CN1072280C - Method for preventing carbon-steel cooling apparatus from corrosion by sea water and apparatus thereof - Google Patents

Method for preventing carbon-steel cooling apparatus from corrosion by sea water and apparatus thereof Download PDF

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Publication number
CN1072280C
CN1072280C CN97111369A CN97111369A CN1072280C CN 1072280 C CN1072280 C CN 1072280C CN 97111369 A CN97111369 A CN 97111369A CN 97111369 A CN97111369 A CN 97111369A CN 1072280 C CN1072280 C CN 1072280C
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China
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carbon steel
cooling tube
seawater
sacrificial anode
sea
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Expired - Fee Related
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CN97111369A
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CN1201080A (en
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苏方腾
康飙
刘申生
张琦
辜志俊
张志刚
张春
王周成
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Second Department Of Fujian Institute Of Material Structure Chinese Academy Of Sciences
Fujian Oil Refining Chemical Co ltd
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Second Department Of Fujian Institute Of Material Structure Chinese Academy Of Sciences
Fujian Oil Refining Chemical Co ltd
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Abstract

The present invention relates to a method and a device for preventing a carbon steel cooling device from being corroded by seawater, and puts forward a characteristic technique which coats an organic coating in a carbon steel seawater cooling pipe to increase the resistance of the surface of the inner wall of the carbon steel seawater cooling pipe in a system in which an aluminium (or zincum) sacrificial anode is used for implementing cathodic protection to the carbon steel seawater cooling pipe. Cathodic protection electric current can flow towards a deep position in the carbon steel seawater cooling pipe along a pipe axle flow direction, and is uniformly distributed to the inner wall of the carbon steel seawater cooling pipe. All points of the inner wall of the carbon steel seawater cooling pipe reach protection potentials, and are free from the corrosion of seawater, and thereby, the problems of too short cathodic protection distance and too great cathodic protection electric current existing when the cathodic protection is exerted are solved.

