investigating effects of soil resistivity on buried

Corresponding author: Omorogiuwa Eseosa Department of Electrical/Electronic Engineering Faculty of Engineering University of Port Harcourt, Nigeria.

Copyright © 2021 Author(s) retain the copyright of this article. This article is published under the terms of the Creative Commons Attribution Liscense 4.0.

Investigating effects of soil resistivity on buried structures in dry and swampy areas

Omorogiuwa Eseosa * and Kubiat Essien

Department of Electrical/Electronic Engineering Faculty of Engineering University of Port Harcourt, Nigeria.

International Journal of Engineering Research Updates, 2021, 01(01), 011–020

Publication history: Received on 18 February 2021; revised on 23 March 2021; accepted on 26 March 2021

Abstract

Soil resistivity generally decrease with increasing moisture as well as chemical concentration, thus making pipelines buried on varying soils of different properties to experience corrosion. This paper aim to investigate the effect of soil resistivity on buried oil pipelines on selected soils around some swampy and dry land area locations dominated by different international oil prospecting companies (IOC), where cathodic protection systems has been installed with functional transformer rectifier and anode ground bed design. Different methods such as wenner array, schlumberger array, and rod driven methods used for determination of soil resistivity were reviewed and implemented on different locations in Bayelsa (Ogbainbiri, Tebidaba) and Rivers (Bonny Island, Rumuji) State respectively. Approximate measurements were taken at different locations to ascertain the type of cathodic protection required for such underground pipeline buried in different soil types. Soil resistance values for Ogbainbiri (Location A) and Tebidaba (Location B) range from 0.46 Ω -0.06 Ω and 0.49 Ω -0.07 Ω for locations A and B respectively and these values are suitable for buried pipelines around these locations to avoid corrosivity as these locations are swampy in nature. The total and average resistivity values for both locations A and B were obtained and recorded to be 233.76 Ω-m and 33.394 Ω-m as well as 254.51 Ω-m and 36.358 Ω-m respectively. Moreso, Various readings were taken from 1m-90m at varying spacings convenient for optimal value of resistivity as determined by the Stumberger method in the dry land location (Rumuji and bonny island) respectively. 1st polarization cathodic potential measurements were carried out for various locations from test point 1, 2,3,4,5 up to test point 6. Various potential values were obtained for the test points and the remarks obtained from these points at varying distances in kilometers were also recorded. Only this value of 29Ω-m is suitable for deep well ground bed at 83m in the location at Rumuji while in bonny island, 8.5Ω-m is suitable for deep well ground bed at 53m depth.

Keywords: Soil resistivity; Dry and swampy areas; Corrosivity

1. Introduction

The resistivity of an electrolytic environment usually soil or water is an expression of its ability to support electrochemical current exchanges associated with corrosion cells. Resistivity provides a reasonable approximation of the corrosiveness of the environment in general. The lower the resistivity, the more corrosive the environment will be. Knowledge of the corrosiveness of the environment can be considered in three ways:

How severe a proposed pipeline or other structure is likely to be affected along planned right-of-way (R.O.W) How severe an existing structure is being affected What steps can be taken to control the effects of exposure to corrosive environment.

In addition, it may be possible to estimate corrosion rates of commonly used metals in specific ranges of resistivity. Such estimates must be made with considerable care because corrosion rates are often influenced by many factors, including variations of resistivity along a structure, chemical constituents of the environment as well as individual corrosion mechanisms at work e.g., pH, oxygen concentration, etc.,). Whether measurements are made using a technique that

