Welding Tips and Tricks

Hi all,
job I'm booked in for is to make up some new stainless steel cooling coils to replace these rotted out galvanised steel coils.
All good.

The rusty coils came out of this stainless steel tank which now has rust hanging off it:
Looking for ideas please to clean up the tank to shiny without causing it to rust.

Wow - you do get some star jobs ! - nothing mechanical is going to be good as it will likely embed iron / rust into the surface ( but you could just try a poly strip disc with light pressure to see ) which leaves you with blasting - I've done it & should work OK but very slow & a shape like that means you will be wearing most of it ! - chemical can work but the only commercial easy to buy product here is likely unheard of where you are which leaves electrolytic as the only other viable way I know of - think that is the least outlay method I'd try - I don't have any stainless that contaminated to test it on for results & time scale but I think it would be fairly quick - if you don't have a bought unit they can be improvised quite easily - or if you plugged the outlet & filled it with liquid it could be done by the reverse plating method using an electrolyte as simple as sugar soap solution.

2-pronged attack likely needed...

Get all the loose rust off of it and make sure you wash away any loose rust particles that can be a source for new contamination. Grinding and blasting the rust should be used with care as it can drive the rust particles deeper into the stainless surface, but others likely will have experience with that and perhaps more specialised blasting media.

Then a chemical 'attack' with nitric / hydrofluoric acid pickling to chemically eat away the rust particles until they are all gone. Of course any pitting and surface un-evenness caused by the rust contamination on the stainless will not go away so it may keep looking grey and blotchy. You should then be able to work on the surface with polishing gear for stainless surfaces to get rid of most of the pitting (if present).

Once the whole stainless container is nice and smooth and shiny again then finalising with a passivation solution (also often nitric acid but with extra chemicals) should give it the best corrosion resistance for the future. And make sure to keep any airborne steel/ferrous particles away from the container as you work on it or you end up with 'all new' rusty spots

Bye, Arno.

We will want pics of the finished product. Looks real interesting!

https://summitbrands.com/iron-out-rust- ... rs/powder/
This stuff is pretty safe. I mix it in with our water softener pellets to keep the rust stains out of the water fixtures. Check with a water treatment company. They make iron filters that are like a water softener set up that strip iron out of the water. You might be able to pump water from the tank through one. You can also get the liquid used to clean the iron out of the filter sand I think it’s potassium permanganate.

https://www.uswatersystems.com/blog/201 ... move-iron/