Steel In High Temperature Water Research Articles

Corrosion of 316L stainless steel in high temperature water and steam: effects of simultaneous proton irradiation

316L stainless steel was exposed to 320 °C hydrogenated water and 480 °C hydrogenated steam for 24 h and 72 h while simultaneously irradiated with 5.4 MeV protons to yield a damage rate of 7 × 10–7 dpa/s. Oxide films characterized in cross-section STEM revealed chemical and morphological differences. High levels of radiolysis in water resulted in significantly reduced corrosion rates while inducing dissolution of the inner oxide layer, whereas in steam the effects of radiolysis are insignificant. Conversely, displacement damage effects are negligible in water but significantly increase the corrosion rate in the steam condition through the growth of inner oxide porosity.

Corrosion of 316L stainless steel in high temperature water and steam: Mechanisms of corrosion

316L stainless steel was exposed to 320 °C hydrogenated or aerated water and 480 °C steam for up to 72 h to determine the aqueous corrosion mechanisms. The thermodynamics of the corrosion process are interpreted using a new concept called the excess volume which predicts stable formation of pores in the inner oxide layer. Corrosion rates are found to be correlated with inner oxide porosity. Inner oxide thicknesses were measured, and thermodynamic modelling was used to determine that the rate-limiting step of corrosion is fluid transport of oxygen via pores in the inner oxide layer.

Effects of surface finishes, heat treatments and printing orientations on stress corrosion cracking behavior of laser powder bed fusion 316L stainless steel in high-temperature water

Stress corrosion cracking (SCC) of laser powder bed fusion 316 L stainless steel in oxygenated high-temperature water environments with chloride addition at 288 °C was studied. The influences of surface finishes (as-built, mechanically polished, Hirtisation® and shot peened), heat treatments (solution annealing at 1066 and 1150 °C and hot isostatic pressing) and the printing orientations on SCC were evaluated. Hirtisation resulted in a lower SCC susceptibility than as-built or polished surface while shot peening showed the lowest apparent SCC resistance. A high annealing temperature decreases SCC resistance. The effect of printing orientation is material and environment dependent.

General corrosion behavior and mechanism of low-temperature plasma nitrided 17–4PH stainless steel in high temperature water

The general corrosion behavior and mechanism of low-temperature plasma nitrided 17–4PH stainless steel with and without a work-hardened layer in high temperature water were investigated. The general corrosion test was conducted under high temperature (280 °C) and high pressure (13.3 MPa) circulating water conditions. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were employed to reveal the underlying mechanism. The results showed that, for the non-nitrided specimens, high density of grain boundaries and dislocations in the work-hardened layer accelerated the formation of the inner oxide and the deposition of the outer oxide, which reduced the corrosion resistance. Besides, the increased surface roughness also enhanced the deposition of the outer oxide layer. For the nitrided specimen without a work-hardened layer, the nitrided layer was composed of expanded martensite. The compressive residual stress in the expanded martensite could inhibit element diffusion, thus reducing the thickness of the inner oxide layer and mitigating corrosion. While for the nitrided specimen with a work-hardened layer, the nitrided layer was mainly composed of γ’-Fe4N twins, which induced intergranular corrosion and reduced the corrosion resistance. Besides, the diffusion of nitrogen from the nitrided layer into the solution during the corrosion process influenced the local H+ content in the solution, subsequently impacting the deposition of the outer oxide particles. In conclusion, the presence of a work-hardened layer is undesirable for plasma nitriding in improving corrosion resistance in high temperature water. These findings can provide valuable insights for the extension of the material's service life.

Microstructural Understanding of Flow Accelerated Corrosion of SA106B Carbon Steel in High-Temperature Water with Different Flow Velocities.

All light or heavy water reactors fabricated with carbon steels suffer from flow-accelerated corrosion (FAC). The FAC degradation of SA106B with different flow velocities was investigated in terms of microstructure. As flow velocity increased, the major corrosion type changed from general corrosion to localized corrosion. Severe localized corrosion occurred in the pearlite zone, which can be the prior location for generating pits. After normalizing, the improvement in microstructure homogeneity reduced the oxidation kinetics and lowered cracking sensitivity, causing a decrease in FAC rates of 33.28%, 22.47%, 22.15%, and 17.53% at flow velocity of 0 m/s, 1.63 m/s, 2.99 m/s, and 4.34 m/s, respectively. Additionally, localized corrosion tendency was decreased by reducing the micro-galvanic effect and tensile stresses in oxide film. The maximum localized corrosion rate decreased by 21.7%, 13.5%, 13.8%, and 25.4% at flow velocity of 0 m/s, 1.63 m/s, 2.99 m/s, and 4.34 m/s, respectively.

