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The zincic layer that nodular cast iron is in charge of is anticorrosive researc
From;    Author:Stand originally
Preface reachs gas industry to be applied quickly widely in water as canal of nodular cast iron, 900 thousand tons when produce per year a quantity to increase to 2001 by 100 thousand tons of 1990 of our country, occupy all casting iron pipe to produce per year the 50% above of the quantity. What nodular cast iron is in charge of is anticorrosive and direct the long-term use sex that matters to conduit and security, because this is,measure technology tubal a network and a of moving state main index. According to 10 typical city findings shows, net static leakage breaks feed pipe of our country town rate achieve 12 ~ 13% , exceeded a country to ask urban leakage breaks rate control to be in far 6% the following standards, conduit is so anticorrosive it is us all the time current a popular task. Current, canal of nodular cast iron uses cement liner to regard as inside anticorrosive form, zinc adds bitumen to regard as outside anticorrosive form, had made in manufacturing technology finish, anticorrosive processing undertakes after beardless construction is installed. This already became domestic and international nodular cast iron to provide the general way of manufacturer home, anticorrosive effect is very apparent also. One, the current situation of anticorrosive research is in zincic layer in the research with anticorrosive conduit, the bridge walks along Shenggebanmusong in the front row of the world all the time, began the research of zincic layer the earliest 1938. Experiment via the iteration of countless kinds of too old stuff, found finally apply to cheaply definitely the anticorrosive material below most circumstance -- zinc, be in formal 1958 ground to use zincic layer on its conduit product anticorrosive. Nowadays, zincic layer is outer defend be proved to be one of the most significant anticorrosive step inside limits of already alive bound, prolong the service life of conduit effectively. Bridge of Mu Song of holy dagger class passes research to discover, outside anticorrosive composition means: Lacquer of zincic layer bitumen is had inseparable defend admirably the effect, among them zinc layer is having conclusive effect. In European standard EN 545: 1994 " canal of water supply nodular cast iron, pipe fitting " the in, and in – of international standard ISO 8179 1: 1995 (E) " nodular cast iron is in charge of -- outside coating -- the first part " the 4.4th in Dou Youming sets truly: Zincic layer density is not gotten under 130g/m2, local lowest density is not gotten under 110g/m2. In GB/T17456 of level of our country state -- 1998 in, used – of international standard ISO 8179 equivalently 1: 1995. Our country's anticorrosive to zincic layer research is less, and be in abroad, especially bridge of Mu Song of holy dagger class, anticorrosive to zincic layer research has had 60 old histories. In the in-house standard in bridge of Mu Song of holy dagger class, zinc anticorrosive form is canal of nodular cast iron certainly outside bitumen outside basic standard anticorrosive layer, apply to the agrotype of great majority, outside the standard that the nodular cast iron that at the same time this also is the developed country such as Europe provides anticorrosive mode. 2, soil is in charge of caustic   to nodular cast iron 1. Electrochemistry corrodes metal and electrolyte solution contact to be able to produce electrochemistry effect, voltage arises between its surface and solution, namely electrode potential. Metallic surface because blemish of crystal boundary, crystal, be mingled with, stress and exterior injury differ and the meeting may exist different photograph, the inhomogenous sex on these electrochemistry makes metallic surface microcosmic and departmental electrode potential is different, formed corrode galvanic cell. The loses partly electron with low potential, become metallic ion, enter solution, call positive pole; The electron flows to the share with high potential, make negative electrode. The result that this kind of galvanic cell reacts, cause form in metallic surface many ferruginous. The cell of oxygen great difference that nodular cast iron runs (see a picture 1) : When conduit of nodular cast iron buries the underground of locate moisture, the backfill earth of coping is relatively loose and be apart from the ground close, and bottom basically is raw land, earthy and compact and be apart from the ground far. Oxygen can cause the aerobic chroma that conduit fluctuates to differ from coping infiltration, and electrode of conduit itself since, it is electrode coupling lead; Water is electrolyte, form then " batteries of oxygen great difference " . The graph forms iron of   of batteries of oxygen great difference to lose an electron to enter water film on 1 conduit cross section, oxygen gets the electron becomes oxyhydrogen ion. 2. Microbial corrosion microbial corrosion also is a kind of electrochemistry is corroded, because corrode the certain put in order that microbial breed changed the material interface that contacts to it with metabolism to change character,what what differ is medium. Customarily can divide the oxygen that it is be disgusted with to corrode become reconciled oxygen. Sulfate is reductive bacterium SBR is microbial in the biggest to corroding an influence, the oxygen of be disgusted with with most research is corroded cause germ. The person such as Von Wogozen Kuhr put forward classical depolarization to change theory 1974, because the activity of SBR passes hydrogenation,the dot corrode that thinks to bury ground casting iron pipe is enzymatic metallic surface deoxygenate, total reaction form is as follows: 4Fe SO42- 4H2O 3Fe (OH) bacterium of good oxygen of   of 2 FeS 2OH- is iron oxidation bacterium, vulcanization bacterium and iron bacteria, the action generation that carries sulfur bacterium is vitriolic OK happening good oxygen is corroded. These bacteria achieve 10~12% vogue to be able to survive in vitriolic chroma, can be opposite cast-iron generation is corroded badly. Another kind of reason is in good oxygen the condition issues metallic surface to the bacterium multiplies and form rugged irregular biomembrane. Microbial activity makes biomembrane core condition produces change, value of the chroma that be like oxygen, PH, acid-base value, make metallic surface forms division of yin and yang, cause galvanic cell reaction. 