PIPELINES: INTERACTION OF PIPELINES WITH SEA BED

INSTABILITY OF THE SEA BED

Traditional stability design method is to treat the seabed as stationary and immovable.

This assumption is not correct The stability of a pipeline cannot be considered in isolation from the

stability of the seabed on which its rests.. If the pipeline is unstable the stability of the seabed is likely to be

marginal at best. If the sea bed is unstable, the pipeline becomes unstable with it. In extreme wave and current conditions the seabed begin to move

in response to hydrodynamic forces, and the pipeline also moves due to active sediment transport.

Pipeline – partial buried

If the pipeline is initially partially buried and a top layer of the seabed

begins to move, then the following three things will occur:

1) The pipeline will be exposed to hydrodynamic forces over a greater

fraction of its diameter.

2) The fluid moving past the line will have a density greater than water

because of the presence of seabed particles.

3) A smaller fraction of pipeline will be embedded in stationary

material and the resistance to lateral movement will therefore be

much reduced.

PIPELINE INSTALLATION METHODS

Lay – barge method

Frequently used technique for marine pipeline construction

This method is versatile, flexible and self-contained.

Initially it is expensive to mobilize a lay – barge to remote location

but once the barge is in place, it can start work and operate as

efficiently as anywhere else.

It was originally developed in shallow water in the 1940s.

The first larger diameter installed by this method was about 100m.

The average lay rate was 6.9km/day and the peak lay rate was 7.8

km in 24 hours.

Two methods are S – Lay and J - lay

S – lay method of pipeline

S - LAY

S – LAY CHARACTERISTICS

PIPELAY VESSEL CATEGORY

FIRST GENERATION LAY BARGE

SECOND GENERATION LAY BARGE

THIRD GENERATION LAY BARGE

FOURTH GENERATION LAY BARGE

PIPELAY PROCEDURE

INITIATION

LOADING AND STORAGE

END PREPARATION

DOUBLE JOINING

FIRING LINE

FIRING LINE

WELDING

NDT

REPAIRS

FINAL CONTROL OVER STINGER

BUCKLE DETECTION

J –LAY METHOD OF PIPELINE

J - LAY

J- LAY SEQUENCE

J – LAY BENEFITS

TOWING METHOD

TOWING METHOD

PIPE STRINGING YARD

PIPE INSTALLATION METHOD

PIPE LINE INSTALLATION METHOD

PIPE LINE INSTALLATION METHOD

ADVANTAGES AND DISADVANTAGES OF TOWING METHOD

FLOAT AND SINK METHOD

FLOAT AND SINK METHOD

REE – LAY METHOD

REE – LAY METHOD