Force Main Condition Assessment: New Technologies & Case Studies

Transcription

1 Force Main Condition Assessment: New Technologies & Case Studies Andy Dettmer, Ph.D., P.E. CMOM Workshop August 19,

2 Three takeaways 1. Most of your force mains are good 2. We can pinpoint the few, bad pipes 3. Condition assessment is cost effective 3 Force Mains are Special Soil Gravity Pipe CCTV is usually enough Pressure Pipe Requires Advanced Tools & Analysis 4 2

3 8,000 miles inspected prove that most pipe is in good condition 96% of pipe is in good condition We only need to address 4% of our pipelines! 3% has some deterioration Find the Weak Link Manage individual assets 5 An assess & address approach quickly reduces risk and is cost effective Plan & Prioritize Field Inspections 1% Repair, Rehab, or Replace 3% When needed Reinspection Schedule 6 3

4 Pipe materials fail differently and require customized assessment techniques 2010 US Wastewater Force Main Inventory Ductile Iron, 47% Steel, 4% PCCP, 12% Some is 3/8 Thick Some is 1.5 Thick Cast Iron, 12% PE, 1% PVC, 14% AC, 5% RCP, 4% WERF Guidelines for the Inspection of Force Mains (2010) Force Main Failure Modes: What are we looking for? Age is not the primary factor so what is? Material quality and manufacturing Design Environmental Operational 3 rd party damage Installation Failures are often a combination of several factors 4

5 Inspection tools designed to pinpoint bad pipe for targeted repair & replacement 9 Magnetic Flux Leakage (MFL) 46% & 56% 90% Wall Loss 10 5

6 Electromagnetic (EM) tools for different field conditions EM, CCTV, Sonar, & GIS mapping Manned Entry Robotics Free Swimming Diameter: 36 + Dewatered or Depressurized Pipeline Diameter: 18 + Depressurized (Dewatering not required) Diameter: 16 + Ideal for long distance inspections Free Swimming Electromagnetic Inspection 12 6

7 24 Flanged Outlet Damaged 30 Concrete Pipe Pinpointed for Repair 13 Damaged 30 Concrete Pipe Pinpointed for Repair 14 7

8 13 Bar Breaks & Cylinder Corrosion Detector free swimming PipeDiver tool for 16 steel, ductile & BWP Passed 20 Butterfly Valve (9 clearance) 20 Steel Pipe 16 8

9 Defects identified in 20 Steel Pipeline Pipe repair not reported by contractor Dent from rock 17 External Corrosion Identified in 20 Steel 9

10 External Corrosion on 48 Ductile Iron Pipe 6 x 9 external corrosion on 48 DIP PipeDiver Sonar quantifies debris & air pockets in gravity siphons Air Pocket Tee/Branch Debris 10

11 Leaks and gas pockets are precursors to larger failures in force mains Gas pockets may compound the effects of hydraulic transients and reduce capacity PVC Failure Sahara provides location and size of leaks and air pockets 11

12 Air pockets restrict flow and can facilitate crown corrosion 23 SmartBall provides location and size of leaks and air pockets 24 12

13 New analysis techniques can distinguish air pockets from bubbles and air slugs Entrained Air Bubbles Entrained Air Slugs Corrosion in Air pocket Erosion 72% of air pockets are not at known high points (500 miles inspected) 26 13

14 8/20/2014 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 28 14

15 Grate blocks outgoing pipe Net blocks outgoing pipe Net captures SmartBall when discharged from Force Main 29 Force Main Discharge 30 15

16 8 DIP Force Main Most gas pockets not at known high points 15 Gas Pockets Total 4 Test Pits Chosen for Excavation and Wall Thickness Measurements 16

17 Wall thickness measurements showed sufficient safety factor (8 DIP Force Main) Wall thickness measurements were within Casting Tolerance for 8 DIP 17

18 SmartBall & Sahara can now provide pipe by pipe data Pipe Wall Assessment (PWA) Technology Pipe # 402 Station Two large stress anomalies *click for further details PWA measures relative stress in pipe wall due to groups of pits in 24 Cast Iron Pipe 36 18

19 How much deterioration before pipe fails? Structural Performance Curves based on multiple finite element simulations Level of Deterioration % in BWP Yield Curve at 15ft deep 200 Yield Limit Pressure (psi) Limit of 8 Bar Breaks and 32% Wall Loss at 115psi, 20 MGD (no surge) 0 10% 30% 50% 70% Broken Bars in BWP & Cylinder Corrosion

20 54 steel pipe structural model 39 Transient Pressure Monitoring is a Low cost, High Value Assessment Tool Transient pressure spike exceeded pipe design pressure Typical SCADA system misses critical transients 40 20

21 Pump cycling can induce damaging transient pressures Pipe Design 200 psi Vacuum can damage pipe 7.7 psi 41 Estimate Remaining Useful Life Using Condition Data and Statistical Models 350 Predicted Failure Occurrences Reinspect in 10 years 30 to 40 years until significant number of failures Time to Yield (years) 42 21

22 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 43 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) 44 22

23 How much does assessment cost? What is it worth to you? In terms of percent of replacement costs? 50% of replacement cost? WERF % of replacement? WERF % to 5% of replacement WERF % 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 45 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 46 23

24 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) 47 TIME FOR THE TEST 1. Most of your force mains are GOOD 2. We can pinpoint the, FEW BAD pipes 3. Condition assessment is cost effective, but WE NEED TO START BUDGETING TODAY! 48 24

25 Force Main Condition Assessment: New Technologies & Case Studies Andy Dettmer, Ph.D., P.E. CMOM Workshop August 19,