In our previous post on sanitary hose longevity we addressed primarily mechanical issues and how they can affect the life of a sanitary hose assembly. This post will focus on thermal stress and the affects they have. As a general rule, the higher the temperature a hose sees, the more stress is put upon it.
If your sanitary hose is going to see high temperatures, material selection is probably going to be the most important issue that will prolong the life of your sanitary hose assembly. Here are some guidelines on material selection:
- For food grade applications, temperatures approaching 150⁰ F (think CIP) render most clear PVC hoses unusable. There are several choices of food grade rubber hoses that operate to around 200⁰F and can even accept open end steam cleaning but not steam pressure.
- Sanitary silicone hose assemblies can endure high temperature and steam sterilization cycles, although we normally do not recommend them for continuous steam service. Silicone hose assemblies can also be autoclaved.
- Teflon (PTFE) lines hose normally has excellent thermal properties. The liner material can tolerate steam sterilization as well as low pressure continuous steam. When choosing a sanitary Teflon hose assembly, care should be taken to make sure the hose had suitable outer construction to withstand the thermal conditions your hose could see. Specifically, we do not like to specify a Teflon hose that has a lot of rubber filler material in the cover for applications that see intermittent steam. We have had problems in the past with the end connections coming loose due to expansion and contraction of the rubber liner after thermal cycling.
Here are some other issues to consider for sanitary hose assemblies used in higher temperature applications:
- Most hose manufacturers lower the working pressure rating on their products as the temperature increases. Make sure to pay attention to this when specifying your hose. A hose rated at 150PSI at ambient temperature may not be rated that high at your application temperature.
- If the hose is going to be subjected to multiple steam cycles, it will probably see a significant amount of vacuum on the cool down cycle. Make sure that what you select has not just the working pressure but the vacuum pressure rating as well. Also consider the use of antistatic hoses in steam applications.
- Try to limit tight radius bends with sanitary hose assemblies that are operating at elevated temperatures. Hose liners tend to soften at higher temperatures and are more prone to kinking.
So, you are thinking, these are all great tips, but you didn’t answer the question how long is my sanitary hose assembly is going to last? The reality is, we can’t. There are too many variables. Specifying a great hose isn’t a complicated, esoteric idea that always has a slam dunk answer. It is a lot of little things done right. If you pay attention to the tips shown above as well the ones we listed in our previous post on mechanical properties, you’ll have a pretty good tool set to allow you to specify a sanitary hose assembly that will give you optimal life span, whatever that is. If you are still unsure, or maybe just need some validation of your ideas, contact one of our sales engineers. We do this everyday.