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116 Summary of Durability Evaluation Methods 1.0 Introduction This appendix summarizes the most commonly accepted independent (i.e., not published by a pipe trade organization) quantitative service life calculation methods for concrete and metal pipes. No known methods are in use to calculate the estimated material service life (EMSL) of thermoplastic pipes. The EMSL of thermoplastic pipes is based on the material performance specifications and details of the resins used in the pipe manufacturing process. The materials are thus generally assigned a fixed EMSL regardless of the environ- mental parameters at the site. Thermoplastic culvert pipes for highway drainage applications are usually assigned EMSL values between 50 and 100 years. 2.0 Reinforced Concrete Pipe Methods Concrete culverts are constructed in a large variety of round, elliptical, arch, and rectangular box sizes and have the ability to withstand a wide range of loading and environmental con- ditions. There are no definitive design methods for estimating concrete culvert service life. As a result, the designer is required to make judgments about the severity of the environmental conditions and the offsetting nature of a variety of design accommodations. One method of accommodating a harsh environment is the addition of extra sacrificial concrete cover over the reinforcing steel. Typically, where severe abrasion is anticipated, at least 2 in. of additional concrete cover is recommended. Sulfate- resisting concrete or high density concrete should be used where acids, chlorides, or sulfate concentrations in the surrounding soil or water are detrimental. Generally, if soil and/or water have a pH of 5.5 or less, concrete pipe should be required to have extra cover over the reinforcing steel or a protective coating. Table 1 lists methods that can be used to determine EMSL values for reinforced concrete pipes. The EMSL values obtained using these different methods can vary widely so the RP selects the lowest EMSL value from the methods used. The limitations and range of parameters for which each method is applicable are described in detail for each method below. 2.1 Hurd Model The Hurd model was developed for use at sites with pH values of 7 or lower, and is given by the following equation: 123.5 15.55 0.42 1.94 2.64 EMSL pH Slope Rise Sediment Rise( )= ÃÃï£«ï£ï£¬ ï£¶ï£¸ï£· â â where: EMSL = estimated material service life (years) pH = pH of the water Slope = pipe invert slope (%) Sediment = sediment depth in pipe invert (inches) Rise = vertical pipe diameter (inches) The Hurd model was developed for conditions where the pH is less than 7.0. For conditions where the pH is greater than 7.0, the primary degradation mechanism that forms the basis of the Hurd model was assumed not to occur. As such, for pH values greater than 7.0, the EMSL is reported to be con- servatively estimated as a value less than the EMSL with a pH value of 7.0 (Potter 1988). 2.2 Hadipriono Model The Hadipriono model is applicable to sites with pH values between 2.5 and 9, and is given by the following equation: 33.23 160.92 log 4.16 0.28 0.5EMSL pH Slope Rise = â + Ã â Ã â Ã A P P E N D I X C
117 where: EMSL = estimated material service life (years) pH = pH of the water Slope = pipe invert slope (%) Rise = vertical pipe diameter (inches) 2.3 Ohio DOT (ODOT) Model The ODOT model comprises two separate equations, depend- ing on the pH level. For pH values between 2.5 and 7: 0.349 11.204 7.758 0.834 5.912 EMSL pH Slope Sediment Rise( )[ ]= Ãï£«ï£ï£¬ ï£¶ï£¸ï£· â â For pH values greater than or equal to 7: 3.5 5.9 0.52 0.31 EMSL K Flow Slope( )= ï£«ï£ï£¬ ï£¶ï£¸ï£· where: EMSL = estimated material service life (years) pH = pH of the water Slope = pipe invert slope (%) Sediment = sediment depth in pipe invert (inches) Rise = vertical pipe diameter (inches) Flow = velocity rating number (1ârapid, 2âmoderate, 3âslow, 4ânegligible, 5ânone) K = abrasive constant (0.9âwithout abrasive flow, 1.19âwith abrasive flow) 2.4 Florida DOT (FDOT) Model The FDOT model includes a number of parameters such as the concrete cover depth and specifications of the concrete mix design. The equation is given as follows: 1000 1.107 4.22 10 2.94 10 4.41 0.717 1.22 0.37 0.631 10 14.1 3 EMSL C D K W pH S C ( ) ( ) ( ) = â Ã â Ã + â â â â where: EMSL = estimated material service life (years) C = Sacks of cement per cubic yard D = Depth of concrete cover over reinforcing