Overview:

This article explains how AutoPIPE Vessel uses creep properties when determining allowable stress, where creep data is defined, and the purpose of the Creep Apply option for EN 13445-3 nozzle reinforcement calculations.

Question 1: Does AutoPIPE Vessel perform creep calculations?

Yes. AutoPIPE Vessel considers creep properties when the selected material contains creep data in the material database. The CREEP table provides the average stress to cause rupture in 100,000 hours at the design temperature. The program interpolates the creep value at the specified design temperature.

To perform creep-related allowable stress evaluation, the selected material must have a creep rupture strength value available for the applicable design temperature.

Example

For example, P265GH has creep strength values in the material table from 380 degC to 480 degC.

How to add creep properties to a material

1. 1. Open the material Stress Properties.
   2. In the Add Properties drop-down list, select Creep.
   3. After Creep is added, enter the required creep values and the corresponding details for the applicable temperatures.
      
      

How allowable stress is selected

AutoPIPE Vessel compares the code allowable stress with the creep strength value and uses the governing minimum value. If the code stress is lower than the creep strength, the code stress governs. Otherwise, the creep strength governs and the applicable safety factor is applied to determine the final allowable stress.

Question 2: What is the effect of the Creep Apply option?

The Creep Apply check box is available under Vessel Properties (or Heat Exchanger Properties) > Operating Conditions > Creep and Fatigue. One check box is available for each chamber, such as Chamber 1, Chamber 2, Chamber 3, or Shell side / Tube side for a heat exchanger. The option is disabled for chambers that do not exist in the model and is unchecked by default.

For EN 13445-3, select Creep Apply when the chamber design temperature is in the creep range, meaning that the nominal design stress is governed by time-dependent creep material properties.

Important distinction

The Creep Apply check box does not control whether creep properties are used for allowable stress. Allowable stresses in the creep range are derived automatically from the material database and design temperature. Creep Apply enables additional opening/nozzle restrictions for EN 13445-3.

Design-code applicability

Note: For other pressure codes, including ASME VIII Div. 1 and Div. 2, PD 5500, CODAP, AD 2000, GB 150 and GOST, the Creep Apply option is ignored by the calculation even though the check box may remain editable.

Effect on nozzle reinforcement calculations for EN 13445-3

When AutoPIPE Vessel is permitted to increase nozzle dimensions to satisfy reinforcement requirements in Optimized Design mode, the program checks the eab/eas thickness ratio against the limit from Fig. 9.4-15. If reinforcement cannot be achieved within the applicable limits, the nozzle is reported as not satisfactory and messages such as "Impossible to increase the thickness" or "Reinforcement impossible" may be reported.

Notation from EN 13445-3 Clause 9

Implemented limit curves

The relevant Fig. 9.4-14 and Fig. 9.4-15 limits are implemented as follows:

When the Fig. 9.4-15 check fails, the nozzle status is set to Not Satisfactory.

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See Also

Bentley AutoPIPE Vessel

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