research article experimental investigation on corrosion

Research ArticleExperimental Investigation on Corrosion Effect onMechanical Properties of Buried Metal Pipes

Yingbo Hou1 Deqing Lei1 Shujin Li1 Wei Yang1 and Chun-Qing Li2

1School of Civil Engineering and Architecture Wuhan University of Technology Wuhan 430070 China2School of Engineering RMIT University Melbourne VIC 3001 Australia

Correspondence should be addressed to Chun-Qing Li chunqinglirmiteduau

Received 20 June 2016 Revised 5 August 2016 Accepted 8 August 2016

Academic Editor Flavio Deflorian

Copyright copy 2016 Yingbo Hou et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Corrosion has been found to be the most predominant cause for failures of buried metal pipes A review of published literature onpipe corrosion reveals that little research has been undertaken on the effect of corrosion onmechanical properties of pipe materialsand almost no research has been conducted on corrosion effect on fracture toughness The intention of this paper is to present acomprehensive test program designed to investigate the effect of corrosion on mechanical properties of metals in soil Two typesof metals namely cast iron and steel are tested under corrosion in three different environments A relationship between corrosionand deterioration of mechanical property of metals is developed It is found in the paper that the more acidic the environmentis the more corrosion the metal undergoes and that the corrosion reduces both the tensile strength and fracture toughness of themetalThe results presented in the paper can contribute to the body of knowledge of corrosion behavior and its effect onmechanicalproperties of metals in soil environment which in turn enable more accurate prediction of failures of buried metal pipes

1 Introduction

Pipelines are essential infrastructure that play a significantrole in a nationrsquos economy social well-being and quality oflife Most of pipes are made of metals for example cast ironand steel and located underground in soil It is estimated thatabout 85 of water distribution pipes are cast iron and steel[1] Due to their long-term service and exposure to aggressiveenvironment in soil aging and deterioration of metal pipeshave resulted in an unexpected high rate of failures Forexample the failure rate of cast iron pipes can be as high as39 bursts per 100 km per year in Canada [2] whilst the failurerate of water mains in Australia is 20 breaks per 100 km peryear on average [3] As is well appreciated the consequenceof pipe failures can be socially economically and environ-mentally catastrophic resulting inmassive disruption of dailylife considerable economic loss widespread flooding andsubsequent environmental pollution and even casualties andso forthTherefore there is awell-justified need to thoroughlyinvestigate the causes of pipe failures

Experience and investigation of pipe failures suggest thatcorrosion of metals both cast iron and steel is the most

predominant cause of pipe failures [4 5] Since corrosionis linked to almost all pipe failures it has become a globalproblem for all stakeholders in particular engineers and assetmanagers of buried metal pipes [6 7] As such considerableresearch has been undertaken in the past few decades oncorrosion of metal pipes more perhaps for cast iron pipesas represented notably by Doleac et al [8] Dean Jr and Grab[9] OrsquoDay et al [10] Randall-Smith et al [11] Kirmeyer et al[12] Camarinopoulos et al [13] Sadiq et al [14] Panossian etal [15] and so on Due to different environments the mech-anisms of corrosions are different for internal and externalsurfaces of the pipe For internal corrosion depending onthe substance to be conveyed in the pipe various factorsincludingmicrobial effects can cause corrosion [16] whereasexternal corrosion is mainly due to corrosive chemicals insoil [17] Pipe corrosion in soil is an interaction between thepipematerials and the soil environment [18]There are severalstimulating factors that lead to the pipe external corrosion insoil environment [5 19] Moisture temperature pH valuesmineral salt content sulfides organics precipitates and soon are major factors that contribute to external corrosion of

Hindawi Publishing CorporationInternational Journal of CorrosionVolume 2016 Article ID 5808372 13 pageshttpdxdoiorg10115520165808372

2 International Journal of Corrosion

pipes in soil [20] Metal corrosion in soils is determined pri-marily by a combined effect of these factors It also dependson the physical and chemical characteristics of the soils

A review of published literature on pipe corrosion ascited above (and also see references) reveals that most of thecurrent research focuses on corrosionmechanisms corrosionprogress and corrosion rate frommaterial perspective Littleresearch has been undertaken on the effect of corrosion onmechanical property change of pipe materials and almost noresearch has been conducted on corrosion effect on fracturetoughness of pipe materials As is well known it is themechanical properties of the pipe materials that govern thebehavior and eventual failure of the pipes It is thereforeimperative to thoroughly examine the effect of metal cor-rosion on its mechanical properties The understanding andknowledge of corrosion induced deterioration of mechanicalproperties ofmetals can prevent future failures ofmetal pipes

There are two main modes of pipe failure by rupturedue to the reduction of wall thickness of the pipes and byfracture due to the stress concentration at the tips of cracksfor example corrosion pits or in general defects in the pipes[21] The mechanical properties corresponding to these twofailure modes are tensile strength and fracture toughness ofthemetal A detailed examination of most published researchin this area (see references) suggests that current researchon corrosion induced pipe failures focuses more on loss ofstrength than toughness An inspection of failures of trunkmains in service reveals that most cast iron water mainfailures are of fracture type that is the failure is caused by thegrowth of a crack and subsequent collapse of the pipe [22] Itis therefore essential to study the deterioration of both tensilestrength and fracture toughness of the metals to enable moreaccurate prediction of pipe failures

The intention of this paper is to experimentally investigatethe effect of corrosion on mechanical properties of metalsused as pipe material A comprehensive test program isdesigned to observe monitor and evaluate corrosion behav-ior of metals and its effect on their mechanical properties indifferent environments Two types ofmetals namely cast ironand steel are tested under corrosion in three environmentsas represented by pH values From the analysis of testresults a relationship between corrosion and deteriorationof mechanical property of metals is developed It is believedthat tests on the effect of corrosion on mechanical propertiesof metals are one of few of the kind The results producedfrom the tests can contribute to the body of knowledge ofcorrosion behavior and its effect on mechanical propertiesof metal in soil environment which can equip engineers andassetmanagers inmitigating the risk of failures ofmetal pipes

2 Design of Test Specimens

21 Specimen Materials Cast iron and steel have been themost predominant pipeline material before the 1980s [21]Among various types of cast irons and steel grey cast iron andcarbon steel are perhaps the most widely used pipe materials[12 23] Because of this it is reasonable to select these twotypes of materials for corrosion investigation due to theirwide use and also long service Cast iron and steel have quite

Table 1 Chemical composition of test materials (wt)

Material C S P Mn SiQ235 steel 0176 0023 0019 0465 0233HT200 cast iron 32 012 0015 09 16

differentmechanical properties although they have been usedfor the same purpose of pipes Cast iron is brittle materialwhilst steel is ductile Cast iron has been widely used inpipeline industry due to its comparatively low cost but ithas been replaced by steel in pipeline industry for its greaterstrength and ductility

As is well known the mechanical properties of metalare affected by its chemical composition morphology andmicrostructure which vary significantly In this study Q235plain carbon steel and HT200 grey cast iron are selected asthe testing materials due to their wide use in pipe industryin China and availability on market [1 24] The chemicalcomposition of Q235 steel and HT200 cast iron is shown inTable 1

22 Specimens for Tensile Strength Specimens for tensilestrength test were made according to ASTM E8M13 StandardTest Methods for Tension Testing of Metallic Materials [25]The testing specimens are recommended single-edge bend[SE(B)] in the standard of which the dimensions shouldcomply with the following requirement

119871 ge 4119863 (1)

where 119871 is the gauge length and 119863 is the diameter of themiddle part of the specimen within gauge length 119871 Forthe sake of comparison the specimens of the two differentmaterials for tensile strength test are intentionally made withthe same dimensions The specimen for tensile strength isshown in Figure 1(a)

23 Specimens for Fracture Toughness Specimens for fracturetoughness test were made according to ASTM E1820-13 Stan-dard Test Method for Measurement of Fracture Toughness[26] In this standard the key is to control the width of thespecimen since it is the most important factor that affectsthe resulting fracture toughness Depending on the width ofthe specimens there can be two types of fractures the planestress fracture and plane strain fracture For the plane stressfracture the fracture toughness decreases with the increaseof specimen width and stabilizes at a certain width forwhich plane strain fracture occurs This width is determinedaccording to ASTM E1820-13 as follows

119861 ge 25 (119870IC120590119910

)

2

(2)

where 119861 is the width of the specimen 119870IC is the fracturetoughness and 120590119910 is the yield strength of the material

By (2) the width for selected cast iron specimen withthe grade HT200 was calculated to be 119861 = 20mm Howeverfor the selected Q235 steel the calculated width for the

