Corrosion Testing D Rossi Cathodic
Corrosion Testing D Rossi Cathodic
Corrosion Testing D Rossi Cathodic
SYSTEM DESIGN
Presented By
DENIS L ROSSI P.E.
CORROSION ENGINEER
New England C P Inc.
Corrosion Fundamentals
What is corrosion?
Steel Mill
Bridge
Rust
Iron Ore
Iron
Oxide
Refining
Pipe
Underground Pipeline
Cathode
Little or no corrosion occurs at the cathode
Electrolyte
Ionized solution capable of conducting electricity
Corrosion of Metals
Current Flow
Anode
Cathode
Current Flow
Electrolyte
CARBON ROD
(CATHODE)
+0.30mV
ZINC CASE
(ANODE)
-1.10mV
MOIST PASTE
(ELECTROLYTE)
WIRE
(CONDUCTOR)
i
i
Soil
(Electrolyte)
Appliance(External
Connection)
i
i
CI Water Main
(Cathode)
insulator
Steel Gas Service
CI Water Main
Potential*
Pure Magnesium
-1.75
Magnesium Alloy
-1.60
Zinc
-1.10
Aluminum Alloy
-1.00
Cadmium
-0.80
-0.70
-0.50
Cast Iron
-0.50
Stainless Steel
-0.50 to + 0.10
-0.20
Titanium
-0.20
Gold
+0.20
+0.30
Dissimilar Soils
Varying oxygen content
Varying resistivities
Mechanical Stresses
Bending and Gouges
Cutting of threads
Stray Currents
Iron Pipe
(Anode)
- 500mV
Iron Pipe
(Anode)
- 500mV
Brass Valve
(Cathode)
- 300mV
Corrosion
Cathodic Area
(protection)
Copper
Anodic Area
(corrosion)
Steel
Earth (Electrolyte)
Corrosion Current
Corroding Area
Protected Area
Return Path
Anodic Area
Cathodic Area
Oxygen Concentration
Corrosion Cell
Backfill
More Oxygen - Cathodic - Protected
Pipe
Corrosion Currents
Oxygen Concentration
Corrosion Cell
Rock
Anodic Area
Cathodic Areas
Pipe
Corrosion Currents
Anodic Area
Wood Bed Block
Scarred/Damaged Surface
Corrosion
Threads, scratches and dents are anodic
to undisturbed surfaces along the pipe.
Dissimilar Soils
Corrosion
Anodic Area
Cathodic Area
Gas Pipeline
(-)
Cathodic Protection
Rectifier
(+)
Anode Groundbed
Current Discharge
(Corrosion)
Current Discharge
(Corrosion)
Water Pipeline
Stray Current
Summary
Corrosion Cell
*Anode
*Cathode
*Electrolyte
*Metallic Connection
Protective
Coating
Applied on a properly applied surface
Have sufficient adhesion to the pipe
Sufficient strength to resist cracking
Have sufficient strength to resist damage due
handling and soil stress.
Compatible with cathodic protection currents
Coatings must also be:
Inspected for damage prior to lowering in the ditch
Must be protected from damage from adverse ditch
conditions.
Precautions must be taken to protect coated pipe that is to
be installed by boring.
Cathodic Protection
Provide a level of cathodic protection for
the entire length of the underground
structure.
Cathodic protection levels must be
controlled so as not to damage coatings.
Electrical Isolation
Insulating devices must be installed on the
steel pipe so as to facilitate electrical
isolation.
Mains @ Tie-ins and crossings with other
utilities
Services - @ the main and the service riser
Casings insulated from the carrier unless both
carrier and casing are cathodically protected as
a single unit.
Atmospheric Corrosion
Pipelines that are exposed to the atmosphere
must be cleaned and either coated or
jacketed with a material suitable for the
prevention of atmospheric corrosion.
Steel service risers and meter installations
must be coated to the outlet side of the
meter bar.
Other
Exposed Pipe Inspection
Further Investigation if additional corrosion is
evident.
Inspect coatings for damage
Inspect bare pipe for pitting and uniform wall loss.
Cathodic Protection
Elements of a Corrosion
Control System
Break electrical path
to whats not
being protected
Connect to more
negative metal
Coating
Limit Area in Contact with Electrolyte
Anode
Pipe Coating
Pipe
Current through Soil
t
Magnesium Anode
Sealing
Compound
Black Wire
Lead Seal
Cloth
Sack
Steel Core
Magnesium
Bar
Gypsum Powder
Note: Anodes should be installed 18 below and 18 to the side of the pipe.
The anode should be also be soaked with water before backfilling.
Do not carry by the wire.
Rectifier Groundbed
IJ
IJ
Rectifier
Anode Groundbed
Typical Arrangement of
Cathodic Protection For Tanks
Rectifier
Tank
Tank
Anodes
Structure Section
MHW
Steel Pile
MLW
Galvanic or Impressed
Current Anodes
Corrosion Testing
Pipe
-0.85
Test Box
Pipe Lead
Corrosion Monitoring
Mains - Once a Year
Ensure Test Box Availabilty
Corrosion
Wood
Anode
Cathodic Protection Current
Current
Pipe
Sheeting
Backfill
Coating
Protected
Pipe Wall
Mastic Application
MASTIC
Other
Test Wires not connected to anode.
No dielectric union on service entrance or
service regulator vent.
Underground electrical contact with other
metallic structure.
Isolator installed incorrectly or not at all.
Isolator installed and not indicated.
Test boxes paved over.
Telemetry not isolated.
Summary
Corrosion Cell
Anode
Cathode
Electrolyte
Metallic Connection