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averages the resistivity for a volume of soil (i.e.Wenner four pin methods) or obtain values at individual points, it is often valuable to subject the data to statistical analysis that can project the lowest resistivity likely to be encountered at locations that were not tested. However, resistivity profiles can be extremely useful in determining the need for a type of cathodic protection. This is especially true for bare structures that may require protection only for sections with coating damage where resistivity values are low. Resistivity is also useful in predicting the resistance to earth of an anode ground bed based on the size, spacing, number and configuration of the anodes. This is often critical in the selection of the appropriate galvanic anode alloy or the ratings of impressed current rectifiers. Soil resistivity is a broad indicator of soil corrosivity since corrosivity is associated with electrochemical reaction in soils. It is widely used and generally considered to be the dominant parameter in the absence of micro-biological activity reactions in soils such as high soil resistivity resulting in slow down of corrosion reactions and verse versa. Soil resistivity generally decreases with increasing moisture as well as concentration of chemical species. Based on limited experience to soil conditions, pipelines could be subject to corrosion if the soil resistivity is less than 2000 Ω-cm which is an indication of a wet soil containing chlorides. Sandy soils have a high resistivity of more than 20,000 Ω-cm and therefore considered the least corrosive soil. On the opposite, Clay soils, especially those contaminated with saline water are on the opposite end of the spectrum with resistivity of the order of 1,000 Ω - cm are considered to be highly corrosive. (Gautam, M.2012). Table 1.0 shows ranges of soil resistivity in relation to their corrosivity:

Table 1.0 Ranges of soil resistivity in relation to their Corrosivity

S/N SOIL RESISTIVITY(Ω-CM) SOIL CORROSIVITY

1 Under 1500 Very Corrosive

2 1500 – 3500 Moderately Corrosive

3 Over 3500 Slightly Corrosive

The present tendency in the protection of pipe lines against soil corrosion is away from a uniform coating for the entire length of the line and towards application of coatings selected with respect to the corrosive character of soils involved. This calls for knowledge of varying soil condition and a means of locating local corrosive soil areas. Such areas, commonly termed “hot spot” which are prevalent in many types of soils and it is in these regions that pipe lines suffer the greatest deteriorations. The investigation of such corrosive areas is a matter of considerable importance, both with respect to the selection of coatings for new pipelines and the reconditioning of old ones. The corrosion rate of the buried-structural materials is mainly influenced by six different soil parameters like moisture content, pH, resistivity, oxidation-reduction potential, chloride and sulfate content. Estimation of such soil parameters can give an indication of the soil corrosivity towards the buried-structural materials like mild steel pipes. The main motivator of this paper is based on the fact that, corrosion attacks are frequently responsible for pipelines failures. Protection of buried pipelines against corrosion is a complex process of underground metallic materials which is a very widespread problem. Structures such as crude oil pipelines are some of the structures reported to have been affected by soil corrosion all around the world (Levlin E.B,2008; Ovri N. and Ofeke W. 2008; Rim-ruken and Awatefe, 2006; Chukwu et al., 2008). The major cause of the deterioration of underground pipeline is the soil and it is caused by moisture, pH, redox potential, microbes in the soil (Emujakporue O.G, 2003). Underground pipeline corrosion can be investigated with electrical resistivity and potential methods are used to detect areas of coating damage which eventually becomes anodic point along the buried underground pipeline. The paper aim to investigate the effect of soil resistivity on buried oil pipelines on selected soils around some swamp and land area locations dominated by different international oil prospecting companies (IOC), where cathodic protection systems has been installed with functional Transformer rectifier and anode ground bed design.

2. Literatures review

Soil resistivity measurements are made by injecting current into the earth between two outer current probes and measuring the resulting voltage between two inner potential probes placed along the same straight line. When the adjacent current and potential probes are close together, the measured soil resistivity is indicative of the surface soil characteristics; however, more measurements would be required. When the probes are far apart, the measured soil resistivity is indicative of average deep soil characteristics throughout a much larger area. In principle, soil resistivity measurements are made using spacing (between adjacent current and potential probes) that are, at least, on the same order of magnitude as the maximum size of the grounding system (or systems) under study. It is, however, preferable to extend the measurement to traverses to several times the maximum grounding system dimension, where possible.


