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ABSTRACT The susceptibility or Alloy 22 (N06022) to crevice corrosion may depend on environmental or external factors and metallurgical or internal factors. Some of the most important environmental factors are chloride concentration, inhibitors, temperature and potential. The presence of a weld seam and second phase precipitation in the alloy are classified as internal factors. The localized corrosion resistance of Alloy 22 has been extensively investigated in the last five years, however not all affecting factors were equally considered in the studies. This paper discusses the current findings regarding the effect of many of these variables on the susceptibility (or resistance) of Alloy 22 to crevice corrosion. The effect of variables such as temperature, chloride concentration and nitrate are rather well understood. However there are only limited or no data regarding effect of other factors such as pH, other inhibitive or deleterious species and type of crevicing material and crevice geometry. There are contradictory results regarding the effect of metallurgical factors such as solution heat treatment. inhibitors INTRODUCTION Several corrosion resistant nickel-based families of alloys exist. These include commercially pure nickel (Ni) (e.g. Ni-200 or N02200), Ni-copper (Cu) alloys (e.g. Alloy 400 or N04400), Nimolybdenum (Mo) alloys (e.g. B-2 or N10665), Ni-Chromium (Cr)-Iron (Fe) alloys (e.g. Alloy 600 or N06600) and Ni-Cr-Mo alloys. 1 The family of Ni-Cr-Mo is rather large and continuously growing. They include alloys such as C-4 (N06455), C-276 (N10276), C-2000 (N06200), 59 (N06059) and 686 (N06686). 1,2 Alloy 22 belongs to the Ni-Cr-Mo family of nickel based alloys and contains nominally 22% Chromium (Cr), 13% Molybdenum (Mo) and 3% tungsten (W). 2 The Ni-Cr-Mo alloys were designed to withstand the most aggressive industrial applications, including reducing acids such as hydrochloric and oxidizing acids such as nitric. Chromium is the beneficial alloying element added for protec- tion against oxidizing conditions and molybdenum is the beneficial alloying element to protect against reducing conditions. 1,3-4 The base element (nickel) protects the alloy against caustic conditions. 1,3-4 All three elements, Ni, Cr and Mo act synergistically to provide resistance to environmentally assisted cracking in hot concentrated chloride solutions. 1,3-4 The alloying elements Cr and Mo also provide resistance to localized corrosion such as pitting and crevice corrosion in chloride containing solutions. Some of the Ni-Cr-Mo alloys also contain a small amount of tungsten (W), which may act in a similar way as Mo regarding protection against localized corrosion. 5 Ni-Cr-Mo alloys are practically immune to pitting corrosion but they may suffer crevice corrosion under aggressive environmental conditions.
- Materials > Metals & Mining (1.00)
- Materials > Chemicals (1.00)
- Government > Regional Government > North America Government > United States Government (0.47)
- Energy > Power Industry > Utilities (0.46)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
ABSTRACT The study of the electrochemical behavior of Alloy 22 was carried out in 4 M NaCl, and 4 M NaCl with sulfate additions of 0.4 and 0.04 M between 45 and 105 oC with Multiple Crevice Assembly (MCA) specimens. The susceptibility to corrosion was found to decrease in the presence of sulfate in solution. INTRODUCTION Alloy 22 (UNS N06022) is a nickel alloy rich in chromium and molybdenum. It possesses a high degree of corrosion resistance. Alloy 22 exhibits a low general corrosion rate under most conditions and has exceptional localized corrosion resistance in most environments [1-8]. For this reason, Alloy 22 is used in a wide variety of industrial applications. While the effect of sulfate ions (SO4 2-) on localized corrosion has been extensively characterized for stainless steels (SS) and some nickel (Ni) alloys, relatively little data in this area of study is available for Alloy 22. It has been found that SO4 2- ions have the ability to mitigate several forms of localized corrosion including pitting corrosion, crevice corrosion, and stress corrosion cracking in chloride (Cl-) environments in stainless steels and nickel alloys [9-22]. However, some authors have found that SO4 2-could also act as a promoter of localized corrosion under certain environmental conditions in some stainless steels and Ni alloys [16, 17, 23, 24]. In a study of various grades of stainless steels including AISI 304, 316, 317L, 321, as well as 15-7PH, Alloy C and Alloy F, Man and Gabe [19, 20] found that greater ennoblement of the pitting potential occurred among alloys with the higher molybdenum (Mo) content. Although ennoblement of the pitting potential increased with increase in concentration of SO4 2- in solution, only a 400 mV increase in the pitting potential could be achieved within a solution of 10% SO4 2- and 3% Cl-. Their experiments showed that compared with nitrate (NO3 -) and hydroxyl (OH-) where increases of up to 800 mV were achieved; SO4 2- was not as efficient an inhibitor. In certain cases, they even found carbonate to be a more effective inhibitor than SO4 2-. Studies carried out in Cl- solutions with Inconel 600 showed that SO4 2- was an effective inhibitor of pitting corrosion and stress corrosion cracking [15, 18]. Chang and Yang [15] found that over a temperature range of 25-70 oC, in solutions with chloride concentration ([Cl-]) of 0.001 to 0.1 M with sulfate concentration ([SO4 2-]) of between 0.0001 and 0.1 M, the presence of SO4 2- was generally characterized by an increase in the pitting and repassivation potentials, and a less extensive pitting attack in polarized specimens of Inconel 600. The pit sizes and density were also found to decrease with increase in [SO4 2-]. The interruption of growth or continued propagation of cracks in Inconel 600 in the presence of SO4 2- in a Cl- environment at 250 oC led Ashour [18] to conclude that the solution at progressing crack tips was made less aggressive by the presence of SO4 2-. It was observed that SO4 2- seemed to change the morphology of attack of the crack surface from intergranular to transgranular mode of failure. The intergranular crack growth rate was thus hindered with increase in [SO4 2-]. The critical stress intensity factor (KISCC) also increased with increasing [SO4 2-]. In the presence of SO4 2-, cracks did not propagate under free load at the corrosion potential on Alloy 600. SO4 2- was also thought to hinder the dissolution of alloy 600 by adsorbing on to the active sites of the fracture surfaces, thus preventing continued dissolution by Cl- probably by the formation of a Cr oxide layer, which is stable at high temperature (~250 oC) [18].
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
ABSTRACT Alloy 22 (N06022) is highly resistant to crevice corrosion in pure chloride (C1-)solutions. Little research has been conducted to explore the resistance of this alloy to other halides such as fluoride (F-) and bromide (Br-). Even less information is available exploring the behavior of localized corrosion for Alloy 22 in mixtures of the halide ions. Standard electrochemical tests such as polarization resistance andcyclic potentiodynamic polarization (CPP), were conducted to explore the resistance to corrosion of Alloy 22 in deaerated aqueous solutions of 1 M NaC1, 1 M NaF and 0.5 M NaC1 + 0.5 M NaF solutions at 60ยฐC and 90ยฐC. Results show that the general corrosion rate was the lowest in the mixed halide solu- tion and the highest in the pure fluoride solution. Alloy 22 was not susceptible to localized corrosion in the pure fluoride solution. In 1 M NaC1 solution, Alloy 22 was susceptible to crevice corrosion at 90ยฐC. In the mixed halide solution Alloy 22 was susceptible to crevice corrosion both at 60ยฐC and 90ยฐC. INTRODUCTION Alloy 22 (N06022) is nickel (Ni) based and contains nominally 22% Chromium (Cr), 13% Mo- lybdenum (Mo) and 3% tungsten (W). 1 Alloy 22 belongs to the Ni-Cr-Mo family of nickel based alloys, which also include alloys such as C-4 (N06455), C-276 (N10276), C-2000 (N06200), 59 (N06059) and 686 (N06686). 1 The Ni-Cr-Mo alloys were designed to withstand the most aggressive industrial appli- cations, including reducing acids such as hydrochloric and oxidizing acids such as nitric. Chromium is the beneficial alloying element added for protection against oxidizing conditions and molybdenum is the beneficial alloying element to protect against reducing conditions. 2-4 The base element (nickel) protects the alloy against caustic conditions. 2-4 All three elements, Ni, Cr and Mo act synergistically to provide resistance to environmentally assisted cracking in hot concentrated chloride solutions. 2-4 The alloying elements Cr and Mo also provide resistance to localized corrosion such as pitting and crevice corrosion in chloride containing solutions. Some of the Ni-Cr-Mo alloys also contain a small amount of tungsten (W), which may act in a similar way as Mo regarding protection against localized corrosion. 5 Ni-Cr-Mo alloys are practically immune to pitting corrosion but they may suffer crevice corrosion under aggres- sive environmental conditions.
