Hello guys, I have a question on Cf factor used in IS:875

When we programmed the IS-875 code in PV Elite in 1995 we were told that by our Indian dealer and an Indian company assisting us, that Cf (force coefficient or shape factor) should be 0.7 for cylindrical vessels.

But, recently we were pointed the paragraph 6.3.2.2 in IS:875 (Part3) , page 38/40 that we need to find Cf based on the vessel height to diameter ratio.

User can always overwrite Cf using the shape factor input field from Tools menu -> Configuration.

What is typically used in the Indian companies?

Typically 0.7 is used in Indian Companies. However i have come across one project (for Indian Refinery) where we had taken higher Cf value.

Cf value was increased based on the H/D ratio. Refer the detail below.
For e.g. for H/D Ratio (up to 2) - Cf--> 0.7, H/D Ratio (>2 up to 5) - Cf --> 0.8 etc... Maximum of Cf taken was 1.2

Shell/skirt thickness were increased to overcome the bending stress due to wind moment in operating condition.

If you review the IS-875 table 23, it is indicating to use a higher Cf value, based on the H/d ratio.

It seems that you are not using the higher Cf value all the time. IS-875 also has option to do more detailed procedure to compute the Cf.

We may have to add a check box for it instead of using the higher Cf value per table 23 in IS-875.

Another question for H/D of (> 10 and < 20 ) Cf = 1.0

For infinity the Cf is 1.2.

I am going to assume h/D value of > 40 as infinity. Hopefully this will satisfy everybody.

For all H/D values greater than 20, we had considered Cf value of 1.2