Untersuchung über das Korrosionsverhalten von Zirkoniumlegierungen. IV. Das Lochfraßverhalten Zirkoniumlegierungen

Investigation into corrosion behaviour of zirconium alloys. IV-Pitting behaviour of zirconium alloys Electrochemical investigations into the resistance of a number of Zr-alloys in different solutions against pitting corrosion have shown that additions of Va- and VIa-group metals and in particular Ti improve the resistance of pure Zr. Metals forming local elements decrease pitting corrosion resistance. Minor amounts of Fe, Ni and Cr have practically no influence. The pitting corrosion resistance of Zr and its alloys decreases with increasing concentration of chloride ions in the solutions. Additions of SO₄-ions retard the beginning of the pitting but do not shift the pitting corrosion potential. NO₃-ions on the other hand produce a real inhibition. Newly developed methods for the quick determination of the pitting corrosion potential were very useful for the described investigations.     

Stainless steel reinforcing bars – reason for their high pitting corrosion resistance

In harsh chloride bearing environments stainless steel reinforcing bars offer excellent corrosion resistance and very long service life for concrete structures, but the high costs limit a more widespread use. Manganese bearing nickel‐free stainless steels could be a cost‐effective alternative. Whereas the corrosion behavior of stainless steels in alkaline solutions, mortar and concrete is quite well established, only little information on the reasons for the high pitting resistance are available. This work reports the results of pitting potential measurements in solutions simulating alkaline and carbonated concrete on black steel, stainless steel DIN 1.4301, duplex steel DIN 1.4462, and nickel‐free stainless steel DIN 1.4456. Duplex and nickel‐free stainless steels are fully resistant even in 4 M NaCl solutions with pH 13 or higher, the lower grade DIN 1.4301 shows a wide scatter between fully resistant and pitting potentials as low as +0.2 V SCE. In carbonated solutions with pH 9 the nickel‐free DIN 1.4456 shows pitting corrosion at chloride concentrations ≥3 M. This ranking of the pitting resistance can be rationalized based on XPS surface analysis results: both the increase of the Cr(III)oxy‐hydroxide and Mo(VI) contents in the passive film and a marked nickel enrichment beneath the film improve the pitting resistance. The duplex DIN 1.4462 shows the highest pitting resistance, which can be attributed to the very high Cr(III)oxy‐hydroxide, to a medium Mo(VI) content in the film and to a nickel enrichment beneath the film. Upon time, the protective properties of the surface film improve. This beneficial effect of ageing (transformation of the passive film to a less Fe²⁺ containing, more hydrated film) will lead to higher pitting potentials. It can be concluded that short‐term solution experiments give conservative results in terms of resistance to chloride‐induced corrosion in reinforced concrete structures.     

Effect of chloride ions on corrosion behaviour of austenitic nickel and nickel free stainless steels in phosphoric acid solutions

The effect of chloride ions' presence (0·005–1·0M NaCl) in phosphoric acid solutions (5, 40 and 75%) on the corrosion behaviour of three austenitic stainless steels (an experimental steel Fe–18Cr–12Mn–0·6N and two trade grades, Fe–18Cr–9Ni and Fe–14Cr–15Mn–0·2N) has been studied by potentiodynamic polarisation measurements. The surface examinations of the samples tested involved X-ray photoelectron spectroscopy as well as optical and scanning electron microscopy. It was established that chlorides added to phosphoric acid solutions deteriorate the general corrosion resistance, and under anodic polarisation, they provoke pitting corrosion. The composition of the stainless steels significantly influences its corrosion behaviour in the phosphoric acid solutions containing chloride ions. The replacement of nickel with manganese and nitrogen on top of lower chromium content has a strong negative effect on the corrosion resistance.     

The resistance to stress corrosion cracking of some Cr–Ni–Fe austenitic steels and alloys

Abstract

Stress-corrosion cracking testing by a variety of methods has been carried out in chloride and caustic environments on a series of Cr–Ni–Fe austenitic steels and alloys containing between 10 and 25 % of chromium and 15 and 45% of nickel. Limited testing has also been carried out on alloys containing additions of molybdenum and copper. The tests have confirmed that increasing the nickel content reduces the susceptibility of Cr–Ni–Fe alloys to stress-corrosion cracking in chloride solutions. Chromium content also affects cracking susceptibility but to a lesser degree. Stress corrosion susceptibility in caustic solutions is affected by these alloying elements in a different way. The results are discussed in relation to currently proposed theories of stress-corrosion cracking.     