3, zincic layer is anticorrosive layer of action mechanism zinc is an active covering layer, superexcellent protective performance shows on anticorrosive effect: 1. The potential of electrochemistry protection iron is - 0.440mV, and zincic potential is - 0.763mV, the potential that compares iron is low, the potential of oxygen is 1.4mV. The voltage between such zincic oxygen is bigger, form galvanic cell more easily, get cast-iron tube wall protective thereby. 2. The covering layer that forms stability pursues bitumen of zinc of canal of 2 nodular cast iron is anticorrosive   is in layer sketch map to contact a process with environmental soil in, the material such as the carbonate in metallic zinc and earth combines the carbonic acid zinc that cannot dissolve, this diaphragm closely felt is on tube wall, form compact and successive, not dissoluble, cannot the coating of leakage. Coating in the bitumen over zincic layer sealed pore also has all in all effect, can promote zincic layer change to become stability with the zincic salt that cannot dissolve. Chemical reaction form is as follows:   of   of Zn2 CO32- ZnCO32- of   of   of ZnZn2 2e- 3. In scathing ego is carried in conduit more or installing a process, may produce local loss. Zinc issues rapid change to become zincic ion in the action of galvanic cell. Zincic ion passes bitumen layer the action of sealed pore is migratory cover loss, form stability protect zincic layer with what cannot dissolve. Zn2 CO32- ZnCO32- pursues sketch map of heal of ego of 3 zinc layer   4, the importance with zincic anticorrosive layer Shenggebanmusong the bridge and cooperation of company of Suez Lyonnaise Des Eaux, the findings of 49 cop in caustic to the extreme soil shows: ■ zincic layer is anticorrosive conduit: Service period 16 ~ 19 year, have two conduit only, ply of cast-iron tube wall of 0.5mm ~ 0.7mm is corroded. ■ the layer that do not have zinc is anticorrosive conduit: 85% conduit are corroded. The bridge is opposite Shenggebanmusong 1961-1974 year an used cop the findings about corroding a respect: Anticorrosive canal number of channels measures bitumen zinc outside bitumen anticorrosive conduit amount ends outside the layer 1974 the end of the year, cankerous conduit amount 35 9 is in 1961-1974 year during, use conduit length (the layer of bitumen of   of conduit amount 2.55 0.14 that every 1000km of Km) 13700 65150 damages has / outside the layer that do not have zinc anticorrosive experiment: sample cent is two groups, a group only daub bitumen layer, layer of zinc of another group of daub, plus bitumen layer, it is next in the center of print lay off is identical the cut of dimension, in placing solution of NaCl M/10 ~ Na2SO4 M/100 again, immerse one year, take out finally, undertake sample is compared. The result shows, only the anticorrosive layer of the print of daub bitumen, especially cut part sufferred destroy, lost protective action basically, and the anticorrosive layer of the print of zincic bitumen keeps in good condition, cut part also got very good heal, refer to next graphs 4. Graph layer of zinc of   of experiment of heal of ego of 4 zinc layer is acting all in all action on anticorrosive function: On one hand, formation compact not deliquescent diaphragm is adherent go up in tube wall, can land of very old rate decreases electrochemistry and corrode microbially; On the other hand, metallic zinc still is had fight percussive plasticity to be out of shape ability, strengthen the protection to conduit. Anticorrosive ability still mirrors zincic bitumen in both and mutual on the action between: Zinc and cast-iron between and very good agglutinate sex is had between zinc and bitumen, build to conduit and outside had a complete protection protective screen, prevent anticorrosive be no longer in force. Zinc still can carry bitumen agency action, those who make the change of zincic salt and ego heal sex is migratory, expanded to defend further ability, make the scar that appears possibly gets seasonable rehabilitate. So the organic union of zinc and bitumen arose to defend faultlessly the effect, both be short of one cannot. Use bitumen plasticity data only outside conduit of anticorrosive nodular cast iron, get in anticorrosive process all round the stress action that edaphic place brings to bear on and the influence that difference in temperature changes, produce the irregular crackle of penetrable and anticorrosive layer easily, create anticorrosive be no longer in force. Because lack zincic layer,in traumatic place distinctive ego cicatrizations to use, conduit lost due protection basically, cause corrode. 5, conclusion is current, the use unit that some nodular cast iron of our country run, did not realize the value with zincic anticorrosive layer. To save investment, the person is layer of zinc of ground leave out, use monolayer bitumen to defend only. From the point of long-term economic point of view, this thes loss outweights the gain, shortened greatly the service life of conduit, the security that gives pipeline buries next hidden trouble. System of pipeline of holy dagger class (China) to the craft of zincic layer control takes very seriously, to maintain the interest of the user, do not allow to manufacture to be in charge of without the nodular cast iron of gush zinc, in order to ensure the anticorrosive effect of conduit reachs service life. Method of high-pressured report gush is used in craft, fuse metallic zinc silk come spray zinc layer, made even, compact, tall adhere. Return the quality with strict set to detect at the same time the system supervises his to carry out a result, write the manufacturing record that day, content includes: Density of layer of weight of layer of diameter of inspection frequency, canal, time, zinc, zinc is waited a moment. 1984, british water research center made conclusion thinks: Outside the zincic layer that nodular cast iron is in charge of anticorrosive it is very important, decrease effectively corrode. Bridge of Mu Song of holy dagger class thinks, to strengthen conduit outside anticorrosive ability, be necessary to increase the density of zincic layer 200g/m2. To canal of nodular cast iron, so far, zinc increases pitch outside anticorrosive should be best also be the basiccest defend material. To caustic the conduit laid of stronger area, can be in defend basically on the foundation of the layer, film covers adscititious polyethylene, or polyurethane coating, or the form such as polyethylene coating, will undertake special protection. Note: The bibliographical reference of the article is taken for the most part from Yu Shengge data of interior of Ban Musong bridge, offer everybody to consult only. About a few data that the article uses we need not make an explanation.

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