2 Evaluation of corrosion protection properties of additives for waterborne epoxy coatings on steel

格式：pdf
大小：431.52 KB
文档页数：9

Progress in Organic Coatings44(2002)217–225Evaluation of corrosion protection properties of additivesfor waterborne epoxy coatings on steelF.Galliano∗,ndoltLaboratoire de Métallurgie Chimique,Département des Matériaux,Ecole Polytechnique Fédérale de Lausanne,CH-1015Lausanne EPFL,SwitzerlandReceived23September2001;accepted8February2002AbstractThe development of environment compatible additives for corrosion inhibition in waterborne coatings requires test methods which yield signiﬁcant results on a short time scale.The present study aims at the evaluation of the effect of corrosion inhibiting model additives on the performance of a waterborne epoxy coating using electrochemical and non-electrochemical methods which measure different properties. Electrochemical impedance spectroscopy(EIS),linear sweep voltammetry,mechanical pull-off tests and scanning acoustic microscopy (SAM)in combination with image analysis are used.Two kinds of corrosion inhibiting additives are employed:an organic inhibitor based on a carboxylic acid neutralized by a polysiloxane base,and ZPA,an inorganic pigment with inhibiting properties.The results obtained show that corrosion inhibiting additives drastically modify the adhesion,water uptake,blistering behavior and substrate protection of waterborne epoxy coatings.Both additives improved the dry adhesion and reduced blistering under cathodic polarization conditions.The experimental approach described in this paper should be useful for additive development and for coating formulation because it yields a more complete picture than can be obtained by single methods of how a given additive affects the coating performance in a corrosive environment.©2002Elsevier Science B.V.All rights reserved.Keywords:Waterborne coatings;Corrosion inhibition;Additives1.IntroductionThe introduction of strict regulations in the use of volatile organic compounds(VOCs)has brought about the devel-opment of solvent-free coating technologies like powder coatings,electrocoatings,UV curable coatings and water-borne systems.Waterborne coatings have gained increasing importance for many applications.These coatings usually contain different additives such as extenders,dispersion agents,defoamers,ﬁllers and corrosion inhibitors.The choice of a functional additive requires a good knowledge of its interaction with other additives and pigments,its com-patibility with the binder and the substrate and its inﬂuence on the adhesion properties[1].Additives can interact with waterborne paint system in different ways with correspond-ing consequences for the corrosion protective properties. For example,a previous study performed in our laboratory showed that the selection of a suitable dispersion agent was crucial for the performance of coated steel samples sub-jected to corrosion tests[2],the reason being that it affects ∗Corresponding author.E-mail address:federico.galliano@epﬂ.ch(F.Galliano).the wetting properties of the binder emulsion with respect to the substrate and the pigments.The degradation of a polymer-coated metal occurs after water penetrates at the coating–substrate interface,where failure mechanisms such as osmotic blistering,cathodic de-lamination and anodic undermining may be initiated[3,4]. Corrosion inhibiting additives are designed to react at the metal surface by improving adhesion and slowing down the electrochemical reactions.In modern coatings traditional inorganic inhibitors such as chromates,lead oxides,etc. are being replaced by less harmful inorganic[5,6]and or-ganic compounds[7,8].Inorganic pigments like phosphates, molybdates,vanadates,silicates and borates are commonly used for the protection of solvent-borne and waterborne coatings.Environmentally friendly organic inhibitor formu-lations speciﬁcally designed for waterborne coatings are an attractive alternative[9].The development of corrosion inhibiting additives re-quires test methods which yield signiﬁcant results in a time as short as possible.Salt spray and different cyclic exposure tests are widely used in the coating industry,but these tests yield essentially qualitative information.More recently,electrochemical methods,especially electrochem-ical impedance spectroscopy(EIS),have found increasing0300-9440/02/$–see front matter©2002Elsevier Science B.V.All rights reserved. PII:S0300-9440(02)00016-4218F .Galliano,ndolt /Progress in Organic Coatings 44(2002)217–225Table 1Complete paint compositions IngredientsEpoxy binder (Beckopox-Hardener EH 623W)Dem.water TalcIron oxideCalcium carbonate Bentone SD2Borchigel L75Additol XL 270With/without inhibitorinterest for testing of coatings,because these methods are capable to yield mechanistic data which can be quantiﬁed by using suitable models [10,11].On the other hand,EIS data acquired in long term exposure tests,often scatter con-siderably and require,especially in the case of damaged coats,parallel experiments on several samples and a statisti-cal evaluation [12,13].The adhesion properties of coatings are crucial for corrosion protection and durability of a coat-ing system.Corrosion cells can deteriorate the adhesion of organic coatings on steel because the rise in pH at cathodic locations on the surface can lead to cathodic disbonding and blistering.Several authors have studied the mechanism of cathodic delamination and disbonding using different methods [14–17].In our laboratory scanning acoustic mi-croscopy (SAM)has recently been used for monitoring the blister formation due to the loss of adhesion during open circuit immersion tests [2].For the development of corro-sion inhibiting additives it is important to be able to measure by what mechanism a given additive affects the coating performance and on which property of the metal-coating system has the most effect.The goal of the present study is to evaluate the effect of two model corrosion inhibiting additives on the performance of a waterborne epoxy coating using a variety of electrochemical and non-electrochemical methods which measure different properties.2.Experimental2.1.Materials and samples preparationThe fully formulated paint system utilized in this work is composed of a waterborne amine-modiﬁed epoxy binder,Table 2Scheme of the tested properties PropertyMeasurement technique Measured or calculated valuesCoated samples Bare steelLong term immersion resistance EIS Water uptake,coating resistance,polarization resistance,double layer capacitance X Water diffusion barrier EIS Diffusion coefﬁcientXAdditive inhibition LSVCathodic and anodic currents XAdhesionPull-off test Bond strengthX Cathodic delamination resistanceSAMBlister growth rate,maximum blistering propagationXadditives and pigments as reported in Table 1.The effect of two different inhibitors was evaluated.Inhibitor (A)was a proprietary organic inhibitor (IRGACOR 287,Ciba Spe-cialty Chemicals)containing carboxylic acid for corrosion inhibition [18]neutralized with a polysiloxane base for im-proving solubility and adhesion properties [19].Inhibitor (B)was a commercial zinc–aluminum phosphate pigment (Heucophos ZPA,Heucotech LTD)known for its corrosion inhibiting properties.The weight percentages were 0.6%for inhibitor (A)and 8.3%for inhibitor (B),respectively.In-hibitor (B)replaced an equivalent mass of calcium carbon-ate in the base paint,in order to maintain the same weight proportion of inorganic solids in the coating.Low carbon steel panels (190mm ×105mm,Chemetall Gmbh)were used as substrates.They were cleaned in an ultrasonic bath by a 1:1mixture of ethanol and acetone and painted using a steel bar coater drawn at a constant speed.Curing was carried out at 80◦C for 30min and the panels were allowed to completely dry for 24h at 40◦C.The ﬁnal average thickness was 45±3␮m for the different coatings as measured by optical methods.Panels were then cut to obtain 24mm ×24mm specimens which were stored in a desiccator.2.2.Experimental techniques usedFor the characterization of the coating performance,elec-trochemical and non-electrochemical techniques were used.Immersion tests were performed using EIS for the evaluation of the performance of the coated system.The LSV technique was employed to study the inhibitive properties of the addi-tives on the bare steel surface.The effect of the additives on the adhesion of the coating to the substrate was determined by pull-off tests performed under dry conditions.Finally,the effect of the additives on cathodic delamination and blister-ing was studied using in situ SAM of cathodically polarized specimens and image analysis.A summary of the different properties evaluated by the measurement techniques used is given in Table 2.2.3.EIS experimentsAll EIS experiments were conducted using a Gamry PC potentiostat connected to an 8-channel ECM8multiplexer.The setup was driven by CMS 300software which permittedF.Galliano,ndolt/Progress in Organic Coatings44(2002)217–225219 to automate the experimental procedure.Sequentialimpedance spectra were acquired at well deﬁned time in-tervals under constant experimental conditions.A specimenarea of11mm diameter was exposed for28days to a5wt.