Jörg Theis
Senior Application Engineer, Intergraph Germany

Why Evaluating Creep Conditions for High-temperature Piping Is Important

CAESAR II 2017 features the ability to evaluate piping operating within the “creep” range. The basis for this evalutation is defined in the EN 13480 code standard, but it can be used with all piping code jobs as well.

What is creep and why should I use this?

Creep is the slow, permanent deformation of a solid material under mechanical stresses. Creep occurs during long-term exposure to high levels of constant stress below the yield strength of the material. If a piping system needs to work over a long time, you should evaluate this condition.

For example, in higher temperatures when you use a standard steel, the creep range starts at about 750°F/400°C, and the material begins to creep over a longer time period. For some components, such as supports with a design temperature in the creep range, a time-dependent design is recommended.

The equation from EN 13480
(Section 12.3.5-1) is:

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Vol.3 | Issue 11 | November 2016
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Did you know that the Classic Piping Input is grouped into blocks of related input fields? Double-click the chevrons (>>) in the upper right corner of any group to display additional input fields in a separate dialog box.

For example, when you double-click the chevrons on the deltas (DX, DY, DZ) field grouping, the software opens the Edit Deltas dialog. Within this dialog, you can specify the element length and define the Direction Cosines for the element based on the direction of the previous element. These additional inputs are especially useful when you work with skewed elements.

Read the complete article.
The (p_c d_o)/(4e_n ) + (0.75iM_A)/Z section of the equation is the Sustained (SUS) stress, where MA refers to the resultant moment due to sustained loadings, just as in EN 13480, 12.3.2-1. This calculation is exactly the same as a SUS load case in CAESAR II when you specify piping code EN 13480.

The (0.75iM_C)/3Z section of the equation is the creep evaluation, where MC is the resultant moment due to thermal expansion and alternating loads, just as it is specified in EN-13480 (12.3.4-2 or 12.3.4-2, depending on the liberal stress setting).

Read the complete article.

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