Pipeline Integrity Management Through Intelligent Pigging Survey
Authors: Choumar Ali A. 
Published: December 2007

Introduction

Onstream inspection of pipeline by intelligent pigging survey (IPS) has become of a paramount importance in the management of pipeline integrity. In some countries (USA) IPS is becoming mandatory by legislation. This is to safeguard the interest of public as well as pipeline owners against any or all of the following, which may be caused by a pipeline failure:–Environmental damage–Hazard to lives–Loss of investment/business interruption.

Integrity parameters for pipelines are induced by specification at the design and construction stages and by subsequent operating philosophy through several measures e.g. material and wall thickness selection, cathodic protection, surface protection (coating & wrapping), corrosion inhibition by chemical injection, sampling of process, periodical operational cleaning and water displacement by pigging, just to mention a few.

Intelligent pigging provides a method of gauging the performance/effectiveness of these measures while in service and determines how fit for continued service a pipeline is. The main advantage of IPS is that a pipeline can be assessed to its full length without service interruption. It further serves as the foundation for a pro-active maintenance programme to safeguard against the consequences of failures.

REASONS OF IPS

There are many reasons why a pipeline operator would carry out IPS. These could be one or a combination of the following:–Baseline survey to provide a benchmark or a finger print against which to gauge future conditions.–Detection and assessment of internal corrosion caused by process variables.–Detection and assessment of external corrosion caused by deteriorating coat and wrap, C.P. system, harmful backfilling and environment.–Pipeline coating condition and repair programme. - Girth weld crack detection in susceptible environments.–Pipeline tally, right of way, topography and dimensional.

OBJECTIVES OF IPS

Objectives again would vary and would include:–Verification of line condition against current service requirements.–Verification of adequacy of line condition to meet a projected change in future production requirements e.g. higher throughput/higher pressure.–Development of cost benefit analysis of potential repairs against pipeline replacement with new to meet the business objective(s).

HIGHLIGHTS ON TYPES OF IPS TOOLS

There are many intelligent pig tools available on the market of different types, techniques, physical sizes and technical capabilities.

Within the context of integrity or condition assessment of pipelines the discussion herein will focus on metal loss detection and sizing accuracy together with their technical and commercial positive (or negative) impact on pipeline integrity management programme(s) using the following IPS techniques.

Basically, most common two techniques are: Magnetic Flux Leakage and Ultrasonics (MFL & UT).

1. Magnetic Flux Leakage (MFL) Technique

MFL tools work on principle of magnetising the pipe wall and then detecting the flux leakage caused by metal (loss or gain) or other anomaly relative to change in pipewall thickness. Assessment of the metal loss itself is done indirectly through calibration and experience of the log interpreter. MFL results are qualitative (volumetric) i.e. rely on interpretation.

These MFL tools can be run in oil, gas or a multiphase system with a minimal (5-10%) detection threshold. Reporting capability depends on steel quality i.e: in the case, of seamless pipe, higher nose level reduces capability and accuracy.1.1 Low Resolution/Conventional (1st Generation) Tool: Used for metal loss detection internally and externally, but with no discrimination. These tools report on metal loss in bands (in order of magnitude). No sizing, therefore incapable of accurately assessing against specific pressure requirements.

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