Stainless Steel vs Copper Heat Exchanger Coils

Stainless steel and copper coils at a glance

General differences to review before fixing the material. Final selection depends on the actual media, conditions and project specification.

Start with the media on both sides of the tube

A coil has two wetted surfaces: the inside, which carries the heating or cooling medium, and the outside, which sits in the tank liquid, process fluid or air stream. The material has to suit both, including concentrations, contaminants, temperature range and any cleaning chemicals used between batches.

Write these conditions down before choosing a grade. A material named without the service conditions cannot be checked, and a later change of material usually changes the tube size, wall, forming route and price.

• Medium inside the tube and its temperature and pressure
• Liquid, product or air outside the tube
• Chlorides, acids, ammonia or other aggressive constituents
• Cleaning or sanitising chemicals and their temperature

Heat transfer: the conductivity gap is smaller in practice

Copper conducts heat far better than stainless steel. Published property data give about 340 W/m·K for C12200 phosphorus-deoxidised copper and about 16 W/m·K for 304 stainless steel at 100 °C.

In many liquid coils the overall heat transfer is limited mainly by the fluid films on each side of the tube and by fouling, not by the tube wall. Spirax Sarco makes the same point for submerged tank coils: the conductivity of the coil material matters less than the combined film resistances. A stainless coil can therefore perform close to a copper coil of the same surface area in some services, while in others the difference is significant. The thermal review should use the actual fluids, temperatures, flow and allowable fouling rather than material conductivity alone.

Corrosion and compatibility

Copper tube is widely used for water, glycol and air-conditioning and refrigeration service, where ASTM B280 is a common tube standard. Copper is not suitable for ammonia (R717): refrigeration compressor maker BITZER notes that R717 attacks copper materials and that lines and heat exchangers in ammonia systems should be steel or stainless steel.

Stainless steel is commonly chosen for food, beverage, many process chemicals and services that need hygienic cleaning. Its main watch-point is chloride exposure, which can cause pitting or stress corrosion cracking in some conditions. Nickel Institute guidance shows that the right stainless grade depends on the specific service, so the choice between 304, 316L or another alloy should follow the media data rather than a general rule.

Hygiene, cleaning and surface condition

Where the coil is in contact with food, beverages or a product that must not be contaminated, stainless steel is usually the starting point. State the required surface condition, any pickling and passivation after welding and forming, and how the coil will be cleaned in place or removed for cleaning.

For copper coils, confirm that the cleaning chemicals and the tank liquid are compatible with copper and with any brazed joints.

Forming, joints and connections

Copper is softer and easier to bend, and its joints are typically brazed. Stainless steel needs higher forming forces and more allowance for springback, and its connections are usually welded or threaded. In both materials, tight bend radii relative to the tube diameter increase the risk of ovality or wall thinning, so the drawing should identify which dimensions are controlled.

Mark the connection type, size and orientation on the drawing, together with any fittings, flanges or mounting plates the coil must carry.

What drives the cost difference

Material price per kilogram is only one part of the cost. Tube length, wall thickness, number of circuits, forming complexity, joints and fittings, surface treatment, testing and documentation all contribute, and they differ between the two materials for the same duty.

Comparing quotations is only meaningful when both are based on the same duty, the same service conditions and the same inspection scope.

What to state in your enquiry

Send the drawing or main dimensions together with the service data below. If you already have a preferred material and tube standard, name them; if not, state the conditions and ask for a material review.

• Media inside and outside the tube, with temperatures
• Operating and design pressure
• Preferred material and tube standard, for example ASTM A269 or ASTM B280
• Cleaning method and surface requirements
• Connections, quantity and required inspection documents