CORROSION ALLOWANCE AND ASME B16.34

[smh345]

ASME B16.34 does not appear to allow for any corrosion allowance in the WT. I know that the WT required per the standard is very conservative and is based on very low stresses. Does any one have any views regarding ASME B16.34 WT and corrosion allowances? Is it necessary to increase the thickness over and above ASME B16.34 requirements if you could demonstrate by calculation that the thickness is adequate, and still in compliance with the standard?

 

[bvi]

Valves are selected by pressure rating (same as B16.5 flanges) without addition of corrosion allowance. You really don't have an option to add a corosion allowance in any case, since you will be purchasing a standard valve (e.g. Class 300).

 

[smh345]

cb4 - valves are selected by class, but they must also meet the wall thickness (WT) requirements per Table 3. If I have a customer asking for valves to meet ASME B16.34 and also to includ a 3mm CA, how should this be addressed? He is asking for the CA as this is a design requirement of the carbon steel piping system.

 

[bvi]

The disconnect appears to be that someone is purchasing a valve and specifying a corrosion allowance. In my experience, valves are selected, and corrosion allowances are not specified in their purchase. The system has a CA which effects, for example, the schedule pipe that is selected. But even in the example of pipe, the necessary pipe thickness is determined and the pipe is ordered without specifying a CA. Further, in my experience, valves are ordered for the design pressure and temperature, without additional consideration given to the required corrosion allowance. I suspect you are dealing with an inexperienced purchaser.

However, if based on their experience, they want some thickness greater than the B16.34 minimum, then I suppose you would need to supply a valve that had that thickness.

 

[kriger]

I have similar problems with this as smh345. Normally I work in the European tradition with nominal pressure (PN). Now, I could have a system that should be designed for 27 bar and 80 °C. On the first hand one would select PN 40. But then when additional corrosion allowance is required, I feel it is getting complicated.

E.g. if 5 mm corrosion allowance should be added to a DN 200 flange I would need it in PN 160 (according to DIN 2638) to have it with 5 mm more neck wall thickness than the one in PN 40 (according to DIN 2635). I asked a dealer of flanges and he said that I should just order it as PN 40, but with additional (non-standard) wall thickness.

For flanges the difficulties seem not so big, but when it comes to asking for additional corrosion allowance on valve bodies, I am not sure how to cope with it. Can a valve manufacturer tell me what pressure rating I need, if I give the design pressure and temperature and the corrosion allowance?

 

[unclesyd]

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