Page 369 - Pipelines and Risers

340 Chapter 18

Leak Detection
Two types of pig are available for leak detection.

The first type aims to acoustically detect leaks in on-stream liquid pipelines by means of the
escaping noise. Acoustic pigs are offered by Maihak and recently by TW Osterreich. With
this type of pig it is considered feasible to detect leaks at a leak rate of about 10 liters per
hour.

The second type of pig aims to detect leaks in shut-in pipelines by measuring the flow or
differential pressure over the pig. Service with this type of pig is offered by pipetronix and H
Rosen Engineering.

18.3 Maintenance

18.3.1 General
The principle function of maintenance is to ensure that physical assets continue to fulfil their
intended purpose. The maintenance objectives with respect to any item of equipment should
be defined by its functions and its associated standards of performance.

Prior to setting out to analyze the maintenance requirements of equipment it is essential to
develop a comprehensive equipment register. In general terms the equipment included will
relate only to onshore pipelines (or onshore sections) since maintenance work on subsea
pipelines is not foreseen, that is, all subsea equipment should be. designed to be maintenance
free throughout the design life expectancy of the pipeline. This is not to say that remedial
work on a subsea pipeline will never occur, but only that it should not be a planned
occurrence. However in the case of subsea pipeline repairs, it is prudent for most operators to
keep a set (or to share a set) of emergency pipeline repair equipment on stand by. This may
include repair equipment such as pipeline repair clamps and full hyperbaric welding spreads.
This equipment should be maintained along with onshore pipeline equipment.

Generally preventive maintenance is carried out on onshore pipeline equipment with
dominant failure modes (e.g. wear out of pump impellers) at pre-determined intervals or to
prescribed criteria, with the intent to reduce the probability of failure or the performance
degradation of the item. It should go without saying that all maintenance work should attempt
to minimize the effect to normal production operations. (e.g. schedule critical activities to
coincide with a planned pipeline shutdown).

Maintenance should be carried out on all pipeline associated equipment (e.g. pipeline valves
and actuators, pig traps, pig signalers and other pipeline attachments). Maintenance
procedures and routines should be developed with account taken of previous equipment
history and performance.