Comparative Study of Microbial and Non-microbial Corrosion of X60

Journal of Applied Sciences Research, 4(7): 833-838, 2008
© 2008, INSInet Publication
Comparative Study of Microbial and Non-microbial Corrosion of X60
Steel Exposed to Produced Water
1
1
Y.T. Puyate and 2A. Rim-Rukeh
Department of Chemical Engineering, Rivers State University of Science and Technology,
Port Harcourt, P.M. B. 5080, Port-Harcourt, Nigeria.
2
Department of Integrated Science, College of Education,
P.M.B. 2090, Agbor, Delta State, Nigeria.
Abstract: A comparative study of microbial and non-microbial corrosion of X60 steel exposed to
produced water is presented. The laboratory investigation involves X60 steel coupons immersed in two
batch reactors 1 and 2. Reactor 1 contains produced water with 0.5ppm dissolved ozone added on weekly
basis to eliminate the microorganisms naturally present in the water, while reactor 2 contains the same
volume of produced water with 2g of artificial fertilizer (N PK 15-15-15) added on weekly basis as
nutrient-supplement to promote growth of microorganisms in the produced water. It is shown that the
corrosion rate of X60 steel influenced by microorganisms in the produced water is about 94% greater than
non-microbial corrosion of the metal. The corrosion induced chemical reaction in both reactors is firstorder, and microbial corrosion results in pinhole-size pits on the surfaces of the metal.
Key words: Corrosion; X60 steel; Produced water; Microorganisms; Fertilizer
production, transport, and storage oil facilities amounts
to some hundreds million US dollars per year in the
United States. [8 ]
It is well known that exposure of steel or
any kind of metal in natural water induces the
development
of
microbial film called biofilm.
Biofilms are thin distributed films formed by
microorganisms such as bacteria, algae and fungi
and their associated exopolymers, on the surface of
metals. The presence of biofilm on a metal surface
often leads to highly localized changes in the
concentration of the electrolyte constituents, pH, and
oxygen levels.[9 ] The metabolic processes of the
microorganisms are sustained by chemical reactions
energized by nutrients obtained from the surrounding
environment. These processes can influence the
corrosion behaviour of materials by introducing or
enhancing local chemical changes at the surface of the
metal and producing a localized acid environment.
Such conditions produce corrosive deposits and alter
anodic and cathodic reactions, depending on the
environment and organisms involved. The deposits
often stimulate the development of localized form of
corrosion such as pitting. [1 0 ] Although X60 steel is
susceptible to corrosion, it is the material for
construction of most pipes used in the oil sector in
Nigeria due to its low cost, high strength, and ease of
field make-up by welding.
INTRODUCTION
The extent to which a corrosion process will
proceed is determined by a number of factors
which may be biotic (living) or abiotic (non-living).
The abiotic factors include scratches, abrasion on metal
surfaces, and presence of salt and corrosives in the
surrounding medium. The biotic factors involve the
activities of microorganisms and such a corrosion
process is known as microbiologically influenced
corrosion (M IC) or biological corrosion (i.e.
biocorrosion). [1 ] MIC may, therefore, be defined as an
electrochemical process where microorganisms are
able to initiate, facilitate or accelerate corrosion
reaction without changing its electrochemical nature.[2 ]
The participation of microorganisms in a corrosion
process was ignored in the past, [3 ] but is now
acknowledged and remains the focus of present and
future research work. [4 ] Biocorrosion is reported in
many systems such as underground pipelines,[5 ]
water treatment plants,[3 ] nuclear power industries, [6 ]
and marine structures.[7 ] It is estimated that about
20 percent of all corrosion damage of metals and
building materials are microbiologically influenced
and enhanced. For example, damage caused by
microbial corrosion in stainless steel heat exchangers
within 8 years amounts approximately to 55 million
US dollars, and microbial corrosion damage in
Corresponding Author: Y.T. Puyate, Department of Chemical Engineering, Rivers State University of Science and
Technology, Port Harcourt, P. M. B. 5080, Port-Harcourt, Nigeria.
833
J. Appl. Sci. Res., 4(7): 833-838, 2008
Produced water (or formation water) is one that
accompanies crude oil and gas from a producing well.
