This article was originally published on May 9, 2022, and updated on June 23, 2025.
In harsh process environments, even the most durable components can degrade over time—especially thermowells, which are your first line of defense for temperature sensors. Exposure to corrosive chemicals, high-velocity flow or abrasive media can wear down thermowells, risking measurement accuracy and system reliability.
That’s where coated thermowells come in. As a trusted leader in temperature instrumentation, Ashcroft helps engineers extend equipment life and ensure process stability by offering different coatings for specific conditions.
In this article, you’ll learn how thermowell coatings work, the different types available and how to choose the best option to protect both your instruments and your process.
What is Thermowell Coating?
A coated thermowell can protect against contamination in critical applications and prolong the life of your thermowell. It can also help prevent contamination in food/beverage and chemical applications that have strict sanitary requirements by helping to ensure the thermowell does not fail.
A coated thermowell is a standard thermowell (commonly 316 SS) enhanced with an engineered protective layer to prevent contamination in critical applications and prolong the life of your thermowell. This added coating provides a barrier against threats, including:
- Corrosive chemicals: acids, alkalis, solvents
- Abrasive particles: steam-entrained solids, mineral slurries
- Cross-contamination: critical in food, beverage, and pharmaceutical processes
Types of Thermowell Coating Types
There are a number of different coatings to choose from depending on your application. PFA/PTFE and stellite are the most commonly used to protect thermowells, here is a quick review of both types:
1. Perfluoroalkoxy (PFA) and Polytetrafluoroethylene (PTFE) Coatings
PFA and PTFE options are similar in that they both involve fluoropolymer layers that are applied to the thermowell through dipping or spraying. They offer excellent chemical resistance, a low friction and non-stick surface and a wide temperature range of 200 °C to +260 °C (–328 °F to +500 °F). Plus, they are biocompatible and FDA-compliant, making them ideal choices for aggressive chemical processes, pharmaceuticals, food & beverage and sanitary applications.
2. Stellite (Hard Alloy) Coatings
This stellite coating option is thermal-sprayed cobalt‑chromium alloy, which is often blended with tungsten carbide or aluminum oxide. It offers exceptional wear resistance as well as high resistance to erosion and abrasion, and it is sturdy against mechanical shock and high-temperature durability. For those reasons and more, stellite coatings are often used in abrasive slurry flows, high-velocity steam, mining environments and sand applications.
Choosing the Right Thermowell Coating for Your Needs
Figure 1: Thermowell coatings by application
Benefits of Using a Coated Thermowell
Choosing the right thermowell coating protects your equipment and delivers several long-term operational advantages.
- Extended service life in corrosive or abrasive environments
- Reliable temperature readings, thanks to environmental protection
- Sanitary, food-safe operations with PTFE or FDA-grade coatings
- Cost-effective option for reducing sensor and equipment replacement costs
How to Order a Coated Thermowell
Ashcroft offers coating options for all thermowell configurations. Before you request a quote, take a moment to:
- Assess your application conditions – identify media type, temperature, flow and abrasion factors.
- Select compatible thermowell material, typically 316 SS; consider exotic metals if needed.
- Choose the right coating layer, balancing chemical and mechanical requirements.
- Consult Ashcroft’s experts for optimal coating thickness, application methods, and lead times.
Ready to Learn More?
Now that you understand the purpose of a coated thermowell and when it’s appropriate to use one, you will be able to ensure that your temperature measurement equipment remains safe in your application.
The following articles may provide answers to additional questions you may have about thermowells:
- How to Calculate Thermowell Stem Length for your Temperature Instrument
- Fitting a Thermowell to Bimetal Thermometers or RTDs/Thermocouples
- What is a Thermowell Wake Frequency Calculation?
- How Much Do Thermowells Cost? 5 Factors that Influence Price
Contact us anytime to speak to a product specialist who can answer any additional questions you have. In the meantime, download our guide for help choosing instruments for highly corrosive and harsh oil and gas applications.
