So I often work with large diameter flanges designed according to MSS SP-44, and recently have an increasing need to check for failure due to external forces. I started with CII flange analysis tool and then moved to ASME Sec VIII Div 1&2. I created an excel spreadsheet following all of the calculations presented in Div 2, section 4.16 Design Rules for Flanged Joints.

I've been through MSS SP-44, B16.5 and B16.47 and found the links that state that these calculations are covered for all the sizes I'm working with. The problems come up when I start to compare my results with CII.

To test my calculations, I used a 6" ANSI 300 flange. All the info needed for this should fall in the default CII database. Some of my data adds up, but the part that raises a red flag for me is the output from CII for Effective gasket seating width (b) and Diameter of gasket load reaction (G).

Both of these should come directly from Div2, Tables 4.16.1, 4.16.2, and 4.16.3. CII even allows me to put in my exact gasket dimensions according to Flexitallic.

Using a 6" spiral gasket having O.D 8.25" and I.D. 7.1875", according to Table 4.16.2, N=0.25". Table 4.16.3 shows b_o=0.125", and by section 4.16.6.1, step 3, b=0.125" & G=7.71875.

CII is giving me an output showing b=0.2331 and G=7.6538. Both these values are throwing off several other calculations.

So I guess my main question is "Does CII use other calcuations or include other parameters in these calculation that aren't stated in the help facility dialogue boxes?"

There may be other issues, but this is the most obvious and easiest to check.

yes, strange it should be 7.71875, in fact if you check with database of equivalent pressure in Caesar, there G is 7.72.