With threaded connections and a choice of sizes, it’s easy to create projects from the black pipe and fittings found at home improvement stores or in scrap metal piles.
But can you weld black iron pipe?
Its unique feel and appearance add a great vintage/industrial look to any plans—but do you have any idea what the black coating is?
Let’s find out what black iron pipe is all about.
Welding black iron pipe
You can weld black “iron” pipe because it’s made of mild steel, not iron. Black steel pipe can be welded using any welding method used for steel. This includes MIG, flux core, TIG, and stick arc welding.
But black-pipe fittings are made of malleable black iron. Black-iron fittings are difficult to weld without causing damage to the fitting.
What is black metal pipe?
Often mistaken for cast iron because of its heft and dark appearance, they make black steel pipe of mild steel. It’s usually low-grade and not galvanized.
With good corrosion resistance and strength, they commonly use black pipe for natural gas and propane lines, steam lines, and fire sprinkler systems.
The phrase “black steel pipe” is a generic term rather than a specification. It’s used in the trades when referring to regular steel pipe rather than a galvanized steel pipe.
What is the coating on black steel pipe?
The manufacturing process results in a dark iron oxide coating on black steel pipe. This coating improves corrosion resistance over bare metal.
To further inhibit rust, manufacturers may use a variety of coatings such as coal tar enamel, lacquer, and oil.
Is it safe to weld black pipe?
Yes, because black pipe isn’t galvanized with zinc, there’s no risk of creating poisonous zinc-oxide fumes while welding. Normal safety precautions are sufficient.
Removing mill-scale and other manufacturing coatings (inside as well as outside) is a good practice to reduce fumes and ensure a quality weld. It’s always a good idea to provide adequate ventilation and use a respirator.
Is black malleable iron weldable?
The heating of white cast iron for days creates malleable iron with beneficial properties. Black pipe fittings made of malleable iron are tough with good resistance to wear and shock.
“If malleable cast iron is heated above its critical temperature, approximately 1700℉ (925℃), the carbon will recombine with the iron, transforming back into white cast iron.“L. Jeffus “Welding Principles and Applications” (8th Edition, p.668)
So, black iron fittings are not good to weld because the heat of welding will change their characteristics. The fittings become brittle and prone to cracking.
Brazing, or braze welding at a temperature under 1700℉ is a good way to join iron fittings with black steel pipe.
Another alternative is to use weldable forged iron pipe fittings like these socket weld fittings.
Can you weld black pipe to steel?
Yes, black pipe is mild carbon steel. You can weld it to other carbon steel using routine steel-to-steel welding methods.
This guy makes it look so easy in this fascinating video:
Because it’s plain old mild steel, you can weld black iron pipe, also known as black steel pipe, using whatever welding method you prefer for steel.
And, with proper cleaning and preparation, there is no additional risk when welding black pipe.
However, malleable iron fittings are difficult to weld, so brazing is a better way to go. Otherwise, you can use socket weld fittings.