CONDITION ASSESSMENT AND RISK MANAGEMENT OF WATER MAINS SAVES TENS OF MILLIONS OF EUROS?
International Public Works Conference 2011
Canberra 21 - 25 August 2011
Geert Jan van Heck
24-8-2011
Overview of the presentation
• Waternet
• Development of water supply in Amsterdam
• WRK Water Transport Company
• Problem Analysis: Pipeline Integrity
• Condition Assessment and Risk Analysis
– Remaining life of the PCP elements
– Risk identification & analysis
– Risk management of leaking joints
• Conclusions
Waternet:
• since 2006
• drinking water
• waste water
• surface water
• safety behind dykes
• groundwater management
• lowest possible social cost.
Waternet is the first water-cycle company in the Netherlands
City of Amsterdam
Amstel, Gooi en Vecht
Regional water management Board
Some key figures
• 1.2 M Clients
• 1700 employers
• 2700 km drinking water mains
• 3600 km sewerage
• 9500 hectares open water
• 800 km dykes
• natural reserve > 1000 hectares
Amsterdam water supply Historical development
• 1851, Dune Water Company
• Source: Kennemer Duinen
• 1853, bucket of water for 1 cent
• Increasing demand for drinking water
• Depletion of water reserve in dunes
• … infiltration?
WRK Water Transport Company
• Established in 1952
• Provide pre-treated water
• 1957 water reached the dunes
• Capacity increased in 1960’s and 1980’s
• Capacity 259 million m3/y
• Delivering 150 million m3/y
WRK 1 & 2 pipelines
• pre-stressed concrete elements
• length of 6 meter
• spigot and socket joints
• WRK 1: 1954, diam 1500 mm
• WRK 2: 1964, diam 1200 mm, 2 pipelines
• Arkel & Bonna
• on piling (in peat ground)
• total length > 210 km
• yearly supply 100 Mm3
Problem Analysis
• High amount of leakage
• Leaking joints
• Cracked & collapsed pipes
• Dyke integrity
• Replacement & relining of pipes (1995-2005)
• Pressure reduction (2000)
• Increased control (2005)
Problem Analysis continued
• Supply interruptions & effect for clients
Dune area, flora & fauna
• Reducing ground cover < 0,5m
Proposals 2003-2005
• Desk study 2003/04 – Pipes at point of collapsing
– Hydrogen embrittlement damage
– Replacement 16 km WRK 2 PCP
• Additional investment proposals 2005
• Total > €85 million
• Approved … but needed?
Condition Assessment & Risk Analysis • … investments on hold!
• Remaining life of the PCP elements
• Risk identification & analysis
• Risk management of leaking joints
– Cause – effect analysis
– Leak size & detection
– Joint openings
• Remaining life of:
– Rubber gaskets
– Repair clamps
Remaining life of PCP elements(2005-2011)
Pre-stressed Concrete Pipe elements
• Wire breaks (quantity, location)
• Origin of wire-breaks
• Remaining strength
• Remaining life
Wire breaks • Eddy Current scanning
• Scanning 27 km WRK 1 & 2
• 4 pipes with ‘extreme abnormalities’
• Excavating several pipes
• X-ray check & removal of concrete shell
• Some differences
• Re-interpretation of results: 3 pipes > 150 breaks
Origin & age wire breaks
• Literature review
• Laboratory tests: microscopic, chemical analysis, mechanical
• Field tests for stray currents
• Tension corrosion
• Old cracks
Remaining strength (1)
Full scale testing (pipes with & without wire breaks)
• Internal water pressure
• Crown pressure
• Pipes ruptured at 16-20 bar
• Working pressure 4-6 bar
Remaining strength (2)
Material characteristics:
• Drill cores, slabs & pre-stressed wires
• Laboratory tests: mechanical, composition
• Concrete quality improved
• Pre-stress reduced
• Brittle steel & high tension in
wire … breaks?
Remaining strength (3)
Modeling
• Findings tests
• Amount of wire breaks
• Foundation type
• Safety factors
• External loads
• Pumping pressure
• … 3 critical pipes by capacity increase
Remaining life pipe elements
• Cracks from time of production
• ‘no reason to believe amount of wire breaks will grow’
• ‘remaining life under present circumstances very long’
• 3 critical pipe elements
Cause–effect diagram & measures for leaking joints
WRK PRE-STRESSED CONCRETE PIPELINE
MAIN PROBABLE CAUSES EVENT POSSIBLE CONSEQUENCES
7Displaced repair
clamp
1 Improperly placedRepair clamp not
sealing
2 End of lifetime Gasket not sealingImproper
sealing
8Improper water
hammer measures
9 Operational error Water lossHigh direct
costs
3 Short circuit10
Valve closed too fast Water hammer17
Large joint 20Unscheduled
maintenance
Long supply
interruption
Insufficient supply
capacity
Drought 19LEAKING
JOINT
21 Ground
instability
23 Colapsed
infrastructure
High environmental
and/or social costs
4Tree roots (&
storm)Flooding
14Ground movement 22 Piping
Unstable ground
11Activities third
parties*
5 Improper design
Connection between
old & new pipeline
sections
6Improperly
constructed
Excessive lateral
pressure
15Angular deviation
18 Cracked
joint
7Pipe not properly
tied downFloating pipe
Unstable foundation
Piling improper
placedFailing pipe support
Piling broken 12Pipeline improperly
laid
16 Uncificient ground
coverage
13 Land subsidence * Activities third parties include: construction, farming, traffic, planting
Main probable causes
Event Possible effects
Measures: inspection
monitoring
research
restriction & supervision of third party activities
…
grote kans
aanzienlijke
kans
Beperkte kans
weinig kans
Location of critical parts
High risk
• Likelihood of failure
– Frequency
– Causes
– Condition
• Consequences of failure
– Supply interruptions (MTTR)
– Repair costs
– Damage to surroundings
Specific measures
Mapping critical parts
Leak size & identification
• Large vs. small leaks
• Hidden leaks
– … difficult to detect
– … high consequences: ground instability
• Try-outs with different techniques:
– Noise loggers (500 l/h)
– Combined sensors (60 m3/h)
– Smartball (5 l/h)
Detection limits
• Smart Ball
• Acoustic in line leak detection
• Data stored inside ball
• Point leaks 5 l/h?
• Leaking joints?
• Critical leakage size?
2011 …
• Testing
• Modeling
Joint openings
• 1995 - 2010
• Inside dewatered pipe using caliper
• Identification of:
– Large openings
– Angular deviation
– Stability
• Preventive placement of repair clamps
Gaskets & repair clamps
• Condition assessment
• Remaining life rubber
– Gaskets > 10 years?
– Repair clamps 50 years?
• Assembling
• Corrosion of rings
Continuation 2011 …
• Scenario analysis
• Risk matrices
• Leak size & identification
• Elaboration of montoring system … pilots
• Long term financial plan
Conclusion
• Condition assessment & risk management
– Insight in remaining life of parts
– Specify & locate risk of failure
– Identify proper measures
– Saved tens of millions of euro’s!!!!
• Additional research needed
• Monitoring
– Internal-external
– Causes-events-measures
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