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INTRODUCTION ABSTRACT Cladding/overlay thickness measurements were made on several primary air ports fabricated from alternative composite tubes installed in a kraft recovery boiler to document the fireside corrosion. Laboratory corrosions tests were then conducted to reproduce the relative corrosion rates determined by the field thickness measurments. It was found that all of the major available composite tube systems are suceptible to corrosion. Hydrated sodium sulphide and oxygen in combination with sodium hydroxide are implicated as major components in the liquid environment that causes the corrosion. Prevenative measures discussed include the need for a well-sealed port, and the likely need to avoid having black liquor droplets contacting the port tubes while dehydration is incomplete. Composite 304L stainless steel/SA-210 carbon steel tubes have replaced conventional carbon steel boiler tubes as the construction material for the lower-furnace of kraft recovery boilers to resolve the general fireside corrosion problems experienced with conventional carbon steel boiler tubes. While composite tubes have been very successful in resolving that concern, they have introduced other unanticipated problems. One such problem involves corrosion or balding, which has been observed predominantly on primary air port opening tubes. Corrosion of the 304L stainless steel cladding has occurred on both the cold-side surface and the fireside surface of primary air port opening tubes. Corrosion is a concern because of the potential for a water leak and subsequent explosion resulting from a smelt-water reaction. To resolve the more serious composite tube cracking problem, boiler tube suppliers have promoted the use of alternative co-extruded tubes, weld-overlaid tubes, and chromized tubes. Several North American mills have installed primary air ports fabricated from those alternatives. Based on reported inspection results, those alternatives are susceptible to corrosion, some more so than others. Several mechanisms have been proposed to account for the corrosion, which include corrosion by molten hydroxide, molten smelt and molten pyrosulphate. However, until a consensus on the true mechanism is attained, a resolution to this problem may not be achieved. Paprican has been involved in a collaborative United States Department of Energy research program with Oak Ridge National Laboratory to address the composite tube cracking problem in kraft recovery boilers. One task of the multi-disciplinary research program has been to identify the most likely corrosive environment that causes corrosion of primary air port composite tubes. This was done by conducting careful corrosion surveys within a single North American recovery boiler over an extended time frame to determine relative corrosion resistance of the various composite tubes installed, and by conducting lab-based corrosion testing to reproduce that relative corrosion resistance. This report documents the results of those efforts. RECOVERY BOILER INSPECTION OBSERVATIONS The relative corrosion resistance of composite tubes fabricated into primary air ports was determined from the analysis of inspection data, and from measuring the cladding/overlay thickness as a function of time. Essential design and operation details of the recovery boiler, within which observations and measurements were made, are provided below. The recovery boiler under study is a 1997 Babcock and Wilcox (B&W) single-drum cogeneration unit constructed using 2½ in. (63.5 mm) diameter tubes on 3 in. (76.2 mm) centers in a membrane-type design with a sloped floor. The unit typically burns 3.6 million lbs (1.63 million kg) of black liquor dry solids
- Materials > Metals & Mining > Steel (1.00)
- Government > Regional Government > North America Government > United States Government (1.00)
- Energy (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 When designing for corrosion resistance, the cost of the material must always be weighed against the alloy?s corrosion resistance. Though Ni-Cr-Mo alloys offer excellent corrosion resistance, the cost of these alloys can be quite high. Austenitic stainless steels, though attractive from a cost standpoint, can fail in service leading to downtime and other subsequent costs. An alloy that can bridge the gap between these two alloy groups would deliver nearly the corrosion resistance of the Ni-Cr-Mo alloys without the upfront cost would be desirable. Alloy 27-7MO has been shown to achieve this goal in many applications. This paper will discuss both laboratory and plant corrosion testing in applications where cost savings can be achieved by either eliminating failures or decreasing upfront expenditures. Environments and components examined will include heat exchangers, phosphoric acid, sulfuric acid, and other relevant applications. INTRODUCTION Many materials are available which exhibit excellent resistance to general corrosion in a given medium (see Table 1 for compositions of several tested alloys). Unfortunately failure of a component can occur very quickly by a localized attack (pitting and/or crevice corrosion). By examining the Pitting Resistance Equivalency Number (PREN) and results from corrosion tests that focus