The stress on F&D head is extremely high in ANSYS Workbench as compared to ASME VIII Div-1.

[Sachin Poudel]

Issue: The stress on F&D head is extremely high in ANSYS Workbench as compared to ASME VIII Div-1 calculation.
Vessel OD: 96”, 106” Seam-Seam
Thickness: 0.4375”
Pressure: 105 psi
Material: SA-24 316L.
The baseplate of Leg as fixed.

I did ANSYS analysis for F&D (ASME 80:10) head. The obtained Eq. stress was 35,000 psi (Membrane stress: 25k) which is extremely high as compared to code calculation. Code calculation gives 14,000 psi.

I performed a similar comparison with the 2:1 Ellipsoidal head. The ANSYS Eq. Stress was 18,000 psi (Membrane Stress: 12,000 psi). This is close to code calculation, code calculation gives 11,500 psi stress.

Also, there was high stress (30k psi) in SUPPORT LEG for the F&D head and just 9k in the ellipsoidal head.
The setup and procedure of analysis were the same for F&D and Ellipsoidal head but there was a high deviation from the code calculation in the case of F&D head while analysis of Ellipsoidal head is in line with code calculation. What can be the cause of deviation in the F&D head?

PS: I have ignored stress concentrated at a point due to singularity.

 

[TGS4]

When you say "code calculation", exactly which calculation are you meaning?

 

[Sachin Poudel]

By code Calculation, I mean ASME Section VIII, Div-1.

 

[TGS4]

I mean, what EXACT calculation/formula are you using. There are multiple calculations in UG-32, Code Case 2260, Appendix 1-4(d), and 1-4(f). Each gives a slightly different result.

May I suggest you take a look at this paper for some additional formulae.

 

[DriveMeNuts]

I would recommend getting a copy of "ESDU 67017 - Elastic Stresses in the Torispherical Head of a Pressure Vessel of Uniform Thickness"
It has tables and graphs of the principal stresses in the knuckle and crown on the inside and outside surface for all sorts of t/D, KR/D, CR/D. From standard ASME Tori's to 2:1 Ellipses.

 

[CKerr]

You say the membrane stress was 25k but your figure shows 17k? Also, looks like there's some bending in the legs in the first figure; is gravity applied? Are there other loads applied?