NEW
MATERIALS
INVESTIGATION OF
ENAMEL A. B.
AND
CORROSION
OF
CORROSION
COATINGS S. Es'kov, I. Shabrov,
IN
ACID
CONTROL
RESISTANCE MEDIA UDC 6662 93:62 0.193.001.5
E. A. Shabrova, and E. N. Stekhina
A c c o r d i n g to the valid OST 2 6 - 0 1 - 1 - 70 "Enameled Vessels and Equipment, General Technical Specificat i o n , , the c o r r o s i o n r e s i s t a n c e of enamel coatings of chemical equipment is a s s e s s e d f r o m two p a r a m e t e r s : r e s i s t a n c e to 20, 24% solution of h y d r o c h l o r i c acid and 4% solution of sodium hydroxide at their melting points. The r e a s o n for this selection is that these media are considered to be the m o s t active with r e g a r d to enamel coatings. However, the specification p a r a m e t e r s cannot always be considered as objective c r i t e r i a in a s s e s s ing the c o r r o s i o n r e s i s t a n c e of the coating in other media of p r e s e n t - d a y chemical technology which normally consist of s e v e r a l solutions. In this connection, we c a r r i e d out an experimental c o m p a r i s o n of c o r r o s i o n r e s i s t a n c e of the a c i d - r e s i s tant grade 54 and acid-alkali r e s i s t a n t enamel 1513Ts, which are used to p r o t e c t chemical equipment in solutions of organic and inorganic acids m o s t frequently used in technological p r o c e s s e s p e r f o r m e d in enamelled equipment. The tests were c a r r i e d out on enamelled specimens in conditions meeting the r e q u i r e m e n t s of OST 26-011 - 7 0 . T h e t e s t d u r a t i o n w a s 100h. The solution was changed at intervals of 10 h and the specimens w e r e weighed after e v e r y 10, 30, 50, 70, and 100 h. It was found that after 20-30 h the loss of m a s s becomes constant and the kinetic loss curve becomes a straight line. F o r this reason the following equation, given in [1], was used to calculate the c o r r o s i o n r e s i s t a n c e of enamel coatings: Am 98,76 Sd~ where P is the c o r r o s i o n r a t e , r a m / y e a r ; Am is the loss of m a s s of the specimen, rag; S is the area of i n t e r action of specimen with the reagent, m2; d is the area of the m a t e r i a l being tested, g/cm3; and T is the test duration, h. Applying this equation to the calculation of c o r r o s i o n rate of 54 and 1513Ts enamel coatings whose average densities a r e 2.4 and 2.56 g/cm 3, respectively, we obtain p
2
45,04 Am - - -
An analysis of the investigation r e s u l t s of the c o r r o s i o n of enamel coatings (Table 1) shows their high protective p r o p e r t i e s in acid solutions at boiling point. Changes in the solution concentration have p r a c t i c a l l y no effect on the c o r r o s i o n r e s i s t a n c e of enamels. The investigation of s e r v i c e conditions of e n a m e l - c o a t e d equipment showed that the working media t e m p e r a t u r e frequently exceeds the boiling point of acid solutions. Since with i n c r e a s i n g t e m p e r a t u r e of acid solutions the intensity of c o r r o s i o n p r o c e s s e s i n c r e a s e s , it is essential to know the m a x i m u m p e r m i s s i b l e s e r v i c e t e m p e r a t u r e s of coatings for the selection of enameled equipment. These t e m p e r a t u r e s w e r e calculated f r o m the experimental data using equation [2] : t--~0
Kt=Kto2 at', where Kt, Kto are the l o s s e s in the specimen m a s s at specified t e m p e r a t u r e t and test t e m p e r a t u r e to, r e s p e c tively, m g / c m 2, and At is the t e m p e r a t u r e factor (according to [3] for industrial enamels At = 10-11~ for our calculations we a s s u m e At = ll~ T r a n s l a t e d f r o m Khimicheskoe i Neftyanoe Mashinostroenie, No. 10, pp.21-22, October, 1978.
