HCL ACID AND STAINLESS STEEL TANKS

[rosshol]

Hi, I am a bit concerned. My engineers are builing a Stainless steel (316) tank to hold highly concerntrated HCL acid. I believe we would be best to use other material as the potential to eat through the stainless welds is high. I would appreciate a bit of advise.

Kind Regards

 

[mrtangent]

my understanding (depending on HCl conc) is that 316 is unsuitable for concentrated HCl.

If you want to check try an internet search on corrosion tables.

If the HCl is concentrated I would recommend the tank to be lined.

 

[Zoobie]

I agree with james1030bruce. In fact I don't recall ever seeing a SS hydrochloric acid tank (after working with 35% HCl for 6 yrs).

Below is something I found on-line:
All concentrations of hydrochloric acid will attack stainless steels because the acid destroys the passivity.

Lining may be an option but I would look at other materials. HCl tanks are often constructed of FRP. There are a whole host of resins you could use but you would be safe with Derakane 411 or the equivalent Hetron resin. If the tank is a small one than you may be able to get away with PP or something like it.

You must also give consideration to vapor pressure. Higher concentrations give off some really nasty fumes. Its been a while but I think the vapor pressure more than doubles going from 32% to 35%. You may need a vent scrubber on the tank.

 

[cub3bead]

High density crosslinked polyethylene or C276 are your choices for an unlined tank. See the following reference.

http://www.xpress-link.net/ChemResult.asp

Lots of info at PolyProcessing's site on storage of conc. HCl.

http://www.polyprocessing.com/

 

[ChemFemme]

We just had to replace a significant amount of SS piping (both 304 and 316) due to leaks caused by low concentrations of HCl over time. Our Storage tanks were FRP, but the piping and valves were not. Severe corrosion occurred mainly at the Heat Affected Zone of the welds over a period of ~2 years.

My advice is to steer clear of SS with any concentration of HCl. I believe 100% HCl would be acceptable; however, as soon as it's diluted to even 99%, you have free chloride ions that will attack the stainless.

 

[MJCronin]

rosshol,

In hydrochloric acid, stainless steels will pit and eventually fail. Some types of storage tanks that have been used sucessfully include: "Epoxy Vinyl Ester Resin" lined FRP, crosslinked HD polyethylene and rubber lined carbon steel.

Supposedly, there are "superaustenitic stainless steels" which may be used for storage or transport of diluted hydrochloric acid....I would stay with the "tried and true" and stick with an established tank design.

Is there a storage and handling guideline available from your acid supplier ? Dow chemical used to have one....

How many gallons of acid are you going to store and what will be the concentration and temperature ?

More information can be found on:

http://www.polyprocessing.com/pdf/literature/PositionStatements/HYDROCHLORIC_ACID.pdf

http://www.proco-fwi.com/index004.asp

http://www.hghouston.com/dcforum/DCForumID1/191.html

http://www.olinchloralkali.com/products/hydro_acid.asp

http://www.derakane.com

and best of all....

http://www.chlorineinstitute.org/Bookstore/ProductDetail.cfm?ItemNumber=2314

What kind of piping system will adjoin the tank ? what kind of pumps, valves, vents etc will you use ?

my opinion only....

-MJC

 

[praja]

Rosshol

ChemFemme is correct the free chloride ions will attack the stainless steel. The tank will pit and possibly leak. If you must line the tank go for your dual laminated PVC. Or even Rubber.

 

[Zoobie]

I just remembered an incident from way back. We had a plastic tank for 35% hydrochloric acid on an ion exchange skid. During commissioning some of the fittings on the outlet were found to be stainless. How were they found? Obvious corrosion (and not just a bit). When were they found? Within hours!

 

[bewdley]

Froma personal experience, on commercial HCl solutions (30 - 32 % w/w) I have used always PE (not necessarily reticulated) for small tanks below 30 °C, FRP (but choose the right resin) 30 to 70 °C. I presune reinforced PE to be an alternative. In one occasion I had to heat the HCl before the reaction to some 120 °C, and I used grade I titanium for the HEx and the pipes. Beware of solar radiation, I had PE tanks collapse due to that.

 

[schnipp]

You will need a fume scrubber.

You will need to consider piping. Try finding some lined pipe.

Wrap flanges for safety sakes.

Treat HCl with the utmost respect.