on the localized corrosion resistance of candidate alloys, a better understanding of material performance can be achieved. Tests have been performed on a variety of alloys in various seawater-base environments, sulfuric acid environments, and phosphoric acid environments and suggest possible alternatives to the cost of some high performance alloy candidates and the high costs of downtime and repair associated with inadequate materials. Unlike testing in pure reagent grade acids, other corrosive media like chlorides and fluorides have been added to simulate aggressive conditions that might be found in actual chemical processing service. For heat exchangers, often the most extreme conditions are encountered not with the product, but with the cooling or heating fluid. Seawater, as an abundant cooling medium in marine and coastal operations is often used in heat exchangers. Therefore heat exchangers must utilize materials that can resist both general and localized corrosion by seawater. In addition to seawater, many heat exchangers use small additions of chlorine to control the problems associated with bacteria and other marine life. Thus, not only seawater, but seawater with additions of chlorine is used, which can significantly increase the corrosivity of the environment. Conventional stainless steels like 304 and 316 have limited resistance to this environment and are very susceptible to general attack, as well as pitting or crevice corrosion and even chloride-induced stress corrosion cracking. Often, commercially pure (C.P.) grades of titanium are used for their excellent resistance to these environments. While titanium is a good technical choice, its price or especially its availability often impedes its use and consideration as a practical material of construction. Other Ni-base corrosion resistant alloys (CRA?s) like UNS N10276, UNS N06022, UNS N06625 and UNS N06686 have been qualified and used in marine heat exchangers due to their excellent resistance. Unfortunately, raw material price volatility, especially that of nickel and molybdenum, leads to higher prices on these CRA?s that might limit their use. Conventional 6% molybdenum super-austenitic stainless steels like UNS N08367 or UNS N08926 have also been considered for this service. These alloys offer greatly improved resistance to localized corrosion when compared to standard stainless steels, but
- Materials > Metals & Mining > Steel (1.00)
- Materials > Chemicals > Commodity Chemicals (1.00)
- Energy > Oil & Gas > Upstream (0.87)
- Materials > Metals & Mining > Titanium (0.74)
Corrosion Behavior of Experimental and Commercial Nickel-Base Alloys in HCI and HCI Containing Fe3+
Holcomb, Gordon R. (US Department of Energy) | Covino, Bernard S. (US Department of Energy) | Bullard, Sophie J. (US Department of Energy) | Matthes, Steven A. (US Department of Energy) | Ziomek-Moroz, Malgorzata (US Department of Energy) | Adler, Thomas A. (US Department of Energy) | Alman, David E. (US Department of Energy) | Jablonski, Paul D. (US Department of Energy)
ABSTRACT The effects of ferric ions on the corrosion resistance and electrochemical behavior of a series of Ni-based alloys in 20% HCl at 30ºC were investigated. The alloys studied were those prepared by the Albany Research Center (ARC), alloys J5, J12, J13, and those sold commercially, alloys 22, 242, 276, and 2000. Tests included mass loss, potentiodynamic polarization, and linear polarization. INTRODUCTION Hydrochloric acid (HCl) is second to sulfuric acid in the numerous and diverse applications of the manufacturing and synthetic chemical industry. It is an extremely corrosive and aggressive acid depending on its concentration, temperature, and oxidizing impurities. A couple of uses are the pickling and chemical cleaning of steel in pharmaceutical industries. In such applications in the chemical process industry, steel (including stainless steel), and copper alloys cannot generally tolerate exposure to HCl; therefore, the use of nickel alloys is essential. These alloys possess the ability to passivate in the presence of HCl, yet in many cases high HCl concentrations or high temperatures can disrupt the alloy?s passive state. The Ni-Cr-Mo alloy group has been shown to be one of the most versatile alloy groups and particularly corrosion resistant in aqueous solutions. The commercial alloys studied include Haynes-242, Hastelloy-C22, -C276, and -C2000 and are henceforth referred to as 242, 22, 276, and 2000. The Albany Research Center (ARC) of the U.S. Department of Energy has developed a set of Ni-base alloys, J5, J12, and J13, whose alloying content is similar in many respects to the commercial alloys. The compositions of the alloys are shown in Table 1. TABLE 1 - NOMINAL ALLOY COMPOSITION OF TEST ALLOYS (WT%, BALANCE Ni) The work presented here is a comparison between commercially available nickel alloys and newly developed ARC alloys. The purpose was to investigate the electrochemical behavior and corrosion resistance of the alloys in solutions of 20 % HCl and 20% HCl plus 700 ppm ferric ions (Fe 3+) at 30°C. It was of interest to better understand the general corrosion properties of the ARC alloys for possible future applications. EXPERIMENTAL PROCEDURE Materials The commercial alloys selected for this