%NaCl solution at room temperature.Impedance measure-ments were performed every20min for theﬁrst12h,thenevery2h for24h and then every12h until the end of theexperiment.When a20min interval was used,the analyzedfrequency ranged from10to105Hz,for longer intervalsfrom10−1to105Hz.In the case of premature coating fail-ure the experiment was stopped.From3to6samples ofeach type of coating were tested and evaluated.The classicequivalent circuit model for painted metals[10]was re-gressed individually to each impedance spectra to calculatethe following model parameters:R s electrolyte resistance,R p paint resistance,C p paint capacitance,R ct charge trans-fer resistance and C dl double layer capacity(here a constantphase element was used).Data collected in theﬁrst12h,with an analyzed frequency range10–105Hz,were treatedwith a simpliﬁedﬁtting circuit that included only R s,R p andC p(Randles circuit).A satisfactoryﬁt could be obtainedfor all data sets.In the followingﬁgures,mean values ofthe calculated parameters are reported together with therespective standard deviations.The water uptakeφwas calculated from the measuredcoating capacitance C p using the Brasher–Kingsbury equa-tionφ=log(C p /C p0)log80(1)where C p0is the coating capacitance extrapolated for t→0.The evolution of theﬁt parametersφ,R p,R ct,and C dl, with immersion time was used to monitor the coating ing the theory of Fickian diffusion for immersed supported coatings,the water uptakeφcan be analytically expressed as a function of timeφ(t)[20].By utilizing Eq.(1) the coating capacitance is analogously described as a func-tion of time C p(t)C p(t) C psat =1−8π2n=∞n=01(2n+1)2exp[−(2n+1)2π2Dt/4l2](2)where C psat represents the coating capacitance value whenwater saturation in the coating occurred and l the coating thickness.The above equation can be reduced,for short immersion time,to a linear relation between the coating capacitance and the square root of time(see Eq.(3))and the water diffusion coefﬁcient D W can be easily obtained by a linearﬁtting procedure[21]C p(t) C psat ∼=8π2D W tl20.5(3)2.4.LSV experimentsThe LSV experiments were conducted using a Solartron 1287electrochemical interface controlled by a commercial software.Linear potential sweeps were started at−1.6V until1.2V(relative to a Hg/HgSO4reference electrode),at a scan rate of2mV s−1.Rotating disc electrodes made from a CK45steel rod of5mm diameter embedded in araldite and polished with400,600,1000grit emery paper were used in all the experiments as working electrodes at a rota-tion rate of400rpm.A platinum coil was used as counter electrode.An aerated0.12M NaClO4solution was chosen as supporting electrolyte and maintained at a temperature of 25±1◦C.Because the inhibitors used have a low solubil-ity in aqueous solution all experiments were performed at saturation conditions.For this2g l−1of the inhibitor were contacted with the electrolyte for24h and thenﬁltered,a procedure suggested by Amirudin et al.[5].Before each experiment,the pH of the test solutions was adjusted to 7.5by addition of NaOH or HClO4.Two samples of each series were tested to check for reproducibility.2.5.Pull-off adhesion experimentsSamples in dry conditions were sandwiched in an align-ment jig between15mm diameter aluminum cylinders utilizing an epoxy adhesive(Araldite Rapid,Ciba Specialty Chemicals).A12h curing was allowed at a pressure of 30kPa and the resulting specimens were then subjected to tensile testing in a tensile machine(Lloyd2000R)at a cross-head speed of2mm min−1.Reported adhesion strength values are averaged overﬁve measurements.2.6.Cathodic delamination experimentsBlistering and cathodic delamination was studied on scribed samples using SAM.The cathodic delamination and blistering process was accelerated by cathodic polarization of the specimens[17]using an Amel5000potentiostat. The edges and the back of the samples were insulated with araldite and the exposed coating surface was scribed for a length of5mm with a diamond tool.The samples were then placed horizontally in a recipient containing a 5wt.%NaCl solution.A graphite counter electrode and a Ag/AgCl reference electrode(SSE)were inserted in the tank and the samples were cathodically polarized at−1.1V SSE.The region adjacent to the scribe was monitored in situ by SAM,which detects changes in the acoustic impedance at the interface between coating and substrate[2,17,22].The SAM measurements were performed using a Honda Scan-ning Ultrasonic Flaw and Imaging HA-711in conjunction with a focused piezopolymeric(PVDF)transducer with a center frequency of80MHz.At this frequency,the vertical resolution of the acoustic microscope was about15␮m. Further details on the SAM image acquisition procedure are reported elsewhere[2].SAM images were digitally scanned and processed by a commercial image analysis software. The total blistered area and the maximum blister propaga-tion distance from the scribe were determined as a function220F.Galliano,ndolt/Progress in Organic Coatings44(2002)217–225Fig.1.Water uptake(a),paint resistance(b),charge transfer resistance(c)and double layer capacitance(d)as a function of immersion time in5wt.% NaCl solution.F.Galliano,ndolt/Progress in Organic Coatings44(2002)217–225221of time.Two samples of each series were tested to assurereproducibility.3.Results3.1.EIS resultsPlots of water uptake,paint resistance,double layer ca-pacitance and charge transfer resistance for the blank coat,and the coats containing(A)and(B)inhibitor,respectively,are reported in Fig.1.Standard deviation plots are also in-cluded.In theﬁrst30h the water uptake values(see Fig.1a)increase steeply for all the tested coats,denoting a fast dif-fusion of water into the coatings.The initial period was fol-lowed by a slower almost linear increase for the remainingtest duration.No clear saturation plateau was observed,abehavior that may be related to the swelling of the poly-mer matrix[21].The data show the highest water uptakefor the blank coating followed by the coat formulated withinhibitor(A)and then by the one with(B).At longer im-mersion time,(B)containing samples exhibited a discon-tinuous trend of the water uptake,corresponding to theloss of adhesion and onset of blistering.Visual observa-tion of(B)samples at the end of the test revealed someblistering while samples(A)were not blistered and stillwell adherent.As a general observation one may note thatthe amount of water taken up by these waterborne epoxycoatings(6–9vol.%)was always higher than that measuredfor solvent based epoxy coatings of analogous thickness(2–6vol.%)[23].The coating resistance(see Fig.1b)presents a very sharpdecrease in theﬁrst hours followed by a plateau value thatis always lower than107 for all the coats.This indicates limited protective properties of the coatings studied.Thecoating resistance is the highest for(B)containing coats fol-lowed by the(A)containing coats and then by the blankcoats.At longer exposure times,a degradation of the barrierproperties of(B)samples is observed and R p approachesthe values measured for(A)samples.The same trend foundfor R p is observed for the charge transfer resistance R ct(seeFig.1c).At short immersion times(<200h)the inhibitingaction of(B)is more effective than that conferred by the(A)and both the inhibitors show higher R ct values than theblank coat.At longer immersion times,R ct for samples(B)drops to values observed for the blank coat,because blister-ing occurs and the metal–paint interface accessible to watersensibly increases.The(A)samples on the other hand ex-hibit an almost constant value for the entire test duration.Animportant scattering in the R ct values characterizes the sharptransition to blister formation observed on(B)samples.Theresults for the double layer capacitance(see Fig.1d)arequalitatively consistent with those of R ct in that the onset ofblistering on the(B)samples is again clearly detected.Thedata scattering for(B)samples is very large,typical for anon-uniform coatingdegradation.Fig.2.Coating capacitance normalized as a function of the square root of exposure time.Calculation of the slope allows the determination of the water diffusion coefﬁcient,D W.The water diffusion coefﬁcient D W was calculated from the C p values as function of time using Eq.(3).The sat-uration capacitance was estimated from Fig.2as the ca-pacitance measured at the transition of water uptake from fast to slow linear increase[23].Since the blank coat and the coat with inhibitor(A)present the same capacitance behavior at short immersion times,the calculated water diffusion coefﬁcient is the same within experimental er-ror.On the other hand,(B)containing coats showed a lower diffusion coefﬁcient(see Table3)indicating that the ZPA pigment slowed water diffusion.The overall picture emerging from EIS measurements clearly shows a bene-ﬁcial effect of both additives on the corrosion properties of the waterborne epoxy coating system.The use of ZPA inhibitor provided the best corrosion resistance at short immersion times but at longer exposures a sensitive loss of protective properties was observed.A similar behavior for zinc phosphate pigments has been described by other authors[24].3.2.LSV resultsThe experiments were performed in air saturated solutions where the reduction of oxygen is the predominant cathodic reaction.The polarization curves measured in the0.12M NaClO4solution with and without inhibitor are shown in Fig.3.The(A)inhibitor(Fig.3a)does not appreciably in-Table3Diffusion coefﬁcients for water as evaluated from coating capacitance data Sample D W×10−10(cm2s−1)Blank,with(A) 2.7±0.5With(B) 1.1±0.2222F .Galliano,ndolt /Progress in Organic Coatings 44(2002)217–225Fig.3.Linear sweep voltammograms for low carbon steel rotating disc electrode in 0.12M NaClO 4supporting electrolyte with or without (A)additive (a)and (B)pigment (b).