Page 151 - Pipeline Pigging Technology

Pipeline Pigging Technology

different contexts. The following definitions are included to avoid misunder-
standings:

Intermediate testing: Flooding, precleaning, gauging and hydrostatic
pressure testing performed on separate pipeline sections after
completion of the laying operation/laying season.
Precommissioning: Consists of welding-sphere removal, cleaning and
system pressure testing.
Commissioning: Consists of dewatering, drying and pressurization.

Pigging operations

The Zeepipe challenge - pigging of the world's longest subsea gas pipeline
- will represent a further development within pigging technology; it is almost
twice as long as the present largest single-section offshore gas pipeline.
The long-distance pigging concept was evaluated and decided upon
during the conceptual phase. Several studies were performed and most of the
relevant operators and pig manufacturers were consulted. Some of the
manufacturers claimed that their present standard pigs would be capable of
running this distance. Most of them, however, believed that some develop-
ment or design work would be necessary.
The main characteristic of the Zeepipe system is the pipeline length, and
consequently the large schedule impact from any requirement for repeated
pigging operations. It is less effective and requires more resources to perform
effective cleaning of longer pipelines. A precleaning operation is therefore
included in the intermediate testing operation which is performed on shorter
sections prior to tie-in. Furthermore, cleanliness during laying operations is of
paramount importance.
Pigging during the project phase will consist of flooding, gauging and
precleaning during intermediate testing and welding-sphere removal, clean-
ing and dewatering during precommissioning and commissioning.
During normal operations, only inspection pigging, including necessary
pre-pigging to prove the pipeline every fourth to sixth year, is foreseen.

Pigging conditions

The main area of concern related to pigging length is wear, i.e. wear down
of the discs and cups in contact with the pipe wall.

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