hastelloy

What is the Difference Between Hastelloy® and Incoloy®?

Hastelloy® and Incoloy® are both members of the “superalloy” family, also known as high-performance alloys. As such, they have several key characteristics in common. They both possess excellent mechanical strength, especially at high temperatures, and they are both highly resistant to corrosion and oxidation. However, there are also several important differences to note between these two superalloys, including their chemical composition, their weldability, and their suitability for different applications.

Hastelloy®

Hastelloy® (milled by Haynes) is a nickel-molybdenum alloy. There are many different grades of Hastelloy®, many of which are nickel-chromium-molybdenum alloys. Each of these grades has been optimized for a specific purpose, but all of them are highly resistant to corrosion. The inclusion of molybdenum makes Hastelloy® harder, stronger at high temperatures, and also makes it great for welding applications. These alloys are easily fabricated and formed. They have good ductility and can be forged and cold worked.

Hastelloy® has outstanding resistance to highly oxidizing and reducing agents, making it a great choice for moderate to severe corrosive environments. It is commonly used for pipes and valves in the chemical processing and petrochemical industries. It is also used in nuclear reactors and chemical reactors, and is excellent for pressure vessels and heat exchangers.

How Does Incoloy® Differ From Hastelloy®?

Incoloy® (milled by Special Metals) is a nickel-iron-chromium alloy. There are also many different grades of Incoloy® available. Most of these grades were designed specifically for high temperature applications. Incoloy® is relatively easy to fabricate, and can be made using the same machines and processes used to make stainless steel. Its high iron content makes it a more cost effective solution for many applications. In general, Incoloy® is not suitable for severely corrosive environments, but some grades have been designed for increased corrosion resistance, even in harsh environments.

Incoloy’s® high temperature strength and resistance to seawater, brine, sour gas, and chloride make it ideal for use in the oil and gas industries. It is also used for propeller shafts, hot vessels for food and water, chemical processing equipment, gas turbines, aircraft, and tank trucks. Alloying Incoloy® with other elements can further increase its resistance to chemically corrosive environments such as sulfuric and phosphoric acids, and nuclear fuel.

High Performance Hastelloy® and Incoloy® from Continental Steel

Continental Steel is proud to supply high-performance superalloys for your specific application. Contact us today to learn how we can provide you with the solutions you need.

Does Welding or Fabricating Nickel Alloys Affect Corrosion Resistance?

Maintenance, repair, and operations (MRO) teams can especially attest that MRO processes are being increasingly upgraded and updated with new, specialized materials. As new construction methods take hold, new challenges are being introduced to mechanical, plumbing, or electrical device maintenance and replacement.

Superalloys are popular in MRO processes due to their mechanical strength, resistance to creep, surface stability, and corrosion and oxidation resistance. These qualities lead to improved performance and longer life with less maintenance and easier repair.

High performance nickel alloys are used in a diverse range of industries and processes. These include aircraft, automotive, chemical processing, electrical resistance heating, electronics, telecommunications, marine, and oil and gas extraction.

What makes nickel superalloys so attractive is their resistance to corrosion and oxidation. Varieties of high performance nickel alloys include Incoloy®, Hastelloy®, Inconel® and Monel®. Each of these alloys has certain properties which make them suited for MRO applications. In particular, each alloy has certain machining and welding properties that make them more efficient and resistant to corrosion and wear.

Incoloy®

Incoloy is a line of superalloys produced by the Special Metals Corporation, a group of companies that specialize in inventing, producing, and distributing high-performance nickel alloys for specialized engineering projects, which includes inconel and monel.

Incoloy is an age-hardenable nickel-iron-chromium alloy with trace amounts of molybdenum, copper, titanium, and aluminum. There are currently 22 grades of incoloy, and they are broadly used for range of applications including oil and gas well piping, chemical processing, heat exchangers, nuclear facilities, and caruburizing equipment.

Incoloy is best suited for corrosion resistance in wet environments like plumbing systems or pipelines. It can also maintain its austenitic structure through extended periods of exposure in high temperatures.

Incoloy is best worked in temperatures of 1600°F (850°C) to 2150°F (1175°C). For best results, it is recommended to rough machine the material before age hardening and finishing after heat treatment. Incoloy’s maximum corrosion resistance and strength is achieved after aging and hot-working the alloy in the 1600°F (870°C) to 1800°F (980°C). Cold-working certain grades of incoloy make it behave similarly to other grades, such as incoloy 925, which behaves like 825 when cold-formed except with a higher work-hardening rate.

