Tank Shell Thickness

Please help me out to solve this :- I did some calculation but i donot know is it ok or not

Design Temp=120 degree c= 248 F

Design Pressure= 1.0 kg/sqcm/FV= 14.233 psi

Joint Efficiency = 0.7

Corrosion Allowance = 3mm.

Material = IS 2062 Gr.B

CST OD= 2200 mm.

CST THK assumed = 10 mm.

CST ID= 2180 mm.

Distance Between Stiffener = 3000 mm.

Max Allowable Stress = 20000 Psi

CST Inner Radius = 1090 mm.

For internal Pressure UG-27

Case 1= Circumferential Stress

t= PR/SE-0.6P

t=1.10803 mm.

Reqd t= 1.10803+ CA= 1.10803+3=4.1080 mm.

Case 2= Longitudinal Stress

t=PR/2SE+.4P

t=0.553mm.

Reqd t= 0.553+ CA= 0.5535+3=3.5535 mm.

Hence thickness 10 is ok for internal pressure .

Now for External Pressure (where i got prob in finding Exact Value of A & B)

UG-28

CST t=10 mm (Assumed)

Corrosion Allowance = 3 mm.

so t become = 10-3*2=4 mm.

Do/t= 550

L/do=1.36

Value of A Which I find is = .000068

Now A fall on left of material / temp curve so i have to calculate value according to

Pa= 2AE/3(Do/t)

E= 200 Gpa =29007500 psi

Pa= 2*0.000068*29007500/3*550

Pa=3945.02/1650

Pa= 2.3910 Psi

P=14.233

So according to design thickness is not Appropriate .

Please check this Calculation and let me know where I m wrong as i think some where i m doing some mistake .. or may be full calculation wrong ..

Hope to get vice reply soon ..

This is my First Post .

Regards

Varun