Example of thermal degradation on immersion heater.

With thousands of uses for heat transfer fluids it is nearly impossible for any heat transfer fluid manufacturer to recommend an exact oil change interval or maintenance schedule. Each application has its own unique circumstances that contribute to the degradation of heat transfer fluid (a.k.a. thermal fluid, thermal oil, hot oil).

Each heat transfer fluid will also react differently depending on the environment it’s used in, and the differences in these environments can be extreme, ranging from just a few months to 10+ years.

System Maintenance

Most fluids require little maintenance, but there are a few things to consider:
  • Consult your fluid vendor and equipment manufacturer before making any changes to your system. A proper system is engineered around the user’s needs and fluid. Changes to a system’s design such as a pump or function such as adding more users (reactors, presses, etc.) can negatively impact a fluid. Take meter readings (flow, pressure, in/out temperature) when a system is new and monitor and log them on a regular basis. Any significant changes should be explored immediately.

  • It’s also important to follow a recommended fluid analysis program. Usually available for free or for a nominal fee from your vendor, these analyses enable early detection of any changes to a fluid. This allows time for system corrections that stop the fluid degradation and often improve the fluid’s condition.

  • Fluids typically break down either through oxidation or thermal degradation. Both of which are easily detected through regular analysis and are often preventable.

When to Replace Fluid

While the quality of the fluid you choose will ultimately determine its service life, a fluid’s life expectancy is also influenced by system design and configuration. A system open to the atmosphere where hot fluid comes in contact with air will likely suffer from oxidation. Also, the hotter the fluid and the more air exposure there is, the shorter the fluid’s service life will be. Oxidation generally results in heavy sludge deposits, or in severe cases, the fluid thickens to the point where it won’t flow from the system when cold.

A closed system generally doesn’t suffer from oxidation, but both open and closed systems can suffer from thermal degradation, which is the result of a fluid being heated past its temperature limit.

Thermal degradation can be ongoing in cases where perhaps a boiler or heater is not properly specified, or from improper system shut down or startup. In either case, a thermally degraded fluid will typically have reduced flashpoints, and if severe enough, high boiler carbon-like deposits.

Ideally, you want to change your fluid before it becomes degraded, and the best way to ensure this is to have your vendor perform regular fluid analysis. If a system change is done in time it should be just a matter of thoroughly draining the system, inspecting and refilling.

Waited Too Long to Replace the Fluid? Time for a System Cleaning.

Duratherm often is contacted by companies with systems in a catastrophic state, either completely plugged with sludge or with fluid thickened to the point where it won’t drain. Other times we get proactive enquiries where signs of trouble are just beginning.

In either case, Duratherm has a complete line of system cleaners to cover the lightest or heaviest cleaning job. From full strength solvents to additive style cleaners, we’ve yet to encounter a system we couldn’t fix.

Duratherm’s latest development in fluid cleaning and maintenance is the new Fluid Rejuvenator. If your system is suffering from oxidation or sludge deposits, Duratherm’s Fluid Rejuvenator can revitalize your fluid and extend its service life.

Contact Duratherm today for a free fluid evaluation or to discuss our complete line of Heat Transfer Fluids and System Cleaners.

(800) 446-4910