A common application of mandrel bending of pipe is for pipe bollards. A bollard is one of a series of posts preventing vehicles from entering an area. Bollards can be as simple as a straight pipe embedded vertically in the ground, or they can be made of pipe with four bends in two planes. The most common bollards that utilize pipe bending are those with a U shape or a flat-back-U design. Painted yellow, these are often seen protecting the pumps in gas stations or guarding equipment in factories.
In order to provide maximum protection in the horizontal length of the bollard, the two 90 degree bends are often done with a tight radius. Such bending requires using an internal support or mandrel to ensure that there will be no ovality or other distortion at the bend. Common pipe sizes for bollards are 4, 5 and 6in OD pipe.
The flat-back-U pipe bollard shown above is made of 6in outside diameter, Schedule 40 pipe with two 90 degree 12in center-line-radius bends. The width of the bollard is 10ft; the above-ground height of the bollard is 2ft minimum; and the bollard will be embedded 3ft deep into a concrete footing.
The two bends are 2D, i.e. the center-line radius (12in) is two times the outside diameter of the pipe (6in). Such bends are prone to rippling on the inside radius of the pipe, but with the proper tooling, material, and process, a very smooth, ripple-free bend can be achieved.
This particular order called for 110 pieces to be shipped on one flatbed, a challenge because the load was at both the dimensional and weight limits without permits. The shipping department nested one bollard within the other and stacked them horizontally to the height limit allowed. An unusually long 53ft flatbed was used to carry the load. And the shipping team secured the load with considerable strapping and wood blocking to create a safe means of transport.
Pipe bollards are just one example of a product employing mandrel bending of pipe. Other applications include roll-over protection (ROPS), elbows for process piping, handrails, and exhaust tubes.