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

Question

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

Sachin Poudel (Mechanical)

(OP)

26 Jun 21 07:26

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 (Mechanical) · Answer 1 · 2021-06-28 19:37:13

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

Sachin Poudel (Mechanical) · Answer 2 · 2021-06-29 03:28:56

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

Sachin Poudel (Mechanical)

(OP)

29 Jun 21 03:28

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

TGS4 (Mechanical) · Answer 3 · 2021-06-29 15:42:57

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 (Mechanical) · Answer 4 · 2021-12-11 13:13:19

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 (Mechanical) · Answer 5 · 2022-02-14 13:25:05

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?

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