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Pre-inspectton-survey activities

PRE-INSPECTION-SURVEY ACTIVITIES
FOR MAGNETIC-FLUX INTELLIGENT PIGS

INTRODUCTION

The determination of the accessibility of a pipeline prior to intelligent
inspection, and deciding on the level of preparation that will be required, are
sometimes subject to differences of opinion between pipeline operators and
inspection contractors. This may ultimately result in a failure to achieve the
specified inspection results.
The pipeline operator expects the inspection survey pig to report pipe-
wall anomalies (internal and external) as small as 12mm diameter and only
3mm deep. These are to be found and sized in, for example, a 30-iti diameter,
100-km long pipeline, which has a pipe-wall surface of 478,536sq m. It is
obvious that the pipe wall should be accessible and the running conditions
should be optimized in order to achieve the desired inspection result.
Just for comparison, a 30-in intelligent pig travelling at 3m/s produces
approximately 150,000 measurements per second, and passes over a 12-mm
anomaly in 0.004sec. In this available time, the sensors must record measure-
ments to determine and confirm the metal loss and decide on internal or
external location.
This paper describes the possible causes for misunderstanding by detailing
all the activities required prior to a pre-inspection survey. The fact that a single
cleaning pig run does not produce conclusive information on the pipe-wall
surface condition may give rise to misunderstanding. Hence, this subject and
many others are detailed below.
Pipeline surveys are carried out as part of an overall maintenance pro-
gramme; the inspection contractor should therefore have access to all
relevant pipeline data in order to be able to present the survey report in the
format that fits the maintenance programme.

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