Det Norske Veritas - Germanischer Lloyd

Interference between Trawl Gear and Pipelines
 N DNV-RP-F111

Annotation

Scope and application

The objective of this RP is to provide rational criteria and guidance on design methods for pipelines subjected to interference from trawling gear; including the impact, pull-over and possible hooking phases. Design criteria are given as well as guidance on applicable calculation methods.

For pipelines subjected to global buckling, such as:

1) pipelines with release of effective, compressive axial force (buckling) prior to trawling, or

2) pipelines with release of effective, compressive axial force simultaneously with trawling, i.e. the trawl load triggers global buckling,

global response analyses are required in combination with the trawl load assessment.

The global buckling analyses needs to include sensitivity studies of governing parameters such as pipe to soil interaction in accordance with DNV-RP-F110, to establish the proper functional load condition factor.

This document is applicable to rigid pipelines with outer steel diameters larger than 10" (i.e. the smallest pipe diameter tested in model tests have been used as basis for this RP). However, if measures are taken in the analyses to account for scaling effects outside of the model test validity range, the methodology reflected in this RP may still be applicable. Typically, this would involve special assessments of soil to pipe interaction factors (ref. Figure 3-3), global bending stiffness of pipeline and factors related to relative sizes between pipe and trawl equipment.

For pipelines with outer steel diameter less than 10", the soil reduction factors based on Figure 3-3 should conservatively be based on 300 mm outer diameter for impact load calculations.