Check whether the phenomenon that looks like rust on a heat exchanger, sometimes in the form of rust-colored dots or rust-colored lines resembling cracks in the exchanger, is actually rust. Can a new heat exchanger rust? Rust on a heat exchanger? We explain.
You purchased a plate heat exchanger, received the shipment – and your attention was drawn to rust-colored lines or dots. Is it possible for a plate heat exchanger – made of stainless steel plates – to rust already in the box, even before coming into contact with water?
✅ No, we reassure you – plate heat exchangers are produced using vacuum brazing, meaning the steel plates are joined together using copper brazing material (which has a corrosion-like color).
✅ The method of manufacturing plate heat exchangers – specifically the vacuum brazing process – explains the presence of copper traces that resemble rust.
Copper is heated to temperatures of up to 450 ℃, at which it takes on an almost liquid form. In this form, it is used to permanently bond the plates of the heat exchanger. This is why the sides of the heat exchanger have a copper-colored appearance – because it is indeed copper. Some people mistake this for rust – which seems absurd after checking the manufacturing process.
Copper also leaves behind traces that cannot be cleaned off if the front or back plate of the heat exchanger gets dirty. However, this has no technical significance, no impact on the quality of the exchanger's performance – and therefore most manufacturers do not consider this a defect that would warrant a warranty claim or replacement of the item.
Moreover, most plate heat exchangers likely have similar irregular – smaller or larger copper traces, which some people mistake for rust – regardless of the manufacturer or brand, as this is a result of the characteristic manufacturing technology.
During production, the copper used as brazing material for the steel plates sometimes leaves marks on the front or back plate of the heat exchanger. Most often, it takes the form of rust-colored lines (which some interpret as cracks in the plate) or dots. These are copper traces and have nothing to do with rust or corrosion. They are purely visual – with no impact on the deterioration of the exchanger's performance. These traces also cannot affect the shorter lifespan of the plate heat exchanger in our installation.
✅ The front or back plate of the heat exchanger cannot crack – we don’t need to explain that this is not possible with steel. Try to recall if you know of any steel elements that crack.
In reality, the corrosion of a plate heat exchanger before installation or before contact with water is technically almost impossible. Yes, heat exchangers can corrode in the long term – even if they are made of stainless steel – but they must have specific conditions for this, e.g., an extremely aggressive medium must be used. This could be saltwater (some heating systems add salt, similar to chlorine generators in recreational pools). It could also be untreated groundwater (depending on the level of harmful minerals and salts, the hardness level – but corrosion of a heat exchanger is not that easy, and even with an aggressive medium, it takes time.
✅ Nevertheless, regardless of the type of steel used – corrosion of a heat exchanger before its use is essentially impossible – and the rust-colored coating has little to do with rust apart from the similar color.
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Update 3-2025
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