API tubing is the devise used to transport oil or natural gas from the hydrocarbon reservoir to the earth surface. Tubes mainly include three different kinds, namely non-upset tubing (NU), external upset tubing (EU) and integral joint tubing (IJ). NU refers to the tube whose ends are threaded and coupling directly without being thickened. EU means both ends of the tube are thickened, threaded and then coupling. IJ refers to the tube whose ends are connected without coupling, one end being threaded through internal thickened and the other through external thickened.
API divides tubing grades into three different kinds. First is for all tubing in grades H40, J55, and N80. Second is for restricted-yield tubing grades L80, C90, and T95. Last is for high-strength tubing in seamless grade P110. The API grade letter designation was arbitrarily selected to provide a unique name for various steels. Numbers in the grade designation indicate the minimum yield strength of the steel in thousand psi. API defines the yield strength as the tensile stress required to produce a specific total elongation per unit length on a standard test specimen.
API Tubing are supposed to bear the pressure during the extraction period, which means it should be of great pressure resistance and proper malleability. Besides, it ought to be sized to perfectly satisfy the expected rates of oil and gas products, neither too big nor too small. API 5CT and 5B make specific requirements to the production of tubes, such as tensile strength, yield strength, elongation and hardness, etc.