steel (inches) K = Chloride concentration (ppm) W = Total water percentage in the concrete mix (%) S = Sulfate content (ppm) This equation was developed for a 60-in. diameter pipe. The adjustment factors given in Table 2 must be applied depending on the actual pipe size: Figures 6-4 and Table 6-5 of the FDOT Optional Pipe Material Handbook (February 2012) illustrate the use of this equation and provide a chart showing the relationship between service life, chloride concentration, and pH. Durability Method Reference Notes Ohio DOT Model Potter, 1988 Based on large data set over wide range of pH and size values. Includes an abrasive component. Hurd Model Potter, 1988 Method developed for large diameter pipes in acidic environments. Hadipriono Model Potter, 1988 Method includes wide pH range. Florida DOT Model Florida DOT, Optional Pipe Materials Handbook, 2012 Considers corrosion to be the only mechanism of degradation. Table 1. Methods for determining EMSLs for reinforced concrete pipe. Table 2. Florida DOT conversion factors for different size culverts. Pipe Diameter (inches) Factor Pipe Diameter (inches) Factor 12 0.36 48 0.76 18 0.36 60 1.00 24 0.41 72 1.25 30 0.48 84 1.51 36 0.54 96 1.77 42 0.65 108 2.04
119 3.0 Metal Pipe Methods The design service life of corrugated metal pipes will nor- mally be the period in years from installation until deteriora- tion reaches the point of either perforation of any point on the culvert or some specified percent of metal loss. Different methods used to estimate service life use different definitions of service life. 3.1 Galvanized Steel Pipe A number of methods are available for estimating the EMSL of galvanized steel pipe. The California Method is the most widely accepted and is recommended for use if no state- or location-specific research is available that indicates another method is more suitable. The other methods are modifications of the original California Method. Table 3 lists the methods that can be used to determine EMSL values for plain galvanized steel pipes: The basic assumptions used to determine service life for standard metal pipes may also be extended to metal struc- tural plate pipes (AASHTO M 167/M 167M). One advan- tage of metal plate is the ability to specify thicker plates for installation in the invert of the structure while keeping the rest of the plates thinner (meeting structural loading requirements only) for economy. This provides greater protection where corrosion and abrasion will typically be most severe. 3.1.1 California Method A chart useful for application of the California Method is presented in Figure 1. The following equations can also be used: For pH values greater than 7.3: 1.47 0.41EMSL R= Ã For pH values less than 7.3: 13.79 log log 2160 2490 logEMSL R pH[ ]( )= â â Ã Where R is the minimum resistivity (ohm-cm). The resulting EMSL value must be multiplied by a factor depending on the gage thickness (see Table 4): 3.1.2 AISI Method The AISI is very similar to the California Method, with a different definition of the conditions that occur at the end of the useful service life. The chart titled âChart for estimating average invert life using AISI Method (AISI 1994)â is useful for application of the AISI Method. The following equations can also be used: For pH values greater than 7.3: 2.94 0.41EMSL R= Ã Durability Method Reference Notes California Method California Test 643, Method for Estimating the Service Life of Steel Culverts, 1999 Includes combined effects of corrosion and abrasion. Based on soil/water pH and resistivity. Service life of pipe considered to be until time of first perforation. American Iron and Steel Institute (AISI) Method Handbook of Steel Drainage and Highway Construction Products, AISI, 1994 Modification of California Method. Service life of pipe considered to be until 25% thickness loss in the invert. Federal Lands Highway Method Federal Lands Highway, Project Development and Design Manual, 2008 Modification of California Method. Increase the EMSL by 25% after first perforation. Colorado DOT Method CDOT-2009-11, Development of New Corrosion/Abrasion Guidelines for Selection of Culvert Pipe Materials, 2009 Calibration of California Method to state- specific conditions with a limited data set. Florida DOT Method Florida DOT Optional Pipe Materials Handbook, 2012 Modification of California Method to include a minimum steel thickness of 16 gage. Table 3. Methods for determining EMSLs for plain galvanized steel pipe.
