Corrosion Control for Water/Wastewater Industry

Transcription

1 Corrosion Control for Water/Wastewater Industry Presenter: Mongkol Mahavongtrakul, P.E. Corrosion Engineer San Francisco Public Utilities Commission LOCATION: Brown & Caldwell, Walnut Creek June 14, 2016

2 Types of pipes used within SFPUC Coating and lining selection for pipe corrosion protection factory and field applied. Cathodic Protection Principal and Implementation Use of the sacrificial anode and impressed current on the steel pipe and ductile iron pipe. On-going projects

3 System s Map The transmission lines are from Hetch Hetchy Reservoir in Yosemite National Park to Downtown San Francisco. Corrosion Responsibilities: Tesla to Hetchy Reservoir by Hetchy Engineering Tesla to Downtown San Francisco by SFWD

4 Pipe Materials Welded steel pipe Ductile Iron Pipe Vitrified clay pipe HDPE pipe

5 Prestressed Concrete Cylinder Pipe

6 TYPICAL WATERMAIN LEAKS Transmission Line Leaked on December 6, 1988 Due to CP Interference Before Cathodic Protection, the Average Leak Rate: 5 Leaks per month for Distribution System 5 Leaks per year for Transmission System After Cathodic protection Leak rate reduces significantly.

7 Catastrophic Failure of the Pipe Prestressed Concrete Cylinder Pipe (PCCP) Ruptured in early 1989 in South San Francisco. Operations and Maintenance formed the Corrosion Control Team

8 Another Unpleasant Day A broken Pre-stressed Concrete Cylinder Pipe shoots a geyser of water 100 feet into the air The pipe rupture, which took nine hours to repair, resulted in a loss of 70 million gallons

9 ONE LUCKY DAY Maintenance Personnel observed water leak on the roadway. The water was from Pipeline which is PCCP during the backfill/return to normal service by Operations. We caught it before pipeline ruptured.

10 Corrosion Control for the Pipelines Typical Corrosion Control strategies: Coating/Lining Electrical Isolation Pipeline continuity Cathodic Protection

11 Mill applied Lining Materials Existing Lining Material Coal Tar Enamel Cement Mortar Epoxy Polyurethane New lining material Cement Mortar Epoxy Polyurethane Glass fuse lining

12 Mill applied Coating Materials Existing Coating Materials Coal Tar Enamel Coal Tar Epoxy Cement Mortar Epoxy New coating material Cement Mortar Epoxy Polyurethane Moisture cured polyurethane Three layer tape with cement mortar coating

13 Cement Mortar Coated pipe AWWA C200/C205 3/4 Mortar Coating Welded Wire Fabric Steel Pipe 1/2 Mortar Lining

14 Field Applied Coating Materials Aboveground Epoxy Moisture cured polyurethane Cement Mortar Underground Epoxy Polyurethane Cement Mortar Tape Wrap Heat Shrinkable Sleeve (for pipe joints) Polyethylene Encasement for Ductile Iron Pipe

15 Polyethylene Encasement for Ductile Iron Pipe

16 One of the many methods for joint Coating

17 SUCCESS OF COATING AND LINING Good Specifications Surface Preparation Surface Cleanliness/Contamination Depth of Anchor profile Dehumidifier Application Surface Temperature Recoat Window Coating Inspection Dry film thickness measurement Within the Mils Specified Uniformity Evenly applied Holiday Detection High/Low Voltage Holiday Detection

18 Preventing Lining Failure

19 ELECTRICAL ISOLATION Insulating Flange Joints Monolithic Joint

20 Corrosion Control by Cathodic Protection The use of direct current from external to oppose the corrosion current from the infrastructure. Note:» Corrosion is not stopped.» Corrosion is transferred to a less valuable structure (anode).

21 Cathodic Protection Systems Galvanic Anode Impressed Current

22 Galvanic Anode Cathodic Protection Current is generated from a metal at a higher energy level.

23 Types of Galvanic Anodes Magnesium Zinc Aluminum

24 Microscopic View of a Corrosion Cell Cathode Anode Microscopic Corrosion Cell on the Surface of a Pipeline

25 Corrosion of the Metal Will Cease Once the Applied Cathodic Protection Current Equals the Corrosion Current Cathode Anode Metallic Connection Electrolyte Cathodic Protection Current Cathodic Protection Anode

26 AC STEP DOWN TRANSFORMER IMPRESSED CURRENT CATHODIC PROTECTION BRIDGE RECTIFIER PIPELINE A N O D E

27 Electrical Schematic ANODE SHUNT BOX RECTIFIER 120V AC AUTOMATIC + - RE ELECTRODE REFERENCE PIPELINES DEEP WELL ANODES

28 CP SYSTEM Antenna Vent Pipe Deep Anode Column Deep Anode Column

29 System Characteristics Galvanic No external power Fixed driving voltage Limited current Small current requirements Used in lower resistivity environment Usually negligible interference ICCCP External power required Voltage can be varied Current can be varied High current requirements Used in almost any resistivity environment Must consider interference with other structures

30 POTABLE WATER Hetch Hetchy Water Supply and Treatment City Distribution System WASTEWATER

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