Study for Determination of Industrial Water Corrosivity in Kashan Fajre Sepahan Galvanizing Mills During 2005-2006 Iran
A. Ahmadi Motlagh
This research was carried out in Kashan Fajre Sepahan Galvanizing mills (KFSGM) for evaluation of water corrosivity during 2005-2006. A total of 18 samples were taken from various points of the water supply system for testing the specific parameters and calculation Langelier Index (LI), Ryznar Index (RI) and Pukorious Index (PI). This research showed that in raw water (sand filter effluent) LI were positive as well as RI and PI were lower than 7 which means that mentioned water is not corrosive. Also LI in treated water by reverse osmosis process was negative and RI and PI were higher than 7, so, this water has corrosive properties. Finally, calculated indexes indicate that according to LI, conditioned water is not corrosive but based on RI and P. this water tend to corrosivity which this findings is compatible with literature review statement. So it is recommended that, for water conditioning addition of preservative chemicals to be continued but at the same time another alternatives such as pH adjustment, air stripping and deoxygenating, control of carbonate concentration and split flow treatment should be studied.
Corrosion is destruction of a matter such as metals in
responses to reaction with environment. This environment can be a liquid
media such as water flowing in pipes and solid media such as soil in contact
with buried pipes. Corrosion can be occurs due to various processes including
physical, chemical, biological and electrochemical reactions (Saatchi,
1993; Pishnamazi, 2005; Oram, 2007).
In the world, every year several billion dollars loses
via corrosion in industrial activities. In our country (Iran) especially
in the past two decade which was in economic and scientific development
stage, these problems exist as an economical challenge (Saatchi, 1993).
For the best operation of a boiler or cooling tower, the water quality
control is detrimental factor. In the past, our researches have been focused
upon leakage and economical damages of corrosion but generally health
and aesthetic aspects of water quality weren`t considered (Log et al.,
2004). At the present, since metal pipes for water transmission is commonly
used in the world, so water industry have to consider effects of corrosion
upon water quality and conversely (Dietrich, 2004).
Unfortunately, in our country limited studies was carried
out in the field of corrosion. Findings of a study in Zarrinshahr city
(Iran) water distribution system show that high concentrations of lead,
cadmium and zinc in drinking water relates to corrosion of internal walls
in galvanized pipes (Shahmansori and Pormoghadas, 2004).
Kashan Fajre Sepahan Galvanizing Mills (KFSGM) has been
set in operation since 1999. Its products are a lot of galvanized sheets
(105 tons year-1). Water consumption in these mills is 600
L tone-1 of products. At the beginning, one of the main problems
facing with was corrosion, especially in cooling towers. Thus one of the
attempts was feeding of two preservative chemicals (DM and 8410 as trade
name) to cooling water. It is to notify that since now a comprehensive
research was not carried out on corrosion control in mentioned mills,
so this research was conducted in KFSGM.
MATERIALS AND METHODS
This research is an experimental study which carried out during 2005-2006
upon samples collected from the various points of KFSGM water supply system.
The water supply system includes deep well, raw water storage tank, sand
filter, ion exchange and Reverse Osmosis (RO) process. Some of treated
water after conditioning feeds to three cooling towers. Flow diagram of
water supply system in KFSGM is showed in Fig. 1. A total
of 18 samples were taken for testing, including 6 samples from raw water
after sand filter (filter effluent), 6 samples from the effluent of reveres
osmosis (treated water) and 6 samples from conditioned water in cooling
towers (conditioned water). Analysis of samples has been carried out by
methods described in standard methods for examination of water and wastewater
book (ADHA, AWWA and WPCF, 1995). Upon each sample 11 parameters including
total hardness, calcium hardness, conductivity, total alkalinity, sulfate,
chloride, pH, temperature, Total Dissolved Solids (TDS), CO2
and Dissolved Oxygen (DO) has been analyzed. Finally three Indexes, Langelier
Index (LI), Ryznar Index (RI) and Pulkorious Index (PI) calculated for
evaluation the rate of water corrosivity.
The formulas for calculation of LI, RI and PI are as
below (Pishnamazi, 2005; Hammer, 1986; Salvato, 2003):
||TDS factor based on mg L?1 of TDS
||Temperature factor based on ?F
||Flow diagram of water supply system
Calcium hardness factor based
on mg L?1 as CaCO3
Alkalinity factor based on mg L?1 as CaCO3
||Total alkalinity mg L?1 as CaCO3
Table 1 shows, the average concentration of TDS, temperature,
calcium hardness and total alkalinity of filtered water were 3329.20 mg
L-1, 70.70 °F, 702.00 mg L-1 and 122.33 mg L-1
as, respectively. In addition average of DO and CO2 were 8.90
and 11.75 mg L-1 as respectively. Also as it is revealed in
this table, for reveres osmosis effluent average concentration of TDS,
DO, CO2, chloride and sulfate were 93.77, 5.02, 4, 33.02 and
11.51 mg L-1, respectively, For conditioned water range of
electrical conductivity was 1817.00 to 8690.00 μmhos cm-1.
Also the average of TDS, DO, CO2 and Cl– concentrations
were 3023.00, 7.80, 0 and 563.23 mg L-1.
Table 2 shows the summary of values for pH and three
indexes to evaluation of water corrosivity in KFSGM. Regarding the table
it is revealed that in raw water LI, RI and PI were +0.36 to +0.93, 6.11
to 6.79 and 6.17 to 6.95 as, respectively. In addition, only LI in treated
water were negative but in other cases were positive.
||Analysis of water quality in KFSGM
||Values of various indexes for water
corrosion control in KFSGM
Analysis of filtered water (raw water) in KFSGM shows
that LI is positive as well as RI and PI were lower than 7 which means
that mentioned water is not corrosive. A positive Langelier index is indicative
primarily of calcium carbonate (scale) deposition; a negative index number
is indicative of increasing water corrosivity with -2.0 considered high.
