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Heat-fusion joints

Entry in Joining methods · Updated · Written by the Know Your Pipes editors from the sources listed under References

Pipe heat fusion joins thermoplastic pipe by heating the two surfaces to be joined to melting temperature, pressing them together and letting them cool under pressure, so the polymer chains re-form as one piece without glue, solder or a gasket.[2] It is used on polypropylene (PP-R pipe) and on polyethylene water service pipe.

Fusion is a trained-installer method that needs a temperature-controlled heating tool and the pipe maker's procedure. This entry describes the methods; it does not replace the maker's training or instructions.

1 Methods

Socket fusion heats the outside of the pipe end and the inside of the socket fitting at the same time, then the pipe is pushed into the socket and held until the joint cools.[1] The Plastics Pipe Institute recommends mechanical equipment rather than hand tools for sockets larger than 2 in CTS.[1] The other heat-fusion methods are butt fusion, saddle fusion and electrofusion.[3] One PP-R maker lists hand socket welding for 16–63 mm pipe, butt welding for 160–450 mm and electrofusion for 20–250 mm.[3]

For polyethylene, ASTM F2620 is the standard practice for heat-fusion joints and names socket, butt and saddle fusion procedures.[4] For polypropylene, ASTM F2389 covers pressure-rated PP piping for water service, hot-and-cold water distribution, hydronic heating and irrigation.[5]

2 Temperatures and times

For PP-R and PP-RCT socket fusion, one valve maker's instructions call for a tool temperature of about 500°F ± 18°F (260°C ± 10°C), checked with a thermometer.[2] Heating, joining and cooling times rise with pipe size and with cold weather:

Socket fusion times for PP-R (one maker's chart)
Pipe OD (nominal)Heating time, above 41°FHeating time, below 41°FCooling time
20 mm (1/2 in)5 s8 s2 min[2]
25 mm (3/4 in)7 s11 s2 min[2]
32 mm (1 in)8 s12 s4 min[2]

PP-R makers publish their own charts, one maker citing the DVS 2207 Part 11 guideline for socket welding.[3]

3 Limits

A fused joint only works between compatible materials: PP-R products are made to be fused to pipe of the same PP-R or PP-RCT material, not a different plastic.[2] Over-inserting the pipe in the heating tool narrows the bore.[2] Connections from fused piping to copper, PEX or threaded parts are made with the maker's transition fittings. See which pipe for which job for where these pipes are used.

See also

  • PP-R pipePolypropylene random-copolymer pressure pipe, joined by heat fusion, used for plumbing and hydronic systems mostly in larger buildings.
  • Polyethylene water service pipeFlexible black or colored PE tubing buried between the water main or well and the house; cold water only.
  • Push-fit fittingsFittings that seal by pushing tube into an O-ring and locking device; covered by ASSE 1061 for PEX, copper, CPVC and PE-RT.
  • PEX crimp ringsCopper rings squeezed around PEX over a ribbed insert fitting; made to ASTM F1807 or F2159 and checked with a go/no-go gauge.
  • PEX clamp (cinch) ringsStainless steel bands with a tab, closed by a ratcheting tool over PEX insert fittings; an ASTM F2098 alternative to copper crimp rings.
  • PEX expansion fittingsFittings joined by stretching PEX tubing and a ring, then letting the tube shrink back onto the fitting; ASTM F1960 and F2080.

References

  1. Plastics Pipe Institute, "Socket Fusion" — plasticpipe.org
  2. Red-White Valve Corp., "Fig. 500AB Series PP-R and PP-RCT Valve Installation Instructions" (2025) — redwhitevalvecorp.com
  3. aquatherm GmbH, "aquatherm green pipe: welding parameters" — aquatherm.de
  4. ASTM International, "ASTM F2620-20, heat fusion joining of polyethylene pipe and fittings" (2020) — store.astm.org
  5. ASTM International, "ASTM F2389-21, pressure-rated polypropylene piping systems" (2021) — store.astm.org