Here is the detailed introduction of the API steel pipe including the physical properties. API steel pipe in steel pipe industry has stable proportion of 42% ~ 42% in recent years. And the welded pipe has a rising trend. API steel pipes and welded steel pipe is the reliability of the materials and their variety adaptability is strong, especially to adapt to the thick wall and the production of alloy steel. The main problem is high investment, high cost, complicated manufacturing process, wall thickness and heat tolerance. The welded pipe is actually the deep processing product of sheet. With conditions of the similar price, API pipe improves its market competitiveness due to its reliability. As the ceaseless improvement of quality of steel plate and the raising of the level of welded pipe technology some equipment parts of the API pipes begin to occupy the market. But the possibility is replaced by welded pipes and this is only a very limited area.