NEW
MATERIAL
CORROSION
AND
CORROSION
RESISTANCE
CONTROL
OF
[. A. Efimov, N. and B. I. Lur~e
G.
ALUMINUM
ALLOYS UDC 669.7][5.018.8
Smetanina,
Since t h e r e a r e insufficient data for d e t e r m i n i n g the suitability of a l u m i n u m alloys f o r equipment and p a r t s o p e r a t i n g in c o r r o s i v e m e d i a , we m a d e bench and field t e s t s of the c o r r o s i o n r e s i s t a n c e of s e v e r a l a l u m i n u m alloys in plants and installations of the c h e m i c a l and o t h e r b r a n c h e s of i n d u s t r y (see Table 1). The p r o p e r t i e s of the m e d i a in which the t e s t s w e r e m a d e a r e given in Table 2. dP/dT, mm/yr
O,O8 Oto3"q
21
zo to
0
m.w~,mm . ~ t I s s ~ ml ~
6 S;?;-9
a
;
a
/
80
2
80
qO 0,2
0 o,oo~
/
/
3
,,o
b
o
o,ooz
b
c~oof c
6
0 004
0 f
YJ
0
~M
c
o,oo~ o, ooz 0,001
I/
7O
o
0,oo5
/
20
I0
gtb
a/
,
o,5
t z.
!Io 8
~""-'
~ 1,o d
Fig. 1
t,s
2~0 ~, yr
0
o,s
t,o
Cs
,,,or, yr
d
Fig. 2
Fig. 1. V a r i a t i o n of the c o r r o s i o n r a t e dP/d~- of different a l u m i n u m alloys with t e s t ing t~me at the V o s k r e s e n s k Chemical Combine (a), P o d o l ' s k C h e m i c o m e t a l l u r g i c a l Plant (b), Moskhlado Combine No. 3 (c), and Klin Synthetic F i b e r Combine (d): 1) A M g - P ; 2) AMts-M; 3) A M g - 6 - M ; 4) AMg61; 5) AMg6-T; 6) AV-T1; 7) AVA-T1; 8 ) A V T; 9) AD35-T1; 10) D16-T. Fig. 2. V a r i a t i o n of the nominal u l t i m a t e s t r e n g t h Kb of the different a l u m i n u m alloys with with the t e s t i n g t i m e ~- at v a r i o u s plants. Notations the s a m e as in Fig. 1. T r a n s l a t e d f r o m K h i m i c h e s k o e i Neftyanoe M a s h i n o s t r o e n i e , No. 1, pp. 16-18, J a n u a r y , 1970. 01970 Consultants Bureau, a division of Plenum Publishing Corporation, 227 ~;~est 17th Street= New York~
N. Y. 10011. 4ll rights reserved. This article cannot be reproduced .for any purpose whatsoever without permission of the publisher. A copy of this article is available from the publisher for $15.00.
31
T h e i n t e n s i t y of c o r r o s i o n a t t a c k on s a m p l e s s u b j e c t e d to b e n c h t e s t s w a s d e t e r m i n e d b y m e a n s of"
u~
t h e c o n d i t i o n of t h e s u r f a c e , w h i c h w a s e x a m i n e d b y e y e a n d w i t h a x5 m a g n i f y i n g g l a s s ( s a m p l e s h e l d in a d e s i c c a t o r , and a l s o s e v e r a l s a m p l e s w i t h a c h a r a c t e r i s t i c t y p e of c o r r o s i o n a t t a c k a f t e r r o u t i n e o p e r a tional tests were photographed); =.
