Flange Bolt Torque Settings for Plastic Pipe Systems
The above table gives torque settings for plastic flanges, whether using metal or PVC backing rings. As long as your plastic pipe is aligned correctly during installation, and you are using an EPDM or FPM gasket, there is no need to tighten beyond these limits. It is very dangerous to "pull a pipeline straight" by a few degrees by tightening a flange into a fixed body. PVC and ABS pipe is not designed to flex and, although there is some give in it, stress put on the pipe will weaken the system, especially if it is subjected to impact at a later date.
There can sometimes be a temptation, especially if they are on the other side of the site you are working on or you have left them in the workshop, to tighten flanges without using washers. This will have two main effects: the first is that it will lead to risk of the flange being misaligned as the nut heads are often similar to the size of the bolt hole; but especially because it makes taking it apart again ten times more difficult, especially when a little bit of corrosion is thrown in the mix.
Risk of Overtightening
Overtightening of flanges can lead to cracking of plastic fittings, so care must be taken to ensure the correct torque is applied. The above table is a guideline as to how much your bolts should be tightened. Torque wrenches are relatively cheap items and we recommend purchasing and using one, to avoid potential damage to plastic pipe parts.