Could everyone help analyze what caused this?
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What caused this sealing surface issue? The medium consists of formation materials (shale gas water), sand (in small amounts), and hydrogen sulfide ； RJ-sealed, all connected to gate valves; the inner diameter of the gate valve is 65 mm, while that of the flange is 55 mm
It is caused by corrosion due to the medium used. Because the medium contains at least water, hydrogen sulfide, etc., it can easily cause electrochemical corrosion of metals.
It’s clearly acid corrosion – corrosion that occurs over time as areas not covered by gaskets are exposed to acidic water.
Strange! Is the sealing surface uneven, and are the flange and pipe connected by socket welding?
Where to look? The flange sealing surface, or the weld surface between the pipe and the flange?
The medium contains hydrogen sulfide, but it also has sand. Only that ring is corroded. And this phenomenon only occurs on the skid-mounted intake pipeline. Other drainage, sewage, and exhaust pipelines do not have this issue. What I analyzed was that the diameter of the valve was larger than the inner diameter of the flange, resulting in direct erosion of the flange’s sealing surface.
No, the flange is butt-welded with a neck; that ring is the result of corrosion.
For necked butt-weld flanges, why is the sealing surface corroded in this way?
The metal has corroded! Is it because the pipe protrudes a bit more, resulting in a greater welding thickness and thus better corrosion resistance?
Come and learn*; for corrosion protection, polyaniline coatings are used