Page 493 - Pipelines and Risers

460 Chapter 24

the steady bottom current velocity at the height of the bundle. The bundle is considered stable
when actual submerged weight is greater than calculated minimum, applying a safety factor of
1.1.

Bundle expansion due to the temperature and pressure of the product in the flowlines shall be
considered. The geometry of the installed bundle is such tat the flowlines are attached to the
carrier pipe at the extreme ends only via a solid bulkhead. Over their length the flowlines are
supported by spacers maintaining their positions relative to and parallel with, each other and
the carrier pipe. The carrier pipe is supported over its length by the seabed. Expansion of the
flowlines exerts loads on the bulkhead which in turn mobilizes the carrier pipe which is itself
constrained by seabed friction. The bundle is a system with boundaries at a free end and at the
associated anchor point. The bundle expansion analysis includes determining external and
internal forces acting on the system, calculating axial strain of system and integrating the axial
strain of unanchored bundle to determine the expansion.

The check on flowline equivalent stresses is important especially with high temperature
applications not only for the higher thermal loads produced but also the reduction in yield
strength with some materials.

Carrier stresses shall be looked at during the carrier selection and should be reviewed in light
of the stresses determined during the expansion analysis.

Design Criteria for Bundle System
The carrier and the sleeve pipes shall be designed in accordance with the criteria given in
Chapter 4. The deduction of large D/t ratio of carrier and sleeve pipes on bending moment
should be accounted for in the maximum allowable bending moment criterion defined in
Chapter 4.

Global equivalent stress in the carrier pipe during installation shall be limited to 72% of yield
stress. Local equivalent stress in the carrier pipe during installation shall be limited to 90% of
yield stress.

The hydraulic, chemical and temperature monitoring tubes located within the bundles could
also be designed according to those Chapters.
The design criteria shall be applicable for the design situations of installation, hydrotest and
operating.

Wall Thickness Design Criteria
The wall thickness design of pipes within the bundle system shall take into account the
following.