research, 242, 22, 276, and 2000, are extensively used in the chemical processing industry as well as pollution control and waste treatment industries. Having both chromium and molybdenum as alloying metals gives these alloys the ability to be used in both oxidizing and non-oxidizing applications. The ARC developed alloys, J5, J12, and J13, were not initially developed for the use in corrosive aqueous environments, but rather for high temperature gaseous environments. The fabrication and modification of these alloys was designed to increase formability and efficiency as well as to reduce the cost of low coefficient of thermal expansion nickel-base superalloys. Their primary use is intended for interconnect applications in intermediate temperature solid oxide fuel cells These alloys were used in the current research to further understand their behavior and to extend their applications. Sample Preparation Each sample coupon was machined to approximately 1 x 0.5 in (2.5 x 1.25 cm) with a 0.125 in (0.32 cm) diameter hole near the one of the short edges. Coupon thickness was approximately 0.04 cm for J5, J12 and J13, and approximately 0.15 cm for 242, 22, 276 and 2000. All sample surfaces and edges were polished to a 600-grit finish and engraved with the alloy type and designated sample number. Before the mass loss test, samples were cleaned with methanol in an ultrasonic cleaner and then air-dried. Density measurements of each
- Materials > Metals & Mining > Nickel (0.55)
- Government > Regional Government > North America Government > United States Government (0.54)
- Materials > Metals & Mining > Steel (0.54)
- Materials > Chemicals > Commodity Chemicals (0.54)
INTRODUCTION
ABSTRACT The results of an electrochemical study performed on duplex, superduplex, austenitic and superaustenitic stainless steel in halide containing sulfuric media are presented and compared. In particular, the specific role of chloride and fluoride ions on both localized and uniform corrosion was investigated. From these results, the use of the duplex stainless steels family in the chemical industry, flue gas desulphurization process and hydrometallurgy is discussed.
During the last 20 years, the effect of chloride concentration and temperature on the corrosion resistance of stainless steels in chloride containing sulfuric acid solutions has been widely investigated. More recent studies provided additional data, particularly for modern duplex and superduplex grades. Thus, for numerous stainless steel grades, potential ? pH diagrams have been plotted for two concentrations of chloride (3% and 6%), two temperatures (140°F/60°C and 176°F/80°C) and for 0.5
- Materials > Metals & Mining > Steel (1.00)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (0.54)
ABSTRACT Nickel alloys have been utilized for decades in sulfuric acid service in the chemical processing industry. Laboratory and filed data are assimilated for nickel alloys that have historically been used in sulfuric acid applications. Performance data for recently developed nickel alloys are analyzed. The alloys are ranked for applicability by acid concentration and temperature. INTRODUCTION Sulfuric acid is one of the world?s most important industrial chemicals as it is used in a variety of industrial processes. World production exceeds 100 million metric tons per year. Diluted acid is very corrosive while concentrated acid at ambient temperature is customarily stored and processed in carbon steel equipment. The corrosivity of the acid varies with concentration, temperature, its velocity relative to exposed surfaces, and with the nature of possible contaminants. Dilute acid is very reducing in nature. At greater concentrations, it begins to take on an oxidizing character. Concentrated acid (above 87% by weight) is oxidizing in nature. Thus, dilute and intermediate strengths of the acid can be contained by materials resistant to reducing conditions while stronger concentrations require materials resistant to oxidizing media. Selection of a metal or alloy for a particular process depends primarily on the reducing or oxidizing nature of the solution as determined by acid concentration, and the corrosive effects of aeration, temperature and the nature of impurities. Selection depends on factors such as velocity, film formation, continuity of exposure, allowable metallic content of the solution, and physical properties of the alloy. The most commonly used nickel alloys in processes containing dilute sulfuric acid are alloys 25-6MO, 27-7MO and other 6% molybdenum super-austenitic stainless steels, 825, 020, and G-3. For aggressive, hot, sulfuric acid environments, alloys 625, 622, C-276, and 686 are required. For concentrated acid higher chromium alloys such as 690 and 693 are used. DISCUSSION Nickel and Its Alloys Nickel retains a face-centered-cubic (FCC) austenitic crystal structure up to its melting point, providing freedom from ductile-to-brittle transitions and minimizing the fabrication problems that can be encountered with ferritic metals. In the electrochemical series, nickel is more noble than iron but more active than copper. Thus, in reducing environments, nickel is more corrosion resistant than iron, but not as resistant as copper. Alloying with chromium provides resistance to