Corrosion has occurred in the pipelines protected by anode protection
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We dried the acid pipelines and applied anodic protection; the material used is 304L with a wall thickness of 10 millimeters. These pipelines have been in use for 5 years, and one of the elbows has started to leak. The other elbows also show significant corrosion, with a wall thickness of only 5–6 millimeters. The straight sections are in better condition, as their thickness is still over 9 millimeters. Isn’t it said that anodized pipes with a wall thickness of 6 millimeters can be used for 20 years? How could it corrode in just 5 years? The acid-producing pipes we use are made of 316L material, and without any anodic protection, they have been in use for 5 years without any leaks.
There should be a dead zone; we have encountered similar situations before
The impact force at the elbow is much greater
Is there a dead zone in anodic protection? Have all of your elbows also experienced corrosion and thinning? Also, recently the current fluctuation in this cathodic protection pipeline has been quite significant, ranging between 1 and 20 A. When there was a leakage, I didn’t stop the system; instead, I made a box using carbon steel plates and enclosed the entire leaking elbow inside it, planning to deal with it when I have the chance.
In addition to erosion caused by scouring, another reason might be that the elbow area cannot be fully filled with concentrated sulfuric acid, resulting in poor anodic protection.
Elbows are more prone to corrosion; compared to straight pipes, it’s simpler to use high-silicon stainless steel instead
Anodically protected pipes have specific requirements regarding the flow rate of sulfuric acid; a high flow rate prevents the formation of a passivation layer, which in turn accelerates pipe corrosion