PVC Bending Loads
Under bending stress PVC pipe will bend rather than break. However, the following precautions are very important:
- In below-ground installations, the pipes must have uniform, stable support.
- In above-ground installations, proper, correctly spaced supports must be provided.
- In above-ground installation, pumps, valves and other heavy appendages must be supported independently.
Installing Pipes on a Curve
When installing PVC piping, some changes in the alignment of the pipe may be achieved without the use of direction-change fittings such as elbows and sweeps. Deflection at rubber ring joints or other mechanical joints and/or controlled longitudinal bending of the pipe, within acceptable limits, can achieve the small direction changes in the pipeline, required to accommodate natural land gradients or to avoid obstacles.
Joint Deflection
The allowable angular deflection at the pipe joint varies depending on the manufacturing tolerances of the spigot and the socket but for design purposes all Vinidex rubber ring joints can be assumed to allow a maximum deflection of 1°. This is approximately equivalent to a 100mm offset for a 6m pipe. In most circumstances, the required change in direction can be taken up over several pipe lengths, perhaps in combination with pipe bending. Tighter curves can be achieved by cutting pipes to insert more joints, and/or the use of PVC couplings that effectively double the deflection available.
Note that this angular deflection is only available when pipes are jointed to the witness marks. If pipes are pushed to the back of the socket, movement of the spigot is restrained and the deflection is severely restricted
The effective radius of curvature obtainable for various pipe lengths is given in the table below.
Effective radius of curvature for 1° deflection at the joint
| Pipe length (m) | Approximate offset (mm) | Radius of curvature (m) |
| 12 | 200 | 688 |
| 9 | 150 | 516 |
| 6 | 100 | 344 |
| 4 | 70 | 229 |
| 3 | 50 | 172 |
| 2 | 35 | 115 |
| 1 | 20 | 57 |
Bending of pipes
Small diameter PVC pipes are sufficiently flexible to allow some bending of the pipe barrel in order to install on a curve. Deflection through bending is not practicable, due to the large forces required, for pipe sizes above about DN 200 particularly for the higher pressure classes.
The amount of bending that can be applied is limited by the axial flexural stress and strain levels induced in the pipe, which must be acceptable, in combination with other stresses and strains, for long term service. Vinidex recommends that for pipe under pressure, the bending radius should not be less than 300 times the diameter.