- Materials > Metals & Mining (1.00)
- Government > Regional Government > North America Government > United States Government (0.47)
- Energy > Oil & Gas > Upstream (0.36)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
ABSTRACT Laboratory experiments were designed to determine the influence of polarization (ยฑ175 mV vs. saturated calomel electrode) in natural fresh water and in dilute microbiological media (1:100 Luria- Bertani broth) on biofilm formation on 316L stainless steel. Biofilms formed on all polarized and unpolarized surfaces within 120 hours. Variability among the surfaces was detected with environmental scanning electron microscopy. Polarization influenced microbial settlement in both media. Biofilm formation on polarized surfaces may not represent natural biofilms formed in the absence of polarization. INTRODUCTION Physical separation of anodes and cathodes and subsequent measurement of some electrochemical parameter have been used to detect biofilm formation and to evaluate the electrochemical impact of biofilms.1-3 In some cases polarization has been used.1, 2 Angell et al.1 used a concentric ring 304 stainless steel electrode to demonstrate that a consortium of sulfate-reducing bacteria and a Vibrio sp. maintained a galvanic current between the anode and cathode. In their electrode design, pitting was induced by passage of a 11 ยตA cm-2 current density to a small (0.031 cm2) anode. The anode was concentric to, and separated from, the cathode (4.87 cm2) by a Teflonยฎ (polytetrafluoroethylene) spacer. Current was applied for seventy-two hours either during or after microbial colonization. Once the applied current was removed the resultant galvanic current flowing between the anode and the cathode was monitored by a zero resistance ammeter. They found that a current was maintained in the presence of a microbial consortium. No current was measured in a sterile control. Licina and Nekoksa2 developed a probe consisting of ten 316 stainless steel concentric rings separated by epoxy. A potential (which varies according to experimental conditions) is imposed for 1 hour each day between the electrodes so that the electrodes are alternately anodes and cathodes. The metal discs are polarized to produce an environment conducive to biofilm formation. The applied current, required to achieve a pre-set potential between electrodes, remains stable until a biofilm forms. Once a biofilm is established, current increases consistent with a decrease in the polarization resistance. The generated current, current that continues to flow between the electrodes after the external polarization has been removed, is another indication of biofilm development. In the absence of a biofilm the generated current is expected to be zero. In the presence of a biofilm some current is expected to flow. While the Angell et al.1 and the Licina and Nekoksa2 probes are similar in that both rely on separation of anode and cathode regions for detection of microbial presence, there are significant differences. The concentric ring electrode1 provides a technique by which microbiologically influenced corrosion (MIC) can be studied and is not intended to represent any natural situation. The commercial probe2 is intended to provide information about an operating system (such as a flowing cooling water piping) that can be used to make decisions about cleaning or treatment. The probe designs also differ in the motivation for polarization. Angell et al.1 induced pitting in the anode. Franklin et al.4 and Little et al.5 were among the first to demonstrate that bacteria are attracted to anodic sites. The spatial relationship between corroding ferrous materials and bacteria has been demonstrated using several techniques and electrolytes.6-8 There is general agreement among investigators that bacteria are attracted to anodic sites on ferrous materials. Polarization of the multiple ring probe does not cause localized corrosion and is designed to encourage biofilm
- Materials > Metals & Mining > Steel (0.77)
- Energy > Oil & Gas > Upstream (0.49)
- Water & Waste Management > Water Management > Constituents > Bacteria (0.49)
ABSTRACT Different studies have been made using conventional electrochemical polarization techniques to establish mechanisms for the action of sulfate reducing bacteria (SRB) in microbiologically influenced corrosion (MIC). Nevertheless, there has been practically no detailed follow-up correlating the corrosive process with time and open circuit potential, corrosion products, sessile bacterial growth and attack morphology, to establish the mechanisms of this action. This research project designed an experimental structure to make these correlations utilizing the hydrogen permeation technique as its principal electrochemical tool to follow the cathodic reaction of hydrogen evolution, coupled with any other electrochemical, microbiological or chemical technique that would permit following up on the anodic reaction. The study began by reviewing the classic cathodic depolarization theory using an SRB strain identified as Desulfovibrio desulfuricans subespecie desulfuricans ATCC 7775 and a palladium sheet as a substrate with and without cathodic polarization. Later, sheets of carbon steel and iron were used to study the ferrous ions influence in the progression