Page 137 - Pipelines and Risers

110 Chapter 8

The pipeline is assumed to be air filled for the on-bottom stability analysis when considering
the installation phase. For the installation condition, a minimum specific gravity of 1.1 is
required.

8.2 Force Balance: The Simplified Method

The lateral pipeline stability may be assessed using two-dimensional static or three-
dimensional dynamic analysis methods. The dynamic analysis methods allow limited pipe
movements or check of structural strength, the acceptance criteria for dynamic analysis is
explained in chapter 8.3, which is a summary of chapter 4. The static analysis method may be
expressed by Eq. (1.3) in Chapter 1.

83 Acceptance Criteria

8.3.1 Allowable Lateral Displacement
The selection of the allowable lateral pipeline displacement shall be based on several factors,
such as:

National regulations.
Distance from platform or other restraint.
Sea bed obstructions.
0 Width of surveyed corridor.

If no further information is available, then the following may be used for the allowable
maximum lateral displacement of the pipeline in the operational condition:

- Zone 1 (over 500 meters from an installation): 20 meters.
- Zone 2 (less than 500 meters from an installation): 0 meters.

These criteria can be relaxed or replaced if other relevant criteria (e.g. limit-state based
strength criteria) are available.

8.3.2 Limit-state Strength Criteria
General
Limit-state based strength criteria have been discussed by Bai & Damsleth (1997), who have
presented potential failure modes and design equations as well as design experience on
detailed design projects, Details are given in Chapter 4.