Bend stiffener and intermediate flexible riser union

[andbacus]

I was questioned about the need of bend stiffeners close to the edges of intermediate flexible riser connections (rigid connections usually in repaired joints, providing transition flexible->stiff->flexible), in order to avoid damage due to excessive bending and consumption of fatigue life mainly during installation.

My first opinion was that, whether the depth and location does not provide significant dynamic bending to the pipe after it is installed, such bend stiffener will not be necessary, because the flexible pipe will not bend very much under normal installation conditions. Furthermore, the number of cycles in higher bending loads during the installation of such an intermediate riser connection is not supposed to affect fatigue life significantly.

However I have wondered a lot about this issue lately, I don´t feel very sure. I would like to hear someone else´s opinion or experience.

 

[TPENKT]

Andbacus,

First of all I would be very careful about rules of thumb on this issue, however I can contribute a bit.

Bendstiffener requirements and design are usually based on a dynamic analysis of the full configuration which will show both whether it is required, however also provide you design input for the stiffener. The dynamic analysis will also show any inertia effects on the mass concentration (along the line) you may have at the joint.

I agree that it is not a fatigue issue, more an extreme overbending issue (polymer and structural utilisations). If the installation method are relatively flexible you may be able to install the flexible riser without bending stiffener(s).