Design of Contraflow Cleaning PIG for Pipeline Maintenance

Conventional Pipeline Inspection Gauge (PIG) is a device used to remove solid
deposit from the pipeline wall and driven by the fluid flow. For single offshore
pipeline application, it needs to be launched from the manifold at the seabed which
has drawbacks on the water depth restriction and requires intervention from the
surface to launch the PIG. The current trend on the PIG design to overcome this
challenge is to develop a counter flow PIG for single offshore pipeline application
which is unequipped with the PIG launcher at the manifold.
Two of the commercial counter flow prototypes are contraflow tetherless mechanical
crawler developed by the Astec Development Ltd. which has a drawback of poor
traveling speed and Durham Pipeline Technology (DPT) crawler developed by
University of Durham which has a drawback of discontinued motion. In this research,
it is focused on the generation of a model of PIG with the function of wax removal.
The requirement of the PIG design includes the ability to travel in both forward and
reverse direction at a constant speed. In order to come out with the expected results,
the scope of the research work is limited to the generation of the conceptual design of
the PIG, product architecture and configuration design defined of the proposed
concept and generation of Computational Aided Design (CAD) model of the proposed
concept.
A systematic design based on Dieter's approach is adopted to design a PIG. It consists
of conceptual and embodiment phases. In the conceptual design phase, the PIG design
starts with problem definition, generating number of possible concepts using
functional decomposition method and selecting the most promising concept using
conceptscreening method. The most promising concept of PIG design consists of five
modules, specifically: drive mechanism, turbine for drive mechanism, flow control,
turbine for wax removal and wax removal module. Furthermore, a layout and
configuration of critical components of the most promising concept is performed in
the embodiment phase.
The PIG is designed with reference to the product design specification document of the pipeline operating condition ofpressure of 15 MPa, fluid velocity of 1 m/s and a
pressure drop across the PIG of 31 kPa. The PIG design begins with the analysis of
the impeller to determine the maximum power that can be generated from the fluid
flow. The turbine module has a function to provide power to drive the drive
mechanism and the wax removal module. Dimension of the impeller that can generate
maximum power is calculated based on the meridional and cascade flow analysis.
Furthermore, to ensure the valid assumption of the design parameter that is used to
determine the dimension of the impeller, a CAD model of impeller is simulated using
the Fluent software.
In order to travel in a constant speed, the turbine for drive mechanism module is
attached with flow control module which uses a perpetual mechanism of a poppet
valve and a spring in the crawling mode and a magnetic mechanism in the return
mechanism. For the drive mechanism device, a cam follower with bristle is used in
the PIG design. The calculation of the cam follower mechanism follows the bristle
theory that has been developed by Stutchbury. For wax removal, a cutting tool is used
in the PIG design where the design of the cutting tool refers to the cutting tool
standard used for machining process.
Based on the preliminary analysis, the PIG design can move in a counter flow at
speed of 0.03 m/s with the time ratio between the PIG movements in forward
direction and stationary condition of 4.28. The PIG design can remove wax solid
deposit with a maximum shear strength of 81 kPa. The outcome of this research is an
assembly drawing of the PIG design.