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1、华能上海石洞口第二电厂阴极保护介绍-铝阳极镁阳极锌阳极测试桩阴极保护牺牲阳极镁合金牺牲阳极镁牺牲阳极Introduction of cathodic protection for Huaneng second Shanghai power plantThe cathodic protection of the whole power plant of Huaneng Shanghai stone cave second power plant mainly includes the following contents.1. underground steel pipe pile, under
2、ground pipe, buried steel structure protection2. circulating water pipe (in plant part) protection3. the circulation water pipe (outside the factory part) protects4. circulating pump room rack, rotary sieve and the circulating pump pump body protection5. condenser protection6. steel pipe pile protec
3、tion for coal unloading wharf.Among them, 1, 2, 4, 5 by the United States Sargen - Lundy engineering design, third design by the Shanghai Tunnel Engineering Institute, sixth by Shanghai rot corrosion new technology research and design.1 Cathodic Protection of underground steel pipe pile, underground
4、 steel pipe and buried steel structureAccording to the Shanghai area soil, for independent (without electrical connection line special) the steel pipe pile, underground pipelines, underground steel structure student does not require the use of anti-corrosion coating, sacrificial anode or external cu
5、rrent special preventionAs long as the wall thickness of the steel pipe pile is properly increased, the service life of the steel pipe pile can be prolonged. In the design, because without any protection measures, as long as appropriate increase of steel pipe pile wall thickness to extend its servic
6、e life. set upBecause of the lack of protection measures, the design redundancy of the steel pipe pile wall is considered as 1.5mm at the annual corrosion rate of 0.025mm. These independent underground steel members are simpler in construction. Experience tableMing, such a design margin is feasible.
7、In the design of the main power plant, chimneys, warehouse and other large buildings of steel pipe pile, underground pipelines and other underground steel structure, composed of a non independent system in electric power plant and their lightning protection and grounding connection. stayThis part of
8、 the steel structure is affected by AC stray current, and the corrosion rate is more serious than that of the independent steel structure system.In order to reduce the influence of stray current on the steel structure, the sacrificial anode method is adopted to protect the steel structure. During co
9、nstruction, the sacrificial anode is placed in a suitable range after the steel member is in place, and is connected with the structural parts. The whole plant is buried more than 500 zinc - aluminum - cadmium alloy sacrificial anode, the design life is 40 years.October 1998,The potential values of
10、the steel pipe pile grounding network of the main building, chimney and so on are measured (see Table 1).Table 1 measurement of protection potential of steel pipe pile grounding network (relative to Cu/CuSO-4) -VTable 1 shows that the potential of the steel pipe pile grounding network in the main bu
11、ilding is between -0.660 -0.674V, close to the natural corrosion potential of steel, steel pile is in the corrosive state, the coal conveying belt, Zhanqiao, dust catcher, steel pipe and steel pipe pileThe grounding network is less than -0.85V, the protection potential is not enough, and the protect
12、ion degree is expected to reach about 80%. Therefore, the grounding network is under the state of insufficient protection. The analysis shows that the quantity of anode is not enough and the distribution is unevenMain cause。2 buried circulating water pipe (part of the plant) protectionIn the past, p
13、eople take a single inner and outer coating of glass steel to contact or outsourcing but because the pipeline installed in coating damage between pipeline and soil, or buried pipeline coating itself after the occurrence of natural aging, corrosionIn these bare surfaces, corrosion currents increase g
14、reatly in these regions, resulting in accelerated corrosion of the pipes and even perforation.In coastal areas, the soil resistivity is low, and the soil resistivity in Chinas coastal areas is generally about 20 m, and the size of soil resistivity is an important sign of soil erosion. The standard f
15、or Soil Corrosivity in general areas is shown in table 2.Table 2 standard for Soil Corrosivity in general areasAt present, the combined measures of coating anticorrosion and cathodic protection are adopted for the protection of buried circulating water pipes. External coating can improve the surface
16、 resistance. In order to reduce the influence of stray current on other steel structures, sacrificial anode method should be adopted for cathodic protection.The outer diameter of the buried steel circulating water pipe is 3.1m, the wall thickness is 12mm, and the total length is about 3000m. In addi
