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HCl corrosion resistance using Platinum group metal coatings

HCl corrosion resistance using Platinum group metal coatings

(OP)
thread338-315503: HCL corrosion of various metal types

Although various SS alloys can work well with wet HCl gas and liquid HCl there are certain coatings that can also protect against HCl corrosion of some steels . Various Pt group alloys are highly resistant to HCl as is Ta.
The difficulty is the high melting point of these metals and in getting a continuous , defect free coating at a workable thickness . Some of these metals are also either too soft or too brittle when used as pure materials . Alloys seem to work best .

Does anyone have experience with Platinum group coatings for HCl resistance ?

Coating must flex with a bending part such as a leaf contact or spring .
Concentration above 28% , temp. 250 ℃ .

RE: HCl corrosion resistance using Platinum group metal coatings

Briefly used tantaline but not sure how it would work on a flexing par or how much hydrogen embrittlement (which you'd expect with tantalum at high HCl concentration and high temps like 250C) would matter. Had a valve with it but one small knick through the coating and it was basically game over.

RE: HCl corrosion resistance using Platinum group metal coatings

(OP)
Tried Tantalize and had the same problem . Not durable enough for parts with contact to hard surfaces.
Thanks for the reply.

RE: HCl corrosion resistance using Platinum group metal coatings

How big is this part? What is mechanically required from it? That is very hot for such a concentration, and adding in a mechanical abrasion mechanism I'm not sure you have much, if any, options. Too hot for long term fluoropolymer. Even a pure Ta or Ta alloy like Ta2.5%W if strong enough would struggle after some time I think from hydrogen embrittlement. Graphite is hardly flexible enough plus no resin will last at those temps. Maybe a silicon carbide can withstand the acid but again, not going to be flexible!

I will be watching this, I've got some applications with hot HCl (36%, 180C, 160psi) and our options are very limited even at these conditions, and I don't have nearly as difficult "flexibility" requirement. Please share if you do come up with something!

RE: HCl corrosion resistance using Platinum group metal coatings

(OP)
Part is a torsion spring w. Max 180° rotation .
Must last 12,500 reps.
Made of super alloy w. High Cobalt & Moly.
My thought was either a sacrificial coating or pure barrier w. Platinum group metal alloy.
We are experimenting with various combinations now.
Corrosion occurs on outside dia. at about 150-200 reps Max .
Pt itself may work but chlorides ware present and seawater .
The only other HCl " impervious" metals would be Pt group and other nobles.
Perhaps Au ?
The HCl remains liquid due to high pressure .
Any info on high concentration HCl condituions is appreciated .

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