Case spiral heat exchanger tubes


Producing laser welded stainless steel spiral heat exchanger tubing for domestic water heaters in long continuous lengths.


Supra 444/4521 nickel-free ferritic stainless steel.

Delivery & Benefit

Sole processes around 500 tonnes of Supra 444/4521 strip a year to produce over 1 million meters of tubing. High quality strip ensures zero failure rate combined with major cost savings over other stainless steel grades.

Taking quality to extreme lengths for heat exchanger tubing

Sole’s factory might be based in a remote farm location in the forests of Norway. But the components it produces are desired by a growing number of water heater companies across the world. The reason is Sole’s unique capability to produce high quality laser-welded heat exchanger tubing in lengths up to 40 meters. And a critical element in this success is Outokumpu’s Supra 444/4521 stainless steel strip.


A new tube mill – a new stainless steel supplier

The story begins back in 2006. That’s when Sole decided to stop buying in tubing and invest in its first tube mill to produce its own tubing. Outokumpu was the natural choice to supply the steel strip, which was then 316L. As Sole has grown, Outokumpu has been there to provide support every step of the way, including the changeover to Supra 444/4521 in 2012. Thor Reidar Bratthen, Managing Director Sole AS, explains:

“There were a number of reasons for making the switch to Supra 444/4521. First is that it is an extremely cost-effective material and also met our requirements for formability and weldability. Also, we knew that our customers were adopting it for their water tanks, so it made sense to use the same steel grade.

“Outokumpu gave us great support throughout the changeover process. And we know that we can always rely on them for good quality and short delivery times. Naturally, we review other steel suppliers from time to time. But they just cannot provide the same quality.”


Nickel-free stainless steel

Supra 444/4521 is a nickel-free, molybdenum alloyed ferritic stainless steel with good cold formability and high strength. As a ferritic stainless steel, it has high resistance to chloride-induced stress corrosion cracking. Because of its stabilization, Supra 444/4521 can be welded in all dimensions without becoming susceptible to intergranular corrosion.

Nickel has historically been an alloying element with volatile pricing. Supra 444/4521, being nickel-free, offers the potential for more stable long-term price development.


A unique capability to produce spiral tubing

Sole has developed a confidential and highly guarded process that gives it the unique capability to produce long lengths of laser-welded spiral tubing, from 6 up to 40 meters. Thor Reidar Braathen takes up the story:

“Currently, no other manufacturer can produce the same type of tubing in such a long continuous length. That’s critical to the quality and long life of our product. Because when you have to join two lengths together you introduce another potential point of failure.

“Every length of spiral tubing we manufacture is pressure tested. If we detect even the slightest leak then we scrap it. That’s why we rely on the quality of the steel strip. Because what may seem like tiny surface imperfections can result in a poor laser weld.”


Failures in the field are unknown

Sole is currently processing around 500 tonnes of Supra 444/4521 strip a year to produce over 1 million meters of spiral tubing. But for Thor Reidar Braathen it is the quality that is most important:

“In all the time we have been making spiral tubing we have never had a failed product returned from the field. Not one. That is a testament to the quality of our processes and the quality of the stainless steel we use. We are very happy with Outokumpu.”

Recommended products and insights


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.

Energy and heavy industry

In energy and heavy industry, failure is simply not an option. When one single mishap can explode into a full-blown crisis, only stainless steel can deliver the assurance of control that you depend on.

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