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Corrosion Prediction Software and Corrosion Modeling Software EVSCompass®: Extreme Value Statistics for Corrosion Modeling and Corrosion Life Prediction
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Overview and Application Examples of EVSCompass  Extreme Value Statistics for Corrosion Modeling and Corrosion Life Prediction 

Extreme value statistics (EVS) has been used since the 1950s for extrapolating corrosion damages (maximum pit depth, crevice depth, crack depth etc.) from small lab samples, field coupons, or partial coverage inspection blocks to larger area of structures and assets at present or future times. WebCorr's EVSCompass is the only device and OS independent EVS software on the market for corrosion modeling and life prediction of corrodible structures and industrial assets. FEED designers, engineers, consultants, maintenance and inspection personnel, asset owners and operators, and government regulators can quickly and accurately determine:
The probability of failure (POF) is an important factor in API 580 RiskBased Inspection and API 581 RiskBased Inspection Methodology. EVSCompass is a powerful EVS software tool that goes beyond the prediction of the probability of failure (POF) in time (POF vs service life) and in space (POF vs area, POF vs wallthickness), it predicts the time to FIRST leak or perforation, the number of leaks at any given time, the depth of corrosion and the number of pits exceeding the specified depth at any future time. For partial coverage inspection, EVSCompass determines both the size and number of inspection blocks to minimize uncertainties. The unique capabilities of EVSCompass help assets owners, operators, and government regulators make quantitative riskbased decisions pertaining to the future conditions and operations of structures and assets. EVSCompass is a highly effective and powerful tool for the following applications: Corrosion Modeling Corrosion Life Prediction RiskBased Inspection (API 580 RiskBased Inspection and API 581 RiskBased Inspection Methodology) NDT/NDE Partial Coverage Inspection (EVS Extrapolation in Space and in Time) Asset Integrity Management (such as Pipeline Integrity Management) External Corrosion Direct Assessment (ECDA) Internal Corrosion Direct Assessment (ICDA) Marine and Offshore Inspection and Assessment Aboveground Storage Tank Corrosion Inspection and Assessment Underground Storage Tank Corrosion Inspection and Assessment Leak Prediction for Pipelines, Vessels, Storage Tanks, Boilers, Condensers, and Heat Exchangers
EVSCompass is a cloudbased software that works on any device running any OS without the need for users to install or download anything. Figure 1 below shows an overview of the user interface of EVSCompass.
Figure 1 EVSCompass: Extreme Value Statistics software for corrosion modeling and corrosion life prediction of structures and assets.
EVSCompass: Extreme Value Statistics Software Application Example No.1 Prediction of Pitting Corrosion in Type 316L Stainless Steel: Seeing the Bigger Picture of the Distant Future EVS Extrapolation in Space and in Time In Figure 1 above, type 316L stainless steel coupons of 2" by 2" (4 in^{2}= 0.00258 m^{2}) with a thickness of 0.5" (12.7 mm) were immersed in chloride solution at 50^{o}C for durations ranging from 49.50 hours to 528 hours (2.063 to 22 days) in the laboratory. For each exposure duration, a number of identical coupons (from 3 to 15) were used. The maximum pit depth on each coupon was measured and entered in EVSCompass. The 5 exposure durations produced 5 datasets. For a surface area of 1 ft^{2} (12"x12"=144 in^{2}=0.0929 m^{2}), EVSCompass predicts that: (1) the time to first leak or perforation of the 12.7 mm plate is 882 days; (2) after 11 years (4015 days), the number of leaks or perforation holes is 63 (675x0.0929=63); (3) the time to 100th leak or perforation is 8871 days (24.3 years); (4) the hole area at 11 years is 9.955% of the total surface area; (5) the depth of the largest pit at 11 years is 24.532 mm; (6) the depth of the 100th largest pit at 11 years is 8.999 mm; (7) the number of pits exceeding 0.5 mm at 11 years is 215 (2318x0.0929=215); (8) the time for the first 100 pits to exceed 0.5 mm is 5 days; (9) the probability of failure at 11 years for wall thickness of 12.7 mm is 100%; (10) the service life for wall thickness of 12.7 mm at 5% probability of failure is 170 days; (11) For partial coverage inspection (PCI), the maximum area of EVS extrapolation under the current settings is 2.01 m^{2}.
