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

4

Where can you find Waternet?

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

THANK YOU!

Questions?