Pipe joints in cast-iron water mains Which joint type is most commonly used for cast-iron (CI) water-supply pipes in distribution systems?

Introduction / Context:
Joining methods for water pipes affect leakage, installation speed, and maintenance. Cast-iron (CI) pipes have historically used bell-and-spigot (socket and spigot) joints as the default connection in distribution networks.

Given Data / Assumptions:

• Traditional CI pipelines for potable water distribution.
• Typical jointing materials: lead caulking or rubber rings.

Concept / Approach:
Socket and spigot joints provide flexibility for thermal movement and minor settlement, are straightforward to assemble, and have long field experience. Flanged joints are used mainly at appurtenances (valves, pumps) and not for long runs. Dresser couplings are repair/transition fittings. Flexible expansion joints are special fittings, not the general joint type. Welding is not applicable to CI pipes.

Step-by-Step Solution:

Verification / Alternative check:
Standard CI pipeline catalogs specify bell-and-spigot as the routine joint, with accessories as needed.

Why Other Options Are Wrong:

• Flanged: for equipment tie-ins, not long distribution runs.
• Dresser couplings: repair/transition joints.
• Flexible expansion: special movement accommodation, not general use.
• Welded butt: not used with CI material.

Common Pitfalls:
Overusing flanged joints in buried mains; they are costlier and less tolerant to ground movement.

Final Answer:
Socket and spigot joint (lead or rubber gasketed)