Hot & cold

Sami Anteroinen


The Plate & Shell concept used in Vahterus’ innovative heat exchangers requires thin plates to make it work. The material of the thin plates needs to be highly corrosion resistant.


Outokumpu delivers quality stainless steel grades Supra and Forta for the heat exchangers to resist corrosion as well as to tolerate high pressures and temperatures.


Steel grades: Outokumpu Supra 316L and Outokumpu Forta

Heat exchangers bring on the heat or keep you nice and cool, but they are by no means a new invention: the Germans, for example, have been at it since the 1890’s. However, for the longest time within Plate & Frame construction, rubber seals were used in-between moulded steel plates. The problem here was that the seals did not handle high temperatures and operating pressures very well.

The solution, invented by Vahterus CEO Mauri Kontu, was Vahterus Plate & Shell: a fully welded heat exchanger. An outcome of completely original product development, Plate & Shell was the first of its kind as it hit the market in 1991 – and the basic idea behind the product has been the same ever since.


Completely new structure

Before Vahterus, plate heat exchangers were rectangular, and they had four holes. This presented a challenge with regard to welding. In the completely new structure, the plates were made circular, and they were fully welded into a pack, with a protective shell around it. Only two holes were made into the heat exchanger plate.

It takes a lot of theoretical competence to understand how heat moves in the plates through the heat exchanger in an optimal manner. To pull this off, you need top-category materials – such as stainless steel. Paavo Pitkänen, Technology Director at Vahterus, says that since the plates in question are quite thin, corrosion is an issue. “We have to use high alloy materials to avoid the risk of corrosion.”


Winning combination

To this day, the selection of high quality stainless steel is an important step in Vahterus’ heat exchanger design in order to ensure product compatibility and resistance to corrosion.

Currently, Vahterus is primarily using Outokumpu’s Supra 316L and Forta grades. With its round and fully welded steel construction, Vahterus unit offers a durable solution that can stand high pressures and temperatures. Because of the compact size, it requires only 25% of the surface compared to Shell & Tube heat exchangers.

The construction creates high turbulence between the plates enabling exceptionally high thermal efficiency. These features allow the user to take full advantage of a compact heat transfer solution in extremes of temperature and pressure, which was not possible in traditional compact heat exchangers.


Valuable collaboration

Pitkänen considers it rather remarkable that even as Vahterus was a pretty small industry player at the start of the century, the level of service from Outokumpu was outstanding from day one. “For example, the technical support has been there every time we need it,” Pitkänen says. Furthermore, Outokumpu has invited the company to participate in the testing of completely new steel grades – deepening the cooperation even more.

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The Supra range contains stainless steel products designed for highly corrosive environments. Outokumpu Supra range stainless steels have a good resistance to uniform corrosion in many organic and inorganic chemicals. The addition of molybdenum enhances the alloy’s corrosion resistance in many acidic environments.


The Forta range contains duplex and other high strength stainless steels that enable thinner structures and weight reduction (measured in Rp0.2 > 400 MPa. PRE 16 to 43).

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