120 Table 4. Galvanized steel pipe gage thickness factorsâCalifornia method. Gage 18 16 14 12 10 8 Factor 1.0 1.3 1.6 2.2 2.8 3.4 For pH values less than 7.3: 27.58 log log 2160 2490 logEMSL R pH[ ]( )= â â Ã Where R is the minimum resistivity (ohm-cm). The resulting EMSL value must be multiplied by a factor depending on the gage thickness (see Table 5): 3.1.3 Federal Lands Highway Method The Federal Lands Highway (FLH) Method is also a modifi- cation of the California Method. A chart useful for application of the FLH Method is presented as Exhibit 7.3-B. The following equations can also be used: For pH values greater than 7.3: 2.39 0.41EMSL R= Ã For pH values less than 7.3: 22.41 log log 2160 2490 logEMSL R pH[ ]( )= â â Ã Where R is the minimum resistivity (ohm-cm). The resulting EMSL value must be multiplied by a factor depending on the gage thickness (see Table 6): 3.1.4 FDOT Method The FDOT Method is also a modification of the California Method. A chart and table useful for application of the FDOT Method are presented in Figure 6.1 and Table 6.2, respectively. The following equations can also be used: For pH values between 7.3 and 9.0: 1.84 0.41EMSL R= Ã
121 For pH values between 5.0 and 7.3: 17.24 log log 2160 2490 logEMSL R pH[ ]( )= â â Ã Where R is the minimum resistivity (ohm-cm). The resulting EMSL value must be multiplied by a factor depending on the gage thickness (see Table 7): 3.1.5 Additional Service Life Due to Coatings Additional service life due to protection by coatings is gen- erally included by adding on a predetermined number of years to the calculated service life using one of the afore mentioned methods. Predetermined service life add-on values depend on the abrasion characteristics and type of coating. Add-on ser- vice life year values can range from 10 to 80 years. Table C9.0 from the MTO (2007) provides an example of the allowable additional service life values used for various coatings for that agency. 3.2 Aluminized Steel (Type 2) Pipe 3.2.1 FDOT Method The FDOT Method for estimating material service life of aluminized (Type 2) steel can be applied using a chart presented as Figure 6.2 or by using the table presented as Table 6.3. The following equations can also be used: For pH between 5.0 and 7.0: 50 log log 2160 2490 logEMSL R pH[ ]( )= â â Ã For pH between 7.0 and 8.5: 50 log 1.746EMSL R( )= â For pH between 8.5 and 9.0: 50 log log 2160 2490 log 7 4 8.5EMSL R pH[ ]( )( )( )= â â Ã â â Where R is the minimum resistivity (ohm-cm). Gage 18 16 14 12 10 8 Factor 1.0 1.3 1.6 2.2 2.8 3.4 Table 5. Galvanized steel pipe gage thickness factorsâAISI method. Chart for estimating average invert life using AISI Method (AISI 1994).
