Journal of Environmental Protection, 2011, 2, 1341-1346
doi:10.4236/jep.2011.210154 Published Online December 2011 (
Copyright © 2011 SciRes. JEP
The Influence of Gas Flare Particulates and
Rainfall on the Corrosion of Galvanized Steel
Roofs in the Niger Delta, Nigeria
Ajah Ekpeni Obia1, Hanson Effiong Okon1, Samuel Aji Ekum1, Eyo Effiom Eyo-Ita1,
Ekpang Ajah Ekpeni2
1Department of Architecture, Cross River University of Technology, Calabar, Nigeria; 2Department of Chemistry, Cross River Co-
llege of Education, Akamkpa, Nigeria.
Received August 3rd, 2011; revised September 9th, 2011; accepted October 18th, 2011.
An experiment was conducted to determine the influence of air-borne particulates exuded from gas flare chambers and
rainfall/rain water pH in the rusting of metallic building materials, particularly the galvanized iron roofing sheets, in
the Niger Delta Region of Nigeria. Gas flaring and rain fall in this region are rated to be amongst the highest in the
world. In this experiment, specimens of the metal (galvanized iron) were exposed in the atmosphere for one year, across
four sites within the region. The monthly readings of concentrations of particulate matter (aerosol ) and rainfall at the
sites were recorded. Equally, the average pH values of the collected rainwater were determined and recorded corre-
spondingly. Multiple linear regression, analysis of variance (ANOVA) and Pearson Product Moment Correlation statis-
tical analyses were performed on the obtained data and the outcome indicated that, with an R2 = 0.678, there was sig-
nificant influence of industrial aerosol concentration, precipitation and pH on the degradation of galvanized iron roof-
ing material in the region. It was also established that their individual influences were less than their joint impact, sug-
gesting synergism. The ANOVA test further indicated that corrosion was severe in the industrial sites of Ibeno and
Ebocha while Ekuri (the control station) recorded the least impact. This study recommends a discontinuation of gas
flaring in th e region wh ile research on environ mentally resilient , relatively cheap and sustainable alternative materials
should be encouraged.
Keywords: Galvanized Iron, Gas Flares, Mass Loss, Pollutants, Rainfall
1. Introduction
Metallic corrosion is an inarguably intractable problem in
the construction industry. Global cost of corrosion to the
industry is astronomical; especially in the developed and
emerging economies [1-3]. Yet modern construction can
safely be said to be most promoted and sustained with
metals. Such unique qualities as durability, tensile strength,
malleability, amongst others, make metals enviable com-
ponents of modern construction. Unfortunately, this high
profile material has one major shortcoming, susceptibi-
lity to corrosion attack. There is the universal tendency for
any metallic material to return to its natural stable state
(through corrosion) and that is often not the state in which
humans would prefer to use it [4,5]. This vulnerability is
higher in some metals than others.
In the building industry, iron, steel, aluminum and zinc
are common on account of low cost and availability. Often
times, some measures are taken to protect these metals
against wear. Iron is galvanized (covered with protective
zinc coating) and used as roof coverings. The material
(galvanized iron) finds high use in the developing world,
particularly the high rainfall regions like Niger Delta
Region of Nigeria, where it is largely used as roofing ma-
terial. The advantages of this material over the other two
main rivals in roof covering, aluminum and asbestos, for
instance, are quite obvious hence, its unassailable de-
mand by the low and medium income earners as well as
property developers.