International Journal of Corrosion 3

D = 250

D1 = 15D = 200

L2 = 83L1 = 317 L = 140

+

+

(a) For tensile strength

2413

80

21 a = 200

W = 400

B = 200L = 1800

(b) For fracture toughness

Figure 1 Test specimen (unit mm)

test specimen is as large as 1700mm which is too largeto be practical for both corrosion and fracture tests Sincethe primary purpose of this study is (1) to experimentallyexamine how corrosion affects the fracture toughness ofthe Q235 steel but not to determine its accurate value offracture toughness and (2) to compare the corrosion effecton fracture toughness for different metals (ie steel and castiron) it is justifiable to select a smaller but with same size asthat for cast iron specimens for both corrosion and fracturetoughness tests This is because all test specimens should beunder the same corrosion and fracture conditions and hencerelative comparison of fracture toughness change over timeand with each other is valid Besides the accurate value offracture toughness of the Q235 steel has been determinedwith different methods as shown in for example Zhao etal [27] and Dong et al [28] Small size specimens of steelfor fracture toughness tests have also been used in otherstudies as shown in literature [29] Therefore the width ofspecimens for fracture toughness test for Q235 steel wasselected the same as that for cast iron The specimen forfracture toughness is shown in Figure 1(b)

24 Manufacture of Specimens All test specimens were man-ufactured by specialist mechanical technicians For tensilespecimens themanufacture was straightforward For fracturetoughness the specimens should theoretically be precrackedby fatigue Experience and literature survey have shownthat it is impractical to obtain a reproducibly sharp narrowmachinednotch thatwill simulate a natural crackwell enoughto provide a satisfactory fracture toughness test result [27]The most effective alternative is to produce a precrack acomparatively short fatigue crack which is extended froma narrow notch There are three forms of notches to start afatigue crack (known as fatigue crack starter notch) whichare straight through notch chevron notch and notch endingwith drilled hole Different forms of fatigue crack starternotches shall meet different dimension requirements In thisstudy the straight through notch was employed as fatiguecrack starter For detailed specifications of specimen sizeconfiguration and preparation refer to ASTM E1820 [26]

Table 2 Soluble chemical composition of soil sample (wt)

Chemical CaO MgO K2O Na

2O

Content 092 154 217 060

Table 3 Chemical composition in simulated soil solutions (gL)

Chemical CaCl2sdot2H2O MgSO

4sdot7H2O KCl NaHCO

3

Content 0036 0190 0069 0540

3 Test Methodology

31 Simulation of Corrosive Soil Pipe corrosion is elec-trochemical reaction between the pipe material and thecorrosive agents in the ambient soil In order to representthis reaction in the laboratory it is necessary to simulate theworking environment of the pipes There are two methods tosimulate the working environment one is to bury the pipein a box of real soil and the other is to immerse the pipe ina solution that contains main chemical elements extractedfrom the real soil (known as soil solution) Literature reviewssuggest that most of current research employs soil solutionsfor pipe corrosion test in soil [30 31] Therefore this studyalso employed the soil solution for corrosion test Oneadvantage of using soil solution is the ease to control thetesting variables and also monitoring of corrosion behavior

For convenience soil in local land with pipes underneathwas selected The chemical composition of the selected soilwas analyzed and is shown in Table 2 This compositionwas used to make soil solution The chemical analysis ofthe soil indicates that the pH of the soil is 80 So the basesolution used for corrosion test has pH of 80 The chemicalcomposition of the soil solution used in the corrosion test isshown in Table 3 which was made based on the principle thatthe key chemical elements of soil sample and soil solution arethe same [30 31]

Since metal corrosion under natural soil conditions willtake a long time to have any significant effect on its materialproperties and to achieve the research objective within the


time period of the project acceleration of corrosion appearsto be necessary for almost all corrosion tests (eg [5 32])Thus acceleration of corrosion was adopted in this test Aliterature review suggests that pH value will accelerate thecorrosion of metal exponentially [33] For this reason threevalues of pH were selected for the simulated soil solution sothat the variation of pH effect on corrosion can be studiedBased on research experience and pretrial pH of 30 wouldaccelerate the corrosion sufficiently to have significant effecton the mechanical properties of the metal within the projectperiod With the pH of natural soil being 80 a middle valueof pH of 55 was selected

Different values of pH were achieved by adding sulfuricacid and maintained the same during the whole test periodIt may be noted that the added sulfuric acid may react withthe chemicals in the solution but this reaction would happenin exactly the same manner as with the soluble chemicals innatural soil [30 31]The point is that pH values of all solutionwere maintained the same and used as the measurement forthe solution

32 Test Variables As discussed in the instruction of manyfactors that affect corrosion of metals in soil and its effecton mechanical property the chemical compositions of soiland metal are the most influential In this study the chemicalcomposition of the soil was represented by pH and that ofmetal by grade Therefore the pH values of the soil solutionand the type of metal were selected as the main testingvariables as well as their change with time Three values ofpH were selected for soil solution as discussed above whichare 80 55 and 30 Two types of metal were selected forcorrosion test and its effects on mechanical properties whichare carbon steel and grey cast iron To obtain the variationof corrosion and its effect on mechanical properties of metalsover time three points of timewere selectedwhich are 90 180and 270 days (or 3 6 and 9 months) respectivelyin additionto initial time that is before corrosion Thus there are fourpoints in time in total These times were selected basedon the literature review and research experience to ensurethe measurable corrosion and significant property change ofmechanical properties of the specimens (eg [5 32])

For statistical studies three duplicates weremade for eachspecimen with the designated test variables Therefore thetotal number of test specimens is 3 (pH values) times 2 (two typesof metal) times 2 (properties) times 4 (time points) times 3 (duplicates) =144

The measurement of the test includes (i) corrosion cur-rent (ii) weight loss (iii) tensile strength and (iv) fracturetoughness Corrosion current was measured every day in thefirst week of the test and then weekly until the end of testsOther three parameters were measured at initial point andthree designated points of time giving four measurementsover time

33 Test Setup and Procedure Immersion corrosion test wasconducted according to ASTM G31-2012a Standard Guidefor Laboratory Immersion Corrosion Testing of Metals [34]in room temperature with soil solutions of three pH values

Figure 2 Specimens immersed in soil solution

(30 55 and 80) for a duration of three time periods of90 180 and 270 days The specimens made of Q235 steeland HT200 cast iron were washed using 50 acetone Theywere then dried and placed in the containers of designatedsoil solutions In each container 6 specimens 2 for mechan-ical property (tensile and fracture) and 3 duplicates wereimmersed in the solution as shown in Figure 2 In totalthere are 18 containers representing different pH values (3055 and 80) and materials (cast iron and steel) Duringimmersion time pH values in different containers weremeasured using a pHmeter and controlled by adding sulfuricacid Corrosion tests in all 18 containers were run in parallel

To monitor the corrosion behavior wires were welded ontwo specimens of each type (labeled 1 for tensile specimenand 4 for toughness specimen) in each container andcorrosion currents of the specimens were measured using anampere meter At each point of three designated times thatis 90 180 and 270 days specimens were taken out of thesolution formeasurement of weight loss tensile strength andfracture toughness for three pH values and both steel and castiron Weight loss of the specimens was measured accordingto ASTMG31-12a Tensile strength was tested on WAW-1000material testing system as shown in Figure 3(a) Fracturetoughness was tested on MTS landmark testing system asshown in Figure 3(b) Both tensile and fracture toughnesstests were carried out by laboratory technicians to ensure thequality of the test results

4 Test Results and Analysis

41 Corrosion Current Corrosion current has long been usedas a major indicator for corrosion behavior of metals [4 12ndash15 35] In this study corrosion currents were monitored overthe whole test period and recorded using an ampere meteras shown in Figure 4 The results of corrosion currents arepresented in Figures 5 and 6 for steel and cast iron specimensrespectively It can be seen from the figures that the corrosioncurrents are in general very scattered This is not unexpecteddue to the random occurrence and growth of corrosion Itmay also be attributed to the accuracy in measuring thecurrent due to aggressive environments

Figures 5 and 6 indicate that although each point ofmeasure corrosion current is scattered the general trendof corrosion currents is clear which is decreasing with the


(a) (b)Figure 3 Test facilities tensile (a) and fracture toughness (b) testing systems

Figure 4 Monitoring of corrosion current

exposure time This means that current rate is high at thebeginning of the corrosion and decreases over time As itis well known corrosion is an electrochemical process Theacidic environment can initiate the corrosion but the progressof corrosion needs the supply of oxygen which is not readilyavailable to keep the high corrosion rate These results areconsistent with other results reported in the literature as wellas research experience [5]

Figures 5 and 6 also show that corrosion currents aregenerally larger for more acidic solution that is smaller pHvalue in particular at the beginning This is again consistentwith results published in literature For example a studyby Panossian et al [15] shows that the smaller pH is thelarger corrosion currents are indicating that acid can inducemore corrosion Though corrosion currents in solution withsmaller pH are comparatively larger the decreasing rates ofcorrosion currents (ie the slope of the curve) are irregularexhibiting the randomness of corrosion behavior Corrosioncurrents in solutions with pH of 80 and 55 have the largestand the smallest decreasing rates respectively In general thedifferences in variation rates of corrosion current (the slopeof the curve) for different pH are 266 between 30 and 55and minus250 between 55 and 80

