Head - Why does my 2 to 1 head not have a K of 1

You may think that your D/2h ratio should result in a K factor of 1.0, but have you considered your internal corrosion allowance. K is defined as “a factor in the equations for ellipsoidal heads depending on the head proportion D/2h”. If you look at Appendix 1-4(c) you can see the equation used to determine K (shown below). When solving for K you will need to make sure your D and h are in the corroded condition to satisfy UG-16(e).

Example 1: Supposed to 2:1 Ellipsoidal Head

ID = 16 in

h = 4 in

Inside CA = 0.0625 in

Example 2: Actual 2:1 Ellipsoidal Head

ID = 16 in

h = 4 in

Inside CA = 0 in