نحوه محاسبه ضخامت لوله

B31.3 T=PD / (2(PY+SEW))

B31.4 T=PSED/2

B31.8 T=PD/2ETF

t=T/P

P= Internal pressure (psig)

D=OD (Inch)

S=Allowable stress  

B31.3 :Appendix A table A1

B31.4: S=0.75 (SMYS) smys: minimum yield stress

B31.8: S=yield stress

E=Ej=Basic quality factor for longitudinal weld joints(weld joint efficiency)

B31.3 table 302.3.4

B31.4 & 31.8 Ej=1 (without FBW method)

Y=values of coefficient from table 304.1.1

W=Weld strength reduction factor (for SMLS,w=1)

Welded up to 510 c,w=1,at 815 c ,w=0.5 –from 510 to 815 interpolate)

Temp. range for liquid pipeline is -29 up 120 ,gas -29 up 204 so w=1

T=temperature drawing factor (when temp. increase ,press. Increase so:

Up to 250 c,T=1 & upper 250c T=0.95

F=class location

4 class for popular crowded (1 div 1=0.8 div 2=0.72)