corrosion damage of oil line tubes

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UDC 669.14.018.298.3:620.193

CORROSION DAMAGE OF OIL LINE TUBES FROM

CHROMIUM-MOLYBDENUM-CONTAINING STEELS

IN HIGHLY AGGRESSIVE PRODUCED ENVIRONMENTS

M. A. Vyboishchik,1 A. V. Ioffe,2 E. A. Borisenkova,2 T. V. Denisova,2 and A. V. Sorokin2

Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 10, pp. 29 – 33, October, 2012.

The effect of chemical composition and structure of the metal of oil line tubes on the evolution of corrosion

damage is studied for aggressive conditions of oil gathering. The corrosion resistance of the tubes is shown to

depend on their chemical composition and structure of corrosion products on the surface.

Key words: tube steels, corrosion resistance, corrosion products, evolution of damage.

INTRODUCTION

An urgent task of the recent period is creation of tube

steels with elevated endurance under operating conditions.

This is connected with growth in the watering and in the con-

tents of CO2, H2S and sulfate-reducing bacteria (SRB) in

transported environments, i.e., with permanent intensifica-

tion of the effect of the corrosion-active components of the

environments on the tubes. Comparative field tests [1] have

shown that oil line tubes produced from steels 13KhFChA

and 08KhMFA possess a higher corrosion resistance in envi-

ronments containing elevated amounts of H2S and CO2 than

the traditionally used steels. Grade 08KhMFA combines high

mechanical properties with corrosion resistance, which de-

termines the prospects of its application. The aim of the pre-

sent work was a detailed study of the mechanism and kine-

tics of development of corrosion damage in steels alloyed ad-

ditionally with Cr, Mo, and V and inoculated with REM for

operation under conditions of highly aggressive transported

environments.

METHODS OF STUDY

We performed field tests of coils cut from tubes 219 mmin diameter and 8 mm thick produced from steels 13KhMFA,

08KhMFChA, 20KSKh and 20. All the coils were mounted

in one pilot division into an oil-gathering header in a manner

not disturbing the laminar flow of the environment and pre-

venting the appearance of electrochemical corrosion between

steels with different contents of carbon.

The chemical compositions of the studied steels are

given in Table 1. The heat treatment consisted of normaliz-

ing, which provided formation of fine grains in the structure

Metal Science and Heat Treatment , Vol. 54, Nos. 9 – 10, January, 2013 (Russian Original Nos. 9 – 10, September – October, 2012)

5190026-0673/13/0910-0519 © 2013 Springer Science + Business Media New York

1 Tolyatti State University, Tolyatti, Russia (e-mail: [email protected]).2 Samara Engineering-Technical Center, Samara, Russia (e-mail:

[email protected]).

TABLE 1. Chemical Composition of Studied Steels

SteelContent of elements, wt.%

Si Mn Cr Mo Ni Al Cu N Nb Ti V Ca P S

13KhFA 0.09 0.35 0.54 0.58 0.002 0.02 0.034 0.03 0.004 0.018 0.004 0.046 0.001 0.01 0.002

08KhMFChA-1

(37 ppm Ce) 0.07 0.34 0.53 0.66 0.131 0.16 0.038 0.14 0.003 0.029 0.003 0.063 0.002 0.005 0.001

08KhMFChA-2

(45 ppm Ce) 0.07 0.35 0.52 0.66 0.125 0.16 0.036 0.15 0.004 0.028 0.002 0.063 0.002 0.005 0.001

20KSKh 0.21 0.26 0.55 0.02 0.003 0.03 0.025 0.05 0.007 0.004 0.002 0.001 – 0.01 0.006

20 0.21 0.24 0.42 0.03 0.003 0.04 0.037 0.04 0.007 0.001 0.002 0.002 0.001 0.01 0.004



of the metal and relatively high corrosion properties (all thesteels had grains of size No. 9). Each steel was studied in two

different states to obtain additional information. For exam-

ple, the tests of two specimens of steel 13KhFA after operat-

ing periods of different duration (221 and 515 days) allowed

us to compare the results obtained for the rate of corrosion,

the structure and the composition of the corrosion products.

