GI Pipes in Sri Lanka: Classes, Sizes and Uses Explained

GI (galvanized iron) pipe is steel pipe with a zinc coating that fights rust — which is why it has stayed the default choice for Sri Lankan plumbing, water pumping and fencing for decades. But "GI pipe" on a price list covers three different wall thicknesses, and picking the wrong class is the most common buying mistake we see.

The three classes: A, B and C

• Class A (light): thinnest wall. Fine for low-pressure work like fencing tubes, handrails and cable protection — not for pressurised water lines.
• Class B (medium): the everyday plumbing class. Domestic water lines, bathroom and kitchen plumbing — the standard choice for houses.
• Class C (heavy): thickest wall, highest pressure rating. Deep well and pump riser pipes, high-pressure lines, and structural jobs where strength matters.

The classes share the same outside diameter, so fittings interchange — what changes is wall thickness and the pressure the pipe survives.

Common sizes and where they fit

• 1/2 inch (15 mm): tap connections, single-fixture water lines
• 3/4 inch (20 mm): standard house branch lines
• 1 inch (25 mm): main house supply lines
• 1 1/4 – 2 inch (32–50 mm): pump delivery lines, larger supplies
• 2 1/2 – 4 inch (65–100 mm): deep well risers, irrigation mains, industrial lines

Hot-dip vs pre-galvanized

Hot-dip galvanized pipes are dipped in molten zinc after manufacture — the coating is thick, wraps every thread and cut edge, and is what you want for plumbing and anything outdoors. Pre-galvanized sheet is zinc-coated before the pipe is formed and welded, leaving the weld seam as the weak point for rust. For water lines and coastal sites, insist on hot-dip; the small price difference is paid back many times over in pipe life, especially within salt air range of the coast.

Three checks before you buy

• Match the class to the job: Class B for plumbing, Class C for pump and pressure work — never save on wall thickness for a pressurised line.
• Check the coating: an even, dull-grey zinc layer inside and out. Bright shiny patches or bare weld seams mean a thinner coating.
• Threads matter: clean, fully formed threads make leak-free joints. Rough threads are the top cause of weeping joints that call for rework.

FAQ

Can GI pipes be used for drinking water? Yes — zinc-coated steel is accepted for potable water lines, which is exactly why Class B GI remains the standard for house plumbing in Sri Lanka.

GI or PVC for a house? GI handles heat, impact and outdoor sun far better; PVC is cheaper and never corrodes. Most houses use GI for the pressure lines and exposed runs, PVC for concealed drainage.

Seegaan stocks G.I. pipes in Heavy and Medium classes alongside square tubes and MS pipes in Colombo, with island-wide delivery. For a quote call +94 11 239 6384 or message us on WhatsApp.

AI-generated (Flux via Writeseed), 2026-11-10