Slightly positive is the goal. A Ryznar index number of less than about
6.0 is indicative primarily of the start of calcium carbonate (scale)
deposition; an index number greater than 6.0 to 7.0 is indicative of increasing
water corrosivity (Pishnamazi, 2005; Salvato, 2003). Study in Birjand
plain showed that groundwater in these regions were not corrosive and
LI was positive. This is compatible with our study results in KFSGM (Asghari
Moghadam and Zia, 2005). Since CO2 concentration is not considered
in calculation of LI, so presence of CO2 in filtered water
(about 12 mg L-1) can cause corrosion of galvanized piping.
Measured CO2 in filtered water can probably due to low distance
between KFSGM and previous Kashan solid waste sanitary landfill site.
Leachate in sanitary landfill contain high CO2 gases, carbon
dioxide is heavier than air so move down through soil layers and finally
reach to ground water (Salvato, 2003). This problem can results to, internal
pitting and tuberculation of iron and galvanized pipes and steel water
tank walls as in the past in KFSGM (Dietrich, 2004).
Based on analysis of treated water (RO effluent) LI has been negative
in all samples (Table 2), also RI and PI were higher
than 6, that means treated water is corrosive and in long time can do
damages to metal piping and galvanized tanks and facilities. Reverse osmosis
process is high efficient for TDS removal. In this case RO process reduced
TDS from 3329.2 mg L-1 in raw water to 93.7 mg L-1
in treated water, thus removal efficiency calculated 97%. Although TDS
reduction help to corrosion control, but decrease of calcium concentration
(soft water) and alkalinity can be result in corrosiveness properties
in mentioned water. Also decreased pH, presence of DO and CO2
in treated water can increase the rate of corrosion effectively (Pishnamazi,
2005; Oram, 2007; Dietrich, 2004; Chalkeshamiri, 2002; Mc Laughhan and
Calculated Indexes in our study indicate that according to the LI, conditioned
water is not corrosive but based on RI and PI (Table 2)
this water tend to corrosivity. Based on literature review there are contradictory
results related to LI, RI and PI. In some cases LI shows that water is
corrosive but RI and PI do not confirm this trend. In the most cases results
that obtained by PI is true for water samples with pH higher than eight
(Pishnamazi, 2005; Pakshir et al., 2004).
Study in Scolord city, has been showed that optimum iron
protection against corrosion achieved when CaCO3 were in super
saturation condition. Also reduction of CO2 and addition of
calcium silicate as preservative agent to water will usually result in
reduced corrosion to a considerable level (Hem, 2001). So for corrosion
control in KFSGM facilities, it is recommended that addition of preservative
chemicals for water conditioning, to be continued but at the same time
another alternatives such as pH adjustment, air stripping and deoxygenating,
control of carbonate concentration and split flow treatment should be
studied (Edwards, 2004; AWWA, 1990).
1: ADHA, AWWA and WPCF, 1995. Standard methods for the examination of water and wastewater. Washington DC., pp: 135-144.
2: Asghari, M.A. and H. Zia, 2005. Study for hydrochemical properties of the Birjand plain groundwater. http://www.ngdir.com/Symposium /Symposium.asp.
3: AWWA, 1990. Water Quality and Treatment. McGraw-Hill, New York, pp: 1091-1102.
4: Chalkeshamiri, M., 2002. Principal of Water Treatment. ArkAn Publication, Iran, pp: 299-333.
5: Dietrich, A.M., 2004. Health and aesthetic impacts of copper corrosion on drinking water. Water Sci. Technol., 49: 55-62.
Direct Link |
6: Edwards, M., 2004. Controlling corrosion in drinking water distribution systems. Water Sci. Technol., 49: 1-8.
Direct Link |
7: Hammer, M.J., 1986. Water and Waste Water Technology Prentice-Hall, New Jersey, pp: 282-284.
8: Hem, L.J., E.A. Vik and A. Bjoernson-Langen, 2001. Water treatment to reduce internal corrosion in the drinking water distribution system. Water Sci. Technol., 101: 91-96.
Direct Link |
9: Log, T., G. Simpson, H.K. Hanssen, M. Robinson, J. Hubble and S.A. Parsons, 2004. Scale and corrosion control with combined dolomite/calcite filter. Water Sci. Technol., 49: 137-144.
Direct Link |
10: McLaughhan, R.G. and R.M. Stuetz, 2004. A field based study of ferrous metal corrosion in ground water. Water Sci. Technol., 49: 41-47.
Direct Link |
11: Oram, B., 2007. Corrosion, Saturation Index, Balanced Water in Drinking Water Systems. http://www.water-research.net/corrosion.htm.
12: Pakshir, M., A. Moalem, A.A. Nazarboland and S.H. Abbasi, 2004. Limitations of corrosion and scaling indexes in industrial systems. Water Wastewater, 51: 60-66.
13: Pishnamazi, S.A., 2005. Water Corrosion Control in Industry. Arkan Publication, Esfahan, Iran, pp: 242-251.
14: Saatchi, A., 1993. Corrosion Engineering. Esfahan Technical University, Iran, pp: 1-25.
15: Salvato, J.A., 2003. Environmental Engineering. 5th Edn., John Wiley and Sons Inc., New Jersey, ISBN: 0471418137, pp: 310-465.
16: Shahmansori, M. and H. Pormoghadas, 2004. Leaking of microelement due to internal corrosion. J. Res. Med. Sci., 8: 30-34.