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8/20/2014
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Force Main Condition Assessment:New Technologies & Case Studies
Andy Dettmer, Ph.D., P.E.
CMOM Workshop
August 19, 2014
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Three takeaways
1. Most of your force mains are good
2. We can pinpoint the few, bad pipes
3. Condition assessment is cost effective
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Force Mains are Special
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Gravity Pipe
Pressure Pipe
CCTV is usually enough
Requires Advanced Tools & Analysis
Soil
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8,000 miles inspected prove that most pipe is in good condition
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3% has some deterioration
We only need to address 4% of our pipelines!
96% of pipe is in good condition
Find the Weak Link
Manage individual assets
An assess & address approach quickly reduces risk and is cost‐effective
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Plan & PrioritizeRepair, Rehab, or Replace
Field Inspections 1%
ReinspectionSchedule
3% When needed
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WERF Guidelines for the Inspection of Force Mains (2010)
Pipe materials fail differently and require customized assessment techniques
Cast Iron, 12%
Ductile Iron, 47%
Steel, 4%
PCCP, 12%
PVC, 14%
AC, 5%
RCP, 4%PE, 1%
2010 US Wastewater Force Main Inventory
Some is 1.5” Thick
Some is 3/8” Thick
Age is not the primary factor…so what is?
• Material quality and manufacturing
• Design
• Environmental
• Operational
• 3rd party damage
• Installation
Failures are often a combination of several factors
Force Main Failure Modes: What are we looking for?
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Inspection tools designed to pinpoint bad pipe for targeted
repair & replacement
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Magnetic Flux Leakage (MFL)
1046% & 56% 90% Wall Loss
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Electromagnetic (EM) tools for different field conditions
Manned‐Entry
Diameter: 36”+
Dewatered or Depressurized Pipeline
Robotics Free‐Swimming
Diameter: 18”+
Depressurized (Dewatering not required)
Diameter: 16”+
Ideal for long distance inspections
EM, CCTV, Sonar, & GIS mapping
Free‐Swimming Electromagnetic Inspection
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Damaged 30” Concrete Pipe Pinpointed for
Repair
24” Flanged Outlet
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Damaged 30” Concrete Pipe Pinpointed for
Repair
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13 Bar Breaks & Cylinder Corrosion
24 Detector free‐swimming PipeDiver tool for 16” steel, ductile & BWP
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20” Steel Pipe
Passed 20” Butterfly Valve
(9” clearance)
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Defects identified in 20” Steel Pipeline
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Dent from rock
Pipe repair not reported by contractor
External Corrosion Identified in 20” Steel
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External Corrosion on 48” Ductile Iron Pipe
6” x 9” external corrosion on 48” DIP
PipeDiver – Sonar quantifies debris & air pockets in gravity siphons
Debris
Air Pocket
Tee/Branch
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Gas pockets may compound the effects of hydraulic transients and reduce capacity
Leaks and gas pockets are precursors to larger failures in force mains
PVC Failure
Sahara provides location and size of leaks and air pockets
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Air pockets restrict flow and can facilitate crown corrosion
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SmartBall provides location and size of leaks and air pockets
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New analysis techniques can distinguish air pockets from bubbles and air slugs
Corrosion in Air pocket
Entrained Air SlugsEntrained Air Bubbles
Erosion
72% of air pockets are not at known high points (500 miles inspected)
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SmartBall data confirms gas pocket location including increased velocity within hydraulic jump
High velocity
Insertion of SmartBall through check valve, spool piece or flange near lift station
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Net blocks outgoing pipe
Net captures SmartBall when discharged from
Force MainGrate blocks outgoing pipe
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Force Main Discharge
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8” DIP Force MainMost gas pockets not at known high points
15 Gas Pockets Total
4 Test Pits Chosen for Excavation and Wall Thickness Measurements
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Wall thickness measurements showed sufficient safety factor (8” DIP Force Main)
Wall thickness measurements were within Casting Tolerance for 8” DIP
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SmartBall & Sahara can now provide pipe‐by‐pipe data
Pipe # 402Station 99+49.02
Two large stress anomalies
*click for further details
Pipe Wall Assessment (PWA) Technology
PWA measures relative stress in pipe wall due to groups of pits in 24” Cast Iron Pipe
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How much deterioration before pipe fails?
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Structural Performance Curves based on multiple finite element simulations
Level of Deterioration %
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0
50
100
150
200
250
0 5 10 15 20
Pressure (psi)
Broken Bars in BWP
30‐in BWP Yield Curve at 15ft deep
Yield Limit
Limit of 8 Bar Breaks and 32% Wall Loss at 115psi,
20 MGD (no surge)
10% 30% 50% 70%& Cylinder Corrosion
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54” steel pipe structural model
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Transient Pressure Monitoring is a Low‐cost, High Value Assessment Tool
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Typical SCADA system misses critical transients
Transient pressure spike exceeded pipe design pressure
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‐7.7 psi
Pump cycling can induce damaging transient pressures
Vacuum can damage pipe
Pipe Design 200 psi
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Estimate Remaining Useful Life Using Condition Data and Statistical Models
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0
50
100
150
200
250
300
350
0 20 40 60 80 100
120
140
160
180
200
220
240
260
280
300
320
340
360
380
400
Predicted Failure Occurrences
Time to Yield (years)
30 to 40 years until significant number of failures
Reinspect in 10 years
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Recommended scope for force main inspection
1. Data Collection & Walk the Pipe
2. Data Gap Analysis & Prioritization
3. Hydraulic Evaluation & Transient Monitoring
4. Leak and Gas Pocket Assessment
5. Pipe Wall Assessment
6. Structural Modeling (Safety Factor)
7. Remaining Useful Life Modeling
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Budgeted vs actual costs based on WERF utility survey 2009
• Typical annual budget for condition assessment
– $1.57 per foot (actual cost was $2.58)
• Typical annual budget for repair & cleanup
– $2.56 per foot (actual cost was $21.47)
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How much does assessment cost?
• What is it worth to you?– In terms of percent of replacement costs?– 50% of replacement cost? – WERF 2010– 1% of replacement? – WERF 2010– 2% to 5% of replacement – WERF 2007– 11% of replacement – WERF 2010
• What is the value?– Value = benefits ‐ costs
• The Benefits: where the pipe is leaking and where the pipe is about to fail
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How much does it really cost?
• Internal inspection technologies: $2 to $15 per foot (each)
• Holistic force main assessment scope:– Risk assessment– Hydraulics, transient pressure monitoring– Internal & external corrosion assessment– Leak, gas‐pocket, and structural wall assessment– Structural modeling
• Typically 2% to 9% of replacement costs
• Assessment Program: $10 to $20 per foot – best value
• Project‐by‐project basis: $15 to $30 per foot
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Recommendations for design & construction of new force mains
1. Perform base‐line structural inspection before commissioning (preferred)
2. Require zero leakage (at minimum)
3. Full diameter pigging stations (preferred)
4. Full diameter access flanges (at minimum)
5. 4” access ports (preferred)
6. 2” access ports (at minimum)
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TIME FOR THE TEST
1. Most of your force mains are _____
2. We can pinpoint the ____, ____ pipes
3. Condition assessment is cost effective, but… ________________________________
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WE NEED TO START BUDGETING TODAY!
GOOD
FEW BAD
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Force Main Condition Assessment:New Technologies & Case Studies
Andy Dettmer, Ph.D., P.E. ‐ [email protected]
CMOM WorkshopAugust 19, 2014