The comparison of Figures 5 and 6 also shows thatcorrosion of cast iron is slightly faster than steel As suggestedbyDean Jr andGrab [9] one of the reasons for this can be thata higher carbon content in metal can incur a larger corrosionrate

42 Weight Loss Before the test all specimens were cleanedand weighed After immersion specimens were taken out

at three designated points of time that is 90 180 and 270days respectively Figure 7 shows the progress of corrosionactivity in terms of change in color rust accumulation anddistribution Then they were dried cleaned and weighedagain Weight loss was calculated as reduction in weightof each specimen before and after immersion Weight lossis normalized by surface area and expressed in g sdot mminus2 toeliminate the influence of differences in shapes and exposureareas Figure 8 shows the results of weight loss for steeland cast iron specimens respectively where each point isthe average of three measurements of weight The range ofcoefficients of variation of weight loss at each point is from009 to 022 over the test period

Figure 8 shows that the weight decreases with time almostlinearly for both steel and cast iron specimens which isdifferent from the results of corrosion current (which isnonlinear over time) The reason could be that the weightloss represents the cumulative effect of corrosion which ismore gradual whilst the corrosion current represents theinstantaneous rate of corrosion which is more fluctuatedIt can be seen that weight loss is larger with smaller pHvalue that is pH = 30 This is consistent with the resultsof corrosion current It can be also seen from Figure 8 thatthe trend of weight loss of both steel and cast iron specimensis almost the same although the weight loss of cast ironspecimens due to corrosion is slightly larger Again this isconsistent with the results of corrosion current As can beseen from the figure there is not much difference in weightloss when pH values are between 55 and 80 in particular forcast iron

43 Yield Strength Reduction The main objective of thisresearch is to investigate the effect of corrosion onmechanicalproperties of metals as represented by tensile strength andfracture toughness For this purpose specimens were takenout of the immersion after 90 180 and 270 days of corrosionrespectively Then they were cleaned and loaded to failure intension on the testing machine in Figure 3(a) The resultsof tensile tests are shown in Figure 9 where each pointrepresents an average of three testing results The range ofcoefficients of variation of tensile strength reduction at eachpoint is from 011 to 019 over the test period


0001002003004005006007008

0 30 60 90 120 150 180 210 240 270

Cor

rosio

n cu

rren

t (m

A)

Immersion time (day)

Specimen 1Specimen 4

(a) pH = 30

0

001

002

003

004

005

006

0 30 60 90 120 150 180 210 240 270

Cor

rosio

n cu

rren

t (m

A)



(b) pH = 55

0

001

002

003

004

005

006

0 30 60 90 120 150 180 210 240 270

Cor

rosio

n cu

rren

t (m

A)



(c) pH = 80

Figure 5 Corrosion current in steel specimens in solutions of different pH values

From Figure 9 it can be seen that the tensile strengthdecreases with time due to corrosionThis is the case for bothsteel and cast iron materials The results of Figure 9 providegood evidence that corrosion does affect the mechanicalproperty of metals This is mainly due to the fact thatcorrosion penetrates the surface of the specimens destroyingthe compactness of the specimen surface It can be seen inFigure 7 that surfaces of all corroded specimens are rougherandmore porous than intactmetals whichmakes it easier forcorrosive agents or other elements for example O and Cl toingress into the metal The ingress of corrosive agents andorelements can alter the chemical composition of metal viachemical reactions of these agents and elements It can alsochange the morphology or microstructure of the metal Asis known chemical composition and morphology are mainfactors that determine the mechanical property of metals Asa result the mechanical property of the metal changed

Table 4 shows the corrosion induced deterioration ofmechanical properties of steel and cast iron at three timeperiods of test It can be seen that the reduction of tensilestrength increases with the exposure time for both steel andcast iron These results are in agreement with the results ofweight loss which shows a linear increase with time (Figure 8)

as discussed above Also seen from the table is the factthat the reduction of tensile strength of cast iron is largerthan that of steel This is again consistent with the results ofboth corrosion current and weight loss indicating that highcarbon content in metal may not only lead to more corrosion[9] but also have more effect on tensile strength Table 4 alsoshows that in the first period of exposure the reduction oftensile strength is larger for more acidic environment (iepH = 30) but later in the third period the reduction oftensile strength is larger for less acidic environment (ie pH= 80) indicating that high acidity may accelerate corrosionof metal but may not necessarily accelerate the corrosioneffect on its mechanical properties which is determined byits chemical position morphology and microstructure asdiscussed previously

44 Fracture Toughness Reduction Fracture toughness ofmetals is determined by three-point bending test as shownin Figure 3(b) From this test the fracture toughness can becalculated as follows

119870(119894) = [119875119894119878

(119861119861119873)1211988232]119891(119886119894

119882) (3)


000

002

004

006

008

010

0 30 60 90 120 150 180 210 240 270

Cor

rosio

n cu

rren

t (m

A)



(a) pH = 30

Cor

rosio

n cu

rren

t (m

A)


000001002003004005006007

0 30 60 90 120 150 180 210 240 270


(b) pH = 55

Cor

rosio

n cu

rren

t (m

A)


000001002003004005006007

0 30 60 90 120 150 180 210 240 270


(c) pH = 80

Figure 6 Corrosion currents in cast iron specimens in solutions of different pH values

where

119891(119886119894

119882) =

3 (119886119894119882)12[199 minus (119886119894119882) (1 minus 119886119894119882) times (215 minus 393 (119886119894119882) + 27 (119886119894119882)

2)]

2 (1 + 2119886119894119882) (1 minus 119886119894119882)32

(4)

and 119870(119894) is the calculated 119870 for the bend specimen at load 119875119894119878 is the support span119861 and119861119873 are the width and net width ofspecimen respectively 119886119894 is the current crack length and119882is the height of the specimen (see Figure 1(b)) In this studythe fracture toughness values that is 119870IC were determineddirectly from the testing machine as outputs using the built-in program

The results of fracture toughness reduction are shown inFigure 10 where again each point represents an average ofthree testing results The range of coefficients of variation offracture toughness reduction at each point is from 012 to 017over the test period It can be seen from the figure that thefracture toughness also decreases with time due to corrosionThis is true for both steel and cast iron materials Theresults of Figure 10 again provide the evidence that corrosiondoes affect the mechanical property of metals for the samereason as explained for the tensile strength In addition it

can be seen in Figure 7 that the penetration of corrosioninto the metal is not evenly distributed In most cases thelocations that are damaged incur themost corrosion forminglocalized corrosion pits This is true especially when there isa precrack where the corrosion is the most severe leadingto the extension of the crack of the specimen As it isknown the crack extension is the most affecting factor forthe determination of fracture toughness [21]

In addition from Table 4 it can be seen that the corrosioninduced deterioration of fracture toughness is remarkablylarger than that of tensile strength under the same conditionsThis indicates that corrosion has larger effect on fracturetoughness than tensile strength of the metal The reason canbe that as explained above corrosion pits extend the existingdefects of the metal which reduce the fracture toughnessAlso the reduction of fracture toughness for cast iron isalmost twice that of steelThe results of all fourmeasurements


(a) For specimens at 6 days (steel left cast iron right)

(b) For specimens at 30 days (steel left cast iron right)

(c) For specimens at 90 days (steel left cast iron right)

(d) For specimens at 180 days (steel left cast iron right)

(e) For specimens at 270 days (steel left cast iron right)

(f) Details of a very corroded specimen cov-ered with rusts

Figure 7 Photos of corroded specimens at different exposure periods


0200400600800

10001200

0 30 60 90 120 150 180 210 240 270Immersion time (day)

Wei

ght l

oss (

gmiddotm

minus2)

Trend (pH = 800)

Trend (pH = 550)Trend (pH = 300) pH = 800

pH = 550

pH = 300

(a) For steel

0200400600800

1000120014001600


Wei

ght l

oss (

gmiddotm

minus2)

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron

Figure 8 Weight loss of specimen

290292294296298300302304306308310

0 90 180 270

Yiel

d str

engt

h (M

Pa)

Trend (pH = 800)

Trend (pH = 550)

Trend (pH = 300) pH = 800

pH = 550

pH = 300


(a) For steel

160165170175180185190195

0 90 180 270

Yiel

d str

engt

h (M

Pa)


Trend (pH = 800)

Trend (pH = 550)

Trend (pH = 300) pH = 800

pH = 550

pH = 300

(b) For cast iron

Figure 9 Tensile strength reduction of specimen

(corrosion current weight loss tensile strength and fracturetoughness) suggest that high carbon content in metal can notonly lead to more corrosion but also incur larger effect onmechanical properties