oxidation thus providing a broad spectrum of alloys for optimum corrosion resistance in both reducing and oxidizing environments. Nickel-based alloys have a higher tolerance for alloying elements in solid solution than stainless steels and other iron-based alloys while maintaining good metallurgical stability. These factors have prompted development of nickel-based alloys to provide resistance to a wide variety of corrosive environments. As seen in Figure 1, many alloying elements can be combined with nickel in single-phase, solid solution over a broad composition range to provide alloys with useful corrosion resistance in a wide variety of environments. For example, molybdenum and tungsten improve resistance to reducing acids. Copper also improves resistance to reducing acids, particularly non-aerated sulfuric acid. Chromium improves resistance to oxidizing corrodents. Alloys containing these elements provide useful engineering properties in the annealed condition without deleterious metallurgical changes resulting from fabrication or thermal processing. Table 1 exhibits the chemical composition of alloys evaluated in this study. N
- Materials > Metals & Mining > Nickel (1.00)
- Materials > Chemicals > Commodity Chemicals (1.00)
INTRODUCTION ABSTRACT Material selection for corrosive chemical services should be based on life cycle cost for the plant equipment. Often corrosion resistant alloys and non-metallic materials have suitable corrosion resistance for a given application. Equipment design, fabrication, operating, maintenance and salvage expenses are essential elements in life cycle costs calculations. The risks associated with equipment operation, maintenance, inspections and salvage expenses are frequently neglected in calculating life cycle costs yet they often are the major portion of total life cycle costs. Risks arising from maintenance, inspection and salvage actions are different for equipment constructed of non-metallic materials of construction than those constructed of corrosion resistant alloys; these differences that affect life cycle costs are discussed. Petrochemical industries, pulp & paper industries and petroleum production experiences indicates that the major component of life cycle costs for process equipment are the maintenance costs occurred after placing the equipment in service. Equipment constructed of highly corrosion resistant alloys, such as high alloy stainless steels, nickel based alloys and reactive metal generally are typically more costly to fabricate and install than equivalent equipment constructed of non-metallic materials. However material selection should not be based on initial installed cost but instead on life cycle costs. In general the maintenance, risk and salvage yearly expenditures are greater for non-metallic equipment compared to those for metallic equipment. A comparison of the likely life cycle costs occurred by both metallic and non-metallic equipment after installation will assist those selecting materials of construction. The purpose of this paper is to highlight those maintenance and inspection practices required during the service lives of non-metallic process equipment that differ from such practices required for metallic equipment. These differences should be considered when choosing between various materials of construction using life cycle cost considerations. Depending upon service conditions and economics non-metallic equipment may or may not be preferred over equivalent metallic process equipment. Life cycle costs include fabrication and installation cost plus those operating, maintenance, risk and salvage expenses likely to be experienced by equipment throughout its service. Included in life cycle costs are the maintenance and other outlays associated with loss of containment (leakage), loss of functionality and insuring equipment integrity. When all expenses are considered, equipment constructed of corrosion resistant alloys frequently is less expensive on a life cycle cost bases than equivalent equipment constructed of non-metallic materials even though the non-metallic equipment had a lower installed cost. Non-metallic process equipment as described in this paper refers to fixed equipment (vessels, tanks and piping) that has a suitable corrosion resistant non-metallic surface exposed to the process. Non-metallic process equipment can be constructed of a homogenous nonmetallic material or can consist of a non-metallic corrosion resistant layer of suitable thickness supported on a non-metal or metallic structural frame. A metallic structural substrate is almost always carbon steel. Failure of the protective non-metallic coating or lining over a structural substrate in aggressive corrosive service can result in extremely rapid substrate corrosion leading to leakage. Fiber Reinforced Plastic (FRP) equipment as a rule consists of a FRP structural substrate with less corrosion resistance than the more corrosion resistance inner la
- Materials > Metals & Mining (1.00)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (1.00)
- Energy > Oil & Gas > Upstream (1.00)
