when the fitter fit-up the nozzle to shell (Duplex), normally they will fit-up more (+5 mm) from center line (projection) compared with drawing, because they claim the projection will fall (2-3 mm) during welding. any one can explain what actually make the projection to fall?

The shrinkage (very high in austenitic and duplex steels) causes the shell in way of the nozzle weld tol set in much more than with carbon steel. You may see it direclty once visualyy examine the item.
Mauro

thanks you...

zola25 is correct.

This extra length of projection in fit-up is common practive at our facility especially when fabricating stainless stell pressure vessels.

When final projection length of a flanged nozzle is extremely critical, we weld the nozzle on first and then fit-up the slip on (or weld neck) flange at the exact desired projection form center dimension. Hopefully that makes sense.

Robert P.

Having an extra projection length might be correct if it has a fabricating element. The weld can ascertain the exact dimension needed to the duplex. It can form the better look you desire into that work.

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