Atmospheric corrosion needs electrolytic medium to
take place [5-9]. Therefore, the presence of moisture on
the metallic surface is an obvious pre-condition for the
metal to degrade. Some scholars suggest that extreme pre-
The Influence of Gas Flare Particulates and Rainfall on the Corrosion of Galvanized Steel Roofs 1342
in the Niger Delta, Nigeria
cipitation is likely to have a less impact on corrosion than
drizzle or dews [6]. If the argument were to hold, we
would have shorter replacement intervals (lifespan) of
galvanized iron roofing sheets in the savannah (middle
belt) region of Nigeria than the high equatorial rainforest
of the south. That situation is seen to be the reverse; there
is a greater tendency to change roofs in the south, parti-
cularly the southeastern axis and Niger Delta where the
rainfall regime is ranked amongst the highest on the Globe
Quite a lot of reasons have been adduced to explain
this phenomenon in the Delta, ranging from pollutant
concentration (natural and industrial) to decline in prod-
uct quality. The first reason stems from the fact that the
region is inundated with gas flare points (there are 123
flare points in the region with a daily output of 50,000
cubic metres of gas) and this is considered to be amongst
the highest in the world [12]. It is also one of the wettest
zones with the richest ecosystems on earth [13-15]. More
so, the combustion in the chambers in Niger Delta is at
best incomplete, leading to the release of large amount of
particulates often noticed as visible orange plumes from
the flare stacks [16]. Thus, it is necessary to examine the
combined influence of these two factors. This study is
therefore aimed at determining the influence of gaseous
aerosols (particulates) and precipitation (rainfall) on the
corrosion menace, especially the degradation of galva-
nized iron, the major roofing material in Nigeria.
2. Materials and Methods
2.1. The Study Sites
Four exposure sites were chosen across the region under
study. Though the zone is noted for its high rainfall and
intense flaring activities, the distribution of these events
is not uniform. The four sites were chosen to capture as
much of these variables as possible. The sites were at
Qua Iboe Oil Terminal (QIT), Ibeno, in Akwa Ibom State,
designated as “M” and National Agip Oil Company
(NAOC), Ebocha in Rivers State, designated as “N”. Oth-
ers were at Ekuri, “O” and Ogoja, “P”; all in Cross River
State of Nigeria. Ibeno is a coastal community by the
bank of Atlantic Ocean and with oil facilities. Ebocha is
about 100 km away from the sea and is an industrial
zone with oil facilities as well. Ekuri is a village situated
deep inside the dense Cross River rainforest, at the foot
of Oban hill, and free from any form of industrial activity.
This rolling high land is an extension of the Cameroon
massif that is noted for its high relief rainfalls. Ekuri is
thus chosen as a control station in this study on account
of its being free from industrial activities. Ogoja is an
urban area with savannah vegetation and comparatively
less rainfall. It is an administrative headquarters with no
industries. Table 1 shows a brief descriptive classifica-
tion of the sites based on pollution and environmental
factors while Figure 1 shows the map of Niger Delta
region with the study sites. The average temperature of
the region oscillates around 30˚C except at Ogoja where
average temperature is 32˚C. The relative humidity in the
region is in the range of 80% - 90% all year round.
2.2. Materials
The basic materials and equipment used for the experi-
ment included the local commercial brand of corrugated
galvanized iron roofing sheets (zinc), a wooden rack and
plastic strings. Others included automatic high precision
air quality monitoring station (manufactured by ELE In-
ternational of England) attached with climatic and pol-
lutant sensors, a sensitive analytical electronic weighing
balance specifically designed for indoor use and having a
range of 0 mg - 21.0 gm and plastic buckets. The balance,
manufactured by Adam Equipment Company Limited,
United Kingdom, is specially used to weigh light objects
in the laboratory when a high degree of accuracy is ex-
pected. The rain gauge sensor attached to the environ-
mental station had a capacity of 0.5 mm per tip and ac-
curacy of one percent. The corrugated iron specimens
were cut to small sizes of 100 mm × 150 mm to conform
to the requirements of ISO 9226 [3,9]. The small size is
to minimize error of measurement and to facilitate easy
handling during the experiment. Several small replicate
specimens are known to give higher accuracy than a sin-
gle large sheet [10]. The aerosol monitoring was done
with an AMS950IS Intrinsically Safe Air-borne Particu-
late Monitor manufactured by CASELLA Limited, United
Kingdom. Other facilities used in the experiment included
10-litre plastic buckets, 2-litre plastic bottles and a one-
metre high stool.
Table 1. Site cl assi fication.
