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Technical Note PP 811-TN
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PE Flange Connections

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Flange Connection

Flanged joints are made using a DriscoPlex¬ģ Flange Adapter that is fused to the pipe then¬†joined to a mating flange adapter or a mating appurtenance flange. A back-up ring is fitted¬†behind the flange adapter‚Äôs sealing surface flange as shown in Figure 2-1 and bolted to the¬†mating flange. DriscoPlex¬ģ Flange Adapters have a serrated sealing surface. At lower pressure,¬†typically 100 psi or less, a gasket is usually not required. At greater pressure, the serrations help¬†hold the gasket in place.

The back-up ring is required for polyethylene flange joints in order to develop uniform pressure around the entire sealing surface. Without a back-up ring, a polyethylene flange will leak between the bolts. Standard back-up rings are convoluted ductile iron with AWWA C207 150 lb drilling. Other available back-up ring materials are steel, primer-coated steel; epoxy coated steel, stainless steel or fiberglass. In below ground service, coatings and cathodic protection may be needed to protect metal back-up rings from corrosion. One edge of the back-up ring bore must be radiused or chamfered. This edge fits against the back of the sealing surface flange.

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PE_Flange_Adapter

Service pressure ratings for back-up ring¬†designs and materials will vary. Consult¬†the back-up ring supplier for the¬†maximum recommended rating. The¬†service pressure rating for the back-up¬†ring should meet or exceed the service¬†pressure of the pipe. Typically, back-up¬†rings are ANSI Class 125 for gravity¬†applications, ANSI Class 150 or AWWA¬†C207 for pressures up to 267 psi (200 psi¬†for 20‚ÄĚ to 24‚ÄĚ sizes), and ANSI Class 300 for¬†higher pressure.¬

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Flange adapters are long enough so that they can be clamped in a fusion machine like a pipe end. The back-up ring is fitted to the flange adapter before fusion, so external fusion bead removal is not required.

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Technical Note PP 811-TN