Hi have surplus water feed and return pipes in my home. I can't isolate them so will need to freeze. House built 1970's. They're as far as can tell Carbon/mild steel pipe, 28mm dia. Wish to cap them off. Can I use brass compression fittings? Like in the pic. Or do I need to use steel fixings? Like a 28mm threaded plug. Local plumber wanted to order in very heavy compression caps at £24 ea. seemed a bit much. Advice appreciated. Thanks