Technical information - flangevalid · 2018. 7. 11. · Welding neck flanges DN100 PN40 according to DIN EN 1092-1 of 1.4571 Head bolts according to DIN EN ISO 4017 and nuts DIN EN

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● Technical information

● FEM analysis of a flange connection DN100 PN40 with

grooved- gasket with graphite supports compared to the cal-

culation according to DIN EN 1591-1, edition 2011 and 2014

1. Goal of the FEM analysis

The purpose of the FEM analysis is to check the surface pressures of the seals and bolt forces

determined in the calculations according to DIN EN 1591-1, issues 2011-08 and 2014-04.

2. Introduction

In the analytical flange calculations according to DIN EN 1591-1:2011-08 and DIN EN 1591-

1:2014-04, the mean surface pressures of the serrated gaskets are determined, among other

things. The flange connection was tested with the numerical FEM analysis ®flangevalid in ANSYS

Mechanical for a comparison. In order to have comparability of the results, the same values for the

prestressing force of the screws according to DIN EN 1591-1:2011-08 and according to DIN EN

1591-1:2014-04 were also taken into account for the FEM analysis. The setting behaviour of the

grooved-gasket according to DIN EN 13555 was taken into account.

3. Load cases

As load cases, the mounting prestressing of the screws was selected in accordance with the cal-

culation according to DIN EN 1591-1:2011-08 for the bolt material, observing the maximum pre-

stressing force. This corresponds to 72 % utilization of yield strength Rp0,2 (79.280 N). The calcu-

lation according to DIN EN 1591-1:2014-04 yields 81 % with utilization of the yield strength Rp0,2

(89.652 N).

Calculated screw prestressing forces according to DIN EN 1591-1

Bolt force Screw load Deviation

Rules/calculation N % %

DIN EN 1591-1:2011-08 79,280 72 -

DIN EN 1591-1:2014-04 89,652 81 +12.5

§§53245

§§§§532455324553245






Subsequently, a design pressure of 25 bar (2.5 MPa) was applied. As additional operating loads,

axial forces of FZ = 2,500 N and a bending moment of MX = 7,500 Nm) are applied. For com-

pleteness, a stationary temperature calculation with the following assumptions

Flange connection not insulated

Ambient temperature 20 °C

Temperature increase inside from 20 °C to 180 °C

Free convection

was performed in the first step.

4. Materials

The materials used are

Welding neck flanges DN100 PN40 according to DIN EN 1092-1 of 1.4571

Head bolts according to DIN EN ISO 4017 and nuts DIN EN ISO 4032 of strength class

A4-70 according to DIN EN ISO 3506-1 for the screws and DIN EN ISO 3506-2 for the

nuts

Grooveded gasket made of 4 mm serrated profile with 0.5 mm graphite supports.






The seal is modelled as a circular ring surface, taking into account the non-linear sealing proper-

ties according to DIN EN 13555.

5. Geometry import

The flange connection was modelled with flangevalid System Designer, imported into ANSYS

Design Modeler and subsequently imported into ANSYS Mechanical.

Figure 1: Geometry import of the entire flange connection, ®flangevalid System Designer in

ANSYS Design Modeler






Figure 2: Cross-linking of the serrated gasket

Figure 3: Cross-linking of the entire flange connection






Figure 4.1: Mechanical model of the entire flange connection with conditions according to DIN EN

1591-1:2011-08, screw load during installation 79,280 N.

Figure 4.2: Mechanical model of the entire flange connection with conditions according to DIN EN

1591-1:2014-04, screw load during installation 89,652 N.






6. Calculation results

Figure 5.1: Max. equivalent stress on the entire flange connection with values according to DIN

EN 1591-1:2011-08

Figure 5.2: Max. equivalent stress on the entire flange connection with values according to DIN

EN 1591-1:2014-04






Figure 6.1: Max. equivalent stress on the screws with values according to DIN EN 1591-1:2011-

08

Figure 6.2: Max. equivalent stress on the screws with values according to DIN EN 1591-1:2014-

04






Figure 7.1: Surface pressure of the serrated gasket, with values according to DIN EN 1591-

1:2011-08, min. 34.13 MPa - max. 109.65 MPa

Figure 7.2: Surface pressure of the serrated gasket, with values according to DIN EN 1591-

1:2014-04, min. 34.68 MPa - max. 127.22 MPa






Figure 8.1: Setting behaviour of the serrated gasket after assembly, with values according to DIN

EN 1591-1:2011-08, min. 0.41 mm on the inner edge, max. 0.51 mm on the outer

edge

Figure 8.2: Setting behaviour of the serrated gasket after assembly, with values according to DIN

EN 1591-1:2014-04, min. 0.41mm at the inner edge, max. 0.52 mm at the outer edge






Figure 9: Increase in bolt force (working load), with values DIN EN 1591-1:2011-08, from

mounting condition to operating condition, (from 79,280 N to 88,164 N)

Increase in bolt force (working load), with values DIN EN 1591-1:2014-04, from

mounting condition to operating condition, (from 89,652 N to 98,052 N)

Figure 10: Real temperature distribution with uninsulated flange and initial temperature of 20 °C

to 180 °C






6. Summary

The conventional analytical calculation according to DIN EN 1591-1:2011-08 differs considerably

from the numerical calculation according to FEM.

The mean surface pressure for the operation of the serrated gasket according to DIN EN 1591-

1:2011-08 was determined to be 12.91 MPa. The surface pressures calculated in the FEM analy-

sis, Figure 7 vary from at least 34.13 MPa on the inner edge of the seal to 109.65 MPa on the

outer edge of the seal. Simple interpolation results in an average surface pressure of 71.84 MPa.