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This allows for fine tuning of the soil model if there is more than one soil layer present. Often, it will be found that the maximum probe spacing is governed by other considerations such as the maximum area of the available land which is clear of interfering bare buried pipeline. Soil resistivity measurements are used to obtain a set of measurements that may be used to yield an equivalent soil model for the electrical performance of the earth. The results, however, may be unrealistic if adequate background investigation is not made prior to the measurement. The background investigation includes data related to the presence of nearby metallic structures, as well as the geological, geographical, and meteorological information of the area. For instance, geological data regarding strata types (soil layer) and thicknesses would give an indication of the water retention properties of the upper layers and therefore their expected variation in resistivity between the layers; then make a comparison of recent rainfall data against the seasonal average. Such background investigation is usually included as a part of the soil measurement procedure and is used in the determination of the soil model. Factors such as maximum probe depth, lengths of cables required, efficiency of the measuring technique, cost (determined by time and the size of the survey crew), and ease of interpretation of the data must be considered when selecting the test type. Three common test types are

Wenner 4-Probe Method Schlumberger Array. Driven Rod (3-Probe)

In homogenous isotropic earth, the resistivity is constant; however, if the earth is non-homogenous and the electrode spacing is varied, a different value of resistivity will be found for each surface measurement. This measured value of soil resistivity is referred to as the apparent resistivity, ρa as measurement is used in the calculation of the soil model and it is not the actual value of resistivity. This reinforces the requirement for an accurate soil model and the three common test types, measurement techniques and test methods equations are presented.

2.1. Wenner Array

In the Wenner method (See Figure 2.1a and b), all four probes are moved for each test, with the spacing between each adjacent pair remaining the same. In this method, it is possible to measure the average resistivity of the soil between the two center probes to a depth equal to the probe spacing between adjacent probes. If the probe spacing is increased, then the average soil resistivity is measured to a greater depth. If the average resistivity increases as the probe spacing increases, there is a region of soil having resistivity at the greater depth Figure 2.1a while figure 2.1b determines apparent resistivity based on the surface measurements.

Figure 2.1 a and b Wenner four-probe method

Considering equation 2.1

ρa = 2πaR 2.1

Where: ρa is apparent resistivity (Ω.m), a is probe spacing (m), R is measured resistance (Ω). If the ratio between the probe penetration b is similar to the spacing of the four probes, then figure 2.1b must be used as the apparent resistivity


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and will be matched closer to the probe depth. It is suggested that when there is more than one layer of soil this equation allows for greater accuracy in the determination of soil depths.

2.2. Schlumberger Array

The Schlumberger array (Figure 2.2) requires that the outer probes be moved four or five times for each position of the inner probes. The reduction in the number of probe moves also reduces the effect of lateral variation in the test results. Considerable time savings can be achieved by using this method, since there will be fewer probe placements than those required by the Wenner method, with similar results. The minimum spacing accessible is in the order of 10m (for a 0.5 m inner spacing), thereby necessitating the use of the Wenner configuration for smaller spacing. Lower voltage readings are obtained when using the Schlumberger arrays. This may be a critical problem where the depth required to be tested is beyond the capability of the test equipment or the voltage readings are too small to be useful.

Figure 2.2 Schematics diagram Schlumberger array

The Schlumberger array is more complex, with the spacing between the current probes not equal to the spacing between the potential probes. However, because of the complexity and high cost of Schlumberger method of measuring resistivity, our test was limited to the four pin Wenner method but some readings/data based on Schlumberger method were used for the study.

2.3. Driven Rod Method

The driven rod method (Figure 2.3) is generally employed where transmission line structures are located. This method is preferred because the measurements can be obtained without varying the spacing as required by the previous methods using equation 2.3.

Figure 2.3 Determine the apparent resistivity based on the surface measurements.

p_a=(2〖πb〗_2 R)/(ln (2b_2)/d) 2.2

Where: ρa is the apparent resistivity (Ω.m),b2 is the length of the driven rod in contact with the earth (m),d is the spacing between the current probes (m),R is the measured resistance (Ω)


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2.4. Review of Buried Pipeline/Corrosion Failure