t h e d e g r e e a n d d e p t h of c o r r o s i o n a t t a c k (the first was determined with a planimeter and the second with a needle micrometer);
I
I
I
I
I
o
o,
~
~
0
0
I
I
t h e c o r r o s i o n r a t e K, d e t e r m i n e d g r a v i m e t r i c a l l y by the formula I
I
I ~" ~
r-I
I
I
i
I
I
i
1
o
o
,o
I
c:;
I
o
c; c;
c~
m(I --
/Tl 1
where K is the corrosion rate, g/m2.yr; m 0 is the i n i t i a l m a s s of t h e s a m p l e , g; m I i s t h e m a s s of t h e s a m p l e a f t e r c o r r o s i o n t e s t s , g; F i s t h e a r e a of t h e s a m p l e , m2; T i s t h e t e s t i n g t i m e , y r s ; the corrosion permeability, formula
determined by the
p = ~K-lo-3 ~, o
o
o
9
o
o
o
o
o
o
I
I
o
o
o
Lo
~
o~
o
where P is the corrosion permeability, mm/yr; i s t h e d e n s i t y of t h e a l u m i n u m s a m p l e , g / c m 3 ;
c3 c3 ~ ~. & d
~ 0~. o
o
co
i
o
.~
iS
o
9
o
r
I
I o
o
o
U~ 0
~0 0
I
L3 9
C'0
~0
"V ~
I
I
~
7
o
o
o,
o
o
o
~
c;
c;
c;
~
c;
~d ~d r
i
32"
o,
o
"
LO 0
~o
"
w h e r e K b i s t h e c h a n g e in t h e n o m i n a l u l t i m a t e s t r e n g t h of t h e a l l o y s r e s u l t i n g f r o m c o r r o s i o n , %; ~bo and Crbl a r e the u l t i m a t e s t r e n g t h s b e f o r e and a f t e r c o r r o s i o n t e s t s , k g / m m 2. Extraction corrosion was studied by the metallographic method. T h e e l e m e n t s of t h e e q u i p m e n t s u b j e c t e d to c o r r o s i o n w e r e e x a m i n e d v i s u a l l y (field t e s t s ) a n d in s o m e cases samples were taken from the parts for examination. T h e v a r i a t i o n of t h e c o r r o s i o n r a t e w i t h t h e t e s t i n g t i m e a t d i f f e r e n t p l a n t s i s s h o w n i n F i g . 1.
o
<
0
UO 0
9 d o
<
t h e v a r i a t i o n i n t h e u l t i m a t e s t r e n g t h of t h e a l loys, determined by the formula ~bo- - 0bl Kb= ~ 100, %0
o 9
3,
I
I
I
U n d e r t h e i n f l u e n c e of c o r r o s i v e m e d i a t h e m e c h a n i c a l p r o p e r t i e s of t h e a l u m i n u m a l l o y s a r e i m p a i r e d ( F i g . 2) due to c o r r o s i o n , w h i c h m u s t b e t a k e n into account in designing structural elements intended f o r o p e r a t i o n in t h e s e m e d i a . I n t e n s e c o r r o s i o n a n d a s u b s t a n t i a l d r o p in u l t i m a t e s t r e n g t h o c c u r u n d e r t h e i n f l u e n c e of HC1 v a p o r s a n d i n t h e p r e s e n c e of g a s e o u s C12. T h u s , t h e u s e of a l u m i n u m a l l o y s f o r p a r t s e x p o s e d to s u c h m e d i a is inexpedient.
TABLE 2
Unit aumber
Average anAverage annual relative nual temperType of humidity in tture in the test chamber chamber, ~
Type of unit
Content of corrosive gases and vapors in air, m g l m s
[the
NO2
i%
Contact plant of the Vosl~esensk Chemical Combine . i Chlorination plant of the Podol'sk Chemieometallurgical Plant Compressor plant of the Moskblado Combine No.3 . Viscose :fiber plant of the Klin Synthetic Fiber Combine.
