pipe is filled with river sand. closed at both ends and then can be bent as you wish. sometimes heating may be needed.
For industrial pipe bending for pipe in diameters from 2 inch upward, induction bending is probably the best method. The pipe is heated using electrical induction and then bent using a pre-programed machine. In this method, you can get a precise bend with no wall thinning on the outside portion of the bend. It is also quicker and usually cheaper than other methods. This method can provide extra long radius bends that made for much better fluid flow characteristics. It can also eliminate the use of conventional welded fittings for very high pressure systems and systems were corrosion or erosion can occur at weld joints.