SCC behaviour of laser powder bed fused 316L stainless steel in high-temperature water at 288 °C

Stress corrosion cracking (SCC) behaviour of laser powder bed fused stainless steel 316L was evaluated with U-bend testing in oxygenated high-temperature water at 288 °C. The effects of solution annealing temperature (1066, 1150 and 1200 °C), surface finish (as-built and wire cut) and the sample orientations on the SCC behaviour were studied. The results show that a higher annealing temperature introduces further recrystallization, coarsening of the oxide inclusions and a decrease in resistance to SCC. A wire cut surface leads to a higher susceptibility to SCC than the as-built surface. Sample orientation was found not to affect the SCC susceptibility.

Effect of heat treatment on corrosion behaviour of additively manufactured 316L stainless steel in high-temperature water

Post-manufacturing heat treatment (PMHT) effect on the corrosion behaviour of directed energy deposition (DED) 316L stainless steel was investigated in hydrogenated water at 325 °C. As-DEDed and residual stress relief PMHTed (850 °C/2 h) specimens exhibited similar corrosion resistance, showing thick and thin inner oxide layer on the Cr-depleted cell interior and Cr-rich cell boundary, respectively. Composition homogenization PMHTed (1150 °C/1 h) specimen showed the best corrosion resistance with the much thinner inner oxide layer. The enhanced corrosion resistance of the PMHTed DED 316L than wrought 316L could be related to the unique large grain in DED 316L.

Clarifying the mitigation effect of proton irradiation on the intergranular oxidation of 316L stainless steel in high temperature water

The role of proton irradiation in the intergranular oxidation of 316L stainless steel after long-term immersion in simulated PWR primary water was clarified by comparing the microstructural and microchemical features of oxide between the irradiated grain boundary (GB) and its un-irradiated counterpart. As such, the interference from difference in GB structure can be ruled out. Surprisingly, the results reveal that the intergranular oxide penetration in the irradiated region is shallower than that in the un-irradiated region. It is found that Si segregated at the irradiated GB diffuses outwards preferentially and gets oxidized due to its high diffusivity and affinity to oxygen. The Si-enriched oxide in the intergranular oxide tip of irradiated GB can act as a temporary diffusion barrier for oxygen, although it tends to dissolve near the sample surface. Meanwhile, the efficiency of elements (especially Cr) transport along irradiated GB to the oxidation front is promoted mainly due to the vacancies created by preferential diffusion of Si, resulting in higher Cr content at the intergranular oxide tip. The combination of Si and Cr enrichments in the intergranular oxide tip can enhance the resistance to oxidation and eventually leads to a lower oxidation rate for the irradiated GB. For the first time, our study determines that irradiation can enhance the intergranular oxidation resistance of stainless steel after long-term immersion in simulated PWR primary water when the sample is not stressed.

Role of Hydrogen in Metal Oxidation—Implication to Irradiation Enhanced Corrosion of Ni-Based Alloys and Stainless Steels in High Temperature Water

Hydrogen plays various roles in metals or at metal–environment interfaces. Well known effects on metals are hydrogen embrittlement, hydrogen enhanced local plasticity, hydrogen enhanced strain-induced vacancy, hydrogen accelerated oxidation, hydrogen-induced creep, and their synergy. In this study, the potential roles of hydrogen in materials degradation are demonstrated and studied by two different tests. One is the high temperature oxidation of Ni-based alloy in various environments with hydrogen penetration, and the other is the effects of neutron flux/fluence on the oxidation kinetics and SCC of 316L and 316LN stainless steels, regarding a possible role of transmuted H from N. The results emphasize that the hydrogen either permeated into metals from surrounding environments, such as high temperature water or gaseous hydrogen, or generated in metals by nuclei transmutation, such as hydrogen transmuted from N atoms in metals, which can promote metal oxidation through multiple mechanisms. Apparently, the oxidation/corrosion phenomenon is a synergy of sub-mechanisms. For instance, dissolved hydrogen (DH) is usually believed to slow down the corrosion process for lowering the open circuit potential (OCP). However, H also facilitates the transport of the cations in oxide, thereby accelerating the corrosion process. In this bi-mechanism system, two different, contradictory mechanisms work and exist simultaneously. Therefore, whether the metallic materials are benefited or degraded by the H during its oxidation process depends on which sub-mechanism is dominant. Namely, hydrogen can play the role an oxidant in the metal and metal/oxide interface to pre-oxidize metal elements, such as Cr, Ni, and Fe, and possibly promote inward oxygen diffusion and the oxidation rate at the interface. Moreover, hydrogen may play a role as a reductant in oxides where existing oxides can be reduced. Then, the protective capability of oxides will be decreased to result in corrosion acceleration at the metal–oxide interface. These phenomena were observed in Ni-based alloy and possibly austenitic stainless steel containing N such as 316LN SS. This work demonstrates a part of the role of hydrogen on oxidation, and more extensive and systematic work is needed to delineate the role of hydrogen on oxidation with and without irradiation.

