There are two key elements that need to be considered when looking at how often a heat transfer fluid should be replaced. The first is the type of application, for example in plastic extrusion, engineers can expect oil to last between 4,000 – 6,000 hours, while in asphalt storage there are instance where operators can use the same oil change for up to 25 years, if its properly maintained.
Secondly, the care that is taken over maintenance and testing will inevitably play a role in the longevity of a heat transfer fluid. Those companies which do regular fluid analysis and take advantage of their fluid supplier’s expertise will understand the rate of degradation and can act accordingly to reduce or eliminate the need for a total system shutdown just to replace fluids. For example, replacing just 10 percent of the fluid on a regular basis can extend the lifespan of the system fluid without the need for a complete fluid replacement.
On the other hand, those who forgo regular testing typically act reactively when production is affected, at which point maintenance becomes much more time-consuming and expensive. For example, if a system traditionally works at 550°F, operators may see their thermostat creeping up to 580°F over the years, as the system is forced to work harder due to the fouling of heat exchange surfaces or increasing fluid viscosity.
In the worst-case scenarios of degradation, the fluid will not circulate well enough to maintain production, or cracking will cause the boiling point of the fluid to fall dangerously close to the operating temperature, which causes pump cavitation and creates a significant safety concern. After the point of no return is reached, a total unplanned shut down is necessary to drain, clean, flush and recharge the system with fresh oil. This has a direct negative impact on the businesses’ bottom line with up to four days of lost production added to expensive repair costs.