Many welding experts said it couldn’t be done. But after many years of trials, Tetra Pak has succeeded in making a smooth weld from the inside of the tube of a tubular heat exchanger that meets the most exacting hygiene standards.
Even though Tetra Pak launched its first P2P tubular heat exchanger in 1996, it took until 2016 to meet the requirements of the 3-A Standard, an American sanitary standard recognized globally. Approval was granted after the introduction of a new weld between the tube and the tube case.
This particular weld is now so smooth that it does not have irregularities on the surface such as crevices, where bacteria can hypothetically attach and build up. In food processing, hygiene is extremely important, and with the new weld, Tetra Pak designers aimed to eradicate any potential food safety risk whatsoever in a product-to-product heat exchanger.
Their innovative idea was a weld made from the inside of the tube. “We started from scratch in 2009 by making contact with as many welding experts as we could, but not many people believed in our idea. Many experts said, ‘That won’t work’,” recalls Niklas Wisén, Manufacturing Manager at Tetra Pak in Lund, Sweden.
After a few false starts and many years of research, Tetra Pak developed a welding process that worked. It took a further two years of development work in the workshop to master the innovative technique of welding from the inside of the tube. A patent is pending for the new welding method which involves welding in an inert atmosphere free from oxygen. A critical part of the process was the shift to a new special grade of stainless steel – the details of which are a closely guarded secret.
In May 2018, product-to-product tubular heat exchangers with the new welds were launched. The welds are a feature of the whole range of tubes for product-to-product heat transfer.
3-A stamp of approval
The purpose of 3-A Sanitary Standards is to protect public health when using sanitary equipment. One of the specific goals is to ensure that all product contact surfaces can be mechanically cleaned, and be dismantled easily for manual cleaning or inspection.
“The 3-A Standard gives our design a stamp of approval and opens up the P2P market for large international customers with really high demands on hygiene,” says Jenny Navred, the Project Leader at Tetra Pak closely involved in developing the new weld.
In the USA, the 3-A Sanitary Standards are used as a basis for regulations from the USDA and FDA for food manufacturing. For customers in other parts of the world, meeting the 3-A Standard is not necessary, but 3-A is seen as a strong indication of sound sanitary design.
- Corrosion is a well-known risk when operating heat exchangers. Read about how to prevent an everyday risk becoming a problem.
- Read about how corrosion or cracking – and the resulting food safety risk – can be avoided by choosing a heat exchanger with a floating protection system.