thePetroStreet

My general ? is can I design a 12' tall x 12' dia x 3/16" thk stainless steel tank to 650 code using a 20" manway flange and blind flange burned out of 3/4" SS plate instead of a standard nozzle/flange with bolt on blind flange?

Reason would be for less expense.

Appreciate your help,
Robert P.

Your question is regarding blind flange only that you want to make that from a plate?

Yes, may I make blind flange from plate instead of buying an expensive blind flange.

I was told this is not acceptable yet I have seen such in the past.

Based on described conditions (diameter, heignt, shell thickness, pressure = atmospheric, temperature = ambient), 3/4" SS plate can be used as flange and cover (blind).

Comment:
If considered 17 ft of height, API 650 requires a thickness of 10 mm (3/8 inches) for the cover/blind whereas a thickness of 6 mm (1/4 inches) for the flange. Moreover, 28 Nos. 20 mm diameter bolts and 24 mm diameter bolt hole size is required.
For other details and dimensions (like inner diameter, outer diameter, bolt circle diameter, etc.), please refer API 650 11th Edition, June 2007
Table 5-3: Thickness of Shell Manhole Cover Plate and Bolting Flange
Table 5-4: Dimensions for Shell Manhole Neck Thickness
Table 5-5: Dimensions for Bolt Circle Diameter Db and Cover Plate Diameter Dc for Shell Manholes
Figure 5-7A Shell Manhole
NOTE: Appendix S is silent for any change in values of above mentioned tables. Hence, can be used as it is.

Hope the answer would be satisfactory to your requirement.
OPEN for DISCUSSION.

I agree with anwer.
Adequate explanation.