It is an integral component of hydrocarbon recovery
process and is usually produced during drilling and
production phases of a well. Naturally, the crude oil
and produced water contain various microorganisms
which must be removed to avoid microbial corrosion of
internal surfaces of pipes conveying these materials
before/and after separating the oil from the produced
water and gas. The produced water obtained from the
se p a r a t i o n p ro c e s s is tre a te d to e lim ina te
microorganisms before discharging into the receiving
water body.
A particular difficulty in the assessment and
control of microbial corrosion is the inability to
distinguish b etween co rrosion caused by
m icroo rganisms and that caused b y nonmicroorganisms. This point was emphasized by Geiser
and Lewandowski[1 1 ] and Pryfogle [1 2 ] who suggested that
corroded materials should be physically inspected for
mosaic deposits on the metal surfaces as a means of
distinguishing microbial corrosion from non-microbial
corrosion. This paper presents a comparative study of
microbial and non-microbial corrosion of X60 steel
pipe exposed to produced water during production of
crude oil from a producing well and/or during
separation of the oil from water and gas.
The 0.5ppm dissolved ozone used in the study was
prepared by NEK Technical, Port Harcourt, Nigeria.
The produced water used in the study contains four
groups of microorganisms: [1 5 ] (i) Hydrocarbon Utilizing
Bacteria (HUB) such as Pseudomonas sp. and Bacillus
sp.; (ii) H eterotropic Bacteria (HB) such as
Pseudomonas sp., Bacillus sp. and Norcadia sp.; (iii)
H ydrocarbo n U tilizing F un gi (H U F ) such
Saccharomyces sp., Penicillium sp., and Candida sp.;
a n d (iv ) H etero tro pic F ungi (H F ) su c h a s
Saccharomyces sp., Penicillium sp. and Candida sp.
Table 2 shows some measured parameters of the
produced water, where the average value of each
parameter was calculated from a set of five
experimental readings.
Preparation of X60 Steel Coupons: Sheets of X60
steel were obtained from Tricorr (Nig) Ltd., Port
Harcourt, Nigeria, and cold-cut to the dimensions 10cm
x 5cm x 0.5cm for each coupon. The cold-cut
technique was used in order to maintain the integrity of
the steel and avoid probable effect of heat-affected
zone (HAZ) on the corrosion process of the metal.
The coupons were surface-finished by scrubbing with
80 grit sand-papers, sterilized by dipping in pure
ethanol, and degreased by washing them in acetone.
The exposed surface area of each coupon is 115cm 2
and is calculated as 2(Lw + Lh + hw) where L =10cm
is the length of each rectangular coupon, w = 5cm is
the width, and h = 0.5cm is the thickness (or height)
of the coupon. Ten (10) pieces of X60 steel coupons
were prepared for the study, and the mass of each
coupon ranges from 19.95 to 20.03g.
M ATERIALS AND M ETHOD
M aterials: The materials used in the study are 0.5ppm
dissolved ozone, NPK 15-15-15 fertilizer, X60 steel
coupons, two (2) batch reactors, and produced water.
T he inorganic fertilizer (N P K -15 -15 -15 ) was
manufactured by NAFCON (N ational Fertilizer
Company of Nigeria) in 1999 and contains 0.15g of
nitrogen, 0.065g of phosphorus, and 0.125g of
potassium. X60 steel presents a microstructure of
ferrite and Table 1 shows the elemental composition
of the metal.
Ozone is a bluish gas with a characteristic pungent
odour. It is an oxidizing biocide that is partially soluble
in water and highly unstable as it readily reverts to
oxygen. The solubility of ozone in water is related to
the amount of ozone in the carrier gas stream. Thus, it
is important to produce a gas stream containing a
relatively high amount of ozone. For example, the
maximum solubilities at 25 0 C for gas stream containing
1% and 3% ozone are 2.7 and 8.1 ppm respectively.[1 4 ]
These maximum levels are not obtained in practice
because of out-gassing of the carrier gas which
removes some of the dissolved ozone. Solubility of
ozone also decreases with increasing temperature.
Ozone degrades [1 4 ] with pH, being fairly stable under
certain conditions at pH of 6, and stable at pH of 10.
