Enclosed atmospheric corrosion in ship spaces

Abstract

The process of enclosed atmospheric corrosion within ship spaces is investigated. It is proposed that corrosion rates are influenced mainly by three parameters; time of wetness, salt deposition and temperature. Assuming atmospheric corrosion to be primarily cathodically controlled, it is shown that, as a first approximation, the rate of atmospheric corrosion is linearly proportional to both temperature and salt deposition. This is shown to be consistent with available experimental data. An equation is presented for the prediction of corrosion rates within ship spaces exposed to an enclosed atmosphere, such as cargo holds and ballast tanks, on a per voyage basis. The influencing parameters identified in this study, and the proposed model, provide a starting point for future probabilistic modelling of one component of ship corrosion, namely, enclosed atmospheric corrosion.     

Corrosion monitoring of nickel-containing steels in marine atmospheric environment

Corrosion monitoring of nickel-containing steels has been performed in a natural atmospheric environment using AC impedance technique. A pair of identical comb-shape steel electrodes embedded in epoxy resin was used as a probe electrode for the corrosion monitoring. Three different probes of ordinary carbon steel, 2.5%Ni- and 5%Ni-containing steels were exposed to a natural marine atmosphere for the period of 14 months. The instantaneous corrosion rate of the steels was monitored by continuous measurements of the polarization resistance, and time of wetness of the steel surface was determined from high frequency impedance. The measurement was automatically carried out with an AC corrosion monitor placed at the exposure site, and data transmission between the exposure site and laboratory was performed through cellular phones.     

Corrosion failure of marine steel in sea‐mud containing sulfate reducing bacteria

The corrosion failure behavior of marine steel is affected by stress, which exists in offshore structures at sea‐mud region. The sulfate reducing bacteria (SRB) in the sea‐mud made the steel more sensitive to stress corrosion cracking (SCC) and weaken the corrosion fatigue endurance. In this paper, a kind of natural sea‐mud containing SRB was collected. Both SCC tests by slow strain rate technique and corrosion fatigue tests were performed on a kind of selected steel in sea‐mud with and without SRB at corrosion and cathodic potentials. After this, the electrochemical response of static and cyclic stress of the specimen with and without cracks in sea‐mud was analyzed in order to explain the failure mechanism. Hydrogen permeation tests were also performed in the sea‐mud at corrosion and cathodic potentials. It is concluded that the effect of SRB on environment sensitive fracture maybe explained as the consequences of the acceleration of SRB on corrosion rate and hydrogen entry into the metal.     

Corrosion behaviour of stainless steels in aqueous solutions of methanesulfonic acid

The corrosion behaviour of different grades of stainless steel in five commercial products labeled as 70% aqueous methanesulfonic acid was investigated. Chemical analysis showed that these products contain different amounts of impurities, most probably the consequence of the production procedure. Three austenitic stainless steel grades, 304, 316 and 316Ti, are widely used for storage and transportation vessels for methanesulfonic acid (MSA). Corrosion behavior has been studied by electrochemical techniques, immersion tests and by surface analysis. The selected stainless steels are highly stable in the most purified acid, but the presence of impurities in MSA disrupts the metal’s surface, leading to corrosive attack.     

Corrosion of stainless steels under heat transfer conditions in nitric acid

Abstract

Novel test rigs are described for the study of the corrosion of metal specimens under controlled heat fluxes. In the corrosion of stainless steels in nitric acid, tests at various heat fluxes with steel surface temperature kept constant have shown that the cooler acid present at the surface under higher heat fluxes leads to slightly smaller corrosion rates than under isothermal conditions. Crevice corrosion can develop under the gasket sealing the stainless steel specimen to the test cell. This crevice corrosion can produce enhanced corrosion rates (by factors up to 100), not only on surfaces within the crevice, but also on those external to the crevice. The factors influencing the development of crevice corrosion are discussed.     

