The answer is yes, galvanized pipe can be repaired under certain conditions.
Galvanized pipe is iron pipe coated with zinc to prevent corrosion from environment elements such as dirt when it is underground and moisture/humidity when used indoors. Until 30 or 40 years ago galvanized pipe was used extensively to supply water to homes and for the piping inside the house. Although it was one of the most durable products of its time, over time the zinc coating on the interior of the pipe can deteriorate causing the pipe to erode from the inside and eventually break/leak. Often the leak will occur where threads have been cut into the pipe because 30% to 40% of the material was removed when cutting the threads making this area thinner and weaker than the rest of the pipe.
Although every job has a different set of circumstances that can affect the outcome of a repair, it may be possible to repair a leaky/broken galvanized pipe. There are two areas where a repair may be the best choice, in a wall/ceiling/crawlspace or underground. However, every repair stands on its own merits and there is no set standard when it comes to repair of galvanized pipe. A broken galvanized pipe is often repiped due to several factors. If the pipe passes through a slab or footing and the pipe is in direct contact with concrete there is no way to determine the condition of the pipe. Also, although a visual inspection may indicate the adjoining pipe is in good condition, there is no way to inspect the interior of the pipe which may have eroded over time. Of course the longer the pipe has been in service the greater the likelihood that the repair will not be successful. The biggest hazard of a galvanized repair is that when working on the pipe you may disturb and damage the pipe several feet away from where you are working.
A leak/break in a wall, ceiling, attic or crawlspace may be repairable but this repair is subject to several conditions. To repair the pipe you must either be able to remove the pipe from two existing fittings and thread in a new piece or the damaged section of pipe must be cut out, the cut pipe ends rethreaded in place and a new section of pipe installed. The biggest problem with the second method is it can be extremely difficult to successfully cut new threads into the pipe with limited working room. Also the pipe may be so corroded inside that the repair process causes a break in an adjoining section of pipe.
Repair of a pipe in the ground is subject to the same methods used for fixing a pipe in a wall or ceiling but has the added hazard of jack hammering the floor and digging up the pipe to expose it to work on. Either of these actions can cause the pipe to vibrate and a corroded pipe may break or begin to leak in one or more additional locations. Additional breaks/leaks usually will not be noticed until water is turned back on after the original repair is complete.
So while a repair to a galvanized pipe may be possible if the adjoining pipe is in good condition, the possibility of additional damage caused by working on a deteriorated pipe makes the repair an iffy proposition.