Why Should You Use Anti-Static Liners for Certain PTFE Sanitary Hose Applications

February 13, 2014
Aflex Pharmaline Hose is Available with an Anit-Static PTFE Liner

Aflex Pharmaline Hose is Available with an Anit-Static PTFE Liner

Every day at Holland, we help customers identify solutions to their high purity fluid transfer issues. One product that we specialize in and are especially proud of are our sanitary hose assembly offerings. We cut and crimp all of our hoses in house and pride ourselves on not only our quick turnaround, but also our ability to select the correct hose for many challenging applications. Today we will take a look at one niche area of sanitary hose, anti-static Teflon hose, by going over what static electricity is and what we do to combat it in specific applications.

To begin, let’s look at why static electricity can be pretty scary. Static electricity is a kind of electric charge that stays in one place- it is static after all. It is the opposite of current electricity which moves from one place to another along a defined path in a circuit.

Static generally builds up when insulators or insulated conductors are rubbed. In order to get rid of static electricity, we have to turn it into current electricity by creating a circuit. That’s what happens during a lightning strike: so much electric charge builds up in a cloud that the air between the cloud and the ground no longer acts as an insulator. And while anyone playing the best round of golf in their life probably won’t admit this, lightning can be pretty scary. So can static discharges in industrial applications. A spark near something explosive and you have a fireball on your hands. Even at a smaller scale, handling delicate electronic after walking through carpet can lead to damage. This is where anti-static products come in and we’ll spend the rest of this post focusing on why anti-static hoses are useful.

There are two ways we can prevent static build up in a hose: by physical methods or by chemical means. For hoses, this can mean a highly conductive wire is run through them, or, more commonly, through the addition of additives to the tube liner that helps conduct and dissipate static charge. The latter is the approach Aflex Hose takes with their Pharmaline, Pharmalex, and BioFlex product offerings.

First and foremost, it’s important know why static is particularly problematic with Teflon. The conductivity of Teflon is exceptionally low, 10-25 S/m. Compared to silicone, (1.56 *10-3 S/m) and even rubber (10-14), the conductivity of Teflon is exponentially lower. This is why we don’t see the same antistatic emphasis on Silicone and FGR hoses. The antistatic products offered by Aflex are essential in applications where media passing through the hose have a conductance of less than 10-8S/m. Fluids that are especially problematic are fuels, solvents, freons, and WFI. For reference, the conductivity of WFI is 1.1*10-8 S/m at 20 C (keep in mind, that same water is used for clean steam) and the conductivity of Toluene, used in many CIP chemicals is 10-12 S/m at 20 C. All multi-phase media, like powder and air, as well as steam can also create a static hazard and should use anti-static grade hose.

For these challenging fluid handling applications, the antistatic Teflon liner Aflex offers is manufactured from FDA approved PTFE and less than 2.5% “High purity” Carbon black material. Aflex antistatic liners meet FDA requirements 21 CFR 178.3297 and European Commission Directive 2007/19/EC. AS grade hose also confirms to the requirements of USP Class VI.

It’s important to note that antistatic liners not only prevent things from going “BOOM!”, but also help extend the life of a hose. As alluded to earlier, we see this most frequently in WFI and Steam applications. In these applications, the fluids low conductivity, high velocity, and intermittently high temperatures build up charge in a non-conductive hose. This charge then tries to “move” to earth ground. This leads to tiny pinholes in general purpose Teflon hose liners. In the Pharmaline and Bioflex hose this is evident when you start to see the silicone cover look like a balloon. It goes without saying that high purity fluid applications can greatly benefit from the use of antistatic liners and the marginally higher hose cost is quickly offset by longer life and no product loss.

In sum, any time you are trying to identify a hose for a new application it is important to consider not only the chemical characteristics and compatibility of potential hoses, but also the electrical properties. With high flow, low conductivity fluids, contact Holland today about our antistatic product offerings.