High Pressure Waterbox

This example demonstrates analysis of defects in a high pressure waterbox as found in the power generation industry.

The waterbox consists of a chamber with inlet and outlet pipes, a tubeplate section across the top and cover plates at the bottom. The tubeplate region contains many bore holes. In the example shown, defects were included at the bore of a drain hole located close to the edge of the tubeplate region. In other analyses alternative defects were introduced near the same drain hole, and at various depths along the upper internal radius of the main waterbox chamber.

Due to the complexity of the tubeplate and the potential size of the model, the analysis was conducted in three stages using submodelling:

• analysis of a quarter symmetry global model in which the tubeplate region is modelled using a transversely orthotropic material model
• first submodel in which the details of the drain hole and nearby tubeplate holes are included
• second submodel in which the cracks are introduced

In the global model and first submodel the compliance of the crack was simulated by release of degrees of freedom on the symmetry plane to give a crude approximation of the crack position.

Pressure and thermal transient analyses were carried out to provide stress intensity factors along the crack fronts.