Thoughts on a gas condensate line being decommissioned
Thoughts on a gas condensate line being decommissioned
(OP)
Hi there,
I'm no specialist in decommissioning of pipelines, so would like some thoughts from those with some experience in this. I've got a gas condensate line that's been shut in for several years now and looking to be decommissioned. First task is to actually work out what could actually be in the line having been shut in for so long!
My initial thoughts are water, oil, residual chemicals, iron scale, etc. But I have a few questions:
1. Since this line is no longer at pressure - when operational it was at 70 barg. Currently at 3barg - is it at all possible there would be hydrates present if the line is no longer at pressure?
2. Are any chemicals in particular (for example, corrosion inhibitor, methanol) known to degrade and cause sludge that could also be in the pipeline?
High level comments/thoughts would be appreciated for now.
I'm no specialist in decommissioning of pipelines, so would like some thoughts from those with some experience in this. I've got a gas condensate line that's been shut in for several years now and looking to be decommissioned. First task is to actually work out what could actually be in the line having been shut in for so long!
My initial thoughts are water, oil, residual chemicals, iron scale, etc. But I have a few questions:
1. Since this line is no longer at pressure - when operational it was at 70 barg. Currently at 3barg - is it at all possible there would be hydrates present if the line is no longer at pressure?
2. Are any chemicals in particular (for example, corrosion inhibitor, methanol) known to degrade and cause sludge that could also be in the pipeline?
High level comments/thoughts would be appreciated for now.





RE: Thoughts on a gas condensate line being decommissioned
RE: Thoughts on a gas condensate line being decommissioned
Future PE Engineer
Pet project I am working on to help other engineers, not much yet hoping to get it grow as I learn more
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RE: Thoughts on a gas condensate line being decommissioned
RE: Thoughts on a gas condensate line being decommissioned
Learn from the mistakes of others. You don't have time to make them all yourself.
RE: Thoughts on a gas condensate line being decommissioned
If you are looking for some guidelines BSEE has some regulations on decommissioning of pipelines. You might be able to use those as a go-by to develop a strategy for your particular job
Future PE Engineer
Pet project I am working on to help other engineers, not much yet hoping to get it grow as I learn more
http://www.peexamquestions.com
RE: Thoughts on a gas condensate line being decommissioned
The fact it is still at 3 bar is good as it shows it's not completely broken. You get hydrates as the pressure increases and temperature decreases, not at 3 bar.
I doubt you have any serious sludge or debris in your line as it wans't flowing.
Your issue is that in order to de-commission the line, first you need to re-commission it(!) This means looking at any records you have of its material, inspections or use to see where issues could arise (low spots, damaged coating etc). What is the CP like?
If you know it holds 3 bar, is this enough to send a foam pig down it and try and clear some of the liquid out of the way or do you need more pressure? Or can you just flow water into it and flush out the contents into an atmospheric tank at this pressure even if slowly? Once you get mostly water you can then pressure test it to the lowest figure you can get away with so that you can clear the pipe of water with pigs, initially foam pigs then perhaps something more like a bi-di to clear it all out of the way using nitrogen normally.
Then depending on the size, you normally need to cut it into sections and seal each section before abandonment or fill it with grout / foam concrete to stop it collapsing.
How you do this and what permissions and approvals you need vary widely by country and jurisdiction and what promises were made (if any) when the line or system was built. Equally how long you remain liable for it after abandonment also varies a lot from nothing to 10 years plus.
Normally it is a good idea to get an environmental study completed to demonstrate that your chosen methd is the BPEO (best practical Environmental Option) to cover you if it starts leaking after you've abandoned it.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Thoughts on a gas condensate line being decommissioned
RE: Thoughts on a gas condensate line being decommissioned
Before you start injecting air to run cleaning pairs, make sure you put a buffer of nitrogen before the air. There is a nice post by zzz as on selecting air compressors to clean pipelines. I'd assume you have enough liquid in the pipeline to fill up the highest single elevation change
RE: Thoughts on a gas condensate line being decommissioned