ﬂuence the oxygen reduction reaction and the limiting ca-thodic current is the same as without inhibitor.In absence of inhibitors the anodic branch of the curve follows a typi-cal active dissolution behavior.The addition of inhibitor (A)leads to lowering of the anodic dissolution current and to an anodic shift of the corrosion potential of about 100mV .The surface of the samples tested in the (A)containing solution presented,after the test,large patches of unattacked metal.It is concluded that (A)in an anodic inhibitor in agreement with previous studies performed with similar compounds [18].The polarization curves in the inhibitor (B)contain-ing solutions (Fig.3b )are characterized by a slightly lower limiting current for oxygen reduction,while the anodic part of the curve is not signiﬁcantly modiﬁed with respect to the pure supporting electrolyte solution.This conﬁrms that (B)is a cathodic inhibitor reducing the rate of oxygen reduction [25].3.3.Pull-off adhesion resultsThe data reported in Table 4indicate that both additives provided an important increase of the coat–substrate bond strength compared to the blank coat.The pull-off force in presence of additive (B)was the highest,but it must be borne in mind that the failure was located within the coating and not at the interface.The same was observed in presence of additive (A).Thus both additives conferred to the coatingTable 4Pull-off adhesion test in dry conditions Sample Bond strength (MPa)Detached area Blank 7.7±3.760±20With (A)19.7±4.00With (B)27.1±3.9F .Galliano,ndolt /Progress in Organic Coatings 44(2002)217–225223an adhesive strength exceeding its cohesive strength.On the other hand,for the blank coat the rupture occurred primar-ily at the coating–metal interface as a result of a deadhesive failure.Polysiloxane additives are well known as adhesion promoters in the organic coating technology [19]and the re-action mechanism has been extensively studied in the past years [26].On the other hand,to the authors’knowledge,the marked increase of coating adhesion caused by the presence of ZPA has not been investigated in detail so far and fur-ther studies are needed to elucidate the interfacial reactions involved.In summary,the adhesion tests prove that both ad-ditives (A)and (B)signiﬁcantly improved the adhesion of the coating to the substrate.3.4.SAM resultsObservation by SAM of the metal–polymer interface permitted to follow the formation of blisters with time in the vicinity of a previously made scribe.Cathodic po-larization of the scribed samples accelerated the cathodic disbonding and blistering process.The cathodic reaction provides hydroxyl ions and short-lived radical intermediates which weaken,by hydrolization and oxidation,the adhesive strength at the metal–polymer interface [16].This permits advancement of the delamination front and penetration of solution.As a result blisters are formed where the interface adhesion is weakest.Unfortunately,the limited vertical res-olution of our microscope (∼=15␮m)did not allow us to detect the penetration of liquid at the interface before blis-ters were formed.As an illustration,Fig.4showsblistersFig.4.SAM image of the coat formulated with (A)after 53h of cathodic polarization.At the center of the image there is the scribe mark.formed in the vicinity of the scribe on a coat containing inhibitor (A)after 53h of cathodic polarization.The occurrence of the blistering was always preceded by a delay time where presumably an initial disbonding was going on,as previously described by Crossen et al.[22].Once the ﬁrst blisters appeared,it was possible to follow their growth and the formation of new blisters.To quantify the SAM observations image analysis was utilized.In Fig.5the total blister area and the maximum blistering propaga-tion away from the scribe (an average of the two opposite directions)are plotted as a function of time for the three dif-ferent coats tested.A linear relationship between blistered area and time is observed.From the slope the growth rate of the blister area was calculated and results are also shown in the ﬁgure.Assuming that,during the cathodic delamination process,water and ions must diffuse at the coating–metal in-terface from the scribe to the blister,one would expect from simple diffusion theory that the maximum distance from the scribe to blisters increases linearly with the square root of time.Such a relationship has been found by Leng et al.[16]who explained the behavior in terms of a mechanism in-volving cation transport at the metal–polymer interface and limiting the delamination kinetic.The data of Fig.5b for the blank coat and for the coat with inhibitor (A)yield the ex-pected relationship,whereas the behavior of the coating with inhibitor (B)differs in that the maximum distance from the scribe at which blisters form is much smaller and increases very slowly during the test duration.This coating also ex-hibits a much longer initiation time before blistering occurs.The inhibitor additives signiﬁcantly affected the blister formation kinetics.Blank samples,after 14h,exhibit large blisters which spread rapidly far from the scribe.After 87h the surface of the samples was completely covered by blis-ters and the test was stopped.On (A)containing samples blisters were detected only after 22h and the size of blis-ters remained small although the blister front advanced quite rapidly.The blister growth rate of the blank was about 3.7times larger than that of the (A)containing sample (0.75and 0.20mm 2h −1,respectively),but the maximum blister-ing distance from the scribe was only 1.7times larger (1.37and 0.81mm h −0.5,respectively).For the (B)containing samples the ﬁrst blisters were detected after 76h and devel-oped at a rate of 0.08mm 2h −1.The maximum distance for blistering stabilized after about 164h.The different results show that inhibitor (B)effectively slowed down blistering under cathodic polarization conditions.Inhibitor (A)also yielded a reduced blister area compared to the blank coat but it was less effective in slowing the spreading of blister formation.Several factors may contribute to the beneﬁcial effect of (B)on blister formation and growth.The adhesion test showed that (B)generally improves the adhesion of the coating and the LSV experiments indicated that (B)inhibits the cathodic partial reaction.Finally,the solubility of the (B)pigment apparently increases with increasing pH [27]per-mitting a higher concentration at the cathodic delamination front,where the hydroxyl ions are produced.224F .Galliano,ndolt /Progress in Organic Coatings 44(2002)217–225Fig.5.Blistered area (a)and maximum blistering propagation from the scribe mark (b)as a function of time during cathodic delamination experiments at −1.1V SSE in a 5wt.%NaCl solution.4.ConclusionsThe present study demonstrates the usefulness of apply-ing a variety of experimental methods for characterizing the effects of corrosion inhibiting additives on the performance of waterborne coating systems.The obtained data show that corrosion inhibiting additives drastically modify properties such as adhesion,water uptake or blistering,and they also provide evidence that different additives affect these prop-erties differently.The experimental approach described here allows one to identify speciﬁc effects of coating additives which should be useful for their optimization and for coat-ing formulation.Two kinds of corrosion inhibiting additives were em-ployed:an organic inhibitor based on a carboxylic acid neu-tralized by a polysiloxane base (A),and ZPA (B)which is an inorganic pigment.EIS showed that (A)was beneﬁcial over an immersion time of 1month in a saline solution,whereas the inhibitor (B)exhibited the best performance at short im-mersion times.Polarization curves of low carbon steel sub-strates showed that (A)inhibits the anodic partial reaction while (B)is a cathodic inhibitor inhibiting oxygen reduction.Both inhibitors greatly improved the adhesion of the coating under dry ing SAM in conjunction with image analysis blister formation in saline solution under cathodic polarization conditions could be quantiﬁed.F.Galliano,ndolt/Progress in Organic Coatings44(2002)217–225225Results showed that addition of additive(A)led to a re-duction in blister size and growth rate,but the maximum distance from the scribe where blisters formed was not sig-niﬁcantly affected.Additive(B)dramatically reduced the progress of the blistered front and the blister growth rate.The enhanced adhesion and the cathodic inhibition are thought to be responsible for the effectiveness of additive(B)for re-ducing blistering.The different data show that both additives (A)and(B)tested here improved coating performance,but their relative effectiveness depends on the system properties studied.AcknowledgementsThe authors thank A.Braig,D.Renoux and M.Frey from Ciba Specialty Chemicals Inc.,Basel Switzerland,for pro-viding the paint systems and the additives.Dr.A.Kulik kindly permitted the use of the SAM at the Institut de Génie Atomique,EPFL Lausanne.Financial support from CTI Bern is gratefully acknowledged.References[1]K.Dören,W.Freitag, D.Stoye,Waterborne Coatings,Hanser/Gardner,Cincinnati,1994.[2]V.Guillaumin,ndolt,Corr.Sci.44(2001)179.[3]H.Leidheiser Jr.,Corrosion38(1982)374.[4]T.Nguyen,J.B.Hubbard,J.M.Pommersheim,J.Coat.Technol.68(1996)45.[5]A.Amirudin,C.Barreau,R.Helouni,D.Thierry,.Coat.25(1995)339.[6]R.C.MacQueen,R.R.Miron,R.D.Granata,J.Coat.Technol.68(1996)75.[7]G.Reinhard,P.Simon,U.Rammelt,.Coat.20(1992)383.[8]P.Agarwal,ndolt,Corr.Sci.40(1998)673.[9]A.Braig,.Coat.34(1998)13.[10]F.Mansfeld,J.Appl.Electrochem.25(1995)187.[11]P.L.Bonora,F.Deﬂorian,L.Fedrizzi,Electrochem.Acta41(1996)1073.[12]W.S.Tait,J.Coat.Technol.66(1994)59.[13]J.A.Grandle,S.R.Taylor,Corrosion53(1997)347.[14]H.Leidheiser Jr.,J.W.Wang,L.Igetoft,.Coat.11(1983)19.[15]D.H.van der Weijde,E.P.M.van Westing,J.H.W.De Wit,Corr.Sci.36(1994)643.[16]A.Leng,H.Streckel,K.Hofmann,M.Stratmann,Corr.Sci.41(1999)579.[17]M.Kendig,R.Addison,S.Jeanjaquet,J.Electrochem.Soc.137(1990)2690.[18]G.T.Hefter,N.A.North,S.H.Tan,Corrosion53(1997)657.[19]P.Walker,J.Adhes.Sci.Technol.5(1991)279.[20]J.Crank,G.S.Park,Diffusion in Polymers,Academic Press,London,1968.[21]E.P.M.van Westing,G.M.Ferrari,J.H.W.de Wit,Corr.Sci.36(1994)957.[22]J.D.Crossen,J.M.Sykes,T.Zhai,G.A.D.Briggs,Faraday Discuss.107(1997)417.[23]F.Geenen,Ph.D.Thesis,Technische Universiteit Delft,TheNetherlands,1991.[24]R.Romagnoli,V.F.Vetere,Corrosion51(1995)116.[25]bouche,M.Traisnel,Surf.Coat.Int.10(1994)404.[26]C.Reinartz,W.Fürbeth,M.Stratmann,Fresenius J.Anal.Chem.353(1995)657.[27]T.Schauer,W.M.Liu,L.Dulog,Eur.Coat.J.3(1997)292.。

