A half-pipe (180 deg) or seg pipe (120 deg) coil is a heat transfer system where the heating or cooling fluid is circulated through the coil to affect the temperature of the contents in the main vessel. The coil is normally coved with an insulating material to optimize the efficiency of the heat transfer. Half pipe coils can be applied continuously or in zones. Half pipe coils are often utilized in conditions with moderate temperature differential and controlled heating or cooling. Sudden or severe temperature differentials in the coil or vessel can cause thermal stress corrosion failures.