HYDROGEN SULFIDE INDUCED CONCRETE CORROSION

Transcription

1 HYDROGEN SULFIDE INDUCED CONCRETE CORROSION Presented by Tim Matheis Monday, October 19, Evoqua Water Technologies LLC

2 Outline Background Objectives Methods Data Results 2014 Evoqua Water Technologies LLC PAGE 2

3 Background Corrosion Impacts Texas 2014 Evoqua Water Technologies LLC PAGE 3

4 Background Corrosion Impacts Kentucky Ohio 2014 Evoqua Water Technologies LLC PAGE 4

5 Background Corrosion Impacts 1991 USEPA report to congress 89 cities participating in the survey $6 billion spent on sewer rehabilitation 32 cities reported sewer collapses 81% were believed to be due to hydrogen sulfide corrosion. 70% of the respondents reported hydrogen sulfide corrosion at the treatment plant Evoqua Water Technologies LLC PAGE 5

6 Background Source of Hydrogen Sulfide 2014 Evoqua Water Technologies LLC PAGE 6

7 Background Mechanism of Concrete Corrosion Step 1 Aerobic bacteria deplete available oxygen Step 2 Anaerobic bacteria convert sulfate to sulfide Step 3 Sulfide combines with wastewater acidity to form hydrogen sulfide Step 4 Insoluble hydrogen sulfide escapes to headspace Step 5 Hydrogen sulfide is biologically oxidized to sulfuric acid Step 6 Sulfuric acid weakens the concrete structure Acid reacts with calcium hydroxide matrix H 2 SO 4 Concrete Pipe H 2 SO 4 H 2 SO 4 SO = H 24 S H + S = O 2 Biologically Active Slime Layer 2014 Evoqua Water Technologies LLC PAGE 7

8 Background Corrosion Impacts 2014 Evoqua Water Technologies LLC PAGE 8

9 Background Source of Sulfuric Acid H 2 S + 2O 2 Sulfur Oxidizing Bacteria H 2 SO 4 Sulfuric Acid (aq) Thiobacillus Intermedius ph ~ 4 Thiobacillus Thiooxidans ph ~2 ` 2014 Evoqua Water Technologies LLC PAGE 9

10 Concrete Corrosion Study - Objectives Deploy samples at two similar locations in the wastewater collection system Allow H2S exposure in one sample Remove H2S in second sample Expose samples in an operating collection system for 2 years Sanitation District 1 located in Northern KY Measure exposure conditions in both samples Long Term Hydrogen Sulfide Monitoring Quantify concrete corrosion loss of mass over time Measure compressibility before and after exposure Quantify effect of atmospheric hydrogen sulfide on a concrete sample 2014 Evoqua Water Technologies LLC PAGE 10

11 Study Area Airport PS Centerplex PS MH Discharge MH Discharge 2014 Evoqua Water Technologies LLC PAGE 11

12 Background Summary of Test Sites Similar Force Mains Same Collections Basin / Water Quality Similar Retention Time Similar Atmospheric Conditions (Rain, Temp, Humidity etc) True Control Not Used (The test would take 4 years to complete) Parameter Airport PS - Untreated Centerplex PS - Treated Average Daily Flow (MGD) Forcemain Length (feet) ,820 4,400 Forcemain Diameter (inches) 6 8 Average Retention Time (hr) Evoqua Water Technologies LLC PAGE 12

13 Background Sulfide Elimination Treated Centerplex Station Treated Hydrogen Sulfide Eliminated with the use of a Nitrate Salt Nitrate Salt is 60% active solution of a combination of calcium nitrate salts Nitrate harmlessly converted to Nitrogen Prevents sulfide formation Used for Odor Control 2014 Evoqua Water Technologies LLC PAGE 13

14 Methodology Sample Concrete Coupons Concrete coupons Fabricated by third party contractor. Fabricated of Type II Portland cement in accordance with specifications outlined in ASTM C150 Testing and curing was performed in accordance with ASTM C192 Concrete Coupons Curing 2014 Evoqua Water Technologies LLC PAGE 14

15 Methodology Concrete Coupons 2014 Evoqua Water Technologies LLC PAGE 15

16 Methodology SulfideTesting Hydrogen Sulfide Vapor Concentration (5 min intervals) Dissolved Sulfide (monthly) 2014 Evoqua Water Technologies LLC PAGE 16

