Galvanised Flange Face 2

[STEPSWIFT]

We recently had to undergo HDG for spools and some of the serration on the RF flanges was not visible due to excess Galvanisation.

It is not possible to remove the Galvanisation.
Th 3rd party inspector has rejected this as we do not follow MSS SP-6 and ASME B 16.5 .

Has any body had the same problem and is there a way to resolve.

 

[EngineerTex]

Why can you not remove the galvanizing?

Engineering is not the science behind building. It is the science behind not building.

 

[EdStainless]

A simple acid wash will strip the Zn and not damage the underlying steel.
Do it gently a few times for best results.

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P.E. Metallurgy, Plymouth Tube

 

[STEPSWIFT]

In theory the galvanisation has only covered the flange face, we have tried to remove by means of acid but this has not been possible. To minimize the situation we have carried out a Hydrotest proving to the Client that this will to effect the Seal of the spool.

would like to know if anyone has had a similar problem and if there is any Norm that allows this excess on the flanges.

we have followed ASTM 123 but it does not make reference to this situation.

 

[EngineerTex]

Have you contacted a media blast company? Someone in the know should be able to select a gentle abrasive that would remove the zinc and leave the underlying steel undamaged.

Engineering is not the science behind building. It is the science behind not building.

 

[moltenmetal]

The purpose of the serrations is to provide surface roughness to ensure that your gaskets grab properly and seal properly. What's your bet that hot dip galvanizing does something similar? As long as your flange faces aren't irregular because the zinc didn't drain away properly and left "drips" which solidified on the flange faces, you're likely fine leaving well enough alone.

If you've galvanized the pipe, you're not operating under hot conditions- galvanizing loses its effectiveness completely above 400 F Serrations are much less of a concern if you can get away with soft gasket materials. So unless you've got some cold but otherwise very high pressure pipe spools, which are galvanized for external rather than internal corrosion and where the gasket faces are not exposed to corrosives, the best thing to do is likely to leave well enough alone. Hydrotest, then do a sensitive leakage test on the flanges. If they don't leak, leave them alone.

Of course if people don't care about solving problems but instead want to follow rules without understanding WHY the rules exist, you can bring in a mobile machining operation and machine new serrations onto the flange faces. That will remove the zinc and make the underlying steel subject to the corrosion you were trying to protect against by galvanizing them, but it will meet the stupid rule!

 

[Arron_]

I don't know what the conditions are but we had some low pressure spools galvanized when I was an apprentice, we had to take the galf off the gramophone by applying heat with an oxy torch and wire brushing the galv off.

 

[EdStainless]

Arron, breathing Zn fumes isn't one of my favorites.

MM, Or does the HDG fill grooves and make a slicker surface?
IF the they are still rough then it shouldn't hurt, but it still shouldn't be there.

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P.E. Metallurgy, Plymouth Tube

 

[Arron_]

EdStainless I don't think many people would enjoy breathing Zn fumes. Good fume extraction is an obvious requirement.