I would like to start a discussion about how to interpret the corrosion allowances in the EN13480-3?

For dimensioning the wall thickness in the internal pressure design the integration of the corrosion allowances is clearly defined.

You need to increase the ordering wall thickness so that even after corrosion there still is enough wall to resist against pressure. but for the longitudinal stresses (chapter 12) the description is much more fuzzy:

Code: Alles auswählen

```
Stresses shall be determined for nominal thickness.
NOTE Wall thickness reductions, allowed by the technical conditions of delivery for seamless and welded pipes are covered by the stress limits.
```

but in the NOTE there suddenly is a clarification for manufacturing only: Normal manufacturing tolerance does not need to be considered.

So what about corrosion?

Lets have a look at some other codes: (all translations are done by me and are not official)

FDBR – Richtlinie Berechnung von Rohrleitungen

9.4.1 Rohrelemente

"... Dabei sind für die Ermittlung der Querschnittswerte (Trägheitsmoment, Querschnittsfläche) der Bestelldurchmesser und die Mittelwanddicke einschließlich Plattierung zugrundezulegen"

"... the sectional characteristis (moment of inertia, surface) are based on the ordered wall thickness including plating."

10.1:

"Die Spannungsermittlung wird daher bei bestelleter Mittelwanddicke mit der Bestellwanddicke abzüglich der Abnutzungsabschläge durchgeführt."

"The stress calculation is done with the ordered wall thickness minus corrosion and erosion allowances."

CODETI

C 3.2.1.4

Les calculs de flexibilité doivent être effectués en utilisant les épaisseurs nominales et la vérification des contraintes en utilisant les épaisseur définis en C.3.2.6.3

The flexibility calculation must be done using the nominal thickness and the stress analysis based on the thickness defined in C.3.2.6.3 angegebenene Wanddicken.

C.3.2.6.3

"e_f : Epaisseur de référence utilisée pour le calcul des contraintes: epaisseur de demi-plage des tolerances c1- et c1+ diminuée des surépaisseurs de corrosion ou d'érosion eventuelles."

"e_f : reference thickness for the calculation of stresses : average thickness between tolerances c1- and c1+ reduced by allowabces for corrosion and erosion"

ASME B31.3

302.4 Allowances

In determining the minimum required thickness of a piping component, allowances shall be included for corrosion, erosion and thread depth or grove depth.

So basically all other codes require to take into account the corrosion allowances for the longitudinal stresses as well.

How do you deal with the corrosion in your pipe stress calculation?

CODETI even take into account the reduced wall thickness for the calcualtion of the SIFs.

Any comments are welcome.

Best regards

AR