Electrochemical corrosion characteristics of Ni-Resist type 2 in sea water containing ferrous sulphate

Abstract

The corrosion characteristics of Ni-Resist type 2 alloy in sea water have been determined in relation to dissolved oxygen (DO) content, pH, and concentration offerrous sulphate (injected to inhibit corrosion of copper based alloy condenser tubes). The alloy underwent uniform cathodically controlled corrosion so that relatively high pH and low DO provide an acceptable environment. Compared with similar pH conditions in the absence of added iron, Fe²⁺ dosing of aerated sea water to ≤100 ppm at pH<5 increased the corrosion rate, whereas dosing at 1000-2400 ppm (pH<5) decreased it. Addition of ferrous sulphate to deaerated sea water further suppressed the already low corrosion rates in this medium. Even under aggressive conditions of anodic polarisation, the alloy showed near uniform attack of the major constituent metals, leaving, however, a graphitised surface. The possible stagnation of a concentrated ferrous sulphate solution injected into the condenser circulating cooling water system has been considered. It is also concluded that ferrous sulphate dosing does not alter the stress corrosion cracking susceptibility of the alloy.     

An Empirical Relationship Between Time of Cracking and Variation in Composition in Stress Corrosion Studies in Mattsson's Solution

Abstract

An empirical equation has been derived for quantitative determination of the contribution by different chemical and physical factors towards the total cracking time in the stress corrosion cracking of copper-manganese alloys in Mattsson's solution. Three alloys containing 3·9 to 8·1 % of Mn, showing intergranular cracking, have been studied at different pH and copper concentrations of the solution and the results were used for the formulation of the equation. Cracking times calculated from the proposed equation for any set of variables were shown to correspond well with the observed values within allowable limits of deviation.     

Effect of Stress and Impressed Current on Tarnish Film Growth on α- Brass in Ammoniacal Copper Sulphate Solutions

Abstract

The effect of two important parameters of stress corrosion cracking, namely, stress and impressed current, on tarnish formation on brass in ammoniacal copper sulphate solution has been investigated. The impressed current produces a maximum in film thickness on the anodic side which has been explained on the basis of different reactions of C_U2O formation. Applied stress has been found to favour film formation up to a stress level equal to the proof stress of the metal.     

Untersuchungen zum Einfluß von Sulfationen auf die chloridinduzierte lokale Korrosion am Stahl 1.4541 bei Temperaturen bis zu 280°C und gleichzeitiger Werkstoffdehnung

The influence of sulphate ions on stress corrosion cracking for stainless steel AlSl 321 with constant extension rate in aqueous chloride solution at temperatures up to 280°C CERT (Constant extension rate test: ? = 3·10 ⁶ s ¹) was used to study the inhibition effect of sulphate ions on stress corrosion cracking. Smooth tensile round specimens (AlSl 321) have been tested in solutions with sulphate (10 ²m Na₂SO₄) and chloride ions (10^?3m NaCl. 5. 10 ³m NaCl) at 150°C and 280°C. The presence of sulphate in chloride solutions increases the time to fracture and the reduction of area in comparison to pure chloride solution. The reason is the lower concentration of corrosive hydrogen near the fracture surface in comparison with tests in chloride solutions. The stress corrosion cracking is completely inhibited by the ratio of 10:1 for sulphate and chloride ions in the solution. The fracture surface investigated by Scanning Electron Microscopy has shown a cleavage type of fracture in chloride solutions and a ductile fracture in sulphate/chloride mixtures. The diffusivity of corrosive hydrogen is increased at 280°C in comparison to 150°C. Therefore at 280°C the corrosive hydrogen is able to diffuse into the inner part of the specimen and to influence the fracture mode.     

The stress corrosion cracking of admiralty brass in sulphate solutions

The field of occurrence, the severity and the morphology of the stress corrosion cracking (s.c.c.) of Admiralty brass exposed, under open circuit conditions, to sulphate solutions have been determined, as a function of acidity and of Cu²⁺ content, by means of ‘U’-bend and of constant load tests. Depending upon the solution pH, cracking exhibits two different modes: intergranular in strongly acidic solutions and transgranular in a wide range of moderately acidic and in alkaline solutions. The transition in the cracking mode occurs near the borderline conditions of Cu₂O stability; in the same conditions the maximum susceptibility to s.c.c. has been observed. Different roles played by Cu₂O in the nucleation and in the propagation stages of transgranular cracking are discussed.     