Experimental M ethod: Twenty (20) litres of produced
water obtained from a flow station in Rivers State,
Nigeria, was divided equally into two batch reactors 1
and 2. Ten millilitres (10ml) of 0.5ppm dissolved
ozone (a biocide) was added to batch reactor 1 to
eliminate the microorganisms naturally present in the
produced water. T he choice of dissolved ozone as
biocide is a result of its reported biocidal efficacy on
a broad spectrum of microorganisms.[1 6 ,1 7 ] Two
grammes (2g) of NPK 15-15-15 fertilizer was added to
batch reactor 2 to serve as source of nutrients for the
microorganisms in the produced water. The use of the
fertilizer as nutrient-supplement for microorganisms in
the produced water is due to its reported efficiency. [1 8 ]
Five (5) prepared X 60 steel coupons were completely
immersed in each batch reactor and the experimental
set-up was left for a test period of 2016 hours. To
ensure that living microorganism does not exist in
batch reactor 1 throughout the test period, 10ml of
0.5ppm dissolved ozone was added to this reactor on
weekly basis. Accordingly, 2g of the fertilizer was
834
J. Appl. Sci. Res., 4(7): 833-838, 2008
Table 1:
C (% )
0.199
Elem ental com position of X60 steel. [1 3]
M n (% )
P (% )
S (% )
1.59
0.016
0.018
Cr (% )
0.015
N i (% )
0.007
M o (% )
0.008
V (% )
0.004
Cu (% )
0.024
Al (% )
0.024
Fe
98.095
Table 2.: Som e m easured param eters of produced water used in the
study
Param eter
Average value
pH
5.7
Turbidity (N TU )
105
Conductivity (µs/cm )
37080
Chloride (m g/l)
2513
N itrate (m g/l)
1.2
Sulphate (m g/l)
9.8
TD S (m g/l)
18500
D O (m g/l)
6.10
Iron (m g/l)
11.8
TM C(cfu/m l)
10 4
TD S (Total D issolved Solids); D O (D issolved O xygen).
Table 3: M easured tem peratures in the two
Exposure tim e (hrs) 0
672
1008
Reactor 1 (EC)
26.3
26.7
27.1
Reactor 2 (EC)
26.4
26.8
27.1
batch reactors
1344 1680
27.2
26.5
27.3
27.1
2016
27.3
26.8
Fig. 1: Variation of TMC with time.
added to batch reactor 2 on weekly basis to maintain
continuous supply of nutrients to the microorganisms
in this reactor during the period of the experiment.
A coupon was retrieved from each reactor, washed,
dried, and weighed at intervals of time (0, 672, 1008,
1344, 1680, 2016 hours). The corrosion rate of X60
steel coupon was determined using the mass-loss
technique as [1 ]
ÄM × 3.45 × 10 6
Corrosion rate (mpy) = -----------------------Añt
within 672 hours and maintained at an average level
of about 10 7 cfu/ml for the rest of the test period.
The drastic reduction of TMC in reactor 1 is due to
the biocide which eliminated the microorganisms in this
reactor after 672 hours, while the drastic increase of
TMC in reactor 2 is attributable to growth of
microorganisms in this reactor resulting from
continuous supply of nutrients by the fertilizer.
Figure 2 shows the variation of corrosion rate of
coupon with time in the two batch reactors from which
it may be seen that the corrosion rate in reactor 2 is
higher than that in reactor 1. Earlier work by
Costello [2 1 ] indicates that microorganisms can cause
corrosion rate to increase by about 1000 – 100,000
times greater than in the absence of microorganisms,
and microbial corrosion has the potential to produce
extra-ordinary corrosion rate of 25mpy. [2 2 ] However, the
microbial corrosion in the present study is greater than
the non-microbial corrosion by about 94% and the
maximum microbial corrosion rate obtained in the
present analysis is 2.08mpy; this may depend on the
types of microorganisms in the produced water, the
nutrient-supplement used, and whether or not corrosion
inhibitory elements are present in the produced water.
T he c o rro s io n ra te s in re ac tor 1 (witho ut
microorganisms) may be due to chemical components
of the produced water like chloride, sulphate, nitrate,
and iron (see Table 2), Also, the low corrosion rates in
reactor 1 probably indicate the presence of corrosion
inhibitory elements in the produced water which would
also affect the corrosion rates in reactor 2. T he key
feature for enhancement of corrosion in reactor 2 is the
presence of deposit (biofilm) on the metal surfaces.