EVSCompass is designed with endusers in mind without the usual learning curve associated with a new software. Users simply enter the basic information such as material, service environment, area of coupons or inspection blocks, total surface area of the structure, exposure time and durations, and the maximum pit depth for each coupon or inspection block at each exposure duration. Figures 25 show the options for materials, service environments, exposure time, and type of charts to display.
Figure 2 Extreme Value Statistics software for corrosion modeling and corrosion life prediction of structures and assets: option for Material of Construction
Figure 3 Extreme Value Statistics software for corrosion modeling and corrosion life prediction of structures and assets: option for Service Environment.
Figure 4 Extreme Value Statistics software for corrosion modeling and corrosion life prediction of structures and assets: option for Exposure Time.
Figure 5 Extreme Value Statistics software for corrosion modeling and corrosion life prediction of structures and assets: option for different types of plots.
Seeing the Bigger Picture of the Distant Future EVS Extrapolation in Space and in Time: The surface area of coupons used in laboratory tests was 4 in^{2} (0.00258 m^{2}) for a maximum duration of 22 days. Figure 6 shows prediction results by EVSCompass when the surface area is extrapolated to 2.58 m^{2} (1000 times) and the exposure time to 365 days. The time to first leak or perforation is 800 days, the time to 100th leak or perforation is 1028 days. For partial coverage inspection (PCI), EVSCompass determines that the maximum surface area for extrapolation is 2.02 m^{2}. EVSCompass recommends two options to extend the extrapolation to the total surface area of the structure: (1) by increasing the number of inspection blocks from the current 15 to 16; or by increasing the minimum surface area of the inspection blocks from the current 0.00258 m^{2} to 0.0033 m^{2}. The probability of failure vs. service life is selected in Figure 6. In Figure 7, the probability of failure vs. surface area is selected. Figure 8 show the plot of the probability of failure vs. wall thickness.
Figure 6 Extreme Value Statistics software for corrosion modeling and corrosion life prediction of structures and assets: Probability of Failure vs. Service Life.
Figure 7 Extreme Value Statistics software for corrosion modeling and corrosion life prediction of structures and assets: Probability of Failure vs. Surface Area.
Figure 8 Extreme Value Statistics software for corrosion modeling and corrosion life prediction of structures and assets: Probability of Failure vs. Wall Thickness.
EVSCompass: Extreme Value Statistics Software Application Example No.2 Prediction of Pitting Corrosion in Aluminum Alloy: Seeing the Bigger Picture of the Distant Future EVS Extrapolation in Space and in Time Figures 9 and 10 show another application example of EVSCompass in corrosion modeling and life prediction. Aluminum alloy Alcan 2SO coupons of 129 cm^{2} were immersed in Kingston tap water at 25^{o}C for various durations from 7 to 365 days. Maximum pit depth on each coupon at 5 exposure durations is entered into EVSCompass as shown in Figure 9 below. For a large structure with an area of 1000 m^{2} (that is 77,519 times of the area of coupons) and a wall thickness of 2.54 mm, EVSCompass predicts that: (1) the time to first leak or perforation is 991 days; (2) the number of leaks or perforation after 5 years (1825 days) is 24/m^{2}; (3) the time to the 100th leak or perforation is 997 days; (4) the hole area after 5 years exposure is 21% of the total surface area; (5) the depth of the largest pit on the 1000 m^{2} surface area after 5 years is 3.09 mm; (6) the number pits exceeding 1.27 mm after 5 years is 108/m^{2}; (7) the time required for the first 100 pits to exceed 1.27 mm is 98 days; (8) the probability of failure at 5 years for the wall thickness of 2.54 mm on the 1000 m^{2} surface is 100%; (9) the service life for the wall thickness of 2.54 mm in the 1000 m^{2} surface is 3 days at the POF of 5%; (10) for partial coverage inspection, the maximum area of extrapolation is 0.809 m^{2}; (11) EVSCompass recommends two options to extend EVS extrapolation to the entire surface area of the structure: (a) by increasing the number of coupons or inspection blocks from the current 10 to 32; (b) by increasing the area of coupons or inspection blocks to 15.9438 m^{2} (shown in Figure 10 below); (12) the maximum pit depth vs. service life is plotted in Figure 9.
