Registration of Plastic Fittings
PVE-5246, Last Updated: Mar 22 2018, By: LRB
Plastic pipe can be calculated and registered in Canada under the code rules found in B31.1 or B31.3. But a registered piping plastic piping system also needs registered plastic fittings. Burst testing or Calculations with FEA are two methods of justifying fittings for registration.
TSSA has a standard to cover the burst test pressures used for unlisted materials (like plastics):
GUIDELINES FOR THE REGISTRATION OF NON-NUCLEAR FITTINGS IN THE PROVINCE OF ONTARIO (Download Guidelines):
Burst test factor of safety from the guideline (Appendix D):
- 4x – for all materials not listed below
- 6x – cast iron
- 10x – glass
- 10x – non-metallic, non-automated fabrication process
Although molded plastic parts are made with automated processes justifying a 4x factor, we are sometimes required to use a 10x factor. These factors are for Ontario only, other provinces do not have guidelines.
When more than one grade of plastic is used, each grade needs to be tested. That, combined with the need for conservative safety factors can make using burst testing too conservative or expensive. Read more about burst testing on our website
B31.3 provides allowed stress levels for calculating plastic fittings. B31.3 Table B-1 and B31.1 table III-3.2.1 provide Hydrostatic Design Stress (HDS) allowed stress levels for many common plastics. The Plastics Piping Institute (PPI) has a larger list of HDS list of HDS values here. Where the B31.1/31.3/PPI listings overlap, identical HDS values are provided.
With an allowed HDS, the fitting can be calculated either by using standard code rules or as shown in the illustration below, by FEA (or by a combination of both). FEA provides detailed insight into the failure mechanism of a plastic fitting which usually results in a higher allowable operating pressure than achievable when burst testing is used. When more than one grade of plastic is used, only the weakest has to be analyzed.