Heat Exchanger with UNS S32750

What is a heat exchanger?

A heat exchanger is a device used to transfer heat between two or more fluids. Heat is transferred by conduction through the exchanger materials which separate the mediums being used. The fluids are separated by a wall that has high thermal conductivity. The fluids can be single or two phase and, depending on the exchanger type, may be separated or in direct contact. The thickness of the wall is designed to prevent the mixing of the fluids or the possibility of direct contact between them. Included in the process is a working media that rejects or absorbs heat from the liquid being processed. A shell and tube heat exchanger passes fluids through and over tubes, where as an air cooled heat exchanger passes cool air through a core of fins to cool a liquid.Devices involving energy sources such as nuclear fuel pins or fired heaters are not normally regarded as heat exchangers although many of the principles involved in their design are the same.

Can UNS S32750 be made into a heat exchanger?

ASME SA 789 UNS S32750 is a duplex especially designed for service in aggressive chloride-containing environments. It has very good resistance to localized corrosion and stress corrosion cracking in combination with high mechanical strength. Its temperature range is typically listed as -50° to 300° C (-58° to 572° F). Is one of the most commonly used steel materials for making heat exchangers. S32750 is the standard grade of super-duplex stainless steel based on 25% chromium, 7% nickel and significant additions of molybdenum, manganese and nitrogen, designed for demanding applications which require exceptional strength and corrosion resistance can bear to 570° F. Below is the chemical composition list of UNS S32750:

Alloy 2507 combines high tensile and impact strength with a low coefficient of thermal expansion and high thermal conductivity. These properties are very suitable for many structural and mechanical components.Duplex 2507 possesses excellent mechanical properties. Often a light gauge of 2507 material can be used to achieve the same design strength of a thicker nickel alloy. The resulting savings in weight can dramatically reduce the overall cost of fabrication.

What types of Heat Exchanger are available?

Double-pipe heat exchanger

In double pipe heat exchangers, we have a large pipe with a small pipe inside it concentrically, and all the heat transfer process occurs inside the larger pipe. One fluid flows through the inner of a small pipe, and another fluid is between the two pipes, and that is how the inner pipe acts as a conductive barrier. The outside or shell side includes fluid flow passing on the inner side or tube side.

Shell-and-tube heat exchanger

Shell and Tube Heat Exchangers are one of the most popular types of exchanger.A shell and tube exchanger consists of a number of tubes mounted inside a cylindrical shell. Two fluids can exchange heat, one fluid flows over the outside of the tubes while the second fluid flows through the tubes. The fluids can be single or two phase and can flow in a parallel or a cross/counter flow arrangement.

Plate Heat Exchanger

plate heat exchanger (PHE) is a highly efficient device that consists of multiple heat transfer plates held in place by a fixed and a loose pressure plate. The gasket arrangement on each heat transfer plate provides two separate channel systems that enable the primary and secondary media to flow in a counter-current manner without mixing.

What other steel materials can be made into heat exchangers?

Different types of steel materials have different production standards for heat exchangers. 

Stainless steel heat exchanger production standards:

ASTM A213: Standard Specification for Seamless Ferritic and Austenitic Alloy-Steel Boiler, Superheater, and Heat-Exchanger Tubes. The main material grades available are SS 304 / 304L / 304H, SS 310 / 310S, SS 310H, SS 316 / 316L, SS 316H, SS 317 / 317L , SS 316TI, SS 321 / 321H, SS 347 / 347H, SS 904L, etc.

ASTM A269 : Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for General Service. The main material grades available are SS 304/304L/304LN, SS 316/316L/316LN, SS 317/317L, SS 321, SS347, 254SMO, etc.

ASTM A789: Standard Specification for Seamless and Welded Ferritic/Austenitic Stainless Steel Tubing for General Service. The main material grades available are S31803, S32205, S32705, etc.

Nickel alloy heat exchanger production standards:

ASTM B163: Standard Specification for Seamless Nickel and Nickel Alloy Condenser and Heat-Exchanger Tubes. The main material grades available are Nickel 201, Nickel 200, Inconel 600, Inconel 625, Incoloy 825, etc.

ASTM B474: Standard Specification for Electric Fusion Welded Nickel and Nickel Alloy Pipe. The main material grades available are Inconel 800, Hastelloy C276, Hastelloy C22, Hastelloy B2, Monel 400, etc.

Application fields of heat exchangers

1. Seawater coolers: Selecting the right tube material for heat exchangers operating in seawater used as a cooling medium is critical. Seawater contains large amounts of sodium chlorides and solid particles such as sand silt and organic solids. In such a severe environment, need to select a grade with high resistance against both localized corrosion and erosion corrosion.

2. Oil refining: To recover heat in the different processes, heat exchangers are deployed in plants where they typically operate under severe corrosion conditions. Most leakage in heat exchangers is attributed to corrosion on the tubing. Stainless steel and, in particular, duplex grades, including S31803, S32205 and S32750, can overcome such problems.

3. Chemicals: Special grades are used in heat exchangers in many demanding chemical processes, including the production of inorganic acids and caustics. Seamless tubes offer the required high reliability in these often critical applications.

4. Power generation: Heat exchanger tubes can be found in condensers, feedwater heaters and wastewater handling equipment. Our steel grades fulfil the high quality standards for use in both conventional fossil fulled power plants as well as nuclear power stations.

5. Flue gas cleaning / desulphurisation: Environmental demands call for effective gas cleaning equipment. For heat exchangers handling sour gas under condensing conditions, high alloyed austenitic grades. The higher alloyed duplex stainless steels can be suitable.