Short Answer: Many years.
Long Answer: It is extremely rare for a ZVA tube to break for any reason. This is why we give a standard 2 year warranty on all our tube welds. We even sell an extended 5 year warranty for those who are interested.
Why don’t they break? For one thing, we put every tube we make through a rigorous QC process for one, rejecting every tube that fails any single test. And then we put a sample of every batch of tubes through a destructive test.
Mechanically, our tubing is very strong, and our weld is many times stronger than the tubing.
If tubes don’t break, then how could it happen?
The most obvious reason is that it may have been cut. Sometimes this happens if someone closes a sump without seeing the tube. It’s almost always an accident. You can tell when the tube is cut because the edges of the cut are very straight.
There is another reason why the tube can break – chemistry.
Without getting too complicated, water breaks the mechanical weld. That’s right, our weld is mechanical, and water breaks it apart.
Like velcro, the polymer chains that make up our tubing join together during the welding process. The ends are like bent fingers that hold onto each other. Mechanically, this is incredibly strong.
However, our tubing is made to resist oils, the kind of oils that are found in metalworking fluids. If our tubing is exposed to water, the water attacks the polymers, relaxing the fingers. When the fingers straighten, the ends of the weld let go. And the weld breaks.
Where does the water come from?
A machining center is designed to hold metalworking fluid (MWF) that makes cutting metal much easier than not using anything at all. If you use straight oil, the cutting is easy but there is too much heat. If you use straight water, then there is very little heat but the cutting is hard. Also, with water, the expensive machine will rust and be ruined. By using a specific mixture of oil and water, the cutting can be easy and cool at the same time.
The problem is that the MWF is made to be used at an exact ratio of water to oil. Most of the time this ratio is 10 parts water to 1 part MWF concentrate. If someone doesn’t mix the MWF correctly, then the ratio changes.
If the ratio becomes 12 parts water to 1 part MWF concentrate, then that means there is too much water in the mixture.
This is where the water comes from. This “free” water is available to attack the weld of our tube. And the mechanical weld breaks.
However, this free water is also available to damage the more expensive machine. This free water also makes cutting more difficult, so that tools don’t last as long.
In this way the ZVA tube weld works like an electrical fuse. It breaks at the weld indicating the presence of too much water. Replacing a failed tube is very inexpensive and easy. Repairing an extremely expensive CNC machining center is difficult.
This is why, when Zebra learns of a tube break, we take extra care to learn about how the customer is taking care of their machine and their MWF. We teach them that the skimmer is giving them a warning. Once our customers understand that, they appreciate the information and learn to take better care of their machines.
How Zebra changed the market.
When the ZVA was first introduced 20 years ago, there were many tube breaks. We took care of all our customers and learned why the breaks happened. If the break is our fault, we always replace the tube for free. If the tube break is because of chemistry, we replace the tube one time for free, but we teach the customer why this happens.
Today, there are almost no reports of tube breaks due to chemistry. We are proud to have taught our customers the proper way to maintain their sumps. Not only does this mean they have fewer problems with the skimmer, but their machines and their production work much better.