Pipe joint solution

Core challenges and preliminary preparation

Before connecting unthreaded galvanized pipes and PVC pipes, the following challenges need to be clarified:

1. Material differences: PVC and metal have different thermal expansion coefficients, and temperature changes may cause the interface to loosen.
2. Galvanic corrosion: Metal-plastic contact may accelerate the corrosion of the galvanized layer (dielectric isolation is required).
3. Size adaptation: The outer diameter (OD) of galvanized pipes and PVC pipes is inconsistent, and a matching transition joint is required.

Preparation:

Tool list: pipe cutter, deburring tool, tape measure, wrench, PVC glue, rubber coupler or compression joint.

Material inspection: Confirm that there is no severe rust on the surface of the galvanized pipe and no cracks on the PVC pipe.

Detailed explanation of connection methods

Rubber coupler (Fernco Coupling) – suitable for drainage and low-pressure systems

Applicable scenarios: non-pressure scenarios such as basement drainage and irrigation systems.

Advantages: No threads required, fast installation, low cost.

Steps:

Cutting and cleaning:

1. Use a rotary cutter to cut the galvanized pipe and PVC pipe to a flush position, ensuring that the port is free of burrs.
2. If the galvanized pipe is rusty, use sandpaper to polish it until it is smooth.

Install the coupler:

1. Loosen the stainless steel clamp of the rubber coupler and put it on one end of the galvanized pipe.
2. Insert the PVC pipe into the other end of the coupler and adjust the alignment.

Fix the clamp:

Use a screwdriver to tighten the clamp evenly to avoid uneven sealing caused by one-sided force.

Note:

1. Choose a coupler that fits the pipe diameter (such as a 2-inch pipe requires a 2-inch coupler).
2. Avoid using it in high temperature or high pressure environments, as rubber is prone to aging.

Compression Fitting – Medium and low pressure water supply system

Applicable scenarios: household water supply pipes, small pressurized irrigation systems.

Advantages: Strong sealing and can withstand a certain water pressure.

Steps:

Select adapter:

Purchase a compression joint for galvanized pipe to PVC (usually made of brass, with a metal compression ring on one end and a PVC socket on the other end).

Install the metal end:

Put the metal end of the compression joint on the galvanized pipe, tighten the nut, and use the compression ring to squeeze the pipe to achieve a seal.

Connect the PVC end:

Apply special glue to the PVC pipe mouth, insert the joint socket, and keep it for 30 seconds to cure.

Notes:

1. The outer diameter of the galvanized pipe must be strictly matched with the inner diameter of the compression ring. An error of more than 1mm may cause leakage.
2. Before the pressure test, it needs to stand for 2 hours to ensure that the glue is completely cured.

Flange Joint – Industrial or large diameter system

Applicable scenarios: factory pipelines, large drainage systems (pipe diameter ≥ 4 inches).

Advantages: strong pressure bearing capacity, easy to disassemble and maintain.

Steps:

Welding flange:

1. Weld a steel flange on the end of the galvanized pipe (rust-proof treatment is required).
2. Glue the PVC flange with bolt holes to the end of the PVC pipe.

Alignment and sealing:

Place a rubber gasket between the two flanges and tighten them diagonally with bolts to ensure uniform pressure.

Notes:

1. Welding must be performed by professionals to avoid the release of toxic gases from the high temperature of the galvanized layer.
2. Bolts need to be checked regularly to prevent rust and loosening.

Transition Cement – temporary or low-cost solution

Applicable scenarios: temporary repairs, non-drinking water systems (such as rainwater pipes).

Advantages: No additional joints are required, and the cost is extremely low.

Steps:

Processing the galvanized pipe end:

Grind the galvanized pipe end to increase the adhesion of the glue.

Apply transition glue:

Use PVC-Metal special glue (such as Oatey® Heavy Duty) to evenly apply it to the connection between the galvanized pipe and the PVC pipe.

Fixing and curing:

Press the two tightly and fix them with a clamp for 24 hours.

Notes:

1. Only suitable for low-pressure scenarios, long-term use is prone to failure.
2. Glue may contain harmful substances and is prohibited for drinking water pipes.

List of tools and materials

Summary

The connection between non-threaded galvanized pipe and PVC pipe needs to be flexibly selected according to the specific scenario:

1. Drainage/low-pressure system: Rubber coupler is preferred, which is low-cost and easy to install.
2. Water supply/medium-pressure system: Compression joint or flange is more reliable.
3. Temporary repair: Transition bonding can be used as an emergency solution.