3 Causes of Static Discharge Disasters
by Neil Ide, on 3/14/18 12:00 PM
Avoid these three mistakes that can lead to electrostatic build up
“Once the charge is large enough to overcome the dielectric strength on the hose core, the electrons punch through the hose core to ground, tearing a hole in the hose.”
- Neil Ide, Swagelok Northern California
In fluid systems, static discharge can spell disaster.
When specific fluids flow through a hose, a static charge can build up. The faster the flow, the faster a charge builds up. When the charge voltage gets high enough, it will discharge right through the hose interior lining to the exterior metal braid, burning a hole through the lining.
So today let's go over three mistakes that can lead to static build up:
1. Underestimating the risk of static build up
A discharge at the wrong time can lead to explosions and fires. But those aren’t the only disasters a static discharge can cause. In semiconductor manufacturing, dielectric fluorocarbon heat transfer fluids are a part of daily life. They prevail because the industry needs fluids that don’t interfere with high amounts of RF and extreme voltage potentials required for wafer processing.
A leak caused by static discharge can shut down an entire wafer operation, incurring exorbitant downtime costs. Prevention is key, and there are some hose options that do just that through static dissipation. Many Swagelok hoses are constructed with a carbon black-fill option in the nylon, PTFE, or PFA core material for static dissipation.
2. Overlooking the triboelectric effect
Triboelectric charging (also known as the triboelectric effect) causes the buildup of electrons from the friction between two typically non-conductive materials. As fluid races through a hose, islands of free electrons start to build up on the surface of the hoses inner lining. If the inner lining of the hose is not conductive, the electrons will pile up creating a massive static charge measurable in tens of thousands of volts.
Once the charge is large enough to overcome the dielectric strength on the hose core, the electrons punch through the hose core to ground, tearing a hole in the hose. Adding a slightly conductive layer of carbon black to the inner lining of the hose makes the loose electrons spread out and dissipate (usually through the end connections).
3. Using nonconductive hose in the wrong place
It is important to consider the electrical properties of the hose core, the reinforcing layer(s), and the overall end-to end assembly to ensure the desired results. A hose is considered conductive if it easily carries a charge from one end connection to the other, even if the core does not contain carbon black. The charge is carried through the metal reinforcing braid. If the core does not contain carbon black, the media in the hose is electrically insulated from the wire braid, making it possible for a charge to build along the core tube.
So how can you tell which kinds of hose are right for your application? Hoses with the potential to be conductive are identified in the Swagelok catalog with an (M). Hoses that are static dissipative are identified in the catalog with an (Ω).
Base on the construction of the hose and the type of end connection, conductive hose can be broken down into four categories:
- All metal hoses (FX, FM, FJ, FL, Convoluted Tube) – These hoses have all metal construction, with the ends welded on, and should be considered conductive.
- Fluoropolymer (PTFE) swaged hoses (T) – With the metal braid and an end connection swaged on, there is intimate contact between the metal braid, collar and end connection. They should be considered conductive.
- Fluoropolymer (PTFE) crimped hoses (B, X, S, C, J, W) – After crimping, the metal braids have an intimate contact with the collar, but the collar may not be in contact with the end connection due to the design of the collar/insert interface. These hoses have the potential to be conductive.
- Fluoropolymer (PFA) crimped hoses (U) – After crimping, the teeth of the collar bites down into metal braids, making contact between the two, however, the collar may not be in contact with the end connection due to the design of the collar/insert interface. These hoses have the potential to be conductive.
What's next: You don't have to go it alone with hose selection or hose assembly. Get help with product selection ("Help Me Choose") and/or get hose built for you right here in Fremont:
(Prefer to talk live? Please give us a call at 510-933-6200.)