Everything You Need To Know About Thermal Fluid Care
Fluid maintenance is as important as maintaining mechanical parts. If your system is not running as it should, it may be time to perform maintenance on your thermal fluid. HEAT can help you diagnose and correct these problems, even helping to avoid downtime.
Read on to learn more about some symptoms of degraded or contaminated thermal fluid, how to take corrective action, and keep your process running safely.
Why is my system acting up?
Usually because your fluid is degraded or contaminated. If you were to take a sample of your oil, you'd likely find that the chemical properties have changed, and it is past the point of normal behavior. If you wait too long to correct this problem, it could be hazardous.
Now that you know what's happening to your system, it's important to figure out WHY that's happening. Failure to make the proper corrective measures may lead to any replacement fluid becoming immediately recontaminated.
Symptoms of Fluid Degradation or Contamination
These symptoms are common indications that maintenance must be performed. The sooner the problem is diagnosed, the less risk there is of system downtime.
- Batch times longer
- Heat-up or cool-down times longer
- Pressure drops higher
- Temperature at process exchanger has changed
- Pump cavitation
- Overflow from expansion tank
- Relief from PSVs
- Gurgling sounds
- Fluid color has changed
- Fluid odor has changed
- Pipe & valve corrosion
- Fluid leaks
- Seal failures
- Vessel jackets plugged
- Instrument lines plugged
- Unable to start up at low temperatures
- Over temperature alarms
- New vibrations
- Lower flow rates
- Sludge from drains
- Unable to remove heater bundles
- Fouling/plugging of pipe
Root Causes
Okay, you have fluid quality problems...now what?
Here are some likely culprits. Once you know which of these is happening, you need to figure out what caused it.
Thermal Stress Degradation
Specific deficiencies in test results will clearly indicate when the fluid has been damaged from thermal stress. This is where individual molecules of the fluid are being exposed to surface (film) temperatures that are higher than the fluid molecules can tolerate. This typically occurs from a High-Temperature Excursion of the system fluid temperature; or from a low flow condition of the fluid through the heater; or when the heat flux rate of the heater design is too high.
Likely Cause:
- High-temperature excursion – This condition typically occurs with a specific failure in the control system which allows the bulk fluid temperature to reach excessive temperatures and trigger a high-temperature alarm. An excursion can also occur when operators intentionally increase the bulk fluid temperature to a setpoint that is beyond the design maximum to achieve a short-term production need. In either case, the temperature excursion will cause the fluid quality to degrade by forming insoluble solids. The fluid condition will progressively worsen until the cause has been eliminated and corrective actions are taken to restore the fluid quality.
- Low flow conditions – Low Flow is a very common cause of fluid degradation. Heater coil designs typically assume that the full flow rate will always be maintained. Conditions such as pump cavitation, or a partially closed manual valve or a stuck control valve, can drastically reduce the system flow rate across the heater coil. When the actual flow rate is not in balance the heater’s capacity and flux rate, the fluid will be locally overheated in the coil and experience thermal stress degradation, causing the formation of insoluble solids.
Oxidation Degradation
Test results will also show when an oxidation reaction is damaging the fluid. This is where the fluid is being exposed to oxygen at high temperatures which forms organic acids and eventually reacts to form various types of solids in the fluid.
Likely Cause:
- Hot atmospheric expansion tank – Many users avoid the issue of venting off low boilers by using an atmospheric expansion tank. Unfortunately, this can only be done when the tank is always maintained at low ambient temperatures and the fluid has a vapor pressure less than one atmosphere at the operating temperature. If, at any time a thermal fluid is exposed to air at temperatures above 250°F it will cause oxidation degradation of the fluid and can also allow moisture intrusion into the fluid. Having a hot expansion tank is a common problem with systems that routinely go through batch heating and cooling cycles. Each time the fluid goes through a heat up cycle, the fluid will thermally expand sending hot fluid up into the expansion tank with every cycle. The oxidized fluid will form organic acids which then form sludge solids in the fluid.
Event Related Degradation
Test results can also indicate when fluid damage has been caused by the introduction of a foreign contaminant. This could be the result of using the wrong make up fluid, or with the failure of a heat exchanger where a contaminant is leaking into the fluid.
Likely Cause:
- Incorrect or contaminated make-up fluid – Plant maintenance departments are frequently required to manage a wide range of industrial fluids from lube oils to hydraulic oils to glycols to various brands and types of thermal fluids. This can lead to accidentally adding the wrong make-up fluid into the system. Another common mistake is adding contaminated waste fluid from the system vent or overflow tanks back into the system.
- Process Equipment leak – The introduction of foreign contamination into the thermal fluid frequently occurs with undetected process equipment leaks. Production products such as polymers or chemicals can leak into the thermal fluid when heat exchangers or vessel jackets develop cracks or corrosion that allows this cross-contamination to occur. Cooling fluids can also contaminate thermal fluids in the same way.