912
0009-2355/78/0910-0912 $07.50
9 1979 Plenum Publishing Corporation
TABLE
1 ICortc~iOn IMax.permissible I ratesofen- Iservice ~memp"(~.C) I I . , lOt eqmp ent yam ~tamel (mmty~enamel coating
Acid U
1513Ts
s4
5
0,12
o,2~
0,08
136 131
131 120
[ 155
o,o~ 0,07
o,os 0,06
1~7 133
0,07
o, I6 {
139
130 128
{ 30
5O
0.03 0,03 O,15
0,03 0,04 O,12
145 146 127
145 142 130
5 2o
0,07 0,15
0,04 0,13
132 123
141 125
0,06
6,68
0,12
,as
0,03 0,04 O,08
0,04 0,05 0, 09
I44 I4t 135
--
004 o,o6
-
I
Hydroclsloric
"~ 513T: ~4
12o
0,05
L
Sulfuric
5 20
Orthophosphoric Nitric
56
Oxalic Citric
Aoetic
{ s .
260 45
{57
o,o4 o,o6
o,o4
,54 13S
-
,54 }
13o 124
140 IS7 133
1
141 136
~'No additionsof fluoride compoundsare allowed.
TABLE 2 Corrosionratdvlax, permissible -~mm/'r' of Iservice temp.(*C) t YJ lofequipment with .namel 9 enamelcoating I I k513Ts 54 ] 1513Ts ~4
Testing method
I
SpecificationI ~ / R4202 1958 (Japan) L
504
SpecificationASTM~ I i92 : C283--54 (USA) I
o,o.__22
0,02
162
0,01
3Z
O, 11
176
0,01
0,17
132
International specifi- 1 4a cation UTE/13 : j
;7;?
I I 336
0,01
I I
162
132
{
125
168
The numerator gives he experimental data for the phase and the denom nator gives the same for the vapor phase. A c c o r d i n g to the catalog [4] the p e r m i s s i b l e c o r r o s i o n rate for which the coating retains its workability for 2-5 y e a r s is 0.5 mrm/yr. This value is adopted as the limiting c o r r o s i o n rate. The calculation r e s u l t s of m a x i m u m p e r m i s s i b l e s e r v i c e t e m p e r a t u r e of e n a m e l s 151Ts and 54 in the investigated media a r e given in Table 1. The r e s u l t s of l a b o r a t o r y investigations of c o r r o s i o n r e s i s t a n c e of enamel coating 1513Ts in 75% aqueous solution of sulfuric acid and 90% of lithium nitride at solution t e m p e r a t u r e s of 200 and 250~ for 60 and 8 h , r e s p e c t i v e l y (the cycle length in the lithium nitride solution was 10 h and in the sulfuric acid solution 4 h). The c o r r o s i o n rate of 1513Ts enamel under limiting conditions is 0.05 and 0.08 m g / c m 2 o r 0.03 and 0.35 r a m / y e a r , respectively, which is substantially below the p e r m i t t e d value (0.5 m m / y e a r ) . Table 2 g2ves the r e s u l t s of the determination of c o r r o s i o n r e s i s t a n c e of enamels 1513Ts and 54 by methods used by foreign f i r m s producing enameled chemical equipment. The t e s t s w e r e c a r r i e d out at the boiling of 20, 24% solution of h y d r o c h l o r i c acid (106-109~ It was found that the m a x i m u m p e r m i s s i b l e s e r v i c e t e m p e r a t u r e s in 20, 24% h y d r o c h l o r i c acid solution calculated f r o m experimental data obtained by standard method J I S / R 4 2 0 2 - 1 9 5 8 and A S T M / C 2 8 3 - 5 4 a r e 25-30~ higher than the data calculated f r o m the r e s u l t s obtained for 100 h with a change of solution e v e r y 10 h. The A m e r i c a n and Japanese standard specification methods do not p r o ~ d e for change of solution while the test
913
duration is 192 and 504 h, respectively. Testing of specimens with a change of solution imitates the actual service conditions of equipment and the results of such tests provide a basis for a m ore objective evaluation of the possible service conditions of the coating. LITERATURE
1. 2. 3.