The nature of X60 coupon retrieved from reactor 1
(without microorganisms) after 2016 hours is shown in
(1)
where ÄM is the mass-loss (g) of the coupon, A is the
total exposed surface area of the coupon (cm 2 ), ñ is the
density of the coupon (g/cm 3 ), and t is time (hours).
Temperature and total microbial count (TMC) in the
two batch reactors were measured throughout the test
period, where temperature was measured using a multiparameter water quality monitor (Model, 600 UPG),
and TMC was determined using the rapid agar dipstick
technique.[1 9 ]
RESULTS AND DISCUSSION
The temperature in the two batch reactors varies
from 26.3 0 C to 27.3 0 C (see Table 3), which is
consistent with the temperature range 25 o C - 30 o C for
microbial growth.[2 0 ]
Figure 1 shows the variation of total microbial
count with time in the two reactors. The TMC in
reactor 1 decreases drastically from 10 4 to zero after
672 hours and maintained at this level throughout the
remaining period of the experiment, while the TMC in
reactor 2 increases tremendously from 10 4 to 10 6 cfu/ml
835
J. Appl. Sci. Res., 4(7): 833-838, 2008
Fig. 2: Variation of corrosion rate of coupon with
time.
Fig. 4: Corrosion coupon after 2016 hours of
exposure to produced water treated with NPK
15-15-15 fertilizer (showing biofilm on metal
surface).
Fig. 3: Corrosion coupon after 2016 hours of
exposure to produced water treated with
0.5ppm dissolved ozone (showing smooth
surface without biofilm).
Fig. 5: Photograph showing pits on the surface of
coupon retrieved from reactor 2 after
2016hours when deposits on the surface have
been removed.
Fig. 3, where mosaic deposit was not formed on the
metal surfaces. Figure 4 shows X60 coupon retrieved
from reactor 2 (containing microorganisms) after the
exposure time of 2016 hours, with thick deposit
(biofilm) on the metal surfaces. After removing the
deposit on the coupon surfaces in Fig. 4, pinhole-size
pits were observed on the metal surfaces (Fig. 5) which
is attributable to the activities of microorganisms in the
produced water.
Figure 6 illustrates the mass-loss of coupon
retrieved from both reactors during the period of the
experiment,
indicating
non-linear
relationship
between ÄM and t. The mass-loss of coupon is greater
in reactor 2 than reactor 1, which is expected and is
due to the higher corrosion rate in reactor 2 than
reactor 1. W hen log of mass-loss is plotted against
time for both reactors, an approximate linear
relationship is obtained (see Fig. 7), confirming a first-
836
J. Appl. Sci. Res., 4(7): 833-838, 2008
continuing work. The corrosion induced chemical
reaction in both reactors is first-order, and microbial
corrosion results in pinhole-size pits on the surfaces of
the metal.
REFERENCES
1.
2.
3.
Fig. 6: V ariation of
exposure time.
mass-loss
of
coupon with
4.
5.
6.
7.
8.
9.
Fig. 7: Plot of log (mass-loss) of coupon against time.
order chemical reaction in both reactors. This method
of using a linear relationship between log of mass-loss
and time to determine the order of a chemical reaction
is reported in the literature.[2 3 ,2 5 ]
10.
Conclusion: An experimental study on the microbial
and non-microbial corrosion of X60 steel immersed in
produced water is presented. It is shown that the metal
corrodes with or without microorganisms in the
produced water. Corrosion of X60 steel in the absence
of microorganism may be due to chemical components
of the produced water like chloride, sulphate, nitrate,
iron, etc. The influence of microorganisms is significant
and results to about 94% increase in the corrosion rate
of X60 steel when NPK-15-15-15 fertilizer is used as
nutrient-supplement for the microorganisms in the
produced water. The low corrosion rates of the metal
in reactor 1 (without microorganisms) may indicate the
presence of corrosion inhibitory elements in the
produced water which would also affect the measured
corrosion rates in reactor 2; this is not investigated in
the present analysis and remains the focus of
11.
12.
13.
14.
15.
837
Bradford, S.A., 1993. Corrosion Controls. Van
Nostrand Reinhold, New York.
Videla, H.A., 1986. Mechanisms of MIC. In
Proceedings of the Argentine – USA W orkshop on
Biodeterioration (CONCICET – NSF), edited by
Videla, H.A., Sao Paulo, Brazil, 45-48.
