The three primary joining methods are threaded connections, welded joints, and adhesive bonding. Each has distinct advantages, limitations, and suitability depending on material, depth, pressure, and environmental factors.

1. Threaded Connections.

Threaded connections involve screwing pipe sections together using male and female threads, often with a separate coupling (socket) or threads machined directly onto the pipe ends.

Key Characteristics:

Suitability: Primarily used for;

• Steel (carbon or stainless).

• uPVC, CPVC, HDPE (with molded or mechanical threaded fittings).

• Ductile iron.

Advantages:

• Ease of Installation/Disassembly: Simple to install without specialized heavy equipment or heat, and easily disassembled for maintenance or adjustments.

• Reusable in many cases.

• Generally less expensive than welding.

Disadvantages:

• Leak Potential: Higher risk of leakage compared to a well-executed weld, often requiring sealants (Teflon tape or jointing compound).

• Limited Strength: May not be suitable for the highest-pressure or highest-stress applications.

Common Thread Types for Boreholes:

API Round Thread and API Buttress Thread are common for steel casing in oil and gas and deep water well applications, offering good tensile strength.

National Pipe Taper (NPT) or British Standard Pipe Taper (BSPT) are common for general-purpose threaded pipe in various applications.

Flush Joint Threads are often used on PVC casing to maintain a consistent external diameter.

2. Welded Connections.

Welding joins pipe sections by melting the ends and allowing them to fuse, creating a permanent, leak-free connection.

Key Characteristics:

Suitability: Primarily used for steel casing and screen pipes.

Advantages:

• Superior Strength: Creates a very strong, robust, and permanent joint, often as strong as or stronger than the pipe material itself.

• Leak-Free: A properly executed weld provides a seamless, leak-proof joint, critical for high-pressure or critical applications.

Disadvantages:

• Skill Requirement: Requires highly skilled labor (coded welders) and specialized, costly equipment.

• Inflexibility: Permanent joint, making modification or repair difficult and time-consuming.

• Heat Impact: The heat from welding can cause distortion or change the metallurgical properties of the pipe material (Heat Affected Zone or HAZ).

Welding Techniques: Common techniques for pipe include TIG, MIG, and Stick (Shielded Metal Arc Welding). For large-scale production, methods like Electric Resistance Welded with High Frequency (ERW/HF) are used to make the pipe itself.

3. Adhesive/Solvent Cement Connections.

This method involves chemically bonding plastic pipes (most commonly u-PVC) together using a solvent cement.

Key Characteristics:

Suitability: Exclusively used for PVC and CPVC (plastic) pipes.

Advantages:

• Simple/Fast Installation: Relatively quick and easy to apply without specialized heat or tooling.

• Corrosion Resistance: The joint maintains the chemical inertness of the PVC pipe, resisting corrosion.

• Strong Bond for Plastics: Solvent cement chemically fuses the pipe and fitting surfaces to form a single, homogeneous piece.

Disadvantages:

Material Limitation: Only suitable for plastics.

Requires Careful Preparation: Proper surface cleaning and priming is essential for a reliable, high-strength bond.

Cure Time: Requires a set time before the joint can withstand pressure or stress.

Technique: Solvent welding uses a primer to soften the plastic surfaces and a solvent cement to fuse the pipe (spigot end) into the fitting (socket or bell end).