A Pipe Network Data Model for Defect Tracking
Paul C. Marsh
Geomatics Engineering Manager and Mike Garaci, Senior GIS Analyst
The Pressure Pipe Inspection Company 4700 Dixie Road
Mississauga, Ontario L4W 2R1 Canada
Abstract:
A typical Pipe Network model is composed of nodes and links for contiguous waterlines; however, current
inspection technologies collect more detail than this traditional model can present. This paper outlines a new hybrid
model approach for managing the hydraulic requirements of water systems with inspection and defect tracking
activities. Using UML and starting with the ArcGIS water model prepared by ESRI, the hybrid model tracks
individual pipe segments with inspection and integrity information while still maintaining the hydraulic modelling
capability.
New inspection techniques offer pipeline operators to grow beyond direct condition information and map
placement of assets. As an example, the RFEC/TC technology for PCCP pipe offers utilities information not only
on a per pipe segment basis but also at sub-regions along each pipe. Pipe failure modelling, risk to operations
management, and cost analysis involve more detailed, and direct information leading to better investment decisions.
The hybrid model displays data in plan and profile views. The plan view of a typical water network drawing shows
the horizontal position of links and nodes and integrates with hydraulic analysis programs. An associated profile
view, similar to as-constructed drawings, presents the individual pipe segments and their related defect information.
The new model lends itself to numerous other data presentation options to highlight asset tracking, data trending and
analysis.
Introduction
Traditional Pipe Network Models use a node and link database to represent Water Conveyance
Systems. Links are water mains that convey water from one point, or node, to another point, or
second node. Thus, the atomically defined database elements are Waterlines from start to end
and nodes. Nodes are typically anything that controls the flow of water or changes the properties
of the waterline, e.g. a coupling between waterlines of differing materials.
Changing Requirements
This node link data structure was suitable for collecting water related infrastructure asset
management data. Examples include fire hydrant testing results to establish C factors for
waterlines. In addition, this data structure is good for water quality data from water monitoring at
consumers and from within the distribution system. Water supply capacity planning is
particularly well suited to this data structure as hydraulic analysis software uses the same data
structure.
Recent advances in non-destructive testing of pipes have begun to collect greater amounts of and
more detailed data than is suitable for this traditional data structure. These technologies include;
CCTV inspection of Wastewater pipes, magnetic flux leakage to determine pitting and Remote
Field Eddy Current/Transformer Coupling, (RFEC/TC). For the purposes of our discussion, we
will focus on RFEC/TC inspections and the types of data produced. We will also limit our
discussion to the application of RFEC/TC inspections to Pre-Stressed Concrete Cylinder Pipe or
PCCP.
A RFEC/TC inspection is performed from the inside of a pipe by a remote unit that is operated
by staff who ensure that the equipment is properly collecting data while it is propelled through
the pipe. The equipment collects a signal later analyzed for pipe structural defect detection.
Figure 1 Typical RFEC/TC Scan Result
The signal identifies the start and end of each pipe segment. Defects are tracked according to
their relationship with a specific pipe segment and related to an overall position within a
waterline.
New Problems:
PPIC has inspected over 2,000 kilometres of PCCP water conveyance infrastructure. With all of
this experience collecting, interpreting and analyzing data, there are some common problems
addressed with the new hybridized data model.
#1 When a defective pipe is reported, it is often just one pipe or even several pipes spaced
out over several thousand feet. Pipes are then replaced individually and not an entire waterline
between nodes. The past practices of replacing an entire line between two nodes are too costly
for transmission mains. This is one of the major advantages for performing the RFEC/TC
inspection. The RFEC/TC inspection identifies a specific pipe segment for replacement or repair
instead of replacing an entire line.
#2 In almost every inspection, there is a discrepancy found between what was actually
inspected from what was reported on As Constructed plans. The RFEC/TC inspection is sensitive
to pipe properties and when a series of pipes are out of sequence from that reported on the
Construction Lay Schedule or the As Constructed Plans, this is detected in our signal. This
means that an RFEC/TC inspection can report a more accurate profile of pipe data that is
typically contained in most clients engineering documents of record.
#3 The use of accurate GPS survey technology to geographically fix the position of surface
features is very important to the accurate reporting of pipe defect position. This would be true for
subsurface features like bends and other pipe route inflection points; however, because they are
buried infrastructure, fixing their exact position is not possible with a GPS survey technology.
#4 The reproduction of the original survey line stationing is very difficult to establish within
the GIS and often similarly difficult to establish in the field. Consequently, when representing
pipe geometry as a profile the original station series is not preserved exactly as it was recorded.
Thus reporting a pipe as being at station XX+YY from the GIS Profile is not usually consistent
with the client’s original station series.
#5 When a pipe is removed from service it is not typically cast aside but is usually kept for
analysis. Thus each pipe removed from service represents considerable value for information
both for RFEC/TC and for long term asset management information. This creates a need to
preserve data within the data structure rather than merely keeping a representation of current
assets.
