Application Note

Gauges with Chemical-Resistant Coating: A Smart Solution for Highly Corrosive Applications

By Instrument Guru – WIKA – 02.02.17

Many applications in the chemical and refining industry, in fertilizer plants, and in scrubbing systems work with extremely aggressive media – and thus require bulk storage of highly corrosive or acidic chemicals that react with stainless steel. Therefore, it is not the best idea to use traditional instruments, many of which are made of stainless steel, to measure tank levels, as those gauges would degrade quickly and, consequently, provide inaccurate information.

Transmitters and other non-contact components, such as those that use radar, are an option; however, they do not provide the reliable mechanical visual indication that many customers prefer. Some alloys made of nickel, zirconium, titanium, and other materials may be resistant to the chemical in the tank, but instruments made of these exotic alloys are expensive, and their production has long lead times.

The Smart Solution to Oxidation Problems

A smart solution to oxidation problems is a chemical-resistant coating on a traditional level gauge so it can withstand the attack of aggressive media.

Instruments coated with chemical resistant materials such as Tefzel® (a modified ethylene tetrafluoroethylene, or EFTE), Halar® (ethylene chlorotrifluoroethylene, or ECTFE), Kynar® (polyvinylidene difluoride, or PVDF), and PTFE (polytetrafluoroethylene) will give uninterrupted service for very long periods of time.

In the case of applications that require threaded vessel connections, threaded flanges made of special alloys can be attached to the tank, and then connected to a coated level gauge. This setup improves production turnaround times and is less expensive than gauges made entirely of exotic alloys.

WIKA offers magnetic level indicators and level chambers coated in various chemical-resistant materials, as well as level chambers built entirely from plastic. On a typical WIKA chemically coated gauge, a coating of chemical-resistant material 0.015″ – 0.03″ thick is applied to every part of the gauge, from the flange faces on the vessel connections to the precision float, protecting the gauge from the effects of the media.

We work individually with each customer to find the best coating material for each application. For example, WIKA engineers have provided coated level instrumentation for tanks used to store acid to balance water pH during production of rubber products. WIKA gauges coated with Tefzel®, the most popular coating, have been used in sulfuric acid and sodium hydroxide applications for years without any issues. Coated gauges are a smart, cost-effective, and reliable option for tank level measuring in extremely aggressive media.

Take From: Wika