New plate heat exchanger - any cracks or signs of rust?

You purchased a plate heat exchanger, received the shipment, and noticed rusty-colored lines or dots. Is it possible for a plate heat exchanger, constructed from stainless steel plates, to rust even inside the box, before coming into contact with water?

Is the newly purchased heat exchanger showing signs of rust on the plates? Can an unused plate heat exchanger rust?

No, let's calm down – plate heat exchangers are manufactured using a vacuum brazing method, where steel plates are joined together using copper brazing material (which has a color resembling corrosion). Copper is heated to temperatures of up to 450 ℃, at which it becomes almost liquid. In this form, it is used to permanently bond the plates of the heat exchanger. Hence, the copper color visible on the sides of the heat exchanger is indeed copper. Some people mistake this for rust, which, upon understanding the production process, seems absurd. It also leaves traces that cannot be removed in case of dirt on the rear or front plate of the heat exchanger. However, this has no technical significance, no impact on the performance of the heat exchanger, and therefore, most manufacturers do not consider it a defect warranting replacement or warranty claims.

✅ Most plate heat exchangers probably have similar irregular – smaller or larger – copper traces, resembling rust to some people, regardless of the manufacturer or brand, as it is an effect of the characteristic production technology.