Sulphuric Acid pipeline decommissioning

[Tess72]

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

 

[jari001]

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.

 

[LittleInch]

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.

 

[Tess72]

Thank you,
I will show a drawing shortly

 

[Tess72]

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

 

[EdStainless]

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?

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P.E. Metallurgy, Plymouth Tube

 

[Tess72]

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.

 

[Tess72]

for EdStainless..what about displacement with gasoil??

 

[LittleInch]

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.

 

[Tess72]

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

 

[LittleInch]

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.

 

[jari001]

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.

 

[Tess72]

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

 

[LittleInch]

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.

 

[EdStainless]

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.

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P.E. Metallurgy, Plymouth Tube

 

[Tess72]

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

 

[EdStainless]

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.

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P.E. Metallurgy, Plymouth Tube

 

[Dhurjati Sen]

Dear Tess,

What do you plan to do after decommissioning the line?
What is the piping material?
Is the line underground?

If you want to use the line for some other service, the piping material is CS and the piping is not underground, install low point drains by hot tapping.

Regards.

DHURJATI SEN