Exploring thermal fluid analysis 02 November 2023

thermal fluid analysis System maintenance being carried out. Thermal fluid analysis pictured at left and below

Regular thermal fluid sampling and analysis enables businesses to proactively monitor fluid condition and intervene before issues impact production

How do you know when a kitchen sink is about to clog and overflow? Most residential pipes are hidden, so food waste and product build-up can go unnoticed until it leads to damage. In manufacturing, leaving pipework unmonitored can lead to unexpected downtime and safety issues, particularly when working with thermal fluids, so proactive monitoring is the best way to prevent these problems.

Thermal fluids are designed to operate effectively for many years, but over time, operating at and maintaining high temperatures means that the oil will naturally degrade. Thermal fluid analysis provides a deep dive into the condition of the oil and allows businesses to gain expert advice about how to effectively maintain the fluid and the system. Analysis also ensures health and safety compliance with The Dangerous Substances and Explosive Atmospheres Regulations (DSEAR) of 2002 and UKEX (formally the Explosive Atmosphere Directive ATEX 137 in the UK).

To comply with relevant safety regulations, such as DSEAR in the UK, manufacturers must take proactive steps to reduce the risk of fire or explosion caused by working with dangerous substances. If this fluid is left unattended, for example, fluid degradation – where thermal oils can be broken down into carbon molecules that stick to the pipes – can occur, reducing heat transfer efficiency. If not monitored effectively, degradation may go unnoticed until it causes significant production issues and system failure, leading to costly downtime and risk to health and safety.

Instead of reacting to issues, regular thermal fluid sampling and analysis enables businesses to proactively monitor fluid condition and intervene before issues impact production, extending thermal oil lifespan and reducing maintenance costs.


Effectively monitoring heat transfer oil condition requires engineers to regularly take samples of the oil and send it to a specialist for analysis. Historically, thermal fluid experts conducted seven tests. However, in our experience, conducting 11 tests provides results that best reflect the reality of what’s happening inside the system.

Once the sample arrives to an independent lab for testing, an analytical chemist will examine its appearance, looking at the colour and for any particulates in the fluid. Fluid colour can range from clear and bright – which is common to newer fluids – to hazy, which can be a sign of high-water levels, to dark, which shows there is a high level of carbon build-up in the system. These initial observations are confirmed in later steps to ensure the thermal fluid specialist provides the best recommendations.

Testing the water content of the oil is vital to regulatory compliance. At high temperatures, any water in the system and oil will change to steam and expand, increasing the pressure in the system. By analysing water content, analysts and heat transfer fluid specialists can advise on how best to reduce the risks associated with high pressure.

The next step is to test viscosity and assess the impact the fluid has on the system pumps. If a fluid is too thick, flow rate will reduce, increasing the pressure on the pumps. This reduced flow rate can create hot spots in the system, leading to inconsistent heating or cooling of products that results in waste products, increased damage to the system and rising maintenance costs.

Measuring the level of carbon in the system is key to understanding the degree of system fouling. If the thermal fluid expert detects high levels of carbon deposits, it suggests that there is more carbon in the system, which can harden in the pipes, acting as an insulator. As a result, the entire system heat transfer efficiency will reduce and more energy is required to heat up the system. Manufacturers should consider how they can prevent carbon build-up as it can create hot spots that accelerate wear on the pipes and increase the risk of leaks.

Analytical chemists will then test the total acid number (TAN). If the fluid is acidic, it can lead to increased corrosion of the system and accelerated carbon creation. By measuring this parameter, manufacturers can understand how the fluid impacts the pipes of the system, ensuring that it can slow down degradation and reduce the frequency of scheduled maintenance needed to replace corroded parts.

Particulate quantity and iron tests highlight the degradation of components of the heat transfer system. Both tests can show signs of wear in the system that need addressing so that manufacturers can intervene before the wear turns into a dangerous leak.

Manufacturers should also look at the results of the Pensky-Martens Closed Cup flash point, Cleveland Open Cup flash point and fire point tests to reduce health and safety risks. Industry standards suggest that the closed flash point of the fluid cannot be below 100°C, because it means the fluid could ignite at lower temperatures, so these tests are vital to understanding if the fluid is safe to use.


Once analysis is complete, the thermal fluid expert delivers a report to the plant manager, organising findings into cautions, actions, or serious findings. At this point engineers can take the recommendations and plan interventions based on the priorities in the report. Monitoring thermal fluid condition over time and looking for trends helps users anticipate when the system will require maintenance before a failure occurs.

Maintaining an efficient heat transfer system is integral to productivity, so manufacturers should consider how they can effectively monitor fluid inside the system. For example, Global Heat Transfer’s Thermocare service offers both on-site and remote technical support to help manufacturers rapidly sample and analyse fluid. From this, manufacturers can track fluid condition, anticipate and resolve issues quickly and implement preventative measures to extend fluid lifespan, reduce downtime and the facility’s environmental impact, and ensure system compliance.


The by-products of fluid degradation will impact the condition of the thermal fluid system, so proactive system maintenance is as important as fluid maintenance. Conducting regular system walk-rounds enables engineers to detect system issues before they impact production. During the inspection, engineers can monitor gauges to understand what is happening inside the system and look out for shaking pipes or slow production areas. Early intervention to solve these problems, by proactively cleaning, fixing or replacing parts, can increase uptime, reduce energy usage and lower maintenance costs.

Clive Jones, managing director of Global Heat Transfer

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