potential E = –1.2 V. Potentials in steels were determined relative to the standard
chlorine-silver reference electrode (CSRE).
It has been established that there was shift of corrosion potential in a positive
direction (by + 0.15 V) in APC of specimens of 06Cr1-U steel tubes after operation
and a significant reduction of current of anodic steel dissolution compared to the tube
specimens before operation. For example, when E= -0.1 B, current density decreased
from 3∙10
-2
to 1.5∙10
-4
A/cm
2
, that is, 200 times (Fig. 6, curves 1 and 2).
test time, hours
Figure
5.
Kinetics of corrosion in
06Cr1-U steel (1) and 20 steel (2)
in a chloride-acetate solution
Figure 6. APC obtained with samples
of 06Cr1-U steel pipes in 0.1 N NaCl:
before service (1) and after service (2)
Cathode polarization curves (CPC) obtained in a solution of 1N H
2
SO
4
+1.5 g/l
CS(NH
2
)
2
, have shown that the cathode current (І
к
) of hydrogen emission on specimens
of 06Cr1-U steel tubes was almost 100 times lower than that of the specimens of steel
20 (Fig. 7) which contributes to a lower hydrogen saturation of 06Cr1-U steel. A
similar pattern was observed in cathodic hydrogen saturation of these specimens during
4 hours at a potential E = –1.2 V (Fig. 8, curves 1 and 3). Besides, magnitude of the
cathode current on 06Cr1-U decreased by 1.7 times steel tubes after operation as
compared to the current before operation and, on the contrary, it increased by 1.2 times
for the steel 20 tubes. Therefore, the difference between currents before and after
operation was as high as 5 times (Fig. 8, curves 2 and 4) indicating an increase in
resistance of the 06Cr1-U steel tubes to hydrogen saturation during operation. Thus, it
was proved that corrosion resistance of 06Cr1-U steel tubes increases during operation
and becomes considerably higher than that of st. 20 tubes.
The 06Cr1-U steel tubes also showed high resistance to sulfide stress corrosion
cracking (SSCC) when tested in a chloride hydrogen sulfide-containing medium in a
medium by standard A method, NACE TM 0177. None of the specimens failed in the
base time at tensile stresses corresponding to 0.75 σ
0.2
steel.
Following the tests for resistance to hydrogen cracking (HC) according to the
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