Corrosion behavior of martensitic and precipitation hardening stainless steels treated by plasma nitriding

Plasma nitriding is a well established technology to improve wear and corrosion properties of austenitic stainless steels. Nevertheless, in the case of martensitic stainless steels, it continues being a problem mainly from the corrosion resistance viewpoint.In this work, three high chromium stainless steels (M340, N695 and Corrax) were hardened by ion nitriding at low temperature, intending to preserve their corrosion resistance.Corrosion behavior was evaluated by CuSO₄ spot, salt spray fog and potentiodynamic polarization in NaCl solution. Microstructure was analyzed by optical microscopy, SEM (EDS) and glancing angle X-ray diffraction. All the samples showed an acceptable corrosion resistance in experiments with CuSO₄, but in salt spray fog and electrochemical tests, only Corrax showed good behavior. The poor corrosion performance could be explained by chromium carbides formed in thermal treatment stage in martensitic steels and chromium nitrides formed during nitriding, even though the process was carried out at low temperature.     

Effect of environmental factors on steel plate corrosion under marine immersion conditions

Abstract

This study considers different environmental factors affecting corrosion under marine immersion conditions and proposes a mathematical model incorporating their effects on corrosion degradation through the ship life. The study adopts a nonlinear function of time as the reference corrosion model calibrated with operational corrosion data at long term average conditions to represent the corrosion behaviour under standard environmental conditions. Based on previously obtained field data, a corrosion deterioration model is developed, in which a correction factor is proposed to account for the effect of each environmental factor. These multiplicative factors correct the standard prediction of corrosion degradation to obtain short term estimates under any specific environmental condition. Then, a long term estimate of corrosion degradation is determined by summing the short term corrosion contributions during the various discrete time periods in which the ship life can be decomposed. A numerical example of a representative application of the new empirical based corrosion model is presented, to demonstrate how to apply the model.     

Corrosion behaviour of corrugated lean duplex stainless steels in simulated concrete pore solutions

This work studies the corrosion behaviour of two corrugated lean duplex stainless steels (SAF 2001 and 2304 grades) in eight alkaline solutions (carbonated and non-carbonated, saturated Ca(OH)₂ solutions with different chloride contents). 2001 stainless steel is a new grade in market because of its composition. 2304 is a grade previously studied under different conditions. However, its use as reinforcement in concrete is new. Studies are carried out by polarization curves following scanning electronic microscopy (SEM) and optical observations. Results are compared to those of carbon steel and austenitic AISI 304 and duplex SAF 2205 under similar conditions. After corrosion tests in alkaline media with chloride, ferrite tends to corrode selectively in 2304 duplex, while austenite corrodes selectively in 2001 under the same conditions. The influence of the duplex microstructure on attack development and morphology is analyzed. The electrochemical parameters obtained from the polarization curves suggest 2001 could replace 304 keeping the structure its corrosion performance (and with clear economical advantages). 2304 shows better corrosion behaviour than the more expensive 304, but somewhat lower than the excellent behaviour shown by 2205.     

Versatility of superaustenitic stainless steels in marine applications

Corrosion of construction materials in marine applications is a major problem. The frequent variations in chloride ion concentration and temperature experienced by a system pose a serious threat. This investigation evaluated the performance of superaustenitic stainless steels in marine applications by potentiodynamic anodic polarization studies. The concentrations of metal ions such as iron, chromium, and nickel at different impressed potentials were analyzed by inductively coupled plasma spectrometry, which revealed little tendency for leaching of metal ions.     

温度对304不锈钢在液态Sn中腐蚀行为的影响

Sn是一种低熔点金属,其导热性高可用作快中子反应堆中的液体冷却剂。与目前所使用的的液态钠冷却剂相比,Sn具有更好的化学稳定性及遇水或空气不易燃烧的特点。在快中子反应堆中,不锈钢是应用广泛的主回路管道,本文研究了Sn与304不锈钢的化学反应,讨论了温度对304不锈钢在液态Sn中腐蚀行为的影响,结果表明,当温度低于823K时,发生点蚀,当温度高于823K时,发生溶解。     

Comparative evaluation of environment induced cracking of conventional and advanced steam turbine blade steels. Part 2: Corrosion fatigue

Corrosion fatigue crack propagation rates have been determined for two steam turbine blade steels, PH13-8, a candidate steel for advanced turbines, and FV566, typical of conventional turbine blades. The testing was undertaken in simulated condensate environment, 300 ppb Cl⁻ and 300 ppb , at 90 °C using trapezoidal loading with a rise time of 20 min to simulate two-shifting (switching on- and off-load on a daily basis). Aerated and deaerated conditions were tested, the former being more representative of the retained aeration in the chamber as the system comes on load. In aerated solution at ΔK = 20 MPa m^1/2 the cyclic crack growth rate for the PH13-8 steel was about a factor of two lower than that for the FV566 steel but the reverse was true for deaerated solution. In both cases, the difference in growth rates diminished with increasing ΔK. Although the cyclic crack growth rate is high the number of cycles per annum is small and the direct impact on overall life may be modest, but not insignificant. The observed cracking behaviour is best explained by a hydrogen assisted cracking mechanism.     

