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

 

[ash9144]

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.

 

[foodprojengr]

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.

 

[ash9144]

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.

 

[foodprojengr]

What material do you recommend?

 

[tickle]

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.

 

[foodprojengr]

What metal would recommend. Hastelloy?

 

[ash9144]

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.

 

[foodprojengr]

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.

 

[MJCronin]

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

 

[foodprojengr]

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

 

[sparky970]

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

 

[foodprojengr]

Lined with what?

 

[ash9144]

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.

 

[foodprojengr]

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.

 

[BenThayer]

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.

 

[foodprojengr]

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.

 

[tickle]

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?

 

[foodprojengr]

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

 

[moltenmetal]

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).