REQUIRED MINIMUM THICKNESS COVER FOR NITROGEN INJECTION 1

[Nazil1]

I’ve been asked to calculate the minimum thickness of a custom blind flange, which will serve as a cover after nitrogen injection and then be transported to the site. My boss estimated a thickness of around 9-10 mm, given that the design pressure is only 2 bar.

Here’s the input data I’m using:

Design pressure: 2 bar (nitrogen)
OD of the flange: 1129 mm
ID of the flange: 900 mm
Design temperature: 35°C
After performing manual calculations and using PV Elite, I’m getting a much higher thickness than my boss’s estimate. The minimum thickness calculated in CodeCalc is around 83 mm. I also tried using the floating head configuration, but the results are still close to this value.

Has anyone here experienced a similar situation, or does anyone have insights into why my calculated thickness is significantly higher than expected? Could I be missing something in my calculation or methodology?

Thank for your help!

 

[LittleInch]

What flange are you attaching it to? Code and pressure rating?

ASME VIII always gives you thick flanges.

Ask him how he estimated that thickness. Looks a bit thin to me. Has he not included bending?



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[Nazil1]

@LittleInch That is the cover that will be customized and will be installed to the girth flange. The cover I mean can be a blind flange or a cover as shown in figure UG-34 (j) and (k). The input data that I provide is girth flange data. So, that's why I ask if you all have had such an experience or can share insight for me. Thank

 

[CuMo]

9-10mm is really too thin for such a large diameter blind.

The force across your blind will be at least: The area within the 900mm ID multiplied by your pressure or:
Force [Newtons] = (900mm/2)^2 x Pi x P (where P is your pressure)
Since you're working in SI units, it's best to convert your pressure to N/mm^2.
2 BAR G = 0.2 N/mm^2 (MPa)

Then F ~ 127235 N or this is approximately 12.7 metric tonnes of force across your blind (the weight of a BUS!)

This is just to illustrate what kind of force you will be "restraining" with this cover.

You're looking atleast at 50mm thick blind if made from mild steel.
I suggest as a minimum - at least find standard EN 1092-1 and look at Table 10. Dimensions of PN 2,5 flanges. Look up a DN1000 or DN1200 blind dimensions - thickness C4.
Ask someone with experience to check your design before you go ahead with manufacture!

 

[LittleInch]

I understand that, but assume you are connecting to some sort of flange. What is that flange?

Custom flanges are a bit problem to design with the required level of safety. There is often a desire to just fab something from a scrap bit of steel as it's "Only temporary".... You don't know and that thought process kills people.

There is about 13.5 tonnes of force on that blind flange at 2 bar. If that blind fails it could very easily kill people as it flies off.

Stick to your calculation unless you can find an alternative way of doing it that you personally are happy to stand next to that flange when they pressure it to 2 bar....

I agree with the post above which was written whilst I was writing the above.



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[Nazil1]

Thank you @LittleInch

Previously, I had 2 discussions and even argued with my manager, this is the 3rd time, so I am asking here, I recommend the minimum required thickness as I have explained. Then my manager said "is it not too thick?" for economic reasons.

Thank you for your advice. Your last sentence is a reminder for me.

 

[LittleInch]

The other one to avoid is not to weld on channel or ribs onto a flat sheet of thinner steel. Doesn't work either....



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