Mechanisms of stress corrosion cracking for iron base alloys in hot Ca(NO3 )2 solution

Abstract

The stress corrosion cracking (SCC) susceptibilities of a series of iron base alloys were evaluated in a 2M Ca(NO₃ )₂ solution at a temperature of 90°C. The inclusion distributions in each material were established using quantitative metallography and energy dispersive X-ray analysis (EDX). Electrochemical and microcorrosion measurements were also performed. Cracks were predominantly associated with pits that initiated at ruptures in the oxide film at potentials more anodic than -25 mV or by dissolution at sulphur containing inclusions at potentials more cathodic than -25 mV. Reducing the inclusion content and/or the activity of the inclusions in iron base alloys moves the minimum potential for cracking to more anodic potentials but does not eliminate SCC. The addition of sulphate to the test solution increased the susceptibilities of the alloys.     

An ac impedance study of the de-alloying of fe---ni alloys, and its relevance to chloride scc of stainless steels

The electrochemistry of Fe---3Ni and Fe---IONi alloys has been studied using chloride and sulphate solutions at pH 1 and 80°C. There is evidence for porous de-alloyed layers in chloride solution, but not in sulphate solution. The results support the view that chloride causes stress-corrosion cracking of austenitic stainless steels because it promotes de-alloying.     

Strain rate induced stress corrosion cracking in buried pipelines

Abstract

Transgranular stress corrosion cracking (TGSCC) has been observed in buried pipelines where the metal is in contact with a dilute solution under a disbonded coating. It is already known that such cracking involves the evolution and permeation of hydrogen at the crack tip, as previously observed in nuclear pressure vessel steels and other low alloy steels under variable loading. This cracking mechanism is much more influenced by loading conditions (crack tip strain rate) than by the solution chemistry. With reference to pipeline steels, several authors claim that it is difficult to reproduce in the laboratory the actual cracking morphology observed in the field. The present paper presents and discusses the results of tests where the fracture surface appearance observed in pipes taken from service has been reproduced. In this work, attention has been focused on mechanical factors rather than chemical parameters. It is proposed that the term low pH stress corrosion cracking, normally used to define the cracking phenomenon, is inappropriate and can be misleading. If greater attention is paid to strain rate and loading parameters, TGSCC in buried pipelines can be reproduced in laboratory tests (with no major influence of solution pH) and the phenomenon can be better described. Through a comparison with data in the literature data describing the behaviour of landslides, the hypothesis that crack growth occurs only during short intervals, followed by long periods where only generalised corrosion takes place, is proposed. This is consistent with features observed on the fracture surfaces of pipelines that failed in service.     

The predictability of stress corrosion cracking susceptibility of steels in acetate solutions from potentiodynamic polarization curves

Stress corrosion cracking susceptibilities of mild and low alloy steels in acetate solutions, assessed using slow strain-rate testing techniques, correlate well with those predicted on the basis of data from fast and slow sweep rate potentiodynamic polarization curves. Accurate prediction of cracking susceptibility necessitates allowances being made for changes of solution pH which occur during stress corrosion and polarization tests. A predictive technique which allows for these pH changes has been developed, and when implemented yields polarization data that indicates the influence of potential, steel composition and solution temperature on cracking susceptibility. The stress corrosion cracking of steels in acetate solutions is intergranular and occurs only when the electrochemical conditions correspond to those of a predicted potential-pH domain that is associated with the Fe²⁺/Fe₃O₄ transition.     

Stress corrosion cracking of armco iron in phosphate solutions

The stress corrosion cracking of Armco iron was examined in 0.033 and 1.0 M sodium orthophosphate solutions of pH 4.0, 7.0, and 9.0 at 25–100°C in constant strain-rate tests. In 1 M solution of pH 4.0 there formed in Armco iron deep intergranular cracks at potentials ? 150 to ? 50 mV (SCE) and anodic currents of 0.4–8 A/m², and also shallow transgranular cracks at ca. ? 250 to ? 50 mV and 1–30 A/m². Intergranular cracking has been associated with the presence of the oxide passivating film of moderate protectiveness and it was ascribed to deterioration of this film on grain boundaries of the metal by segregated admixtures. Transgranular cracking has been associated with the presence of less protective layers and their rupture along deformation bands.     

