I have calculated by appendix 13 of ASME section VIII Div 1 for a Box Header Air Cooler's Header Box of Containing Pressure of 40 bar with h=340 and H=150, The thickness is coming around 50 mm for TOP/Bottom and Tube/Plug Sheet. I want to know whether the thickness is seems abnormally higher or its a standard thickness required for 40 bar pressure?

Thanks in advance.