Elbow to manufacturers customized, anti-corrosion, order cycle long. The cold bend can be bent with a ready to use straight pipe bender. Once completed, not two times anti-corrosion. There is an oil standard for cold bend pipe construction, and there is enterprise standard for west east gas pipeline project. But the open area with elbow bend will do, only consider the cost, elbow heating, bending 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