A Pipe Network Data Model for Defect Tracking
Possible Options:
ArcGIS Water Wastewater data model, (ArcFM)
This data model presents some of the objects that we need but it does not specifically contain
pipe segments. This data model is based on the same node link models implemented previously
and by many other industry groups.
Dynamic Segmentation
Using a linear addressing scheme to create dynamic segmentation of a waterline would present
an opportunity to represent pipe segments as an event table with specific geometry from the
linear address scheme. Thus, a pipe would be from station XX to station YY and with a waterline
between nodes 43 and 44 a specific geographic position would be recorded based on the dynamic
segmentation of the waterline.
There are circumstances when this data structure is quite effective for pipe property data;
however, it is very dependent on the accuracy of the linear addressing scheme and this creates an
unacceptable physical representation dependency. In particular, the use of interpolated positions
based on vertexes of the waterline does not provide adequate pipe segment and pipe joint
positional data.
Pipeline Open Data Standard, PODS
A consortium of companies working from the base of a single project for a particular client
created PODS version 1.0. The use of the word standard with respect to the work undertaken is
not appropriate as changes have been made by several companies including a new version of the
model created using UML diagramming with ESRI extensions. This is really a competitive
commercial data structure and not a true standard.
While there are some interesting aspects to this data structure, its background in the oil & gas
industry limits its applicability to the water industry. Specifically, there are not the data
structures that we need to address the jointing aspects of PCCP pipe. Steel pipe is typically
constructed and installed as a welded continuous pipe while PCCP and Ductile pipe are
constructed of short, (12 ft, 16 ft & 20 ft) segments with bell and spigot ends that possess a
gasket connection.
A Proposed Solution
Conceptual Approach
Our approach is based on work performed by Intergraph for its Smart Plant Software used on
North Sea Oil Platforms. This conceptual approach introduces five high level objects used in the
data model as shown in the following figure.
Figure 2 Data Model Approach
Figure courtesy of Bob Humphrey of Intergraph
This approach provides two distinct objects that fulfill differing functions within our data model.
The Plant Item object represents the process function of the plant or in this case Water
Transmission facility. If we are only interested in material flow properties, then we need go no
further than this object. However, process functions are fulfilled by Service Items or equipment.
This establishes a relationship between a process representation and an equipment representation.
This figure of the Data Model Implementation shows the use of ArcGIS Water Data model for
Plant Items or process model while the Service item is the PPIC Pipe Segmented Data Model.
Process components verses Equipment components
The process portion of the data model maintains the original node link data model approach. The
use of ArcGIS water data model provides a node link data model but any of the several in the
water industry would also work. The node link data model provides everything in the database
that would be needed for a detailed hydraulic assessment for water capacity planning purposes.
The Equipment component portion of the database repeats an instance within the database for
each process component but provides greater attribute detail. In fact, there is a many to many
relationship created in the database between equipment components and process components.
This provides historical tracking of equipment, (pipes) for providing water conveyance within a
waterline.
Plan verses Profile
Modelling pipelines of any sort presents a common modelling problem of representing a three
dimensional system in a two dimensional space. Despite improvements in 3D rendering
software, modelling systems in three dimensions continues to challenge pipeline data models.
Our model structure is a 2½ dimensional representation of the pipeline and provides for the three
dimensional real-world pipeline via separate, but associated plan and profile views.
A plan view of the pipeline represents the process elements of the database model in a
planimetric layout traditionally used in most pipeline or network models. Nodes represent all
types of fittings such as manholes, air valves, or elbows while edges characterize the pipeline
between nodes. Information about the edge pertains to the entire length of pipeline between the
two nodes. At this level, traditional network and hydraulic modelling can occur. For example,
one can perform water traces, isolate valves, or determine disconnected areas of the network
In contrast, the profile view presents the individual pipe segments. This side view of the pipeline
does not lend itself to any world coordinate system. Thus, we plot the pipe segments using the
pipe lay station number for the X-axis against elevation on the Y-axis. Most evident in the
profile view are elevation changes between pipe segments because our model incorporates the
slope at every pipe joint. Each pipe segment also displays its inspection result and defect
location (see figure 4).
Figure 4 Typical Plan & Profile GIS View
A unique PipeID uniquely identifies pipe segments, which are joined to GIS features in the
profile and plan views. Likewise, a SysID uniquely identifies each node and waterline in the
plan view. The pipe segments in the profile view and the process components of the plan view
connect in the data model via these two identifiers. By giving each pipe segment the SysID of its
process counterpart, we create a relationship between the process and equipment representations
in the data model. If a pipe segment is replaced on a particular waterline, its SysID value is set to
null but the PipeID is maintained and so are all of the inspection results that are linked to that
pipe.
Survey Stations and GPS
In order for the database to be the basis of field operations and investigations, accurate spatial
information is a necessity. Much of the PCCP water infrastructure across North America is over
30 years old. The age of the system coupled with outdated as-built lay drawings leaves many
pipeline managers speculating about the exact location and composition of their system. While
an RFEC/TC inspection provides the precise number, type, and relative position of pipe
segments along a transmission line, the inspection cannot give real world coordinates to these
features.
A GPS (Global Positioning System) survey provides centimetre level accuracies for surface
features (e.g. manholes, air valves, blow offs, marked point intersections). After an RFEC/TC
inspection has accurately corrected the pipelines lay schedule, interpolating the buried pipe
segment’s real world position requires at least two GPS points (up and downstream from the pipe
segment) in addition to pipe length, slope, and pipeline bearing characteristics.
With a GPS survey, if a pipeline between two known points contains numerous changes in
horizontal bearing, the accuracy of a pipe segment location in such an area will decrease. The
error is estimated to be a maximum of 75% of a standard pipe length; however, there are
circumstances where this could be greater depending on length between nodes and number of
bearing changes.
In most pipeline Construction documents there are inconsistencies with the original lay schedules
station numbering. Station numbering is the accumulated distance travelled by the pipeline from
an arbitrary starting point (usually the beginning of the pipeline). During construction, a survey
creates this numbering system, however; when contractors build pipelines using small individual
sections that are later joined, the station numbering survey tends to have errors that are corrected
by using a mathematical equation to adjust the Station numbers. Ultimately, the original station
numbering is not a true representation of the distance travelled by the pipeline but is a relative
positioning technique.