17、tion, the epoxy asphalt anticorrosive coating is adopted in the combined protection measures, and the cathodic protection method is adopted by the sacrificial anode methodThe utility model is characterized in that a circulating water pipe is provided with 1452 (127 * 127 * 722, approximately 97.5kg)
18、 zinc anodes, and the inner bottom of the circulating water pipeline is arranged with 9m intervals to make 0.914m leaveLane (see Figure 1). In addition, a total of about 2500 earth bed anodes are embedded around the circulating water pipe. The anode weight of each site is about 22kg, and the materia
19、l is zinc aluminum cadmium alloy sacrificial anode with a diameter of 6mmThe reinforcement is welded directly to the circulating water pipe (see Figure 2). In order to reduce the grounding resistance of ground anode, buried sacrificial anode is also used as filling material. Its composition is 30% g
20、esso powder,60% bentonite and 10% industrial sodium sulfateThe thickness of the filling material is not less than 50mm, and the filler around the anode can be uniformly mixed, the thickness is uniform, and the dense packing material is pre packed with cotton cloth bags and sealed on the spot. The bu
21、rial depth of buried sacrificial anode is from the top to the top of the anodeNo less than 1m is appropriate.Fig. 1 Schematic diagram of sacrificial anode installation in circulating water pipeFig. 2 Sketch of installation of sacrificial anode outside circulating water pipeAt about 10 days after the
22、 sacrificial anode is buried, the pipeline will be polarized to the general protection potential range. At this time, the ground potential of the recycled water pipeline can be measured by the terminals of several special wiring boxes. After the sacrificial anode is put into operation,Periodically t
23、est the potential of the pipe and adjust the quantity and position of the sacrificial anode when necessary, until the pipe is in a protective state.At present, the measured protective potential values are shown in table 3.Table 3 data table of protection potential measurement for circulating water p
24、ipe (relative to Cu/CuSO4) -VBecause the sacrificial anode of the circulating water pipe is not checked, the situation of the sacrificial anode is unknown, and the sacrificial anode in the tube is not too big to be evaluated. Referring to the standards and standards formulated by the Ministry of pet
25、roleum industry of ChinaThe protection potential value should be -0.85V or more negative (relative to the Cu/CuSO-4 reference electrode). As shown in Table 3, the potential of the protection is between -0.940 and -1.409VBetween the Cu/CuSO-4 reference electrode, visible protection is very good. The
26、analysis shows that the anode of ground bed plays a major role because of low soil resistivity.3, the circulating water pipe (outside the factory) protects the outside part of the plantThe circulating water pipe means the two water intake pipes and two drain pipes from the circulating pump house to
27、the intake and drainage of the Yangtze river.The intake and drainage pipes of the power plant are made up of concrete assembled pipes whose wall thickness is 0.3m. The inner diameter of the two water intake pipes is 4200mm, each length is 889.60m, and the inner diameter of the drainpipe is 4200mm, e
28、ach length is twoDegree is 383.80m. Most of this section does not use cathodic protection. But in the vertical ascending section of the intake pipe and the drain pipe, the sacrificial anode method is adopted for protection (see Figure 3). 36 vertical lifting sections are installed in the tunnelZAC-1
29、 type anode, each anode weight of 80kg, 4 segments, a total of 114 in the jacking pipe section of the steel grille and concrete pipe section, equipped with 25 ZAC-2 type anode, each anode weight 39kg, 4 paragraphA total of 100.The sacrificial anode of Zn - Al - CD alloy produced by China ship 725th
30、Research Institute is selected.Fig. 3 the vertical ascending section of the drain pipe is protected by sacrificial anode methodDue to failure to check, the sacrificial anode status of the vertical lift section of the drain pipe and drain pipe cannot be confirmed.4 circulating pump room rack, rotary
31、sieve and the circulating pump pump body protectionTrashrack, rotating filter and pump body and other equipment in the circulating water pump plays an important role in the power plant, and poor working environment, so in the design, in addition to considering the convenient replacement and using hi
32、gh quality materials, using appropriate cathodic protection measures.The circulating water pump station, pump and rotary sieve rack body adopts external current protection method. A total of 12 adjustable auxiliary anodes and 3 reference electrodes were set up. Auxiliary anodeCorrosionService provid
