Mothballing for Non-Piggable Pipe

[zayed78]

Gents,

I have segments of ~ 50 m Non-Piggable Pipe at well site ass you this section we can to run pig through it for cleaning or chemical treatment. Due to our situation we forced to suspended all our production wells and we applied the massive suspension / Mothballing for main flow line and individual flow lines by using pigging with corrosion inhibit /biocide batch treatment then blown and dry, However we faced problem regarding a well site piping as you know the such piping experienced corrosion due to deposit of scale inside it which cause corrosion so I need you advise about the optimum suspension method for such case??

Note that suspension period could be reaches 3 years or more fluid inside the pipe crude oil with water (water cut could be 50 % to 95%)

Zayed

 

[dik]

On an earlier thread, I posted the following link on pigging A very interesting technical file:

https://www.aucsc.com/_aucsc speake... Period 9 & 10 Difficult to Pig Pipelines.pdf

Dik

 

[zayed78]

Dik,
Thank you very much for useful link I read through it but no info about Mothballing for non-Piggable Pipe!!. In my case no way to run pig to install launcher /receiver.

 

[zdas04]

dik,
That was an interesting attachment, TDW always does good work.

zayed78,
You didn't say much about the magnitude of the problem. You have to ask yourself "what makes this line non piggable?" Some of the common reasons are:
[ol 1]
[li]Just lacking pigging facilities[/li]
[li]Intrusions like thermowells in the line[/li]
[li]Bends to short for pigs to pass[/li]
[/ol]

For #1 I've often been able to break a flange on both ends, stick in a pig, put a pierced blind on both ends, run a hose over to some catchment on the "receiver" end, and run the pig with a low pressure/low capacity air compressor. Works great for minimal cost, I typically use a short turbo pig for this.

For #2 and #3, I use the same procedure as #1, but use an uncoated foam pig that gets torn up in the process, but always come in. If you do this, get 5-10 pigs for each location and run them until the bits you recover are reasonably dry.

With any of the options, when you are satisfied with the results, shut the valve on the receiver end, pressure the line as high as the air compressor can go, and rapidly blow the line down to try to carry any remaining debris out of the line. I do this 2-3 times to make sure that no foam remains in the line.

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[dik]

I didn't know and thought it might be one or more of the issues you noted... prior to the thread, I had no idea of what pigging was. I had no idea of how many different types of pigs there were.

I'd assumed that mothballing was 'scrapping' but don't know.

Dik

 

[zdas04]

dik,
Mothballing is pretty common. If you leave liquid standing in a line for months or years, it may not be suitable for purpose when you try to turn it back on. The water has microbes in it that are really hard on steel, the water chemistry often leads to corrosion problems. When you mothball the line you are basically removing the water and often adding an inert gas to keep oxidation at bay. The reasons for taking a line out of service for extended periods often relate to the economics of the market prices or prolonged infrastructure problems (e.g., the refinery is going to be out of service for 6 months for a turn-around and you don't have access to an alternate facility).

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[dik]

Thanks Dave... just vaguely familiar with MIC. I didn't know that about mothballing... I had thought that as part of the 'cleanup' would be that they would run a 'cleaning' pig down the line...

Dik

 

[mk3223]

If possible, the pipe section may be isolated and removed for cleaning.

 

[zdas04]

mk3223,
That is often true of above-ground piping. With 50m segments of buried piping is way too disruptive to remove for cleaning (we wouldn't do it in upstream Oil & Gas, if we pulled up the line for cleaning we'd scrap it and put new back in when/if the facility came back on line.

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[dhengr]

What would happen if you vented this pipe line to the ambient atmosphere, filtered the inlet air so you were not filling the pipe with fine sand dust, and put a small suction fan on the outlet end? If you just close it down with two values at the ends, you have a humid environment within the pipe where the microbes, etc. can thrive. If you clean it, by whatever is the best method, neutralize the interior contents by whatever is the best method, then keep it relatively dry by some relatively inexpensive methods mightn’t that save the infrastructure?

 

[zdas04]

dhengr,
I've seen that tried, but the standing liquid (usually mostly high-TDS water, but often it has oil on top) will sit there for a very long time (air exchange inside the pipe is really slow so the pipe generally moves towards 100% RH and evaporation stops). While the liquid water sits in the pipe, the microbes start reproducing and their waste starts eating through the pipe.

Putting a "small suction fan" on the pipe assumes that you don't need significant velocity to shift the contaminants in the line and that really doesn't work (because you do want to shift the contaminants).

The best method is to dry the line out with pigs, get the humidity to near zero with dry nitrogen at a slight positive pressure, and monitor the pressure on the on a regular schedule (and top it up when it falls below a specified overpressure).

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[LittleInch]

Well first you normally get rid of the contents by either flushing it through with hot water and possibly some detergent and or blowing it through with Nitrogen or CO2.

final flush could be either some sort of "nice" oil, say lubricating oil or something like MEG to pick up all the bits of water or drain it downa nd fill it with Nitrogen and leave it with no pressure or fill it with water with oxygen scavenger and biocide in it.

Many ways to do this depending on accessibility, fill / drain points, how long you're going to leave it etc etc

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