123 Table 6. Galvanized steel pipe gage thickness factorsâFLH method. Gage 18 16 14 12 10 8 Factor 0.8 1.0 1.2 1.7 2.2 2.6 The resulting EMSL value must be multiplied by a factor depending on the gage thickness (see Table 8): 3.3 Aluminum Pipe Estimates of service life for aluminum pipe can be made based on an FDOT Method, applied through the use of Fig- ure 6.3 or Table 6.4. The EMSL value depends on the minimum resistivity, pH, and gage thickness. The end of useful service life is defined as the time to first perforation. No explicit equation was found for these relationships. When installed within acceptable pH and soil resistivity ranges (typically 4.0 to 9.0 and > 500 ohm-cm, respectively) aluminum pipe (AASHTO M 196/M 196M) can provide a significant advantage over plain, galvanized steel pipe from a corrosion standpoint. It is therefore possible to use aluminum pipe in lieu of a thicker walled or coated (and thus more expen- sive) steel pipe. Because aluminum is softer than steel, it is more sus- ceptible to the effects of abrasion. This is particularly true for higher velocity flows that produce a scraping action, as opposed to lower velocity flows that allow the bedload to roll over the culvert surface. Where high velocity flows (15 ft/s or greater) carrying a bedload are prevalent, use of aluminum should be carefully evaluated. As with all metal pipes, invert loss is caused by a combination of abrasion and corrosion and, thus, the severity of both conditions must be considered. 4.0 Example Material Service Life Calculations The use of various quantitative methods for estimating material service life is demonstrated in this appendix. The use of a number of available software programs to assist in the estimating of service life is also demonstrated.
124 Table 7. Galvanized steel pipe gage thickness factorsâFlorida DOT method. Gage 18 16 14 12 10 8 Factor -- 1.0 1.3 1.8 2.3 2.8
125 M T O G R A V I T Y P I P E D E S I G N G U I D E L I N E S ( M A Y 2 0 0 7 ) Table C9.0 EMSL for Steel Pipe Coatings / Laminations Water Side Coating3 EMSL Max. AbrasionLevel2 (See Table C8) Soil Side Add-On Years Aluminized Type 2 (Sizes 1.3 to 3.5 mm) Refer to Figure B5 3 - Lamination3 Add-On Years to Plain Galvanized EMSL Polymer Coated1 (sizes 1.3 to 3.5 mm) 10 â 40 (Ref.erence 1) 20 â 70 (Reference 2) 50 (Reference 3) 30 (Reference 4) 3 3 - 3 - 50 -75 - - Notes: 1. Polymeric sheet coating provides adequate abrasion resistance to meet or exceed 50 year design service life for Abrasion Level 2 or below (see Reference 1) 2. No abrasive resistant protective coatings are recommended above Abrasion Level 3 (see Reference 1.) 3. Specific add-on values should be selected based on environmental conditions (abrasion, pH, resistivity, and low soil moisture content) and experience in comparable environments. Upper limits should be considered for the most favourable environmental conditions, (non-abrasive, high pH and resistivity) while low limits should be considered for the maximum abrasion level and most corrosive environments. (See reference 2). References: 1. California Highway Design Manual, 2002, pg 850-18 2. CSPI, 2002, pg 353 3. Ohio DOT 4. FHWA, 2000 Optional Pipe Material Handbook February 2012
126 Gage 18 16 14 12 10 8 Factor -- 1.0 1.3 1.8 2.3 2.8 Table 8. Aluminized steel (Type 2) gage thickness factorsâFlorida DOT method.
