Coatings for Measuring Instruments - ICS Schneider Messtechnik GmbH

The demands on process applications are becoming increasingly complex, and measuring instruments must meet the highest standards and function reliably—even under harsh environmental conditions or when in contact with aggressive media. In industries such as chemicals, petrochemicals, oil and gas, and hydrogen applications, coatings are often essential. They enhance product durability, performance, and functionality, thus contributing to process efficiency and safety.

What types of coatings are available?

For the parts of measuring instruments that come into contact with the media, a wide range of special materials and coatings are available for specific applications. These include:

Coating Material	Applications	Properties
Gold	Hydrogen applications	Creates a barrier against H2 molecules, prevents hydrogen permeation
ECTFE	Chemicals, petrochemicals	Resistant to common acids and alkalis, high-temperature resistance
CrNi Steel with PFA	Oil and gas industry, chemicals	Resistance to chemicals, high-temperature resistance, antistatic properties
Wikaramic®	Pulp and paper industry, abrasive processes	Abrasion-resistant, suitable for flush-mounted diaphragm seals, high mechanical strength

When is it recommended to use a coating?

Coatings are particularly advisable when precise measurement of challenging media is required. These challenging media include aggressive, corrosive, abrasive, highly viscous, heterogeneous, toxic, hot, or aseptic substances. These media place high demands on the material of the measuring instruments, which can be protected by suitable coatings.

How does a coating work?

During the coating process, a thin layer of one material is applied to the surface of another material. This layer acts as a protective barrier between the structural material and the environment. In the world of measuring instruments, this means that usually only the parts that come into direct contact with the media are coated. For diaphragm seals or process transmitters, it is therefore advisable to coat the diaphragm. WIKA applies coatings in precise nuances to conserve resources while providing optimal protection.

Advantages of coatings

Coatings such as ECTFE, PFA (antistatic and FDA-compliant), or gold are applied precisely where needed. This minimizes costs and conserves resources. For example, coatings with CrNi steel, gold, or Wikaramic® allow diaphragm seal tops or media-contacting parts of a diaphragm seal with a flange connection (e.g., WIKA type 990.27) to be used at a maximum permissible operating temperature of 400 °C (752 °F).

However, it should be noted that the maximum permissible operating temperature of the diaphragm seal system is limited by the joining technology, the system fill fluid, and the measuring instrument. For example, a diaphragm coated with ECTFE is resistant to common acids and alkalis, which is often necessary in the chemicals or petrochemicals industries. CrNi steel with an antistatic PFA coating is resistant to chemicals and can withstand high temperatures, making this coating ideal for the oil and gas industry. Wikaramic® is particularly recommended for flush-mounted diaphragm seals in the pulp and paper industry or for processes with abrasive media.

Gold coating for hydrogen applications

An excursion into the application of gold coatings shows that a coated diaphragm, whether on a measuring instrument or a diaphragm seal, is standard at high temperatures and corresponding concentration gradients. The gold coating acts as a "barrier" for H2 molecules and significantly slows down the process of hydrogen permeation. This ensures the integrity and functionality of the measuring instruments in hydrogen applications.

Conclusion

The choice of material and coating for the media-contacting parts of measuring instruments strongly depends on the application conditions. In addition to temperature requirements, the pressure load and resistance to the media must be considered. Suitable coatings not only contribute to the longevity and reliability of the measuring instruments but also ensure that precise and consistent measurements can be made, which is crucial for product quality and safety in various industries.

By understanding the different coatings and their applications, companies can make informed decisions to optimize their processes and maximize the lifespan of their measuring instruments.

Process Transmitters

WIKA CPT-20, CPT-21 Process transmitter

With capacitive ceramic measuring cell

Datasheet
User Manual
User Manual
User Manual