Selection and Application Guide for Corrosion Resistant Nickel Alloys

(HY-industry Technology Center)

 

  • Nickel alloys combine excellent corrosion resistance, strength, toughness, metallurgical stability, processability and weldability. Many nickel alloys also have excellent heat resistance and are ideal for chemical corrosion resistance at high temperatures and temperatures, and are increasingly used in the petrochemical industry.

  • The wrought nickel-based alloy (defined as an alloy containing more than 45% nickel) introduced here includes various types of wrought corrosion resistant alloys commonly used in the chemical industry.

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1) alloy properties

  • Nickel alloys are more expensive than stainless steel. However, economic comparisons based on initial costs rather than life cycle costs can be misleading. For example, the price of Ni-Cr-Mo alloy is about 5 times that of 18Cr-8Ni stainless steel and twice that of super austenitic stainless steel. However, due to the excellent corrosion resistance of nickel alloys, the initial cost increase can often be compensated for by extended equipment life, reduced maintenance costs and long-term cost savings from minimal downtime.

  • The physical properties of nickel alloys are very similar to those of 300 series austenitic stainless steels. The thermal expansion rates of nickel-base alloys and carbon steels are approximately equal, and are significantly lower than those of 300 series stainless steels.

  • Although the thermal conductivity of pure nickel is higher than that of carbon steel, the thermal conductivity of most nickel alloys is significantly lower, and in some cases even lower than the thermal conductivity of austenitic stainless steels.

  • In addition to pure nickel, the strength of nickel alloys used in the chemical processing industry is much higher than that of 300 series stainless steel. Nickel alloys also have very good ductility and toughness. The maximum allowable stress for most alloys used in chemical equipment can be found in Volume VIII of the ASME Boiler and Pressure Vessel Code.

  • Nickel alloys are full austenitic microstructures. Almost all nickel alloys used in the chemical industry are solid solution strengthened. Their increase in strength comes from the addition of effective hardening elements such as molybdenum and tungsten rather than the formation of carbides. Like austenitic stainless steels, solid solution nickel alloys cannot be strengthened by heat treatment and can only be strengthened by cold working.

  • Another large class of nickel-based alloys can be strengthened by precipitation hardening heat treatment. Most of these alloys are used exclusively for ultra-high strength applications such as deep oil and gas production and alloys used in ultra high pressure processes.

  • Precipitation hardening nickel-based alloys have limited application in chemical equipment, in addition to valves and rotating mechanical parts. Such alloys include gas turbines, combustion chambers, and heat resistant superalloys used in aerospace applications.

2) corrosion resistance

  • Nickel alloys have a higher level of resistance to corrosion of various acids, bases and salts than conventional stainless steels and super austenitic iron-based alloys. A prominent advantage of nickel alloys is their excellent corrosion resistance in aqueous solutions containing halide ions. In this respect, nickel alloys are far superior to austenitic stainless steels, which are susceptible to corrosion by chloride and fluoride ion solutions.

  • The excellent corrosion resistance of nickel alloys not only shows lower metal loss, but also shows better resistance to local corrosion, especially resistance to pitting/crevice corrosion, intergranular corrosion and stress corrosion cracking. These forms of localized corrosion are the main cause of corrosion failure in the chemical industry compared to uniform corrosion.

  • The excellent corrosion resistance of nickel alloys is partly due to the lower reactivity (relative to iron) inherent in nickel, as indicated by its relatively inert oxidation potential in the electromotive force (EMF) sequence. Similar to stainless steel, chromium-containing nickel alloys have a passivating ability (ie, spontaneously form an ultra-thin, tough surface oxide that acts to effectively prevent corrosion).

  • Another advantage of nickel over iron is that nickel can accommodate a large proportion of alloying elements without forming a brittle phase. Alloy addition elements which improve corrosion resistance are usually chromium, molybdenum and copper. The role of alloying elements will be briefly described below.

3 )Welding Guide

  • Most nickel alloy welds use manual electric arc welding (SMAW), gas shielded tungsten arc welding (GTAW), and gas shielded arc welding (GMAW). Nickel alloy weldments have very good ductility and their low thermal expansion characteristics reduce residual stress and bending deformation. Only post-hardening grades require post-weld heat treatment. Refer to the Nickel Alloy Welding Rod and Filler Metal Technical Conditions issued by the American Welding Society (AWS)

  • The welding process of nickel alloy is very similar to the welding process of austenitic stainless steel. However, because the nickel-rich weld bath is more viscous and less permeable, it may be necessary to improve joint shape and welding techniques in order to obtain a fully penetrated weld. Nickel alloys do not allow the presence of contaminants than steel materials, which can cause weld cracks.