Corrosion behaviour of duplex stainless steels sintered in nitrogen

Duplex stainless steels obtained through powder metallurgy (PM) technology from austenitic AISI 316L and ferritic AISI 430L powders were mixed on different amounts to obtain biphasic structures with austenite/ferrite ratio of 50/50, 65/35 and 85/15. Prepared mixes of powders have been compacted at 750 MPa and sintered in N₂-H₂ (95% and 5%) at 1250 °C for 1 h. Corrosion behaviour, using electrochemical techniques such as anodic polarization measurement, cyclic anodic polarization scan and electrochemical potentio-kinetic reactivation test and double loop electrochemical potentio-kinetic reactivation double loop test were evaluated. For duplex stainless steels, when austenite/ferrite ratio increases the corrosion potential shifts to more noble potential and passive current density decreases. The beneficial effect of annealing solution heat treatment on corrosion behaviour was established and was compared with corrosion behaviour of vacuum sintered duplex stainless steels. The results were correlated with the microstructural features.     

Corrosion and passivation of low-temperature nitrided AISI 304L and 316L stainless steels in acidified sodium sulphate solution

304L and 316L steels were nitrided at 425 °C for 30 h and examined at various depths in 0.1 M Na₂SO₄ acidified to pH 3.0. In the near-surface region with about 7-14 wt% N, at potentials of active state anodic currents were much higher than those for untreated steels, whereas in deeper regions with <7 wt% N the currents were only slightly increased in comparison with untreated steels or they were even lower in passive and transpassive states. Surface films were composed of oxygen-containing species on top and of Cr-N species in deeper layers. It is suggested that strong corrosion of near-surface regions is associated with nitride precipitates. Beneficial effect of low nitrogen concentrations can be due to initially accelerated corrosion which leads to larger amounts of passivating species and to the accumulation of corrosion resistant chromium nitrides.     

Corrosion and tribological properties and impact fatigue behaviors of TiN- and DLC-coated stainless steels in a simulated body fluid environment

In this study, the corrosion and tribological properties of TiN and DLC coatings were investigated in a simulated body fluid (SBF) environment. The ball-on-plate impact tests were conducted on the coatings under a combined force of a 700 N static load and a 700 N dynamic impact load for 10,000 impacting cycles. The results indicated that the TiN and DLC coatings could achieve a higher corrosion polarization resistance and a more stable corrosion potential in the SBF environment than the uncoated stainless steel substrate SS316L. The good corrosion protection performance of TiN could be due to the formation of a Ti-O passive layer on the coating surface, which protected the coating from further corrosion. The superior corrosion property of the DLC coating was likely attributed to its chemical inertness under the SBF condition. The TiN and DLC coatings also exhibited an excellent wear resistance and chemical stability during the sliding tests against a high density polyethylene (HDPE) biomaterial. Compared to the DLC coating, the TiN coating has a better compatibility with the HDPE. However, the impact tests showed that the fatigue cracks and the coating chipping occurred on the TiN coating but not on the DLC coating.     

Corrosion of hot-rolled 430 stainless steel in HCl-based solution

The mixtures of hydrochloric acid and hydrogen peroxide were employed as the environmental friendly pickling solution for 430 hot-rolled stainless steel in this study. Increase of HCl concentration accelerates the corrosion rate of base metal, however aggravates the intergranular attack in sole hydrochloric acid solution. Addition of oxidant (H₂O₂) boosts the corrosion potential of stainless steel significantly resulting in the change of electrode action. At high oxidant content (0.6?mol?l^?1 H₂O₂), a corrosion product film accumulates onto the surface and the corrosion is then governed by the mass-transport at the film/stainless steel interface. The random dissolving of metal ions because of the film leads to brightening of stainless steel surface and the local corrosion is suppressed.     

