Materials for Low pH Slurry at Elevated Temperatures?

[wlc1]

I am currently looking at an application using a dilute sulfuric acid slurry with a pH of less than 1.5. The process may reach 500F and 700psig for extended periods of time. I am searching for a cost efficient piping material for this application. Today a large range of products are available, Alloy 20, Hastelly (multiple grades), 904L, Duplex, Super Duplex, Zirconium and Tantilum. These materials all have different corrsion rates (well published at lower temperatures)and prices. The process will require extensive field welding.

I would like to hear from others about their experiences they have had with similar operating conditions. Also a publication that may compare corrosion rates at elevated temperatures for a dilute sulfuric acid application.

 

[Goahead]

Would you consider ceramic piping instead?

http://www.welding-advisers.com/

 

[wlc1]

Thanks for the reply. At this time we do not want to go this root.

 

[wlc1]

Sorry, root should be route.

 

[stanier]

Have you considered glass lined steel?

 

[wlc1]

Stanier,

At this time we would like to avoid lined pipe.

 

[ApC2Kp]

wlc1,
One early article from Advanced Materials & Processes March 2000, by James S. Grauman and Tony Say, detailed the selection and application of titanium for autoclaves used in the High Pressure Acid Leach process for nickel laterite ores. Since then it seems several newer developments like Detaclad and nanostructured titanium oxide have been tested in pilot plants. A Google search of 'high pressure acid leach' brings up 266 items of interest.
Field welding of titanium has its problems, mainly keeping the oxygen out of welding area. A medium vacuum glove box at the construction jobsite will allow some "field welding" of titanium spools, even if spools are not being welded in the final installed position.

 

[moltenmetal]

The big question is: chloride? Do you have any? Do you have LOTS? And what else is in that solution? And how dilute is the sulphuric acid?

If it's a low-chloride system, there's at least some Fe in the solution and you're not in strongly reducing conditions, you may be into conventional "high pressure acid leach" type conditions as mentioned by the previous poster and commercially pure titanium will probably serve well. Acid addition dip tubes will need to be made of tantalum. Note that the ASME limit for Ti is 315 C, and the safe allowable stress is derated rapidly with temperatures approaching this limit.

If you have lots of chloride, you'll need titanium grade 7, and even that may not last forever. Crevice corrosion becomes a big problem.

Of course, your process may be nothing like HPAL for laterite ores and titanium might be a disastrous fit for your application. But at least this gives you a starting point for your materials selection research.

As to the welding of titanium, you don't need a glovebox- all you need is a skilled, knowledgeable titanium TIG welder with the right technique, an approved procedure, and suitable shield gas equipment.

 

[EdStainless]

I don't think that Ti will like the abrasion.

The use of Ta may be unavoidable, at least in the mixing section where high variations in concentration occur.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[moltenmetal]

EdStainless: if indeed it is a high pressure acid leach service, which it certainly sounds like it is, titanium is commonly used for this application and with excellent success. The only tantalum components are the acid addition dip tubes and block valves. And the titanium survives despite the abrasion you're concerned about.