Stress-Corrosion Cracking of Cast Iron—Nickel—Chromium Alloys

Abstract

The stress-corrosion behaviour of three chromium—nickel—iron alloys, viz. 25Cr—20Ni—Fe (HK Alloy), 24Cr?24Ni?11/2Nb?Fe (IN—519) and 18Cr—37Ni—Fe (HT Alloy), has been examined in a number of chemical environments known to promote stress-corrosion c:racking in wrought alloys of similar composition. The tests were carried out in sodium and magnesium chloride solutions, sodium and potassium hydroxide solutions and in a number of sulphur acid environments, e.g. sulphur dioxide plus hydrogen sulphide, often described as poly thionic acid.

The alloys generally showed resistance to cracking in chloride environments as good as or better than that which would be expected from wrought alloys of similar composition; when cracking did occur in these environments it was predominantly transgranular. The alloys were susceptible to cracking in the other environments where the attack was exclusively interdendritic; this may have been associated with the large amount of interdendritic chromium carbides present in the cast structures. The niobium containing alloy IN–519 showed better resistance to cracking in these environments.     

Pitting,Crevice and stress corrosion resistance of high chromium und molybdenum alloy stainless steels

This paper presents new data on the resistance of recently developed high-alloy stainless steels to localised corrosion in chloride solutions. Pitting potential was determined in artificial sea water, and critical pitting temperature CPT in very aggressive FeCl₃ solution. Critical crevice corrosion temperature CCT was tested in the same FeCl₃ solution. Stress corrosion measurements, made in a more familiar NaCl solution by the drop evaporation method, demonstrate that alloy stainless steels with high chromium and molybdenum have very long failure times, comparable with those of nickel alloys found to be SCC-resistant under practical conditions. Stainless steels of 20 Cr 25 Ni 6 Mo type showed the best resistance to localised corrosion.     

New stainiess steels for sea water applications. Part. 1: Corrosion and mechanical properties of ferritic stainless steels

Two experimental ELI ferritic stainless steels (22 Cr – 2.5 Ni – 3 Mo and 22 Cr – 2.5 Ni – 3 Mo – Ti) prepared in laboratory and a commercial one (21 Cr – 3 Mo – Ti) were investigated. Electrochemical and laboratory exposure tests were carried out to define the localized corrosion resistance (pitting and crevice) of such steels in chloride solution. Intergranular and stress corrosion resistance was also evaluated. Room temperature tension tests and impact tests were performed. 22 Cr – 2.5 Ni – 3 Mo – Ti and 21 Cr – 3 Mo – Ti steels are immune to intergranular corrosion whatever temperature they are heat treated at and have the same pitting corrosion resistance as a function of temperature; crevice corrosion of 22 Cr – 2.5 Ni – 3 Mo is decidely better than in the commercial 21 Cr – 3 Mo – Ti. The experimental steels were immune to stress corrosion in hot chloride environment.     

Corrosion characteristics of the wrought Ni‐Cr‐Mo alloys

This paper concerns the wrought, nickel‐chromium‐molybdenum (Ni‐Cr‐Mo) alloys, a family of materials with a long history of use in the chemical process industries. Their attributes include resistance to the halogen acids and resistance to pitting, crevice attack, and stress corrosion cracking in hot, halide salt solutions. The purpose of this paper is to characterize the performance of the Ni‐Cr‐Mo alloys in several key chemicals, using iso‐corrosion diagrams. These indicate the expected corrosion rates over wide ranges of concentration and temperature. Furthermore, the differences between individual Ni‐Cr‐Mo alloys, and their behavior relative to the stainless steels are defined. The data indicate benefits of both a high chromium content and a copper addition, as used in Hastelloy® C‐2000® alloy.     

