Gas and oil wells and their production facilities use many heavy duty valves. Valves used in wellhead equipment are subject to high temperatures and extremely high pressures. Valve piping combinations often contain special globe valves (called choke valves) and gate valves. Special shut-off valves are used to regulate the flow from the well. In addition to wellheads, there are facilities on gas and oil fields that require valves. These include process equipment for the pretreatment of natural gas or oil. These valves are usually carbon steel material, lower grade.