Identification & Mitigation of System Corrosion

Identification & Mitigation of System Corrosion

Nate Ver Heul

MWEA Lagoon Seminar

February 21, 2013

Definition

cor·ro·sion [kuh-roh-zhuh n] noun

The deterioration of a material or its properties because of a reaction with its environment.

• Bacterial

• Electrochemical

Corrosion in Wastewater Systems

Bacterial (H2S) Corrosion

Understanding…H2S Corrosion

• Colorless, poisonous, flammable, explosive gas

• Smells like rotten eggs

• Desensitizer

H2S >10 ppm = concern for system integrity


Health and Safety Impact of H2S

H2S Level (ppm) Health Effects

0.0005 Noticeable smell

0-10 Irritation of eyes, nose and throat

10 Exposure limit

10-50 Headache, dizziness, nausea, difficulty breathing

50-200 Severe respiratory irritation, convulsions, coma and possibly death


• Sulfate is reduced to sulfide

• Anaerobic digestion

• Sulfide combines with Hydrogen to form H2S gas

• H2S oxidates to Sulfuric Acid in presence of moisture

Facultative Lagoon


• How do sulfates get into collection systems?

• Sulfur cycle

• Corrosion on the rise

• Less heavy metals

• Less inflow and infiltration

Identifying…H2S Corrosion

• What it looks like/Potential signs

• Blackened wastewater or sludge

• Concrete

• Cement is attacked – soft, easily crumbles

• Reinforcing steel – rust bleeding

• Ferrous Piping, internal and external

• Pitting, discoloration

Identifying...H2S Corrosion

• Where to look

• Headworks

• Transfer Structures

• Force Mains

• Low velocities

• Long detention times

• Sections not flowing full

• Air release manholes

• Discharge manholes

Look out for high points in force mains


585

590

595

600

605

610

615

620

625

630

0 1000 2000 3000 4000 5000 6000 7000 8000

Ele

vati

on

(ft

)

Distance from Lift Station (ft)

Pipe Inv. El. vs. HGL

(1,000 gpm in force main)

Pipe Inv El

HGL El

Look out for high points in force mains


585

590

595

600

605

610

615

620

625

630

0 1000 2000 3000 4000 5000 6000 7000 8000

Ele

vati

on

(ft

)

Distance from Lift Station (ft)

Pipe Inv. El. vs. HGL

(820 gpm in force main)

Pipe Inv El

HGL El


• Where to look

• Underdeveloped/Oversized Lift station wet wells

• Sewers

• Lines with minimal flow

• Long, flat sewers

• Turbulence

• Transition and drop manholes

• Pipe slope changes

• Downstream of Industries

Identifying...H2S Corrosion

• How to measure

• Televising, Air Monitoring

Panoramo MH Viewer


Red Arrow Odalogger

OdaLog Results


Red Arrow Odalogger

OdaLog Results


Coating/Lining

Mitigating…H2S Corrosion

Polymer Concrete Manholes


Cured in place pipe


Chemical addition


Biofilters


Aeration


Electrical Sealoffs


Electrochemical Corrosion

Understanding…Electrochemical Corrosion

• Return of Metals to their Ores

• Dissipation of energy consumed by mining, refining and manufacturing


• Electrical potential

• Anode

• Cathode

• Electrolyte

• Solution of acids,

bases or salts

Galvanic Series

(Atlas Steel Technical Note No. 7 "Galvanic Corrosion“)


Iron Corrosion Schematic (chem1.com)


Identifying…Electrochemical Corrosion

• What it looks like

Identifying…Electrochemical Corrosion

• Where to look

• Ferrous piping or tanks in aggressive soils

• Pumping chambers

• Above grade piping

Cathodic protection

- galvanic/ sacrificial anodes

Mitigating…Electrochemical Corrosion

Cathodic protection

- Impressed current


Anodizing

Galvanizing


Isolation of dissimilar metals


Polyethylene encasement


Recommendations

• Know your system

• Corrosion Detection and Monitoring Strategy

• Maintain records

• GIS

• Maintenance procedures

• Monitor potential problem areas regularly

• Proper system design

Thank You

Identification & Mitigation of System Corrosion

Documents

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