Determination of critical pitting temperatures for Ni?Cr?Mo alloys using electrochemical noise measurements

The determination of critical pitting temperatures (CPT) in various test solutions like ferric chloride solution according to ASTM G48 or “Green Death” solution is a common test method for the comparative assessment of the pitting corrosion resistance of highly alloyed steels and Ni? Cr? Mo alloys. In addition to the well‐known disadvantages of standard methods, like long test times, subjective examination, and large scatter, for the highest alloyed Ni? Cr? Mo alloys no stable pitting corrosion can initiate even at the highest test temperatures. This paper describes the limitations of standard test methods and shows how these problems can be solved by an alternative test solution and an adjusted test method. By capturing and examining the current noise under potentiostatic conditions during continuous heating in a 4.5 M calcium chloride solution the transition from metastable to stable pitting corrosion as a criterion for CPT can be detected in a reproducible way.     

Corrosion resistance and mechanical properties of nickel-bearing ferritic stainless steels

Additions of nickel to ferritic steels containing 25–28% Cr and 2–4% Mo increased the impact toguhness especially when more than 2% Ni was present. The effect of nickel content increased up to 4% Ni, the largest addition studied. Steels stabilized with niobium had lower transition temperatures then did corresponding steels stablizied with titanium. Steels containing 4% Ni required annealing at 1050 C to avoid intermetalic compounds. It was also noted that nickel reduced the upper shelf energy in the Charpy impact test and eliminated a sharp transition from ductile to brittle behaviour. No definite effect of nickel on pitting potential was pound but steels in the series 25Cr-3.5 Mo-Ni-Ti consistenly had more noble pitting potentials and greater resistance to crevice corrosion than the 28 Cr-2Mo-Ni-Ti steels. Nickel contents of 1 or 2% tended to improve crevice corrosion resistance while larger nickel contents were somewhat ditrimental. Nickel strongly reduced critical current densities for passivity both in l N H₂SO₄ and in l N HCL and yielded corresponding increases in resistance to corrosion by these acids. Although 1% Ni or more caused the annealed steels to be susceptible to stress corrosion cracking in MgCl₂ boiling at 140 C, while the as-Welded steels containing 4% Ni did not crack in boiling 25% Nacl at pH 1.     

The Estimation of Localized Corrosion Behavior of Ni-Based Dental Alloys Using Electrochemical Techniques

The aim of this study is to investigate the electrochemical behavior of the five non-precious Ni-based dental casting alloys in acidified artificial saliva. For comparison, nickel was also investigated. In order to study the localized corrosion resistance, the cyclic potentiodynamic polarization (CCP) and electrochemical impedance spectroscopy were performed. Scanning electron microscopy (SEM) observations were made after the CCP tests. The Ni-Cr alloys with chromium (14-18%) contents were susceptible to localized corrosion. The Ni-Cr-Mo alloy with contents of chromium (??13%) and molybdenum (9%) presents a dangerous breakdown, but have a zero corrosion potential so that the difference between them is around 650?mV. The Ni-Cr-Mo alloys with higher chromium (22-25%) and molybdenum (9-11%) contents had a much larger passive range in the polarization curve and were immune to pitting corrosion. Pitting resistance equivalent (PRE) of about ??54 could provide the Ni-based alloy with a good pitting corrosion resistance.     

Passivierungsverhalten und Spannungsrißkorrosion von Eisen-Mangan-Chrom-Legierungen in Natriumchlorid-Lösung

Passivation behaviour and stress corrosion cracking of iron-maganese-chromium alloys in sodium chloride solution Electrochemical experiments with MnCr steels (20–28% Mn, up to 12% Cr) in 3% NaCl solution. High Mn contents reduce the passivation tendency, while increasing Cr contents broaden the range of passivity. The formation of surface layers is due primarily to a direct reaction with the solution (good adhesion, high protective value) and, secondarily, to precipitation from the solution (porosity, low protective value). The tendency to form secondary layers increases as the Cr content is reduced. In oxygen containing solution there is a pronounced corrosion in the pitting range. At low Cr contents, stress corrosion cracking is mostly transcrystalline, at higher Cr contents (8–12%) it is intercrystalline, in particular when Cr carbide precipitations are present at the grain boundaries. In the range of transcrystalline corrosion the susceptibility to selective corrosion extends beyond the pitting potential. At higher Cr contents there may be pitting without any indication of stress corrosion cracking.     

