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ODOR AND CORROSION CONTROL: Winning the Battle on Both Fronts
WEBINAR TALK 3: Sulfide and Ammonia Corrosion Chemistry: Problems and Solutions in your WWTP
Odor and Air Quality Committee
Brien Clark, NACE CP4, PE MAY 2015
SULFIDE AND CORROSION
Internal Corrosion of Wastewater Systems
H2S+2O 2 H2SO4
SO42-+organic matter
S2-+2H+ H2S
AnaerobicBacteria S2-+H2O+CO 2
Sludge and silt
H2S
H2S
H2S
H2S
Sulfur Reducing Bacteria
Sulfur oxidizing bacteriaH2S+2O 2 H2SO4
SO42-+organic matter
S2-+2H+ H2S
AnaerobicBacteria S2-+H2O+CO 2
Sludge and silt
H2S
H2S
H2S
H2S
Sulfur Reducing Bacteria
Sulfur oxidizing bacteria
• Dominated by Formation of Sulfuric Acid
Free Sulfide Species
Sulfide Corrosivity Summary
TEMP Steel C.I. 304 SS 316 SS Cu Brass Nickel AluminumHydrogen Sulfide (H2S) low ( <100° F) Hydrogen Sulfide (H2S) high( =>100° F) Bisulfide (HS1-‐) low ( <100° F) Bisulfide (HS1-‐) high( =>100° F) Sulfide (S2-‐) low ( <100° F) Sulfide (S2-‐) high( =>100° F) Sulfuric Acid (H2SO4) low ( <100° F) Sulfuric Acid (H2SO4) high( =>100° F) Warning! General indication of corrosivity, not all factors accounted! Do not use for design!
LEGEND > 50 mpy 2-‐50 mpy < 2 mpy
Primary parameters that influence the production of sulfides n Temperature of the wastewater: As the
temperature increases, the rate of biological reactions increases and the concentration of sulfides will also increase.
n Dissolved oxygen concentration: As the concentration of DO increases in the wastewater, the concentration of sulfides will be reduced.
Primary parameters that influence the production of sulfides n Wetted surface area: As the depth of
wastewater flow increases, the wetted surface area of the pipe increases. As the wetted surface area increases, so does the number of microorganisms within the pipe.
n Headspace: As the allowable enclosed
headspace increases, the amount of surface area available for sulfur-oxidizing bacteria increases.
Primary parameters that influence the production of sulfides n Geometry: A flat sloped pipeline will reduce
the flow velocity which increases sedimentation, diminishes the rate at which oxygen becomes dissolved in the wastewater.
n Turbulence: Hydraulic conditions that cause splashing or hydraulic jumps promote the release of hydrogen sulfide.
Corrosion Control Involves
n Material Selection n Design (Proper Design Flows) n Linings
n PVC Sheeting (T-lock) n Spray-applied (Polyurethane / Epoxy)
n Control of Hydrogen Sulfide Evolution n Inhibitors n Turbulence
n Cathodic protection (metals)
Material Selection is Key for Metals n Headspace corrosion is difficult to combat
Coatings and Linings are Important
n Concrete in headspace should be coated
Reasons for Potential Problems & Failures of Coating Projects n Specifications are not clear and confusing
(outdated) n Specified products not designed for their
intended use n Under-manned job site n Applicator experience (Keeping it cheap) n Applicator (Blaster / Sprayer) not familiar
with material “Read and understand TDS” n Surface preparation n Contamination between coats
Proper Application and Inspection of Linings is Extremely Important
Coating Inspection Requirements
n Ambient Conditions for Prep & Application n Compressed Air Cleanliness n Abrasive Cleanliness n Pre-Cleaning Requirements n Surface Prep Cleanliness n Surface Prep Roughness n Generic Coating Selection n Coating Storage Requirements n Coating Mixing Requirements n Coating Thinning Requirements
Control by Coatings
n Advantages n Provides first line of defense against corrosion n Provide a barrier to the electrolyte and protect
the metal Usually dielectric material that prevents electron and ionic current flow.
n Maintenance can be performed by in-house maintenance personnel
n Material readily available
Control by Coatings
n Disadvantages n Specific conditions need to be present n Coatings need to be properly inspected n Coatings need to be maintained n Premature failures, If not properly applied n Flammable n VOC Constraints
Control by Sheet Goods n Advantages
n No special application equipment required n Provide a barrier to the electrolyte and protect
the metal Usually dielectric material that prevents electron and ionic current flow.
n No Ambient Condition Restrictions
Control by Sheet Goods n Disadvantages
n Requires certified installers initial installation and maintenance
n Need to be properly inspected n Premature Failures, If not properly installed n Expensive
Concrete Condition Inspections
Carbonated Cleaned Cleaned
So how far do you go to remove damaged concrete? n YOU-GO-All-THE-WAY!
How do I get a good coating?
n Consistent up-to-date specifications based on experience, availability and applicability.
n Contractor pre-qualification or minimum qualifications (SSPC QP-1/QP-2/QP-3)
n Applicator experience (resumes) n Applicator attitude (why am I painting this)
Observation of workmanship and of applicators
n Inspection and documentation of the job site conditions.
Cathodic Protection is Useful
AMMONIA AND CORROSION
Common Sources of Ammonia
Agricultural: Fertilizers and animal feedlots. Fertilizers may contain high content of ammonia in form of ammonium nitrate and phosphate. Human excrement: Organic nitrogen in urea
Ammonia/Ammonium Exposure NH3, (NH4)+
Ammonium Corrosivity Summary
LEGEND > 50 mpy 2-‐50 mpy < 2 mpy
TEMP Steel C.I. 304 SS 316 SS Cu Brass Nickel AluminumAmmonium Hydroxide low ( <100° F) Ammonium Hydroxide high( =>100° F) Warning! General indication of corrosivity, not all factors accounted! Do not use for design!
Corrosion Mitigation
n Material selection – Avoid copper-based metals n Stainless steel alloys have good resistance to
ammonia. n If copper unavoidable, use appropriate
protective coating
