We are carrying out analysis for an offshore platform duct connecting Gas turbine exhaust to Waste Heat Recovery Unit. We need to calculate SIFs at Miters and tees. Table D of B31.3 code is applicable for D/T less than/ equal to 100 (as per note-1). For our case duct dia. 40",thk.6mm, i.e D/T >100.
Please suggest how to calculate SIFs in this case.

Regards,

First,

Congratulations for actually reading the code including all its notes!

FEA or actual testing can be used to derive SIFs. The reason for this approximate limit is because the assumed beam element behavior starts to cease as the D/T ratio increases. It is not a linear function either, that is D/t=99.99 OK versus D/t=100.01 not OK.

What is commonly done is to use a combination of FEA and beam element analysis to analyze the system. Addressing localized loads/ stresses via FEA.

Hi,

There is an FEA program called FE Pipe for just this purpose. This program handles all D/t problems and many more petrochemical FE problems and is very easy to use after a days training. A company of consultants called FERN in the UK normally handles this software. Failing which you will have to thicken up the wall thickness until D/t is less than 100, may be an expensive solution.