Wax in a pipeline 8

[Faster7]

dears I want to share you a problem that we face in our pipeline.
that we receive a high amount of wax in terminal during pigging specially during pigging operation and some times it lead to blockage in terminal control valves and accumulated wax in bottom of tanks.
the pipeline is 28" OD 1500 km transfer crude oil from main fields and two injection points .
now the main suspected causes are. the crude characteristics , combined with the laminar flow and the terrain change.
this in short
please if you experienced such problem like that share your ideas and how you solve that.
Regards

 

[1503-44]

Generally you want to stay in the turbulent flow range and keep temperatures above wax appearance temperature.

If you only get wax precipitation in a certain area, or especially during pigging, you can often handle that by adding heating capability to the pig trap, or build a special heated trap with a heat traced connection where you can flush the wax into a special heated wax storage tank and turn the heat on when you want to empty that tank. You should not let it get into any tank that is not heated, or cannot reach the wax melt temperature from natural solar radiation.

Sometimes you can avoid most of the problems by only doing pigging during summer when your pipeline may run at temperatures higher than the wax precipitation temperature.

Exactly how you might want to handle the wax may depend on several things...
What is the wax content of the crude?
At what oil temperature does the wax precipitate?
How much of your pipeline operates below wax appearance temperature?
Where are the low temperature (below wax appearance temperature) zones on your pipeline? Only at the terminal? In mountainous areas? Under a river crossing?
Is the low temperature seasonal, or more or less constant.
How much wax do you get in the pig trap. Some, a lot, totally full?
How often do you pig?
Do you get wax formation at pump stations or other critical equipment?
Is it feasible, or advantageous to melt it, then reinject it into the pipeline?
Will plugs form if the pipeline is stopped?
What is the wax shear strength?
How solid is it when the wax does form and if that can that be dissolved by a lighter oil or naphtha?

Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

OK, so this is the GNPOC line in Sudan yes?

First off why are you pigging? to reduce the wax or some other reason?

What sort of velocity are you pigging at? - if you've got laminar flow you must be crawling along? Usually wax clearance pigs have a bypass to send the wax ahead of it in a cloud of wax particles to avoid getting the pig stuck.

Pigging waxy lines is not easy and the results are as you say - clogged valves, filters and wax in the base of the tank.

You can try the things mr 44 mentioned, but really your only long term solution is to remelt the wax as it come into the terminal in a long pipe in pipe annular heater or inject lots of chemical ( if they work) to decrease the WAT. Anything else will just clog up. Given that you probably need to maintain a significant back pressure as it comes down off the ridge of those hills close to Port Sudan, you don't want your control valves clogging up....

As Mr 44 says, get to know your "wax". There are many different types with different properties. Also from personal experience I know the ground temperature in Sudan gets very high in summer, which will reduce or eliminate your wax deposition. I worked on the design of the other Sudan line and I think the GNPOC was not insulated or heated?, but had much lower WAT than the PDOC line which needed heater stations to prevent solidification.

Now if your flow rate is quite low then the heater size will be low, but you're still talking MW of power I suspect. You need to heat the crude to the WDT - Wax Dissolution Temperature, which is usually 5 to 10C higher than the WAT.

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

 

[Faster7]

many thanks
I do appreciate your valid inputs. now we are in a deep discussion about this issue and this inputs help too much.
thanks again. I really grateful for that.
LittleInch yes you r write

 

[georgeverghese]

See if ShellSwim wax pour point modifier additive helps your crude oil - we used ShellSwim 11T PPD ( pour point depressant) in many of these waxy crude oil pipelines. There are similar additives from Chevron and ExxonMobil also, since they have extensive experience in waxy crude oil operations in Sumatra, Indonesia and elsewhere in Asia - call the nearest Chevron or ExxonMobil office for advice.

https://archives.datapages.com/data/ipa/data/009/009001/501_ipa0090501.htm

These additives cost a bomb - your poor JV company may most likely get ripped off for this. In the short term, you may have to purchase this directly from some supermajor or their local subsidiary, but see if your Company can find some suitable generic PPD which may be much cheaper in the longer term.

 

[LittleInch]

Apart from the cost you also need to do some tests on live crude as not all crude respond to PPD. Also the level of depression of temp is often only 5 to 10C.

I suspect GNPOC is now running at a small fraction of its capacity and the internal heating you get from these high viscosity waxy crude only works at higher flow rates.

So less money to spend on the extra heaters it actually needs.

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

 

[brimmer]

If you want to spend money you can try a wax dispersant chemical, that will prevent adhesion to pipe walls, numerous chemical vendors carry these and are quite commonly used. If your pipeline is leading to processing, you will need to complete a compatibility study to ensure the chemical does not upset processing operations.

 

[GD2]

Zidapi,
There are so many research and techniques available to mitigate your problem - few of which had been suggested by my colleagues. Talk to a Process Engineer if you have or engage an consultant to correctly give you an appropriate solution.
It’s a common problem and so are different techniques.

GDD
Canada

 

[Pipeline55]

Typically the most effective "tool in the tool box" for managing waxy oil pipelines is to have an effective operational pigging program in place designed by a competent and experienced pipeline engineer supported by a corrosion and process and / or flow assurance engineer. It is good to set an objective or goal which might be no more than XX kg / barrels of wax in the receiver per run to avoid excessive wax handling and pigs trapped in receiver inlet valves. Typically an effective bi-di with jetting is a good design to then build on if needed. Of course sometimes this runs out of oomph in more challenging cases so additional strategies might be needed such as trap / tank heating (only done that to unblock trap drain lines myself), wax handling equipment (split axial cassettes are good to get wax out in one go and then slice it up), procedure tweaks (leave pig receiver bypass open till pig arrives at barred tee), injecting wax suppressants (please don't believe labeled as wax inhibitors, mainly disappointing, 20-30% effective and expensive), running multiple pigs in the line (for long lines and / or low velocities, complex to manage over time) can add value BUT these should be in addition to and not a substitute for an effective operational pigging program. Debris mapping technologies such as the Pathfinder pig and Innervue pressure pulse surveys can help (helped me alot) understand the amount and location of wax deposition (wax modelling uncertainty not great) and with multiple surveys the effectiveness of the operational pigging program can be further tweaked. Finally monitor the fouling factor in real time, it is most enlightening to tweaking pigging.

 

[hacksaw]

In many countries "pigging" is offensive so the formal term "pipeline scraper" is used.

Crude assay test, are mandatory in all pipe line design, where wax or asphalt content.

 

[Pipeline55]

Hacksaw, Apologies for using any potentially offensive terms. Littleinch used the term earlier without any pushback so I thought it would be OK / appropriate as it the term that is most widely used in the industry (not every device scrapes) including the Middle East where I worked extensively.

 

[SJones]

@55

Sound advice. Don't worry about wokery.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[Pipeline55]

Thanks Steve, Andy.