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#8991 - 12/12/06 08:28 AM Zick Analysis and Saddle Calculation
saurabh.gajwani Offline

Registered: 03/30/06
Posts: 17
Loc: New Delhi
Please suggest me for the followings points:-

(i) For calculating Circumferential Stress at Horn of Saddle, Pvelite does not consider thickness of wear/wrapper plate except when saddle location satisfy A<= R/2 condition.I think it has nothing to do with saddle location as for bending both shell and wrapper plate thickness play their role. I studied from D. Moss, that also not take into account wrapper plate thickness but from Zick Analysis Papers which states wrapper plate thickness shall be taken into account if saddle location is near to head but it does not tell how much near ?In my opinion both thicknesses i.e. shell and wrapper thickness shall be taken into account.

(ii) For calculating required Anochor Bolt area for Shear Stress Pvelite takes Bolt Allowable Stress corresponding to Pressure bolt's allowable stress while Criteria for allowable stress for structural parts are different i.e.
For Tension, Allowable Stress = 0.6 x Sy
For Shear, Allowable Stress = 0.4 x Sy
For Bending, Allowable Stress = 0.66 x Sy
where, Sy = Yield Stress

(iii) Also load due to Friction force (Cofficient of friction X Operating Weight) shall be shared only by fixed saddle support.
Hence, Required anchor bolt area = Frictional Force / (N * Allowable shear stress)
where, N = No. of Anchor bolts for Fixed Saddle.
Am I right ?

Saurabh Gajwani
Engineer- Mechanical (Static Equipments)
Saipem Triune Projects Pvt. Ltd.
New Delhi - 110044
Mobile :- 9873732200

#9299 - 01/09/07 01:00 PM Re: Zick Analysis and Saddle Calculation [Re: saurabh.gajwani]
Ray_Delaforce Offline

Registered: 01/02/03
Posts: 743
Loc: Houston, TX
(i) The wrapper plate is not included in the stress calculation at the horn of the saddle when A<=R/2, so you are quite correct on this point. The reason for this is to be found in the guidelines in the: ‘Pressure Vessel Design Handbook’ by Henry H Bednar, and the: ‘Pressure Vessel Handbook’ by Eugene F Megyesy. We have followed those guidelines in our software. In PV Elite, there is provision for performing the saddle analysis per the British Code: PD 5500. In that code, different criteria are applied. The inclusion of the wrapper plate in the calculation depends upon the subtended angle of the wrapper plate, and its width. Whilst I may share your opinion with regard the R/2 ratio, we have taken the conservative course in our software.

(ii) The bolt shear stress and tensile stress are not governed by the code rules, as the supporting structure is not part of the vessel envelope. The user can over ride the values PV Elite uses by default. That is according to the discretion of the user.

(iii) You are right about the friction force. However, you can change the friction coefficient suggest by PV Elite to your liking.

Ray Delaforce
CADWorx & Analysis Solutions
Hexagon PPM


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