EN13480 - out-of-roundness

Festigkeitsberechnungen von Druckteilen
Pressure vessel design
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r2user
Beiträge: 137
Registriert: Mi 14. Sep 2011, 10:18

EN13480 - out-of-roundness

Beitrag von r2user » Mo 3. Dez 2018, 12:45

Hi

The out-of-roundness µ (see EN 13480-4, 7.4.1) for external pressure design acc. to chapter 9 must be less than or equal to 1 %, and local flat deviation is less than or equal to e. When ordering pipes (e.g. acc to EN10216-3) the tolerances for diameter are typically 1% which means an out-of-roundness of 2%. That means you can´t use a standard pipe with tolerance D2 ( +/- 1.0 %) acc. to EN ISO 1127 ! if you use the formula in chapter 9 for external pressure design.
How should we deal with this contradiction? How can we design piping against external pressure using EN13480-3?

Best regards

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rickand
Beiträge: 12
Registriert: Mi 14. Sep 2011, 09:49

Re: EN13480-3 - out-of-roundness

Beitrag von rickand » Mo 3. Dez 2018, 13:11

Hi

Thank you for your question and thank you for also submitting it to the EN13480-3 MHD Helpdesk.

There is actually this incoherence between the tolerances of currently available piping material and the limitiations for out of roundness in the calculation of EN13480-3 chapter 9. I have tried to find where the limitations come from:
EN13480-3 chapter 9 was based on CODETI which has the same chapter. CODETI seems to be inspired by BS5500 Chapter 3.6 which refers to PD6550-3 "explanatory supplement to BS5500:1988 'Specification for unfired fusion welded pressure vessels'".
Therein they explain that they have taken a combined theoretical and experimental approach. In the experimental approach they included 700 well documented tests but in these tests they excluded all shapes of radius tolerance > 0.5%.

As we cannot simply redo the test I am in favour of a theoretical approach:

1.) Define the acceptable safety-margins for buckling:
- factor 3 against elastic buckling
- factor 1.5 against plastic buckling
2.) give the formulas which define the maximum pressure that respects these limitations for straight pipes

I have prepared a documentation for this problem and a proposed modification to chapter 9 of EN13480-3. This proposal is currently under investigation in the TC 267 WG 3 (normative commitee for EN13480-3):
EN_13480-3_Out_off_roundness_r3.pdf
Any comments are welcome.

Best regards
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