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Installing Rubber Gaskets with Plastic Pipe

Universal Gaskets supplies elastomeric flange gaskets for GRP, Polyethylene, Polypropylene and other plastic pipe lines.

Plastic by its nature will deform under stress and does not return to its original shape after the stress is removed. Steel backing rings are normally used with plastic flanges to distribute the stress under the stud nuts more evenly and to reduce deformation. However the stress is never evenly distributed and highly stressed areas will deform or creep over time.

A mild steel bolt tightened to half its yield stress has a strain of only 0.05% or 0.025mm in a 50 mm long stud (between nuts). Thus any deformation of the plastic behind the backing ring will significantly reduce bolt tension and reduce seal efficacy.

Installers should note:

  • Good quality elastomeric gaskets are preferred with plastic piping as the gasket acts as a spring and maintains the sealing stress as the plastic deforms
  • Flange bolts should be retightened a few days after installation to compensate for initial plastic deformation