Corrosion on 90 elbow at the top (inlet) of produced water tank

[engr2GW]

Hello,

I have a low pressure vessel which water dump line is connected to the atmospheric tank. there has been occurrence of some kind of corrosion (or erosion) on the 90 elbow that ties to the top of the tank inlet.
I know that we can have sand in the vessel, but I don't think sand can be carried by such low velocity from a vessel operating at 35psig dumping to atmospheric tank.
could it be that pressure drop at the elbow leads to conditions that causes the corrosion? because it seem to happen in that particular elbow.
ALSO
I am thinking of installation an internally coated elbow at that point since it is unlikely that it is erosion, any suggestion as to what kind of replacement? I'm thinking Victaulic coated fitting?

THANKSK FOR YOUR HELP

As much as possible, do it right the first time...

 

[bimr]

It does not take a large velocity to move sand. A velocity of 3 ft/sec is enough.

Would suspect that the corrosion is due to erosion from the sand plus the aerated conditions (oxygen rich) at the top of the tank.

Since you don't say, one assumes that it is steel materials. You can line the elbow or use a heavier schedule of material.

 

[mrfailure]

Note that the sources for erosion versus corrosion are different. You will need to identify which failure mode before you can take corrective action. Erosion should be easy to identify - you'll see evidence of longitudinally-oriented damage at the elbow. If you cannot easily see it, you can always use a boroscope to perform visual inspection. You should also do some d-meter measurements of the elbow to determine how much (if any) wall you lost.