What is the best stainless steel for heat exchangers?

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Heat exchangers are critical components in a range of industrial and commercial systems. Heat exchangers basically allow the transfer of heat from one gas or liquid to another, without the two coming into direct contact. It can be liquid-to-liquid, gas-to-liquid or gas-to-gas. Heat exchangers can heat a cool substance and cool a warm substance, which is important for systems that need to maintain a steady temperature.

How Do Heat Exchangers Work

To put it simply, heat exchangers will circulate two substances (which can be either gas or fluid) alongside each other, but in separate pipes, plates or containers. One of these substances will be hot and the other will be cold. As they circulate through the heat exchanger, heat will transfer from the hot substance to the cold one until they reach the desired temperature. Thus heating the cool substance up and cooling the hot substance down.

Types of Heat Exchanger

The best type of material for a heat exchanger will really depend on its application. There are quite a few different heat exchanger types, which can be used in different ways. Take a look below.

Air Cooled Heat Exchanger

A finned tube heat exchanger or air cooled heat exchanger, uses air to cool a liquid or gas contained in the pipes. These air cooled heat exchangers are more environmentally friendly and cost-effective than water cooled heat exchangers, as there&#;s no need for a running water supply.

Water Cooled Heat Exchanger

This type of heat exchanger runs water in one pipe and the liquid or gas in the other pipe. The water is typically used as a coolant, to remove heat from the process media. It can be more expensive than an air heat exchanger, but it offers more control as air is affected by the surrounding climate.

Shell and Tube Heat Exchanger

A shell and tube heat exchanger is basically any heat exchanger where liquid or gas is passed through tubes enclosed in a metal shell. This type of heat exchanger can be used to heat or cool. It&#;s also suitable for use with noxious gases, as it&#;s contained within a metal box. It&#;s most often used in high pressure applications, like oil and gas or chemical industries.

Double Pipe Heat Exchanger

This type of heat exchanger has a smaller pipe inside a larger pipe. One pipe will hold a hot substance and the other will have a cold substance. This type of heat exchanger is a great way to save floor space, as it is quite compact.

Plate Heat Exchanger

Also known as a gasket plate heat exchanger, these heat exchangers have a series of plates lined up together, with hot or cool fluids passed through the plates alternatively. So one plate will have a hot substance and the next will have a cool substance, and heat will transfer between the two.

Scraped Surface Heat Exchanger

A scraped surface heat exchanger is often used when there is a sticky or viscous material in use, as is often the case in the food industry. Basically, there is a cylinder, surrounded by a jacket and vacuum. Steam or a hot gas is circulated in the vacuum between the jacket and cylinder to heat the material in the cylinder. Inside the cylinder is a rotating scraper blade which stops the material getting stuck to the side and makes sure heat is distributed evenly throughout the material.

Material Properties to Consider

When selecting materials for use in a heat exchanger, it is important to consider the following factors:

1.

Thermal Conductivity

The most important factor when choosing a material for heat exchangers is thermal conductivity. Thermal conductivity is how well a material can conduct heat. Materials with high thermal conductivity are more effective at transferring heat, which makes them the perfect choice for heat exchangers. Materials with high thermal conductivity include copper, aluminum, and brass.

2.

Corrosion Resistance

Heat exchangers are often exposed to corrosive environments, which can compromise their structural integrity and performance if you choose the wrong material. That&#;s why we recommend corrosion-resistant materials. If you&#;re working with chlorides or hydrogen sulfide, for example, you&#;ll need a material that is resistant to chloride induced stress corrosion cracking.

3.

Cost

The cost of the material is also an important consideration when selecting materials for use in a heat exchanger. While materials such as copper and aluminum have high thermal conductivity, they can be expensive, making them less cost-effective for certain applications.

4.

Compatibility

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It&#;s important to ensure that the material used in the heat exchanger is compatible with the liquids or gases it will be in contact with. You&#;ll have to consider the liquids or gases you want to treat and find a compatible alloy. Otherwise corrosion could render your heat exchanger unusable in a matter of months, if not weeks! Our metallurgists can help you find compatible metals.

5.

Fabrication

Fabrication is also important when selecting a material for a heat exchanger. You should consider that heat affected zones or welded sections could affect performance. Plus, some materials are harder to work with than others, which can impact the overall cost and lead time for your heat exchanger.

The Best Materials for Heat Exchangers

Here at NeoNickel, we stock a great supply of alloys suitable for use in heat exchangers. Take a look at some of our recommended alloys below:

Alloy 600

Alloy 600 has excellent heat resistance and oxidation resistance up to temperatures of °C. It&#;s often recommended for use in the heat treatment industry (like furnace doors or rollers), but would be suitable for heat exchangers too.

Alloy C276

Alloy C276 is one of the most corrosion resistant alloys, which also demonstrated good thermal conductivity. We&#;d recommend it when one of the treated gases or liquids is particularly corrosive, like in the petrochemical or chemical processing industry.

Alloy 321 Stainless Steel

Alloy 321 is a stainless steel with great heat resistance at temperatures of up to 870°C, which makes it perfect for application in heat exchangers. It also demonstrates good thermal conductivity.

