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Section 7. Ecology
Mammadova Fafida, Azerbaijan State University of Oil and Industry E-mail: farida.mamedova@yahoo.com
INVESTIGATION OF THE MINERALIZED WATER CORROSIVE AGGRESSIVENESS
Abstract: In given work the results research by corrosive aggressiveness of mineralized waters are given. To corrosion three kinds of metals were subjectedA steel 3, steel 20 and steel 40. As corrosive medium the different types of mineralized waters have been used. In results of investigations it have been determined that after 240 hours of tests the corrosion rapidity becomes stability. Also in results of conducted research it have been determined that the corrosion rapidity in the seawater softened by Na-ion-exchange is high than in the seawater. Metal corrosion rapidity in the vaporizer concentrate is lower, than in the wet and softened seawater. Deceleration of corrosion rapidity is explained by biocarbonate decay on high temperature and formation of hydrates and carbonates in the vaporizer concentrate.
Keywords: mineralized water, corrosive aggressiveness, corrosive medium corrosion rapidity, static conditions, electrochemical method, Na-zeolite softening.
One of the criterions for normal work of the new The corrosion investigations were carried out by manufactures is to choice and substantiates the ma- gravimetrical means. 3 sorts of metals were investi-
terials using for equipment production.
Today to improve technical-economical indicator of desaltng the ion-exchange way of waters demineralization, which are investigated weakly, is used widely. The aim of the present work is to estimate the metals corrosion stability and to give recommendations over choice or production of equipment working on mineralized waters.
Table 1. - Dependence of corrosion rapidity of St 3 on exposition time in 20° temperature
gated for corrosion stability: St 3, St 20 and St. 40 working on mineralized waters. As corrosive medium the different types of mineralized waters: were used seawater (Caspian), softened seawater and its concentrates. The investigations results of St 3 are shown in Table 1. (n > Jr8)
Exploitation term T, h Corrosion rapidity g/m'. h
Seawater Softened sewater Vaporizer concentrate
1 2 3 4
40 0.25 0.32 0.085
80 0.36 0.23 0.87
120 0.32 0.18 0.83
Section 7. Ecology
1 2 3 4
160 0.29 0.15 0.090
200 0.27 0.13 0.086
240 0.26 0.12 0.088
280 0.25 0.11 0.085
As shown in the present table in first 72-80 hours of tests the corrosion rapidity in the seawater is comparatively high, and then it decays. After 240 hours of tests the corrosion rapidity practically becomes stabilize on the level 0.11-0.12 g/m2. h. Corrosion of the examples surface has a point character. The corrosion products are placed in two layers. The first layer is red, friable, passes easily into solution. The second layer is the black deposit. The color of solution after tests became red with existence of sediment as flocks of Fe(OH)3.
Irregularity in the time of the steel corrosion rapidity in the seawater is explained by, that the corrosion produst layer is packing and raises its thickness and it results in deceleration of cathode process. Chlorine ions having mobility and a small radius influences on the anodic process more intense at the beginning of the exposition time, than at the finish, and it is explained by the absorption forcing of oxygen and formation of soluble metal flocks Rising of the sediments thickness also results in reduction of oxygen diffusion to the metal surface, and thereby decelerates the corrosion rapidity.
In accordance with the table data in the same tests period the corrosion rapidity in the seawater softened by means of Na-eationization is greatly high, than in the seawater end is equal to 0.27-0.3 g/m2.h This circumstance can be connected only with two factors;
Table 2. - Galvanostatic characteristics for St.
the first: oxygen solubility in the softened seawater is higher, than in the seawater, the second. existence of the inflexibility minerals in the seawater obviously favors to formation of the protective film on the metal surface. Given corrosion character in the softened seawater is shown with the areas of separate points and spots, at the same time the metal surface is dull.
Metal corrosion rapidity in the vaporizer concentrate is lower, than in the wet and softened seawater and is equal to 0.08 g/m2.h. Deceleration of corrosion rapidity is obviously explained by bio carbonate decay on high temperature and formation hydrates and carbonates in the vaporizer concentrate increasing pH of the solution to 9.5-10. At the same time owing to of increasing solution saline the oxygen solubility increases.
Estimation of corrosion rapidity of investigated exemplars by the ten-point scale of metal corrosion stability (State Standard) shows, that in the seawater and softened seawater the abyssal index of the corrosion rapidity is within 0.1-0.3 mm/year, i.e. belongs to the 6 point (low stability), and for vaporizer concentrate this index is equal to 0.07 mm/year, i.e. belongs to the 5 point (stable).
Experimental tests of St. 20 corrosion stability in the softened seawater in the range of temperature 40-800C was carried out by means of electrochemical method and are shown in (table 2). 20 in the softened water in static conditions
Current density J, MA/sm- Potential displacement E, mV
t = 20 °C t = 40 °C t = 60 °C t = 80 °C
Potential mV
Anode Cathode Anode Cathode Anode Cathode Anode Cathode
1 2 3 4 5 6 7 8 9
450 440 380 385 430 430 440 440
1 2 3 4 5 6 7 8 9
480 430 400 380 440 425 440 440
700 425 420 375 445 420 445 435
750 420 440 370 450 400 450 435
770 410 460 365 460 365 460 435
790 400 480 365 470 380 460 430
800 490 550 360 550 375 460 430
The St. 20 corrosion rapidity on the temperatures water by the Mg-Ne-cathode scheme is more prefer-
40, 60, and 800 C determined by the data of this table able. In this cases a mostly all magnesium ions stay
shows they are 0.5, 0.68, and 0.87 g/m2.h. relatively. in the softened water. The results of galvanostatic
From the technological point of view in some characteristics of ST. 20 in Mg-Na-cathode water
cases to hold the previous softening of mineralized are given in (table 30).
Table 3. - Gatvanostatic characteristics for St 20 in concentrate of vaporizer in static conditions
Current. density J. mkA/snv Potential displacement E.mV
T = 40 °C T=60 oC T = 50 oC
Potential, mV
Anod Cathode Anod Cathode Anod Cathode
0 355 340 395 380 370 310
20 390 330 450 350 400 315
40 440 325 525 340 495 285
60 580 350 630 337 590 300
80 620 353 650 330 660 330 '
100 775 355 675 327 750 340
120 695 353 700 325 770 337
Analyze of this table data shows that the temperature increasing of limit diffusion current in the dynamic conditions is higher, than in static conditions. Corrosion rapidity is: in static conditions 0.12, in dynamic conditions on the temperature 40, 60 and 800 C and 800 C - 0.62 and 0.83 g/m2.h. relatively.
Comparison of obtained results of ST. 20 corrosion rapidity determination on two types of softened waters shows, that the corrosion rapidity in Mg-Na-cathode water is lower, than in Na-cathode
water. In this connection can be supposed the probability of diffusion barrier preventing forward contact with trivalent metal oxide, and it serves depolarizer of cathode process.
So displayed, that in case of thermo-softened water using in spite ofhagher corrosive aggressiveness of seawater softened by Na-and Mg-Na-cathode it is not necessary to take measures for metals corrosion protection - it can be limited by known metods. More corrosion stability has the steel of St. 20 sort.