Site Enviroment Location Unique characteristics
“M” QIT, Ibeno Marine/industrial 04˚32N/07˚55Ea seaside oil facility with flare points that burn that burn all-year round
“N” NAOC Ebocha industrial 05˚28N/06˚41Ea rural village with gas flare points that burn all-year round
“O” Forest Ekuri Non-marine/rural 04˚31N/07˚45Ea clearing in the near Ekuri village
“P” Ogoja Non-marine/urban 06˚39N/08˚48Eopen field in a school compound
Copyright © 2011 SciRes. JEP
The Influence of Gas Flare Particulates and Rainfall on the Corrosion of Galvanized Steel Roofs 1343
in the Niger Delta, Nigeria
Figure 1. Map of Niger Delta of Nigeria with the study sites.
2.3. Experimental Procedure
The experiment involved the atmospheric exposure of the
local commercial galvanized iron, as described previ-
ously, for 12 months. Periodic monitoring of the concen-
trations of particulate matter exuded as by-products of
combustion at the flare chambers and the amount of rain-
fall was carried out within the same period. Sample spe-
cimens of 100 mm × 150 mm were cut from a one milli-
metre thick sheet of the metal and cleaned by prickling to
remove scales and other products, polished, degreased and
weighed before exposure [3,6,9,17-19]. The samples were
suspended on a rack with the aid of plastic strings tied to
nails fixed onto the wooden frame and inclined at an an-
gle of 22˚, the average slope of roofs across the region
[10]. The rack assembly was fixed on a wooden pole and
raised to a height of 1.2 m to avoid rain splashes from the
surrounding ground. The samples on each rack were pro-
perly labeled and were in quadruplicates. At the end of
each exposure event, the samples were cleaned as before
and re-weighed. The difference between a sample mass
before and after exposure represented the mass loss. The
mean of the replicates’ mass losses in a rack represented
the mass loss at that station. The environmental monitor-
ing equipment with the high sensitive rain gauge sensor
and the fine particulates (aerosol) monitor were placed
close to each rack whenever those parameters were to be
sampled. In all, there were a total of 12 stations distributed
evenly across the four sites. Each rack was made to face
the dominant prevailing wind direction and planted
within a distance of 100 m from each other and from a
flare stack in the case of sites “M”, Ibeno and “N”, Ebo-
cha where gas is flared. Site, “P”, Ogoja was in a school
premises at the out sketch of the town and in the case of
site “O”, Ekuri, a clearing in the forest on elevated hill
(near the village of Ekuri) and free from any tree canopy
or shade was selected (see Table 1).
The rainfall and aerosol monitoring were done be-
tween the hours of 0600 and 1200 and the monthly means
determined. The rain water samples for laboratory analysis
(for pH determination) were collected on event basis,
whenever it was convenient. However, this discrete col-
lection was done within specific periods to reflect the
seasonal variations of rainfall in the region. The water
collection was done in March, the start of the rains, June,
rains and November, the end of rains in the region. The
rain water was collected with the aid of 10-litre plastic
buckets placed on stools one metre high and in an open
field. The collected water sample was put in 2-litre plas-
tic bottles and firmly corked and taken to the laboratory
for analysis.
2.4. Statistical Treatment
The data were analyzed by using SPSS 2007 statistical
Copyright © 2011 SciRes. JEP
The Influence of Gas Flare Particulates and Rainfall on the Corrosion of Galvanized Steel Roofs 1344
in the Niger Delta, Nigeria
software package. The descriptive statistics of the data
were first obtained (the means and standard deviations/
coefficients of variation). Multiple regression analysis and
Pearson Product Moment correlation analysis were fur-
ther performed on the data to determine the relative roles
of the parameters as well as the correlation strength amongst
them. Analysis of variance (ANOVA) was used to de-
termine the means differences among the four study sites.
The choice of these statistical tools is informed by the
complex and multivariate nature of the atmospheric con-
stituents [20].
