Re: Allowable external forces on Wellhead christmas tree equipment.

From: <Gordon.Reddek@Alcan.com>
Date: Tue Jul 20 2004 - 18:46:00 EDT

Maple,

This is a standard problem and not well resolved in the industry. A very safe way to handle this one is to assume that the flange can take only the rated pressure. If you are operating below the rated pressure of the flange then you can use the approach I have listed below where the excess pressure between the design pressure and the flange rated pressure is converted into acceptable loading on the flange. If you are operating the flange a the full rated pressure then I am afraid you are in deep dudu because you do not have excess pressure to convert to applied loads. You then have the following messy options:
1) calculate the flange loads using CAESAR, AutoPipe or another respectable program, then check the design of the flange to one of the pressure vessel codes like ASME VIII Appendix 2. 2) Carry out a finite element analysis.

Now I will put in a free plug. The easy way out of 1) and 2) above is to purchase the program called AxiPro at www.paulin.com. Check it out on the web.

Quote:
The flange external loads are converted to an equivalent pressure and added to the operating pressure to calculate the total flange pressure. The equivalent pressure for external moment and force can be calculated according to B31.7, Nuclear piping code Par 1-704.5(a), as follows:

Peq=(16M/(pi,G^3)) + (4F/(pi.G^2))

where:

M       =       External bending moment
F       =       External axial force (tension only)
G       =       Diameter at location of gasket load reaction

Effective flange pressure = Poperating + Peq

Unquote.

Regards,

Gordon Reddek

Gordon Reddek
Specialist Mechanical Engineer
Alcan Engineering, Level 3, 443 Queen St, Brisbane, Qld 4001, Australia. Tel: +61 7 3328 6424
Fax: +61 7 3328 6990
Email: gordon.reddek@alcan.com

mapte@technip.com
20/07/2004 04:55 PM
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Subject
[PipingDesign] Allowable external forces on Wellhead christmas tree
equipment.

Hi,
We are working for an onshore oil extraction project, including a number of
well head christmas trees and associated piping. The question is as follows:
What are the allowable external forces (due to connected piping) on the flowing wing valve of the well head christmas tree equipment.

We looked in to API 6A, but it clearly states that "The effects of external
loads (i.e. bending moments, tensions, etc.) on the assembly of components are not within the scope of this document". API 6AF (Technical report on the capabilities of API flanges under combinations of load) and API 6AF1( Technical report on temperature derating on API flanges under combinations of loading) talk about load capacity of API flanges in relation with the bore pressure. (No mention of external loading.)

Anybody who has faced a similar problem? What values are used for allowable
loads? Is there any other standard / code that covers this topic?

Have a nice day.
-Mandar.
This message comes from Mandar's desk.

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Received on Tue Jul 20 18:46:00 2004