An epoxy and fiberglass wrap can repair steel pipes while submerged underwater. Repairing small holes in pipes by wrapping them is sure to be much less expensive and disruptive than replacing bad sections of pipe. Divers must have access to the circumference of the pipe and the pipe must be free of its contents to prevent contamination and allow for the wrap to seal the leak.
As always, surface preparation is very important, and is demonstrated in the video with the grinder. The epoxy must form a good bond with the substrate material, not the rust and scale that is on the outside of the pipe.
Jeff Longmoore of TFT demonstrates how this repair is performed in a Youtube video, but does so in a dry environment rather than the actual underwater one.