Root Causes of Fluid Damage
Your best course of action moving forward depends on identifying the root cause of the fluid damage. Not only will the fluid quality need to be restored, but the cause of the fluid damage must be identified and corrected. Failure to make the proper corrective measures may lead to an immediate reoccurrence of the fluid damage. The following is a guide to help you identify, correct, and make changes to restore safe, efficient operations and minimize any future damage.
Viscosity: higher or lower than acceptable range depending on type of fluid damage
Density: higher or lower than acceptable range depending on type of fluid damage
Thermal conductivity: Greatly reduced with most types of fluid damage
Acid number: High Acid Number indicates Oxidation Degradation
Insoluble solids content: Generally, indicates Thermal Stress Degradation
Sludge content: Results from advanced Oxidation, Excessive Venting, or Contamination.
Flash Point: Greatly reduced due to Insufficient Venting
Moisture Content: Indicates contamination or from lack of tank blanketing system
Contaminants Identified: Generally, indicates process leak or incorrect fluid make-up
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.
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.
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.
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.
In most cases a change in fluid quality can be traced to one of the following:
- 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.
- 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.
- 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 250F 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.
- 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.
Taking the time to identify the true root cause can take detective work and sometimes a bit of self-introspection. However, it is critically important to identify this and give your organization the chance for improvement and prevent re-occurrence. Root causes can be wide-ranging in their type and source. The following are just a few examples:
- Control interlocks missing or malfunctioning
- Valves accidentally left closed or left open
- Tank blanketing system missing or malfunctioning
- Insufficient fluid management protocols
- Equipment failure
- Insufficiencies with the existing equipment design
- Operational requirements exceed the capabilities of current equipment
- Insufficient inspection procedures
- Poor workmanship
- 3rd Party contractor
- Fire or Explosion
- Employee Hazards
- Unscheduled Downtime
- Long term Plant Shutdown
- Equipment Damage
- Unplanned Capital Expenditures
- Unplanned Maintenance Expenditures
Inspections and test results will indicate which type of corrective action is required with the fluid. When damage is prolonged and severe, system decontamination will be required. In these cases, simply replacing the fluid will not correct the problem and will most likely make the situation worse. Be sure to understand your root causes before you determine corrective actions.
- Equipment Design or Capacity? – Are repairs, upgrades or replacements of equipment required to prevent fluid damage in the future?
- Processes & Procedures? – Are new procedures or process modifications required to prevent fluid damage in the future?
- System Inspection Protocol – Thermal Fluid System Care is a safety issue. Pro-active inspection programs for thermal fluid systems can prevent conditions that are unsafe for personnel and prevent more severe or catastrophic events from occurring.
- Fluid Stewardship Program – Any Fluid Stewardship program must include:
- Routine fluid testing
- Data tracking of fluid test results to predict fluid maintenance
- Annual 5% fluid replacement schedule
- Annual Light Ends removal schedule
- Monthly Filtration Schedule
- Training on Fluid Care
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