Flanges subjected to external moment

[Cheops]

I am looking for information covering the design of flanges subjected to external moments. Traditionally, an equivalent pressure was calculated using the formula: 16*M/(pi*G^3). But there has been some recent studies indicating that this is too conservative and that a factor of 8 would be more appropriate. Any hints ?

 

[samuelliu]

That will depond on the relationship between the external moment Me and the maximum sustained moment Mm. Refer to NC-3658, ASME BPVC Section III, Div.1, for detals.

 

[Cheops]

Samuelliu, I have a copy of the first 2 pages of NC-3658, taken from the 2001 edition of the Code. When the moment (Mfd) includes dynamic loads, the factor of 8 can be used. But we are having an argument with the Authorized Inspector. The AI feels that section III methods are based on a higher level of NDE and on more control on material and that the formulae specified in there are not necessarily safe for the ASME sec VIII div. 1 vessels. Any comment about that ?

 

[arto]

Look in the old Kellogg's piping book pg. 78 if you want another reference for Peq

 

[LSThill]

Hi Rectangular Tank Design, samuelliu (Mechanical), arto (Mechanical)

API 579 LEVEL III ANALYSIS, Using FE NOZZLE

http://www.codeware.com

or

Nozzle/Pro

http://www.paulin.com/newprg/nozzle_pro.htm

Nozzle/Pro was designed specifically for the instances where excessive conservatism or dangerous designs might result from dated and often inadequate simplified techniques. Nozzle/Pro is "sharpening the pencil", and eliminating uncertainty in a calculation. If a WRC 107 method, for example, in cases where WRC 107 estimates a result within plus or minus 150%, Nozzle/Pro can and will produce a result within 15%, and will produce it much faster.

High resolution graphic plots allow the user to easily verify the data input. The user never sees node or element numbers, since these remain internal to the program. Data input is in the form of geometric details relevant to the section being modeled. Help screens are available to guide the user with data input entries. The finite element mesh is automatically generated with mesh concentration in areas of interest, like weld penetration lines. Input graphics may be displayed with hidden line removal, element shrinkage, and light shaded plots. Output is produced for deformation, code calculated stresses, code allowables, stress intensification factors and nozzle flexibility values. Deformations and stresses can be viewed on screen as multi-color shaded plots, which can be sent to high resolution laser printers or to color inkjet printers like the HP Paintjet XL300. Contoured stress plots and distorted shapes may be viewed with optional hidden line removal, and element separation. Graphic plots may be interactively viewed, with zoom, pan and rotation features allowing viewing at any angle and distance.

For piping stress analysis, ASME B31 expansion stress results are presented. However, since the piping code has several shortcomings and inaccuracies where intersections/nozzles are concerned, code interpretations are derived using input from the ASME Nuclear section III and section VIII division II (nuclear) ASME code cases, and on published fatigue and burst test studies. These relationships between code stresses and code allowables have been verified by comparison to actual failure data. The resultant code stress reports give the maximum code stress, its B31 allowable, and the corresponding ASME section III Class 1, and Section VIII, Div.2 allowables. Detailed stress reports are given for primary, secondary and peak stresses, and the allowed number of cycles for a given stress is also printed. Fatigue evaluation for vessels and nozzles is fully covered by FE/PIPE, using stored fatigue curves from Appendix I of ASME III and Appendix 5 of ASME VIII. Strain concentration factors are included where required. Load cases are automatically set up to satisfy code requirements, based on specified loading conditions. Occasional loads can be evaluated to primary collapse or fatigue criteria.

Stress Intensification factors and flexibilities (axial, in-plane, out-of-plane and torsional) are calculated from the finite element model, and may be applied to B31 analysis of an intersection (e.g. in CAESAR II). These SIF's are independent of the standard B31 SIF tables. FE/PIPE also produces an SIF report which provides comparison with B31.1,B31.3 and WRC 330 values, using the same geometry throughout. By using the SIF's and flexibilities generated by Nozzle/Pro, accuracy of "beam-type" pipe flexibility calculations can be greatly improved. An estimation of load reduction due to the use of the finite element calculated flexibilities, is also provided.



Stress calculation can be made in Nozzle/Pro according to WRC107 and WRC297, and a comparison made with the finite element calculated stresses. This allows the user to be able to see when WRC values are actually valid. This is useful since the WRC guidelines were originally based on a limited range of test data.

Other features of Nozzle/Pro include:
1) Stresses at intersections due to pressure/pressure thrust
2) Thermal Stress due to linear temperature gradients across the wall.
3) Intersection reinforcements models to conform to B31.1 Appendix D

NOZZLE PRO applies automated finite element techniques to analyze pressure vessel nozzles. Built-in intelligent meshing technology is used to evaluate the header/branch intersection and to automatically create a finite element model. Shell header types permitted are hemi, elliptical, conical dished and flat heads, and cylindrical shells. Nozzles may be straight, pad reinforced, or self reinforced. A materials database contains allowable stresses, expansion coefficients, yield stresses etc. Hillside nozzles are permitted, as are nozzles with tilted central axis.

Nozzle loads (forces and moments) are specified by the user, together with number of cycles for operation and occasional load definitions. The program calculates stresses in the header and branch, stress intensification factors (for use in pipe stress analysis programs like CAESAR II), and stiffness values for the intersection. Stress values are compared to values calculated according to ASME B31.1, B31.3, WRC330, ASME III, and ASME VIII Division 2. Nozzle Fatigue analysis is calculated in accordance with Div.2 rules. Tabular reports and stress contour graphics are generated in HTML format.

Leonard@thill.biz

http://www.thill.biz

 

[Cheops]

Arto, I don't have Kellogg handbook for piping(I am a Pressure Vessel guy). Does it use a factor of 8 or 16 when calculating the equivalent pressure ? Thanks.

 

[arto]

They use "16" :
pe = 16M/[pi*G^3] + 4F/[pi*G^2], then combine this equivalent Pressure with actual pressure to check flange [i.e., App.2 calc's. or B16.5 charts]