INTRODUCTION ABSTRACT Sulfuric acid is one of the basic raw materials for the chemical industry. It is used in numerous processes as a reagent, as a catalyst and as a drying agent. Sulfuric acid is very corrosive. AISI types 304 and 316 stainless steels are used to handle very diluted acid at low temperature. At higher concentrations and temperatures the use of materials like high alloyed stainless steels and nickel based alloys becomes necessary. Alloy 20, alloy 825, alloy 31, alloy 59 and Ni-Mo-alloys are some examples. The high alloyed austenitic stainless steel alloy 31 (UNS N08031) and the nickel-chromiummolybdenum alloy 59 (UNS N06059) exhibit good corrosion resistance in sulfuric acid as well as good resistance to pitting and crevice corrosion. Therefore, they find extensive application e.g. in flue-gas desulphurization units of coal fire power plants, in the transportation and recycling of waste sulfuric acid as well as in heaters and coolers also for chloride contaminated acid. This paper compares the corrosion behavior of alloy 31 and alloy 59 in sulfuric acid environments. Corrosion data under different conditions are presented and discussed. The electrochemical behavior of both materials was studied as well. Results of laboratory testing are presented together with examples of applications. Sulfuric acid is one of the most important elementary substances of the chemical industry. The acid has found a wide variety of applications in industry. Examples include the treatment of raw phosphate rocks in the fertilizer industry, the treatment of titanium ores for the production of titanium dioxide, the manufacture of phosphoric and hydrofluoric acid and the wide field of organic chemical synthesis, for example in sulfonation and nitration. Unfortunately sulfuric acid is also involved in the most frequently encountered corrosion problems in the process industry. It is very corrosive and can show a non-monotonous corrosive effect on metals; i.e. under certain condition it can produce large variations on corrosion rate by slight changes in the service conditions. In fact, there is no stainless steel or nickel based alloy suitable over the entire concentration range up to boiling temperature. The diluted and medium concentrated acid is best handled by materials resistant to reducing conditions. AISI types 304 and 316 stainless steels are used to handle very diluted acid at low temperature. At higher concentrations and temperatures the use of materials like high alloyed stainless steels and nickel based alloys become necessary. Alloys typically used are alloy 904L, alloy 926 (a standard 6% Mo-alloy), alloy 825, alloy 20, alloy 31 (a high Cr version of the 6% Mo-alloy), alloy C-276, alloy 59, Ni-Mo-alloys (B-family alloys), etc.. Figure 1 presents the iso-corrosion diagram of several alloys in sulfuric acid; it must be emphasized that the iso-corrosion lines represent a corrosion rate of 0.5 mm/y, which for many applications is already too high and technically not acceptable. Alloys like 825 and alloy 20 have been widely used in sulfuric acid services but not up to very high temperatures; for some concentrations only temperatures up to 50 °C are possible. The nickel based alloy from the C-family alloy 59 and the high alloyed austenitic stainless steel alloy 31 are newer materials for use in sulfuric acid, and in particular alloy 31 shows a more extended suitability. For example, in aerated technical sulfuric acid (up to 90%) the corrosion rate of alloy 31 was <0.1mm/y up to at least 80°C. In addition, these alloys exhibit good corrosion resistance to pitting and crevice corrosion. Metallic materials like zirconium and tantalum can be used f
- Materials > Metals & Mining > Steel (1.00)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (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 More than 95% of the world demand for phosphoric acid is met by the wet-process, which involves the reaction of the phosphate rock with concentrated sulfuric acid. Pure phosphoric acid is only mildly corrosive to metals. However, the presence of impurities in the phosphate ores like chlorides, fluorides and silicates and the free sulfuric acid lead to complex corrosive conditions. The level of impurity depends on the origin of the phosphates and their processing, e.g. washing the ores with sea water further increases the level of chlorides. The corrosive attack is further aggravated by erosion resulting from the presence of phosphate rock particles and gypsum crystals, turbulence and deposit formation. Equipment for production and handling of phosphoric acid typically consists of rubber lined steel, AISI 316L type stainless steel and special steels like 904L and 28. For the most severe conditions nickel based alloys are used. Even though material selection has been continuously optimized, sufficient advantage is not being taken from the new, cost-effective 6%-molybdenum alloy 31 (UNS N08031) yet. This high Cr and Mo containing austenitic steel was designed to fill the gap in cost and performance between stainless steels and nickel alloys and significantly improves service life and reduces failure by localized corrosion when its lower alloyed counterparts are at the end of the usefulness limits. This work reports on the success achieved with alloy 31 in critical parts of the phosphoric acid process. Laboratory results are presented together with field experience and examples of application. INTRODUCTION