Low-cycle fatigue behaviors of 316L austenitic stainless steel in high temperature water: Effects of pre-soaking, dissolved oxygen, and boric acid & lithium hydroxide

Latest studies found that for 316LN austenitic stainless steel (ASS), its LCF life decreased noticeably in high temperature water containing a great amount of dissolved oxygen (DO) (2 ppm DO), compared with that in the water containing 50 or 100 ppb DO. This finding is different from previous studies about ASSs. This study confirmed that the 316L had similar behavior to 316LN. The LCF life of 316L in water containing 1000 ppb DO water was considerably shorter than that in the water containing 50 ppb DO. Addition of boric acid & lithium hydroxide and pre-soaking did not display noticeable effects on the LCF life of this material in the water with 1000 ppb DO, indicating the discrepancy between the latest studies and previous studies was not caused by the boric acid & lithium hydroxide and pre-soaking. This study also confirmed that similar to 316LN, when a certain amount of DO was added into the water, the amount of hydrogen absorbed into the material decreased significantly compared with that when the DO was less than 5 ppb.

Improving the corrosion and stress corrosion cracking resistance of 316 L stainless steel in high temperature water by water jet cavitation peening

Water jet cavitation peening (WJP) was used to improve the corrosion and stress corrosion cracking (SCC) of cold worked 316L stainless steel (316L SS) in high temperature water. WJP induced changes in residual stress and microstructure of the surface layer on corrosion and SCC were investigated. The investigation was conducted by comparing the corrosion and SCC of the un-treated (UT) and WJP treated specimens by exposure tests and slow strain rate tensile (SSRT) tests. The results revealed that WJP obviously improved the corrosion and SCC resistance of 316L SS, which is attributed to the increase of residual compressive stress and the change of the microstructure of the surface layer.

Effects of Potential on the Electrical Conductivity of a Solution within a Crevice of Stainless Steel in High-Temperature Water

This study investigates the effects of potential [electrochemical corrosion potential (ECP)] on the water chemistry within a crevice of stainless steel in 288°C water containing Cl− major anionic impurities. In situ measurements of the electrical conductivity of a solution within a 15-μm-gap crevice (σcrev) were conducted using small sensors installed at different crevice depths. The ECP at the external surface of the crevice specimen (Eext) was controlled by the dissolved oxygen concentration in the bulk water. An increase in Eext from approximately −0.49 VSHE (vs. a standard hydrogen electrode at 288°C) to −0.12 V resulted in an increase in σcrev from 12 μS/cm to 160.3 μS/cm at 21 mm from the crevice mouth. Finite element model analysis taking into account the electrochemical reaction quantitatively reproduced this behavior. Cl− was considered to be the major anionic species transported into the crevice in this potential range. A further increase in Eext up to 0.3 V led to a decline in σcrev. An increase in the flux of oxidizing (O2 and and alkalizing species (OH−) into the crevice was considered the cause of this behavior.

Environmental Fatigue Behavior of a Z3CN20.09M Stainless Steel in High Temperature Water

The low-cycle fatigue behavior of a Z3CN20.09M austenitic stainless steel was investigated and its fatigue life in high temperature water was compared to that in the air at room temperature. It is found that the fatigue life in water at 300 °C was shorter than that in air, and it decreased with the decreasing strain rate from 0.4% to 0.004%/s. The ductile striations having streamed down features were observed at the strain rate of 0.004%/s, indicating that Z3CN20.09M austenitic stainless steel experienced anodic dissolution. The fatigue life obtained in the present experiment was consistent with that using prediction models.