Korrosionseigenschaften laserstrahlgeschweißter Aluminium- und Magnesium-Automobilwerkstoffe

Corrosion behaviour of laser beam welded aluminium and magnesium alloys in the automotive industry The pitting behaviour of unwelded and laser beam welded AlMgSi alloys and an AlMgMn alloy was investigated. Electrochemical investigations and the metallographic determination of the pit volume were used to characterize the susceptibility to pitting corrosion. Both investigation methods showed that, in the unwelded condition, the material AlMgMn was the most resistant. In the case of laser beam welded materials, the resistance to pitting corrosion is lower or also higher than that of the non-affected materials depending on the material combination selected. The material combination AlMgSi0.5/AlMgSi1 F21 proved to be the most suitable. Magnesium extruded alloys with approx. 3 to 8% Al and 0.5 to 0.8 % Zn are susceptible to filiform corrosion and pitting corrosion in aqueous chloride solutions depending on chloride concentration. The resistance of unwelded alloys increases with Al content. On welding of the alloys, the corrosion resistance is determined by the Al/Mg proportion at the surface of the non-affected material and the laser welding seam. The pits occur mainly in the heat affected zone of the welding seam. The laser beam welded material AZ61 HP was found to have the highest resistance.     

Localized Corrosion Characteristics of Nickel Alloys:A Review

There are a great variety of commercial nickel alloys mainly because nickel is able to dissolve a large amount of alloying elements while maintaining a single ductile austenitic phase.Nickel alloys are generally designed for and used in highly aggressive environments,for example,those where stainless steels may experience pitting corrosion or environmentally assisted cracking.While nickel alloys are generally resistant to pitting corrosion in chloride-containing environments,they may be prone to crevice corrosion attack.Addition of chromium,molybdenum and tungsten increases the localized corrosion resistance of nickel alloys.This review on the resistance to localized corrosion of nickel alloys includes specific environments such as those present in oil and gas upstream operations,in the chemical process industry and in seawater service.     

Korrosionsverhalten hochchromhaltiger,ferritischer, chemisch beständiger Stähle

Corrosion behaviour of high chromium ferritic stainless steels Ferritic steels developed for seawater desalination and containing 20 to 28% chromium, up to 5% Mo and additions of nickel and copper have been tested with respect to their corrosion behaviour, in particular in chloride containing media. The materials in the sensibilized state were tested for inter-crystalline corrosion susceptibility in the Strauß-, Streicher-, nitric acid hydrofluoric acid- and Huey-Tests. No intercrystalline corrosion was encountered in the case of the steels with 28% Cr and 2% Mo. The resistance to pitting was assessed on the basis of rupture potentials determined by potentiokinetic tests. The resistance of the steels with 20% Cr and 5% Mo or 28% Cr and 2% Mo is superior to that of the molybdenum containing austenitic types. Addition of nickel yields a significant increase in crevice corrosion resistance; the same applies to resistance in sulfuric acid. In boiling seawater all the materials tested are resistant to stress corrosion cracking. No sign of any type of corrosion was found on nickel containing steels after about 6000 hours exposure to boiling 50% seawater brine even under salt deposits.     

Synergistic effect of Ni and N on improvement of pitting corrosion resistance of high nitrogen stainless steels