Bench
71
19
83
21
59
18
90
20
78.7
8hchekin Chemical Combine
12.8
so, I
HC1
C1,
12
8
NHs
CS z
H2S
30
36
i
_
33
f 0.5
dP/dr,
mm/yr o,oo~ O,oo;r5 ?f
10;10
llo03o 7
\.,,
20
- -
o,ooz~
O'
!%
8'
O,OOgO "%
rO
,
3'
0,0015 0,ooIo o~ooo~
o
o,5
1,o
t5
z,o
0
o5
to
r,yrs
Fig. 3
t5
2,o r, yrs
Fig. 4
Fig. 3. Variation of corrosion rate dP/dr for different aluminum alloys with testing time ~- in the vertical (---) and horizontal ( ) positions: i, I') AMg-P; 2, 2') AMts-M; 3, 3') AMg6-M; 4, 4') AMg61; 5, 5') AMg6-T; 6, 6') AV-TI; 7, 7') AVA-TI; 8, 8') AV-T; 9, 9') AD35TI; I0, i0') DI6-T. Fig. 4. Variation of the nominal ultimate strength Kb with the testing time T for different aluminum samples. Notations the same as in Fig. 3. T h e a l u m i n u m a l l o y s i n v e s t i g a t e d c a n b e r e c o m m e n d e d f o r p a r t s o p e r a t i n g i n m o i s t SO 2 at l o w c o n c e n t r a t i o n s , s i n c e t h e y h a v e a low c o r r o s i o n r a t e in t h i s m e d i u m . T h e c o r r o s i o n r e s i s t a n c e of t h e a l l o y s i n u n i t s 1, 3, an d 4 i n c r e a s e s w i t h d e c r e a s i n g c o n c e n t r a t i o n s of the c o r r o s i v e g a s o r v a p o r and r e l a t i v e h u m i d i t y (in unit No. I t h e c o r r o s i o n r e s i s t a n c e of the a l l o y s i n c r e u s e d in t h e f o l l o w i n g o r d e r : A D 3 5 - T 1 , A M t s - M , A M g 6 - M , A M g 6 - T , A V - T 1 , A M g 6 1 , A V A - T 1 , A M g - P , AV-T). In m o i s t c o r r o s i v e m e d i a a l l o y s A M g 6 , A M g 6 1 , and D 1 6 - T u n d e r g o i n t e r c r y s t a l l i n e c o r r o s i o n and corrosion cracking.
33
To i n c r e a s e t h e operating life, p a r t s and equipment m a n u f a c t u r e d f r o m a l u m i n u m alloys should be designed so as to e l i m i n a t e p l a c e s w h e r e industrial dusts, condensates, and c o r r o s i v e m e d i a can collect, since such a c c u m u l a t i o n s can lead to local attack and p r e m a t u r e failure (Figs. 3 and 4). At the Shchekin Chemical Combine operational t e s t s w e r e made of the jackets f o r pipes c a r r y i n g g a s eous aild liquid i n t e r m e d i a t e p r o d u c t s . P r e v i o u s l y , the j a c k e t s , applied o v e r t h e r m a l insulation, w e r e m a d e of thin h i g h - c a r b o n steel. A c cording to data f r o m the Combine, the concentration of c o r r o s i v e g a s e s in the a t m o s p h e r e around the pipes did not e x c e e d the s a n i t a r y s t a n d a r d (see Table 2). N e v e r t h e l e s s , the steel j a c k e t s c o r r o d e d intensely even with y e a r l y applicatl~ons of two l a y e r s of red lead paint. In the c o u r s e of 1962 a substantial n u m b e r of the s t e e l jackets w e r e r e p l a c e d with AD-1 a l u m i n u m j a c k e t s . Operational t e s t s of the a l u m i n u m j a c k e t s in the following five y e a r s showed t h e i r high c o r r o s i o n r e s i s t a n c e in an in i n d u s t r i a l a t m o s p h e r e . In the entire t i m e these a l u m i n u m j a c k e t s (with a s u r f a c e of about 1000 m 2) have not b e e n r e p a i r e d and no a n t i c o r r o s i o n coatings have been applied. T h e i r condition was still s a t i s f a c t o r y when last o b s e r v e d (there w e r e no t r a c e s of c o r r o s i o n ; they had lost s o m e of t h e i r shine).
34
