Hello.

If a designer is designing a CS vessel with CA of mm. Suppose the flanges are ASME B16.5 Cl.150. They will have a RF of 1.6mm. That implies that there are chances that the RF will get corroded fast and losr its facing. How can we tackle this problem?

Corrosioin allowance is usually considered on the inside surfaces that are in contact with the process. The raised face portion of the flange should not come in contact with the process provided it is gasketed correctly, therefore corrosion allowance should not be a factor here, only on the bore. Or so is my opinion.

chaulklate/sharjeelfaiz:

In the case described, and assuming that the gasket is properly seated, the corrosion will happen on raised faced maximum upto the gasket ID. Beyond the gasket ID the process fluid will not "wet" the riased face.

-jehan

I some what disagree with the replies given above even though I also follow the philosophy of not applying any corrosion allowance on gasket face.

Main reason for the disagreement are as below;

1. All our calculations are considering proper gasket seating. In case of improper gasket seating, leakage will start which is not desirable.

2. If it is considered that no corrosion takes place on gasket face, why designers always ask for weld overlay/ lining on the gasket face also in case of cladded equipment.

3. No joint is perfect, leakage rate however may be negligible and gasket seating is the place where liquid is probably stagnant and not flowing which makes it more corrosive.

4. Many time (not always) designers ask for SS/ allow steel or NACE compliant bolting for SS/ Alloy Steel equipment or equipment in sour service. If galvanic corrosion is not a concern (for dissimilar material) and no leakage expected, we need not consider alloy steel/ NACE compliant bolting??


These are some of the questions I have in my mind but no firm reason for following or not following these requirements.

In my opinion, corrosion possibility is there on gasket face also but the corrosion rate will be very less in this area as compare to other parts of equipment.

Regards