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Tempe PRS regulator/instrumentation UpgradePrimary Regulatory
Sets (PRSs) are gas pressure reduction, metering and filtration
facilitieslocated at each off-take on primary mains, reducing the
pressure from a MAOP of 3,500 kPa tosupply the secondary network
with a MAOP of 1,050 kPa. Construction, operation andmaintenance of
PRS are managed in accordance with the safety and operating plan
(SAOP) andAS2885 suite of pipeline standards. Compliance with
AS2885 is a regulatory requirement (NSW
Gas Supply [Safety Management] Regulation 2002).
14 PRS are installed and there are three main groups or
categories as follows:Group 1 Sites commissioned in 1976 when
natural gas was introduced to the Sydney market.Includes Tempe
PRS.Group 1a Sites commissioned as part of organic growth post
1976. Includes Horsley Park,Haberfield, Wollongong (Cringila) and
Willoughby PRS. Group 2 Sites commissioned as part of the
construction of the Eastern Creek to Penrithprimary main Penrith
PRS.Group 3 The Moorebank PRS was commissioned in 2007 (part of the
Sydney Primary Loop).Most PRSs are located in Sydney and are
situated on public land. Due to limited abovegroundspace, most PRS
are installed in underground concrete pits with lockable lids and
alarms. The
Supervisory Control and Data Acquisition (SCADA) system remotely
monitors these facilities. Nineof the 14 PRS are between 31 and 35
years old. Tempe PRS is 33 years old.
Drivers (need or justification) for upgrading Tempe PRSThe
Primary Facilities section of the Asset Management Plan (AMP)
indicates Jemena AssetManagement (JAM) expects the design life of
PRSs to be 40 years (the same section also refersto 30 to 35
years). PRS are subject to planned (or preventive) maintenance
regimes howeverunlike pipe assets, PRS comprise different
components including regulators, meters, valves,filters, pipes and
instrumentation, all of which can have different lives. Individual
soft components(e.g. associated with filters and regulators) need
to be replaced at regular intervals irrespective ofthe asset
life.
Details pertaining to a number of PRS issues which impact upon
Lifecycle Management areprovided in the AMP. These issues are
summarised as follows:
Many PRSs are over 30 years old. The original Fisher pressure
control valves areexcessively noisy and resulting vibration has the
potential over time to cause serious damageas it did in 2007 when a
weldolet on the Auburn PRS failed due to fatigue. The
excessivenoise level presents an OH&S risk for service
personnel and also breaches EPA Guidelinesfor allowable noise
levels in adjacent residential/commercial areas. Temporary
noisemitigation modifications have been made however they are
ineffective when maintenanceactivities are carried out.
Operation of the Fisher pressure control valves relies on
compressed air and failure rateof the instrument air systems is
increasing. Reliance on electricity supply is also
provingproblematic. In the event of a power failure, bleeding of
natural gas to atmosphere can occur.This is environmentally
undesirable.
Due to the age of the assets, vendors are withdrawing technical
and spare parts support.Depending on its condition, redundant
equipment is used for spare parts. However this has
practical limitations. A number of installations do not meet
mandatory hazardous area standards.
Many PRS are installed below ground in concrete pits which
inherently provide a dampenvironment.
Corrosion of pipework and PRS components is an ongoing problem
as various measurestaken to eliminate dampness have been
unsuccessful.
Below ground pits are classified as confined spaces which
require special access/egressmeasures. Grates are fitted as a
precaution against trips and falls during
maintenanceoperations.
JGN completed a comprehensive Lifecycle Management study in
2008. Risk analyses inaccordance with AS/NZS 4630 were conducted as
follows:
asset risk (levels of service, maintainability, asset
lifecycle-end of life).
technical risk (asset variation [standardization], maintenance
costs, special issues).
financial risk.
compliance risks (standards, OHS, environmental).
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Project driversThe AMP and the Lifecycle Management Report
comprehensively outline the need for, and thebasis of the project.
The engineering assessment (EA) assumes it is not a capacity driven
project.Although primary gas facilities have a nominal asset life
of 30-40 years, it is widely accepted withinthe gas industry that
it is more likely that major facilities (or their components), such
as PRS, willrequire changes or replacement much more frequently due
to changing capacity requirementsand/or technological obsolescence.
Technological obsolescence includes unavailability of spareparts
and lack of manufacturer support. It is considered that JAM and JGN
should adopt astandard nominal asset life for PRS. The period
nominated for this class of asset is not criticallyimportant;
however, the recommendation is made for consistency reasons.
Currently the AMPrefers to 30-35 years and 40 years. The Lifecycle
Management Report refers to 30 years. Differentfigures have the
potential to create reader doubt and/or present unanswered
questions. JGNsdecision to upgrade Tempe PRS is soundly based on
formal technical and financial riskassessments in accordance with
the appropriate Australian Standard. The decision is also basedon a
pressing need to eliminate equipment vibration and to reduce noise
levels to within limits
specified by EPA Guidelines and OH&S legislation. There is
also a pressing need for mandatoryhazardous area standards to be
met.
Options investigatedIt is apparent that JAM has considered a
wide range of options before selecting Option 2 (upgradeusing
existing concrete pit) as the preferred option. While an
aboveground option could satisfy allspecified criteria, the Tempe
PRS EA clearly demonstrates this is not technically or
economicallyfeasible.
JAM has not limited its investigations to known/proven
technology, but has considered newtechnology Cocon 6 which is
undergoing trials overseas.
Third party reviewer understands the pressure regulating
equipment with this technology is locatedin a below ground surface
mounted box accessible via ground level box lids. These boxes
are
not classified as confined spaces and service/maintenance tasks
can be performed at groundlevel. Furthermore, there are other
important considerations and reviewer agrees it is premature
tointroduce this new technology. It may be more suited to new PRS
installations that do not involvecostly retrofitting.
Proposed project scopeThe overall project scope is to upgrade
Tempe PRS to mitigate current risks and ensure continuedsafe and
reliable operation. Table 6-8 indicates key assumptions and
constraints.
