the challenges of wastewater structural degradation and mitigation strategies
TRANSCRIPT
Addressing Infrastructure Corrosion in the Water and Wastewater Market
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Paul Keough is Chesterton’s Marketing Development Manager for the Water and Wastewater Industry. He has been with the company for 17 years and has been in the fluid sealing industry for 37 years. Prior to his current position, Paul was the Business Development Manager for Chesterton, responsible for North American engineering firms in the Mining and Wastewater Industries. He has done sealing presentations to firms such as Fluor, AMEC, Tetra Tech, CDM Smith, Arcadis, AECOM to name a few.
Steve Bowditch is the Global Market Development Manager for ARC Efficiency and Protective Coatings. He has been with the company for 27 years and is a NACE Level III CIP Inspector and SSPC Corrosion Specialist with over 35 years’ experience in the areas of protective coatings development and applications. He is an active contributing member of numerous NACE Technical Committees associated with corrosion prevention and protection and has presented papers on corrosion and associated control technologies.
Host
Presenter
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What will we cover
What is corrosion’s impact to water and wastewater infrastructure
What mechanisms are responsible What are available options to address How protective coatings can protect infrastructure What coatings technologies are available Pro’s and con’s
How to implement a sound coatings program Performance based versus product based specifications Manufacturer’s qualified applicators Installation QA/QC Testing
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Infrastructure at risk
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Annual Cost of Corrosion in Water and Wastewater
$27$28$29$30$31$32$33$34$35$36$37
AWWA FHWA EPA
Billion
• Blocked or broken pipes release as much as 10 billion gallons of raw sewage every year. • US EPA estimates that over $330B needs to be spent over the next 20 years to upgrade existing water/wastewater infrastructures
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Life Expectancy of Buried Cast Iron Pipe
12 22 32 42 52 62 72 82 92 102% Life Remaining 100% 96% 90% 85% 75% 63% 51% 40% 22% 12%
0%
20%
40%
60%
80%
100%
% Life Remaining vs Years in Service
“More than a million miles of pipes are nearing the end of its useful life and approaching the age at which it needs to be replaced.”
(AWWA 2012)
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Increased US Population Shift to Urban Locales
0%10%20%30%40%50%60%70%80%90%
100%
1900 1925 1950 1975 2000 2025
Rural Population Urban Population“Over 75 percent of the nation’s population is served by centralized wastewater collection and treatment systems. “
EPA 2004
Common Mechanism’s of Attack
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Mechanisms Biogenic corrosion: SRB, SOB, H2SO4 (vapor phase) Acidic attack – manufactured acids (liquid phase) Sulfate attack (vapor phase) Carbonation in water (liquid phase) Abrasive erosion / cavitation (liquid phase) Chloride induced corrosion (vapor phase)
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Changing Environment is More Corrosive
Corrosivity of wastewater in USA has changed dramatically in past 35 years
1980 1985 1990 19950
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10
15
DI
SSO
LVED
SUL
FIDE
CO
NCEN
TRAT
ION
(mg/
l)
Corrosion Threshold
Sulfides
1980 1990 2000 2010 2020
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Relationship between pH and Corrosivity to Concrete
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Mechanism of Attack – Biogenic Corrosion
Partial Listing of micro-organisms
known to be present in and deleterious to
concrete water and waste
water systems
Secrete 40% H2SO4
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Mechanism of Attack - Biogenic Corrosion
Other bacteria present in the water convert sulfates to sulfides. This causes the rotten egg smell, hydrogen sulfide gas (H2S).
When the dissolved oxygen concentration falls below 0.1 mg/l, the environment becomes anaerobic becomes septic.
H2S Gas H2S Gas H2S Gas H2S Gas
pH ~ 7 D.O.<0.1 mg/l
Bacteria in the wastewater consume oxygen.
O2 O2 O2
Sewer
Wastewater
Bacteria
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Conditions Favorable for Producing Sulfides
Low dissolved oxygen content High-strength wastewater (in terms of biological oxygen
demand) Low flow velocity and long detention times Turbulence/extensive pumping Elevated wastewater temperatures.
