Loose flange calculations for external pressure

[GD_P]

Hello Forum,

Consider a cylindrical pressure vessel (shell) of 1000 mm OD & with 1150 mm concentric cylinder (jacket). The shell has 2 loose flanges (slip on type) welded at the both ends. The jacket is welded to the loose body flanges of the shell on their back side.
Shell has cover flange on one end & closed dish head at other end bolted to the loose flanges. Shell is under vacuum, whereas jacket is under positive pressure 15 bar.
Now I have doubt regarding the design of the shell loose flange?
Design of the loose body flange is based on the gasket seating, and is far ahead of to be based on operating pressure (external).
But we want to make sure that we are not disregarding the design of of the flange for 15 bar jacket pressure, even if it would have been based on operating pressure instead of gasket seating.
So I am confused what external pressure shall be considered for the flange design?
1 bar
OR
1 + 15 = 16 bar
If 1 bar how , how do I consider the effect of the 15 bar in the jacket which is directly welded on the back side of the flange. Will designing it as closure for 15 bar will suffice?
If 16 bar, as per the ASME sec. VIII div 1 mand appdx 2, which state in 2-11 "The design of flanges for external pressure only", can we consider the flange is subjected to purely 16 bar external pressure?
Please do share your opinion / experience.
Any help or any reference document will be greatly appreciated.
Thanks in advance.

GD_P

 

[DriveMeNuts]

Sounds like pressure on a flat circular plate which has a hole in it.
Table 11.2 of Roark's formulas for stress and strain may provide your answer.
Certainly doesn't sound like something that can be covered by the code.

 

[SnTMan]

If I were to attempt to force this design into an Appendix 2 calculation, I'd design for 16 bar external. I doubt I'd be happy with the attempt.

You are not likely to find any reference documents for your proposed construction.

This is clearly a U-2(g) design.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[MikeG7]

If the jacket is welded onto the back of the ring flange inside of the holes, right. So that makes the jacket chamber:-in that case your flange is the "jacket closing bar" and treat it as per appendix 9, with full design pressure. I can't say that the jacket pressure adds to any force used in the flange rotation design formulas or bolting design checks in App 2
Michael

 

[SnTMan]

You will be pretty much OK with Appendix 2 methods up to the point of calculating flange moments and stresses. Then it gets messy...

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[LittleInch]

A drawing of this end piece would answer a lot of questions here.

As far as I can figure out from your description you have a 1000mm tube/shell on which you have welded a slip on flange of unknown code and unknown pressure rating.

You've then decided to weld on the slightly larger jacket pipe to some part of the flange? So this is acting as an end bulkhead.

This flange then has at one end a blind flange and at the other end a domed end with its own flange so that the dome end is bolted to the flange?

This is weird.

I think your flange face is only seeing 1 barg negative pressure.

However the issue for me will be the connection from shell to flange which is subject to a high external pressure, all bearing on a fillet weld at the end of your very stiff flange.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[GD_P]

Thank you all for your response.
The flange can be designed as closure only, but it will not ensure combined effect of jacket pressure and flange acting under gasket seating condition.
Please find the image attached below for your reference.

I have a options to encounter the design of flange for the jacket pressure, what if I calculate the total load Pj acting on the flange due to external jacket pressure and then calculate the moment due to this load about gasket width centre
Mj = Pj*x, where x is the moment arm.
This moment is then added to the bolt load (for gasket seating) moment to obtain the equivalent moment.
Using this equivalent moment, flange thickness is evaluated.

One more point regarding thermal stresses shell (MOC-CS) is at 105 deg C and jacket (MOC-SS) is at 180 deg i.e., are at different operating pressure. This results in thermal compressive & tensile stresses in the shell & jacket respectively. Now to include to the effect of thermal stresses on the flange design, calculate the thermal force Ft in shell or jacket. Composite slab at 2 temp fixed at one end & free at other bend are considered for evaluating the forces
Calculate the moment Mt = Ft*Ra, where Ra is the centre distance between the shell & jacket.
Now final eq moment is calculated Mfeq= Mo + Mj + Mt.
Subsequently moment Mfeq is used for calculation of flange thickness.

Is this a correct approach?
Is it possible to make it simplified?

Since here we are considering the combined effect of loading, is there any provision to increase the allowable stresses as per code?


GD_P