Description

The method and apparatus of the anti-sea-water corrosion of the cooling tube of carbon steel water cooler
The present invention relates to the seawater is the anticorrosion technique of carbon steel water cooler of water coolant.
Though carbon steel tubing has been widely used as the cooling tube of petrochemical industry water cooler, after water coolant changes seawater into by fresh water, be subjected to sea-water corrosion in the pipe and bore a hole, still there is not effective solution so far.The present industrial cooling tube that still uses the tubing of seawater corrosion resistances such as aluminum brass, stainless steel and titanium as sea water cooler.
For solving the problem that the carbon steel cooling tube is bored a hole by sea-water corrosion, common test method is that cooling tube is applied galvanic protection.In the cathode protection technology that uses impressed current; the negative pole of power supply is connected to cooling tube; positive pole is connected to insoluble electrode (as lead-silver alloys); electric current enters in the pipe along tube axial direction by seawater and flows and disperse to enter tube wall; cooling tube becomes negative electrode and current potential moves to-0.8 volt (with respect to silver-silver chloride electrode) from corrosion potential is negative, can avoid the corrosion of seawater in managing.In the cathode protection technology that uses sacrificial anode, do not use impressed current, become a galvanic cell by the sacrificial anode of low potential and the cooling tube of noble potential, spontaneous electric current flows by the two poles of the earth, and postcooling pipe current potential is negative to move to protection potential, prevents sea-water corrosion.The carbon steel cooling tube is applied the reason that galvanic protection fails is; because of cooling tube caliber little (being generally 20 millimeters); pipe maritime interior waters resistance big (resistance=seawater resistivity * length of tube/tube section); cathodic protection current is difficult to flow towards the interior depths of pipe after entering the mouth of pipe; exhausted most electric current is dispersed near the tube wall the mouth of pipe, only just can obtain the bigger protective current of density in the finite length of mouth of pipe ingress.Far away more apart from the mouth of pipe, current density is more little, thereby the depths can't obtain galvanic protection in pipe." the data of " brief guide of metal corrosion protection technology " (new edition) the 599th page of summary of the 923rd page of corrosion and protection handbook and JSPS chief editor according to the chief editor of mechanical investigations institute of China's chemical industry portion; when the cooling tube of 19 millimeters of calibers is applied galvanic protection in the pipe effectively guard space be 33 centimetres; only account for 5% length of 6 meters long cooling tubes approximately; remaining 95% pipeline section still can not get galvanic protection and is subjected to the corrosion of seawater; so that cathode protection technology fails to be applied to carbon steel cooled with seawater pipe so far, and the carbon steel cooling tube also fails to use seawater as water coolant.What use in power plant and petrochemical factory is aluminum brass and stainless steel water cooler (or condenser), adopts cathode protection technology to prevent the corrosion partly of seawater line up.In pipe, still can not get galvanic protection with pipeline section far away, rely on to seawater and add ferrous ion at tube wall formation ironic hydroxide protective layer from 30 centimetres of the mouths of pipe.Corrosion speed (0.01 millimeter/year) in seawater only is 1/12nd of a corrosion of Carbon Steel speed (0.12 millimeter/year) because of copper or stainless steel, the pipe internal cathodic protection apart from short situation under aluminum brass (or stainless steel) cooling tube still can use cooled with seawater.
In order to extend the distance of carbon steel cooling tube pipe internal cathodic protection; Tokyo industrial experiment institute (see Japan's " corrosion protection technology " 1977 the 26th volume the 12nd phase 711-720 page or leaf) changes block zinc sacrificial anode in the cathodic protection system into zinc powder, the generation galvanic protection effect that contacts with tube wall during by cooling tube with circulating seawer of the zinc powder of 2% concentration.The improved method of this cathode protection technology; section all reach effective cathodic protection potential using degassing seawater (oxygen level is lower than 100ppb) can make during as water coolant carbon steel cooling tube pipe in entirely; but do not reach effective galvanic protection in the pipe during as water coolant at the natural sea-water (containing dissolved oxygen) that uses not the degassing; in addition zinc powder because of its unit weight specific surface area big in seawater from reasons such as dissolving speed are big, this method is not seen practical report as yet.
The purpose of this invention is to provide a kind of improving one's methods of carbon steel water cooler cathode protection technology that be applicable to; it can make the pipe internal cathodic protection length of carbon steel cooling tube near a bit of whole process that extends to cooling tube the mouth of pipe; fully prevent the corrosion of seawater, make the factory of coastland can use natural sea-water to substitute the industrial colling of fresh water as the carbon steel water cooler to the carbon steel cooling tube.
The theoretical foundation that the present invention prolongs pipe internal cathodic protection distance is Monger equation (see U.S. publication Corrosion, nineteen fifty-nine the 15th is rolled up the 417th page):
Ex=Eo?cosh[α(L-x)]/cosh(αL)
Wherein Ex is for putting the changing value of x tube wall at the galvanic protection after potential in the pipe.The protection prepotential is corrosion potential-0.60V, presses the cathode protection technology standard code, must negative move to-0.80V for effectively preventing the corrosion protection current potential, thereby the Ex value must remain on more than the 0.2V.Eo is the changing value of the mouth of pipe at the galvanic protection after potential, and Eo is near 0.5V when using aluminium sacrificial anode.L is cooling tube length (6 meters), and x is the interior distance from the mouth of pipe of pipe.α=2 * (ρ/Rs * d) 1/2, ρ is seawater resistivity (20 ohmcm), and d is cooling tube caliber (19 millimeters), and Rs is the inside pipe wall surface impedance.The Monger equation shows that Rs is the principal element of decision pipe internal cathodic protection distance.When the inside pipe wall impedance reaches 2 * 10 6Ohmcm 2The time, can obtain sufficient galvanic protection in the cooling tube pipe.
