49 CFR §192.151

1. (a)Each mechanical fitting used to make a hot tap must be designed for at least the operating pressure of the pipeline.
2. (b)Where a ductile iron pipe is tapped, the extent of full-thread engagement and the need for the use of outside-sealing service connections, tapping saddles, or other fixtures must be determined by service conditions.
3. (c)Where a threaded tap is made in cast iron or ductile iron pipe, the diameter of the tapped hole may not be more than 25 percent of the nominal diameter of the pipe unless the pipe is reinforced, except that
   1. (1)Existing taps may be used for replacement service, if they are free of cracks and have good threads; and
   2. (2)A 1 1/4-inch (32 millimeters) tap may be made in a 4-inch (102 millimeters) cast iron or ductile iron pipe, without reinforcement.