3. Results
The average periodic readings of various parameters (mass
loss, precipitation, aerosol concentration and pH) are shown
in Table 2. Figure 2 shows the comparative monthly rain-
fall across the sites. High rainfall was recorded between the
months of May and December, except in September where
there was less rainfall. In all, there was rainfall even in the
Table 2. Mean Readings of Mass Loss, Rainfall, Aerosol
Conce ntr ation an d pH of Rain wat er
Site Station
Mean Mass
Loss (mg) Rainfall (mm) Aerosol
“M” M1 19.55 3382.80 17.30 5.20
Ibeno M2 24.80 3286.80 15.50 5.80
M3 38.38 4117.20 14.87 6.80
Mean 27.58 3595.60 15.89 5.93
“N” N1 30.20 2437.20 18.27 5.10
Ebocha N2 41.90 3537.60 20.17 4.60
N 3 28.97 4237.20 14.95 6.00
Mean 33.69 3404.00 17.80 5.23
“O” O1 0.25 666.96 7.82 6.80
Ekuri O2 7.46 1745.40 8.25 6.90
O3 18.24 3066.48 6.72 6.70
Mean 8.65 1826.28 7.60 6.80
“P” P1 10.45 2045.00 16.20 6.10
Ogoja P2 19.50 778.80 11.80 5.90
P3 21.22 2101.20 9.47 6.30
Mean 17.06 1641.67 12.49 6.10
Figure 2. Monthly rainfall across the study sites.
dry months of December to March. The sites also showed
marked variation in rain distribution. The highest yearly
rainfall amount was 4237.20 mm (recorded at station
“N3” at Ebocha site) while the least (666.96 mm) was at
station “O1”, at Ekuri, indicating a high coefficient of
variation of 45.45%. Aerosol concentration and pH pa-
rameters have low coefficient of variation of 33.41% and
12.41%. The output result of the regression analysis shows
coefficients of 26.349 (constant), 0.006 for variable X1
(rainfall), 0.394 for X2 (aerosol concentration) and –4.282
for X3 (pH) of rainwater. The emergent regression model
is as shown thus: Y(mass loss) = 26.349 + 0.006X1 +
0.394X2 – 4.282X3.
Y(mass loss) = 26.349 + 0.006X1 + 0.394X2 – 4.282X3
The measure of significance is 0.045 within the prob-
ability of <0.05, and the coefficient of determination, R2
is 0.678. Computed correlation coefficients reveal rain-
fall as having the highest values of 0.647 (partial), 0.481
(part) followed by aerosols with corresponding values of
0.119 (partial) and 0.068 (part). The values for pH are
–0.236 (partial) and –0.138 (part).
The result of analysis of variance indicates that there is
a significant difference (p < 0.05) in mass loss between
the sites. A Post Hoc Test (LSD) shows that there is a
significant mean difference (25.04 mg) between sites “N”
(Ebocha) and “O” (Ekuri). Also, sites “M” (Ibeno) and
“O” (Ekuri), and “N” (Ebocha) and “P” (Ogoja) showed
significant mean differences of 18.93 mg and 16.63 mg
respectively between them (p < 0.05). On the other hand
the mean differences between sites “M” (Ibeno)/“N”
(Ebocha) (6.11 mg), “M” (Ibeno)/“P”(Ogoja) (10.52 mg)
and “O”(Ekuri)/“P”(Ogoja) (8.41 mg) indicated insignifi-
cant mean differences (p > 0.05).
4. Discussions
The resultant high coefficient of variation of the rainfall
variable (45.40%) suggests that there was a wide differ-
ence in distribution of this parameter across the sites.
Also, the partial correlation coefficient of 0.647 for rain-
fall shows that the parameter contributed 64.7% to the
corrosion problem. Ogoja (site “P”), the northernmost
site (with mean annual rainfall of 1641.67 mm) is at the
southern margins of Nigerian savannah belt and is roughly
400 km away from the sea, hence the weak influence of
the south west trade wind that drives rain from Atlantic
Ocean hinterland. On the other hand, Ibeno (site “M”),
with mean annual rainfall of 3595.6 mm is just by the
bank of the ocean and close to the equator, with low cloud
height and high frequency of rainfall and dews formation.
