Dear Members, The existing design for the pressure vessel is an end cap bolted to the body which is not designed to any pressure vessel code. Currently i'm trying to qualify this pressure vessel to PD5500 code. Due to the derated allowables in the code i couldn't go with the bolted arrangement, In order to qualify the existing design i have to triple the number of bolts for which i dont have space. Not left with much options i decided to go with end cap and threaded lock ring ( Please see attachement-BLOGS). The threads i use in the lock ring is stub acme. Although the thread length and lock ring tensile area are good for 300bar ejection load(internal pressure) as per my calculation, i'm more concerned about the splay out of the lock ring. I did some basic FEA from which the deflection i got was 0.2mm but the stresses are localised and quite high. I'm not sure if i can go ahead with the testing with this fine safety factor margin. Temperature is 20 deg C, but im not overly concerned about this at this stage. Material Body - 65 ksi Lock ring - 80ksi End cap - 80ksi.