Pipeline purge prior to work 3

[IHQ22]

Greetings all,

I have a quick question about pipeline repair procedures. We will be cutting out some pipeline sections to replace them. What is the normal work procedure? Obviously, the sections will be drained of fluid but is a total purge also necessary? The operator suggests that the pipeline be flushed with water, is that the normal procedure?

Again, thank you for your help!

FredG2

 

[EngrPaper]

That would most likely depend on the fluid service of the pipe. What is the fluid?

 

[IHQ22]

Hi EngrPaper,

The fluid is No.2 Oil.

Thanks.

 

[EngrPaper]

For anything combustible, even if not required, I would want to purge the line entirely, not just drain. When we do natural gas work, the line needs to be nitrogen purged. I do not know if water would be an acceptable equivalent for liquid purging, but I would definitely look into it more. Perhaps someone more knowledgeable than me can contribute.

 

[mk3223]

No.2 Oil (diesel?) is a flammable liquid. IMO, you may have operation and Maintenance involved to review the cleaning procedure for the pipeline before turning it over for repair.
Normally, the cleaning of the petrochemical pipe may includes the water wash, and steam out, etc., to ensure the pipe is clean prior to opening up for inspection and work.

 

[IHQ22]

Thank you for your input everyone, I was trying to see if there was a way to avoid contaminating 100,000 USG of water but you are totally right about the flammability of Oil No.2 vapour.

 

[LittleInch]

I'm really not sure you should be asking an internet forum, but the normal procedure is that the pipeline section needs to be "made safe" before cutting into it.

You can do that by a variety of means.

Draining is one way, but only if there is a good steady fall on the pipe, but if you haven't got pigging access ( you give us very few details here) then draining might be the only way in which case flushing with water is quite common to reduce HC content to very low. Prpbaly in the region of 3-4 times pipelines volume would be required to sweep out all traces of oil.

If you can pig it then you can pig out the contents pushed by Nitrogen and then vent.

You'll always get some residue and low points will accumulate a little fluid, but that's life.

A few more details wouldn't go amiss like:
Diameter
length
Piggable?
profile
Is the pipeline operable now? Is it full of holes?
What did they do before?

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

 

[chicopee]

No2 oil is not a flammable liquid. Check NFPA30 and you'll note that No2 oil (or diesel) is classified as a combustible liquid having a flash point at or equal to 100dF. Flammable liquids have flash points lower than 100dF.

 

[IHQ22]

Hi LittleInch,

I am well aware that the pipeline needs to be made safe prior to work. What I am really trying to determine is if someone more knowledgable then I can suggest a better method then purging with water before we go ahead with it. The real problem is the pipeline location, making purging with water a really complicated operation.

Details:
- D = 12 NPS
- L = Approx. 2 miles total
- Pig system is installed but not operational.
- The pipeline is currently "operational" but not in use. It sees very limited usage.

The section where repairs are required is minimal, approx. 12 ft. of pipe need to be replaced. No valve system permits a "localized" purge.

Cheers

 

[KevinNZ]

We do work on systems where water is not allowed in the piping. What we have to do is more work that a water flush. Vacuum, N2 purge, vacuum, N2 and repeat.

 

[LittleInch]

For 2 miles of 12" diesel line I would just blow out the contents using a pig propelled by Nitrogen.

If needed you could run a second for little extra cost to clear out final contents.

Then blow it down, drill a hole in the section to be replaced and drain off any residue then use a cold cutting ? slow grinder to cut the pipe section off.
e.g.

https://www.dwt-pipetools.com/en/pipe-cutting-beveling/pipe-cold-cutting/pipe-cold-cutting-machine/

If you're welding the replacement insert two pigs into the open ends then that seals the end.

If you want o get fancy you can insert expandable pigs which sit either side of the section and are then remotely activated, but they cost a lot and normally only where there is a large volume.



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

 

[IHQ22]

Thanks LittleInch,

I will explore this see if this is something we can propose to the contractor.

Cheers,

IHQ22