漏磁内检测技术在原油管道腐蚀评价分析中的应用

第42卷第1期2021年1月Vol. 42 No. 1January 2021腐蚀与防护CORROSION & PROTECTIONDOI ：10. 11973/fsyfh-202101011漏磁内检测技术在原油管道腐蚀评价分析中的应用苏志华'，欧阳小虎I,王成园'(1.中国石油管道局工程有限公司管道投产运行分公司，廊坊065001； 2.山东大学微电子学院，济南250100)摘要：某原油管道的漏磁内检测结果中存在较多异常点。

针对其中最严重的9个金属损失异常点，依据国内管道内腐蚀评价标准规范，进行了腐蚀评价和压力分析。

将腐蚀评价和压力分析结果作为理论筛选依据，最终优先选择了 8个内检测异常点进行开挖验证和缺陷修复。

通过开挖验证证实了漏磁内检测结果的准确性，证明了漏磁内检测技术可在管道腐蚀评价分析中发挥作用。

关键词：漏磁内检测；腐蚀评价；完整性管理；金属损失异常；失效压力；开挖验证；缺陷修复中图分类号：TE988文献标志码：B 文章编号：1005-748X(2021)01-0050-07Application of Magnetic Flux Leakage Internal Detection Technology inCorrosion Evaluation and Analysis of Crude Oil PipelineSU Zhihua 1 , OUYANG Xiaohu 1 , WANG Chengyuan 2(1. Pipeline Commissioning and Operation Branch Company, China Petroleum Pipeline Bureau Engineering Co. , Ltd.,Langfang 065001, China ； 2. College of Micro-Electronics * Shandong University, Jinan 250100, China)Abstract : There were many abnormal points in the magnetic flux leakage test results of a crude oil pipeline. For the9 most serious abnormal points of metal loss, corrosion evaluation and pressure analysis were carried out in accordance with domestic pipeline corrosion evaluation standards. The results of corrosion evaluation and pressure analysis wereused as the basis for theoretical screening, and finally 8 abnormal internal inspection points were selected for excavation verification and defect repair. Excavation verification verified the accuracy of the internal magnetic fluxleakage detection results, and proved that the internal magnetic flux leakage detection technology could play a role inpipeline corrosion evaluation and analysis.Key words : magnetic flux leakage internal detection ； corrosion evaluation ； integrity management ； metal lossanomaly ； failure pressure ； excavation verification ； defect repair管道完整性评价是管道完整性管理的核心，是识别管道本体安全隐患、确定管道缺陷位置和指导管道本体维修的基础。

