CuNi Corrosion

[Joss10]

Please, any clue as to what may be causing this corrosion?
This pipe is carrying treated, chlorinated drinking water at 45-55 °C.
Water analysis is pH= 6.97-7.87; Salinity 382 mg/lt; Free Chlorine 0.15 ppm (not sure this is always so); Iron 0.75 ppm; Conductivity 600 uS/cm.
Pipes started to corrode 3 years after installation.

 

[racookpe1978]

Was that "line" of loose scale on the bottom of the pipe? or the top?

Was the pipe ever half-full, or drained?

That loose material really doesn't look like the corrosion I'm used to seeing. But I'd like to get other's opinions first..

 

[Joss10]

The scale is not loose, it is perfectly adherent, and yes, it is at the 6 o'clock position.
When you scrape off (with some difficulty) some of this scale, you find a corroded area below.
Strangely, he leak on theis piece of pipe happened on an isolated pit (see attached pic) on the 12 o'clock position.
I don't know if the pipeline was operated half full or opened, but I presume not because it is carrying potable water for the facility where it is installed.

 

[metengr]

It appears to be underdeposit corrosion. Without further information, it is possible the line had either been only partially drained resulting in underdeposit corrosion from MIC (microbiologically influenced corrosion) attack or the debris was left over from improper cleaning during construction, resulting in underdeposit corrosion. Have the debris analyzed.

 

[EdStainless]

I'll echo that comment, have it analyzed.
If this is a potable water line we must assume that it may sit stagnant for long periods of time.
MIC is also my thought, though if this deposit contains a lot of metals (Fe, Mn) or S then it simply could be under deposit corrosion.


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