Overall, the best material for a heat exchanger will depend on the specific application. You should consider important factors like thermal conductivity, fabrication and cost to make sure you choose the appropriate alloy. NeoNickel hold and supply countless alloys, suitable for application in thermal heat exchangers.

If you&#;d like more advice on choosing the correct alloy for a heat exchanger, please get in touch with us here.

Material pricing and availability can fluctuate based on market supply and demand, the quantity required for your exchanger, and the components needed. Copper was a low-cost option a few years ago, but now due to supply, it is more expensive than stainless steel. Conversely, Titanium used to be one of the most expensive alloys but is now more reasonably priced. Typically, the more nickel content in a metal, the higher the price.

Here is the relative ranking for some of the common metal material options by price from highest to lowest:

1. MOST EXPENSIVE: Nickel 200, also known as UNS N, is a commercially pure nickel alloy. It is one of the most widely used nickel alloys due to its excellent mechanical properties and high corrosion resistance. Nickel 200 consists of 99.6% pure nickel, with small amounts of impurities such as iron, copper, and manganese.

2. Alloy 625, also known as Inconel 625, is a nickel-based superalloy known for its excellent strength, corrosion resistance, and high temperature performance. It is composed mainly of nickel, with significant amounts of chromium and molybdenum, along with smaller additions of niobium, iron, and other elements. Alloy 625 is widely used in various industries, including aerospace, chemical processing, oil and gas, and marine applications.

3. Monel 400 is a nickel-copper alloy known for its excellent corrosion resistance in various environments. It is composed of approximately 67% nickel and 30% copper, with small amounts of iron, manganese, carbon, and silicon. Monel 400 is highly resistant to corrosive substances such as acids, alkaline solutions, and saltwater. It is often used in applications where resistance to corrosion, erosion, and high temperatures are essential.

4. Hastelloy C22 is a nickel-chromium-molybdenum alloy known for its exceptional corrosion resistance in a wide range of aggressive environments. Hastelloy C22 is particularly resistant to pitting, crevice corrosion, and stress corrosion cracking. Hastelloy C22 is often chosen for chemical processing and waste treatment.

5. Hastelloy C-276 is a nickel-molybdenum-chromium alloy that is renowned for its corrosion resistance and high-performance properties. While similar to Hastelloy C22, Hastelloy C-276 has lower chromium content, easier weldability, and slightly higher upper temperature limits. Hastelloy C-276 is used in various industries, including chemical processing, pollution control, pulp and paper production, and petrochemical applications.

6. Duplex  is a super duplex stainless steel alloy that offers excellent strength, corrosion resistance, and durability. It is part of the duplex stainless steel family, which combines the desirable properties of both austenitic and ferritic stainless steels. Duplex is characterized by its high levels of chromium, molybdenum, and nitrogen, providing superior resistance to corrosion and high mechanical strength.

7. AL6XN is a high-performance austenitic stainless steel alloy that offers exceptional corrosion resistance and mechanical properties. It is specifically designed to withstand highly corrosive environments, including chloride-rich environments, acids, and seawater. AL6XN is known for its versatility, making it suitable for various applications in industries such as chemical processing, pulp and paper, oil and gas, and desalination.

8. Titanium is a lightweight metal known for its high strength, low density, and excellent corrosion resistance. Titanium is widely used in various industries due to its unique combination of properties.

9. Duplex is a stainless steel alloy with a combination of austenitic and ferritic microstructures, known as a duplex structure. It offers excellent strength, corrosion resistance, and durability, making it suitable for a wide range of applications. Duplex is highly popular in industries such as oil and gas, chemical processing, marine, and pulp and paper.

10. 316L stainless steel is a commonly used grade of stainless steel known for its corrosion resistance, high strength, and versatility. It is an austenitic stainless steel alloy with low carbon content, making it suitable for various applications where resistance to corrosive environments is essential. It is widely used in marine applications, chemical processing, dairy, and pharmaceuticals.

10. 304L stainless steel is a commonly used grade of stainless steel known for its corrosion resistance, versatility, and ease of fabrication. It is an austenitic stainless steel alloy with low carbon content, which enhances its weldability and reduces the risk of sensitization to intergranular corrosion. In comparison to 316L SS, 304L SS has no molybdenum content and it&#;s less resistant to chloride-induce corrosion. It is suitable for general-purpose uses that don&#;t require the enhanced corrosion resistance of 316L SS.

12. LEAST EXPENSIVE: Carbon steel is a type of steel that primarily consists of iron and carbon, with other elements present in smaller amounts. It is one of the most commonly used materials in the manufacturing and construction industries due to its affordability, strength, and versatility.

Typically, the higher priced alloys are also in shorter supply, due to lower demand and the higher cost of carrying inventory. This directly affects the lead-time of these materials, often by 2-4 times that of more common alloys like carbon steel and stainless steel. Quantity of these higher alloys can also greatly affect price. Steel mills typically don&#;t run small batches of tubes or plate or they will charge for the entire mill run if they do.

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