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Flanges ok for Sulphuric acid?
4

Flanges ok for Sulphuric acid?

Flanges ok for Sulphuric acid?

(OP)
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

RE: Flanges ok for Sulphuric acid?

20% sulfuric will rapidly eat your SS316 pipe.  Use flanges only if necessary.  Prefab the pipe and minimize any field welds.

You need to change material of construction.

RE: Flanges ok for Sulphuric acid?

(OP)
My pipe supplier suggested SS316 was ok.  He faxed me a "Chemical Resistance Guide for Valves and Fittings" which showed SS316, Alloy 20, and Hastelloy all having an "A" rating for Sulphuric Acid up to 30%.

Please give me some type of reference to support your comment.  We've already purchased and begun welding the piping.

Thanks.

RE: Flanges ok for Sulphuric acid?

My point of reference is years of experience working in a sulfuric acid plant.

Check Perry's or something that does not come from the guy you are purchasing from.

Also you say it has an A rating up to 30%.  SS316 is good when above 85%.  For that matter carbon steel is fine at 90% and above.  Lower concentration acid has higher corrosion rates than higher concentrations.

RE: Flanges ok for Sulphuric acid?

(OP)
What material do you recommend?

RE: Flanges ok for Sulphuric acid?

Flanges that I have seen installed on 99% H2SO4 have been provided with splash collars to protect workers, particularly along high level pipe racks and valve stations.

RE: Flanges ok for Sulphuric acid?

(OP)
What metal would recommend.  Hastelloy?

RE: Flanges ok for Sulphuric acid?

Hastalloy B would be best.  C would be adequate as well.  Or lined pipe may be more economic.  Back to your original question, the lined pipe would introduce several flanges and as mentioned by tickle you can wrap those with splash guards.

RE: Flanges ok for Sulphuric acid?

(OP)
What about Alloy 20 (carpenter 20)?  THe Cole-parmer site lists Carpenter 20 as A (excellent) and Hastelloy as B (good).

What do you mean by lined pipe?

We're going to try weld this line so we don't have flanges (or minimal number) if possible.

 

RE: Flanges ok for Sulphuric acid?

123.....

Temperature and liquid velocity are also factors in the material selection process

Consider and evaluate flanged PTFE lined piping, install flange guards.... they are cheap

Some info here:

http://www.resistoflex.com/sulfuric.htm

The Resistoflex piping will not be cheap, but easier to install than welding alloy in the field.

Let me guess, this is your first experience specifying piping systems and you boss, a newly degreed MBA, wants results ...NOW!

More stuff:

http://www.complianceonline.com/ecommerce/control/product/~product_id=500881

http://www.eng-tips.com/viewthread.cfm?qid=17535&page=71

http://www2.dupont.com/Clean_Technologies/en_US/assets/downloads/Equipment_FAQs.pdf

Star..???

MJC

   

RE: Flanges ok for Sulphuric acid?

(OP)
Thanks to all who responded to this inquiry.  My main problem here was missing the basic point that lower concentrations of sulfuric acid are more corrosive.  I'm still waiting for a definitive recommendation from a supplier for piping material for 20% sulfuric acid, though the information I pulled from cole-parmer.com and a chart in a Dixon catalog I have seem to indicate that Alloy 20 (also called Carpenter 20) would be best, with Hasteloy as a 2nd choice.

In the last link of the last post, it states on pg. 5 that:

Q.
When should I use stainless steel vs. carbon steel?
A.
Stainless steel should be used in place of carbon steel if iron contamination
is a problem in your process. Also, stainless steel is acceptable for 100%
sulfuric acid - carbon steel is not. Stainless steel is also preferred at low
(<20%) acid concentrations. Stainless steel has a greater resistance to
"hydrogen grooving".


I'm confused by the comment that "Stainless steel is also preferred at low
(<20%) acid concentrations."

I thought less than 20% was more corrosive than 20% and that stainless (304 or 316) would be eaten up at those levels.

