wall thickness calculation 1

[Pras]

Hello,

I am in process of designing a flanged meter housing of Class 1500 rating at design temperature of 464°F in CF3M material. The flanges to be used are of material A182 F316L. The inner radius of the housing is 39 mm ( 1.5354”). I have followed following procedure to determine the minimum the wall thickness of the housing.

(1) OPERATING CONDITION
Calculate the wall thickness as per ASME Section VIII Div. I, UG27 at working pressure of 2386 psig (flange rating) at 464°F, by taking maximum allowable stress of CF3M as 10899 psi (as per ASME section II part-D, quality factor as 0.8). This gives me min wall thickness required as 0.387”

(2) HYDRO TEST CONDITION
Calculate the wall thickness as per ASME Section VIII Div. I, UG27 at working pressure of 5400 psig at 100°F, by taking maximum allowable stress of CF3M as 16000 psi (as per ASME section II part-D, quality factor as 0.8). Here the test pressure of 5400 psi is worked out as (1.5 x Max. allowable working pressure of F316L flange at 100°F) This gives me min wall thickness required as 0.649”.

Hence the final wall thickness selected is 0.649”. Is this procedure correct in all respects?
Please comment.

Pras

 

Hello,

I think that the geometry of your housing will be complex enough to challange the limits of the design rules you are using. Perhaps you should cut-and-try. That is to say, take your best shot at the design but then use a VERY carefully developed finite element analysis model to do the analysis. Finally, proof test it to destruction if it is to be a production item.

Regards, John.

 

[prex]

Your calculation for operating condition seems correct to me (didn't check allowable stress value however).
For hydro test condition you are unnecessarily safe: you may take 90% of minimum yield stress as the allowable stress (21600 psi). As far as I remember this requirement is not in Div.1, but it certainly is in Div.2.
Note also that if this is a single component with a well defined design pressure, you don't need to calculate and test it for the flange rating at ambiente temperature. prex
motori@xcalcsREMOVE.com

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[Pras]

Prex,
Thanks for the reply.
The design pressure for the flanged housing is the maximum allowable pressure at design temperature (464°F)of the flange ( rating) as per ASME B16.5.
As this item is going to be used as a 'Flanged fitting', I think, it needs to be calculated and tested as per 'hydrotest' requirements at ambient temperature as well.
Please correct me if I'm wrong.

Pras

 

[prex]

In my opinion it all depends on how it is going to be used.
If this is a generic component fabricated in multiple copies that is going to be sold to users for installation on an a priori unknown system, then you are OK, and you correctly use the ratings per B16.5.
If it's a single component for a specific installation, then you know in advance the design conditions (it doesn't matter if you define them based on what the flanges may accept) and that's all you need.
prex
motori@xcalcsREMOVE.com

http://www.xcalcs.com

Online tools for structural design