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.
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.
Pumping and thermal treatment of viscous products are the main challenges in a tubular heat exchanger. Tubular heat exchangers (THE) are especially popular for products containing particulate. Tubes have the minimum of obstructions to get in the way of the particulate and can be cleaned easily. But with four basic tubular designs to choose from, which is the one for your product?
Regardless of whether you're producing meatballs in sauce, jam with strawberries, chocolate pudding or plain white milk, the process involves heat treatment, and this usually means using heat exchangers. Your choice of heat exchanger depends on the attributes of the product in question, such as its viscosity and particle size. More complex and demanding products - with particles and higher or variable viscosity - require heat exchangers with a more complex tube design to promote the correct product flow.