Would please help me understand this?

Thanks

RE: Flanges ok for Sulphuric acid?

We have 76% and 98% acid at our plant and use all lined pipe.  While all of our flanges have covers on them.

RE: Flanges ok for Sulphuric acid?

(OP)
Lined with what?
 

RE: Flanges ok for Sulphuric acid?

I don't know what site is recommending SS for low concentration sulfuric, but I do know from experience it will dissolve.  Depending on velocities and temperatures it could take only a few hours for this to happen.

A20 will work but it needs to be at correct velocities and temperatures.  Call your acid supplier or tech resources within company and get these recommendations.

The lined pipe is lined with Teflon (ptfe) and comes in 20' spools or specific length as specified.  All spools would be flanged and should have flange covers.  Also make sure your crews understand how to put it together.

Just curious, why do you even have 20% acid.  It is far better to leave at high concentrations.

RE: Flanges ok for Sulphuric acid?

(OP)
We do research and pilot plant testing for various clients and the ingredient makeup is given to us by our client.  I don't if it would be possible for them to get the same result with a higher % acid being added.

I've got an engineer from  one of the supply companies researching the correct velocity and temp for Alloy 20 for this application.  Thanks for the tip.

It sounds like it would be less complicated from an installation standpoint to install Alloy 20 than to go with teflon lined pipe.

Thanks.


 

RE: Flanges ok for Sulphuric acid?

i am not a big fan of plastic pipe but you might want to consider that as well.  for a small application (you did reference a tote) in low pressure service, it might suffice.

we have used some for moving acid to a cooling tower, etc.

but you have to watch out for UV ratings if outside as well.

RE: Flanges ok for Sulphuric acid?

(OP)
We're considering using pex which is a plastic and very inexpensive.  The problem is getting a flange connection and getting a pressure transmitter in the line.

RE: Flanges ok for Sulphuric acid?

What about a flange taping to attach the PT to plastic pipe.  Or if lap joint flanges are used a machined spacer in resistant material with a taping to sandwich between two flanges?

RE: Flanges ok for Sulphuric acid?

(OP)
We just found the pex supplier won't warranty the pipe for use with this material, so we're probably back to Alloy 20.

RE: Flanges ok for Sulphuric acid?

2
You can use ordinary non-crosslinked polyethylene (HDPE) or even PVC for this application, but PP or PTFE-lined carbon steel pipe is more conventional and robust against accidental damage.  20-30% sulphuric is hazardous enough, so non-metallics should be safeguarded as should flanges and other potential leak points.

Forget about high alloys- using unlined metallic piping for this service is equivalent to using a sledgehammer to jam a very square peg into a very round hole.  

If it truly is pilot scale and this is tubing rather than piping, there are plenty of non-metallic options worth pursuing as long as you keep both pressure and temperature limits in mind.

The stuff will come to you in an HDPE drum.

The problem with PEX isn't the PEX itself- it's the connections.  PEX is usually used in potable and hydronic water applications with brass hose barb type fittings using an external crimp or shrink ring.  Brass = NFG for your application obviously.  Some polysulphone fittings are available from some vendors, but they're limited.  External compression fittings are also available (see Jaco as one example).

 

RE: Flanges ok for Sulphuric acid?

(OP)
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

 

RE: Flanges ok for Sulphuric acid?

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

RE: Flanges ok for Sulphuric acid?

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.

RE: Flanges ok for Sulphuric acid?

(OP)
What do you mean by dHmix?

RE: Flanges ok for Sulphuric acid?

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 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 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.

RE: Flanges ok for Sulphuric acid?

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

RE: Flanges ok for Sulphuric acid?

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

RE: Flanges ok for Sulphuric acid?

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

RE: Flanges ok for Sulphuric acid?

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.

RE: Flanges ok for Sulphuric acid?

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

RE: Flanges ok for Sulphuric acid?

(OP)
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.
 

RE: Flanges ok for Sulphuric acid?

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.

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