See Figure 7.1, Table1.

Tab. 1: Surface pressures according to FEM in comparison to the calculation

According to DIN EN-1591-1:2011-08

Surface pressure Deviation from FEM

Rules/calculation MPa Factor %

DIN EN 1591-1:2011-08 Mean 12.91 5.56 556

FEM Min. 34.13 / max. 109.65 Min. 2,64 / max. 8.49

100 Mean 71.84 1

The mean surface pressure for the operation of the serrated gasket according to DIN EN 1591-

1:2014-04 was determined to be 39.73 MPa. The surface pressures calculated in the FEM analy-

sis, Figure 7 vary from at least 34.68 MPa on the inner edge of the seal to 127.22 MPa on the

outer edge of the seal. Simple interpolation results in an average surface pressure of 80.95 MPa.

See Figure 7.2, Table2,

Tab. 2: Surface pressures according to FEM in comparison to the calculation

according to DIN EN-1591-1:2014-04

Surface pressure Deviation from FEM


DIN EN 1591-1:2014-04 Mean 39.73 2.04 204

FEM Min. 34.68 / max. 127.22 Min. 0.77 / max. 3.20

100 Mean 80.95 1

Figures 8.1 and 8.2 show the setting behaviour of the grooved-gasket during installation, with

values according to DIN EN 1591-1:2011-08 and DIN EN 1591-1:2014-04. On the inner edge, the

seal is pressed by 0.41 mm on each sealing side and 0.51 and 0.52 mm on the outer edge during

assembly. This corresponds to a difference in thickness of approx. 0.1 or 0.11 mm between the

inner and outer edges.

The increase in the operating bolt force (working load), with values according to DIN EN 1591-

1:2011-08 or DIN EN 1591-1:2014-04, is shown from mounting condition to operating condition in

Figures 9.1 and 9.2. It varies from 79,280 or 89,652 N to 88,164 or 98,052 N, i.e. the mean in-

crease in bolt force is 11.2 or 9.4 % (Table 3).






Table 3: Increase of the operating bolt force (working load) according to the calculations with

DIN EN 1591-1 and according to FEM with the values from the calculations according to DIN

EN 1591-1

Assembly Operation Difference

Rules/calculation N N %

DIN EN 1591-1:2011-08 9,965 345.6

DIN EN 1591-1:2014-04 34,436

FEM Values DIN EN 1591-1:2011-08

79,280 88,164 11.2

FEM Values DIN EN 1591-1:2014-04

89,652 98,052 9.4

Difference in % 13.1 11.2 19

The values for the operating bolt forces according to DIN EN 1591-1:2011-08 deviate by 3.5

times from the values of DIN EN 1591-1:2014-04.

The real temperature distribution on the uninsulated flange with an initial temperature of 20 °C to

180 °C is shown in Figure 10. The influences of temperature over the different distribution are not

considered in the analytical calculations according to DIN EN 1591-1 in versions 2011-08 and

2014-04.

7. Evaluation

The values for the increase in bolt forces during operation, between DIN EN 1591-1:2011-08 and

DIN EN 1591-1:2014-04, differ significantly (Section 6. Table 3).

The deviation of the surface pressures on the serrated gasket, during operation, with the same

input parameters, is 556 % lower in the analytical calculation according to DIN EN 1591-1:2011-

08 than in the numerical FEM analysis. According to DIN EN 1591.1:2014-04, the figure is still

204 % (Section 6, Tab. 1 and 2).

Tab. 1: Difference of the calculated surface pressures according to DIN EN 1591-1

Surface pressure Deviation


DIN EN 1591-1:2011-08 12.91 1 100

DIN EN 1591-1:2014-04 39.73 3.01 301

The differences between the analytical and numerical calculation methods, especially the differ-

ences between the analytical calculations according to DIN EN 1591-1 are so large (Table1) that

further investigations must be carried out to check that DIN EN 1591-1:2011-08 and DIN EN

1591.1:2014-04 can be applied appropriately.






More about screws, flanges, seals and sealing systems and their assembly can be found in the

Dichtungsvademecum [Sealing vade-mecum] (ISBN-13: 978-3-934736-23-8, PP Publico Publica-

tions, www.pp-publico.de), in the licensed translation of ASME PCC-1-2010 for the assembly of

standardized steel flange connections (ISBN-13: 978-3-934736-22-1, PP Publico Publications,

www.pp-publico.de) and in our "Technical Information for Sealed Joints" manual

(www.flangevalid.com). Our latest book "10 Schritte zur optimalen, auf Dauer technisch dichten

Dichtverbindung” [10 steps to the optimum, long-term technically tight seal connection] (ISBN-13:

978-3-934736-27-6) was published by PP Publico Publications.

Please visit our website www.flangevalid.com for more interesting information on different sub-

jects.

I will be happy to provide personal technical consulting, even on short notice.

Best regards from Bremen

Grad. Eng. Gerd Lannewehr

Legal disclaimer:

The contents of the technical standards are in part quoted, in part reproduced with the words

used in the standards; the comments and interpretations are based on long-standing experience,

serve as a decision aid and do not substantiate any claim for warranty.

© Grad. Eng. Gerd Lannewehr, Peter Thomsen / ®flangevalid Version date 22/06/2018

Documents

Technical information - flangevalid · 2018. 7. 11. · Welding neck flanges DN100 PN40 according to DIN EN 1092-1 of 1.4571 Head bolts according to DIN EN ISO 4017 and nuts DIN EN