33、es the longest auxiliary anode size of 17.6m and is supported by a pre embedded angle iron and mounted in a thick 6.5mm PVC tube. 4 magnetic saturation constant potential meters are usedPower supply, each output voltage is 50V, the DC current is 75A, and the constant potential meter is provided by G
34、ood-allElectric company. As the impeller, big shaft, shaft are made of stainless steel, so the water pump is not insideApply impressed current protection.As the anode and reference electrode flow is very urgent, the cable is broken, the anode and reference electrode fall off, the PVC tube breaks and
35、 loses protection function, so that the 4 constant potential instrument can not be activated. In 19951996 years, yes1A 1B, the zinc - aluminum rack of - CD alloy sacrificial anode protection. In October 1998, the inspection of 2 circulating water pumps showed that the impeller, shaft and shaft sleev
36、e (all stainless steel) inside the pump body were free of corrosionThe upper part of the pump body is well coated with steel, and the thick white epoxy mortar coating is hard, except that the upper 2 pipe joint has partial (about 0.40m2) off and no corrosion. It is believed that the damage was cause
37、d by the coating at the time of installationIn the impeller tip, the pump body has 3 sections about 40 80cm, deep 20 30mm, width of more than 60mm corrosion zone, the surface of the cavitation area is loose and honeycombed.5 condenser protectionThe cooling pipes and plates of the condenser are made
38、of titanium and have excellent corrosion resistance. The inner wall of the water chamber of the condenser is painted with epoxy heavy-duty coating. Considering the periodic maintenance and maintenance of the condenser, the sacrificial anode protection is adopted for the condenserMethod,In the water
39、chamber of the supporting rod and a manhole cover is equipped with a total of 30 pieces of 250 x 150 x 30mm anode, anode in the water chamber is equipped with a total of 12 blocks of the same size and 4 blocks with 350 x 30mm anode, anodeZinc aluminum cadmium alloy.In October 1998, the sacrificial a
40、nodes in the condenser of unit 2 were investigated. It is found that the cooling pipe and the surface of the condenser are bright, and the epoxy anticorrosive coating on the inner wall of the condenser is intact, and no obvious corrosion exists. But in the support rodAnd the tube plate contact aroun
41、d the width of 10mm over a week of depression, careful inspection, slightly uneven, depth of about 6mm, because the surface coated with a new paint, so no corrosion of the original. In zinc aluminum cadmium alloy anodeOn the surface, there is a rough white shell with a thickness of about 3mm. The fo
42、ur sides of the corner have very little defects. It can be seen that the zinc aluminum cadmium alloy is not sacrifice, and has no proper protection effect.6 steel pipe pile protection for coal unloading WharfThe coal wharf of power plant is loaded with steel pipe pile and is subjected to horizontal
43、shear force. At present, cathodic protection is used to prevent the electrochemical corrosion of steel piles in seawater. This technique has become more and more mature, and it can be adopted eitherThe sacrificial anode method can also be applied by impressed current method. The former has a large i
44、nvestment at one time, but it is quite convenient to manage. Aluminum alloy is used as sacrificial anode, and its service life can be up to 2030 years. It is welded directly with steelThis method is more convenient for the replacement of anode. The advantage of impressed current method is that the c
45、urrent value of cathodic protection can be changed by adjusting the output current of auxiliary anode, when the parameters of seawater medium (temperature, current)The potential of steel pile is within the range of protective potential when the change of speed and salinity is greater. The auxiliary
46、anodes selected by the impressed current method are mainly high silicon cast iron, lead silver and platinum plated titanium. Because there is a big oceanAs a result of the cathodic polarization, the oxide film formed by the combination of OH- and Ca+ and Mg+ ions on the cathode surface can make cath
47、odic protection current at the later stage than the initial protection value of Ca+ (Mg+)Two of the little ones. Foreign literature reports, the most effective protection method of steel pipe pile in seawater splash zone is the use of Monel alloy 400 (66Ni-31.5Cu-1.35Fe-0.90Mn). orderPrior to the la
48、rge power plants in the coastal areas of China, most of the steel pipe piles of the coal terminals were impressed with impressed current cathodic protection.The coal terminal (design capacity is 35000t) is located in the mouth of the Yangtze River. The main water quality is fresh water, and there is sea water intrusion.The corrosion mechanism of steel pile is different from bottom to top, and the soil area and total immersion zone are mainly electrochemical corrosionThe corrosion between the difference zone and the total immersion zone is mainl