Phosphoric acid (H3PO4) is a very important chemical product. A large amount of the world?s fertilizer production is based on this acid. Phosphoric acid is produced by two different methods. The thermal process where phosphoric acid is produced by the combustion of phosphorus with atmospheric oxygen followed by hydration of the oxide obtained. Owing to its high purity this acid is mainly used in food industry. However, this method is of secondary importance because of the high energy requirement. The wet digestion of phosphate rock with mineral acids is the most important process in terms of volume. Wet phosphoric acid process The wet process involves the reaction of phosphate rock (apatite) with sulfuric acid (nitric acid or hydrochloric acid are also used but to a lesser extent) according to the empirical overall formula: Ca3(PO4)2 + 3H2SO4 ¿ 2H3PO4 + CaSO4 Calcium sulphate is a by-product of the process. Depending on the water content, calcium sulphate may take the form of dihydrate, a-hemihydrate or anhydrite. The limit of the dihydrate-hemihydrate transition curve varies according to the process conditions, type of phosphate, impurities and additives. According to the form in which this by-product is generated the variants customary in industrial plants are classified into: - Dihydrate process (CaSO4-2H2O) is the most common process in the industry for producing 26- 28% P2O5 (approx. 36-39% H3PO4) and using relatively low temperature in the attack vessel, typically 80°C, which limits corrosion problems. Among the phosphoric acid producers this is the favorite process due to its ability to efficiently convert various types of phosphate, its flexibility and simplicity of operation and low maintenance cost. - Hemihydrate process (CaSO4-1/2H2O) produces high strength acid (45-50% P2O5 corresponding to approx. 62-69% H3PO4) and operates at higher temperature, typically 100-110°C, which make it significantly more corrosive. - Finally, different combinations of these two processes are possible where a determin
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- Geology > Mineral > Sulfate (1.00)
- Geology > Mineral > Phosphate (1.00)
- Geology > Rock Type > Sedimentary Rock > Phosphate Rock (0.85)
- 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)
- Well Drilling (0.68)
ABSTRACT UNS N06110 is a Ni-Cr-Mo alloy developed for service in highly corrosive environments. It has higher chromium content than the numerous other "C-type" alloys that have been developed in the last six decades. This higher Cr-content gives N06110 alloy greater resistance to oxidizing environments than is exhibited by other C-type alloys. In this paper, the corrosion-resistant properties of N06110 alloy in several severe environments pertinent to the Chemical Process Industry (CPI) are described. The corrosion rates of N06110 alloy are compared with those of Alloy 22 (N06022), Alloy 59 (N06059), Alloy 2000 (N06200), Alloy 686 (N06686), and Alloy 276 (N10276). The corrosion rate of N06110 alloy was measured in a wide range of solutions, including pure acids, mixed acids, oxides, sulfates, organics compounds, and salts. The data shows that N06110 alloy has an excellent corrosion resistance in many solutions, but is best suited for use in wet oxidizing or mildly reducing environments where it demonstrates superior performance in comparison to other Ni-Cr-Mo alloys. The corrosion performance of N06110 alloy in a mixed environment of sulfuric acid plus sodium chloride is discussed in detail. Unusual features of corrosion in this mixed environment are explored. INTRODUCTION Nickel alloys are able to contain greater concentrations of performance enhancing alloying additions, like chromium and molybdenum, than can be accommodated in the iron-base stainless steels. These greater concentrations of chromium, molybdenum, etc., give the Ni-Cr- Mo greater corrosion resistance than is attainable in the Fe-Cr-Ni stainless steels. These Ni- Cr-Mo alloys possess outstanding combinations of strength, ductility, corrosion resistance and fabricability. One of the newer Ni-Cr-Mo alloys is ALLCORR alloy, UNS N06110, which was developed by ATI Allvac for service in highly corrosive environments. It is a single-phase, solid solution, high-nickel alloy. It has higher chromium content than other "C type" alloys that have been developed in the last six decades. This higher Cr-content gives N06110 alloy greater resistance to oxidizing environments than is exhibited by other C-type alloys. Compositions of N06110 and other Ni-Cr-Mo alloys are shown below: Table 1 ? Composition Range Comparison for selected Ni-Cr-Mo alloys. Corrosion resistant alloys typically are used for containing fluids, which generally requires flat product (plate, sheet, strip, etc.). ATI Allegheny Ludlum, an Allegheny Technologies company is a long-standing producer of corrosion-resistant flat-rolled products and has generations of experience with these materials. Processing of flat-rolled product is different from that for long products. This combination of experience and processing offered Allegheny Ludlum the opportunity to re-optimize the composition of N06110 alloy for flat-rolled product production and use. Typical composition of this optimized N06110 product is shown in Table 2, below.
