Here are some common materials used to make black pipe fittings:
Steel
Plain carbon steel is the most common material for black pipe and fittings. It’s durable but can rust over time.
Galvanized steel
Steel that has gone through a zinc galvanizing process to prevent corrosion. More resistant to rust than plain steel.
Black iron
Steel that has been painted or coated black from the factory for an finished aesthetic look. Still susceptible to rust underneath.
Brass
A copper alloy that is more expensive than steel but highly corrosion resistant. Commonly used for potable water lines.
Copper
Excellent corrosion resistance but costly compared to steel. Used for high pressure gas lines or long term indoor piping systems.
Plastic
Materials like PEX (cross-linked polyethylene) or CPVC (chlorinated polyvinyl chloride) are alternatives to metal that won’t rust but have limitations for certain applications.
Stainless steel
An alloy of steel with chromium that has superb corrosion resistance, even in harsh environments. More expensive than other options.
The most typical materials are carbon steel, galvanized steel and black iron due to availability and cost considerations, while brass, copper and stainless provide higher performance for specialized uses.