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Mechanism of Attack - Biogenic Corrosion
SO42- HS- H2S
H2S Gas H2S Gas
H2S Gas
H2S H2S H2S
In water at pH 7, about 50% of the dissolved sulfide converts to H2S gas.
0.00
1.00
2.00
3.00
4.00
5.00
6.00
0
200
400
600
800
1000
1200
3 4 5 6 7 8 9 10
H2S
(aq)
and
HS-
in s
olut
ion
(mg/
L)
H2 S
(g) in air (ppm)
pH
H2S(g)
H2S(aq)
HS-
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Mechanism of Attack - Biogenic Corrosion
On the surfaces above the water, H2S gas is converted to strong sulfuric acid by Thiobacillus bacteria.
This acid corrosion, not “aging”, then dissolves the infrastructure. SO4
2- HS- H2S
H2S
Thiobacillus
+ O2 = H2SO4
Acid Attacks Concrete
And virtually nothing is being done to stop it from happening.
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Mechanism of Attack - Biogenic Corrosion
Where to look Influent pump stations Manways Head works Bar screen chambers Primary clarifiers Grit chambers
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Mechanisms of Attack - Manufactured Acids
Primarily seen in industrial wastewater systems Attack can occur in liquid & vapor phase Rate of attack dependent on concentration, solubility & flow
pH below 12.5 – potassium and sodium depletion pH below 10.0 – calcium hydroxide depletion pH below 8.0 – calcium-silicate-hydroxide gel depletion
Acid – Base reaction Caused by the reaction of an acid and the calcium hydroxide portion of
the cement paste Soluble calcium salt which produces a highly soluble calcium salt
Ca(SO)4 by product. These soluble salts are easily removed from the cement paste
weakening the paste’s structure as a whole.
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Manufactured Acids - pH Effect on Concrete
Source L.A.County San District
0.001 0.01 0.1 1.0 Corrosion Rate (in./year)
7
6
5
1
0
pH
Cor
rosi
on
Ran
ge
4
3
2
0.25
200 yr
100 yr
50 yr 20 yr
8 yr
The life cycle of concrete with a pH of 2 compared to a pH of 4 is 85% shorter
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Mechanisms of Attack – Sulfate Attack SO4 ions react with Ca(OH)2
Na2SO4 + Ca(OH)2 => CaSO4 CaSO4 + C3A => CaO-Al2O3-31H2O
Gypsum(CaSO4) & Tri-calcium sulfoaluminate (CaO-Al2O3-31H2O) are much larger compounds.
Resulting expansive forces cause micro-cracking, exposure of structural steel & disintegration
Where to look • Splash zones (wet/dry) • Wherever H2SO4 attack occurs
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Mechanisms of Attack – Carbonation
Ca(OH2) + CO2 Ca(CO3) + H2O
Forms carbonic acid which causes slow acidic attack of cement paste due to lowered pH
Pore blocking characteristics
Where to look • Secondary clarifiers • Aeration basins – O2 reactors • Chlorine contact basins • Outfalls
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Mechanisms of Attack – Abrasive Attack
Suspended solids in flowing wastewater
Wears cement paste – then aggregate can be dislodged
Influenced by size, quantity of suspended solids plus velocity
Prevalent in collection systems or plant inlet structures
Where to look • Collection systems • Plant inlet
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Mechanisms of Attack – Chloride Intrusion
Chloride ions (Cl-) are found in coastal regions and industrial flows.
Soluble Cl- are transmitted into concrete structure by capillary transport.
Cl- disturb passive oxide film on rebar initiating active corrosion cells.
Rate of reinforcement corrosion increases by over 1000%
Where to look • Coastal Regions • Pipes • Manholes • Chambers • Treatment plant
What Technologies are Available
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Methods to Address
Protective linings material selection Design and fabrication details Evaluation programs Periodic inspections Process changes (wherever possible) Reduce slime layers by removing debris (grit and sand) Control dissolved sulfide through chemical addition Reduce H2S gas release by reducing turbulent flow Protect sensitive surfaces from the effect of acid generation
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Vinyl sheet liners Polyurethane/Polyurea Bag systems Cementitious
Calcium aluminate
Concrete additives Epoxies
Solvent cut/coal tar 100% solids reinforced
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What Coatings Technologies Are Available?