17 Methodology Sample Weighing Prior to each weight measurement: Samples were pressure washed to remove attached growth The scale was calibrated with a 1.000KG standard Sample weighing was performed on samples at 6 month intervals 2014 Evoqua Water Technologies LLC PAGE 17

18 Methodology Compression Testing Compression testing was performed by a certified 3 rd party contractor Compression tests performed as outlined in ASTM C39 Forney FHS Series Premium Compression Tester 2014 Evoqua Water Technologies LLC PAGE 18

19 1/1/2012 2/1/2012 3/1/2012 4/1/2012 5/1/2012 6/1/2012 7/1/2012 8/1/2012 9/1/ /1/ /1/ /1/2012 1/1/2013 2/1/2013 3/1/2013 4/1/2013 5/1/2013 6/1/2013 7/1/2013 8/1/2013 9/1/ /1/ /1/ /1/2013 Atmospheric Hydrogen Sulfide (ppmv) Data Atmospheric Sulfide Airport PS Untreated 68.5 ppmv average H2S ppmv peak Centerplex PS Treated 3.6 ppmv average 32.3 ppmv peak Atmospheric Sulfide Loading at Sites Treated Treated (average) Untreated Untreated (average) 2014 Evoqua Water Technologies LLC PAGE 19

20 1/1/2012 2/1/2012 3/1/2012 4/1/2012 5/1/2012 6/1/2012 7/1/2012 8/1/2012 9/1/ /1/ /1/ /1/2012 1/1/2013 2/1/2013 3/1/2013 4/1/2013 5/1/2013 6/1/2013 7/1/2013 8/1/2013 9/1/ /1/ /1/ /1/2013 Atmospheric Hydrogen Sulfide (ppmv) Data Dissolved Sulfide Airport PS - Untreated 7.2 mg/l average dissolved sulfide 8.9 mg/l peak dissolved sulfide Centerplex PS Treated 0.08 mg/l average dissolved sulfide mg/l peak dissolved 4.0 sulfide with reduced dose 2.0 rate in Spring Dissolved Sulfide Loading at Sites Treated Treated (average) Untreatedl Untreated (average) 2014 Evoqua Water Technologies LLC PAGE 20

21 Data Calcium Nitrate Dosing Calcium nitrate was dosed to obtain a slight residual at the control point Cost cutting in the spring of 2013 cut dose rates in half in April and May Feed Rate (GPD) Nitrate Residual (mg/l) January February March April * 4 0 May * 3 June July August September October November December AVERAGE Evoqua Water Technologies LLC PAGE 21

22 Coupon Mass (lbs) Data Concrete Coupon Mass Summary Airport PS - Untreated Average weight reduced from 29.1lbs to 27.5lbs 5.4% loss of mass Centerplex PS - Treated Average weight reduced from 29.0lbs to 28.9lbs 0.2% loss of mass Concrete Coupon Mass months 6 months 12 months 18 months 24 months Untreated Treated 2014 Evoqua Water Technologies LLC PAGE 22

23 Breaking Compression (lbs) Data Concrete Coupon Strength Summary Initial breaks on samples 4,667PSI Continued hydration accounts for increase in compressive strength Strengthening peaked at 6 months for test coupons. Strengthening peaked at 12 months for control coupons Test Samples Compressive strength reduced 13% Control Samples Compressive strength 9% higher than initial breaks Concrete Coupon Compressibility 7,000 6,000 5,000 4,000 3,000 2,000 1,000-0 months 6 months 12 months 18 months 24 months Untreated Treated 2014 Evoqua Water Technologies LLC PAGE 23

24 Results of Samples Treated to Prevent H 2 S Exposure to an average of 3.5 ppmv over a two year period resulted in: No loss in compressive strength 0.2% reduction in weight of samples 2014 Evoqua Water Technologies LLC PAGE 24

25 Results of Untreated Samples Exposure to an average of 68.5ppmv over a two year period resulted in: 13% reduced compressive strength of samples 5.4% reduction in weight of samples 2014 Evoqua Water Technologies LLC PAGE 25

26 Conclusions 1. Presence of > 60 ppmv H2S impacted coupons 2. Presence of H2S resulted in mass loss of concrete (5% Less) 3. Presence of H2S resulted in loss of compressive strength (>10% lost in 24 months) 4. Treatment to eliminate H2S < 5 ppmv resulted in better concrete condition 2014 Evoqua Water Technologies LLC PAGE 26

27 THANK YOU FOR YOUR ATTENTION 2014 Evoqua Water Technologies LLC