5 Observation and Discussion

From the tests and test results further observation anddiscussion can be made Photos of corroded specimenscan provide some insight into the behavior of corrosion indifferent environments and states From Figures 5 and 6 itcan be seen that corrosion current is the highest at the onsetof corrosion but from Figure 7(a) it can be seen that littlevisible change can be seen in terms of change of color (rust)of specimens although corrosion currents were at their peaksThis again indicates that the corrosion current measuresinstantaneous corrosion rate not the cumulative corrosion Atthis stage corrosive agents penetrated the oxidation film butlittle amount of corrosion was produced This suggests thatcorrosion rate of the specimens is high but actual corrosionin terms of products that is rusts is not accumulated Thecorrosion reaction can be expressed as follows (eg [35])

(a) Anodic reaction

Fe 997888rarr Fe2+ + 2eminus (5)

(b) Cathodic reaction

2H+ + 2eminus 997888rarr H2 (6)

After 6 days of immersion the corrosion currents droppedsharply indicating that the corrosion rate is reduced but cor-rosion itself continues This is demonstrated in Figure 7(a)where the solution turned into a brown color especially forthe solutionwith pH=55The corrosion reactions at his stagecan be expressed as follows [35]

4Fe2+ +O2 + 4H+= 4Fe3+ + 2H2O (7)

2Fe +O2 + 2H2O = 2Fe (OH)2 (8)

4Fe (OH)2 +O2 + 2H2O = 4Fe (OH)3 (9)

With the increase of corrosion hydrogen bubbles showed upin particular in more acidic solution for example pH = 30which can be explained by (6)


14000150001600017000180001900020000


Frac

ture

toug

hnes

s

(MPa

mminus05)

Trend (pH = 800)


pH = 550

pH = 300

(a) For steel

1000120014001600180020002200


Frac

ture

toug

hnes

s

(MPa

mminus05)

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron

Figure 10 Fracture toughness reduction of specimen

Table 4 Reduction of mechanical property ()

(a) For steel

Time period (day) pH Tensile strength Fracture toughness

9030 343 92955 263 75180 139 635

18030 466 115155 386 138080 331 1351

27030 477 149355 456 185080 443 1977

(b) For cast iron


9030 845 65655 324 20580 084 138

18030 862 203655 432 186380 998 3367

27030 1164 290555 989 327980 1431 3399

It was also observed that corrosion in different conditionswas of different forms Corrosion pits were formed aftersurface oxidation film was penetrated which was the casefor all three scenarios of pH values However corrosionpits on specimens in more acidic solution for example pH= 30 were fewer and more evenly distributed than thoseon specimens in less acidic solutions for example largerpH values This is shown in Figure 7(b) where at 30 dayslocalized corrosion pits were more obvious and corrosionproducts began to become flakes Deposits of corrosionproducts in two solutions with lower pH values (30 and 55)were in larger amount

Figure 7(c) shows that specimens were further corrodedand that corrosion products fell down to the bottom of thecontainers and covered up the surface of the specimens Thelatterwould prevent specimens from further corrosion so thatthe corrosion currents in specimens for all solutions reach thelowest values after 90 days

It has also been observed from Figures 9 and 10 thatthe reduction of mechanical properties both tensile strengthand fracture toughness does not follow the same trend ascorrosion current and weight loss That is smaller value ofpH that is more acidic solution does not result in largerreduction of mechanical properties for both tensile strengthand fracture toughness This may be because whilst the pHcan accelerate corrosion of metal it may neither acceleratethe reaction of corrosive agents with chemical elements ofmetal nor accelerate the change of microstructure of themetal In other words the effect of corrosion on mechanicalproperties of metals may not be in the same proportion asthat of pHon corrosion further indicating the randomness ofboth corrosion behavior and its effect onmechanical propertyof the metal Also the reduction of mechanical properties ismore scattered with respect to pH than corrosion currentand weight loss The precision of measurement can alsocontribute to the degree of the disperse Obviously moreexperiments are needed to produce sufficient and quality datafor developing models for corrosion induced deterioration ofmechanical properties of metals

For practical application of corrosion effect on mechani-cal properties ofmetal it is desirable to develop a relationshipbetween measurable parameters of corrosion for exampleweight loss and the reduction of mechanical properties forexample tensile strength and fracture toughness This hasbeen attempted in this study Since the analysis of resultspresented in the previous section suggests that weight losscan be a better measure of corrosion than corrosion currentit is used in developing the relationship Also ideally moredata points (than four) can produce better correlation of thisrelation but time and resources are always the constraintsLiterature and research experience (eg [32]) suggest thatthree data points are minimum Figures 11 and 12 show thevariation of tensile strength and fracture toughness with


0001002003004005006007

0 200 400 600 800 1000 1200

Yiel

d str

engt

h re

duct

ion

()

Weight loss (g)

R2 = 09348y = 00002x minus 00025

R2 = 09931y = 7E minus 05x + 0014

R2 = 09906

y = 6E minus 05x + 00024

Trend (pH = 800)


pH = 550

pH = 300

(a) For steel

0002004006008

01012014016

0 200 400 600 800 1000 1200 1400

Yiel

d str

engt

h re

duct

ion

()

Weight loss (g)

R2 = 09142y = 00004x minus 00167

R2 = 04677

y = 00002x + 00112

R2 = 0928

y = 8E minus 05x + 00074

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron

Figure 11 Tensile strength reduction with weight loss

0

005

01

015

02

025

0 200 400 600 800 1000 1200

Frac

ture

toug

hnes

s red

uctio

n (

)

Weight loss (g)

R2 = 08532

y = 00008x + 00165

R2 = 08098

y = 00004x + 00332

R2 = 07332

y = 00001x + 00305

Trend (pH = 800)

Trend (pH = 550)

Trend (pH = 300) pH = 800

pH = 550

pH = 300

(a) For steel

0005

01015

02025

03035

04045

0 200 400 600 800 1000 1200 1400

Frac

ture

toug

hnes

s red

uctio

n (

)

Weight loss (g)

R2 = 05454

y = 00008x + 01085

R2 = 07184

y = 00007x + 00744

R2 = 08383

y = 00002x minus 00247

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron

Figure 12 Fracture toughness reduction with weight loss

weight loss for both steel and cast iron specimens under threetested environments As can be seen from the figures thereduction of both tensile strength and fracture toughness is byand large in linear relationwithweight lossThough the lowerpH values contribute to greater weight losses mechanicalproperties are more sensitive to weight loss in higher pHvalues that is steeper trend lines as shown in Figures 11 and12 In practice pH values of soil cannot be lower than 5 Assuch results of this study for pH lower than 5 can be closer toreality and hence can be of more practical use

It needs to be noted that the test results presented in thepaper are one step towards establishing understanding andknowledge on corrosion effect on mechanical properties ofmetals The significance of these results lies more in theirtrend more qualitatively than quantitatively It is acknowl-edged that more tests are necessary to produce larger poolof data for sensible quantitative analysis based on which wedevelop theories and models for corrosion induced deterio-ration of mechanical properties of metals This work is beingcontinued by corresponding authorrsquos research team with

more test specimens under different testing variables andenvironments such as real soil environment More resultswill be submitted for publication once they are producedprocessed and analyzed

6 Conclusion

A comprehensive test program has been presented in thepaper to investigate the effect of corrosion on mechanicalproperties of buried metal pipes The corrosion of two typesof widely used metals that is cast iron and steel and itseffect on their mechanical properties have been observedmonitored and evaluated in three different environmentsas represented by pH values From the analysis of the testresults a relationship between corrosion and deteriorationof mechanical property of metals has been developed It hasbeen found that themore acidic the environment is themorecorrosion of metal occurs and that grey cast iron corrodesmore than carbon steel under the same environment It hasalso been found that the corrosion reduces both the tensile


strength and fracture toughness of the metal and the latterreduced more than the former It can be concluded that theresults presented in the paper can contribute to the body ofknowledge of corrosion behavior and its effect onmechanicalproperties of metals in soil environmentThis knowledge canenable more accurate prediction of failures of metal pipes

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

Financial support from Natural Science Foundation ofHubei Province of China under 2015CFB510 FundamentalResearch Funds byWuhanUniversity of Technology of Chinaunder 2015IVA012 and Australian Research Council underDP140101547 and LP150100413 is gratefully acknowledged

References

[1] Y Li B Jiang H Zhao and C Tao ldquoExperimental studyon internal corrosion of grey cast iron pipeline in waterdistributionrdquo Journal of Chemical Information and Modelingvol 53 article 160 1989

[2] J M Makar ldquoPreliminary analysis of failures in grey cast ironwater pipesrdquo Engineering Failure Analysis vol 7 no 1 pp 43ndash53 2000

[3] National Water Commission Australia National performancereport 2009-10 httparchivenwcgovau dataassetspdffile001511265NPR urbanpdf

[4] B Rajani S McDonald and G Felio ldquoWater mains break dataon different pipe materials for 1992 and 1993rdquo Report A-70191National Research Council of Canada Ottawa Canada 1995

