Pipeline 101
Heat Pipes

More than half of the 800-mile-long Trans Alaska Pipeline System is built on permafrost – ground that remains frozen year-round. This permafrost must be kept frozen to maintain pipeline stability. One technique is to use vertical "heat pipes" inside pipeline supports. These pipes contain anhydrous ammonia, which vaporizes at temperatures just below freezing, rises and condenses at radiators above ground when the air temperature is well below freezing. This process transfers ground heat into the air during cold periods, thereby lowering the ground temperature. There are 122,000 individual heat pipes along the pipeline.