Anchored or adhered thermoplastic (vinyls) Spray applied elastomeric polyurethanes
Polyureas
Mat reinforced linings Polyester/Vinylester
Trowel applied aggregate filled lining Calcium aluminates Epoxies
Spray applied high solids -amine cured epoxies
Bottom Line They ALL can fail and they ALL have limitations
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Vinyl Liners
In use for >40 years 60-180 mil thick vinyl sheet Adherent surface must be
flush and flat Adhesive mounted and hot
gas sealed joints More difficult to use in rehab Primary mode of failure is
joint failure, leakage, blistering and delamination
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Spray Applied Polyureas/Polyurethanes
Elastomeric urethane technology Aliphatic or aromatic based Typically 100% solids Good elastic modulus for flexing
applications Good chemical resistance. Rapid cure provides shorter
return to service times Isocyanates create hazardous
exposures Prone to sheet delamination due
to low wet out properties during application
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Mat reinforced linings
Fiberglass saturated sock, mat or chopped strand reinforced.
Typically used with polyester or vinyl ester resins
Excellent chemical resistance Good chemical resistance
Poor elastic modulus for flexing applications
Creates explosive/flammable environment during application
Moisture sensitive Prone to sheet delamination due
to wicking along glass strand
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Trowel applied aggregate reinforced epoxies
Silica/quartz reinforced, typically used with BisA/F or epoxies
Excellent chemical resistance Low permeability High wet adhesion High tensile strength High abrasion resistance High wet adhesion High elastic modulus for flexing
applications
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Spray applied reinforced epoxies
Silicate reinforced, typically used with BisA/F or epoxies
Excellent chemical resistance Low permeability High wet adhesion High tensile strength High flexural strength Moderate abrasion resistance Low elastic modulus for flexing
applications Corrosive hazards
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Critical Properties to Consider
Thickness Smooth concrete (<36 grit finish appearance) allows for 30-60 mil dry film
thicknesses If concrete roughness is> than a 36 grit finish sandpaper increase to 60-120
mil dry film thickness
Flexural strength Necessary for flexing and vertical misalignment which can commonly occur
buried wastewater treatment and collection systems. Values of 4,000 psi or greater for flexural strength and 5 x 106 psi or less for
flexural modulus are good.
Tensile strength Necessary to calculate overburden-bearing capacity and is of paramount
importance to resistance to ground water infiltration. Tensile strengths of 1,800 psi are considered excellent
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Critical Properties to Consider
Bond Strength The bond of the coating to the substrate is perhaps the key element to
achieving a long service life. Bond strength to wet concrete should exceed the cohesive strength of the
concrete, usually above 400 psi.
Permeability Permeability is the property that controls passage of corrodents through the
coating to the substrate. If all other properties and chemistry are equivalent, the coating exhibiting
the highest permeability will typically fail first. A permeability of 10-6 perm inches is typically acceptable.
Chemical resistance Resistant to acidic immersion Resistant to bacterial organisms
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Qualified Applicators
Utilize applicators experienced with specified manufacturers products
Request 3+ years of experience with 5 or more projects completed
Other endorsements such as SSPC QP or ICATS, NACE pre-qualify experience and knowledge but not necessarily with your specified products
Should have a staff person certified to a coatings inspection program such as NACE CIP, SSPC MCI, FROSIO, ICORR.
Certified for confined space, handling hazardous chemicals, PPE, low OSHA EMR
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QA/QC Inspection
Shift from product based to performance based specifications “What you want it to accomplish not how you want it built”
All specifications need standardized tests to describe how a product may be qualified to a approved material ASTM, NACE, ICRI, ACI etc.
QA/QC logs and inspection hold points
Sole source “turnkey supply/apply” Regular inspections
Surface decontamination Surface cleanliness Ambient environmentals
Surface profile/roughness Material log Wet film thickness
Dry film thickness Holiday Test
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? QUESTIONS ?