Iversen, A., 2001. Microbially influenced corrosion
on stainless steels in wastewater treatment plants:
Part 1. British Corrosion Journal, 36(4): 277-283.
Videla, H.A., 1996. Manual of Biocorrosion. CRC
Lewis Publishers, Florida.
Harris, J.O., 1960. Soil microorganisms in relation
to cathodically protected pipe. Corrosion, 10:
441-448.
Mittelman, M., 2003. Microbially influenced
corrosion of sprinkler piping, Corrosion, 49: 13-17.
Pedersen, A.P. and M.W . Hermansson, 1987.
Inhibition of metal corrosion by bacteria,
Biofouling, 3(1): 1-3.
Costerton, J.W . and J. Boivin, 1991. Economics of
microbial corrosion in water systems. International
Conference on Microbially influenced Corrosion,
Paper No. 57, Knox ville.
B o r e nstein,
S .W .,
1991.
W hy
does
microbiologically influenced corrosion occur at or
adjacent to austenitic stainless steel weldments?
Corrosion/91, Paper No. 286, NACE Interntional,
Houston Texas.
Characklis, W .G. and K.E. Cooksey, 1983.
Biofilms and Microbial fouling. Advances in
Applied Microbiology, 29: 93-97.
Geiser, M.R. and A.Z. Lewandowski, 2001. Pit
initiation on 316L stainless steel in the presence of
bacteria,
Leptothrix
discophora. Corrosion,
01257: 1-9.
Pryfogle, P.A., 2002. Geothermal Biocorrosion.
U .S . D e p a r tm e n t o f E n e r g y C o n ve rsio n
Technology, Bulletin Energy, 317: 16-18.
Benmoussat, A. and M. Hadjel, 2005. Corrosion
behaviour of low carbon line pipe steel in soil
environment. The Journal of Corrosion Science and
Engineering, 6(9): 1178-1183.
Rice, R.G. and J.F. W ilkes, 1991. Fundamental
aspects of ozone chemistry in recalculating cooling
water systems. In Corrosion 91/Paper No. 205,
NACE International, Houston, TX.
EIA, 2006. Environmental Impact Assessment of
Obiafu Field Further Development Project Report
J. Appl. Sci. Res., 4(7): 833-838, 2008
16.
17.
18.
19.
20.
No. S-0113. Nigerian Agip Oil Company, Port
Harcourt, Nigeria.
Maxey, B.J. and P.R. Puckorius, 1991. Ozone for
cooling tower systems: Is it a panacea? Corrosion
91, Paper No. 212, N ACE International, Houston,
Texas.
Puyate, Y.T. and A. Rim-Rukeh, 2008. Biocidal
efficacy of dissolved ozone, formaldehyde and
sodium hypochlorite against total planktonic
microorganisms in produced water, Journal of
Applied Sciences, 8(5): 860-865.
Adieze, I.E., R.N. Nwabueze, and G.O.C. Onyeze,
2003. Effect of poultry manure on the microbial
utilization of hydrocarbons in oil-polluted soil.
Nigerian Journal of Microbiology, 17(1): 12-16.
Borenstein, S.W., 1995. Detection, diagnosis, and
monitoring of biocorroson. In Microbiologically
Influenced Corrosion Handbook, edited by G.
Kobrin, Industrial Press Inc., New York, 185-187.
Lee, W . and D.K. Newman, 2003. Microbial iron
respiration: Impacts on corrosion processes.
Applied Microbiology Biotechnology, 62: 134-135.
21. Costello, J.A., 1969. The Corrosion of metals by
microorganisms: A literature survey. International
Biodeterioration Bulletin, 5: 101-106.
22. Corrview, 2004. The limitation of corrosion
coupons, Technical Bulletin, C-15: 1-9.
23. Jones, L.W ., 1988. Corrosion and W ater
Technology for Petroleum Producers. Oil and Gas
Consultants International Inc., Tulsa.
24. Omo-Odudu, D.U. and N.C. Oforka, 1999.
Inhibition of the corrosion of mild steel in
trioxonitrate (v) acid, Nigerian Journal of Physics,
11: 148-153.
25. Rim-Rukeh, A., 2005. Effects of inorganic
fertilizer NPK 15-15-15 and animal (cattle) dung
on waste pit water polishing. Journal of Science
and Technology Research, 4(1): 5-9.
838