After thought a soldering iron is generally for soldering wires or electronic components on PCB boards or small projects like LED lights solar cells etc.
a repair of a pot pan or such is more brazing with a ox-acetylene rig or a torch with enough BTU's to heat the metal and brazing material enough to stick and if it is for cooking it needs to be food safe silver alloys.
Pipe has a range for black iron to stainless and many many alloys so welding butt joints or weld on fittings that bolt together with gaskets or seal rings. each requires a different rod and your welder may need / require AC or DC rods I like P5 / 6011 and 7018 I like a stick welder because I can store rods wire gets oxidized and splatters and it has a feed requirement that id fickle unless you have practice IMHO it is more versatile but not over long term and over complicated machinery.
PVC is great stuff but white PVC is damaged by sun rays it need to be buried or kept from direct sunlight of course that being said I have seen it last a long time I have used schedule 80 for air lines in the shop.
new connections types really not new but it has gone through several changes it's called PEX here is a link PEX connection system
Back in the day there was a law suit over I think it was a similar system but used plastic fittings and polybutylene pipe ??? anywho the fittings would break and the connections would leak, PEX looks like it may have solved the problems.
I have come to the conclusion it is better to run water lines direct to the fixture instead of running pipe in the attic or under the slab the less pipe in the walls or wall / attic spaces leaves less to break and flood it is also good to have drains or faucets and ball valves to shut off the water and back drain it from the home so if it is a cabin or summer home you do not come back to a swimming pool.
Dissimilar metals are the difficult ones to repair like cast iron the repair requires drilling the ends of cracks to relieve stress so it will not continue to crack like glass also if it is a casing for a lathe or some machine that is high tolerance it will never be the same / accurate / true running. it also requires preheating before repair
then there is like tin zinc magnesium pot metal metalized epoxy and a host of others that require special adhesives to bond them not everything can be repaired with superglue.
I helped a friend repair a black plastic fuel tank there is a special repair medium for that we tried it and it worked boy were we surprised repair cost 30 bucks a new tank a few hundred ++
I have repaired metal with beer can metal and pop rivets, 600 mile an hour tape electrical tape a stitching awl and sinew and tar plywood rubber sheet and bolts steel plate and chain boomers emergencies require desperate measures timbers block & tackle chain falls jacks and wedges turnbuckles cables threaded rod and anything else I could make use of.
If the day ever comes a junk yard is your best friend I have a 16 foot X 8 foot rack of all kinds of pipe steel rod I beam sucker rod EMT rebar etc etc sheet tin aluminum angle iron rail and track metal studs and trim boxes of sheet metal screws and another rack of wood 4x4's 2x and 1x lumber the reason I mention this is if you dont have it your stuck I bought a bucket of garage door hinges and another of garage door hardware and a stack of door rail as it has 2 inch angle attached to the side. Garage door sections can be used to build walls with 4X4s i have built shade covers for animals with them silicone caulk the seams and it's dry as a bone.all my animal buildings have angle iron cross bars with corrugated iron doors nothing animal has been able to get in yet. everything ahs a value and use I use a piece of railroad track for an anvil