Page 152 - Pipeline Pigging Technology

The Zeepipe challenge

Except for the length, the Zeepipe design does not contain any features
which will reduce the pigging performance compared to present normal
practice. Rather on the contrary, the system has been designed with careful
attention to pigging, including the following:

internal coating to reduce pipe wall roughness;
constant internal diameter;
full-bore valves and tees;
minimum 5D radius bends;
separate pipe-cleaning procedures during fabrication and coating;
separate procedures and follow-up during pipelaying to avoid internal
debris; and
pipeline precleaning during intermediate testing.

The precautions related to pipeline cleanliness are partly based on earlier
experience, where extensive operational cleaning had to take place after
start-up to remove ferrous debris.
By keeping the pipes clean during fabrication and coating, and by main-
taining the cleanliness throughout the construction phase, simplified and less
time-consuming precommissioning and commissioning operations can be
achieved and operational cleaning can be avoided.

Pigging facilities

Pipeline: The pipeline will be of a constant 966.4mm inside diameter and
have a thin-film epoxy coating with a thickness of between 40 and 60 microns.
The pipes will be of 12.2m nominal length with approximately 100mm at
each end of the pipe uncoated. Thus, of the total length of 810km, approxi-
mately 13km can be assumed to be "bare" pipe. Weld penetration is limited
to 3mm maximum, and out-of-roundness is controlled to 1.5% maximum. All
bends are 5 diameters radius. All tees greater than 40% of the main line
diameter will be barred.

Profile: The water depth at Sleipner is 80m. The longitudinal profile of the
pipeline between Sleipner and Zeebrugge is smooth and gradually rises
towards Zeebrugge.

Pig traps: The pig traps at both Zeebrugge and Sleipner will be bi-
directional or universal. Overall length between closure flange and mainline
block valve is approximately 9m.

133