult in service conditions.

Experiments were performed to determine susceptibility of 90/10 and 70/10 Cu-Ni alloys to sulfide induced corrosion as related to sulfide concentration, sea water velocity, and duration of sulfide exposure. All exposures were conducted in fresh sea water, and the range of experimental variables included sulfide concentration (from sodium sulfide) from 0.007 to 0.25 mg/L, sea water velocity after sulfide exposure from 0.5 to 5.3 m/s, and sulfide exposure times from 1 to 90 days. Results showed that both alloys undergo localized attack in sea water environments with as little as 0.007 mg/L sulfide. The velocity dependence of active attack was minimal in the range tested. Duration of sulfide exposure, particularly at low sulfide concentrations, is a key factor in causing localized corrosion in these alloys and in the degree of attack experienced. On the basis of long term continuous low concentration sulfide exposure, 70/30 Cu-Ni appears to undergo less severe attack than that seen with 90/10 Cu-Ni.