The Influence of Gas Flare Particulates and Rainfall on the Corrosion of Galvanized Steel Roofs in the Niger Delta, Nigeria

doi:10.4236/jep.2011.210154

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Journal of Environmental Protection, 2011, 2, 1341-1346

doi:10.4236/jep.2011.210154 Published Online December 2011 (http://www.SciRP.org/journal/jep)

1341

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.

E-mail: [email protected]

Received August 3rd, 2011; revised September 9th, 2011; accepted October 18th, 2011.

ABSTRACT

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

[10,11].

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˚32′N/07˚55′Ea seaside oil facility with flare points that burn that burn all-year round

“N” NAOC Ebocha industrial 05˚28′N/06˚41′Ea rural village with gas flare points that burn all-year round

“O” Forest Ekuri Non-marine/rural 04˚31′N/07˚45′Ea clearing in the near Ekuri village

“P” Ogoja Non-marine/urban 06˚39′N/08˚48′Eopen field in a school compound

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

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

Code

Mean Mass

Loss (mg) Rainfall (mm) Aerosol

(µg/m3)pH

“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-

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 <

0.05).

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

combination.

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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