[5] H Mohebbi and C Q Li ldquoExperimental investigation oncorrosion of cast iron pipesrdquo International Journal of Corrosionvol 2011 Article ID 506501 17 pages 2011

[6] R A de Sena I N Bastos and G M Platt ldquoTheoreticaland experimental aspects of the corrosivity of simulated soilsolutionsrdquo ISRN Chemical Engineering vol 2012 Article ID103715 6 pages 2012

[7] C Goulter ldquoAn analysis of pipe breakage in urban waterdistribution networksrdquo Canadian Journal of Civil Engineeringvol 12 no 2 pp 286ndash293 1985

[8] M L Doleac S L Lackey and G N Bratton ldquoPrediction oftime-to failure for buried cast iron piperdquo in Proceedings of theAnnual Conference of the American Water Works Association(AWWA rsquo80) pp 31ndash38 Denver Colo USA 1980

[9] S W Dean Jr and G D Grab ldquoCorrosion of carbon steel byconcentrated sulfuric acidrdquo Materials Performance vol 24 no6 pp 21ndash25 1985

[10] D K OrsquoDay R Weiss S Chiavari and D Blair Water MainEvaluation for RehabilitationReplacement American WaterWorks Association Research Foundation Denver Colo USA1986

[11] M Randall-Smith A Russell and R Oliphant GuidanceManual for the Structural Condition Assessment of the TrunkMains Water Research Centre Swindon UK 1992

[12] G J Kirmeyer W Richards and C D Smith An Assessmentof Water Distribution Systems and Associated Research NeedsAWWA 1994

[13] L Camarinopoulos A Chatzoulis S Frontistou-Yannas andV Kallidromitis ldquoAssessment of the time-dependent structuralreliability of buried water mainsrdquo Reliability Engineering andSystem Safety vol 65 no 1 pp 41ndash53 1999

[14] R Sadiq B Rajani and Y Kleiner ldquoProbabilistic risk analysisof corrosion associated failures in cast iron water mainsrdquoReliability Engineering and System Safety vol 86 no 1 pp 1ndash102004

[15] Z Panossian N L de Almeida R M F de Sousa G de SouzaPimenta and R B S Marques ldquoCorrosion of carbon steel pipesand tanks by concentrated sulfuric acid a reviewrdquo CorrosionScience vol 58 pp 1ndash11 2012

[16] L A Rossman R A Brown P C Singer and J R NuckolsldquoDBP formation kinetics in a simulated distribution systemrdquoWater Research vol 35 no 14 pp 3483ndash3489 2001

[17] V Chacker and J D Palmer Eds Effect of Soil Characteristicon Corrosion ASTM Special Technical Publication Ann ArborMich USA 1989

[18] T M Liu Y H Wu S X Luo and C Sun ldquoEffect of soilcompositions on the electrochemical corrosion behavior ofcarbon steel in simulated soil solution Einfluss der Erdbo-denzusammensetzung auf das elektrochemische Verhalten vonKohlenstoffstahlen in simulierten Erdbodenlosungenrdquo Materi-alwissenschaft und Werkstofftechnik vol 41 no 4 pp 228ndash2332010

[19] B Rajani and Y Kleiner ldquoComprehensive review of structuraldeterioration of water mains physically based modelsrdquo UrbanWater vol 3 no 3 pp 151ndash164 2001

[20] J Li R Tang J-F Liu and J-S Liu ldquoThe analysis of soilcorrosion factors in long-distance oil pipelinerdquo EquipmentManufacturing no 9 pp 31ndash33 2012

[21] C Q Li and S T Yang ldquoStress intensity factors for highaspect ratio semi-elliptical internal surface cracks in pipesrdquoInternational Journal of Pressure Vessels and Piping vol 96-97pp 13ndash23 2012

[22] P Marshall The Residual Structural Properties of Cast IronPipesmdashStructural and Design Criteria for Linings for WaterMains Water Industry Research London UK 2001

[23] S K Singh and A K Mukherjee ldquoKinetics of mild steelcorrosion in aqueous acetic acid solutionsrdquo Journal of MaterialsScience and Technology vol 26 no 3 pp 264ndash269 2010

[24] Y H Wu T M Liu S X Luo and C Sun ldquoCorrosioncharacteristics ofQ235 steel in simulatedYingtan soil solutionsrdquoMaterialwissenschaft und Werkstofftechnik vol 41 no 3 pp142ndash146 2010

[25] ASTM E8M13 Standard Test Methods for Tension Testing ofMetallic Materials ASTM International 2013

[26] ASTM-E1820 Standard Test Method for Measurement of Frac-ture Toughness ASTM International 2013

[27] Z Zhao Y Lu and G Sun ldquoExperimental measuring fracturetoughness of Q235 steel by J integralrdquo Journal of WuhanUniversity of Technology vol 24 no 4 pp 111ndash112 2002

[28] D Dong X Zhu and X Mei ldquoAbaqus Q235 simulation onfracture toughness of material Q235 based on flexibility deter-mination method of Abaqusrdquo Computer Aided Engineering vol21 no 4 pp 4ndash6 2012

[29] MWasim C Q Li D J Robert andMMahmoodian ldquoExper-imental investigation of factors influencing external corrosion


of buried pipesrdquo in Proceedings of the 4th International Confer-ence on Sustainability Construction Materials and Technologies(SCMT rsquo16) Las Vegas Nev USA August 2016

[30] M Yan J Wang E Han andW Ke ldquoLocal environment undersimulated disbonded coating on steel pipelines in soil solutionrdquoCorrosion Science vol 50 no 5 pp 1331ndash1339 2008

[31] Z Y Liu X G Li C W Du and Y F Cheng ldquoLocal additionalpotential model for effect of strain rate on SCC of pipeline steelin an acidic soil solutionrdquo Corrosion Science vol 51 no 12 pp2863ndash2871 2009

[32] C Q Li ldquoInitiation of chloride-induced reinforcement corro-sion in concrete structural membersmdashexperimentationrdquo ACIStructural Journal vol 98 no 4 pp 502ndash510 2001

[33] F Long W Zheng C Chen Z Xu and Q Han ldquoInfluenceof temperature CO

2partial pressure flow rate and pH value

on uniform corrosion rate of X65 pipeline steelrdquo Corrosion andProtection vol 26 no 7 pp 290ndash294 2005

[34] ASTM G31-2012a Standard Guide for Laboratory ImmersionCorrosion Testing of Metals ASTM International 2012

[35] L L Shreir R A Jarman and G T Burstein CorrosionButterworth Heinemann 2010

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


pipes in soil [20] Metal corrosion in soils is determined pri-marily by a combined effect of these factors It also dependson the physical and chemical characteristics of the soils

A review of published literature on pipe corrosion ascited above (and also see references) reveals that most of thecurrent research focuses on corrosionmechanisms corrosionprogress and corrosion rate frommaterial perspective Littleresearch has been undertaken on the effect of corrosion onmechanical property change of pipe materials and almost noresearch has been conducted on corrosion effect on fracturetoughness of pipe materials As is well known it is themechanical properties of the pipe materials that govern thebehavior and eventual failure of the pipes It is thereforeimperative to thoroughly examine the effect of metal cor-rosion on its mechanical properties The understanding andknowledge of corrosion induced deterioration of mechanicalproperties ofmetals can prevent future failures ofmetal pipes

There are two main modes of pipe failure by rupturedue to the reduction of wall thickness of the pipes and byfracture due to the stress concentration at the tips of cracksfor example corrosion pits or in general defects in the pipes[21] The mechanical properties corresponding to these twofailure modes are tensile strength and fracture toughness ofthemetal A detailed examination of most published researchin this area (see references) suggests that current researchon corrosion induced pipe failures focuses more on loss ofstrength than toughness An inspection of failures of trunkmains in service reveals that most cast iron water mainfailures are of fracture type that is the failure is caused by thegrowth of a crack and subsequent collapse of the pipe [22] Itis therefore essential to study the deterioration of both tensilestrength and fracture toughness of the metals to enable moreaccurate prediction of pipe failures

The intention of this paper is to experimentally investigatethe effect of corrosion on mechanical properties of metalsused as pipe material A comprehensive test program isdesigned to observe monitor and evaluate corrosion behav-ior of metals and its effect on their mechanical properties indifferent environments Two types ofmetals namely cast ironand steel are tested under corrosion in three environmentsas represented by pH values From the analysis of testresults a relationship between corrosion and deteriorationof mechanical property of metals is developed It is believedthat tests on the effect of corrosion on mechanical propertiesof metals are one of few of the kind The results producedfrom the tests can contribute to the body of knowledge ofcorrosion behavior and its effect on mechanical propertiesof metal in soil environment which can equip engineers andassetmanagers inmitigating the risk of failures ofmetal pipes

2 Design of Test Specimens

21 Specimen Materials Cast iron and steel have been themost predominant pipeline material before the 1980s [21]Among various types of cast irons and steel grey cast iron andcarbon steel are perhaps the most widely used pipe materials[12 23] Because of this it is reasonable to select these twotypes of materials for corrosion investigation due to theirwide use and also long service Cast iron and steel have quite