of the corrosive attack and corrosion products, correlated with open circuit potential, sessile growth and hydrogen permeation. Results obtained permitted establishing a useful correlation for proposing the mechanism for this bacterial action in three stages. The first was controlled by the adsorption of bacterial cells and iron sulfide products, principally mackinawite and pyrite, over the metallic surface, activating it through the formation of micro galvanic corrosion cells which generated a hydrogen permeation peak. The second stage showed bacterial and inorganic equilibrium, in which the metal was slightly ennobled by the formation of a more compact iron sulfide film mixed with polymers generated planktonically by the bacteria. The third stage was controlled by a severe, localized corrosive process configured into groups of deep, rounded holes, produced mainly by local reduction of pyrite to mackinawite, due to the acidity generated by bacterial corrosion, and its subsequent detachment, leaving the base metal active facing a very large cathode made up of different iron sulfide products adhering to the metal: mackinawite, pyrite, esmitite, marcasite, greigite, troilite and pyrrotite. In this more aggressive phase, there was no hydrogen permeation due to the barrier or anti-diffusive effect of the exopolymer. In this final exponential growth stage, the sessile bacteria were around 108 UFC/cm2 . INTRODUCTION The most well-known MIC cases involve sulfate-reducing bacteria SRB, which have been connected with corrosive processes in pipelines and other industrial installations, occasioning powerful impacts on the economy and the environment. A review of research projects carried out to determine the principal causes of this corrosion phenomenon show that even though the first publications about bio corrosion were made at the end of the nineteenth century, it was not until 1960 that the rigorous, mechanistic interpretation of the problem began, save for the pioneering work of van Wolzogen Kuhr and Van der Vlugt1 published in 1934 and known as the classic cathodic depolarization theory, which can be considered to be the first attempt to interpret biocorrosion in electrochemical terms. In the 1960S and early 1970S, publications on biocorrosion were principally focused on objecting to or validating the interpretation of anaerobic iron corrosion by SRB as explained by the previously mentioned theory; nevertheless, this focus made it possible to introduce innovative use of electrochemical polarization techniques and open cir
- Materials > Metals & Mining (1.00)
- Materials > Chemicals (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Water & Waste Management > Water Management > Constituents > Bacteria (0.54)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
ABSTRACT The guide direction today is reduction of vehicle weight and saving of fuel consumption. Magnesium is the lightest of all the commonly used metals and is very attractive for applications in automotive industry. However, environmentally assisted fracture significantly decreases the fatigue and creep resistance, mechanical stability and durability of high-strength Mg alloys. For example, such magnesium applications as wheels, transmission housings, pedals, etc. require good fatigue resistance in corrosive atmosphere. In order to produce parts for the automotive industry it is necessary to develop alloys with formability and durability in active environments. Until recently, corrosion resistance and creep resistance have been considered to be the main issues for long-term durability, reliability and applicability of Mg-based structural materials. These problems traditionally have been separated as corrosion behavior in non-stressed states and creep in non-corrosive conditions. In recent years the importance of environmental effects in many types of fracture processes has been recognized and it seems worthwhile therefore to examine more closely the role of environment in creep rupture as combined stress-environmental effects. So, the investigation of environmental assisted creep is very important as a tool to discover a mechanism of processes going in the tip of a crack and as the phenomenon very influencing mechanical stability of alloys in real service conditions. However, mechanical and corrosion processes develop simultaneously in real environment conditions, and inevitably lead to the appearance of new synergistic effects which significantly reduce the lifetime of Mg-alloys. INTRODUCTION Magnesium alloys are among the best lightweight structural materials with a relatively high strength-to-weight ratio and excellent technological properties. Therefore, magnesium attracts special attention of researchers working in automotive and aircraft industry. Wrought magnesium alloys show excellent mechanical properties, low porosity and very good surface finish of a profile. For instance, die-cast and extruded AM50 alloys have ultimate tensile strength (UTS) of 230 and 290 MPa, tensile yield strength (TYS0.2%) of 125 and 180 MPa and elongation-to-fracture of 12 and 18%, respectively. It is essential to study corrosion fatigue resistance of Mg alloys and to investigate the correlation of corrosion fatigue with the mechanochemical behavior of Mg alloys. Magnesium alloys were submitted