Circulation Heaters that are used in this application have explosion proof terminal housing and made of carbon steel. Thermocouples are also used to regulate temperature accurately as the temperature of crude oil cannot pass 500 degrees F. Additional types of oils that use electric heaters are lubricating oils, heat transfer oils as well as mineral oil and vegetable oil. Each have their own unique flash point and heaters are designed with specific alloys to handle any corrosive side effects.