Table 1 Chemical composition of test materials (wt)

Material C S P Mn SiQ235 steel 0176 0023 0019 0465 0233HT200 cast iron 32 012 0015 09 16

differentmechanical properties although they have been usedfor the same purpose of pipes Cast iron is brittle materialwhilst steel is ductile Cast iron has been widely used inpipeline industry due to its comparatively low cost but ithas been replaced by steel in pipeline industry for its greaterstrength and ductility

As is well known the mechanical properties of metalare affected by its chemical composition morphology andmicrostructure which vary significantly In this study Q235plain carbon steel and HT200 grey cast iron are selected asthe testing materials due to their wide use in pipe industryin China and availability on market [1 24] The chemicalcomposition of Q235 steel and HT200 cast iron is shown inTable 1

22 Specimens for Tensile Strength Specimens for tensilestrength test were made according to ASTM E8M13 StandardTest Methods for Tension Testing of Metallic Materials [25]The testing specimens are recommended single-edge bend[SE(B)] in the standard of which the dimensions shouldcomply with the following requirement

119871 ge 4119863 (1)

where 119871 is the gauge length and 119863 is the diameter of themiddle part of the specimen within gauge length 119871 Forthe sake of comparison the specimens of the two differentmaterials for tensile strength test are intentionally made withthe same dimensions The specimen for tensile strength isshown in Figure 1(a)

23 Specimens for Fracture Toughness Specimens for fracturetoughness test were made according to ASTM E1820-13 Stan-dard Test Method for Measurement of Fracture Toughness[26] In this standard the key is to control the width of thespecimen since it is the most important factor that affectsthe resulting fracture toughness Depending on the width ofthe specimens there can be two types of fractures the planestress fracture and plane strain fracture For the plane stressfracture the fracture toughness decreases with the increaseof specimen width and stabilizes at a certain width forwhich plane strain fracture occurs This width is determinedaccording to ASTM E1820-13 as follows

119861 ge 25 (119870IC120590119910

)

2

(2)

where 119861 is the width of the specimen 119870IC is the fracturetoughness and 120590119910 is the yield strength of the material

By (2) the width for selected cast iron specimen withthe grade HT200 was calculated to be 119861 = 20mm Howeverfor the selected Q235 steel the calculated width for the


D = 250

D1 = 15D = 200

L2 = 83L1 = 317 L = 140

+

+


2413

80

21 a = 200

W = 400

B = 200L = 1800







2O

Content 092 154 217 060



4sdot7H2O KCl NaHCO

3

Content 0036 0190 0069 0540

3 Test Methodology




























0001002003004005006007008

0 30 60 90 120 150 180 210 240 270

Cor

rosio

n cu

rren

t (m

A)



(a) pH = 30

0

001

002

003

004

005

006

0 30 60 90 120 150 180 210 240 270

Cor

rosio

n cu

rren

t (m

A)



(b) pH = 55

0

001

002

003

004

005

006

0 30 60 90 120 150 180 210 240 270

Cor

rosio

n cu

rren

t (m

A)



(c) pH = 80






119870(119894) = [119875119894119878

(119861119861119873)1211988232]119891(119886119894

119882) (3)


000

002

004

006

008

010

0 30 60 90 120 150 180 210 240 270

Cor

rosio

n cu

rren

t (m

A)



(a) pH = 30

Cor

rosio

n cu

rren

t (m

A)


000001002003004005006007

0 30 60 90 120 150 180 210 240 270


(b) pH = 55

Cor

rosio

n cu

rren

t (m

A)


000001002003004005006007

0 30 60 90 120 150 180 210 240 270


(c) pH = 80


where

119891(119886119894

119882) =


2)]

2 (1 + 2119886119894119882) (1 minus 119886119894119882)32

(4)














0200400600800

10001200


Wei

ght l

oss (

gmiddotm

minus2)

Trend (pH = 800)


pH = 550

pH = 300

(a) For steel

0200400600800

1000120014001600


Wei

ght l

oss (

gmiddotm

minus2)

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron


290292294296298300302304306308310

0 90 180 270

Yiel

d str

engt

h (M

Pa)

Trend (pH = 800)

Trend (pH = 550)

Trend (pH = 300) pH = 800

pH = 550

pH = 300


(a) For steel

160165170175180185190195

0 90 180 270

Yiel

d str

engt

h (M

Pa)


Trend (pH = 800)

Trend (pH = 550)

Trend (pH = 300) pH = 800

pH = 550

pH = 300

(b) For cast iron





(a) Anodic reaction



2H+ + 2eminus 997888rarr H2 (6)


4Fe2+ +O2 + 4H+= 4Fe3+ + 2H2O (7)

2Fe +O2 + 2H2O = 2Fe (OH)2 (8)

4Fe (OH)2 +O2 + 2H2O = 4Fe (OH)3 (9)



14000150001600017000180001900020000


Frac

ture

toug

hnes

s

(MPa

mminus05)

Trend (pH = 800)


pH = 550

pH = 300

(a) For steel

1000120014001600180020002200


Frac

ture

toug

hnes

s

(MPa

mminus05)

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron



(a) For steel


9030 343 92955 263 75180 139 635

18030 466 115155 386 138080 331 1351

27030 477 149355 456 185080 443 1977

(b) For cast iron


9030 845 65655 324 20580 084 138

18030 862 203655 432 186380 998 3367

27030 1164 290555 989 327980 1431 3399






0001002003004005006007

0 200 400 600 800 1000 1200

Yiel

d str

engt

h re

duct

ion

()

Weight loss (g)

R2 = 09348y = 00002x minus 00025

R2 = 09931y = 7E minus 05x + 0014

R2 = 09906

y = 6E minus 05x + 00024

Trend (pH = 800)


pH = 550

pH = 300

(a) For steel

0002004006008

01012014016

0 200 400 600 800 1000 1200 1400

Yiel

d str

engt

h re

duct

ion

()

Weight loss (g)

R2 = 09142y = 00004x minus 00167

R2 = 04677

y = 00002x + 00112

R2 = 0928

y = 8E minus 05x + 00074

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron


0

005

01

015

02

025

0 200 400 600 800 1000 1200

Frac

ture

toug

hnes

s red

uctio

n (

)

Weight loss (g)

R2 = 08532

y = 00008x + 00165

R2 = 08098

y = 00004x + 00332

R2 = 07332

y = 00001x + 00305

Trend (pH = 800)

Trend (pH = 550)

Trend (pH = 300) pH = 800

pH = 550

pH = 300

(a) For steel

0005

01015

02025

03035

04045

0 200 400 600 800 1000 1200 1400

Frac

ture

toug

hnes

s red

uctio

n (

)

Weight loss (g)

R2 = 05454

y = 00008x + 01085

R2 = 07184

y = 00007x + 00744

R2 = 08383

y = 00002x minus 00247

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron





6 Conclusion




Competing Interests


Acknowledgments


References















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




D = 250

D1 = 15D = 200

L2 = 83L1 = 317 L = 140

+

+


2413

80

21 a = 200

W = 400

B = 200L = 1800







2O

Content 092 154 217 060



4sdot7H2O KCl NaHCO

3

Content 0036 0190 0069 0540

3 Test Methodology




























0001002003004005006007008

0 30 60 90 120 150 180 210 240 270

Cor

rosio

n cu

rren

t (m

A)



(a) pH = 30

0

001

002

003

004

005

006

0 30 60 90 120 150 180 210 240 270

Cor

rosio

n cu

rren

t (m

A)



(b) pH = 55

0

001

002

003

004

005

006

0 30 60 90 120 150 180 210 240 270

Cor

rosio

n cu

rren

t (m

A)



(c) pH = 80






119870(119894) = [119875119894119878

(119861119861119873)1211988232]119891(119886119894

119882) (3)


000

002

004

006

008

010

0 30 60 90 120 150 180 210 240 270

Cor

rosio

n cu

rren

t (m

A)



(a) pH = 30

Cor

rosio

n cu

rren

t (m

A)


000001002003004005006007

0 30 60 90 120 150 180 210 240 270


(b) pH = 55

Cor

rosio

n cu

rren

t (m

A)


000001002003004005006007

0 30 60 90 120 150 180 210 240 270


(c) pH = 80


where

119891(119886119894

119882) =


2)]

2 (1 + 2119886119894119882) (1 minus 119886119894119882)32

(4)














0200400600800

10001200


Wei

ght l

oss (

gmiddotm

minus2)

Trend (pH = 800)


pH = 550

pH = 300

(a) For steel

0200400600800

1000120014001600


Wei

ght l

oss (

gmiddotm

minus2)

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron


290292294296298300302304306308310

0 90 180 270

Yiel

d str

engt

h (M

Pa)

Trend (pH = 800)