4.
CITED
G. Ya. Vorob'eva, Corrosion Resistance of Materials in Aggressive Media of t,~ Chemical Industry [~, Russian], Khimiya, Moscow (1967). V. V. Vargin, V. V. Grachev, I. Ya. Zorina, et al., "Resistance of an acid-resisting enamel coating at elevated temperatures and p r e s s u r e s , " Steklo Keram., 10, 25-26 (1971}. Yu. V. Rogozhin, V. M. Gladush, L. V. Markina, and A. K. Miglo, "Some technological p a r a m e t e r s of enameling and the properties of enamel coatings for high t e m p e r a t u r e s , " Steklo K e r a m , ~ 58-61, (1976). Enameled Equipment. Catalog of Ts]~TIKhinmefetmash (1974).
CORROSION RESISTANCE
IN N I T R I C
ACID MEDIA
L. P. Lozovatskaya, A. I. P i s k u n o v a , I . K. B u r t s e v a , M. N. S h m a t k o , Ya. E. Gol'dshtein, a n d I. A. L e v i n
UDC 669.018.841
At the Chelyabinsk Metallurgical Plant eight 40-ton ordinary heats of 03Kh18N11 steel with different contents of impurity silicon were produced. The method of steel melting with a reduced silicon content was developed by the Chelyabinsk Scientific-Research Institute of Metallurgy. The composition of heats is given in Table 1. After hot rolling the sheets intended for making specimens were hardened in water at temperatures of 1080, 1120, and 1150~ for 30 rain. After hardening some specimens were subjected to sensitization t e m p e r ing, and heated at 650~ for 1 h. The normally hardened specimen were tested for corrosion in 20, 40, 56, and 65% solutions of HNO3 at t e m p e r a t u r e s of 100, 120, and 130~ and at boiling point and also in a boiling solution of 27% HNO3 containing 4 g/liter of Cr e+ ions. The corrosion rate was determined from the mass loss of two simultaneously tested specimens, from one of which a metallograpl~ic specimen was ground for determining the type of etching of the metal under a microscope. After corrosion tests one of the two specimens was cut across and the resulting surface ground and polished for measuring the intercrystalline corrosion (ICC) penetration depth. Additional electrochemical tests were carri ed out to determine the effect of the steel potential in HNO3 solutions on the etching rate of grain boundaries as a function of silicon content in steel, using the method deScribed in [1]. The tempered specimens were tested for corrosion by the DU method (GOST 6032-75) in boiling 65% HNO3. The corrosion rate was calculated after each test cycle (five cycles of 48 h and each) from the mass loss of two simultaneously tested specimens. Corrosion tests on welded specimens were also c a r r i e d out by the DU method. We carried out the metallographic examination of specimens simultaneously with the corrosion tests in order to determine the type of corrosion and the time needed for ICC to become apparent in the weld zone and the thermal effect area. Welding was performed in argon atmosphere using a welding rod whose analysis was selected in accordance with the chemical composition of the heat concerned. The low silicon heats were welded with Sv-03Kh18Nll wire with a silicon content reduced to 0.14% and with 0.015% C, while the heats with a higher silicon content were welded with ordinary Sv-03KhlSNll wire. Table 2 gives the corrosion test results obtained in nitric acid media of varying oxidation ability of hardened 03Khl8Nll steel specimens with varying silicon contents. It may be seen that in boiling solutions of 56 and 65% HNO~ corrosion rates of steels with different silicon contents differ relatively little. After testing, the specimen surface remained smooth, and no falling-out of grains as a result of ICC Was observed. Translated from Khimicheskoe i Neftyanoe Mashinostroenie, No.10, pp. 22-24, October, 1978.
914
0009-2355/78/0910-0914507.50
9 1979 Plenum Publishing Corporation
