Pipeline Crawlers: Pigging the Unpiggable
Authors: Bybee Karen 
Published: February 2015

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper OTC 21210, ’Genesis Pipeline Crawlers: Pigging the Unpiggable,’ by Andy Kenney, Subsea Integrity, originally prepared for the 2011 Offshore Technology Conference, Houston, 2-5 May. The paper has not been peer reviewed.

Many pipelines cannot be inspected internally because of reductions/changes in inside diameter (ID), extreme angles, 90º miter bends, T- and Y-junctions, or simply having access for pigs without a recovery point. A range of high-powered, tethered, brush-tractor crawlers are delivery systems for applications including internal inspection, cleaning, and repair. The brush-drive system copes with internal pipeline irregularities caused by corrosion, sedimentation, and changes in ID. Only one access point is needed for both insertion and recovery because crawlers can reverse.

Introduction

Conventional intelligent pigging of pipelines is usually a single-directional process (unless flow can be reversed) that requires sufficient product flow to drive the pig, a consistent bore size to allow the drive cups to efficiently occlude the pipeline, and a launch and receive trap at either end of the run.

More than 50% of the global pipeline network (for various reasons) does not enable conventional pigging to be undertaken, and these pipelines are collectively identified under the heading of “unpiggable.” As ongoing development technology progresses to market-ready technology, additional capability becomes available to reduce the percentage of pipelines that cannot be inspected. One technology that falls into this category is high-power “brush-drive” pipeline crawlers.  

Pipeline crawlers that use reciprocating brushes as their source of grip and motive force have been in development for more than 10 years. Fully developed “tethered” production tools are now at the stage of field trials and early operations with a number of companies. Self powered and with high grip and high pull loads at the disposal of the crawler, they are capable of operating in a pipeline independently of most flow conditions, can operate in complex geometries, can be deployed and recovered from a single access point, and can be integrated with existing intelligent inspection tools and cleaning equipment. In essence, they are an enabling technology that can transport existing and established technology used in conventional pigging into an until-now unpiggable part of the pipeline network.

Traversing Pipelines

Propulsion. The crawler tool uses a free-running “brush drive” attached over the body of a reciprocating device, attached to a fixed-brush section. The brushes are designed to be larger than the pipe ID so they will bend to conform to the pipe bore. In this condition, the brushes possess a gripping force in one direction that is much larger than its sliding force in the opposite direction. When the brush drive is moved backward by the reciprocator (drive motor), the grip force of the brush moves the crawler tool along the pipe. When the brush drive is moved backward by the reciprocator, the fixed-brush grip force exceeds that of the drive brush and the drive brush moves forward. By repeating this process, a brush-driven crawler can travel forward.