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Galvanized Pipe and Fittings

Galvanized pipe is steel pipe coated with zinc to slow rust. It was once standard for water lines and is now used mostly for outdoor, structural, fence and some fire protection and air work. This sheet covers identification, where it fits and its limits.

Ref PV-0014ASTM A53ASME B16.3

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

Galvanized pipe is carbon steel pipe, usually ASTM A53, that has been hot-dip coated with zinc inside and out. The zinc corrodes first and protects the steel. Fittings are galvanized malleable iron to ASME B16.3 or galvanized cast iron to ASME B16.4, joined by tapered pipe threads. Sizes and wall thicknesses follow the same NPS and schedule system as black steel pipe. See the master guide to pipe sizes, schedules and wall thickness.

How to identify

Galvanized pipe has a dull gray to silver surface, sometimes with a crystal-like spangle. Black pipe is dark and oily. The stencil shows the standard (A53), grade, size, schedule and "GALV" or similar. Fittings are gray with a zinc finish and a raised cast marking. A magnet sticks to galvanized steel, which helps tell it from aluminum or stainless.

Where it is and is not used

Use	Typical status	Notes
Fence posts, handrails, structural frames	Common	Outdoor corrosion resistance
Dry-pipe and preaction fire sprinkler	Used where specified	Follow NFPA 13 and the project spec
Outdoor and non-potable water	Used in some areas	Corrosion and scale build up over time
Compressed air	Used in some shops	Zinc flakes can clog tools and filters
New potable water lines	Rare in new work	Copper, PEX and CPVC replaced it in most codes
Natural gas	Restricted by many utilities and codes	Use black steel or other approved pipe unless allowed
Welding without precautions	Not acceptable	Zinc fumes cause metal fume fever

Key points

Threading and cutting remove the zinc. Bare threads rust first. Use a zinc-rich paint on cut ends where allowed.
Joining galvanized steel to copper causes galvanic corrosion. Use a dielectric union or fitting.
Old galvanized water lines often restrict flow from internal rust and scale and can release lead from old service connections. Inspect before reusing.
Welding or torch-cutting galvanized steel needs ventilation and fume control. Remove the zinc at the joint where practical.
Use NPT threads and a thread sealant rated for the service. See the NPT thread chart.

Common mistakes

Using galvanized pipe for a gas line where the code or utility forbids it.
Connecting galvanized steel straight to copper.
Mixing black and galvanized fittings in one system.
Welding galvanized steel in a closed space.

Governing standards: ASTM A53 (steel pipe, black and hot-dipped zinc-coated); ASME B16.3 (malleable iron threaded fittings); ASME B16.4 (gray iron threaded fittings). Local plumbing, fuel gas and fire codes.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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