BS EN 12501-2-2003 金属材料的防腐蚀.土壤中腐蚀可能性.低合金和非合金黑色金属材料

BS EN 12501-2-2003 金属材料的防腐蚀.土壤中腐蚀可能性.低合金和非合金黑色金属材料BRITISH STANDARD BS EN12501-2:2003Protection of metallicmaterials againstcorrosion — Corrosionlikelihood in soil —Part 2: Low alloyed and non alloyedferrous materialsThe European Standard EN 12501-2:2003 has the status of a British StandardICS 77.060?????????????????????? ?????????? ?????????????????????????????????????? ??????????????????????????????????????????????????.yang64>>BS EN 12501-2:2003This British Standard waspublished under the authorityof the Standards Policy andStrategy Committee on6 May 2003?? BSI 6 May 2003ISBN 0 580 41779 4National forewordThis British Standard is the official English language version of EN 12501-2:2003.The UK participation in its preparation was entrusted to Technical CommitteeISE/NFE/8, Corrosion of metals and alloys, which has the responsibility to:A list of organizations represented on this committee can be obtained onrequest to its secretary.Cross-referencesThe British Standards which implement international or European publications referred to in this document may be found in the BSI Catalogueunder the section entitled “International Standards Correspondence Index”, orby using the “Search” facility of the BSI Electronic Catalogue or of BritishStandards Online.This publication does not purport to include all the necessary provisions of acontract. Users are responsible for its correct application.Compliance with a British Standard does not of itself confer immunityfrom legal obligations.— aid enquirers to understand the text;— present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep theUK interests informed;— monitor related international and European developments andpromulgate them in the UK.Summary of pagesThis document comprises a front cover, an inside front cover, the EN title page,pages 2 to 12, an inside back cover and a back cover.The BSI copyright date displayed in this document indicates when the document was last issued.Amendments issued since publicationAmd. No. Date Comments.yang6>EUROPEAN STANDARDNORME EUROP??ENNEEUROP??ISCHE NORMEN 12501-2April 2003ICS 77.060English versionProtection of metallic materials against corrosion - Corrosion likelihood in soil - Part 2: Low alloyed and non alloyed ferrousmaterialsProtection des matériaux métalliques contre la corrosion - Risque de corrosion dans les sols - Partie 2: Matériauxferreux peu ou non alliésKorrosionsschutz metallischer Werkstoffe -Korrosionswahrscheinlichkeit in B??den - Teil 2: Niedrig- undunlegierte EisenwerkstoffeThis European Standard was approved by CEN on 21 February 2003.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Management Centre or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the official versions.CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONC O M I T ?? E U R O P ?? E NDE N O R M A LI S A T I O NEUR OP ??IS C HES KOM ITEE F??R NOR M UNGManagement Centre: rue de Stassart, 36 B-1050 Brussels?? 2003 CEN All rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 12501-2:2003 E.yang6>EN 12501-2:2003 (E)2ContentspageForeword......................................................... (3)Introduction .................................................... ..................................................................... . (4)1Scope ............................................................... ..................................................................... .. (4)2 Normative references .......................................................... ..................................................................... .. (4)3 Terms and definitions.......................................................... ..................................................................... .. (4)4 Assessment of the corrosion load in soil for a new structure to be buried (4)4.1Method .............................................................. ..................................................................... . (4)4.2 Criteria............................................................. (5)4.2.1 Soil conditions .......................................................... ..................................................................... . (5)4.2.2 Preliminary Inquiry ............................................................. ..................................................................... (5)4.2.3 Site survey............................................................... ..................................................................... (5)4.2.4 Soil sampling............................................................. ..................................................................... . (6)4.2.5 Backfill materials ........................................................... ..................................................................... .. (7)5 Complementary information for an existing structure............................................................ . (7)5.1 General.............................................................. ..................................................................... . (7)5.2 Investigations and analysis ............................................................ .. (8)Annex A (informative) Procedure for assessing the corrosion load in soil in the case of a newstructure........................................................ ..................................................................... .. (9)Annex B (informative) General principles of soil studies.............................................................. (10).yang6>EN 12501-2:2003 (E)3ForewordThis document (EN 12501-2:2003) has been prepared by Technical Committee CEN/TC 262 “Metallic and otherinorganic coatings”, the secretariat of which is held by BSI.This European Standard shall be given the status of a national standard, either by publication of an identical text orby endorsement, at the latest by October 2003, and conflicting national standards shall be withdrawn at the latestby October 2003.According to the CEN/CENELEC Internal Regulations, the national standards organizations of the followingcountries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland,France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal,Slovakia, Spain, Sweden, Switzerland and the United Kingdom..yang6>EN 12501-2:2003 (E)4IntroductionThis European Standard should be used in conjunction with EN 12501-1, Protection of metallic materials againstcorrosion — Corrosion likelihood in soil — Part 1: General, which describes general principles of the assessment ofthe corrosion load.The method of assessing the corrosion load in the case of a new structure to be installed takes into account theadverse parameters of the soil and environment with regard to corrosion. They have been chosen to avoidunderestimation of the risks of corrosion damage. The assessment is performed considering a bare structure indirect contact with the soil without taking into account any protective system that will be present in service.The complexity of corrosion in soil demands that the measurements and their interpretation are carried out byexperienced personnel. The described method should be adapted in relation to the expected service life of thestructure and to possible future changes of its environment.1 ScopeThis part of this European Standard deals with the assessment of the corrosion load in soil for low-alloyed and non-alloyed ferrous materials in direct contact with soil. Corrosion protection systems and their performance are notcovered by this standard but by specific products standards.This part of this European Standard deals with the case of new structures to be buried and gives information forexisting structures.2 Normative referencesThis European Standard incorporates by dated or undated reference, provisions from other publications. Thesenormative references are cited at the appropriate places in the text, and the publications are listed hereafter. Fordated references, subsequent amendments to or revisions of any of these publications apply to this EuropeanStandard only when incorporated in it by amendment or revision. For undated references the latest edition of thepublication referred to applies (including amendments).EN 12501-1:2003, Protection of metallic materials against corrosion — Corrosion likelihood in soil — Part 1:General.3 Terms and definitionsFor the purposes of this European Standard, the terms and definitions given in EN 12501-1:2003 apply.4 Assessment of the corrosion load in soil for a new structure to be buried4.1 MethodThe method to be applied is based on:?? general concepts and factors influencing the corrosion load given in EN 12501-1;?? criteria defined in the present standard..yang6>EN 12501-2:2003 (E)5The corrosion load is accepted high if no investigation is done for any reason.4.2 Criteria4.2.1 Soil conditionsTable 1 summarises different soil conditions to be examined during either the preliminary inquiry or the site surveyand which indicate a location of high corrosion load, in the absence of further investigation.Table 1 — soil conditions that can lead to a high corrosion loadCharacteristics Circumstances Examples of criteriaType of soilNatural soil Presence of peat, lignite, coal .. in the soilsAreas such as marsh, fen, ..Tidal zonePresence of brackish or sea water tableAnaerobic soils (Possible Microbially Induced Corrosion)Artificial soil Soils containing ashes, slag, industrial by-products, residuesof household refuse, ...Areas backfilled by industrial by-products (any type)Uncontrolled recycled materialsElectrical influenceDevice using DC Close vicinity of DC railways, tramways, underground, ...Proximity of a cathodically protected structure, or anodes, ...Device using AC Proximity of AC power lines, AC railwaysProximity to AC earthing electrodesPollution Contaminated soils Contamination by de-icing salts, manure, fertilisers, leakingsewer, industrial pollutionTopography Hydrography Presence on the pipe route of a low point, a creek or rivercrossing, ...Others Toponomy Indications from the village names of special characters of thenature of soilThree phase boundary Fluctuating water table4.2.2 Preliminary InquiryA preliminary inquiry generally consists of a topographical study, a geological study and an investigation for specificinformation. It enables to identify areas which should be studied with particular attention during the site survey.Annex B gives more detailed information on the way to collect data during the preliminary inquiry.In the absence of further investigation, such as site survey or soil sampling, and if one or more criteria as given intable 1 are met corrosion load is accepted high.4.2.3 Site surveyA site survey consists in collecting additional information (see Table 1) by observations and measurements on theconstruction site; soil resistivity measurements have to be performedand, when appropriate, potential gradientmeasurements.Annex B gives additional information on the way to carry out a site survey.The following criteria allow to assess the corrosion load, based on visual inspection of soil and resistivitymeasurements from the surface during the site survey:.yang6>EN 12501-2:2003 (E)6?? resistivity values below 30 W ??m and/or soil conditions as given in Table 1 indicate locations of high corrosionload;?? if resistivity values are above 30 W ??m, additional investigation such as soil sampling shall be done. However, if the three following conditions are fulfilled together, they indicatelocations of low corrrosion load and no otherinvestigation is necessary:?? soil is sand or gravel,?? resistivity values are above 100 W ??m, for site survey conditions representative of the average soilmoisture content and temperature values,?? soil conditions as given in Table 1 are absent.In addition, in case of a possible electrical influence, whatever its origin, measurements should be taken on site inorder to assess more precisely its effects on the estimation of the corrosion load. If no measurement is performedthe corrosion load is accepted high.4.2.4 Soil samplingSoil samples are taken at various locations on site taking into account the nature, the heterogeneity and thewetness of the soil; the resistivity and pH values of the soil samples are then measured in the laboratory.Annex B gives additional information on the procedure and measurementmethods used for soil sampling.The minimum resistivity value r * and the pH value measured on a soil sample after addition of deionized waterallow to assess the corrosion load using Table 2; the evaluation of soils on the border between two fields ofcorrosion load requires expert knowledge.In addition, a medium corrosion load should be changed to high when heterogeneous soil conditions occur at