I'm using the Bentley AutoPIPE Vessel for calculation of U-tubes of the bundle under internal pressure and external pressure according EN13445-3 and TEMA.
Tubes are procured with tolerance +/-10%, and customer required to have corrosion allowance of 0,4mm (inside 0,2mm + outside 0,2mm).
I've got the report as shown below, specifically for external pressure (test condition) it seems the result given for Pr/S is not well calculated, program is assuming the safety factor S=1,5 instead of S=1,1.
Other points are:
1. why the TEMA RCB-2.31 formula is applicable to the U-Tube bend under external pressure?
2. I don't understand from where is coming the value t1 (t1 is the minimum thickness required for straight tube under internal or external pressure)?
Extract below from Microprotol report:
Tubes of the bundle.
Bundle tube under internal pressure.
Material : X2CrNiMoN22-5-3
temperature in operation : t = 176 °C
Weld joint efficiency : z = 1
Nominal thickness : en = 0,80 mm
External Diameter : De = 18,00 mm
c = corrosion + tolerance
P = internal pressure
f = Allowable stress
ea = en- c
EN 13445:2016 Issue 3 (2016-09) :
Minimum U-Bends thickness TEMA RCB-2.31 : to = t1[1+do/(4R)] = 0,75 mm (R = 48 mm )
Bundle tube under external pressure.
P = External Pressure
t = Temperature
se = nominal yield strength
E = modulus of elasticity
S = safety factor
Analysis thickness : ea = 0,32 mm
EN 13445:2016 Issue 3 (2016-09) [184.108.40.206]
L = 12.062,00 mm
e : Figure 8.5-3
ncyl : Figure 8.5-4
Pr /Py : Curve 1) Figure 8.5-5
R = (De-ea) / 2
Py = se ea / R
Pm = E eae / R
Z = p R / L
Pr /S (MPa)
Minimum U-Bends thickness TEMA RCB-2.31 : to = t1[1+do/(4R)] = 0,91 mm (R = 48 mm )
Appreciate your support.