The inhibitive effect of extraneous ion addition on stress corrosion cracking of alpha-brass

The addition of ammonium chloride, cobalt sulphate, cesium sulphate and ethylene diamine to a Mattsson solution and the addition of ammonium sulphate to the Pugh solution have been found to produce an inhibitive effect on the stress corrosion cracking of alpha-brass in these solutions. Ammonium chloride and ammonium sulphate additions affect the tarnish formation on the specimen as well as the cracking pattern. Electrochemical polarization studies have also been carried out with these two additives. The observations have been explained in the light of adsorption of these ionic species at selected sites on the metal surface and their possible interference with the cathodic reactions.     

Stress Corrosion Cracking of Inconel 600 in aqueous solutions at elevated temperature part I: Initiation and inhibition of corrosion cracking process

The study reported here has been designed to determine the influencing effect of sulphate ions on chloride induced crack initiation of Inconel 600 using compact tension (CT) samples in chloride containing aqueous solutions at elevated temperature up to 250°. The results show that sulphate ions retard the effect of chloride ions on crack initiation in hot water up to 250°. Intergranular stress corrosion cracking (IGSCC) occurs in both chloride solution and in chloride solution with relatively low concentration of sulphate ions. The mode of cracking changes from brittle to ductile failure due to the influence of inhibiting concentration of sulphate. The results are interpreted in the light of repassivation-dissolution controlled mechanism which is the predominant mechanism. The inhibiting effect of sulphate ions on the initiation of corrosion cracking is attributed to the repassivation and the formation of Fe-Cr-spinel oxide layer which is stable also at higher temperature.     

Kurzzeitprüfmethoden zur Untersuchung des Einflusses von Wärmebehandlung und chemischer Zusammensetzung auf die Korrosionsbeständigkeit martensitischer Chrom-Nickel-(Molybdän)-Stähle mit tiefem Kohlenstoff-Gehalt

Short-duration test for evaluating the influence of heat-treatment and chemical composition on the corrosion resistance of low carbon martensitic chromium nickel (molybdenum) steels The following procedures were examined and compared for their suitability as rapid corrosion tests in comparative investigations on the influence of heat treatment and other production parameters on martensitic chromium-nickel-(molybdenum) steels of low carbon content:

• –Measurement of the mass loss in boiling 20% acetic acid, and in some cases 5% nitric or 1% hydrochloric acid.
• –Immersion in sulphuric acid/copper sulphate solution (modified Strauss test).
• –Current density/voltage curves in 1 N sulphuric acid.
• –Measurement of pitting potential und activation pH in 3% sodium chloride solution (on limited scale).

The test materials employed contained 0.032–0.082% carbon, 11.6–16.4% chromium, 3.8–5.9% nickel and 0.31–1.6% molybdenum. The most suitable testing procedures were selected according to the steel type. Up to a mass loss rate of ≥ 0.05 mg · cm^?2 · h^?1 (materials with resistance inferior to steel type 13-6-1) the acetic acid test provides an excellent basis for comparison. Provided the optimal testing temperature is adopted, current density/voltage curves and immersion in sulphuric acid/copper sulphate solution yield usable results with all steel types investigated. The value of the information yielded by the test procedures is generally enhanced by metallographic characterization of the corroded surfaces; in particular the localization of chromium-depleted structure zones is made possible by this.     

Stress corrosion cracking behaviour of 2091 Al—Li alloy in sulphate and chloride containing solutions

Abstract

The stress corrosion cracking resistance of 2091 Al—Li alloy in underaged, and in peak aged condition was investigated in chloride solutions with or without sulphate addition using both the static load technique and the slow strain rate technique. It is shown that the underaged material is more resistant than peak aged material. Sulphate additions to chloride solutions increase the stress corrosion cracking susceptibility. Metallographic cross-section observations show the simultaneous occurrence of other kinds of corrosion: generalised. corrosion, pitting corrosion, intergranular corrosion, and exfoliation corrosion. It appears that stress corrosion cracking susceptibility increases as the extent of intergranular corrosion decreases.     

Effect of pH on corrosion and monotonic loading behaviour of 90Cu–10Ni in 3·5% sodium chloride solution

Abstract

Polarisation studies were performed on 90Cu–10Ni (alloy UNS C70600, hot rolled and annealed) in 3·5% NaCl solutions over a range of initial pH levels. It was found that film formation was dependent on the applied current and the relative concentrations of the ionic species H⁺, (OH)^?, and Cl^? in solution which ultimately influenced the formation of the corrosion products. Constant extension rate tests at different applied currents and pH levels suggested that a higher pH level increased the time to failure although no evidence of stress corrosion cracking was found. These observations are rationalised through surface film formation mechanisms.     