Abstract

The pitting corrosion resistance of Fe18Cr10Mn(0·33–0·69)N, Fe18Cr10Mn1Ni(0·33–0·84)N, and Fe18Cr10Mn0·35N(0–3)Ni alloys were investigated. The pitting potential increased as the N content increased in both Fe18Cr10Mn(0·33–0·69)N and Fe18Cr10Mn1Ni(0·33–0·84)N alloys. The rise in the pitting potential was more pronounced in Fe18Cr10Mn1Ni(0·33–0·84)N alloys than in Fe18Cr10Mn(0·33–0·69)N alloys. However, it was found that Ni alone had no effect on the pitting corrosion resistance of Fe18Cr10Mn0·35N based alloys. Thus, it was concluded that the alloyed N worked synergistically with Ni to promote the pitting corrosion resistance in Fe18Cr10Mn based alloys. Analyses of passive films of Fe18Cr10Mn(0·33–0·69)N and Fe18Cr10Mn1Ni(0·33–0·84)N alloys revealed that N was incorporated into the passive film, with N enriched at the film/metal interface. However, the alloyed N increased the Cr cation fraction in passive films of Fe18Cr10Mn1Ni(0·33–0·84)N alloys, whereas N decreased in that of Fe18Cr10Mn(0·33–0·69)N alloys. This difference was considered as the reason for the synergistic effect between N and Ni in Fe18Cr10Mn based alloys.     

Effect of nickel alloying on crevice corrosion resistance of stainless steels

The crevice corrosion behaviour of stainless steels containing 25 mass% Cr, 3 mass% Mo and various amounts of Ni was investigated in natural seawater. The results showed that ferritic steels containing nickel were more resistant to corrosion than both ferritic steels without nickel and austenitic steels. The superiority of the Ni bearing ferritic steel over the other steels was in close agreement with the depassivation pH of those steels in acidic chloride solutions. The results showed that the addition of Ni to ferritic steel was effective in decreasing the depassivation pH and the dissolution rate in acidic chloride solutions at crevices.     

Reports of Meetings

Abstract

The corrosion resistance of a number of stainless steels and nickel alloys in solutions of pure phosphoric acid boiling under reflux and in similar solutions under conditions of heat transfer has been investigated. The effect of phosphoric acid concentrationand alloy composition on the corrosion rates obtained has been evaluated. The effect of additions of impurities such as fluoride, chloride, silicate and ferric ions on the corrosion behaviour of a number of the alloys in concentrated phosphoric acid under conditions of heat transfer has also been determined; such impurities are often present in wet-process plant phosphoric acid at the evaporator stage. The work has demonstrated that the alloys of highest nickel content generally exhibit the best corrosion resistance in such environments. It has also been shown that whilst chloride ion additions considerably increase the aggressive nature of the environment, fluoride additions in general have very little effect.     

Corrosion of nanocrystalline Ni–W alloys in alkaline and acidic 3.5 wt.% NaCl solutions

The corrosion behaviour of reverse-pulse electrodeposited nanocrystalline nickel tungsten alloys (nc Ni–W) in pH 3 and 10 3.5 wt.% NaCl solutions is investigated and analysed as a function of grain size. A potentiodynamic polarisation study reveals that the corrosion rate of nc Ni–W generally increases with the reduction of grain size in alkaline condition, but decreases with the reduction of grain size in acidic environment. Furthermore, for both environments, nc Ni–W alloys exhibit superior localised corrosion resistance than a microcrystalline Ni control specimen. Factors controlling the corrosion behaviour of these materials, including grain size, tungsten content, passivation and crystallographic texture are addressed.     

Corrosion behaviour of alloy 31 – UNS N08031 – under conditions of oil & gas production

The corrosion behaviour of alloy 31 (UNS N08031‐31Ni – 27Cr – 6.5Mo – 1.2Cu – 0.2N – bal. Fe) was tested in laboratory and field tests in seawater with and without additions of CO₂ and/or H₂S in slow strain rate tests, and in SSC (Sulphide Stress Corrosion) tests according to NACE MR0175. The results demonstrate a high resistance of alloy 31 to localised corrosion. Due to the high chromium and molybdenum concentration, its resistance to pitting and crevice corrosion in chloride‐contaminated seawater is significantly higher than that of alloy 28 and alloy 825 and it equals that of typical nickel base alloys like alloy 625. Alloy 31 is not sensitive to chloride‐induced stress corrosion cracking, either with or without H₂S, or sulphide stress cracking. Alloy 31 is approved for sour gas applications up to LEVEL VI in NACE MR 0175. The combination of properties makes alloy 31 an attractive choice for components in oil and gas production including wirelines, umbilicals, tubing, piping and topside application.