thelevel of the structure, such as:?? presence of a water table (partly submerged structure);?? wide range of r * values of samples ( r *max / r *min > 3);?? wide range of pH values of samples (pHmax - pHmin > 1,5).Table 2 —Corrosion load (free corrosion without concentration cell) > 9,56 – 9,5 HIGH MEDIUM LOWpH4,5 - 6< 4,510 30 50 100r * = Minimum resistivity value after adding deionized water ( W ??m) .yang6>EN 12501-2:2003 (E)74.2.5 Backfill materialsThe corrosion of a buried structure will depend upon the corrosion load of the native soil, but also upon thebackfilling procedure, the backfill materials (especially if they are different from the native soil) and the possibleleaching conditions. An assessment of the corrosion load of imported backfill materials should therefore be carriedout as it may either increase or reduce the effective corrosion load on the structure.Table 3 indicates criteria to be met by the backfill materials in order to lead to a low corrosion load.Table 3 — Criteria for backfill materialsParameters Low corrosion loadResistivityr * > 100 W ??mpHa 6 < pH < 9Sulfide < 10 mg/kgCarbon No visual detection of coal, coke, graphite, carboniferous residuesa Materials outside this pH range, but with low acidity or alkalinity amount, could be considered asleading to a low corrosion load.When industrial by-products are considered as backfill materials, the presence and amount of metallic salts shouldalso be considered in order to avoid possible galvanic corrosion.The use of selected backfill materials as shown in Table 3 can reduce the corrosion load (from high to medium orfrom medium to low), but only when the following conditions are fulfilled:?? no water table or leaching conditions that could cause contamination from the surrounding native soil;?? no mixed soils (native and imported) in contact with the structure.5 Complementary information for an existing structure5.1 GeneralIn the case of an existing structure, the corrosion load in soil is assessed either to perform a diagnosis in order toevaluate the remaining life time of the structure or to establish the reasons of corrosion damages and/or failures onthe structure.As the structure actually lays in the soil, more information can be collected than in the case of a new structure(see EN 12501-1:2003; annex B). This covers:?? the information on the structure itself (such as corrosion effects, operating conditions);?? the characteristics of the soil directly in contact with the walls of the structure;?? the effect of the environment (mainly electrical influences);?? the system of protection (type of coating, cathodic protection, ...).The three steps of the procedure for a new structure can be used for the assessment of the corrosion load; but theinvestigation conducted during preliminary inquiry, site survey and soil sampling will be more complete than for a.yang6>EN 12501-2:2003 (E)8new structure. Moreover, it is also possible to take into accountsamples coming from the structure itself to performthe assessment.Depending on the economical impact, the assessment of the corrosion load in soil will include more or lessextensive field measurements and/or laboratory analyses. The more accurate the assessment of the corrosion loadis required, the more detailed will be the characterisation and the more expert knowledge will be necessary.5.2 Investigations and analysisDuring site survey, electrical measurements such as electrochemical potential of the structure, voltage gradient insoil in the vicinity of the structure will provide information about the electrical influences from surrounding deviceson the structure. Information about the water table will be taken into account.It is possible to take soil samples close to the structure. Chemical data, such as chloride, sulfate, sulfide contents,alkalinity or acidity amount, will generally supplement resistivity and pH values used in the case of a new structure.Soil nature identification and other analyses, such as soil grains size distribution, relative to anaerobic conditionswill be performed to identify the corrosion process taking place in the soil.In the case of an excavation exposing the structure, it is possible to take soil samples in direct contact with thesurface of the structure and, if present, associated corrosion products.The visual examination of the surface of the structure can give information on the type of corrosion effects anddamages and on the corrosion process involved.If necessary, a sample of the structure can be taken together with a sample of soil in contact; this will allow aquantification of the corrosion damages with direct relationship with the soil characteristics and will lead to a betterknowledge of the corrosion load and a better forecast of the remaining life time of the structure.The analysis to be performed on these samples (soil, corrosion products, structure) requires suitable handling andconditioning, and sophisticated equipment only available in specialised laboratories. The high costs of the analysis make it necessary that the investigations to be performed are selected by experienced personnel well aware of allthe particulars of the specific case. Therefore it is not possible to establish a single procedure for assessing thecorrosion load in soil when investigating an existing structure..yang6>EN 12501-2:2003 (E)9Annex A(informative)Procedure for assessing the corrosion load in soil in the case of a newstructureAction AssessmentSoil andBackfill materials?? ??Environment Structure YesPreliminary InquirySufficient information(Criteria)NoYesSite SurveySufficient information(Criteria)SoilSampling CriteriaCorrosion load in soilAfter each step, the decision whether to stop or to continue the investigation can be taken. The possible lack ofinformation is counterbalanced by accepting a higher corrosion load..yang6>EN 12501-2:2003 (E)10Annex B(informative)General principles of soil studiesB.1 Preliminary inquiryB.1.1 GeneralThe preliminary inquiry generally consists of a topographical study, a geological study and an investigation forspecific information.B.1.2 Topographical studyThe topographical study involves the examination of ordnance survey maps and other types of maps; it providesinformation such as:?? ground contours;?? wet areas;?? ponds, swamps, lakes, peat bogs, etc..;?? estuaries, polders, marshes, saline soils bordering the sea;?? water course to be crossed in case of a long line structure.B.1.3 Geological studyA geological study is carried out using geological maps and provides information on:?? the nature and characteristics of the soils;?? the hydrogeology, i.e. the presence of water table.B.1.4 Investigation for specific informationThis involves the collection of data from the local and regional authorities and utilities that can supplement existinginformation with respect to pollution indicators, such as:?? areas polluted by various effluents of industrial or other origins;?? deposits and tips of industrial origin;?? the proximity of other structures (sewers, industrial pipelines, etc.) which could cause pollution;?? industries and transport systems using direct or alternating electric current..yang6>EN 12501-2:2003 (E)11B.2 Site SurveyB.2.1 GeneralThe site survey consists in collecting additional information to be obtained by observations and measurements.Special attention should be given to the most unfavourable conditions, such as locations and periods whenmeasurements are taken.B.2.2 Resistivity measurementResistivity determination by the four pin method, depending on the distance between the pins inserted into theground, gives approximately the overall soil resistivity at a depth equal to pin spacing.These measurements from the surface can provide a vertical resistivity profile and an horizontal resistivity profile of the different soils or layers crossed by the structure. For a given location, it is advisable to carry out themeasurements with two spacings or more, depending on the vertical dimension of the structure.Other measurement methods may also be used: inserting a Columbia probe, three pin method, etc...Resistivity values measured from the surface can help to choose the locations for soil sampling.B.2.3 Measurement of potential gradients in soilThe presence of potential gradients in soil can be checked during the site survey and their intensity measuredwhen possible electrical influences have been detected during the preliminary inquiry.B.3 Soil samplingB.3.1 GeneralSoil samples should be taken in such a way that they will berepresentative for the soil surrounding the structure.The samples should be kept in an airtight bag (e.g. plastic sack) and analyzed as soon as possible in order to avoidany physical or chemical changes in the sample.B.3.2 Minimum resistivity value after adding deionized waterAmong parameters used to characterise a soil, resistivity is the one providing the most information. The soilresistivity depends on the nature and amounts of dissolved salts, particularly chlorides and sulfates, and thereforeon the amount of water present.The minimum resistivity value ( r *) is extrapolated from the evolution of the resistivity of a soil mixture after adding repeatedly known volumes of deionized water to a sample of soil (sieve size < 5 mm). The sample is compressedinto a soil box (by example with two plates electrodes). The measured resistance value is converted to soilresistivity depending on the geometry of the box.B.3.3 pH valueIn the majority of cases, the pH levels of natural soils are comprised between 6 and 9. Soils with a pH below 6 areonly encountered in the natural state in peat or in siliceous soils corresponding with primary geological levels.Very acid or very alkaline pH levels generally indicate pollution of an industrial origin. However in certain geologicalformations, very low pH values may be encountered in soils with originally high sulphide content and where thesulphide has oxidised to sulphate..yang6>EN 12501-2:2003 (E)12The pH measurement is performed on a soil mixture obtained by adding generally two parts of deionized water toone part of soil, and using a pH-meter.B.3.4 Water tableThe presence of a constant or fluctuating (seasonal effect) water table has an effect on the corrosion process.The topographical, geological and environment data usually enable its existence to be predicted.During taking the soil samples, a check can be made on the intrusion of any water into the boreholes as a functionof the depth.B.3.5 HeterogeneityHeterogeneity leads to the formation of concentration cells. This can be assessed either by examination of the soilsamples, or by profile or depth related resistivity determination, respectively for horizontal and verticalheterogeneity (the four pin method is well adapted to perform this evaluation directly on site; see B.2.1).B.3.6 Type of soilThe nature of a soil and its texture provide information on the type of corrosion likely to occur. As an example,Table B.1 gives information on some types of soil.Table B.1 — Types of soilType of soil Resistivity range ( W m) AerationMarine mud 3 - 8 Very lowClays and silts 5 - 20 Low to very lowDry non-marine sands 200 - 2000 HighB.3.7 Microbial activityWith anaerobic conditions surrounding a buried structure, Microbially Induced Corrosion (MIC) may beencountered.When MIC is suspected, special care should be taken during sampling in order to enable an appropriate search forbacteria in accordance with specific procedures..yang6>blank.yang6>BS EN12501-2:2003BSI389 Chiswick High RoadLondonW4 4ALBSI — British Standards InstitutionBSI is the independent national body responsible for preparing British Standards. It presents the UK 6><#00aa00'>view on standards in Europe and at theinternational level. It is incorporated by Royal Charter.RevisionsBritish Standards are updated by amendment or revision. Users of British Standards should make sure that they possess the latest amendments oreditions.It is the constant aim of BSI to improve the quality of our productsand services.We would be grateful if anyone finding an inaccuracy or ambiguity while usingthis British Standard would inform the Secretary of the technical committeeresponsible, the identity of which can be found on the inside front cover.Tel: +44 (0)20 8996 9000. Fax: +44 (0)20 8996 7400.BSI offers members an individual updating service called PLUS which ensuresthat subscribers automatically receive the latest editions of standards.Buying standardsOrders for all BSI, international and foreign standards publications should beaddressed to Customer Services. Tel: +44 (0)20 8996 9001.Fax: +44 (0)20 8996 7001. Email: orders@bsi-global>. Standards are alsoavailable from the BSI website at //.bsi-global>.In response to orders for international standards, it is BSI policy to supply the。