128 Each material type with a quantitative estimation method will be analyzed for three different example cases; namely, an aggressive case, a moderate case, and a non-aggressive case. The three different cases differ in the assumed environmen- tal parameters, as indicated below in Table 9. The assumed environmental values represent the worst case for either the soil-side or water-side of the culvert. Additional parameters that have been taken as constant regardless of the material type being analyzed are summarized in Table 10. 4.1 Non-Aggressive Case Table 11 contains results obtained by using the afore- mentioned equations and charts to estimate material service life for the non-aggressive case. 4.2 Moderately Aggressive Case Table 12 contains results obtained by using the afore- mentioned equations and charts to estimate material service life for the moderate case. Case pH Resistivity ( -cm) Sulfates (ppm) Chlorides (ppm) Non-aggressive 7.5 2000 250 25 Moderate 6.5 1000 500 50 Aggressive 4.5 500 1000 100 Table 9. Assumed environmental parameters for EMSL example calculations. Parameter Value Invert slope 1% Pipe length 50 ft Inside pipe diameter 36 inches Abrasion level Low, mildly abrasive, K = 1.19 (with abrasive flow) Sacks of cement per cubic yard (concrete pipe) 6 sacks Total percentage of water in aggregate mix (concrete pipe) 9% Steel depth in concrete (concrete pipe) 0.5 inches Sediment depth (concrete pipe) 1/8 inch Gage (metal pipe) 16 Table 10. Additional parameters required for example durability assessments. Pipe Material Approach EMSL (years) Concrete Hurd Model < 6025 Note 1 Hadipriono Model 94 ODOT Model 833 FDOT Method 116 Galvanized Steel California Method 43 AISI Method 86 FLH Method 54 FDOT Method 42 Aluminized (Type 2) FDOT Method 78 Aluminum FDOT Method 171 Note 1 â For pH values greater than 7.0, the Hurd model is not explicitly applicable, with the commentary on the method indicating a conservative estimate of EMSL can be taken as less than the calculated value for the pH 7.0 condition holding other parameters constant. Table 11. Example EMSL calculation resultsânon aggressive case.
129 4.3 Aggressive Case Table 13 contains results obtained by using the afore- mentioned equations and charts to estimate material service life for the aggressive case. 4.4 Discussion of Results A number of observations can be made based on these results: â¢ There is a wide variety in the EMSL values for different pipe types. â¢ There is a wide range of values obtained for a single pipe type depending on the method used. â¢ Taking an average value of multiple methods is not recom- mended given the potentially very wide range in values. â¢ As seen from the results of the Ohio DOT concrete EMSL calculations, many of the current methods do not produce Pipe Material Approach EMSL (years) Concrete Hurd Model 3993 Hadipriono Model 84 ODOT Model 11348 FDOT Method 90 Galvanized Steel California Method 16 AISI Method 31 FLH Method 19 FDOT Method 15 Aluminized (Type 2) FDOT Method 63 Aluminum FDOT Method 149 Table 12. Example EMSL calculation resultsâmoderately aggressive case. stable and realistic results across the range of feasible values. Careful consideration of the limitations of each method and review of results is recommended. 4.5 Use of Software for EMSL Calculations Three software programs are demonstrated to show how EMSL calculations can be implemented in an efficient and reliable manner: â¢ HiDISC 1.0 developed for the MTO (not yet publicly released) â¢ CSLE (Culvert Service Life Estimator) 2013 developed by FDOT â¢ AltPipe v 6.08 developed by Caltrans HiDISC and CSLE are stand-alone software programs while AltPipe is an online tool. The following screenshots show the use of these programs for the non-aggressive case. Pipe Material Approach EMSL (years) Concrete Hurd Model 519 Hadipriono Model 58 ODOT Model 366 FDOT Method 54 Galvanized Steel California Method 0 (Not Allowed) AISI Method 0 (Not Allowed) FLH Method 0 (Not Allowed) FDOT Method 0 (Not Allowed) Aluminized (Type 2) FDOT Method 0 (Not Allowed) Aluminum FDOT Method 39 Table 13. Example EMSL calculation resultsâaggressive case.
130 4.5.1 MTO HiDISC 1.0 Example Screen Captures Data Input â Culvert Details Data Input â Hydraulics
131 Data Input â Durability Data Input â Durability
132 Data Input â Durability Output - Steel
133 Output - Concrete 4.5.2 FDOT CSLE 2013 (version 184.108.40.206) Example Screen Captures Data Output
134 4.5.3 Caltrans AltPipe (version 6.08) Example Screen Captures Data Input
135 Output - Steel Output â Concrete, Aluminum, and Plastic
Abbreviations and acronyms used without deï¬nitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACIâNA Airports Council InternationalâNorth America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S.DOT United States Department of Transportation