materials question: inox or pvc for stuff into contact with darkroom chemicals?

[Havoc]

I'd like to automate my Jobo a bit and was wondering if I should use inox or pvc for the material in contact with the chemicals. Inox I can have laser cut, I can weld it (hope it will be tight), it has a good thermal conductivity, reasonably easy to obtain sheet, tubes bolts and bits in it. But I have to treat it after welding. On the other hand, pvc is a lot easier on the tools, can be glued without problem, probably cheaper but it has a lousy thermal conductivity, I'll have to cut and shape everything myself (to measure and fit if I glue) and likely harder to find around here.

So what would be best?

My first idea was to have the water bad in pvc as it is straight flat sheet that can be glued. And the rest in inox for the conductivity and inertness. But then I'll have joints where the inox runs through the pvc.

[jose angel]

Good inox is bestir almost everything. PVC is easier, cheaper and probably more convenient in contact with chemicals. I`d use PVC.
But think that you need marine grade inox. With some usual kitchen type inox you`ll get rust points in a flash.
Don`t know if you need the best thermal conductivity everywhere. Let the water to do the work.

[Havoc]

Good point about the grade, I'll have to check on that. But it is the reason why it needs treatment after welding. And I know you should not use tools used for working steel but keep the tools for inox and steel separated. That's a complication as well.

Would alu be a possibility? No welding, but easy to work, cheap, can be glued. A bit between inox and pvc.

[jose angel]

No, in contact with some chemicals, aluminum is unusable. Don`t ask me which ones.
I tested it time ago when I found a nice aluminum bottle I filled -some weeks before- literally dissolved at the bottom. Cannot remember which chemical; anyway, this day I stopped using aluminum in the darkroom or the kitchen. Well, only for the expresso coffee maker (which BTW doesn`t resist dishwasher detergents, so I`m thinking to replace it with an inox one).
Now, only glass or good plastics in direct, continuous contact with chemicals.

[Phil Hudson]

Some sink manufacturers are using polypropylene instead of PVC now (I'm told it doesn't go as brittle or rigid with age and exposure to chemicals). Not sure if that is any easier to work with?

[Drew Wiley]

I have a big polypropylene darkroom sink. It was affordable, is chemically inert and almost unbreakable, but had to be heat-welded by an expert. It also warps a bit with temp changes.

[Pere Casals]

Both materials will be good, just see what way is faster while working like required. This depends on what you want to build and your tools...

May be you can combine both materials, glued PVC for piping.

But think that you need marine grade inox. With some usual kitchen type inox you`ll get rust points in a flash.

Marine grade would be AISI 316, higher in niquel and lower in chrome than AISI 304, both good enough for that, IMHO, the 304 is cheaper.

A ferritic stainless steel of the 4xx would have less resistance to corrosion, the AISI 430 is used for kitchen spoons etc

https://en.wikipedia.org/wiki/SAE_steel_grades

[jose angel]

FWIW, I have four inox sinks in two darkrooms; three of them made (supposedly) in 304 grade inox. So I ordered the fourth (years ago, custom made) in a higher grade steel.
I assume the problem is the inox quality, so two of them get rust points quite easily, and I have to check regularly for such points and clean them with a Scotch scouring pad. The smallest one is made of commercial kitchen steel (supposedly "plain" 304, from a well know quality manufacturer), always perfect since the first day.
The custom one (an enormous and insanely expensive sink) still show rust points from time to time. Not an issue at all in neither of them, they are used quite often, so I keep them all under control.
But if I neglect that rust points, I`m pretty sure they`d turn to holes (I have experienced it in other sinks).
I understand the issue here is the steel quality. Same "inox standards" doesn`t mean same "proofing quality". It`s hard to know how good the metal sheets really are in the custom built ones, and how good are the cheap ones from stamping manufacturers. They didn´t came with a certified compound label.
BTW, I`m thinking on replacing, -or maybe adding- a new one, for sure it will be plastic (glued PVC).

[Drew Wiley]

You need insulation board under a stainless sink or it will sweat condensation. I wouldn't bother with anything less than 316. Prefer the way I went. The fellow who made it typically welded lead sheets together for nuke reactor cores. His arms & neck were as big as thick as tree trunks. But he had one prosthetic leg. Last I heard about him, some bar bouncer tipped him off balance due to that leg. After he got back up, the bouncer didn't remember anything for another six months. But he was a friend of a friend, so I got that big sink very affordably.

[Havoc]

If I go with inox it will probably be 316L or 304L as those are both readily available and easier to weld. Most likely it will be mixed: inox for the chemicals and pvc for the water baths. Thanks for your input.