Underground Oil & Water Pipelines 1

[Inchtain]

Hello all,

Recently, we repaired a rupture in a water pipeline by replacing a pipe spool. Surprisingly, and after about 6 months we experienced a leak in the same trunkline and in the same replaced new portion.

Could anyone elaborate more on how new welded pipes corrode faster than the older ones? and how to mitigate such rapid corrosion?

Thanks and kind regards,

 

[akpipelineengr]

Could you elaborate on your pipeline?

Pipeline details like size, wall thickness, material grade, design code, design pressure, environmental conditions, and fluid properties would all be helpful to understand your request, as well as corrosion rates observed, corrosion inhibition, details of inspection program, etc.

 

[Inchtain]

Well !

Here are the pipe data:

Year of Construction: 1980
Environment: Desert (North African)
Diameter: 18"
Thickness: 19.05
Material: API 5L Gr. X60
Code: API 1104
Design Pressure: 2800 psi
Design Temperature: 45 degrees Celcius
Fluid: Treated Produced Water+Water from Supply Wells
Service: Water Injection Header
Treatment: Corrosion Inhibitor+Biocide
External Corrosion Protection: Wrapping+CP Protection
Inspection History: Corrosion-Erosion at 6 o'clock Grooving discovered at some pipes and they were replaced.
Recent incident: Accelerated corrosion of one of the new inserted pipes in the form of pitting and extended grooves at 6 o'clock

Thanks

 

[LittleInch]

The only thing I can really think of here is that the new portion wasn't exposed for long enough to the corrosion inhibitor which takes a while to coat the pipe before the corrosive nature of the water acts on it.

Corrosion at 6 o'clock in a water line looks like some form of MIC or something heavier than water ( sand? stones? gravel?) is sitting there and preventing the CI from working in that section of the pipe.

Is this section at a low point where deposits can gather?

This article is typical and if you search for Under deposit corrosion or UDC you'll find a lot more.

It looks to me like your line is susceptible as its got probably salty wate in it at high temperature and unknown oxygen content.
What is the flow velocity in your line?
Do you ever pig it?

Underdeposit Corrosion in a Subsea Water Injection Pipeline

Underdeposit corrosion (UDC), a general term that refers to localized corrosion that develops beneath or around deposits on a metal surface, is a phenomenon that leads to pipeline failures and is one of the most damaging forms of corrosion for oil and gas pipelines. It can occur in subsea water...

www.materialsperformance.com

 

[goutam_freelance]

You did not mention flow velocity.

If the velocity is high locally, erosion may occur, particularly when erosive particles are present.

 

[1503-44]

I believe he said external corrosion, so probably a pinhole or scratch, or poor wrap in the coating. It is unusual, but not unknown to happen within 6mo of installation, especially in acidic, wet soils.

 

[goutam_freelance]

Stray leakage current from electrical system may induce electrochemical corrosion in UG structures. Please check if any such leakage current exists near the corroded area.
https://www.sciencedirect.com/science/article/pii/S2667266924000161

 

[LittleInch]

I believe he said external corrosion, so probably a pinhole or scratch, or poor wrap in the coating. It is unusual, but not unknown to happen within 6mo of installation, especially in acidic, wet soils.

Not clear but he did say extended groove at 6 o'clockand mentioned erosion . That's internal.

 

[HTURKAK]

Apparently there is no internal coating to isolate the corrosive fluids from the pipe wall. The only measurement is Corrosion Inhibitor+Biocide. Is this true ?
My opinion is , repair spool and existing pl material chemical compositions could be different.

 

[GD2]

It's bizarre. only 6 months life out of a replaced pipe. It's like something is scooping the material out.
It's for sure corrosion (pitting) and erosion (the grooving) the culprit.
It's a high pressure water injection line.
Check the velocity and the pipe alignment. Is it something a sag in that section of the line where stagnant fluid is helping in the accelerated corrosion and may be a valve that don't fully close/open just upstream of the section sending stream of jets down the line giving high velocity fluid?

 

[RandomAxe]

It does sound like MIC, '6 o'clock grooving'. You mention produced water - could it be something to do with an increase in sulphate reducing bacteria in the produced water in later field life? Was the spool 100% like for like?

 

[Inchtain]

Thanks for every one for your interesting inputs.

Actually, the pipe used is exactly the same for the existing pipes and there were no any internal corrosion protection apart from the chemical treatment.

The defects are internal and affect the old pipes as well, but they remain acceptable to the minimum thickness required and they are kept under monitoring.

Ironically, the new pipe copied the defect with fast pace.

Other pipe information is as follows:
- Pipe elevations is more or less equal along the route
- No launching/receiving traps for the line to do pigging
- Velocity: 9.9 m/s
- Working pressure: 128 bar
- Working temperature: 40 degrees Celcius
- Water is very salty and contains 6% insoluble particles

Kindest regards,

 

[LittleInch]

Nearly 10m/sec???

I suspect the new pipe simply didn't have time to develop a protective coating which the other pipes might have had time to do before the velocity and saltiness occurred. Corrosion Inhibitor won't work at that velocity and with solids scraping it all off.

If this is carbon steel I'm amazed it's still there tbh.

Why this section gets attacked is not clear, but we don't have the profile or plan view.