Plumbing nightmare!!

Wanted to see why my hot water valve keep leaking. I tried replacing the valves, but it continuted to leak. With further investigation, I saw that the part that screws into the metal pipe had a crack in it. This is the small metal part that the plastic washer makes contact with in order to stop and/or start the water flow. (I don't know the technical term) The are included with new valve system. When I tried to remove it with a large screw driver, it started to strip. I can't get it out and now the water leaks more. I have tried WD40 to lossen it up, but it is now stripped beyond gripping. I fear I will have to replace the entire pipe in order to fix this problem. The challenge with this is that the pipe is over 50 years old and they are metal welded pipes.

Please let me know if there is any other alternatives for me. Thanks.

A bit unsure about exactly what you are trying to remove with a screwdriver, but if you are working on a hot water faucet at you sink, that would take a pipe wrench. Also, WD-40 is good stuff, but it is not a penetrating oil. The best penetrating oil is PB Blaster. Also in a spray can, it works pretty well. However, a faucet will still require more force than a screwdriver. Not sure what you mean by metal welded pipe, but that's the original pipes in a 50 year old house, it is most likely galvanized steel which is threaded screwed together, not welded. The only pipes that one might think of as welded are copper pipes that are soldered together. At that age galvanized pipe is about at the end of its life as they become corroded and rusted. If you put too much pressure with a pipe wrench on the fitting, you could break the pipe and then you'd really have a nightmare! I believe you should consider a professional for this job. He will have the right tools and knowledge to do the job right, and he could analyze the pipe condition and advise you on that as well.