Corrosion is the gradual chemical attack and degradation that results in the conversion of metallic materials into oxides, salts or other compounds. Materials such as metals and its alloys (e.g. steel) that have undergone corrosion lose their strength, ductility and other mechanical properties. Corrosion attacks are frequently responsible for most materials failures. A metallic material is a very widespread problem. Structures such as natural gas and crude oil and water pipes are some of the structures reported to have been affected by soil corrosion all around the world (Levlin E.B, 2008; Ovri N. and Ofeke W, 2008; Rim-ruken and Awatefe, 2006; Chukwu et al., 2008). The failure of gas, crude oil pipeline or water pipe failure is usually accompanied by high degree of environmental, human and economic consequences (Okoroafor C., 2004). The major cause of deterioration of underground pipeline is the soil. Soil corrosion is caused by moisture, pH, redox potential, microbes in soils and soil type. Underground pipe corrosion can be investigated with electrical geophysical methods such as electrical resistivity and potential methods (Bhattarai, J. 2013). These methods are used to detect areas of high corrosion (hot spots) along the buried underground pipeline. The Corrosivity of soils is nearly inversely proportional to their resistivity; that is low resistivity, means a high probability of corrosion (Andrew W. et al, 2005). Resistivity and spontaneous potential are two electrical properties of sedimentary rocks commonly measured. Taken individually, each set of data is inconclusive, but taken together these two measurements provide a good indication of some important lithologic distinctions in the subsurface (Emujakporue O G, 2003). This study was therefore undertaken to demonstrate the effectiveness of the proposed geophysical tools in the delineation of possible areas of underground oil pipeline corrosion that may result in unpleasant human, environmental and economic consequences.

2.5. Electrical Geophysical Methods for Underground Pipeline Corrosion Survey

Electrical properties of the subsurface can be explored by several geophysical methods. The two electrical methods commonly used are the Spontaneous Potential (SP) and the electrical resistivity techniques. The electrical resistivity method is commonly used for the delineation of horizontal and vertical discontinuities in the electrical properties of the subsurface and also for the detection of three – dimensional bodies of anomalous electrical conductivity. In the electrical resistivity method, artificially generated currents are introduced into the ground, and in the presence of variations in the conductivity of subsurface layers, the current flow path is altered as investigated on Corrosion of Buried Oil ( Ekine, A. S.,2008). The electric potential distribution and the resulting potential differences are measured at the surface. The Self potential method makes use of natural currents flowing in the ground that are generated by electrochemical and electro kinetic processes, to locate shallow bodies of anomalous conductivity. The Corrosivity of soils is inversely related to the soil resistivity with low resistivity indicating high probability of corrosion. Certain natural or spontaneous potentials occurring in the subsurface are caused by electrochemical or mechanical activity. The controlling factor in all cases is underground fluids. These potentials are associated with variation in rock properties (mineral contents) at geological contacts, bioelectric activity of Wenner array electrodes configuration was employed for the data acquisition using the R-plus resistivity meter. This equipment has the ability to display apparent resistivity and self-potential values directly on the screen. It also has the advantage of portability and ability to compensate for polarization at the electrodes. The horizontal profiling techniques of the electrical resistivity methods of geophysics was used for determining lateral variations of resistivity using an electrodes spacing of 30.0 feet (about 10 meters), along the path of an oil pipeline, which was buried at a depth of about 10.0 feet (about 3.0 meters). The resistivity and spontaneous potential values, simultaneously displayed on the screen, were recorded. The data obtained from the field were plotted against the electrode spacing on log-linear scales for the resistivity and self-potential respectively.

3. Test

The test consists of 4 pins that must be inserted into the earth. The outer two pins which are the Current probes, C1 and C2 were used to inject current into the earth. The inner two probes are the Potential probes, P1 and P2 which were also used to measure the actual soil resistance of the locations. Probe C1 is driven into the earth at the corner of the area to be measured. Probes P1, P2, & C2 are driven at 5m, 10m and 15m respectively from rod C1 in a straight line to measure the soil resistivity from 0m to 5m in depth. C1 and C2 are the outer probes and P1 & P2 are the inner probes. At this point, a known current is applied across probes C1 & C2, while the resulting voltage is measured across P1 and P2. Ohm’s law was applied to calculate the measured apparent resistance. Probes C2, P1 and P2 was then moved out to 10m, 20m & 30m spacing to measure the resistance of the earth from 0m to 10m in depth. Continue moving the three probes (C2, P1 & P2) away from C1 at equal intervals to approximately the depth of the soil to be measured. Note that the performance of the electrode can be influenced by soil resistivities at depths that are considerably deeper than the depth of the electrodes, particularly for extensive horizontal electrodes, such as water pipes, building foundations or grounding grids.


