API 6A Wellhead & X-mas Tree for Oil and Gas well 

The Christmas tree is an assembly of valves, spools and fittings for an oil well, and to design to direct and control formation fluids from the well. It can provide inlet for production tubing strings, including all components above the tubing head adapter. Christmas tree assemblies can constitute many different kinds of combinations in order to meet any special requirement. Based on their different functions, Christmas trees can be classified into such special Christmas trees as oil production (flowing and artificial lift) Christmas trees, gas (natural gas and various sour gas) production Christmas trees, water injection Christmas trees, thermal recovery Christmas trees, fracturing Christmas trees and acidizing Christmas trees. Different pressure ratings serialize Christmas trees. 

The gas production Christmas tree and tubing head are mainly used to produce gas and inject gas. The relative density of natural gas is low and gas column pressure is low, while well head pressure is high and liable to leakage regardless of gas production and gas injection. Sometimes natural gas contains corrosive media such as H2S and CO2. Therefore, the gas production Christmas tree calls for rigid requirements on both its materials and its sealing characteristics. For the sake of safety, two gate valves are used on the tubing and casing respectively. Some gate valves to be used on high pressure and ultra-high pressure gas wells are integrated valves manufactured from high quality forged steel.