ELEMENTS OF A EFFECTIVE

CATHODIC PROTECTION

PROGRAM

Diego Politano

Con Edison

Agenda

• Design

• Coatings

• Coating Resistance

• Cathodic Protection

• Test Stations

• Isolation

• Existing Transmission Mains

Design

• Try to keep it consistent

– Contractors/employees are familiar with materials

– Installation practices are similar

– Coatings

• Mill

– Extruded Polyethylene

• Field

– Cold applied tape

– Coal tar

– Epoxy

Design (continued)

• Boiler plated approach on

– Short segments of distribution mains

– Services

• Transmission and Distribution installation of long segments of pipe

– Review of layouts

– Technicians are present on site when requested by company inspector

– Technicians log daily activity

• Work done – one line sketch

• Resistance of coating to ground4

Coatings

• Mill Coating - Extruded polyethylene

– Predominately used on our system

– Durable coating

– 40-60 mils thick

– Holiday Detector set at 12kV to 15kV

• Pipe type feeders 18 kV to 20 kV

– Repairs are minimal

Coatings (continued)

• Welded joints– Pipe preparation is key for any coating

– Clean surface

– Cold applied tapes• “X” test QA - technicians

– Two part epoxy - Cost

• Welded offsets– Clean surface

– Coal tar – still effective• Visual and Holiday Detected

– Cold applied tape • with primer if needed

– Two part epoxy

Coatings (continued)

• Be present at the site when requested

• Monitoring coating operation

– Cleaning

– Application

– If coal tar – kettle temperature

– Two – part epoxies – ensure that the thickness readings are taken

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Coating Resistance

• Gas mains

– 1,000,000 ohms per square foot – Transmission

– 500,000 ohms per square foot – DistributionExample:

2πr = πd x L (Backfilled Surface Area)

ΩSq.ft.₌ required measured Ω

Sq.ft (backfilled)

Coating Resistance (continued)

• The more resistant/the less current needed to protect (polarize) the pipe

• Any coating faults are minimal in size

• Faults can be located

– Over-ground survey

– ACCA – A-Frame

• Technicians present

– Witness the holiday detection

– Inspect conditions

– Monitor backfill operation

Cathodic Protection

• Pipe has a highly resistant to ground

• Galvanic anodes

– At the test stations

– Pipe and anodes leads in test station

– Individual anode current measured

• Current in the negative direction

– Anode current effect can be recorded at other stations

Test Stations

• Spaced according to lengths of pipe installed

– Isolating Joint test stations ( approx. 1,000’- 2,500’)

• Color coded test leads

– Magnesium Anode test stations typically placed 500’ apart.

• Detailed drawings

– Locations

– Landmarks

– Other details

Test Stations Continued

• Pipe test leads

• Anode leads

• Test stations are positioned next to pipe and for access near the

surface of the pipe

• 4-32 lbs. anodes at each IJ station

• 2-32 lbs. anodes at test station

• WHY?

– It costs less than opening the street again 12

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Isolation

• Gas Transmission

– 2,500 feet

• Sometimes closer

– Any regulator inlet line

– Isolation between two different vintages

– Regulator vaults

• Distribution

– Isolation joints are installed at:

• Service tee

• Separate different vintages

• Above ground piping14

Existing Transmission Mains

• Transmission system

– Early as1948 coal tar coated pipe

– 97% protected by impressed current

– All test points tested annually (300’ - 500’ apart)

• From original mag-anode system

– Inspected whenever exposed (Inspection Form)

• Third party excavations

• Exposed by company forces

• Condition of coating is documented

• Pipe to soils recorded

• Soil resistivity and pH tested15

Existing Transmission mains (continued)

• Transmission (cont.)

– More information taken the better

– Ensure CP is at or above criteria

• At pipe level

• Four readings taken at each wall

– Coating is intact – no anomalies

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Existing Transmission mains (continued)

• ECDA

– Yields good information

• Get hands on the pipe at excavations

• Thorough inspection

– Investigate areas of pipe to soil readings below criteria taken during ECDA surveys

• Only the close interval survey

– Resurvey

• install more protection

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Technicians

• Eyes and ears in the field

• Training

• Share their experiences with group

– Investigations

– Observations

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Thank you

2007 tape coat

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