Black pipe is primarily usually used for gas supply in the home. It is mostly 3/4-inch in diameter and is threaded at each end. The pipes are connected with black-coated metal couplings. The couplings come in straight, 30-, 45-, 60- and 90-degree angles; "T"-shaped and cross-shaped couplings are also available, for connecting two or more pipes. The railing frame is first put together and then placed into concrete footings, to hold it in place.
Draw a diagram of the entire railing. Don't forget the vertical pieces of pipe at the bottom of the railing that will act as footings--make them 12 inches long. Take into account the required length and height of the structure. Also be aware that black gas pipe comes in pre-existing lengths, but irregular-length pipes can be cut and threaded at most major DIY stores. Contact the local store regarding the different lengths of gas pipe available. Once the diagram has been created, count the number of different length of pipes needed, as well as couplings to hold them together.
Buy all gas pipes and couplings. Place them on the ground so that they exactly match the diagram. Place the couplings between the pipes where the joints will go.
Apply thread compound to one thread at the first piece of pipe at one end of the structure. Screw on the coupling and tighten it with a pipe wrench. Apply compound to the second piece of pipe and thread it into the other end of the coupling. Tighten it with the wrench. Now continue in like fashion applying compound to threads, installing couplings and pipe, etc., until the entire structure has been put together.
Stand the railing up in the position where it will be installed. Mark the location of each of its footings on the ground. Remove the railing. Dig an 8-inch cubed hole at each mark. Place the structure back into position--its footings will enter into the bottom of each hole. Brace the railing at each side to hold it up. Use a level to make sure it is straight.
Mix and pour the ready-mix concrete and pour it into each hole. Make sure the concrete is level with the ground. Wait for it to dry completely, before taking off the bracing on the railing.