Pressure Vessel

did any one help me to understand this formula more detail.

Interior Pressure: VIII-1 UG-27(c)(1,2)
ta [in] = P*Ri/(S*El-0.6*P) tb [in] = P*Ri/(2*S*Ec+0.4*P) tmin [in] = MAX(ta,tb,tminUG16b) tr1 [in] = P*Ri/(S*1-0.6*P) Checkt = tmin <= nt 0.063 <= 0.225 = Acceptable
Exterior Pressure: VIII-1 UG-28(c)

DoT = Do/nt 48/0.225 = 213.333 DoTe = Do/tre 48/0.225 = 213.713 Aa = 10^PVELookup("TableLdo", "Int2DLin", DoT, LDo) 0.0001743 Ba = PVELookup("ExtChart","ExtLookup",chart,extTemp,Aa) 2,410 PaMax [psi] = 4*Ba/(3*DoT) 4*2410/(3*213.333) = 15 CheckPa = PaMax >= Pa 15 >= 15 = Acceptable tre [in] = (3*Do*Pa)/(4*Bb) (3*48*15)/(4*2404) = 0.225 treCorr [in] = tre+Corr+UT+Td 0.225+0+0+0 = 0.225 Bb = PVELookup("BbChart","BbLookup",chart,extTemp,Do,Pa,LDo) 2,404