Figure 9 Extreme Value Statistics software for corrosion modeling and corrosion life prediction of structures and assets: aluminum alloy in Kingston tap water.
Figure 10 Extreme Value Statistics software for corrosion modeling and corrosion life prediction of structures and assets: Optimization of Partial Inspection Coverage EVSCompass: Extreme Value Statistics Software Application Example No.3 Partial Coverage Inspection of Pitting Corrosion in Oil Tank Bottom Plate: Seeing the Bigger Picture  EVS Extrapolation in Space Inspection of a large oil tank carbon steel base plate of 6 mm in thickness was carried out to determine the maximum pit depth distribution. The whole surface area of the oil tank plate was 1040 m^{2}. Due to time, cost, and accessibility considerations, partial coverage inspection using 10 blocks of 1.85 m^{2 }each was randomly selected for pit depth measurements. The maximum pit depth on each of the inspection blocks was entered into EVSCompass (one block showed no pitting and is not included in the data entry). Based on the maximum pit depth data measured using small inspection blocks of 1.85 m^{2}, EVSCompass predicts that the maximum pit depth in the 1040 m^{2 }base plate is 4.297 mm (Figure 11). The chart in Figure 11 shows the pit depth vs. surface area of the base plate. Other timebased predictions are not applicable in this application example for EVS extrapolation in space that has only one dataset available. For EVS extrapolation in time or in time and in space, at least two datasets collected at two different exposure times are required (Figures 110 above).
Figure 11 EVSCompass predicts pitting depth in a large oil tank base plate of 1040 sq.m surface based on the partial coverage inspection.
EVSCompass Extreme Value Statistics Software Application Example No.4 Pitting Corrosion of Carbon Steel in Natural Seawater: Seeing the Bigger Picture of the Distant Future EVS Extrapolation in Space and in Time Carbon steel coupons of 75 mm x 50 mm were immersed in natural seawater for durations of 1.0, 1.5, 2.0, 3.0 and 4.0 years. Maximum pit depth for each coupon at each exposure duration is entered into EVSCompass (Figure 12). Note that the surface area of a coupon (with 2 sides) is 0.0075 m^{2} (75 cm^{2}). EVS Extrapolation of the pit depth to a surface area of 75 m^{2} (10000 times of the coupon area) and the a future time of 10 years produces the following results: (1) the time to first leak or perforation is 9.084 years; (2) the number of leaks or perforation at 10 years is 2772 (75x36.954); (3) the time to 100th leak or perforation is 9.122 years; (4) the hole area at 10 years is 8.762%; (5) the time required for 100 pits to exceed 3 mm depth is 5.311 years; (6) the depth of the largest pit at 10 years is 6.786 mm; (7) the depth of the 100th largest pit is 6.75 mm; (8) the number of pits exceeding 3 mm depth at 10 years is 15358 (75x204.773); (9) the probability of failure at 10 years and 6mm thickness is 100%; (10) the service life for wall thickness of 6 mm at POF of 5% is 2.658 years
Figure 12 EVSCompass predicts pitting corrosion of carbon steel in natural seawater with EVS extrapolation in space and in time.
The powerful applications of EVSCompass are truly unlimited in engineering design, materials selection, process operation, inspection and maintenance, corrosion modeling and corrosion life prediction of structures and plant assets. Click here to contact us for licensing details and experience the power of EVSCompass. 

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