Testing pressure criteria: membrane + bending stress < 1.5*Rp/1.05

[Mihe]

Hi
I am verifying the strength of a thin-walled cylinder that is subjected to hydraulic pressure. The design is not strictly ruled by the pressure vessel code. However since there is no other applicable code Annex C “Design by analysis - Method based on stress categories” of EN 13445 is applied. I think the question is relevant also for ASME VIII division 2.
I have verified that the cylinder complies with the DBF formulas regarding cylinder wall thickness of EN 13445 and fatigue is not an issue for this component.

At the end of the cylinder there is a step that creates bending stress in the cylinder wall. The general primary membrane stress (Pm), local primary membrane stress (PL) and the Primary bending stress (Pb) has been calculated(linearized) by FEA and integration of the stress field according to the code. It is then to be verified that Pm<f and that PL+Pb<1.5f.

The design will be proof tested with 2 times the normal working pressure. For pressure test the stress limit is f=Rp/1.05. That means that in view of PL+Pb the stress limit 1.5*f will be considerably higher than the yield limit (1.5*f =1.43*Rp).
I get the point that the section will not be plastic through the full wall thickness until PL+Pb = 1.5*Rp but I want to be sure that I have not missed any rule or exception in annex C.

Question: -Is it correct that the pressure test load case would be ok in view of Annex C, if:
Pm<f (hence Pm < Rp/1.05) and
PL+Pb < 1.5*f (hence PL+Pm < 1.43*Rp)?
BR/Mihe

 

[DriveMeNuts]

r6155,
What you describe is a fabricator stuff up which the fabricator rectified. That is expected.
What if the issue was with the Purchaser supplied design calculations. Is that also the fabricators fault? I don't think so.

 

[saplanti]

Mihe,

You mention about the step at the end of the cylindrical section. Is this step within the acceptable limits or is this step created by 1/3 or 1/4 rules of the transition?

I guess a sketch would be beneficial for the sake of discussion.

 

[r6155]

@ DriveMeNuts
The user and the manufacturer can agree on a contract at their convenience.

Regards

 

[DriveMeNuts]

There would be no need for a contract on this issue. It is fundamental commercial law.
If it is the design provided by the purchaser which is at fault, then the Purchaser provides a repair design and pays the costs.
If it is the fabricator that stuffed up, then they pay for repairs.
Why would the fabricator pay for the Purchasers stuff up?
In the process trying to squirm and snake your way out of this hole that you have created for yourself, you now come a cross as a troll.

 

[r6155]

@ DriveMeNuts
What are you looking for? If you think you know why you ask?
Do you have any experience in lawsuits for violation of commercial contracts?

Regards

 

[DriveMeNuts]

Yes, and Keep Digging.