Improving the Corrosion and Stress Corrosion Cracking Resistance of 316l Stainless Steel in High Temperature Water by Water Jet Cavitation Peening

Improving the Corrosion and Stress Corrosion Cracking Resistance of 316l Stainless Steel in High Temperature Water by Water Jet Cavitation Peening

Mechanical and metallurgical considerations on the effects of ppb-level chloride on stress corrosion cracking of low alloy steels in high-temperature water

This paper studies the effects of very low-level chloride (< 5 ppb) on the stress corrosion cracking (SCC) growth of low-alloy pressure vessel steel in oxygenated high-temperature water. Chloride levels as low as 3 ppb increase SCC susceptibility. Besides the chemical reason, this paper provides perspectives on the underlying mechanical and metallurgical contributions. A substantial variation was observed from three high-sulphur steels. Sulphur is not the only contributor to SCC. The synergy of material, environmental, and mechanical parameters controlled the crack-tip strain rate and crevice chemistry that govern the SCC response in the high-purity high-temperature water environments at intermediate K.

Acceleration of Environmentally Assisted Cracking Initiation of the Type 316L Steel in High-Temperature Water and Hydrogenated-Steam Vapor Environments

Environmentally assisted cracking of solution-annealed Type 316L austenitic stainless steel with two different surface treatments (polished versus ground) was investigated using the constant extension rate tensile test methodology in high-pressure water at 350°C and low-pressure H2-steam vapor at 350°C, 400°C, 440°C, and 480°C, while maintaining electrochemical corrosion potentials in the NiO stability regime. Flat tapered specimens were used to indentify the threshold stress for cracking (∼400 MPa) under these environmental conditions. Intensive oxidation and typical intergranular cracks were observed to initiate from the polished surface at 400°C and 440°C, whereas wavy cracks initiated on the ground surface. The results indicate that the ultrafine-grained layer formed adjacent to the ground surface effectively suppressed intergranular crack initiation under these test conditions. The slow loading under H2-steam vapor at 400°C under the oxidizing condition (NiO) was found to be a suitable high-accelerated test to study early stages of the cracking.

Corrosion Behavior and Mechanism of Irradiated 304 Nuclear Grade Stainless Steel in High-Temperature Water

Corrosion behavior and mechanism of irradiated 304 nuclear grade stainless steel were studied in simulated pressurized water reactor primary water. The microstructure of the oxide formed on the steel irradiated to different doses over an exposure period range of 25–1500 h was analyzed and compared. It was found that the general and intergranular corrosion rates of the steel were increased with irradiation dose, in correspondence with an evolution of the general oxide and the oxide formed at the grain boundary. Correlation of the oxide evolution with the corrosion kinetics and mechanism has been discussed in detail.

Corrosion Behavior of High-Strength Low-Alloy Steel in High-Temperature Water with Zinc and Aluminum Simultaneous Injection

Oxide films were formed on A508-3 steel in simulated pressurized water reactor (PWR) primary water at the temperature of 561 ± 1 K for 168 h with zinc and/or aluminum injection. Corrosion behaviors of oxide films were analyzed by electrochemical polarization, electrochemical impedance spectroscopy, Mott-Schottky plots, photocurrent measurement, scanning electronic microscopy, and x-ray diffraction. The results showed that zinc and aluminum simultaneous injection technology decreased the corrosion current density, increased the impedance value, made the oxide film more compact, and affected the semiconductor properties of the oxide film. The increase in zinc concentration improved the corrosion resistance to some extent. ZnAl2O4 phase, with extremely low solubility and high stability, had been detected in the oxide film; this substance changed the composition of the oxide film and affected the corrosion behavior of A508-3 steel.

Effects of hydrogen peroxide on 304 stainless steel in high temperature water

Hydrogen peroxide (H2O2), an oxidizer produced by water radiolysis, is considered one of the main contributors to corrosion of the stainless steel (SS) components in the cooling system of nuclear reactors. The detailed understanding of this chemical system is however still missing. The present research aimed to study the effects of H2O2 on 304 SS. The surface morphology and the chemical composition of the SS specimens after experiment were examined using Scanning Electron Microscope – Energy Dispersive X-ray (SEM-EDX). The change in atomic % of Fe, Cr, Ni, and O as a function of temperature will be reported. The corrosion type and possible corrosion products will be proposed and discussed.

Quantitatively related acoustic emission signal with stress corrosion crack growth rate of sensitized 304 stainless steel in high-temperature water

Stress corrosion cracking (SCC) of sensitized 304 stainless steel in high-temperature water was in-situ monitored by coupling acoustic emission (AE) and direct current potential drop (DCPD) techniques. The AE signals were identified using novel recurrence quantification analysis (RQA) and k-mean cluster method. It was found that the RQA is feasible to identify the evolution of different AE waveforms generated by ligament tearing and plastic deformation of the crack tip. The AE cumulative hits rate was linear with the SCC crack growth rate, providing a possibility for applying the AE technique to quantitatively evaluate SCC in high-temperature water.