Paratherm AP is designed to be added to operating hot-oil systems to extend the oil’s useful life. The antioxidant protection additive prevents acids that can form in systems with poorly designed expansion tanks from converting to sludge. When the expansion tank is allowed to warm up, the hot oil can react with oxygen to form acids. Once the total acid number (TAN) reaches 0.3 to 0.4, carbon starts to form. Paratherm AP interrupts this sequence by incorporating a sacrificial antioxidant. Paratherm AP is not a permanent cure, says the company. Sacrificial additives become depleted over time and eventually the protection stops. In effect, antioxidants do not eliminate the need for preventive maintenance; instead, they reduce or delay the need for oil changeout. Periodic testing will help users determine whether the additive is still present.