The best methods for welding incoloy are either using gas-metal-arc welding (GMAW) or gas-tungsten-arc welding (GTAW). For the former method, it is not recommended to go above 180 amps of current in the “spray arc” metal transfer mode.

Hastelloy®

Hastelloy is a high-performance nickel alloy registered by Haynes International, Inc. The primary alloying ingredient in hastelloy is typically transition metal nickel, with various percentages of copper, iron, aluminum, and titanium. Common Grades of Hastelloy include C276 and C22. Hastelloy is especially resistant to high-temperature and high-stress envionrments, and is a great alternative to iron-based alloys in terms of corrosion resistance.

The welding characteristics of hastelloy are similar to austenitic stainless steel, and hence not very difficult to weld with proper care. The preferred method for welding hastelloy is GTAW, GMAW, and shielded metal arc welding (SMAW). Other less common welding methods are plasma arc welding, resistance spot welding, laser beam welding, electron beam welding and submerged arc welding.

One of the most important issues to keep in mind when welding hastelloy is cleanliness. Contamination from greases, oils, lead sulfur, and other elements with melting points lower than nickel can cause severe problems.

Inconel®

The primary alloying ingredient in inconel is nickel-chromium. It is resistant to oxidation and corrosion, especially to chloride-ion stress-corrosion cracking. This makes it well-suited for high heat and high pressure environments. There are currently 25 grades of inconel which are commonly used in chemical and food processing, furnace components, and aerospace and land-based gas turbine parts like jet engines.

When inconel is heated, it has a tendency to form a thick and stable passivating oxide layer that protects any surface from damage. Since inconel tends to quickly work harden, welders need to minimize the number pf passes with an aggressive but slow cut with a hard tool, especially when working with age-hardened grades like inconel 718. Other Commin Inconel alloys are Inconel 600, 601, 625, 825, and x-750.

Inconel also tends to crack and segregate at a microstructural level in the heat-affected zone, which adds to the difficulty of welding it. The recommended ways of overcoming this tendency is through GTAW and electron beam welding.

Monel®

Monel—as we’ve previously talked about—is particularly resistant to high-temperature. It is composed primarily of nickel and copper, with iron, carbon, manganese, and silicon included in various percentages. Monel is highly resistant to corrosion and stronger than pure nickel. Its resistance to hydrofluoric acid, sea water, alkalies, and sulfuric acid makes it ideal for marine and chemical environments.

Monel is relatively easier to machine and weld than inconel, incoloy, and hastelloy. It is generally recommended to use a cold-drawn, stress-relieved filler material to achieve the best machinability and smoothest finish. Monel can also be welded through a wide range of common methods, including GTAW, GMAW, and SMAW.

Corrosive Resistance in Various Nickel Alloys

The rapid pace of advancement in technology has introduced new approaches to traditional applications. As new systems are developed, and existing systems are upgraded, a variety of nickel based alloys are being used to bring about enhanced performance. For the MRO faced with working with these materials, it is important to first have a good understanding their characteristics and composition.

The popularity of superalloys is due to their superior mechanical strength, resistance to creep, surface stability, and resistance to corrosion and oxidation. This allows for improved performance and longer life with less maintenance and easier repair.  They are used in a diverse range of industries and processes, including aerospace, automotive, chemical processing, telecommunications, marine, and oil and gas extraction and processing.

To get a better understanding of these dynamic materials, including the various methods of welding and machining, let’s take a close look at each one.

Incoloy®

Incoloy®—like inconel and monel—is a line of superalloys produced by the Special Metals Corporation, a group of companies specializing in the invention, production, and distribution of high-performance nickel alloys for specialized engineering projects. Incoloy is an age-hardenable nickel-iron-chromium alloy with additional amounts of copper, aluminum, molybdenum, and titanium. It is designed for superior corrosion resistance and strength at high temperatures.

Incoloy is especially resistant to corrosion in aqueous environments like plumbing systems, pipelines, or marine appliactions. It is capable of maintaining a stable and austenitic structure through protracted periods of exposure to high temperatures. Incoloy alloys—there are currently 22 grades—are typically used for a range of applications including chemical processing, oil and gas well piping, heat exchangers, carburizing equipment, and nuclear facilities.

