Flanges ok for Sulphuric acid? 4

[foodprojengr]

I'm overseeing a project where we're running 1 1/2" SS316 pipe that will transport 20% sulphuric acid from a tote via a chemical pump to the top of a makeup chest (tank). There will be, I believe, 4 or 5 90 deg turns.

Is it ok, in your opinion. for us to use flanges, or should it be welded only to prevent leaks. It would be difficult due to space constraints to do all welds.

Thanks

 

[foodprojengr]

moltenmetal,

Are you saying don't use Alloy 20 because it's too expensive? I don't understand your comment.

Can you recommend a good vendor resource that can give me a non-metalic recommendation, which you seem to be suggesting would be preferable to Alloy 20. I need guidance on how to adequately handle the fittings.

It is pilot plant scale (less than 100 ft of linear pipe) but we also want to make sure we don't have a problem with a forklift running into it or it otherwise being compromised. Our main concern is safety, price second.

Thanks in advance.

Dave

 

[foodprojengr]

Another question. When we're diluting 100% sulfuric acid to 20%, we should be adding acid to water, not the other way around, correct?

 

[ash9144]

Wow you're diluting to that strength on purpose too? I do not envy you.

Laboratory protocol is to add acid to water. This is difficult in larger scale since you aren't mixing in a glass beaker.

The more dilute the more corrosive so you need to look at materials of the mix vessel, the interface point between acid and water and how to remove dHmix.

 

[foodprojengr]

What do you mean by dHmix?

 

[moltenmetal]

A pipeline which is corroded through due to inappropriate materials selection is no safer than one which has been physically compromised by a forklift.

PP- or teflon-lined CS pipe will give you both corrosion immunity and mechanical robustness at less cost than A20. Look at

http://www.resistoflex.com

for some info on the system. You can get TFE-lined hoses as well as pipe and flanged fittings, with the liner wrapping over the flanged ends so that they're entirely TFE-lined on all wetted surfaces.

Dilute sulphuric is very hard on metals and alloys- any of them aside from perhaps tantalum. And you can't afford tantalum, as much as you want to promote safety over cost.

You can protect against the forklift with routing, bollards etc. A "motivated" forklift can destroy the best-designed piping system, whatever you make it out of!

Have a look at

http://www.chemline.com

, who have an excellent chemical resistance guide for plastic materials.

Diluting sulphuric is going to be another matter entirely. You need to not only worry about the corrosion due to the varying concentration, but you also have to worry about removing the enormous HEAT OF DILUTION.

 

[ash9144]

Heat of mixing acid and water

It is substantial

If you have a senior engineer at your company you should really ask for some help on this one.

You shouldn't be relying on vendors and a forum of people you don't know for such detailed engineering solutions.

Sulfuric is nasty stuff and things can go badly quickly

 

[KiwiMace]

I've attached a useful doc covering only the 64% to 100% bulk supply concentrations. There is a useful chart on page 6 showing the reaction rate with carbon steel pipe.

Big spike at 83%.

 

[foodprojengr]

We're going to use Alloy 20. Any suggesitions for if it should be Schedule 40 or something else?

 

[foodprojengr]

We're blending 50 gallons of 98.7% sulfuric acid with 200 gallons of water. How do I calculate the heat of dilution?

 

[moltenmetal]

OK: there's asking for help, and there's expecting others to do the work for you.

I think you're crossing the line with that kind of question, if indeed your label of "chemical" is accurate.

 

[skearse]

Smith & Van Ness has all the help you need...

 

[foodprojengr]

moltenmetal,

You're right. Sorry for my laziness. I'm back in engineering after an 8 year stint running a business. I appreciate very much everyone's help on this issue.

 

[RayA1004]

On the heat of mixing (dilution) issue - there are Enthalpy diagrams available that can fairly easily allow you to calculate the final temperature of a mixture of any strengths of sulfuric (from 0% to various oleum concentrations). This chart can also demonstrate why the "Add Acid To Water" rule makes sense.
On the mixing ratios - you mention 50 gal of 98 acid to 200 gal of water to get 20% acid - I suggest you consider the specific gravity of that acid.