PVF Reference Library · Measure & Identify

How to Identify Pipe Material in the Field

Pipe material can often be narrowed down in the field with markings, color, a magnet and, where allowed, a spark test. This sheet explains each check and its limits.

Ref PV-0068ASTM A53ASTM A312

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

What it is

Carbon steel, stainless steel, galvanized steel, cast iron, ductile iron, copper, brass and plastic pipes can look alike when painted or dirty. Fittings, gaskets and filler metals must match the pipe material, so it must be identified first.

Field checks narrow the options. They do not prove the grade. For certain identification, use the mill test report (MTR) tied to the heat number, or a positive material identification (PMI) test with an XRF or OES analyzer.

How to identify

Read the markings. Steel pipe is stenciled or stamped with spec, grade, size and heat number. See How to Read Pipe Markings and Heat Numbers.
Look at the surface. Galvanized pipe has a dull gray zinc coating, sometimes with a spangle pattern. Black steel pipe has a dark mill coating. Stainless has a bright or matte silver finish without rust.
Use a magnet. Carbon steel, cast iron and ductile iron are strongly magnetic. Common 300-series stainless is not magnetic or only slightly magnetic where it was cold-worked or welded. 400-series stainless is magnetic. Copper, brass, aluminum and plastics are not.
Check weight and sound. Cast iron is heavy and rings dull. Plastic is light.
Spark test (only if allowed). Touch a grinder to scrap or a hidden spot. This makes sparks and damages the surface. Never spark test in a hazardous area or on pipe in service without a permit.

Field check table

Material	Magnet	Look	Spark pattern (if tested)
Carbon steel	Strong	Black or painted; rusts	Long bright yellow-white streams with bursts
Galvanized steel	Strong	Dull gray zinc coat	Steel sparks after zinc is removed
300-series stainless	None to slight	Silver, does not rust readily	Shorter, fewer bursts, more orange
400-series stainless	Strong	Silver, may rust lightly	Similar to stainless above
Cast iron	Strong	Rough cast surface, bell ends	Short red streams
Ductile iron	Strong	Often cement-lined, bell and spigot	Short streams
Copper and brass	None	Copper or yellow color	No useful sparks
PVC, CPVC, PE	None	Plastic, light, printed	Not applicable

Key points

A magnet cannot tell 304 from 316. Use markings or PMI.
Coatings and paint hide color. Scrape a small test spot only with permission.
When in doubt, treat it as unknown and get the MTR or a PMI test.

Common mistakes

Calling any non-magnetic pipe 316 stainless.
Using galvanized fittings on stainless or copper lines.
Spark testing near flammable material.

Governing standards: ASTM A53 and ASTM A312 (pipe specifications and marking); ASTM E1476 (guide for metals identification and sorting); the mill test report for the heat.

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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