For realizing purpose of the present invention, be coated with about 250 microns of layer thicknesses at carbon steel cooling tube inwall, impedance is greater than 2 * 10 6Ohmcm 2And heat resisting temperature be 150 ℃ organic coating, one aluminium (or zinc) sacrificial anode be installed and be connected with cooling tube in seawater inlet with lead.Like this, when seawater entered cooling tube, sacrificial anode and seawater and cooling tube were formed a galvanic cell.Wherein the aluminium sacrificial anode current potential is low, becomes galvanic anode, gradates to aluminum ion and discharges electronics.The electric current (cathodic protection current) that galvanic cell produces from anode after seawater enters cooling tube; because of the existing one deck high resistance coating of tube wall; only there is the electric current of small portion to be diverted near the tube wall of the mouth of pipe; most of electric current continues to flow to the interior depths of pipe and be diverted to tube wall equably along tubular axis; make the tube wall each point can both obtain galvanic protection, prevent the corrosion of seawater effectively tube wall.
The sectional view of the device of the anti-sea-water corrosion of enforcement carbon steel cooling tube as shown in Figure 1.This device comprises lead (1), a sacrificial anode (2), two seawater chambers (3,14), a carbon steel cooling tube (6), six roots of sensation reference electrode (5,7,10 etc.), seawater chamber inlet (4), the outlet of seawater chamber (15), rheometer parts such as (16).19 millimeters of figure medium carbon steel cooling tube internal diameters, long 3 meters, inwall scribbles one deck epoxies coating (8), through plastic oil appoint (11) and in connect (12,13) and be connected in seawater chamber (3,14).
The present invention be applied to the carbon steel water cooler the anti-sea-water corrosion of cooling tube device sectional view as shown in Figure 2.This installs mainly by a cooler casing (21), seven carbon steel cooling tubes (6,18,19,20 etc.), an aluminium sacrificial anode (2), a silver/silver chloride reference electrode (5), two cards (17,22) and two seawater chamber compositions such as (3,14).19 millimeters of cooling tube internal diameters, long two meters, interior finishing epoxies coating.Aluminium sacrificial anode (2) is the garden rod of 20 millimeters of diameters, is connected with seawater chamber (3) with thread.
One of advantage of the present invention is that carbon steel cooled with seawater pipe pipe internal cathodic protection distance is increased to more than 6 meters, has changed the distance of cooling tube pipe internal cathodic protection in the past and only be 30 centimetres with interior conclusion.Two of advantage is cathodic protection currents because of the existence of tube wall coating diminishes, and shown in the embodiment of the invention, only is 1/25th before the technological improvement, thus in the cathodic protection system work-ing life of sacrificial anode be before the technological improvement 25 times.Three of advantage is that the present invention need not seawater processings that outgas to cooling usefulness, can use the water coolant of natural sea-water (containing oxygen) as the carbon steel water cooler, has saved the equipment and the expense of degassing processing.
Below in conjunction with accompanying drawing in detail enforcement best way of the present invention is described in detail.
Embodiment 1, (seeing accompanying drawing 1) seawater enter seawater chamber (3) from seawater chamber inlet (4), flow out from outlet (15) through cooling tube (6) and seawater chamber (14), and it is 2 meter per seconds that the adjusting seawater flow makes pipe maritime interior waters flow velocity.Sacrificial anode (2) current potential was-1.10 volts when seawater passed through cooling tube, and carbon steel cooling tube tube wall (9) current potential is-0.6 volt, and two electrodes become the anode (negative pole) and the negative electrode (positive pole) of galvanic cell automatically.After with lead (1) two electrodes being connected; galvanic cell is started working automatically; electric current (cathodic protection current) becomes a loop from sacrificial anode through seawater, epoxy coat (8), cooling tube tube wall (9) and lead (1), and current value is measured as 43 microamperes with rheometer (16).Use silver/silver chloride reference electrode (5,7,10) monitoring respectively at the tube wall current potential of the carbon steel cooling tube mouth of pipe, mid point and pipe end.Battery operated postcooling tube wall (9) moves to-1.11 ,-1.06 and-1.05 volts in that before battery operated-0.6 volt of the current potential of above-mentioned three positions is negative respectively; all above the standard (0.80 volt) of cathodic protection potential; the galvanic protection distance surpasses 3 meters, and each point all can prevent sea-water corrosion in the pipe.
Embodiment 2, as a comparison; after changing inwall into and do not have the exposed pipe of application as Fig. 1 medium carbon steel cooling tube (6); cathodic protection current rises to 1050 microamperes from 43 microamperes, pipe mid point and the terminal tube wall current potential of pipe be respectively-0.65 volt with-0.62 volt, inside pipe wall does not reach cathodic protection potential.The contrast experiment shows that the present invention can solve the too short and too big problem (embodiment 1) of cathodic protection current of the galvanic protection distance that exists when the carbon steel cooling tube applied galvanic protection, effectively prevents the corrosion purpose of seawater to the carbon steel cooling tube thereby can reach.
Embodiment 3, (seeing accompanying drawing 2) seawater enter seawater chamber (3) from seawater chamber inlet (4), flow out from outlet (15) through cooling tube (totally seven pipes such as 6,18,19,20 grades) and seawater chamber (14), and it is 2 meter per seconds that the adjusting seawater flow makes cooling tube pipe maritime interior waters flow velocity.Aluminium sacrificial anode (2) and cooling tube become negative pole (anode) and anodal (negative electrode) of galvanic cell respectively, electric current passes through steel card (17 from sacrificial anode (2) after seawater flows to the cooling tube tube wall, 22) pass to sacrificial anode through the box hat (21) of the screw (23) of ring flange (24,25) and hydroecium and form a current circuit.Seawater during by water cooler galvanic cell start working automatically, at this moment the tube wall current potential of cooling tube end is measured by reference electrode (5), numerical value is-1.095 volts, shows that the carbon steel cooling tube all can prevent the corrosion of seawater to cooling tube effectively from the mouth of pipe to the terminal inwall of pipe.

