I don't know what kind of steel pipe you are referring to but I doubt if it is of the same quality as the steel your barrel is made up of. It may hold for several shots, but if it fails, you will find that it may explode like a small grenade, spraying metal in all directions. If your lucky it may just fly off the muzzle and land down range in one piece. But considering that you are attempting to plug up the holes in the muzzlebrake, I doubt if the latter will occur. Take some electrical tape and wrap it several times around the muzzlebrake and then fire it. That will safely give you some idea of what will happen if your steel sleeve fails under pressure.
If you don't like the muzzlebrake you can sell the barrel and get something you do like, or find a gunsmith that can build you a thread cap for the barrel you have, so you use the brake at the range and the thread cap in the field.
Please don't use the steel pipe, it will just cause you lots of grief later.
GH