If the width of shell reinforcement (pad plate or insert plate) is at least as wide as greater of 1.65*Sqrt(R*T) and d/2, then local thickness (Pad +Shell thickness) should be considered in the WRC analysis.

Please let me know whether it is necessary to check the pad to shell joint also. I am facing a problem where the shell is failing at the shell to pad junction.

Whether i should consider it without pad and just check the nozzle to shell thickness by increasing the local thickness to Pad + shell thickness and then there is no need to check the the nozzle with pad i.e. pad to shell junction.

Please clarify.

Regards,
Bipin Balpatki

Hello Bipin

I presume you are referring to WRC 107. Re-pads are not considered in that bulletin. Re-pads are included in our software, but the re-pad is considered as another patch whose diameter is the diameter of the re-pad.

Dear Bipin,

If above criteria is not meet i.e width of pad is not in line with this requirement, one shall not consider advantage of reinforced pad in WRC analysis.

One shall de select pad in Pvelite & check Nozzle stresses as well as Nozzle to attachment junction stresse.

& this is inline with WRC 297 requirement.

Thanks

Thanx for the reply.

But whether for the nozzles with blind flange (Manholes,Handholesetc), we need to check the nozzle to shell & pad to shell junction either considering pressure thrust Or WRC 368 (any one of them).

If yes then we are facing the problem where shell is failing at the pad junction for pressure thrust, then do i need to increase the shell thickness for such case.

Please respond.

Regards,
Bipin

Dear bipin,

1) Local loadings in shell are arised due to external forces.

2) majorly the same forces are due to external piping , External platform arrangements.

3) manholes, vents, drains etc are not the components which would transfer any local loading to the shell.

4) Majorly local loadings are arised only through process nozzles.

HENCE, junctions @ process nozzles are only requried to be checked with WRC.

Hope I answered your query.

Bipin,

Look in the output of the WRC 107, if the curves for looking up stress due to load "P" are exceeded. If that is the case, then you may be using a wrong tool. WRC 107 simulates pressure thrust as radial load on the vessel puling the nozzle out.

Instead, use WRC 368, it provides stresses due to internal pressure including pressure thrust. There is a check box in PV Elite's nozzle dialog, Local stress Analysis Tab.