I am analysing a PSV piping . This piping is in fact boiler vendor's supply, however I need to verify the analysis due to contractual terms..
The vendor has attached a Pressure balanced expansion joint to the discharge elbow and the size is increased to vent pipe size after the EJ. This makes this one combined system.
The question I am concerned is DLF factor.The vendor has calculated DLF as per B31.1 appendix II. However I understand that since the outlet elbow is further connected to the vent pipe by EJ the PSV reaction forces can cause deflections on that piping also.So the simple calculation of DLF will not be applicable in this case. I modelled the piping from run pipe to silencer with the PSV branch as anchor and found the natural frequencies of the system. I used The time period calculated from this for DLF calculation.
Now the problem is that I get a higher DLF (close to 2) with this method. The vendor says they have always used this design and nobody complained (they have some big names in their client list including some international power majors). They have shown similar drawings used in their past projects approved by clients without any comments.Although they are not sure if the stress analysis was verified by clients .
Am I missing some thing? Any suggestions /Criticism are welcome.