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Light Shell Stiffener Ring abutting Manway neck / PD5500

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CuMo

Mechanical
May 1, 2007
146
Hello folks.
I'm struggling with the following situation.
I have a big diameter thin walled stainless steel vessel with light stiffening rings for the shell cylinder.
Full Vac design condition is present of course.

Our client has requested a specific position for the manway
so that one of the light stiffeners has to "go through" it.

I am almost certain the manway itself will provide a lot more rigidity in the area if compared to the light stiffener
but have been unable to find a procedure which could help me prove it.

Both PD5500 and ASME VIII-1 seem to address stiffener rings with unsupported lengths in an identical way
and if I don't consider the manway - the gap in the ring would be way to great to satisfy any of the codes.
(At least by doing some quick on screen math).
But the manway neck/flange are in place so can't just be ignored I guess.
Have you had this situation before?

Sketch attached for reference.

Any comments welcome!
 
 https://files.engineering.com/getfile.aspx?folder=b311f1f3-3f50-4654-9ce9-8be7ff0b4870&file=Stiffener.png
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Hello,
I don't think that Figure UG 29.2 could be applied in your case.
check interpretation VIII-1-89-275 for more guidance. i think U-2(g) is your way to go.
Regards,


Detailing is a hobby,
 
Are you sure that stiffening rings are required ?- Check it

Regards
 
The attached sketch shows three stiffener rings for 3000 mm eff. length. Personnaly i am not convinced for the necessity of stiffener(s). These rings seem for insulation rather than stiffen rings. What is the design vacuum/ external pressure ?
 
Oh yes. They are required.
It's a 3500mm I/D x 10mm thk 316L shell under full vac. Approximately 6m long.
The maximum allowable external pressure for each section between stiffeners is about 0.14 MPa.
 
Place the reinforcing ring higher than the manway

Be careful with legs, the arrangement of which may cause concentrated loads to be imposed on the shell. The manway shall be located away of legs.

Avoid excessive welds around opening: nozzle to shell, pad and stiffening ring

Are you sure that reinforcing pad is required?

Are you sure that standard flanges race face is good for full vacuum?.

Was wind and earthquake considered?

Regards
 
Thanks r6155.
I think we might move the manway higher rather than the stiffener.
Yes, I've triple checked - the pad is required for nozzle reinforcement.
We have had other vessels with such facings and F/V. Hasn't been an issue so far.
Wind was considered but earthquake isn't a requirement (UK - not actively seismic zone).


Jay, thank you very much!
I think it's worth copying this interpretation in this thread:

"Interpretation: VIII-1-89-275

Subject: Section VIII, Division 1 (1989 Edition, 1989 Addenda), U-2(g) and UG-29(b)

Date Issued: February 13, 1991

File: BC91-011


Question: When a stiffener ring extends completely around the outside circumference of a cylinder and intersects a nozzle, may a connection between a nozzle and stiffener be made if the required moment of inertia of the ring shell section is maintained through the nozzle per UG-29(b) and design and construction details are submitted and accepted by the Authorized Inspector per U-2(g)?


Reply: Yes."
 
Update.
Client agreed for us to move the manway above the stiffener so problem solved.

On the other hand, I was thinking.
If the nozzle is reinforced both for internal pressure and F/V, the zone shouldn't be prone to failure, should it?
If the codes aren't specifically addressing any specific rules for such scenarios - then it's probably fine
if all component calcs are up to standard.
 
Wrong decision. Manway shall be installed as low as possible to facilitate access and egress.

"If the nozzle is reinforced both for internal pressure and F/V, the zone shouldn't be prone to failure, should it?"
YOU ARE SOME CONFUSED, READ THE CODE.

I take the opportunity to comment: the tailing lug should not be placed on the shell to avoid out of roundness, specially for full vacuum, Try to design with two of the legs and temporary device.

Regards
 
Is it possible to install the manway in the bottom of the vessel?

lm
 
It is possible, it depends on the design engineer.

Regards
 
If the stiffeners are for insulation only probably there is nothing wrong with the location of the stiffeners. I guess that the ring name was taken from a generic drawing.

I have to admit that ı did not check the cylinder wall thichness for the full vacuum. Please check it first and confirm they are for insulation only. Otherwise you may find yourself in a finite element analysis to prove the system works under full vacuum as it is.
 
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