Research results. 1. Development of an energy-saving technology for
production of oil and gas line tubes with improved corrosion resistance. The
materials used in the study: specimens of test steels containing 0.06% carbon, 1-2%
chromium and microadditives of niobium (0.025%) and vanadium (0.06%) smelted in
a laboratory LPZ-67 induction furnace and subjected to hot deformation according to
temperature and deformation conditions similar to those used in the manufacture of
tubes as well as specimens of experimental-industrial production tubes of 06Cr1-U
steel (table 1).
Table 1 Chemical composition of samples taken from 06Cr1-U steel pipes
№
melting
Content of chemical elements, %
C
Cr
Cu
Mn
P
S
Si
Ni
Nb
1
0.06
1.07
0.22
0.48
0.017
0.007
0.24
0.11
–
2
0.06
1.08
0.20
0.53
0.007
0.005
0.25
0.10
0.025
The methods applied in the course of the study: quantitative and qualitative light
metallography; translucent electron microscopy; diffraction of inversely scattered
electrons; identification and characterization of high angle grain boundaries including
special boundaries, grain boundaries in ferrite-pearlite steels; comprehensive corrosion
and corrosion-electrochemical studies; study of processing plasticity of tube billets of
06Cr1-U steel by testing specimens for twisting and piercing; studying mechanical
properties of tube specimens by conducting tensile and impact bending tests at negative
temperatures; chemical analysis of the test steels using high-sensitivity "SPECTRO"
GmbH, Germany, "SPECTROMAX" spectrometer; service tests of the experimental
batch of tubes were carried out at the oil and gas enterprises of Ukraine and Russia.
The development process included choice of chemical composition of economic
low-alloy steel, manufacturing equipment and thermal and deformation parameters of
hot tube rolling. Data on the effect of the following factors on the corrosion resistance
of steels were taken into account:
• alloying (chromium, niobium, vanadium) and admixture (carbon, sulfur,
phosphorus, manganese) elements [4-7]. In particular, it was taken into account that
chromium contributes to formation of protective oxide films tightly adhering to the
tube surface during hot deformation, heat treatment and in operation; manganese brings
about liquation heterogeneity of steel and formation of loose corrosion products on the
tube surface in operation that do not possess protective properties and flake off the
surface. This, in turn, leads to formation of microscopic steel-corrosion product
galvanic couples and accelerates steel dissolution. In addition, manganese contributes
to formation of the most harmful nonmetallic inclusions such as manganese sulfides
because of their low solubility in steel. It is known that they contribute to pitting, sulfide
corrosion cracking and hydrogen brittleness. High carbon content in steel aggravates
negative effect of manganese. Microalloying of steel with niobium and vanadium raises
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