Incoloy’s general working range of temperatures is 1600°F (850°C) to 2150°F (1175°C). To achieve maximum corrosion resistance and strength after aging, the alloy should be hot-worked in the 1600°F (870°C) to 1800°F (980°C). When cold-formed, incoloy alloy 925 behaves similarly to incoloy 825, except with a higher work-hardening rate.

The recommended materials for welding incoloy 925 is Inco-Weld® filler metal 725NDUR®, which provides stronger material with better corrosion resistance than incoloy 925. For best results, the preferred methods for welding are gus-tungsten-arc welding (GTAW) and gas-metal-arc welding (GMAW). With the latter method, current levels should not go above 180 amps for standard GMAW power sources in the “spray arc” metal transfer mode.

Hastelloy®

Hastelloy® is a proprietary superalloy from Haynes International, Inc. Hastelloy’s primary alloying ingredient is usually transition metal nickel. This is typically added to other metals like iron, copper, titanium, and aluminum to various percentages. Common Hastelloy Grades include C276 and C22. 

The greatest advantage of hastelloy is its resistance to high-temperature and high-stress environments, specifically the formation of grain boundary precipitates that result from exposure to high heat. It is known for its potential to survive in severely corrosive or erosion prone scenarios where other, more common iron-based alloys would quickly fail.

Hastelloy is particularly resistant to wet chloride gas, chlorine, and oxidizing salts such as ferric and cupric chlorides. It is typically used in nuclear and chemical reactors, distillation equipment, and pipes and valves in the chemical processing.

There are two types of recommended filler materials for hastelloy: matching and overalloyed. Matching filler material means that the filler material is made of the same chemical composition. Overalloyed filler materials mean non-matching, highly-alloyed, highly corrosion-resistant welding filler material, which reduces the chance of preferential weld metal corrosion attack.

The preferred methods of welding hastelloy are GTAW, GMAW, and shielded metal arc welding (SMAW). Due to the sluggish welding and shallow penetration characteristics of nickel-based alloys, it is important to pay careful attention to joint design and weld bead placement to ensure solid welds with proper weld bead tie-in. It is also recommended to grind starts and stops, since these alloys have a tendency to crater crack.

Inconel®

Inconel® is a superalloy where the primary alloying ingredient is nickel-chromium. It is oxidation and corrosion resistant, especially to chloride-ion stress –corrosion cracking, which makes it well-suited for high pressure and heat environments. This is because when inconel is heated, it forms a thick, stable, passivating oxide layer that protects the surface from additional damage. It’s suited to a wide range of temperatures, which makes it a great alternative to other metals like aluminum or steel which are susceptible to creep.

Inconel currently has 25 grades. Inconel 600, 601, 625, 825, x-750 are some of the more commonly used incoloy alloys. They are typically used for furnace components, chemical and food processing, aerospace and land base gas turbine parts like jet engines, and other extreme-service applications.

Inconel has a tendency to quickly work harden, so it is necessary to machine age-hardened grades like 718 with an aggressive but slow cut with a hard tool to minimize the number of passes. Welding inconel is also difficult since it tends to crack and microstructurally segregate in the heat-affected zone. The most common ways to overcome this is through GTAW and electron beam welding.

Monel®

We’ve previously talked about Monel®, focusing particularly on its high-temperature properties. This superalloy is primarily composed of nickel and copper, with trace amounts of iron, manganese, carbon, and silicon. Monel has excellent corrosion resistance and is stronger than pure nickel. Although it is more difficult to fabricate than steel, its high sulfur content gives it better and enhanced machinability.

Monel is ideal for marine and chemical environments due to its resistance to sea water, hydrofluoric acid, sulfuric acid, and alkalies. It has ASME approval for use in boilers, pressure vessels and nuclear vessels. It is typically used in heat exchangers, oil refinery piping, sulfuric acid plants, nuclear fuel production, and pump shafts.

Unlike inconel, incoloy and hastelloy, monel is relatively easier to machine and weld. In general, it is recommended to use cold-drawn, stress-relieved material for the best machinability and smoothest finish. Similarly, monel can be welded through a wide range of conventional welding methods, including SMAW (best for monel 400), GTAW, and GMAW (best for Monel Filler Metal 60).