Two specimens of steel 08KhMFChA with different contents

of cerium were used to obtain data on the required content of

inoculant for chromium-containing steels. Steels 20 and

20KSKh differed in the technique of modification of nonme-

tallic inclusions. In the structure of steel 20 the sulfide inclu-

sions were spheroidized.Prior to performing field tests we determined the me-

chanical and corrosion properties of the steels (Tables 2 and

3). We established that the highest resistance to hydrogen

cracking and sulfide stress corrosion cracking was exhibited

by steel 08KhMFChA (Table 3).

The field tests were performed at an oil-gathering header.

Its operating parameters were as follows: working pressure

5 – 7 atm, volume of transported product 1170 m 3day, wa-

tering of the product 89%, content of SRB (plankton)

1 104 cellsml, mechanical admixtures (total) 12.5 mgliter,

product density 1.054 gcm3, mean temperature of environ-

ment 70 – 80°C.

The transported environments contained (in mgliter)

2.0 H2S, 75.9 CO2, and 23.0 Fe. The total mineralization of

the environments was 75.91 gliter, the pH = 6.6. The ion

composition of the environments (in mgliter) was as follows:

0.26 HCO3

; 4.94 SO42

; 46.095 Cl – ; 2.52 Ca2+; 0.259 Mg2+;29.9 (Na+ + K + ).

The composition of the transported corrosion-active en-

vironment and the operating parameters of the oil-gathering

header (75 mgliter CO2 and 2 mgliter H2S), the watering

(98%), and the high content of corrosion-active component

(46 mgliter Cl – ) reflect high aggressiveness of the environ-

ment and allow us to expect intense carbon dioxide corrosion

in this division of oil gathering. The corrosion damage of

tube specimens manifested itself in the form of general thin-

ning of the wall estimated by the method of ultrasonic check

and local pitting damage determined visually. The phase

composition of the corrosion products was determined by themethod of x-ray diffraction analysis performed with the help

of a DRON-3 device. The structure and composition of the

corrosion products were studied using an “Inspect” scanning

electron microscope (Fei) and a “Edax” chemical analyzer.

RESULTS AND DISCUSSION

The corrosion damage of the tubes was studied after test-

ing steel 13KhFA for 221 days and 515 days; the other steels

were tested after 283 days. We evaluated the following cha-

racteristics:

– mean and maximum rates of general corrosion, whichwere determined in terms of the mean and maximum thin-

ning of the tube wall;

– mean and maximum rate of local corrosion, which

were determined in terms of the mean and maximum depth

of corrosion pits after statistical processing of the results of

50 measurements;

– mean and maximum rates of growth in the diameter of

pits, which characterized indirectly the local corrosion;

– total rate of corrosion damage, which was determined

in terms of the sum of the general and local components of

the damage.

The highest wall thinning is detected on the lower

generatrix of a tube (1.5 – 2 times higher than on the upper

520 M. A. Vyboishchik et al.

TABLE 2. Mechanical Properties of Studied Steels

Steel r , MPa 0.2 , MPa 0.2 r , % KCV , MJm2 at test temperature, °C

– 40 – 50 – 60 – 70

13KhFA 590 490 0.83 30.0 2.4 (100) 2.2 (100) 2.1 (100) 2.0 (100)

08KhMFChA (37 ppm Ce) 610 505 0.83 22.7 2.6 (100) 2.5 (100) 2.4 (100) 2.4 (100)08KhMFChA (45 ppm Ce) 600 445 0.75 28.3 2.7 (100) 2.7 (100) 2.6 (100) 2.5 (100)

20KSKh 630 530 0.84 22.5 0.5 (0) 0.4 (0) 0.4 (0) 0.3 (0)

20 480 285 0.59 29.2 0.4 (0) 0.4 (0) 0.4 (0) 0.3 (0)

Note. The content of the ductile component in the fracture is presented in parentheses in percent.

TABLE 3. Corrosion Resistance of Tested Steels (NACE Standard)

SteelHR, %

K ISSC ,

MPa m12CTR CLR

13KhFA 0 0 41.30

08KhMFChA-1 (37 ppm Ce) 0 0 42.08

08KhMFChA-2 (45 ppm Ce) 0 0 43.28

20KSKh 40 12 35.66

20 20.08 5.90 –

Notations: HR is the resistance to hydrogen cracking (NACE TM

0284–2003); CLR and CTR are the coefficients of crack length and

thickness, respectively; K ISSC is the threshold coefficient of stress

intensity.



generatrix). For this reason we made all the measurements in

the lower, most damaged, region. To reduce the results of all

the tests to one term (283 days), we recomputed the charac-

teristics of steel 13KhFA and the kinetics of their variation

(after 221 and 515 days of testing) for 283 days. All the cha-

racteristics of the corrosion damage are given in Table 4. It

can be seen that the chromium-containing steels have much

higher resistance to carbon dioxide corrosion than the carbonsteels. In addition to the known fact of increase in the resis-

tance to hydrogen damage [2], inoculation with REM also

lowers the manifestation of local carbon dioxide corrosion.

However, the increase in the content of Ce above 37 ppm in

steel 08KhMFChA does not produce a significant result.

Testing of tubes from steel 13KhFA for different terms

(221 and 515 days) allowed us to trace the dynamics of the

evolution of corrosion damage in chromium-containing

steels. The specimens of steel 13KhFA were taken from the

same heat and one batch of tubes. Since the testing condi-

tions were identical, we estimated the effect of the time of

operation on the corrosion parameters. It can be seen from

the data of Table 5 that the main tendency is considerable de-

Corrosion Damage of Oil Line Tubes from Chromium-Molybdenum-Containing Steels 521

TABLE 4. Corrosion Damage of Tube Walls after 283 Days of

Testing

Steel vtot ,

mmyear

vloc ,

mmyear

v p ,

mmyear

v ,

mmyear

C Cr ,

%

13KhFA 0 23

0 51

.

.

0 30

0 41

.

.

91

14 6

.

.

0 54

0 92

.

.

2.9

08KhMFChA-1

(37 ppm Ce)

0 21

0 35

.

.

0 27

0 36

.

.

8 2

115

.

.

0 48

0 71

.

.

3.7

08KhMFChA-2

(45 ppm Ce)

0 23

0 40

.

.

0 21

0 33

.

.

4 3

71

.

.

0 44

0 73

.

.

3.6

20KSKh 0 28

0 43

.

.

0 44

0 55

.

.

61

9 0

.

.

0 72

0 98

.

.

–

20 0 36

0 56

.

.

0 40

0 53

.

.

35 2

37 5

.

.

0 76

109

.

.

–

Notations: vtot and vloc are the rates of total and local corrosions re-

spectively; v p is the rate of growth in the diameter of pits; v is the

total corrosion rate (general + local); C Cr is the chromium content in

the corrosion products.

Note. The numerators present the mean corrosion rates; the denom-

inators present the maximum rates.

à

c

e

b

d

f

500 m

20 40 60 80

2 4 6 8

O; Ca; Fe, wt.%

Cl; Cr, wt.%

22% Ñà

8% Ñl

Layer of corrosion products

Metal of the tube

Ca

Cr Cl

O

Fe

Fig. 1. Structure and composition of corro-

sion products on the internal wall of a tube

from steel 20 after operation for 283 days in

an oil-gathering header: a) surface; b ) corro-

sion products in cross section of the speci-

men; c, d ) distribution of Fe, Ca, O2, Cr and

Cl over the thickness of the corrosion layer

(in the framed rectangular zone); e, f ) struc-

ture in the characteristic radiation of Ca and

Cl respectively (the marked regions contain

their maximum amounts).



celeration of the corrosion processes upon growth in the test

time. The deceleration is the highest in maximum-size pits.

This seems to be connected with the fact that the protective

chromium-containing layer of corrosion products, which

blocks or decelerates the development of local damage, is

more concentrated in larger-size pits.The x-ray diffraction phase analysis of the corrosion

products has also shown the presence of CaCO3 and FeCO3

carbonates, Fe3O4 oxide and FeS and ZnS sulfides in them,

which means that carbonate corrosion is the dominant corro-

sion mechanism for the oil field studied. The presence of

zinc sulfide seems to be connected with the special features

of the oil field and the presence of a water-insoluble zinc-

bearing mineral that precipitates on tube walls.

The metallographic studies and local chemical analysis

of all the specimens have shown substantial inhomogeneity

of the structure and composition of the corrosion products,

which depend much on the structure and composition of the

metal of the tubes. Figures 1 and 2 present the results ob-

tained for steel 20 and 08KhMFChA. The corrosion products

can be divided conventionally into three layers, i.e., an exter-

nal layer with dominance of sulfides in the composition, an

internal layer bearing calcium and iron carbonates, and a

layer directly adjoining the metal of the tube and represented

by a mixture of iron carbonates and iron oxide. The internallayer of the corrosion products on chromium-containing

steels (13KhFA and 08KhMFChA) is enriched considerably

with chromium; its concentration in the layer is 4 – 8 times

higher than in the base metal. It is interesting that the content

of chromium in the corrosion products increases upon

growth in the term of operation (Table 5). We assume that the

chromium has the form of an amorphous phase [Cr(OH) 3

chromium hydroxide]. The intermediate layers of the corro-

sion products are also saturated with chlorine from the trans-

ported environment. In the chromium-containing steels the

content of chlorine does not exceed 2 – 3%; it is distributed

relatively uniformly over the thickness of the layer without

522 M. A. Vyboishchik et al.

à

c

e

b

d

f

20 40 60 80

2 4 6 8

O; Ca; Fe, wt.%

Cl; Cr, wt.%

1.8% Ñl

3.8% Ñr

Ca

Cr

Cl

O

Fe

100 ìêì

Layer of corrosion products

Metal of the tube

Fig. 2. Structure and composition of

corrosion products on the internal wall

of a tube from steel 08KhMFChA-2 af-

ter operation for 283 days in an oil-gath-

ering header: a) surface; b ) corrosion

products in cross section of the speci-

men; c, d ) distribution of Fe, Ca, O, Cr,

and Cl over the thickness of the corro-

sion layer; d , e) structure in the charac-

teristic radiation of Cl and Cr, respec-

tively.



noticeable concentration at the interface of the corrosion

products and the base metal.

Growth in the chromium content in the products of cor-

rosion decreases considerably the rate of corrosion fracture

(Fig. 3). The dynamics of development of the protective pas-sivating chromium-containing layer and its effect on the rate

of corrosion in environments containing carbon dioxide re-

quire additional investigation. According to the data of [3, 4]

the chromium-bearing amorphous phase Cr(OH)3 possesses

a lower conductivity than iron carbonate and suppresses the

electrochemical processes leading to pitting corrosion. In ad-

dition, phase Cr(OH)3 is characterized by ion selectivity and

hinders the diffusion of Cl – , CO32 , and HCO3

ions to the

surface of the corroding steel. Ions of Cl – do not accumulate

on the metalcorrosion products interface and the fracture of

the steel is decelerated.

Corrosion products on tubes from steel 20 and 20KSKhare looser and bear a greater number of cracks and disconti-

nuities than chromium-containing steels. The boundary be-

tween corrosion products and the base metal in steels 20 and

20KSKh is developed poorly, which indicates low adhesion

and possibility of detachment. The upper and lower layers of

corrosion deposits have a more homogeneous composition

and contain an iron oxide and calcium and iron carbonates.

Sulfides penetrate into the middle layers of corrosion pro-

ducts. The corrosion products are saturated with chlorine.

The highest concentration of chlorine is observed on the in-

terface with the metal and amounts to 8% (Fig. 1), which

corresponds to the concentration of chlorine in the trans-

ported environment. Undoubtedly, this accelerates the gen-eral and local corrosion processes. On some regions the car-

bonates are detached, which causes pitting corrosion initiated

by the “carbonates (cathode) – tube metal (anode)” galvanic

couple.

CONCLUSIONS

1. The rate of corrosion of chromium-containing steels

depends on the content of chromium in the corrosion pro-

ducts. Growth in the term of operation of tubes from steel

13KhFA from 221 to 515 days increases the chromium con-

tent in the corrosion deposits from 2.5 to 4.5% and, accord-

ingly, lowers the corrosion from 0.56 to 0.41 mmyear.

2. On tubes from steels 20 and 20KSKh a great content

of chlorides is contained in corrosion products and on their

surface, which accelerates the local and general corrosion of

the tubes.

3. On the surfaces of tubes from steels 13KhFA and

08KhMFChA chlorine does not accumulate, which seems to

be connected with the barrier action of the chromium-bear-

ing corrosion products.

4. Inoculation of the steels with rare-earth metals dece-

lerates local corrosion.

The authors are grateful to specialists of the “VZM” and

“RN-Stavropol’neftegaz” Companies for participation in the

erection of by-pass benches and help with the organization of

field tests.

REFERENCES

1. A. V. Ioffe, T. V. Tetyueva, V. A. Revyakin, et al., “Corrosion-

mechanical fracture of tube steels in operation,” Metalloved.

Term. Obrab. Met., No. 10, 22 – 28 (2012).

2. A. V. Ioffe, T. V. Tetyueva, T. V. Denisova, et al., “Effect of ino-

culation with rare-earth metals on mechanical and corrosion

properties of low-alloy steels,” Vektor Nauki TGU , No. 4,

41 – 46 (2010).

3. C. F. Chen, M. X. Lu, D. B. Sun, et al., “Effect of chromium on

the pitting resistance of oil tube steel in a carbon dioxide corro-

sion system,” Corrosion, 61(6), 594 – 601 (2005).

4. M. Ueda and A. Ikeda, “Effect of microstructure and Cr content

in steel on CO2 corrosion,” in: Corrosion, Sumitomo Metal Ind.

Ltd., Paper No. 96013 (1996).

Corrosion Damage of Oil Line Tubes from Chromium-Molybdenum-Containing Steels 523

0.80

0.75

0.70

0.65

0.60

0.55

0.50

0.45

0 1 2 3 4 5C Cr , %

vcîr , mm year

1

2

3

4

5 6

Fig. 3. Mean total rate of corrosion vcor (general + local) as a function

of the content of chromium in the corrosion products of steels after

different terms of operation: 1 ) steel 20, 283 days; 2 ) steel 20KSKh,

283 days; 3 ) steel 12KhFA, 221 days; 4 ) steel 08KhMFChA-1

(37 ppm Ce), 283 days; 5 ) steel 08KhMFChA-2 (45 ppm Ce),283 days; 6 ) steel 13KhFA, 551 days.

TABLE 5. Corrosion Damage of the Wall of a Tube from Steel

13KhFA

test ,

days

vtot ,

mmyear

vloc ,

mmyear

v ,

mmyear

hcor ,

mm

C Cr ,

%

221 0 25

0 54

.

.

0 31

0 44

.

.

0 56

0 98

.

.

101 2.5

515 015

0 39

.

.

0 27

0 30

.

.

0 41

0 69

.

.

141 4.5

– Change in the characteristics after 294 days, X , %

– 30 – 40 – 32 – 15 – 30 – 27 + 40 + 80



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