Page 188 - Pipelines and Risers

Trawl Impact, Pullover and Hooking Loads 161

where:
6 = The deformation (indentation) of the steel pipe
F = The impact force between trawl board and steel pipe
Q, = Yield stress of the steel pipe.
t = Wall-thickness of the steel pipe

Coating Stiffness, kcl
In general two types of insulation coating are used in the industry: rubber and plastic. Both
rubber and plastic coatings will distribute the load to the steel underneath while they absorb
part of the impact energy. It is recommended that finite element analysis andor experimental
tests are to be carried out in order to obtained load-indentation curves for insulation coating
(&I) and possible effect the coating has on the steel shell stiffness (b2). At early design stage,
no information is available with respect to &I, it is proposed to represent the coating
indentation curve (&I) by empirical equations as below:

Case 1:
&,=a F2 (11.3)

or Case 2:
S,=B F (11.4)

where a and p are empirical coefficients to be calculated by equating the energy calculated
from the above empirical equation with the energy absorption capability of the coating, &,
obtained from the coating tests conducted by the manufacturer.

(11.5)

and

(11.6)

where:
t, = The coating thickness
S,. = The deformation in coating

Solving the above energy equation, we may get: