×
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

Sulphuric Acid pipeline decommissioning

Sulphuric Acid pipeline decommissioning

Sulphuric Acid pipeline decommissioning

(OP)
Hi forum!
We are decommissioning a 8" pipeline in service for sulphuric acid 98%, 1 mile.
we intend to drain the line and after neutralize, but the problem is reaching a sufficient draining of acid.
No drains are installed and the line and seems not piggable due to vertical expansion joints with 90°bends, so displacing the acid by nitrogen purging will leave lot of acid inside.... how to reach a good draining of low points?
do you know if is it possible to pig a line with expansion joints with 90°bends?
any idea on how to drain low points safely?
if we leave lot of acid inside, will the neutralization process give any trouble?

thank to all

RE: Sulphuric Acid pipeline decommissioning

Some pictures or drawings would be helpful to understanding the problem better.

If you have more acid than expected left in the line, the neutralization could generate more heat than was accounted for in safety reviews.

RE: Sulphuric Acid pipeline decommissioning

There are plenty of small flexible or foam pigs which will go round 1.5D (long radius) elbows. Just ask your pigging supplier.

Now how you get the pig in and out is a different story, but for that you need to know what the piping arrangement is at either rend of your line. If you can drop a spool or valve out then this can be used to gain access, but the exot will need to be able to drain the acid away and accept dome has and acid and the pig.

However you need to be sure that there are no instruments sticking into the pipe, All the valves are full bore and wide open and there are no tees.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Sulphuric Acid pipeline decommissioning

(OP)
Thank you,
I will show a drawing shortly

RE: Sulphuric Acid pipeline decommissioning

(OP)
I am also thinking at the acid displacement with an inert and immiscible fluid, so to avoid pigging...it seems a safer solution if praticable

RE: Sulphuric Acid pipeline decommissioning

I have seen people use soft, undersized pigs. While not perfect it will remove a lot more fluid than just gas.
What fluid could you purge with that is non-aqueous and will not react with concentrated acid?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Sulphuric Acid pipeline decommissioning

(OP)
I am not able to upload the sketch...
simply it is a mile of piping with four vertical expansion loops (U bend) like this https://goo.gl/images/5aZcYn.
the pipeline starts on a foreshore area, overpass a public road and lays on a trestle offshore up to a marine loading platform.
clearly it was not designed for the current service..

so we could previously displace as much as possible acid with nitrogen, pig with a set of undersized pigs and then neutralize.

RE: Sulphuric Acid pipeline decommissioning

(OP)
for EdStainless..what about displacement with gasoil??

RE: Sulphuric Acid pipeline decommissioning

Why "undersized" pigs?

Just look at a few pipeline pig sites and talk to some people and you'll get one suited for that use.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Sulphuric Acid pipeline decommissioning

(OP)
I just received the sketches of the line...there are three tees, so the line is unpiggable :(

RE: Sulphuric Acid pipeline decommissioning

what sort and size of tees?

Is the main run the run or do you have right angle turns?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Sulphuric Acid pipeline decommissioning

Please try to upload the pictures again - it will considerably help the forum members help you. I can imagine with proper sequencing, you may be able to pig the necessary volume.

RE: Sulphuric Acid pipeline decommissioning

(OP)
Here is a simplified sketch. line is from Valve A to Valve B. Spare connections (1,2,3) of about 1 metre each, blind flanged

RE: Sulphuric Acid pipeline decommissioning

That's a bit unfortunate.

However you could still use a sphere and also insert a gas connection at point B if you can.

If you can't drain down then you are a bit stuffed really in terms of getting anything in to clear it out.

You said the expansion loops were vertical but you've shown them horizontal?

What is elevation of the various bits?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Sulphuric Acid pipeline decommissioning

I have heard of people clearing lines by blowing smaller balls (piglets?) though them.
This adds momentum to push fluid but allows them to navigate difficult turns.
I have never done this personally so I can't offer any technical assistance.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Sulphuric Acid pipeline decommissioning

(OP)
by pigging with spheres, don't they end up in the spare connections 1,2,3?
Littleinch, expansions loops are vertical..rotate the picture to left..
For the elevation, what do you mean with bit?

I will inform myself on piglets.

by the way, if the line is unpiggable, is it admissible to neutralize the line not drained? by adding small quantities of base, gradually over time?
thank you

RE: Sulphuric Acid pipeline decommissioning

If you add gradually you will end up with a lot of acid that is partly neutralized, and if the piping is metal you will likely destroy it.
Heat and gas generation are the big issues with neutralizing. doing it as quickly as is safe is usually needed.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

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