When designing flat heads and covers, bending stresses

at the edge or in the center of the cover typically control

the design thickness. Per UG-23(c), when loads subject a

component to a combination of primary membrane stress plus

primary bending stress, the stress in the component shall not

exceed 1-1/2 times the maximum allowable stress value in

tension from Section II, Part D. Does this mean that I can use

1.5S for the allowable stress when calculating the required

thickness?

Ikram

No. This means that if you design a flat end with a fancy shape (like with ribs or other strengthening members not described in SecVIII-1), and you deem that formula given in the Code does not describe it with a satsfactory degree of accuracy, you may say you use U-2(g), performing FEA for instance. Then your criteria will be those from UG-23(c).

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Konrad Anikiel

when you are using UG-34 formulas for the unstayed flat haeds, you are designing the flat plates against bending streses only and not against primary memberane stresses. When the flat plate is stressed, it remains not the exactly flat, at that time primary memberane stresses also induced & those are very little as compared to bending stresses. if you are going to take theses stresses also into account, then you may use UG-23(c) criteria.

Dear Konard: Did I say right? Please give your valued comments.

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Thanks & Regards,
Nasir
Welding Engineer
DESCON Engineering Limited.
Lahore, Pakistan.
Mobile # 0092-336-4145402