B31.3 (2024) fig. 323.2.2-1 note 1 min temp of blinds/blanks w/o impact testing

[Martin Jones]

Can someone please explain note 1 regarding nominal thickness T is 1/4 of the total thickness of blind flanges / blank ? Does this for example mean that for a blind/blank of 50mm thickness in A516 Gr.60 normalised (curve D) the actual thickness T to use in table 323.2.2-1 is 1/4 x 50 =12,5 which means that the 50mm blank/blind is OK to -48°C without impact testing (12,5mm wall thickness for curve D = -48°C) ? And what is the reason for reducing the actual thickness to 1/4 when reading data from table 323.2.2-1 ?? Any help greatly appreciated to aid my understanding.

 

[David3399]

That is correct. Total thickness / 4 is the governing thickness. Sec. VIII Div 1 is the same.

 

[GD2]

Stress distribution in a flat plate is more uniform than a cylindrical vessel. A major contributor shear stress in cylindrical vessel has also minor impact in flat plates.
The 1/4 thickness rule by the code is a conservative measure for flatheads and tube sheets for the reduced stress.