The role of pipefitters is similar to that of plumbers with one crucial difference. While a plumber installs pipework that carries water at low pressure, a pipefitter installs, manipulates and maintains pipes that carry liquids or gases at much higher pressures. Piping systems may be required to cope with steam, ventilation, hydraulics, chemicals, fuels and oil. Pipefitting is mainly carried out in industrial settings. Metal pipes are used in industry to better cope with the high pressures to which they are subjected. They may be constructed from carbon steel, stainless steel or other alloy metals. As they come in measured sections and must be connected together, the pipefitter must be able to cut accurately and fuse sections together with techniques like threading, welding and bending. Pipefitting contractors may work in power stations, refineries, factories and offshore, installing and maintaining oil pipelines under the sea, for instance.