Corrosion of nickel-chromium alloys, stainless steel and niobium at supercritical water oxidation conditions

Results of immersion tests of UNS N06625 (alloy 625), UNS S31609 (alloy 316 L), Ni-20Cr alloy and Nb coupons exposed to oxygenated ammoniacal sulphate solution at supercritical water oxidation (SCWO) conditions are presented. The corrosion behavior of the alloy 316 L (UNS S31603) SCWO reactor tubing is also presented under the same conditions. Immersion coupons corroded at a rate not exceeding 40 mm yr⁻¹ while the reactor tube itself corroded at a rate of between 160-1500 mm yr⁻¹, depending on which length of the reactor is considered to have corroded. Morphological and chemical analysis of the oxides present on the coupon samples suggest that iron oxides, which had initially precipitated on the corroding alloy 316 tube surface, were removed by heat flux-driven fluid mechanical action and transported through the reactor where they deposited on the coupons. Niobium was resistant to corrosion at the tested conditions.     

Corrosion behaviour of a dissimilar joint TIG weld between austenitic AISI 316L and ferritic AISI 444 stainless steels

The AISI 444 stainless steel (SS) has become an option to substitute the AISI 316L SS because of its low cost and satisfactory corrosion resistance. However, the use of AISI 444 alloy tubes in heat exchangers causes the welding of a dissimilar joint. The aim of this study was evaluate the corrosion resistance of the tube-to-tubesheet welded by a TIG process composed of AISI 316L and AISI 444. Preparation of samples was executed through replication of tube-to-tubesheet joints. In order to test the corrosion resistance of the welded joint, the following tests were applied: sensitisation, mass loss from room temperature up to 90 °C and electrochemical corrosion tests in 0.5 mol/L HCl and 0.5 mol/L H₂SO₄ electrolytes. The results have shown that the dissimilar joint suffers galvanic corrosion with increased degradation of the heat-affected zone of the AISI 444 tube. Nevertheless, the mechanisms of localised corrosion (pit and intergranular) were more active in the AISI 316L alloy. It is concluded that the dissimilar joint showed better corrosion resistance than the welded joint composed solely of AISI 316L at temperatures up to 70 °C, as the conditions observed in this work.     

Formation of Fe(III)-containing mackinawite from hydroxysulphate green rust by sulphate reducing bacteria

The interactions between Fe(II–III) hydroxysulphate GR() and sulphate reducing bacteria (SRB) were studied. The considered SRB, Desulfovibrio desulfuricans subsp. aestuarii ATCC 29578, were added with GR() to culture media. Different conditions were envisioned, corresponding to various concentrations of bacteria, various sources of sulphate (dissolved  + GR() or GR() alone) and various atmospheres (N₂:H₂ or N₂:CO₂:H₂). In the first part of the study, CO₂ was deliberately omitted so as to avoid the formation of carbonated compounds, and GR() was the only source of sulphate. Cell concentration increases from 4 × 10⁷ to 7 × 10⁸ cells/mL in 2 weeks. The evolution with time of the iron compounds, monitored by Raman spectroscopy and X-ray diffraction, showed the progressive formation of a FeS compound, the Fe(III)-containing mackinawite. This result is consistent with the association GR()/SRB/FeS observed in rust layers formed on steel in seawater. In the presence of CO₂ and additional dissolved sulphate species, a rapid growth of the bacteria could be observed, leading to the total transformation of GR() into mackinawite, found in three physico-chemical states (nanocrystalline, crystalline stoichiometric FeS and Fe(III)-containing), and siderite FeCO₃.     

Advances in the research of nitrogen containing stainless steels

The current status of nitrogen containing stainless steels at home and aboard has been introduced. The function and existing forms of nitrogen in the stainless steels, influence of nitrogen on mechanical properties and anti-corrosion properties as well as the application of nitrogen containing cast stainless steels were discussed in this paper. It is clear that nitrogen will be a potential and important alloying element in stainless steels. And Argon Oxygen Decarbonization (AOD) refining can provide an advanced manufacture process for nitrogen containing stainless steels with ultra-low- carbon and high cleanliness.