Monel Alloy 400 VS Monel Alloy K-500

For those looking for a low-cost, reliable alloy that still offers many of the benefits of its better-known and pricier counterparts, then we think that the Monel alloy 400 is certainly worth a look.

Monel alloy 400 has been around for a long time and yet it is still a versatile choice. We don’t often see alloys staying prominent for so long across multiple industry applications, and like another oldie but goodie, Inconel 625, Monel 400 bucks the trend. However, this adaptable material pre-dates even the popular Inconel 625 by a good margin – it was introduced as far back as 1905. It was and remains popular thanks to its key property: the copper content of 28-34%, which differentiates it from commercially pure nickel, while it still retains many similar characteristics to Nickel 200/Nickel 201.

The reason that we see Monel 400 staying in the mainstream is because it can be employed widely across many different fields, including marine and chemical processing. It has been used for petroleum distillation tower internals, fasteners and fittings, pumps and valve internals for over 100 years. Other applications include process vessels, heat exchanger piping, and gasoline storage tanks.
Because of its properties, it is perfect for high-risk situations, for example in the explosives industry and the pulp/paper industry.

Monel 400

We take a look in more detail at the pipes and tubes that EB China supplies, focusing on the Monel product line
Pipes and tubes are among some of the most useful products for industrial applications, employed in everything from the oil and gas industry, to the aerospace and automotive industries. These demanding environments need components that are built to withstand heat, corrosion and pressure. There are a lot of advantages to using nickel alloy pipes for your industrial projects, and there are many Grades available to suit any project’s requirements.

One of the materials used to produce these high-spec pipes and tubes is Monel. Monel alloys are produced by blending nickel and copper, alongside additional other elements. They offer both exceptional performance and cost effectiveness. Monel alloy pipes and tubes come in two key Grades: Monel alloy 400 and Monel alloy K-500.

Monel alloy 400

Monel alloy 400 is a high-performance alloy that has a 63% minimum nickel content, as well as 28-34% copper. It has significant additions of iron and manganese to give it desirable properties for industrial use. It’s particularly resistant to seawater, which is why it’s often used to carry water in the marine sector. It offers excellent resistance to stress-corrosion cracking in freshwater.

As well as seawater, it’s also highly resistant to hydrochloric and hydrofluoric acids, as well as other corrosive media. Its uses extend into gas storage units and process vessels, as well as in the pulp and paper industry. Due to its ability to withstand high operating temperatures, it’s also a popular choice for heat exchanger piping and the explosives industry.

It’s a solid solution alloy that can be hardened by cold working to make it stronger. In its annealed condition it lacks strength, but it can then be hot worked into a much stronger product, with a full-hard temper seamless pipe offering a tensile strength of 100-130ksi (as opposed to 70-85 ksi in its cold-drawn annealed state).

Monel alloy K-500

The other Monel nickel alloy that Corrotherm supplies is Monel alloy K-500. This is a precipitation-strengthened composition, where titanium (0.35-0.85%) and aluminium (2.3-3.15%) is added during melting to the aforementioned Monel alloy 400.

This material offers a double whammy of exceptional properties. It has the same excellent corrosion resistance as the Monel alloy 400, meaning the pipes and tubes lend themselves to similar applications. However, due to the additional elements in its composition, this nickel alloy can be hot or cold worked, then heat treated, to be substantially stronger and harder than the base alloy.

This is useful in oil extraction, marine and chemical processing, seawater pumps and in the pulp and paper industry. Usually, for seawater piping, pipes and tubes are constructed using a combination of both Monel alloy 400 and Monel alloy K-500. This gives the best of both alloys. While alloy K-500 is the stronger material, it is more prone to stress-corrosion cracking than alloy 400 in some environments.

Monel alloy K-500

Extreme Temperatures

But what makes this alloy so versatile? Well, it has a high strength and toughness over a wide temperature range. On one hand, the alloy is perfect for sub-zero environments due to its strength and hardness, and it doesn’t undergo a ductile-to-brittle transition at even the extreme lows of liquid hydrogen.
At the other extreme, it is also useful at temperatures of up to and including 1,000 degrees Fahrenheit in oxidising atmospheres. In a reducing environment, it can also be employed in even higher temperatures.

Corrosion Resistance

As well as being particularly suited to extremes of temperature, the alloy also offers good corrosion resistance, which is certainly a desirable quality. It is shown to be more resistant to attack by oxidising elements than higher-copper alloys. This is why it is consistently popular in marine applications, as it has very low corrosion rates in flowing seawater. It is also resistant to stress corrosion cracking and pitting in most fresh and industrial waters.
Another beneficial area in which it provides exceptional resistance is in the presence of hydrofluoric acid, in all concentrations up to the boiling point. It is considered one of the most resistant of all commonly used engineering alloys.

Manufacturing process

The Monel Alloy 400 is a solid-solution alloy that can only be hardened by cold working. However it can be hot worked or cold worked followed by annealing. It is a material that remains bright and free from discolouration when heated and cooled in a reducing atmosphere. Whether hot or cold worked, it needs thermal treatment to give it its notable strength and toughness.

It is readily fabricated by standard processes, which means that it can be produced for a wide range of mechanical properties, increasing its versatility. It can also be machined relatively easily, and joined with itself or dissimilar alloys using most conventional welding procedures.

Products are manufactured to the strictest of specifications to ensure quality, and can be custom designed in terms of shape, size and thickness to suit any application. If you would like to find out more about Monel alloys or the range of pipes and tubes that EB China supplies, please Contact Us.


Eternal Bliss Alloy Casting & Forging Co, Ltd.


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