Global optimization: Gas mainline replacement planning
Pipeline replacement evaluation program
A challenge faced by NF is to scope and prioritize capital expenditure allocations to the gas
mainline most in need of repair while continuing to maintain a safe and reliable system. The
Pipeline Replacement Evaluation Program (PREP) was developed in 1994 to assist in
evaluating which potential projects should get first priority. The PREP system was
implemented on the IBM mainframe.
PREP input screens collect leak information, replacement cost, and O&M cost for a given
section of gas mainline over 250 feet in length. Existing leaks are input and the system
calculates projected new leaks over a five-year period. The net present O&M cost for
patrolling and repairing leaks is calculated. (NFGDC, 1995)
Next the net present value for capital replacement for five years is calculated. The system
then calculates a ratio of O&M expense and capital requirements (Figure 1). Ideally, the
ratio exceeds one, meaning the cost to replace is less than the cost of maintaining the main
over a five-year period. The ratio may be less than one, but the PREP score provides a
means to rank all proposed replacement work against the others when other factors apply.
Figure 1
PREP by itself is a useful tool to focus capital spending on projects with the highest value.
But, PREP is useful only after an engineer has identified all possible project areas. This
previously was a time consuming process that involved manual data collection and subjective
evaluation. However, PREP serves as a tool in the ‘tool box’ of Global Optimization. PREP
does not provide any spatial capability, but it does a good job in economic analysis.
Systematic replacement
Systematic replacement was conceived from the recognition that it costs less per foot to
replace larger scale footages of gas main than it does to replace a series of shorter sections
over time. Economy of scale applies since the fixed costs such as moving equipment, crews,
and material to a job site are about the same for both large and small jobs. Systematic
Replacement is not a computer application; rather it is a design philosophy.
Using this basic concept, the object is to chain together a number of shorter projects to build
larger scale jobs with the resulting economies of scale. Once an area is determined to have
sufficient sections with a sufficient PREP score, the object is to incorporate these in an
overall large replacement project. Also, opportunities exist to convert low pressure areas to
medium pressure resulting in projects with less total mainline of smaller diameter. The
philosophy of Systematic Replacement is used in conjunction with PREP, leak analysis, and
Global Optimization.
Leaks
The next step in the progression of better analysis capability was leak plotting. The Leak
Reporting System (LRS) is an existing comprehensive text based system that tracks the life
cycle of leaks. This mainframe based application and data was only available to the
Engineering staff in report format. However, everything that we needed for spatial analysis
except coordinates was in this database. The leak enhancement phase of Global
Optimization required building an interface to the mainframe data and adding a leak symbol
and attribution to our AM/FM/GIS.
The interface was customized in FRAMME by Intergraph. Using a mainframe application to
dump out LRS transactions and an automated file transfer utility, leak data is loaded into our
Oracle leak table.
The second part required was adding new mapping functionality to place leak symbols and
update the attribution. This functionality automated placing the leak symbols since the
source data does not have mapping coordinates, but does have address and measurement
information. A labor-intensive three-month effort was required to place known leaks in New
York and Pennsylvania. A batch function updated the attributes (Figure 2) that are interfaced
to the LRS system giving the leak symbol the intelligence needed for spatial analysis.
Once the data was local to FRAMME and the leak points were plotted, a secondary
application updates the leak symbol with the attributes loaded from the mainframe. This
changes the symbology for each leak type and the status.
Only having the leaks plotted proved to be a significant benefit for replacement planning.
Staff engineers were able to scan plots of their service territories and quickly identify
potential projects. In previous years a laborious process of hand plotting was required. The
maps produced were only good for one season and were quickly outdated.
Figure 2
Remembering that most of our facility data is non-intelligent raster, the leaks needed to
stand-alone as far as analysis is concerned. There are no links to the vector main, so text-based
queries of leaks (correlated to mains) are not possible. So, our next challenge was to
develop the final ‘tool’ needed to pull together all of the other ‘tools’ to enhance selection of
potential replacement project areas.
