Underground Oil & Water Pipelines

[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...

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