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4. Results and discussion

4.1. 1st Soil Resistivity test carried out in Ogbainbiri situated in Bayelsa

Table 4.1 shows the results obtained from the test carried out in Ogbainbiri and Tebidaba situated in Bayelsa state of Nigeria which is swampy in nature.

Table 4.1 Ogbainbiri Survey installation of 1st soil resistivity of one deep well ground bed (Bayelsa state)

ρ =2πaR; where ρ=Resistivity, a=Spacing, R= Resistances

Spacing, a(m) R(Ω) location A R(Ω) location B ρ(Ω-m) location A ρ(Ω-m) location B

10 0.46 0.49 28.9 30.8

20 0.22 0.23 27.65 28.906

30 0.19 0.21 35.819 39.589

40 0.16 0.17 40.218 42.731

50 0.13 0.14 40.846 43.988

60 0.09 0.10 33.934 37.704

70 0.06 0.07 26.393 30.792

TOTAL 233.76 254.51

AVERAGE 33.394 36.358

Table 4.1 describes the spacing of 10m interval and starting from 10m to 70m while taking the values of resistances and resistivities at every point. From table 4.1,it is found that as the spacing increases from the various locations, the resistances reduces from 0.49 Ω -0.06 Ω and 0.49 Ω -0.07 Ω for locations A and B respectively.it will be recalled that both locations are in swampy areas in Bayelsa state. The total and average resistivity values for both locations were obtained and recorded to be 33.76 Ω-m and 33.394 Ω-m as well as 254.51 Ω-m and 36.358 Ω-m for locations A and B respectively. The average soil resistivity value of 35.819Ω-m and a depth of 30m and 26.393Ω-m at a depth of 70m.These are all suitable for the ground bed design to be installed in location ‘A’. At both Ogbainbiri and Tebidaba where these soil data were obtained and are located in swampy area with non-homogeneous wet soil hence both the wenner 4 pin and schlumberger soil resistivity instruments have the capability to give measurements irrespective of the chemical constituents of the environment and individual corrosion mechanism at work e.g. chloride, pH, Oxygen concentration etc.

From table 4.1, positive length of cable from the proposed ground bed to transformer rectifier (TRR) location at Ogbainbiri is about 70m with the following measured values are shown in table 4.2.

Table 4.2 Transformer rectifier readings.

TRR Rating in volts 50Volts Output current in A 3.9A

TRR Rating in Amps 50Amps oil Temp 28 degrees Celsius

Output voltage 2.10V oil Temp level ok OK

The transformer rectifier rated readings are 50V, 50amps with output voltage and current as 2.10V and 3.9A respectively. The oil temperature is recorded as 28oC and this is certified okay.

After the installation of the cathodic protection system (CPS), pipe to soil potential measurement (PSP) were taking along the 45km, 14 inches pipeline from Ogbainbiri to Tebidaba which the design covers and the following readings were obtained and recorded as shown in table 4.3


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Table 4.3 1st Polarized Cathodic Protection Potential Measurements.

S/N LOCATION KM POTENTIAL (-mV) REMARKS

1 Test point-1 Ogbainbiri 0.00 1200 IJ/Surge diverter is ok

2 Test point 2 15.5 1100 Insulation joint is ok

3 Test point 3 16.00 1050 Access was difficult due to water hyacinth



6 TP6 Tebidaba 45.00 990 Insulation joint is ok

The test instrument used was the cu/cuso4 reference electrode or half-cell and multi meter, 1.5mm2 cable. The readings show that the entire pipeline is protected.1st polarization cathodic potential measurements were carried out for various locations from test point 1, 2,3,4,5 up to test point 6.various potential values were obtained for the test points and the remarks obtained from these points at varying distances in kilometers were also recorded.

4.2. 2nd Soil Resistivity Measurement Taken At Obama Clough creek (Bayelsa State) Using Schlumberger Method.