Calendar

Abstract

Stress corrosion cracking of mild steel in a phosphate environment has been investigated at both room temperature. and 100°c: Prediction of this solution as a cracking medium was made on the basis of results obtamed from high and low sweep rate potentiodynamic polarisation curves.

X-ray analysis indicates that at 100°c the stress corrosion behaviour may be related to the type of phosphate film formed at the metal surface.     

Untersuchungen zum Einfluß von Sulfid- und Sulfationen auf die Korrosion des Eisens in alkalischer Lösung

Investigation into the influence of sulfide and sulfate ions on the corrosion of iron in alcaline solution The corrosion behaviour of Armco iron as well as that of a technical high-strength steel was investigated in sulphide - and sulphate-containing electrolytes of pH ～ 12.6. Current density - potential curves show that iron, after successful passivation, remains passive and protected against corrosion in a solution saturated with CaS, CaSO₄ and Ca(OH)₂ at potentials up to 800 mV(EH). Passivation experiments conducted by changing from the active region to various anodic potentials yielded a critical potential region around 300 mV(EH), above which corrosion appeared. Up to E_H = 200 mV complete passivation was observed. The same critical potential region was observed in experiments of repassivation after mechanical damaging of a protective passive layer. Additional tensile stresses of 85%· σ_0,2 caused no stress corrosion cracking at a potential of 500 mV(EH). After damaging the passive layer, through scratching of the stressed wires fracture occured at and above potentials of 300 mV(EH). At 200 mV(EH) repassivation was observed even under tensile load. In a sulphate-free Na₂S/Ca(OH)₂ solution of the same sulphide ion concentration no stress corrosion cracking of the samples occured at any potential up to 800 mV(EH) even after scratching the steel samples. The observed stress corrosion in sulphide - and sulphate-containing electrolytes is to be ascribed to the action of sulphate and not to sulphide ions.     

Corrosion inhibition by tungstate in aqueous solutions and its application to coal–water slurries

Abstract

Corrosion rates of AISI 1010 steel both in the presence and absence of sodium tungstate as inhibitor were determined in chloride–sulphate solutions of concentrations typical of water used in coal plants. Corrosion rate data of AISI 1010 steel as a function of pH and sodium tungstate concentration showed that 100 ppm tungstate at pH 8·5 gave 87% inhibition. When associated with other chemical species in a binary or multicomponent system the inhibitor efficiency rose to 99%. Results obtained with sodium tungstate alone or in association with hydroxyethylidene diphosphonic acid (HEDP) and zinc sulphate are presented and discussed. The application of tungstate inhibitor in coal–water slurries has been explored.     

Stress corrosion cracking of α–β brass in chloride containing waters

Abstract

Slow straining of an α–β brass in aqueous solutions with various concentrations of chloride ion has been used to ascertain the effects of potential, pH, and chloride content on the susceptibility to stress corrosion cracking. The ductility is at a minimum with 55 ppm Cl present and increases at higher concentrations, where dezincification effects become more significant. Anodic polarization increases the ductility loss but the effects are again complicated at high potentials by greater dezincification. The strqjn rate dependence of the embrittlement results in a ductility minimum at 2 × 10^?6. The results are assessed in terms of various cracking mechanisms but seem to be most consistent with a mechanism involving the rupture of a surfacefilm of CU₂O that forms on the alloy in the critical potential range.     

Effects of weld preheat temperature and heat input on type IV failure

Abstract

Type IV cracking refers to the premature failure of a welded joint due to an enhanced rate of creep void formation in the fine grained or intercritically annealed heat affected zone. A great deal of research effort has been directed at understanding the underlying mechanisms for this type of failure, but most have approached the problem from a metallurgical standpoint, and comparatively little effort has been directed at understanding the effects of welding variables. Here the effects of parameters such as the preheat temperature and heat input on the tendency for type IV failure in 9–12%Cr steels have been quantitatively estimated. These calculations have subsequently been verified experimentally to form the first systematic study of welding parameters on type IV cracking. The joint geometry and preheat temperature have been found to ameliorate type IV failures, while the effect of heat input is less significant.