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- 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 Zirconium can be fusion welded to a number of other reactive and refractory metals including niobium, hafnium, vanadium, tantalum and titanium. Fusion welding of zirconium to titanium can result in a weld exhibiting varying final properties which are unpredictable and generally non-reproducible. In the case of zirconium to titanium welds the corrosion resistance is generally less that that of either of the parent metals. In addition, the mechanical properties of the weld are highly variable. This paper presents information on the corrosion resistance and mechanical characteristics of the zirconium-to-titanium fusion weld. The effect of heat treatment is also discussed. This particular weld combination is not generally suitable for fabrication of equipment for use in the chemical processing industry (CPI). INTRODUCTION The zirconium to titanium fusion weld appears to be an attractive weld for several reasons. From the standpoint of possible cost savings with respect to titanium and availability, and perceived improved corrosion resistance, from the zirconium, this weld does indeed appear to be beneficial. This paper presents corrosion and mechanical property data which indicates that fusion welding of zirconium to titanium by commonly used tungsten inert gas (TIG) method is not generally suitable for fabrication of equipment for use in the chemical processing industry (CPI). FIGURE 1 - Zirconium - Titanium weld 150X (zirconium on right) Figure 1 shows the variation in chemical composition possible in a zirconium to titanium autogeneous weld. The light and dark coloration of the weld indicates variable weld pool chemistry. An un-melted section of pure titanium is shown in the center of the weld zone. These photomicrographs also show a range of chemistry, as indicated by coloration changes in this zirconium - titanium weld. Each of these areas has different corrosion characteristics and mechanical properties. This inherent variability in the zirconium - titanium weld composition is the basis for the unpredictable nature of this weld combination when standard welding methods are employed. In specific cases this weld combination may be acceptable if the titanium and zirconium are compatible with the selected media and if stresses are low. Polyakov et. al. discusses an example of a heat exchanger with a titanium tube sheet and zirconium tubes in a welded configuration for use in dehydrating acetic acid. No evidence of corrosion or other damage was noted after 15,000 hours of operation. Although zirconium-titanium homogeneous alloys are not the primary focus of this paper, a brief review will be beneficial. For example, Ti50Zr has been described as having a better corrosion resistance than zirconium in phosphate buffered saline solutions which makes this particular alloy a more suitable biomaterial than pure zirconium or pure titanium. Other studies performed on zirconium-titanium homogeneous alloys in the UK and elsewhere demonstrate that these alloys may be useful for certain biocompatible applications such as dental implants. The Zr50Ti alloy is also used as a sputtering target for surface applications on metal and glass. Zr-Ti homogeneous alloys were also investigated for their corrosion resistance to hot nitric acid. The outcome of that research indicated that a zirconium-titanium alloy of Zr15Ti was immune to stress corrosion cracking (SCC) in hot nitric acid. Typically Zr 702, in a stressed condition, can exhibit SCC in hot nitric acid in concentrations generally above about 70%. For the Zr15Ti alloy, related mechanical data was not included in the study. In addition, the samples tested were in the non-welded condition. This paper is concern