Another section in Bayelsa was also investigated. Pasi earth soil resistivity meter (16GL) was used in this study to record resistivity as the logging progresses. The 16GL earth resistivity meter can carry out and memorize acquisitions with a resolution of 16 bits. The data is treated internally in floating-point format. The acquisitions can be displayed, printed, and transferred on a PC for further processing. The instrument is based on a multiprocessor system that can autonomously generate the energy wave by means of the input of a current by two electrodes MN. The voltage and current acquisitions is done simultaneously with two readings (subsequently mediated), following the user’s data input. At the end of each cycle, the spontaneous potential is dynamically deducted as recommended Active zone is between 39m-80m and the depth is 80m and it is interpreted using geo electric layers. The results obtained is shown in table 4.4.Various readings were taken from 1m-90m at varying spacings convenient for optimal value of resistivity as determined by the Stumberger method.

Table 4.4 2nd Soil Resistivity Measurement Taken At Obama Clough creek (Bayelsa State) Using Schlumberger Method.

AB/2 MN/2 K R P Ωm AB/2 MN/2 K R P Ωm

1 0.3 4.765367 10.45 49.80285 20 3 204.7537 1.69 346.0337

1.5 0.3 11.3112 3.3 37.32696 25 3 322.5787 1.72 554.8353

2 0.3 20.47537 0.9 18.42783 30 3 466.587 1.16 541.2409

3 0.3 46.6587 0.46 21.463 40 3 833.1537 0.43 358.2561

5 0.3 130.4454 0.11 14.34899 45 3 1055.712 0.03 31.67136

7 0.3 256.1254 0.21 53.78633 50 3 1304.454 0.02 26.08907

7 1 75.408 0.53 39.96624 60 3 1880.487 0.09 169.2438

10 1 155.529 0.61 94.87269 80 3 3346.754 0.01 33.46754

15 1 351.904 0.19 66.86176 90 3 4236.987 0.008 33.8959

15 3 113.112 0.42 47.50704

4.3. 3rd Soil Resistivity Measurement At Rumuji/Bonny In Rivers State

Rumuji is in the Dry Land location while Bonny is swampy and the schlumberger method was used to obtain resistivity directly and the results obtained is shown in table 4.5.from the table it was discovered that only this location (29Ωm) is suitable for deep well ground bed at 83m for Rumuji location. It was also noticed from the investigation that for bonny island only this location (8.5Ωm) is suitable for deep well ground bed at 53m depth


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Table 4.5 3rd Soil Resistivity Measurement At Rumuji/Bonny In Rivers State.

Soil Resistivity Taken At Rumuji

No Depth/M App. Resistivity Ωm Comment

R1 4.5 665

10 1213

20 1129

45 254

R2 57 290

R3 60 270

R4 83 29

Only this location (29Ωm) is suitable for deep well ground bed at 83m

4th Soil Resistivity Taken At Bonny Island

No Depth/M App. Resistivity Ωm Comment

B1 4.5 771

10 715

20 689

45 572

B2 53 8.5

Only this location (8.5Ωm) is suitable for deep well ground bed at 53m depth

B3 68 13.3

5. Conclusion and recommendation

Soil resistivity measurement provides a guide in the choice of adequate coating material due to the following:

High electrical resistivity coating reduces the current requirement because the greater the amount of current drained by the coating the better quality coating can permit and the higher lengths of protected pipe. Note that overprotection can damage the coating. Cathodic protection with sacrificial anodes advantages such as sacrificial or galvanic anode is independent of electrical power source; it cannot be incorrectly attached to the structure, no control to current output during the exercise, easy to obtain uniform polarization. Though some disadvantages include high labour cost for installation, large anode burden, high cost of installing to improve a deficient installation.

In Nigeria, different kinds of soil such as sand, loam, clay exist with varying soil resistivity and corrosivity due to their electrolytic nature. Moreso, resistivity and corrosivity with respect to the soil are inversely proportional. From the investigation it was shown that soil resistivity generally decrease with increasing moisture as well as chemical concentration, thus making pipelines buried on varying soils of different properties to experience corrosion. This work successfully investigated effects of soil resistivity on buried oil pipelines on selected soils around some swampy and dry land area locations dominated by different international oil prospecting companies (IOC), where cathodic protection systems has been installed with functional transformer rectifier and anode ground bed design. Different methods such as wenner array, schlumberger array, and rod driven methods used for determination of soil resistivity were reviewed and implemented on different locations in Bayelsa (Ogbainbiri, Tebidaba) and Rivers (Bonny Island, Rumuji) State respectively. Approximate measurements were taken at different locations to ascertain the type of cathodic protection required for such underground pipeline buried in different soil types .This will enable the determination of earth resistance to the anode ground bed based on the size, spacing, number as well as its configuration. Soil resistance values for Ogbainbiri (Location A) and Tebidaba (Location B) range from 0.46 Ω -0.06 Ω and 0.49 Ω -0.07 Ω for locations A and


