Grooved method? Threads on the end of the pipe? There is no tube or pipe in copper with threads. You can end a copper pipe with a connection that is threaded to accept steel pipe.
Absolutely Not!
when joining to lengths of black steel it is necessary to use either Teflon tape or pipe dope, also called leak lock, this is not to seal the joint per say but the tape and doping act as a lubricant on the threads of the joint allowing for the pipe to be turned together tighter also the dope will dry and become a sealant
No, they are both iron based, you only need it between iron and copper.
Ribbed, bendable steel pipe used on combustion engine exhaust system.
There are instances when corrosion occurs at the junction of a carbon steel pipe and a brass valve. This is often the result of a pipe threading failure.
Black steel
For steel tube joining various methods are involved welding , adding a small bit of pipe slightly larger than two pies all having threads insert both pipes into the small bit pipe applying shellac varnish or araldite makes bonding. Another method is brazing and silver brazing
Not sure what you mean by pressure fittings. Threaded fittings for steel pipe are pressure fittings. Steel pipe with a 3/4" O.D. is known as 1/2" I.P.S. (Iron Pipe Size) pipe.
What kind of pipe, the inside or outside, or a tobacco pipe? If it is copper pipe, you can use an emery sand cloth or steel wool.
China is a large country to export steel pipe, if you want to buy steel pipe, you can import from China.
Mexico exports steel pipe and tubes