Claims (8)

1. the method for the anti-sea-water corrosion of the cooling tube of carbon steel water cooler is improving one's methods of cathode protection technology, it is characterized in that, at the external sacrificial anode of an end (2) of carbon steel cooling tube (6), goes up application organic coating (8) at the inwall (9) of carbon steel cooling tube.
2. the method for the anti-sea-water corrosion of the cooling tube of carbon steel water cooler as claimed in claim 1 is characterized in that sacrificial anode (2) is made of aluminium alloy.
3. the method for the anti-sea-water corrosion of the cooling tube of carbon steel water cooler as claimed in claim 1 is characterized in that sacrificial anode (2) also can be made of zinc alloy.
4. the method for the anti-sea-water corrosion of the cooling tube of carbon steel water cooler as claimed in claim 1 is characterized in that, organic coating (8) adopts resistance value greater than 2 * 10 6Ohmcm 2And heat resisting temperature is 150 ℃ a material, and thickness is about 250 microns.
5. the cooling tube of carbon steel water cooler is prevented the device of sea-water corrosion, by cooler casing (21), carbon steel cooling tube (6,18,19,20 etc.), sacrificial anode (2), reference electrode (5), card (17,22), seawater chamber (3,14), seawater inlet (4) and outlet (15), screw (23), ring flange (24,25) form, it is characterized in that sacrificial anode (2) is connected with seawater chamber (3) with thread; Sacrificial anode (2) and carbon steel cooling tube (6,18,19,20 etc.) become negative pole (anode) and anodal (negative electrode) of galvanic cell respectively, electric current flows to through seawater from sacrificial anode (2) behind the cooling tube tube wall of application organic coating by steel card (17,22) pass to sacrificial anode (2) and become a current circuit through the screw (23) of ring flange (24,25) and the box hat (21) of seawater chamber (14).
6. the device of the anti-sea-water corrosion of the cooling tube of carbon steel water cooler as claimed in claim 5 is characterized in that the interior finishing of carbon steel cooling tube has resistance value greater than 2 * 10 6Ohmcm 2And heat resisting temperature is 150 ℃, the organic coating of thickness about 250 microns.
7. the device of the anti-sea-water corrosion of the cooling tube of carbon steel water cooler as claimed in claim 5 is characterized in that sacrificial anode is made of aluminium alloy.
8. the device of the anti-sea-water corrosion of the cooling tube of carbon steel water cooler as claimed in claim 5 is characterized in that sacrificial anode also can be made of zinc alloy.
CN97111369A 1997-06-03 1997-06-03 Method for preventing carbon-steel cooling apparatus from corrosion by sea water and apparatus thereof Expired - Fee Related CN1072280C (en)

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Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101696758B (en) * 2009-10-26 2013-09-04 中国科学院金属研究所 Corrosion control method of trenchless construction large diameter pipeline
CN104532259B (en) * 2014-12-26 2017-10-20 青岛双瑞海洋环境工程股份有限公司 The composite electrochemical device protected for condenser pipe series cathode
CN108103509B (en) * 2018-01-30 2024-04-09 深圳市西谷制冷设备有限公司 Corrosion protection device
CN108396323B (en) * 2018-03-26 2020-11-20 中国海洋大学 Method for cathodic protection of bare steel structure in seawater
CN110846666B (en) * 2019-12-11 2024-04-05 苏州热工研究院有限公司 Condenser cathode protection mechanism and condenser cathode protection potential monitoring system

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1014806B (en) * 1988-01-14 1991-11-20 东芝有限公司 Apparatus and method for electrical anti-corrosion of total-titanium heat-exchanger

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1014806B (en) * 1988-01-14 1991-11-20 东芝有限公司 Apparatus and method for electrical anti-corrosion of total-titanium heat-exchanger

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