When it comes to specialised steels, often the most specialised are the tool steels with precise concentrations of rather exotic elements. However, some applications demand more humble specifications due to cost and the sheer quantity needed. X65 steel is one such steel. It is a low-carbon steel used primarily in the oil and gas industries as a pipe material where sometimes miles of X65 steel pipe are laid in a single application.
In terms of chemistry, X65 steel is quite simple when compared to other specialised steels. It has a very low carbon content (0.10 per cent) compared against other steels. Additional elements are also found in smaller quantities; silicon (0.35 per cent), sulphur (0.005 per cent), phosphorous (0.15 per cent), and nitrogen at 0.015 per cent. Manganese is the most abundant element --- after iron --- at 1.5 per cent. Additionally, X65 has two exotic elements added as needed for specific applications. Vanadium and titanium both add toughness and are sometimes found in small quantities.
In terms of physical properties, X65's most useful property for the pipe-fitting applications is its excellent weldability. The steel is quite tough, with a yield strength (the point at which the steel deforms under pressure) of 986 kpa (143 psi). The tensile strength (the point at which the material necks, or deforms radially) is 1,172 kpa (170 psi). Other properties include a slight ability to be heat treated, but due to the low carbon content X65 cannot be tempered.
X65 is primarily used in the oil and gas industries as one of the primary steels used in pipe. The strength and low cost make X65 much more attractive than other, higher-performing steels since these industries routinely use miles of pipe. The strength of X65 also means it is a good choice for pressurised lines, where the steel's excellent weldabilty ensures strong seals.