×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

sulfuric acid piping

sulfuric acid piping

sulfuric acid piping

(OP)
I know this has been gone over before.
 I have recently had a piping failure with an acid system for ph level control. The piping is 316 stainless. The original piping appeared to be 1/2" socket weld but had a repair/replacement with threaded ball valves which were subsequently welded over the threads.
 The ball valves had begun to leak at the stem from ball deterioration.
 The line was repaired/replaced back to the last socket weld ninety using 304 pipe and fittings.
 This portion of the line had a catastrophic failure within 48 hours. The 304 pipe was eaten through in 3 places and one 4" nipple had split.
 This system uses a small diaphragm pump to move the 98% sulphuric acid about 40 feet to a 3" PVC riser
 Prior to the repair, the line was flushed with city water for worker safety. I am curious as to whether the flush water may have accelerated the corrosion when the system was placed back in service. I know the 304 was probably a bad choice to start with. The original 316 does not seem to be affected.
 Another question. What effect would possible internal sugaring of the pipe wall have on the corrosive action?

RE: sulfuric acid piping

mooseye

I'm not an expert on 304 versus 316, but a couple items in your description gave me pause.

Your post says the 304 piping failed within 48 hours of being installed.  You then ask if flushing the system with water before the repair could have accelerated the corrosion.  I'm wondering how did the water get to the piping that wasn't there when the system was flushed? Even if there was water left in the original piping system, wouldn't it tend to mix and dilute the sulphuric acid?

Your post also asks about internal sugaring of the pipe wall.  As this was new piping, what causes you to think there was internal sugaring? Was it there when you installed the pipe 48 hours earlier?

Patricia Lougheed

Please see FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

RE: sulfuric acid piping

Quote:

What effect would possible internal sugaring of the pipe wall have on the corrosive action?

Sugaring is caused by oxidation of the stainless steel, which means there was no backing (inert) gas when the roots were deposited. Sugaring will result in reduced corrosion reisistance. In addition, this is a reducing acid that requires molybdenum containing stainless steel - 316 minimum, 20Cb-3 preferred.

RE: sulfuric acid piping

"Even if there was water left in the original piping system, wouldn't it tend to mix and dilute the sulphuric acid?"

In response to this - sulfuric acid becomes more corrosive and damaging to pipe as it is diluted, rather than when it is concentrated.

RE: sulfuric acid piping

metengr and SeanB

Thanks for setting me straight.

Patricia Lougheed

Please see FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

RE: sulfuric acid piping

(OP)
I guess I really knew the answers before I asked. Just looking to confirm my suspicions.
 And, no, there was no purge gas used as it was a socket weld. In hindsight, It should have been purged with inert gas even so. I don't think there was actual sugaring present, just the possibility.
  Thanks for the replys!

RE: sulfuric acid piping

I would not use socket weld fittings in this service if water was being used for flushing. A socket weld is sealed only on the outside. Water can get into the crevice. When the sulphuric acid is introduced it becomes a dilute form in the crevice and corrosion will be very rapid.

Better to use butt weld  fittings so there are no crevices. Avoid water if you can unless you can vacuum and hot gas dry the line.

RE: sulfuric acid piping

No-one has touched explicitly on the material issue.  My experience, and more importantly my handy dandy Outokumpu Corrosion Guidebook (which can be had for free and I highly recommend obtaining) says 304 is an absolute non-starter for sulfuric in the full concentration range.  There are a couple of small bands of very low conc (0.25-1%), low temp and low conc (say 10-20%) where the service is "marginal" but the remainder is unequivocally "do not use".

Just my 2 cents, not adjusted for exchange.
Leaky

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources