Chemical Injection Sequence

Data given is grossly inadequate.

Passivation is the first step, not any of the three as mentioned.

DHURJATI SEN

@TugboatEng … I did not mean that we inject one and then the other … No, all of them should be injected continuously as you said. I meant which one should be the most upstream injection, then which one (i.e. the physical location of the injection point).

I usually do the following: the first injection point (the most upstream) for the corrosion inhibitor and the last one (most downstream) for biocide, but I am looking for a document/industry guideline that discusses such thing.

Your question is challenging because the inhibitor and scavenger service similar duties. I would speculate that the scavenger has priority because oxygen has a directly negative impact. Hydrazine raises the PH of the fluid and promotes the formation of black oxides that prevent pitting corrosion. In boilers, oxygen scavengers are the only corrosion inhibitors. The biocide should be last because biologic damage is the most time dependent degredation.

Check with the chemical vendor whether they are compatible each other. There are some cases that oxygen scavenger can interfere biocide's activities. ( ex., oxidizing biocide requires oxygen to kill bacteria so it shall be applied before scavenger injection or non-oxidizing one is to be considered.)

SiHyoung Lee

Well unless it's a really short pipeline, within 100m at most they will all be mixed in with each other.

But it seems rather extreme.

CI tends to produce a film on the inside to prevent corrosion, biocide deals with bugs / bacterial etc and Oxygen scavenger removes oxygen.

What is it you're transporting??

The last two tend to be used for hydrotest water when you're pumping out of a river or something similar and then in operation you just pump in CI.

To pump in the last two in operations seems rather odd.

But compatibility is key - get it wrong and end up with the dreaded "gunge"...

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@LittleInch … we are designing a new pipeline for "treated" oil and gas facility wastewater to injection wells. And the chemicals (types and dosages) were proposed by a chemical vendor.

The inhibitor will take a few pipe lengths from the injection point to become fully mixed with the transported fluid, so it probably makes sense to have that go in furthest upstream. As for the other two, couldn't the chemical supplier come up with a cocktail for a single injection point? Naturally, an extensive qualification programme was undertaken to ensure that the complete mixture works as intended, wasn't it?. I'm taking a guess at a produced water system (possibly a mixed seawater operation) if all three of those chemicals are needed simultaneously.

Steve Jones
Corrosion Management Consultant


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

My guess was right.

Steve Jones
Corrosion Management Consultant


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

Ok, Produced water eh?

Is there a materials break anywhere?

Normally I would want to have the Oxy scav injected and mixed in the last vessel before the pipeline so that the fluid is then at as low an O2 level as you can get before you start entering the presumably C Stl pipeline section.

What levels of O2 are you aiming for? You need to get down in the low (40-50 I think) ppb to be able to see any impact on C Stl. If your water hasn't been oxygenated then you'll be fine using oxy scav, but if it has then you need gallons of the stuff.

CI needs to go in about 10 to 15D upstream of any material break between say CRA and Carbon Steel if you're using a quill injection to allow it to start coating the pipe wall effectively.

Biocide is really for the downhole water to stop the reservoir going sour so could be anywhere along the system. So long as your pipeline doesn't stop for long periods in the warm you should be ok for biocide.



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

Where is the oxygen coming from as it will make life very hard for the inhibitor? Is a PE lined pipeline out of the question, as a triple chemical treatment is going to take a lot of skill and experience to look after, without upsetting the Operations guys when the disposal wells block up?

Steve Jones
Corrosion Management Consultant


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

@LittleInch, @SJones: The line will tie in to another bare carbon steel pipeline! so we need the injection unfortunately. I have tried to push for lined CS, but the injection is still needed for the other portion!

And for the oxygen, some of the water comes from collection pits.

The worst possible source - I wish you luck.

Steve Jones
Corrosion Management Consultant


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

If your water quality is so poor, it's likely conducive. Consider using anodes.