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B respectively. It will be recalled that both locations are in swampy areas in Bayelsa state. The total and average resistivity values for both locations A and B were obtained and recorded to be 233.76 Ω-m and 33.394 Ω-m as well as 254.51 Ω-m and 36.358 Ω-m respectively. The average soil resistivity value of 35.819Ω-m and a depth of 30m and 26.393Ω-m at a depth of 70m.These are all suitable for the ground bed design to be installed in location ‘A’. At both Ogbainbiri and Tebidaba where these soil data were obtained and are located in swampy area with non-homogeneous wet soil hence both the wenner 4 pin and schlumberger soil resistivity instruments have the capability to give measurements irrespective of the chemical constituents of the environment and individual corrosion mechanism at work e.g. chloride, pH, Oxygen concentration etc. Moreso, various readings were taken from 1m-90m at varying spacings convenient for optimal value of resistivity as determined by the Stumberger method. The readings showed that the entire pipeline is protected.1st polarization cathodic potential measurements were carried out for various locations from test point 1, 2,3,4,5 up to test point 6 for various locations .various potential values were obtained for the test points and the remarks obtained from these points at varying distances in kilometers were also recorded. Only this location (29Ωm) is suitable for deep well ground bed at 83m in the location at Rumuji while in bonny island Only this location (8.5Ωm) is suitable for deep well ground bed at 53m depth. This has shown that for economy and overall efficiency, the depth for these areas foe proper resistivity has been determined.

6. APPENDIX

GALVANIC ENERGY SERIES Energy level in Volts VS Cu-CuSo4

S/N METALS ELECTRODE (POTENTIAL)V

1 Magnesium -1.7

2 Aluminum -1.1

3 Zinc -1.1

4 Steel 0.6

5 Steel in concrete with cl- -0.5

6 Steel in concrete without cl- -0.1

7 Copper -0.1

8 Carbon +0.4

9 Silver +0.5

10 Platinum +0.9

11 Gold +1.2

Compliance with ethical standards

Acknowledgments

The authors would like to acknowledge the management and staff of eseogietec engineering company limited whose head office is in port Harcourt, Rivers State in Nigeria (www.eseogietec.com) for all their support academically, materially and financially towards the completion of this task. Their facilities were indeed very useful for this task and the researchers would like to recommend them to other fellow researchers.

Disclosure of conflict of interest

None.


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[3] Emujakporue OG. The correlation of Spontaneous Potential and Apparent Resistivity data from surface vertical electrical sounding in parts of Rivers state.

[4] Gautam M. Investigation on Different Soil Parameters of Tanglaphant-Tribhuvan University Campus-Balkhu Areas of Kirtipur for Their Corrosive Nature. 2012; 62.

[5] Levlin EB. Corrosion of oil pipe systems due to acidification of soil and groundwater. Department of Applied Electro-chemistry and Corrosion Science, Royal Institute of Technology, Stockholm. 2008.

[6] Ovri N, Ofeke W. The Soil resistivity behaviour on mild steel in marine environment. J. Sci. Eng. Tech. 2008; 1117 – 1129.

[7] Okoroafor C. Cathodic protection as means of saving national asset. J. Corr. Sci. Tech., 1.1 (Special Edition). 2004; 1 – 6.

[8] Osella A. Corrosion effects on buried pipelines due to geomagnetic storms. J. Appl. Geophysics. 2009; 38: 219–233.

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[10] Shamsuri SRB. The Effect of Soil Resistivity on Corrosion Behavior of Coated and Uncoated Low Carbon Steel. ME Thesis, Faculty of Mechanical Engineering, University Technology Malaysia. 2010.

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