The result of the ANOVA and the subsequent Post
Hoc (LSD) tests suggest that Ebocha was the most im-
Copyright © 2011 SciRes. JEP
The Influence of Gas Flare Particulates and Rainfall on the Corrosion of Galvanized Steel Roofs 1345
in the Niger Delta, Nigeria
pact site, followed by Ibeno. The least impacted sites
were Ekuri and Ogoja. Ekuri, the control station in the
experiment, was relatively free from anthropogenic pol-
lution as noticed at the two industrial sites of Ebocha and
Ibeno. From the Post Hoc Test the mean mass loss dif-
ference between Ibeno and Ebocha (6.11 mg) is insig-
nificant (p > 0.05), indicating similarity in pollutant com-
position between them. Similarly, the mean difference
between Ekuri and Ogoja (8.4 mg) is insignificant (p <
0.05). On the other hand, Ibeno and Ekuri showed the
largest significant mean difference of 25.04 mg (p <
The lesser correlation (partial and part) values of aero-
sol of 0.119 and 0.068 and the corresponding negative
values for pH of –0.236 and –0.138 could be understood.
The heavy rainfall makes it difficult for particulates (aero-
sols) and aqueous acidic pollutants to remain suspended
in the atmosphere of this heavily wet region for long,
thus masking their influences in the evolving atmosphe-
ric corrosion chemistry. Moreover, only two sites (Ibeno
and Ebocha) are within flare zones while the other two
(Ogoja and Ekuri) are far away from crude oil exploita-
tion activities (400 km and 200 km respectively). Coin-
cidentally, the two aerosol-prone environments are also
zones of heavy rainfall. Thus the diluting and scaven-
ging effect of the rain reduces the apparent concentra-
tion of the atmospheric aerosol and hence pH [5,21] and
thus giving a pseudo-impression of light aerosol concen-
tration across all the sites. As explained, this does not
absolve these parameters from contributing to the corro-
sion build up.
Corrosion in this region could be caused more by dew
as the pH of dew is far more acidic than that noticeable
in the rain water [5]. The high humidity in the region
leads to high frequency of dew formation. The dew wa-
ter-bubbles on the metallic roof surface act as micro elec-
trolyte that helps to initiate and promote corrosion. The
subsequent rainfall would then likely wash away the for-
med corrosion subtracts, thereby exposing the pitted sur-
face to further corrosion attack. Precipitation, include-
ing dew formation, is enhanced by particulates (aerosols)
and acidic droplets (products of gas flaring). These parti-
cles, most of which are hygroscopic, serve as nuclei for
cloud droplets, thus accelerating condensation [18,19]. In
all, the combined influence of all these parameters is
highly significant (R2 = 0.678), suggesting that about
67.8% of the corrosion is attributed to these factors in
Much of the gas flared in this region is methane, which
in combination with a small proportion of other hydro-
carbons such as ethane and propane, constitute about
90% of the total, and as such the temperature of the flares
is expected to be between 1870˚C and 3000˚C and this
figure is far above the 1204˚C at which molecular nitro-
gen begins to oxidize [21]. Therefore, it is evident that
nitrous oxides (NOx) would be abundant within the vi-
cinity of the flare chambers [21]. This invariably leads to
the formation of the highly reactive nitric acid which, in
addition to other acidic hydrocarbon particles of poor
combustion, would be visited on the metallic roofs as
acid rain, thereby initiating and promoting the corrosion
in the region.
5. Conclusions
This study has shown no doubt, that rainfall and gas flar-
ing parameters have contributed significantly to the cor-
rosion of galvanized iron roofs in the Niger Delta. While
little or nothing could be done about the climate, the an-
thropogenic impact of gas flaring could be checked. The
most obvious environmental solution is the discontinua-
tion of gas flaring in the region. The choice of another
roofing material with high resilience to corrosion attack
is an attractive alternative provided it is affordable to the
ordinary low-income citizen of the region. Therefore,
architects and material scientists should research alterna-
tive ecologically benign and sustainable materials. The
paper also recommends that more studies should be un-
dertaken to verify the influence of dews in the corrosion
of metals under such climates as seen in the Niger Delta.
However, it is important to note that effect of gas flaring
is not limited to material degradation; marine and terres-
trial ecosystems are equally impacted besides the direct
health effect often complained about. There is the need
for research into alternative uses for the exuded gases
even as it has an additional economic benefit.
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