Trend (pH = 550)

Trend (pH = 300) pH = 800

pH = 550

pH = 300


(a) For steel

160165170175180185190195

0 90 180 270

Yiel

d str

engt

h (M

Pa)


Trend (pH = 800)

Trend (pH = 550)

Trend (pH = 300) pH = 800

pH = 550

pH = 300

(b) For cast iron





(a) Anodic reaction



2H+ + 2eminus 997888rarr H2 (6)


4Fe2+ +O2 + 4H+= 4Fe3+ + 2H2O (7)

2Fe +O2 + 2H2O = 2Fe (OH)2 (8)

4Fe (OH)2 +O2 + 2H2O = 4Fe (OH)3 (9)



14000150001600017000180001900020000


Frac

ture

toug

hnes

s

(MPa

mminus05)

Trend (pH = 800)


pH = 550

pH = 300

(a) For steel

1000120014001600180020002200


Frac

ture

toug

hnes

s

(MPa

mminus05)

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron



(a) For steel


9030 343 92955 263 75180 139 635

18030 466 115155 386 138080 331 1351

27030 477 149355 456 185080 443 1977

(b) For cast iron


9030 845 65655 324 20580 084 138

18030 862 203655 432 186380 998 3367

27030 1164 290555 989 327980 1431 3399






0001002003004005006007

0 200 400 600 800 1000 1200

Yiel

d str

engt

h re

duct

ion

()

Weight loss (g)

R2 = 09348y = 00002x minus 00025

R2 = 09931y = 7E minus 05x + 0014

R2 = 09906

y = 6E minus 05x + 00024

Trend (pH = 800)


pH = 550

pH = 300

(a) For steel

0002004006008

01012014016

0 200 400 600 800 1000 1200 1400

Yiel

d str

engt

h re

duct

ion

()

Weight loss (g)

R2 = 09142y = 00004x minus 00167

R2 = 04677

y = 00002x + 00112

R2 = 0928

y = 8E minus 05x + 00074

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron


0

005

01

015

02

025

0 200 400 600 800 1000 1200

Frac

ture

toug

hnes

s red

uctio

n (

)

Weight loss (g)

R2 = 08532

y = 00008x + 00165

R2 = 08098

y = 00004x + 00332

R2 = 07332

y = 00001x + 00305

Trend (pH = 800)

Trend (pH = 550)

Trend (pH = 300) pH = 800

pH = 550

pH = 300

(a) For steel

0005

01015

02025

03035

04045

0 200 400 600 800 1000 1200 1400

Frac

ture

toug

hnes

s red

uctio

n (

)

Weight loss (g)

R2 = 05454

y = 00008x + 01085

R2 = 07184

y = 00007x + 00744

R2 = 08383

y = 00002x minus 00247

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron





6 Conclusion




Competing Interests


Acknowledgments


References















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



























0001002003004005006007008

0 30 60 90 120 150 180 210 240 270

Cor

rosio

n cu

rren

t (m

A)



(a) pH = 30

0

001

002

003

004

005

006

0 30 60 90 120 150 180 210 240 270

Cor

rosio

n cu

rren

t (m

A)



(b) pH = 55

0

001

002

003

004

005

006

0 30 60 90 120 150 180 210 240 270

Cor

rosio

n cu

rren

t (m

A)



(c) pH = 80






119870(119894) = [119875119894119878

(119861119861119873)1211988232]119891(119886119894

119882) (3)


000

002

004

006

008

010

0 30 60 90 120 150 180 210 240 270

Cor

rosio

n cu

rren

t (m

A)



(a) pH = 30

Cor

rosio

n cu

rren

t (m

A)


000001002003004005006007

0 30 60 90 120 150 180 210 240 270


(b) pH = 55

Cor

rosio

n cu

rren

t (m

A)


000001002003004005006007

0 30 60 90 120 150 180 210 240 270


(c) pH = 80


where

119891(119886119894

119882) =


2)]

2 (1 + 2119886119894119882) (1 minus 119886119894119882)32

(4)














0200400600800

10001200


Wei

ght l

oss (

gmiddotm

minus2)

Trend (pH = 800)


pH = 550

pH = 300

(a) For steel

0200400600800

1000120014001600


Wei

ght l

oss (

gmiddotm

minus2)

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron


290292294296298300302304306308310

0 90 180 270

Yiel

d str

engt

h (M

Pa)

Trend (pH = 800)

Trend (pH = 550)

Trend (pH = 300) pH = 800

pH = 550

pH = 300


(a) For steel

160165170175180185190195

0 90 180 270

Yiel

d str

engt

h (M

Pa)


Trend (pH = 800)

Trend (pH = 550)

Trend (pH = 300) pH = 800

pH = 550

pH = 300

(b) For cast iron





(a) Anodic reaction



2H+ + 2eminus 997888rarr H2 (6)


4Fe2+ +O2 + 4H+= 4Fe3+ + 2H2O (7)

2Fe +O2 + 2H2O = 2Fe (OH)2 (8)

4Fe (OH)2 +O2 + 2H2O = 4Fe (OH)3 (9)



14000150001600017000180001900020000


Frac

ture

toug

hnes

s

(MPa

mminus05)

Trend (pH = 800)


pH = 550

pH = 300

(a) For steel

1000120014001600180020002200


Frac

ture

toug

hnes

s

(MPa

mminus05)

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron



(a) For steel


9030 343 92955 263 75180 139 635

18030 466 115155 386 138080 331 1351

27030 477 149355 456 185080 443 1977

(b) For cast iron


9030 845 65655 324 20580 084 138

18030 862 203655 432 186380 998 3367

27030 1164 290555 989 327980 1431 3399






0001002003004005006007

0 200 400 600 800 1000 1200

Yiel

d str

engt

h re

duct

ion

()

Weight loss (g)

R2 = 09348y = 00002x minus 00025

R2 = 09931y = 7E minus 05x + 0014

R2 = 09906

y = 6E minus 05x + 00024

Trend (pH = 800)


pH = 550

pH = 300

(a) For steel

0002004006008

01012014016

0 200 400 600 800 1000 1200 1400

Yiel

d str

engt

h re

duct

ion

()

Weight loss (g)

R2 = 09142y = 00004x minus 00167

R2 = 04677

y = 00002x + 00112

R2 = 0928

y = 8E minus 05x + 00074

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron


0

005

01

015

02

025

0 200 400 600 800 1000 1200

Frac

ture

toug

hnes

s red

uctio

n (

)

Weight loss (g)

R2 = 08532

y = 00008x + 00165

R2 = 08098

y = 00004x + 00332

R2 = 07332

y = 00001x + 00305

Trend (pH = 800)

Trend (pH = 550)

Trend (pH = 300) pH = 800

pH = 550

pH = 300

(a) For steel

0005

01015

02025

03035

04045

0 200 400 600 800 1000 1200 1400

Frac

ture

toug

hnes

s red

uctio

n (

)

Weight loss (g)

R2 = 05454

y = 00008x + 01085

R2 = 07184

y = 00007x + 00744

R2 = 08383

y = 00002x minus 00247

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron





6 Conclusion




Competing Interests


Acknowledgments


References















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




000

002

004

006

008

010

0 30 60 90 120 150 180 210 240 270

Cor

rosio

n cu

rren

t (m

A)



(a) pH = 30

Cor

rosio

n cu

rren

t (m

A)


000001002003004005006007

0 30 60 90 120 150 180 210 240 270


(b) pH = 55

Cor

rosio

n cu

rren

t (m

A)


000001002003004005006007

0 30 60 90 120 150 180 210 240 270


(c) pH = 80


where

119891(119886119894

119882) =


2)]

2 (1 + 2119886119894119882) (1 minus 119886119894119882)32

(4)














0200400600800

10001200


Wei

ght l

oss (

gmiddotm

minus2)

Trend (pH = 800)


pH = 550

pH = 300

(a) For steel

0200400600800

1000120014001600


Wei

ght l

oss (

gmiddotm

minus2)

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron


290292294296298300302304306308310

0 90 180 270

Yiel

d str

engt

h (M

Pa)

Trend (pH = 800)

Trend (pH = 550)

Trend (pH = 300) pH = 800

pH = 550

pH = 300


(a) For steel

160165170175180185190195

0 90 180 270

Yiel

d str

engt

h (M

Pa)


Trend (pH = 800)

Trend (pH = 550)

Trend (pH = 300) pH = 800

pH = 550

pH = 300

(b) For cast iron





(a) Anodic reaction



2H+ + 2eminus 997888rarr H2 (6)


4Fe2+ +O2 + 4H+= 4Fe3+ + 2H2O (7)

2Fe +O2 + 2H2O = 2Fe (OH)2 (8)

4Fe (OH)2 +O2 + 2H2O = 4Fe (OH)3 (9)



14000150001600017000180001900020000


Frac

ture

toug

hnes

s

(MPa

mminus05)