to standard mechanical tests before electrochemical ones. The behavior of both stressed and non-stressed magnesium alloys was studied using cyclic polarization method, linear polarization method, and electrochemical impedance spectroscopy (EIS). There are two main reasons for a low corrosion resistance of many magnesium alloys. First, there is an internal galvanic corrosion caused by the second phase or impurity. Second, quasi-passive film of oxide and hydroxide on magnesium alloys is much less steady than passive films formed on magnesium alloys.. This quasi-passivity creates conditions for the occurrence of the most dangerous kind of corrosion ? pitting ? on the surface of magnesium alloys. Magnesium alloys are usually in a passive state in hydrochloric atmosphere and in salt water solutions. Their surface is coated with a very thin film preventing corrosion. Magnesium alloys in these conditions are exposed to pitting in a greater degree than to continuous (general) corrosion. Pitting is dangerous, because corrosion penetrates to a significant depth in separate small sites. The total loss of metal weight in this case is insignificant. General corrosion can be not so significant, while deep pitting can be acti
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
ABSTRACT With a soil resistivity less than 200 ohm-centimeter, tidal water table fluctuations, and a high potential for MIC (microbiologically influenced corrosion) activity, the Florida Everglades is one of the most corrosive underground environments in the United States. This paper discusses corrosion monitoring data of Ductile Iron Pipe in this harsh environment over a three-year period. In this study, uncoated, standard asphalt shopcoated, and polyethylene encased Ductile Iron Pipe were monitored. The evaluation included the use of electrical resistance type corrosion rate probes buried in the soil adjacent to the pipe and also between the pipe surface and encasement for the polyethylene encased pipe. Included were pipe to soil polarization characteristics determined through the application of a cathodic current to extend pipe service life by effectively reducing corrosion rates. The study illustrates that corrosion protection beyond the standard asphalt shopcoating and annealing oxide inherent to Ductile Iron Pipe may be warranted in such extremely corrosive environments as found in the Everglades. INTRODUCTION United States Pipe and Foundry Company has been conducting corrosion evaluations for over 70 years. One test site that has been utilized in these studies since July 2000 is a severely corrosive soil environment in the Florida Everglades. This test site not only contains extremely low soil resistivities of less than 200 ohm-cm, it also contains tidal water table fluctuations and a high potential for MIC (microbiologically influenced corrosion) activity. This extreme environment has been shown to cause complete wall penetration in an unprotected 6 ductile iron pipe (DIP) with a 0.20 wall thickness in less than five years. In the past, corrosion studies in Florida and elsewhere were conducted by burying groups of identicalpipe with different types of corrosion protection systems. The test pipes were then excavated and inspected at periodic intervals (e.g., 1, 3, 6, 12, and 24 years). Control pipe such as uncoated, abrasive blasted, and standard asphaltic shopcoated were buried for comparison. While providing valuable information, years of evaluation were required before obtaining enough data to draw conclusions. Since 2000, efforts at the Everglades test site have included non-invasive electrical and electrochemical data through above ground monitoring stations and correlating this data to corrosion activity (or lack thereof) of the buried DIP. This evaluation included the use of electrical resistance type corrosion rate probes buried in the soil adjacent to the pipe and also under the encasement. Pipe to soil potentials were routinely measured utilizing surface copper-copper sulfate reference electrodes as well as buried permanent silver-silver chloride and zinc reference electrodes. Polyethylene encasement is the most commonly used method of external corrosion protection for ductile iron pipe. 1-5 A pilot survey of 21 USA utilities conducted by the American Water Works Association (AWWA) Engineering and Construction Division reported 95% of the utilities polled use polyethylene encasement for corrosion protection of ductile iron pipe.6 The intent of the polyethylene film is to prevent direct contact of the pipe with the soil and provide an essentially impermeable barrier that restricts the access of additional oxygen to the pipe surface. It provides a uniform environment around the pipe, thereby mitigating local galvanic cells caused by variations in soil composition, pH, aeration, etc.4,7 Numerous reports, publications, and tests document that polyethylene encasement, when properly installed, has been used successfully since 1958 to protect millions of feet of gray and ductile iron
- North America > United States > Alabama (0.29)
- North America > United States > Texas (0.28)
- North America > United States > Colorado (0.28)
- Geology > Mineral > Native Element Mineral > Copper (0.45)
- Geology > Geological Subdiscipline > Environmental Geology > Hydrogeology (0.45)