Weld overlay for steam corrosion 2

[mat211743]

Dear Experts,
We have a carbon steel "Tee" joint in steam service experiencing rapid metal loss. We suspect FAC. I did some research on this forum and found P11 or P22 would be a good substitute to reduce the metal loss. Somebody in our group suggesting weld overlay. I am looking for some advice if it will work? Thanks.

 

[metengr]

If you have actual FAC attack, I would replace the complete Tee joint with a P11 or 1.25%Cr-1/2%Mo low alloy steel material.

The problem with weld overlay is that you will be chasing the FAC damage around the Tee section. The weld overlay with 1.25% Cr-1/2% Mo could be used as a short term fix. Ultimately you will be chasing the FAC damage to another location on the Tee.

 

[EdStainless]

If you need a short term fix while you wait to install the new T then use weld overlay.
But don't delay, this is how people get killed. And now you know that there is a risk.

If you weld overlay continue the overlay well beyond the last visible point of attack. Per Metengr's caution, you will just move the erosion down stream. If the length through the T that shows damage is 24" long you need to go at least that far beyond the area.

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Plymouth Tube

 

[mat211743]

Thanks Metengr and EdStainless. As per my understanding, continuous removal of corrosion products on CS increase the metal loss by FAC. When the Cr content is increased the Cr assists in protective film formation and thus reduce the rate of metal loss. If we do weld overlay by 1.25 Cr material (as suggested by metengr) on back half diameter of the “Tee” (where impinging or erosive effect is occurring) to the full length of the joint, would it not work? Are we not mitigating the flow effect by providing a material that can form stable film? why can't it be a long term solution? Am I missing anything here? Can you please clarify?

 

[EdStainless]

1. Do you know that you still have more than enough wall thickness and the correct mechanical properties for the designed service?
2. You need to go well beyond the areas of obvious attack.
A. You need to protect the areas where the attack is slower and not obvious yet.
B. The transition from the overlay to the regular will cause some local turbulence which might lead to some localized attack.


This will be an ongoing inspection issue. You need to be prepared for that.
Replacing the T is the best route.

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Plymouth Tube