Page 187 - Pipelines and Risers

160 Chapter I I

difference is that the pipeline length to be considered can be much shorter for the impact
response analyses. Figure 11.2 shows the principle that will be employed.

As a result of the dynamic global pipe model, a dent size will be obtained as the description of
the damage to the pipe steel. In addition, analyses results also include time histories of
deformation in steel pipe and coating, and impact force between the trawl board and the
pipeline.

For a balanced consideration of coating material costs and pipeline safety, the impact energy
absorption capability of the coating should be determined based op impact response of
pipelines to trawl board loads. An analytical method is developed to determine the initially
assumed energy absorption capability of the coating. Detailed impact response analyses of the
dynamic system is carried out using non-linear finite element programs to confirm the
assumed energy absorption capability.
A coefficient Ch (d.85) will be applied together with the trawling velocity to arrive at an
effective velocity.

11.4.3 Steel Pipe and Coating Stiffness
General
The local stiffness of the pipe is represented by the stiffness of

the local shell stiffness of the steel pipe, ks
the coating stiffness, hl
Possible effect the coating has on the steel shell stiffness, kf2 - This is because the coating
will distribute the impact load to a wider area on the steel shell, and possibly transfer
certain forces tangentially.

The deformation energy to be absorbed by the steel pipe and the insulation coating are:
E=E,+E,, +EC2 (11.1)

where:
E, = The deformation energy absorbed by the steel pipe while coating is not used (bare
steel pipe)
E,, =The deformation energy absorbed by coating
E c2= The effect of the coating on the energy absorption

Steel Pipe Stiffness, ks
The indentation (6F) curve recommended by STATOIL (1996) for steel pipe is:

(11.2)