- 3/8” or ¾” means the nominal OD of the bolt.
- For Course threads the TPI will be 16 and for fine threads the TPI will be 20.
- Actually that’s according to the American standards. Metric standards define it in eg. M10 * 1.5 where, 10 is the nominal diameter and 1.5 is the pitch.
- If Pitch is not mentioned, then we take it as that thread is belonging to the course group.
Any opening in a pressure vessel is kept to a minimum and for a man entry an elliptical hole is lesser in size than the corresponding circular hole. More over it is prime concern to have a smoothed generous radius at the corners to eliminate stress concentration. Hence other geometrical shapes like rectangle and square are ruled out. To compensate for the loss of material in the shell due to opening, a doubler ring has to be provided around the opening. The thickness of the ring depends on the axis length along the dirrection in which the stresses are maximum and the thickness of the shell. It is important to align the minor axis along the length of the vessel, as the stress in this direction is maximum. Longitudinal stress: Pd/2t where P= pressure inside the vessel, d= diameter of the arc, t= thickness of the shell plating Circumferential stress: Pd/4t More over a considerable material and weight saving is achieved as minor is along the direction of maximum stress.