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Stress Components

The stress components tab is visible only when the Fatigue Analysis option is selected from the Analysis frame in the General tab. The content of the Stress Components tab is presented below:

This tab is used to define the stress components when the line type is steel riser only. This tab is not visible if the type of line is different from Steel riser. The stress could be either computed on the external or internal diameter of the steel section, considering a user-defined number of calculation points along the pipe circumference.

The General tab includes the 4 following frames:

• Stress calculation diameter: select either the outer or inner diameter

• Stress type: select either axial, bending or axial + bending. Axial + bending is to be used for riser fatigue analysis as it account both for stress fluctuations due to tensile and bending loads.

• Circumference data: choose the number of points distributed over the circumference. The default number of section points is 8 which provides reasonable accuracy for most cases. This value may be increased to 16 for more accuracy. A option labelled "Compute envelop of RAOs" is also available, that makes the fatigue damage being calculated based on the maximum stress or tension range in each element. this speeds up fatigue post-processing but yields conservative damage results.

Mean stress correction

In previous versions of DeepLines, fatigue damage was calculated with and without Goodman correction.

Since versions V5R4, fatigue results are provided only with one of the specified correction:

• No correction

• Goodman correction

• Gerber correction,

• DNCGL RP C203 reduction factor either for welded or base material parts.

Note

To help users to check the results, especially when a Mean stress correction factor is requested, more information is provided when histograms are requested (see Fatigue Analysis Results).