  • The high ductility of nickel-rich consumables, the low coefficient of thermal expansion, and the ability to allow dilution of various metal elements make them widely used for the welding of dissimilar metals. It includes not only the welding of nickel-based alloys and iron-based alloys, but also the welding of stainless steel with carbon steel and alloy steel. Similarly, nickel alloys can be deposited on carbon steel surfaces without the risk of cracking.

4 )Types of nickel alloys

  • Nickel alloy products are commercially available in a variety of forms including medium plates, sheets, strips, tubes, joints and forgings. Some nickel alloys also have foundry products which typically have different properties than their forged products.

  • Nickel alloys are generally classified according to their main alloy composition. The nickel alloys widely used in chemical equipment are briefly described below:

Pure nickel Nickel 200

  • Pure nickel Nickel 200 has very good corrosion resistance to various types of reducing acids and salts, but it is not suitable for strongly oxidizing media such as nitric acid. The most important characteristic of pure nickel is its unparalleled resistance to caustic alkali and even caustic corrosion of molten state. Although pure nickel is highly resistant to corrosion in dry halogen media, its corrosion resistance is insufficient below the water dew point. For applications with temperatures above 600 °F, Nickel 200’s derivative grade, Low Carbon Content Nickel 201 (UNS UO2201), is preferred.

Nickel-copper alloy Mone400

  • Like nickel, the corrosion resistance of nickel-copper Alloy 400 performs best under reducing media conditions, while aerated and oxidizing chemicals are detrimental to its corrosion resistance. Alloy400 is very resistant to the corrosion of hydrohalic acids and halides, especially high temperature gases that are resistant to hydrofluoric acid and fluorine or hydrogen fluoride.

  • This alloy is widely used to treat sulfuric acid solutions, seawater and brine. For applications requiring high strength, such as valves and pump components, alloy K-500 (NO5500) is often used, which is a precipitation hardening grade of Alloy 400 (UNS N04400).

Nickel-chromium-iron Inconel 600

  • The addition of chromium to the nickel matrix expands the suitability of Inconel 600 in an oxidizing environment. Although Inconel 600 is moderately resistant to inorganic acids, it has excellent corrosion resistance to organic acids and is therefore widely used in the processing of fatty acids. Inconel 600 is also widely used in the production and storage of hydroxides and alkaline chemicals.

  • Inconel 600 is also an excellent material for high temperature applications where both heat and corrosion resistance are required. The excellent performance of the alloy in high temperature halogen environment makes it an ideal material for organic chlorination processes. Inconel 600 also exhibits excellent resistance to high temperature degradation such as oxidation, carburization and nitriding.

 

Nickel-chromium-molybdenum Inconel 625

  • The addition of molybdenum to the nickel-chromium-based alloy increases the corrosion resistance of the material to oxidizing and reducing inorganic acids and salts. Molybdenum gives the alloy its resistance to chloride ion pitting and crevice corrosion. Inconel 625 is a high-strength material with excellent fatigue resistance. Inconel 625LCF is a derivative of Inconel 625. It is used exclusively for bellows and has excellent resistance to low cycle fatigue and thermal fatigue.

  • Like Inconel 625, Inconel 625 is available as both corrosion resistant and heat resistant. The excellent high temperature strength of Inconel 625, combined with its resistance to halogen corrosion, oxidation and carburization, make it an ideal choice for chemical and petrochemical equipment operating in demanding high temperature environments.

 

Nickel-chromium alloy Inconel 690

  • Inconel 690 is the nickel alloy used in the manufacture of pressure-bearing equipment with the highest chromium content and excellent resistance to oxidizing media. It can be effectively used in hot concentrated sulfuric acid, nitric acid and nitric acid/hydrofluoric acid mixed acid as well as oxidizing salt medium. The high chromium content also increases the corrosion resistance of the material in high temperature vulcanization environments.

Nickel-chromium-iron alloy Incoloy 825

  • Since the alloy contains nearly 30% iron, Incoloy 825 is sometimes included in the super austenitic stainless steel series. It excels in sulfuric acid and phosphoric acid media conditions, similar to Alloy 28, and was developed primarily for use in sulfuric acid and phosphoric acid media. Although Incoloy 825 is resistant to hydrochloric acid corrosion, it is prone to chloride pitting and crevice corrosion, especially in non-flowing, non-ventilating solutions. Incoloy 825 has a high iron content, so it has lower corrosion resistance to alkali and halogen than alloys with higher nickel content.

