Electric heat tracing design for impedance and skin effect systems

When a material is transported by pipeline at a temperature above its surroundings, it will lose heat. Insulation will slow the heat loss, but will not prevent it. Temperature can be maintained by adding heat to make up the loss. This can be accomplished in many different ways. Heating stations can be located along the pipeline to make up the loss at discrete points. The problem with this technique is that the product does not stay at a uniform temperature, and if flow stops the product could lose so much heat that it becomes unpumpable. Heat can be added along the entire length of the pipeline by applying a heater to the pipe. This is commonly called heat tracing. Heat tracing can be accomplished using many different techniques. Steam, hot oil, hot water, and electric heaters are all commonly used methods. Electric tracing can be further broken down into parallel heating cables, series heating cables, self-limiting heating cables, mineral insulated cables, impedance heating, and skin effect heating. Each method has advantages and disadvantages. Here, the authors present an overview of the field and then focus on impedance heating and skin effect heating, and attempt to describe the criteria for selection of the best system for a specific application.