Trend (pH = 800)


pH = 550

pH = 300

(a) For steel

1000120014001600180020002200


Frac

ture

toug

hnes

s

(MPa

mminus05)

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron



(a) For steel


9030 343 92955 263 75180 139 635

18030 466 115155 386 138080 331 1351

27030 477 149355 456 185080 443 1977

(b) For cast iron


9030 845 65655 324 20580 084 138

18030 862 203655 432 186380 998 3367

27030 1164 290555 989 327980 1431 3399






0001002003004005006007

0 200 400 600 800 1000 1200

Yiel

d str

engt

h re

duct

ion

()

Weight loss (g)

R2 = 09348y = 00002x minus 00025

R2 = 09931y = 7E minus 05x + 0014

R2 = 09906

y = 6E minus 05x + 00024

Trend (pH = 800)


pH = 550

pH = 300

(a) For steel

0002004006008

01012014016

0 200 400 600 800 1000 1200 1400

Yiel

d str

engt

h re

duct

ion

()

Weight loss (g)

R2 = 09142y = 00004x minus 00167

R2 = 04677

y = 00002x + 00112

R2 = 0928

y = 8E minus 05x + 00074

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron


0

005

01

015

02

025

0 200 400 600 800 1000 1200

Frac

ture

toug

hnes

s red

uctio

n (

)

Weight loss (g)

R2 = 08532

y = 00008x + 00165

R2 = 08098

y = 00004x + 00332

R2 = 07332

y = 00001x + 00305

Trend (pH = 800)

Trend (pH = 550)

Trend (pH = 300) pH = 800

pH = 550

pH = 300

(a) For steel

0005

01015

02025

03035

04045

0 200 400 600 800 1000 1200 1400

Frac

ture

toug

hnes

s red

uctio

n (

)

Weight loss (g)

R2 = 05454

y = 00008x + 01085

R2 = 07184

y = 00007x + 00744

R2 = 08383

y = 00002x minus 00247

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron





6 Conclusion




Competing Interests


Acknowledgments


References















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials












0200400600800

10001200


Wei

ght l

oss (

gmiddotm

minus2)

Trend (pH = 800)


pH = 550

pH = 300

(a) For steel

0200400600800

1000120014001600


Wei

ght l

oss (

gmiddotm

minus2)

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron


290292294296298300302304306308310

0 90 180 270

Yiel

d str

engt

h (M

Pa)

Trend (pH = 800)

Trend (pH = 550)

Trend (pH = 300) pH = 800

pH = 550

pH = 300


(a) For steel

160165170175180185190195

0 90 180 270

Yiel

d str

engt

h (M

Pa)


Trend (pH = 800)

Trend (pH = 550)

Trend (pH = 300) pH = 800

pH = 550

pH = 300

(b) For cast iron





(a) Anodic reaction



2H+ + 2eminus 997888rarr H2 (6)


4Fe2+ +O2 + 4H+= 4Fe3+ + 2H2O (7)

2Fe +O2 + 2H2O = 2Fe (OH)2 (8)

4Fe (OH)2 +O2 + 2H2O = 4Fe (OH)3 (9)



14000150001600017000180001900020000


Frac

ture

toug

hnes

s

(MPa

mminus05)

Trend (pH = 800)


pH = 550

pH = 300

(a) For steel

1000120014001600180020002200


Frac

ture

toug

hnes

s

(MPa

mminus05)

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron



(a) For steel


9030 343 92955 263 75180 139 635

18030 466 115155 386 138080 331 1351

27030 477 149355 456 185080 443 1977

(b) For cast iron


9030 845 65655 324 20580 084 138

18030 862 203655 432 186380 998 3367

27030 1164 290555 989 327980 1431 3399






0001002003004005006007

0 200 400 600 800 1000 1200

Yiel

d str

engt

h re

duct

ion

()

Weight loss (g)

R2 = 09348y = 00002x minus 00025

R2 = 09931y = 7E minus 05x + 0014

R2 = 09906

y = 6E minus 05x + 00024

Trend (pH = 800)


pH = 550

pH = 300

(a) For steel

0002004006008

01012014016

0 200 400 600 800 1000 1200 1400

Yiel

d str

engt

h re

duct

ion

()

Weight loss (g)

R2 = 09142y = 00004x minus 00167

R2 = 04677

y = 00002x + 00112

R2 = 0928

y = 8E minus 05x + 00074

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron


0

005

01

015

02

025

0 200 400 600 800 1000 1200

Frac

ture

toug

hnes

s red

uctio

n (

)

Weight loss (g)

R2 = 08532

y = 00008x + 00165

R2 = 08098

y = 00004x + 00332

R2 = 07332

y = 00001x + 00305

Trend (pH = 800)

Trend (pH = 550)

Trend (pH = 300) pH = 800

pH = 550

pH = 300

(a) For steel

0005

01015

02025

03035

04045

0 200 400 600 800 1000 1200 1400

Frac

ture

toug

hnes

s red

uctio

n (

)

Weight loss (g)

R2 = 05454

y = 00008x + 01085

R2 = 07184

y = 00007x + 00744

R2 = 08383

y = 00002x minus 00247

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron





6 Conclusion




Competing Interests


Acknowledgments


References















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




14000150001600017000180001900020000


Frac

ture

toug

hnes

s

(MPa

mminus05)

Trend (pH = 800)


pH = 550

pH = 300

(a) For steel

1000120014001600180020002200


Frac

ture

toug

hnes

s

(MPa

mminus05)

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron



(a) For steel


9030 343 92955 263 75180 139 635

18030 466 115155 386 138080 331 1351

27030 477 149355 456 185080 443 1977

(b) For cast iron


9030 845 65655 324 20580 084 138

18030 862 203655 432 186380 998 3367

27030 1164 290555 989 327980 1431 3399






0001002003004005006007

0 200 400 600 800 1000 1200

Yiel

d str

engt

h re

duct

ion

()

Weight loss (g)

R2 = 09348y = 00002x minus 00025

R2 = 09931y = 7E minus 05x + 0014

R2 = 09906

y = 6E minus 05x + 00024

Trend (pH = 800)


pH = 550

pH = 300

(a) For steel

0002004006008

01012014016

0 200 400 600 800 1000 1200 1400

Yiel

d str

engt

h re

duct

ion

()

Weight loss (g)

R2 = 09142y = 00004x minus 00167

R2 = 04677

y = 00002x + 00112

R2 = 0928

y = 8E minus 05x + 00074

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron


0

005

01

015

02

025

0 200 400 600 800 1000 1200

Frac

ture

toug

hnes

s red

uctio

n (

)

Weight loss (g)

R2 = 08532

y = 00008x + 00165

R2 = 08098

y = 00004x + 00332

R2 = 07332

y = 00001x + 00305

Trend (pH = 800)

Trend (pH = 550)

Trend (pH = 300) pH = 800

pH = 550

pH = 300

(a) For steel

0005

01015

02025

03035

04045

0 200 400 600 800 1000 1200 1400

Frac

ture

toug

hnes

s red

uctio

n (

)

Weight loss (g)

R2 = 05454

y = 00008x + 01085

R2 = 07184

y = 00007x + 00744

R2 = 08383

y = 00002x minus 00247

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron





6 Conclusion




Competing Interests


Acknowledgments


References















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0001002003004005006007

0 200 400 600 800 1000 1200

Yiel

d str

engt

h re

duct

ion

()

Weight loss (g)

R2 = 09348y = 00002x minus 00025

R2 = 09931y = 7E minus 05x + 0014

R2 = 09906

y = 6E minus 05x + 00024

Trend (pH = 800)


pH = 550

pH = 300

(a) For steel

0002004006008

01012014016

0 200 400 600 800 1000 1200 1400

Yiel

d str

engt

h re

duct

ion

()

Weight loss (g)

R2 = 09142y = 00004x minus 00167

R2 = 04677

y = 00002x + 00112

R2 = 0928

y = 8E minus 05x + 00074

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron


0

005

01

015

02

025

0 200 400 600 800 1000 1200

Frac

ture

toug

hnes

s red

uctio

n (

)

Weight loss (g)

R2 = 08532

y = 00008x + 00165

R2 = 08098

y = 00004x + 00332

R2 = 07332

y = 00001x + 00305

Trend (pH = 800)

Trend (pH = 550)

Trend (pH = 300) pH = 800

pH = 550

pH = 300

(a) For steel

0005

01015

02025

03035

04045

0 200 400 600 800 1000 1200 1400

Frac

ture

toug

hnes

s red

uctio

n (

)

Weight loss (g)

R2 = 05454

y = 00008x + 01085

R2 = 07184

y = 00007x + 00744

R2 = 08383

y = 00002x minus 00247

Trend (pH = 800)


pH = 550

pH = 300

(b) For cast iron





6 Conclusion




Competing Interests


Acknowledgments


References















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





Competing Interests


Acknowledgments


References















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



research article experimental investigation on corrosion

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