High pressure and large diameter pipe fittings, especially elbows and tees (including pigging tees) are essential and important components of large gas pipeline engineering projects. The stress state of elbow and tee under process medium pressure is far more complicated than that of pressure cylinder in pressure vessel. Tee is an abnormal component with variable wall thickness, whose shape and wall thickness of each part are quite different due to the structure and manufacturing process. The formula method (i. e., mathematical analysis method) stipulated in pipe fitting standards is used to calculate wall thickness for high-pressure large-diameter pipe fittings, which is technically backward and conservative and resource consuming. In addition, under certain design parameters and environmental conditions, some thick-walled tees have exceeded the equipment manufacturing capacity and technological level of Chinese pipe fitting companies. Some important properties of tee products, such as impact toughness at low temperature, cannot meet the requirements of the design, leading to the adoption of other technical measures to improve, leading to potential safety risks for long-term operation of the pipeline. American pipe fitting standard MSS SP-75 High-strength,wrought,butt-welding fittings and ASME B16.9 Factory-made wrought buttwelding fittings prescribe two methods for pipe fitting design and calculation: formula method and verification test method. Imported pipe fittings from overseas manufacturers used verification test method for Shaanxi-Beijing Pipeline, West to-East Pipeline and Shaanxi-Beijing Second Pipeline Projects. The thickness of these pipe fittings is significantly thinner, and they are operating in a safe and reliable manner so far. Therefore, the only way to solve the backwardness of high pressure and large diameter pipe fitting design and the non-conformance of some thick wall tee to the standard is to determine the wall thickness using the verification test method and develop the work and technical procedures associated with the verification test method. Pipe fitting steel standards for China‘’s large gas pipeline engineering and the use of pipe fitting steel are still in the early stages of development. The type of steel, pipe fittings steel series, Charpy V-notch impact test temperature specified by standards and the coordination mechanism between pipe fittings steel raw material companies and pipe fitting company are open to discussion. The tee manufacturing process should be upgraded as soon as possible to improve the low-temperature impact energy value.