How To Install Black Iron Pipe

Difficulty:Ambitious to Expert

Black iron pipe is used primarily for natural or propane gas runs. If you have to work on your gas line, it is essential that you know how to deal with black iron pipe. Remember, always turn off your gas main before you do any work on the line. The smallest spark and smallest leak can cause an explosion. As usual you should check with local authorities when installing gas pipe.

What Is Black Iron Pipe?

Black iron pipe is a steel pipe that is cut to length, threaded, and used in applications such as gas lines and water supply. Working with black iron pipe is demanding, and it can be expensive due to the variety of fittings and equipment needed to install it.

Black Iron Pipe Installation

Installation is work intensive but straightforward. First cut black iron pipe length after the run has been measured.

TIP:Doityourself’s plumbing consultant Wayne McCarthy suggests, “When measuring your next pipe on a horizontal run, screw two 90 degree elbows on hand tight on the verticals. Measure from the inside edge of the fitting on the vertical to the other inside edge and cut that length.”

Hold the pipe in a pipe vise on a stand and cut with a pipe cutter with rotary cutting blades. It is recommended that you use a high-quality cutting oil to help protect the pipe cutter.

Once the pipe is cut to length, deburr the cut end to remove the sharp ridge that will be present when the pipe is finished being cut.

TIP:Wayne says, “Make sure you have a large piece of cardboard or plywood under your cutting and threading area. This will save you a lot of cleaning later.”

The pipe must be threaded to make the proper connection. If you're lucky, you may find pipe in the required length at a plumbing outlet or hardware store. Threading is accomplished with a pipe threader. Use the proper die for the size of the pipe. Fit the die over the end of the pipe, and turn the handle a half turn at a time to cut the thread. Use a good quality cutting oil to protect the die. Continue threading until the thread is the thickness of the die. The thread will be cut on a taper when finished, providing a better seal. Stand the pipe on end when done to dislodge any pipe cuttings. Wipe the threads with a rag. Be careful here -- the pipe threads are very sharp.

TIP:Wayne adds, “You can buy a ratchet type threader for around $30 at discount tool places that will handle pipe up to 1-inch. As most places charge $5 or more to cut one thread this might be more economical in the end. Use a lot of cutting oil and catch it in a bucket with a large screen or strainer over it. This will prevent damage to the cutter and the threads and also allow you to re-use the oil. Backing the die off the threads is not necessary unless the threading die binds. Then back it off about one half turn and continue. To test your threads use a factory threaded end in a fitting and see where it snugs-up. Then cut one on your own and judge your threads from there.”

Attaching Pipe Fittings

Black iron pipe is joined using fittings and connectors. In the typical gas line installation, teflon tape should always be used on the threads to insure there are no leaks. Wrap the teflon tape around the threads, and insert into the fitting. Hand tighten the pipe and then use two pipe wrenches--one on the pipe and the other on the fitting--to tighten the connector.

TIP:Wayne cautions, “Make sure you are wrapping the Teflon tape in the right direction. Facing the end of the pipe you go in a clockwise direction with at least 4 wraps but no more than 6 or 7. Then apply some pipe dope in the same direction. Tighten at least 2 turns past hand tight and if the pipe is still loose you may have to re-cut the pipe.”

Supporting the Pipe

Once everything is in place, it is a good idea to test the pipes for leaks before hanging supports and hangers. Turn on the gas at the main supply. Brush water mixed with common dish soap on the joints. If there are any bubbles, tighten the connection further. Black iron pipe is very heavy, and requires a good deal of support, especially in a long run. Secure the pipe at every joint and fitting to floor joists or other structural members with pipe strapping. A good rule of thumb for supports is every 6 – 8 feet on horizontal piping.

TIP:Wayne says, “On gas pipe a small leak is not allowable and needs to be fixed. If you do have a leak, even us pros get them, you may have to take apart some things to fix the it. Do not try to tighten a joint in the middle of a run, as you are also loosening the joint on the other end.”

Repairing Existing Black Iron Pipe

There may come a time when you need to repair a pipe. Often this occurs at joints and fittings. Shut off the line at the source. Using two pipe wrenches, unscrew the damaged pipe. This can be a struggle – black iron pipe tends to rust and freeze the joints. You may need to use a compound such as WD-40 to free the rust. Reinstall in reverse order, using pipe joint compound and teflon tape.

If the pipe has a leak in the middle of a section, use a reciprocating saw to cut the pipe in two. Remove these two pieces with pipe wrenches. Measure the length and allow 1 inch to compensate for threading. Get threaded pipe at your local hardware, and using a union, reinstall the two pipes. Use Teflon tape and pipe joint compound in the installation. Turn on the supply and check for leaks.

Wayne McCarthy, professional plumber, contributed to this article.