Elbow processing to manufacturers custom-made, anti-corrosion, order cycle long. Cold bend can be bent by straight pipe bending machine. Once completed, not two times anti-corrosion. Cold bend construction technology has an oil standard, west east gas transmission enterprise standards. But the open area with elbow, bend will do, just consider the cost, elbow heating needs, bend cold bend can be, of course, elbow high cost. Sometimes narrow sections must be used such as elbow, rock trench, because the bend radius of curvature is small, generally 6D, elbow 40D.