Finite Element Analysis (FEA)

The following is an example of the results of a strength assessment to confirm the structural integrity of upper and lower adaptors for a Flexible Dynamic Riser:

Analysis was performed based on the higher loads which were generated from an existing [in-situ] production riser global analysis. The upper production and new riser adaptors were the same design and the lower production and new riser adaptor designs were the same. FEA of each adaptor was performed using ABAQUS. The results were assessed in accordance with API-6AF2 [1]. FEA was performed statically using ABAQUS/Standard, with linear elastic material properties and non-linear geometry. The non-linear geometry was used to activate the contact features used to model the bolts. The analysis procedure involved two steps. In the first step, bolt pre-load was applied, while in the second step, external actions, tension, shear and bending moment and internal pressure were applied. From the results of the analysis for the upper and lower adaptors it was concluded that the flange design and the specified bolts and recommended bolt pre-loads were acceptable. Stresses were found to be within allowable limits in accordance with relevant design codes.

Analysis Methodology

FEMs (Finite Element Models) of each adaptor were created by importing the basic geometry directly from CAD models into the pre-processor ABAQUS/CAE, from which half-symmetric models were created using 8-noded hexahedral elements (C3D8R) throughout.

In this particular example, the adaptors (apart from the bolts that were ASTM A320 Gr. L7) were modelled as F60 grade material. Properties for both materials (extracted directly from one of our reports) are presented in Table 3.1 below.