Nickel-chromium-iron-molybdenum “G” alloy

  • The corrosion resistance of the alloy Hastelloy G3 exceeds Alloy 400, Inconel 600 and Incoloy 825 in many applications. This alloy is particularly resistant to corrosion by sulfuric acid and impure phosphoric acid and is capable of withstanding both reducing and oxidizing conditions. The alloy Hastelloy G30, which was later developed, has better welding performance and improved corrosion resistance, especially the corrosion resistance of the weld heat affected zone.

Nickel-chromium-molybdenum “C” alloy

  • Hastelloy C-276 is an excellent alloying material for the chemical industry to deal with highly corrosive media conditions (beyond the capabilities of stainless steel). It has outstanding resistance to various acids, acid salts and other corrosive chemicals. Corrosion ability.

  • Hastelloy C-276 excels in harsh environments such as wet chlorine and hypochlorite. Due to the high molybdenum content of Hastelloy C-276, it has good corrosion resistance to pitting and crevice corrosion caused by chloride ions.

  • The process of finding materials that are better than Hastelloy C-276’s metallurgical and corrosion resistance promotes the development and commercialization of several patented “C” series alloys, which are Hastelloy C-22, 622, 59, 686 and Hastelloy C -2000. The molybdenum content of these alloys is roughly equivalent, and the chromium content is much higher than Hastelloy C-276. Some grades also contain tungsten or copper. The effects of these secondary alloying elements on metallurgical properties and corrosion resistance are complex and are not discussed in this paper.

Nickel-molybdenum “B” alloy

  • Hastelloy B-2 has outstanding corrosion resistance to reducing sulfuric acid, phosphoric acid and hydrochloric acid. It is especially suitable for hydrochloric acid equipment with a full concentration range and temperatures up to the boiling point.

  • Oxidizing chemicals have a detrimental effect on the corrosion resistance of such alloys, especially strong oxidants such as iron ions and copper ions as impurities in the solution.

  • The properties of the later developed alloys Hastelloy B-3 and Hastelloy B-4 were better than Hastelloy B-2. One of the benefits of these new grades is to minimize the formation of undesirable microstructures (which may cause embrittlement) during processing.

 

5 )Development of nickel alloys

  • Like iron and copper, nickel has been used in alloys since entering civil society. But nickel alloys are a latecomer to the chemical industry compared to steel, brass and bronze.

  • The first commercially important nickel alloy was Alloy 400 (monel 400), which was developed and marketed by International Nickel Corporation (later Inco Alloys) in 1905 under the trademark MONEL. The next important milestone is nickel-molybdenum alloy B and nickel-chromium-molybdenum-tungsten alloy C, which were introduced around 1930. Their inventors are Haynes Stellite (now Haynes International), two of which are registered under the trademark HASTELLOY. The next important stage in the development of nickel-based alloys came from Inco, which developed nickel-chromium-iron alloy 600 in 1931 and nickel-iron-chromium alloy in 1949, named INCONEL and INCOLOY.

  • Inco and Haynes used the initial popularity and reputation of these trademarks to introduce approximately 50 corrosion and heat resistant alloys in the MONEL, INCONEL, INCOLOY and HASTELLOY series.

  • Krupp VDM in Germany is a later famous nickel-based alloy developer and producer whose trademarks are Nicrofer, Nimofer and Nicorros.

  • These three world-leading companies continue to develop new nickel alloys and improved alloys of interest to the chemical industry.

 

6)Summary:

  • All of the early patented alloys have long since lost patent protection, and many other manufacturers around the world can now produce these alloys, either with their own trade names or generic alloy names that meet standard or technical specifications. Like pharmaceuticals, there is still debate about the equivalence between generic and patented products.

  • Commonly used standard specifications such as ASTM and DIN may be less restrictive than the standard specifications of the famous alloy development manufacturers. The internal standards of the manufacturer are more strict in controlling the chemical composition and metallurgical parameters of the alloy, and the goal is to ensure higher material properties. .

  • After 20 years of technical study and accumulation, HY-industry has formed its own quality system and completed a series of certifications. The products are exported to more than 70 countries in Europe, USA, Asia, Africa, Latin America, etc.

HY-industry is qualified superalloy supplier.We have more than 20 years experience in kind of Monel,Inconel,Hastelloy production.

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