How to Connect Metal Pipe to Plastic Pipe

Situations requiring the connection of metal and plastic pipes are familiar to homeowners and apartment dwellers needing to repair cold/hot water supply or sewage systems. This is often necessary when connecting internal plumbing (water supply, heating, sewage) to centralized pipelines, replacing damaged pipe sections, or installing appliances like washing machines, boilers, or showers in older buildings.

Connecting Metal and Polypropylene Pipes Without Welding

Due to material incompatibility, two primary methods are used:

1. Threaded Connection: Suitable for pipes up to 40 mm in diameter. Not recommended for larger pipes, as threading requires significant physical effort.

Threaded Connection Methodology

The process follows these steps:

1. Cut the metal pipe.
2. Apply lubricant and thread the pipe using a die or threading tool.
3. Clean the threaded area from metal debris.
4. Wrap the threads with PTFE tape or hemp fibers coated with silicone grease.
5. Screw a specialized fitting onto the metal pipe (metal end with internal threads and plastic adapter on the other side).

First, hand-tighten the fitting, then test the system for leaks. Finally, solder the polypropylene pipe to the plastic adapter.

Union Fitting ("American")

A popular method using a two-part adapter with external/internal threads (metal and plastic sides). Key advantage: easy disassembly. Requires a soldering iron for installation.

Nipple Fitting

A plastic sleeve with embedded steel threads. One end screws onto the metal pipe, while the other is soldered to the plastic pipe. Sealed using hemp or PTFE tape.

Flexible Metal Hose

A hose with sealing collars and flare nuts. Used for connecting pipes in different planes or at a distance. Requires a nipple fitting for plastic connections.

Flanged Connections

Steel loose flange is widely being used to connect pipes exceeding 40 mm in diameter. Sealed via raised face flanges with rubber or paronite gaskets. Advantages:

• Easy installation;
• No specialized tools required;
• Option to install valves between flanges;
• Easy disassembly.

Flange types:

• Flat face (for pipes up to 300 mm);
• Tapered face (over 200 mm);
• Flat face with tapered transition (for enhanced strength).

Other Connection Methods

• Clamps and Couplings: Used for sewage systems.
• Gebo Fitting: Features an internal rubber seal. Installation involves compressing rings with flare nuts.
• Rubber Hose: A DIY method using hose segments secured with metal clamps.

UTMK Company has offices in Poltava, Boryspil, Kyiv, Zaporizhzhia, Dnipro, Kherson, Chernivtsi, and Polish cities: Warsaw, Kraków, Łódź, Poznań. Wide range of pipes and fittings available for wholesale orders with delivery across Ukraine and Europe.