Mitigation of corrosion in concrete bridges

MITIGATION OF CORROSION IN CONCRETE BRIDGES Paul Virmani, Federal Highway Administration, McLean, VAJohn M. Hooks, Federal Highway Administration, McLean, VA BackgroundThe deterioration of various concrete bridge components built in the past with black steel reinforcement is one of the most common, most damaging and most costly problems facing bridge owners in the United States. The major cause of concrete deterioration (cracking, delamination, and spalling), is the corrosion of embedded black steel reinforcing bars as a result of chloride ions (permeating through the concrete cover) in combination with moisture and oxygen. The average black steel reinforced concrete (R/C) bridge deck, in a snow belt State, showed spalling in about 7-10 years. Although prestressed concrete (PS/C) bridge members are generally cast with good control of mix designs and curing regimes, they are still vulnerable to corrosion (of the pretensioned, uncoated strands) similar to that of the black steel in reinforced concrete, albeit after a longer period of service. Since PS/C members rely on the tensile strength of the strands to resist loads, loss of a few strands per member could be catastrophic. Even small corrosion pits cause fracture of a strand, as compared to non-prestressed concrete reinforcing that will literally rust away without breaking.For post-tensioned concrete (PT/C) bridge members (both external and internal prestressing), the voids in grouted ducts and/or excessive bleed water (in certain grout mix designs), in addition to chloride/water entering the rough breached ducts or faulty joints at anchorage locations, will corrode the uncoated strands. The underlying difficulty is that there are no reliable, rapid and cost-effective non-destructive methods to assure owners that completed PT/C structures have met the construction specifications. One of the major inspection concerns is whether the ducts in PT/C members have been completely filled with grout and whether there is a uniform coverage over the prestressing steel.Figure 1. Corroded StrandsMany times, it has been found invariably that the ducts have large voided sections and were onlyfilled partially with grout. In addition, it is very difficult to assess the condition of anchorage areas. Past research has identified that excessive bleed water in certain commercial grouts corroded the strands in a very short time, and that in due time under load, these corroded strands can break prematurely. Since PS/C members rely on the tensile strength of the strand to resist loads, loss of a few strands in members could be catastrophic. Even small pits lead to fracture of a strand, as compared to R/C concrete where the reinforcing will literally rust away (if preventative measures are not taken) without breaking.This paper summarizes the status of various corrosion protection systems in use for construction and rehabilitation with advantages, limitations, issues and concerns for their use to provide cost effective solutions in controlling corrosion in concrete bridges in the United States.Corrosion of Bridges in the United StatesCorrosion of reinforcing bars and prestressing tendons is one of the most significant and unremitting factors in the process of deterioration of bridges. Of approximately 478,336 bridges (not including tunnels and culverts) in the United States, about 78, 609 bridges are rated structurally deficient. Corrosion is the underlying cause of many of these bridges being rated deficient and many more bridges are showing signs of imminently serious corrosion. In combination with water and oxygen, the main ingredient for corrosion is chloride ions from applications of deicing salts in the snow belt region or marine exposure of concrete bridge members. Chloride ions eventually penetrate the concrete cover, react with embedded reinforcement to form expansive corrosion products, causeing concrete to crack with eventual concrete spalling due to debonding of concrete accelerated by traffic induced vibrations.Figure 1. Corrosion Damage to Concrete Bridge PierWhile there is a downward trend in the percentage of structurally deficient bridges, the costs to replace aging bridges increased by 12 percent over a recent 5 year period. In addition, there hasbeen a significant increase in the required maintenance of the aging bridges. Although the vast majority of the approximately 108,000 prestressed concrete bridges have been built since 1960, many of these bridges will require maintenance in the next 10 to 30 years. Therefore, significant maintenance, repair, rehabilitation, and replacement activities for the nation’s highway bridge infrastructure are foreseen over the next few decades before current construction practices begin to reverse the trend.A recent study has determined that the total cost of corrosion in the United States alone is approximately $276 billion/year. This figure represents about 3.1 percent of the Gross National Product (GNP) based on 1998 figures. The dollar impact of corrosion on highway bridges is considerable. The annual direct cost of corrosion for highway bridges is estimated to be $6.43 billion to $10.15 billion, consisting of $3.79 billion to replace structurally deficient bridges over the next 10 years, $1.07 billion to $2.93 billion for maintenance and cost of capital for concrete bridge decks, $1.07 billion to $2.93 billion for maintenance and cost of capital for concrete substructures and superstructures (minus decks), and $0.50 billion for the maintenance painting cost for steel bridges. This gives us an average annual cost of corrosion of $8.29 billion. Life-cycle analysis estimates indirect costs to the user due to traffic delays and lost productivity at more than 10 times the direct cost of corrosion. In addition, it was estimated that employing “best maintenance practices” versus “average practices” could save 46 percent of the annual corrosion cost of a bridge deck reinforced with black steel bars, or $2,000 per bridge per year. Following is a synopsis of various corrosion protection systems for construction of new concrete bridges and rehabilitation of existing salt-contaminated bridge members.Corrosion Protection Systems for Construction of Concrete BridgesEpoxy Coated Reinforcing Bars (ECR)Epoxy coating for reinforcing bars is a barrier system, developed by FHWA in 1974, for the purpose of preventing chloride ions from reaching the surface of the black steel bars. To date, ECR has been used in approximately 100,000 structures including 20,000 highway bridges. Total accumulated usage of ECR is about 4.5 million tons and there are 35 coating plants in North America.At this time, all States (except Florida) use this system extensively. In general, epoxy coated reinforcing bars have shown excellent performance in bridge decks. Excessive defects, bare area and holidays will compromise ECR’s good performance. Experience indicates that prefabrication of bars should be done first and then the coating applied- better performance will result due to avoidance of bending stresses in the coating. ECR top bar mats should not be coupled with a large uncoated cathode, such as a black steel bottom bar mat to avoid macro-cell corrosion currents. ECR reinforcing used in situations involving excessive moisture, salt and high temperatures, marine exposure, highly permeable concrete, cracks, etc. are prone to premature failure. In these situations, a reduction in adhesion of epoxy to reinforcing bars has beenobserved in concrete with or without chloride ions. Long-term corrosion performance of ECRs in concrete cannot be guaranteed on the basis of increased adhesion evaluated by available laboratory screening tests. Accelerated laboratory tests for adhesion (cathodic disbondment, hot water immersion in varying pH and salt) are not the best indicators for ECR performance in concrete.Epoxy coated reinforcing bars have proven to be a cost-effective corrosion protection system for bridge decks, especially when both the top and bottom mats are coated. The premium cost of epoxy coated steel versus uncoated black steel is about 20%. However, the total cost increase on a typical bridge structure is in the range of 1 to 2%. In the United States, the estimated potential savings in bridge deck costs due to ECR use (with projected twice the corrosion-free service life for bridge decks already constructed with ECR instead of black steel) is in the $5 to $10 billion range.Solid Stainless Steel Reinforcing BarsSolid stainless steel reinforcing bars experience corrosion rates of up to 100 times less than black steel and show excellent performance in laboratory in both accelerated corrosion tests and long-term performance in concrete specimens. No macro-cell current can be detected between a stainless anode and a black steel cathode in a salt contaminated reinforced concrete slab. The 316 grade of stainless steel exhibits better performance than the 304 grade steel. The high cost of solid stainless steel bars - around $2 to $3 per pound compared to 15 cents/pound for black steel – can be prohibitive because total structure costs may increase by up to15 to 20 percent versus a structure reinforced with black steel. The process of fabricating bar deformations by welding wire on smooth reinforcing bars has reduced the price by 20 percent. Evaluation of this process is underway compared to normal rolled down stainless reinforcing bar in conventional steel mills, but the supplier of this product from the United Kingdom is currently out of business. Structures reinforced with solid stainless steel reinforcing bars can be expected to provide a maintenance-free service life of greater than 75 years. In the US, there are a few states, namely Virginia, Oregon, New Jersey, Michigan and Montana, using solid stainless steel reinforcing bars on an experimental basis. The high costs for this system can be justified for strategic bridges due to lost man-hours caused by detours and environmental concerns with high traffic density.A good example is the bridge crossing the Middle Fork of the Flathead River on US Route 2 near Essex, Montana. One end of the bridge terminates in Glacier National Park and the other at Flathead National Forest. Heavy snow, frequent salt applications and freeze-thaw cycles result in a harsh environment and any closure of the bridge involves a detour of 300 miles.Figure 2 a. US Route 2 with Stainless Steel Bars Figure 2 b. Stainless Bars & Chairs Stainless-clad Reinforcing barsA promising alternative to the high cost of solid stainless steel reinforcing bars is bars with a stainless steel cladding on the surface. The estimated production cost of 60-75 cents per pound compare very favorably to the $2 to $3 per pound for solid stainless steel bars and is just four times the cost of black steel (resulting in a total structure cost increase of about 5 percent). Stainless-clad reinforcing bars have exhibited excellent performance in accelerated laboratory tests. Issues related to fabrication include: protection of bare cut ends - welding a stainless steel cap on the cut end or stainless metal spray is under evaluation; and deformation and bendability at present may not be as good as that of solids bars. The long-term physical properties and performance of the core steel and the cladding is a concern in the two currently competing processes for manufacturing clad bars – Nuovinox and plasma coated. About 10 to12 field installations are planned by various states in the United States. Early results of laboratory testing indicate a bright future if the price can be held at the present level.Corrosion InhibitorsCorrosion inhibitors, generally mixed in with the water during concrete mixing, present an alternative to epoxy coated reinforcing bars at roughly comparable costs. Performance of inhibitors has been shown to be variable due to varying chemical composition - some are better than others. Basic inhibitor types include anodic, cathodic and mixed (or organic). At this time, calcium nitrite is the only corrosion inhibitor that has shown promise to combat corrosion. Equal amounts of nitrite ions are required in the concrete to counteract the corrosion caused by same amount of chloride ions. For good performance, expected chloride ions at reinforcing bar level for the total design service life should not exceed available nitrite ions. With time, nitrite ions redistribute towards the bottom of concrete slab and eventually can leach out after long-termservice exposure. Corrosion inhibitors are more commonly used in prestressed concrete members due to non-use of coated strands. Corrosion inhibitors are not considered effective for rehabilitation of salt-contaminated structures because there is no efficient system capable of delivering the inhibitor ions to the reinforcing bar level thru hardened concrete. In a marine environment (continuous high salt, moisture and temperature), the use of corrosion inhibitors in conjunction with epoxy coated reinforcing bars is recommended as an effective corrosion protection system.High Performance ConcreteHigh quality (“High Performance”) concrete is the primary corrosion protection system for any concrete structure or element. It is the first defense against intrusion of chloride ions and also to provide high alkalinity for a passive environment for the reinforcement. High quality concrete should have a low w/c ratio, low permeability, be crack-free and provide adequate cover over the reinforcing bars. Most bridge owners in the US employ proven additives such as fly ash, silica fume, polymers, epoxies, or latex modifiers to reduce concrete permeability. These admixtures should be used in optimal amounts so as to not reduce the pH of the hardened concrete. The majority of states are now developing and specifying high performance concrete mix designs and procedures for use in the field to construct bridges with fewer members or slender design at low cost as well as for basic corrosion protection. In one current example of high quality concrete as a protection system, the State of Florida mostly relies on the use high quality concrete with good cover alone for corrosion protection of their bridges located in a marine environment. At present, corrosion inhibitors, stainless steel and clad reinforcing bar, etc. are being used experimentally on a few projects. The Florida Department of Transportation has experienced premature corrosion with ECR in marine environments and they do not use ECR while they continue to evaluate corrosion resistant reinforcing alloys that would perform better than ECR. Rehabilitation Systems for Concrete BridgesCathodic Protection (CP)In the past several decades the FHWA has developed a number of impressed-current, cathodic protection (CP) systems for concrete bridges and approximately five hundred bridges in the United States are currently protected by CP systems – the State of Missouri alone has installed CP on about 200 bridges. The FHWA initially developed a conductive polymer anode for slotted and mounded CP systems. Currently, titanium mesh anode covered with an overlay is a standard impressed CP system for horizontal surfaces, (e.g., bridge decks). The cost of CP installations is reasonable at $6 to 8 per square foot ($0.56 to $0.75 per square meter) of concrete surface but CP systems are being used more in parking garages than on the bridges.Impressed current CP systems require maintenance of rectifiers and other electrical circuits for them to function. If an impressed-current CP system is not properly functioning and polarizing the steel adequately, the structure is not protected and corrosion can continue. Maintenance is asignificant problem for impressed CP systems. The FHWA has now developed tow maintenance-free galvanic CP systems for substructure bridge members and the states of Florida and Oregon are leaders in developing and installing galvanic CP technology for their bridges. Three galvanic anode systems, zinc-hydrogel, zinc-Indium-Aluminum alloy, and zinc alone or with humetants are in use today for inland vertical and upside bridge members away from the water. Galvanic CP systems have broader appeal to the State DOT’s with their limited personnel resources and minimal maintenance requirements. For PS/C, tendon to concrete bond is only reduced slightly for charge transfer equal to 160 years of CP. For PS/C, hydrogen embrittlement is not an issue when polarization is maintained below -0.90v (SCE) and there is a methodology available for qualifying PS/S members for CP. Normally, galvanic anodes are a more suitable choice for PS/C in avoiding accidental hydrogen embrittlement of high strength steel strands because they deliver low currents at low voltages.Electrochemical Chloride Extraction (ECE)Another method of protecting concrete elements from chloride induced corrosion is to move the chloride ions away from the location of the reinforcing steel. This can be done via a procedure known as electrochemical chloride extraction, which in principle is simply an accelerated cathodic protection process. The reinforcing steel in the concrete bridge member (pier column, deck, etc.) is the cathode; a temporary anode is anchored to the outer surface of concrete in an electrolytic solution and a current (0.1 to 0.2 amps per square foot of concrete surface) is applied from a direct current power source. This current is 100-200 times higher than that for cathodic protection and the process is applicable to reinforced concrete only. The procedure takes approximately 4 weeks. The chloride ions move outwards and sodium ions inwards toward the reinforcing bars to eliminate corrosion. In general, the concrete surface is either coated with sealers (substructure) or overlaid with concrete (decks) after chloride removal to inhibit the penetration of future chloride ions.This technology was tested for more than 25 years ago by FHWA at Kansas DOT and Battelle Institute. A number of states have now used this technology and the costs are reasonable. No maintenance is required after completion of the process. The costs of ECE are comparable to use of a CP system, but long-term performance of the process in protecting the concrete member treated with ECE is not yet well known. More research is underway to define criterion for process completion with some assurance of desired corrosion-free service life.Conventional Methods - Overlays, Sealers and PatchingThe majority of bridge owners still prefer and depend on conventional methods over electrical methods such as cathodic protection and electro-chemical chloride extraction process. Low permeability concrete overlays have been shown to extend the life of bridges by 15-30 years. Latex-modified concrete, silica-fume concrete, low water - cement ratio concrete and polymer concrete are the most commonly used overlays to slow down the future ingress of chloride ions. This rehabilitation methodology requires no maintenance after installation, but corrosion continues since chloride still resides at the reinforcement level. After overlay installation, thecorrosion rate somewhat decreases with passage of time due to drying of concrete at reinforcing bar level and the lesser availability of future ingress of chloride ions. The cost of a low permeability overlay at $5 to $10 per square foot ($0.46 to $0.93 per square meter) is reasonable, but it does not stop the corrosion process completely.ConclusionsCorrosion is an inescapable process, since all processed construction materials eventually revert back to their natural form. The FHWA has made much progress in the area of new bridge construction for the last 25 years. The corrosion protection systems that are in use today are performing satisfactorily. More needs to be done in developing corrosion resistant reinforcements and other corrosion protection systems such as corrosion inhibitors and more durable concrete mix designs. Since all materials will eventually degrade, in the future we have to find ways to rehabilitate the so-called corrosion-resistant bridges of today with improved cost-effective methods and technologies. At present, there are 250,000 bridges, which contain black steel and will need rehabilitation in the future. The present challenge is to make CP, chloride removal, and other processes cost-effective for bridge owners to use. Corrosion engineers and scientists will always play major roles in the development of corrosion-resistant materials for more durable new bridges as well as to find more cost-effective methodologies for extending the life of existing bridges.。