- Contamination from recent modifications – Fluid contamination frequently occurs when an existing thermal fluid system has been re-started just after equipment modifications or when there have been upgrades to the components or the capacity within a sub-section of the thermal fluid system. Types of contamination can range from the introduction of rags, gloves or wrenches to residues left behind from cutting fluids, rust, grease, or lubricating fluids. If not handled properly, the shut down and re-start of fluid system can also provide the opportunity cause thermal stress and oxidation degradation to the fluid.
Age Related Degradation
The physical properties of all thermal fluids will naturally degrade over time. Test results will show the gradual decline of the fluid quality. This condition will typically be the easiest to correct if corrective action is taken in a timely manner.
Likely Cause:
- Insufficient venting – As any thermal fluid ages, it will naturally produce low boilers (light ends). If these light ends are not periodically vented out through the expansion tank, they will accumulate and drastically reduce the flash point of the fluid. Light ends are a normal and necessary component of thermal fluids and must be maintained at appropriate levels.
- Excessive venting – Many customers who experience flash point degradation from insufficient venting will over-react by continuously venting (sweeping) the expansion tank. Low boilers are an essential constituent component of the thermal fluid and must be maintained within specified levels. Over venting strips the fluid of all low boilers and only leaves behind the heavier components of the fluid. This type of degradation will lead to the formation of sludge and solids from the accumulation of high boilers.
- Ignoring Partial Fluid Changes – One of the most important steps in maintaining the overall health of heat transfer fluid is to drain and replace 5% of the total system volume with virgin fluid every year. This step is also known as “Sweetening”. As part of an annual fluid maintenance program, the 5% sweetening is the best way to fully maintain the original physical properties of the fluid. When sweetening is done as part of a fluid rehabilitation program, the percentage of volume replacement may range from 10% to as much as 25% depending on the condition of the fluid.
Okay, so how can I rehabilitate my thermal fluid?
Well...it depends on how far gone the fluid is. HEAT has developed a variety of specialized products and services for fluid care or rehabilitation. Each solution is developed individually for each customer.
Fortunately, when fluid degradation and contamination are detected early enough, in most cases the fluid can be rehabilitated. When test results show a problem with the fluid, there are inexpensive maintenance measures that can restore the physical properties of the fluid back to “like-new” conditions.
Unfortunately, dealing with severely degraded fluid is not just as simple as draining out the old fluid and refilling with new. Degraded fluid typically has a large amount of contamination, like undissolved solids. Most of these particles will simply fall to the bottom of the pipes when the fluid is drained and remain in the system. When the new fluid is filled, it will not only pick up this residual contamination, but it will also act as a solvent and begin to dissolve harder coke deposits from the wall of the piping. The result being that your brand-new fluid will be immediately contaminated.
Once thermal fluid undergoes severe oxidation and/or severe thermal degradation, it will no longer have the physical properties necessary to provide a safe and reliable operation for your process. Degraded fluid will produce solid particles and high viscosity sludge that will stick to the inside surfaces of the entire piping system, including process vessel jackets and heat exchanger surfaces. These byproducts of degradation will continually increase to the point where they cause damage, and eventually cause the heater to fail. This type of unplanned shutdown typically results in a plant being shut down while waiting for a new heating system to be fabricated and installed.
Level 1 Corrective Action:
Fluid RehabilitationLevel 2 Corrective Action:
Fluid ReplacementLevel 3 Corrective Action:
System Decontamination
Annual fluid testing is the key to identifying and correcting ordinary age-related fluid degradation issues.
Failure to invest in periodic fluid care maintenance will eventually lead to the much greater expense of replacing 100% of the fluid in the system.
The most effective way to tell if degradation reactions are taking place in your fluid is through routine testing of the fluid for its physical properties. Standard physical properties tests such as viscosity, density, specific heat, and thermal conductivity should be performed. But the most important tests to perform are the Acid Number and the Distillation Range. These results will point to the type of degradation that is occurring.
Much like how a doctor interprets blood test results, fluid test results will indicate when and how degradation is occurring. Some combinations of test results will let you know that you have an oxidation problem. Other combinations will show if the fluid is thermally stressed or if the fluid requires additional venting or even less venting. And finally, they can indicate when the fluid has been contaminated with water or your product or some other foreign materials.
Regular tests of your thermal fluid will keep you informed about its health, and alert you to preventative maintenance that can be performed before your process needs to be shut down.
We recommend using the BOSS 1000 Hot Oil Sampling Device to safely collect the most accurate representation of your fluid.
If you have a problem with your thermal fluid, we know it can be overwhelming. With the right approach, most of the time, your problems can be corrected.
The most important thing to remember is that you are the steward of your thermal fluid - as long as you take the time to properly care for your thermal fluid, it will continue to be a safe and reliable part of your operation for many years.
Contact our experts if you have any questions.