# Calculation of HEX U-tubes under external pressure (EN13445+TEMA)

Dear all,

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 Seamless tube temperature in operation : t = 176 °C Weld joint efficiency : z = 1 Alloy Steel 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) : P (MPa) f (MPa) e+c (mm) s (MPa) c (mm) Pmax (MPa) Horizontal test Operation 7,1 5 428,57 214,67 0,62 0,68 191,7 135 0,48 0,48 15,873 7,9506

 Minimum U-Bends thickness TEMA RCB-2.31 :  to = t1[1+do/(4R)]  = 0,75 mm   (R = 48 mm )

Bundle tube under external pressure.

 Material : X2CrNiMoN22-5-3 Seamless tube P = External Pressure t = Temperature Alloy Steel se = nominal yield strength E = modulus of elasticity S = safety factor Analysis thickness : ea = 0,32 mm External Diameter : De = 18,00 mm c = corrosion + tolerance EN 13445:2016 Issue 3 (2016-09) [8.5.2.2] 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 P (MPa) t (°C) se (MPa) E (MPa) S e ncyl c (mm) Pr /S (MPa) 1,2 0,9 20 176 450 322 201.000 190.440 1,1 1,5 0,0004 0,0004 2 2 0,48 0,48 0,8719 0,8267

 Minimum U-Bends thickness TEMA RCB-2.31 :  to = t1[1+do/(4R)]  = 0,91 mm   (R = 48 mm )

INSUFFICIENT THICKNESS

Many thanks

LG

Parents
• LG,

First I would like to apologize for the lack of response to this question on Bentley Communities.

Secondly this question would be better suited for a service request in order to attached model files, report files, screen shots, etc. to help define your questions and issues. If you were to go to connect.bentley.com to log into your Bentley account you can log your service request there.

I look forward to looking into this issue further with the request of the model files and screenshots of the particular report sections you have in question.