服役环境下拉索全寿命腐蚀曲线分析

服役环境下拉索全寿命腐蚀曲线分析鲍烜平;何政【摘要】腐蚀问题是斜拉桥拉索运营状态下性能最重要的影响因素之一.腐蚀会导致拉索截面削减,构件承载力下降,同时对其抗疲劳性能、延性等性能也会产生重大影响.拉索受力截面积的变化作为衡量拉索腐蚀程度的参数,在研究拉索在腐蚀环境下的各类性能研究都有重要意义.文中综合考虑应力、腐蚀环境以及随机性因素等对拉索腐蚀作用的影响,结合全寿命设计理论,提出腐蚀拉索截面变化率这一参数并通过分段刻画拉索在腐蚀作用下对拉索构件截面变化的影响,建立了一种将统计方法、加速腐蚀试验等相结合的方法以获取服役期内的该参数全寿命时间关联曲线,为拉索寿命的评估和拉索在服役环境下的性能研究提供基础和参考.【期刊名称】《低温建筑技术》【年(卷),期】2014(036)008【总页数】3页(P49-51)【关键词】斜拉桥;拉索;腐蚀;截面变化率;使用寿命【作者】鲍烜平;何政【作者单位】大连理工大学土木工程学院,辽宁大连116024;大连理工大学土木工程学院,辽宁大连116024【正文语种】中文【中图分类】TU392.2拉索内镀锌钢丝的腐蚀相关问题已得到国内外学者广泛关注，加速试验［1］是研究拉索腐蚀机理的主要方法;Deeble等［2］通过实验分析悬索桥拉索腐蚀监测结果，得出温度和相对湿度对拉索腐蚀的影响;Yang等［3］通过盐雾试验分析了拉应力对拉索腐蚀的影响;徐俊等［4］结合实验数据结果分析和数值模拟研究了钢丝力学性能随腐蚀发展的变化规律;Li等［5］提出了以质量损失为标准的拉索腐蚀评定方法;Li等［6］及Nakamura等［7］通过加速腐蚀试验，得出腐蚀对拉索的疲劳寿命存在较大影响;Suzumura等［8］针对拉索镀锌钢丝通过试验方法探究了镀锌钢丝的腐蚀速率影响因素;Barton 等［9］和 Betti等［10］通过加速腐蚀试验发现腐蚀作用下拉索钢丝断裂的伸长率较无腐蚀状态发生变化;对于应力问题，梁雄［11］通过加速试验对模拟酸雨环境下的镀锌钢丝镀锌层在不同应力水平的腐蚀速度进行分析，研究表明应力对镀锌层腐蚀速率有影响。

下载提示

1、下载文档前请自行甄别文档内容的完整性，平台不提供额外的编辑、内容补充、找答案等附加服务。
2、"仅部分预览"的文档,不可在线预览部分如存在完整性等问题,可反馈申请退款(可完整预览的文档不适用该条件!)。
3、如文档侵犯您的权益，请联系客服反馈,我们会尽快为您处理(人工客服工作时间：9:00-18:30)。

Effects of Mineral Additives on Biochar Formation Carbon Retention, Stability, and Properties

页数:7
Formulating High-Performance Waterborne Epoxy Coa

页数:28
Influence of mill scale and rust layer on the corrosion resistance of low-alloy steel in s

页数:11
Fire Resistance of Rectangular Steel Columns Filled with Bar-Reinforced Concrete

页数:10
Influences and water resistance of waterborne intumescent fire resistive coating for steel structure

页数:7
Swelling Properties of Water-Swelling Materials Exposed to Organic Water Pollution

页数:7
Organic versus Hybrid Coacervate Complexes Co-Assembly and Adsorption Properties

页数:9
Effect of phosphorus on the microstructure and mechanical properties of strip cast carbon steel

页数:6
Friction and wear properties of combined surface modified carbon fabric reinforced

页数:7
The corrosion resistance of ultra-low carbon bainitic steel

页数:8
2 properties of water and sand

页数:11
Effect of boron on hot strips of low carbon steel produced by compact strip production

页数:5

2 Evaluation of corrosion protection properties of additives for waterborne epoxy coatings on steel

合集下载

漏磁内检测技术在原油管道腐蚀评价分析中的应用

BS EN 12501-2-2003 金属材料的防腐蚀.土壤中腐蚀可能性.低合金和非合金黑色金属材料

Mitigation of corrosion in concrete bridges

服役环境下拉索全寿命腐蚀曲线分析

文档推荐

最新文档