Page 362 - Pipeline Pigging Technology

High-accuracy calliper surveys

HIGH-ACCURACY CALLIPER SURVEYS

WITH THE GEOPIG PIPELINE

INERTIAL GEOMETRY TOOL

IN THE DEVELOPMENT of the inertial geometry pig, Pigco recognized the
need for relating the pig position to the pipe wall. The sensors used for this
during some of the initial runs provided a very good picture of the inside of
the pipe wall. To meet the need for a high-accuracy calliper with the ability
to accurately locate features, Pigco has improved its Geopig. To provide data
in a useful form that facilitates interpretation, Pigco consulted with its clients
and developed a software-analysis system; and a test-dig programme verified
the accuracy of location and feature measurement. The paper describes the
pig hardware, the analysis software, operations, and the results of the survey.
Potential for structural analysis and the scheduling of maintenance is also
discussed.

INTRODUCTION

Previous inertial pig development

The Geopig was designed to meet a large variety of user requirements
using a modular system which integrates a number of different sensors. The
Geopig can be customized and adapted to fluid or gas lines with minor
modifications. The current versions can inspect pipelines of diameter NPS
lOin (254mm) and above.
The strapdown inertial measurement unit (or SIMU) produces a three-
dimensional measurement of inertial acceleration and angular rate directly
from orthogonal triads of accelerometers and gyroscopes. Two inertial
systems are currently in use: one uses an orthogonal triad of single-degree-of-

343