Corrosion Scab underside of a pipe

[ER_Azza]

Hi All

One of our pipe has a scab at the underside of where the support used to be.
A new pipe support was installed not too far away but the pipe where orig support location is was never prep and recoated.

It is a 4" pipe. NDT shown enough metal thickness. Had tp do RT since PEC was not available.

Question, should I try to remove the scab and apply protective coating, or should I just leave the scab and apply coating on the scab and pipe.
Any advise appreciated.

 

[LittleInch]

Remove the corrosion and clean it back to good metal and then UT to be sure then repair.

Never coat over corrosion. The coating will fail and the corrosion may continue.

A simple maintenance task.

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[ER_Azza]

Hi Mate

Thanks for the tip.

What's the best method to remove the scab?
I've seen previously at a different installation someone use a soft grinder to clean it back to the pipe metal.
Though norm would be using wire brush.

Is there any better way to do it?

 

[LittleInch]

The key thing for any coating is the surface preparation. Wire brushes tend to smooth the surface too much and grinders are a bit brutal. Grit blast is the best but a bit overkill for such a small blemish.

Look at the surface prep requirements of the primer you're using. Clean and grease free is the minimum. You might get away with some hand applied sand paper.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EdStainless]

Often a pin cleaner will do a good job, not too smooth and still clean.

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P.E. Metallurgy, consulting work welcomed

 

[ER_Azza]

Thanks All

Will keep you update.

 

[TugboatEng]

The grinder is the best option for a field repair. Spoon out th pit to mostly shiny metal and recoat. Most people don't commit to spooning out the our which is why they get bad results. I emphasize "mostly shiny metal" because if you go deeper than the bottom of the pit you're doing more damage than the corrosion.

 

[Interpreter888]

Bristle blaster. Cleans metal and gives 1-2 mil surface profile. Great for small spots.

 

[LittleInch]

Like this?

Interesting.

https://en.m.wikipedia.org/wiki/Bristle_blasting

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Interpreter888]

Yes that’s it.