Design of crude oil tank cathodic protection in onshore for 20 years service life PDF

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Design of crude oil tank cathodic protection in onshore for 20 years service life Cite as: AIP Conference Proceedings 2338, 040011 (2021); https://doi.org/10.1063/5.0068079 Published Online: 11 November 2021 Dian Sumantri and Priyo Tri Iswanto AIP Conference Proceedings 2338, 040011 (2021); https://...

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Design of crude oil tank cathodic protection in onshore for 20 years service life Priyo Tri Iswanto PROCEEDINGS OF THE 13TH AUN/SEED-NET REGIONAL CONFERENCE ON MATERIALS (RCM 2020) AND THE 1ST INTERNATIONAL CONFERENCE ON MATERIALS ENGINEERING AND MANUFACTURING (ICMEM 2020)

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CAT HODIC PROT ECT ION DESIGN USING IMPRESSED CURRENT MET HOD Noor Muhammad Bint ang

DESIGN OF IMPRESSED CURRENT CAT HODIC PROT ECT ION FOR Salam Ahdash Fawaz S Al-Fawaz No(7739) Fawaz Alfawaz

Design of crude oil tank cathodic protection in onshore for 20 years service life Cite as: AIP Conference Proceedings 2338, 040011 (2021); https://doi.org/10.1063/5.0068079 Published Online: 11 November 2021 Dian Sumantri and Priyo Tri Iswanto

AIP Conference Proceedings 2338, 040011 (2021); https://doi.org/10.1063/5.0068079 © 2021 Author(s).

2338, 040011

Design of Crude Oil Tank Cathodic Protection in Onshore for 20 Years Service Life Dian Sumantri and Priyo Tri Iswantoa) Department of Mechanical and Industrial Engineering, Faculty of Engineering, Universitas Gadjah Mada, Jl. Grafika No. 2, Yogyakarta 55281, Indonesia a)

Corresponding author: [email protected]

Abstract. Corrosion can cause a gradual and continuous decrease in performance of a structural material used in the oil and gas production process. This decrease in performance can cause some problems, such as personnel safety, plant shutdowns, to a sudden decrease in production levels and structural failure. The potential for corrosion attacks in the oil and gas industry occurs at the production, extraction, refining and storage stages. Billion dollars are spent annually to solve the problem of corrosion in the oil and gas industry. Cathodic protection can be done in two ways, namely by using sacrificial anode cathodic protection (SACP) and impressed current cathodic protection (ICCP). Cathodic protection is considered to be the most effective method of external protection of metal structures with applications of up to 75 percent. This study aims to make a cathodic protection design with ICCP for crude oil tank for improving corrosion resistance in an onshore environment. The results of the ICCP crude oil tank design require 4 tubular MMO titanium anodes with a transformer capacity of 19 kVA and 150 Volt DC voltage. Potential value of tank C before ICCP installation is above -805 mV at all measurement points. This indicates that the tank C is not well corrosion-protected. Potential value of tank C after ICCP installation is far drop below -805 mV at all measurement points. This indicates that the tank C is well protected.

INTRODUCTION Corrosion can cause a gradual and continuous decrease in performance of a structural material used in the oil and gas production process. This decrease in performance can cause very critical problems, such as personnel safety, plant shutdowns, to a sudden decrease in production levels and structural failure. One of the causes of structural failure is corrosion attack [1][2][3]. Failure in the pipeline system due to corrosion attack can result in risks that have an impact on humans, environmental damage and economic losses [4]. The potential for corrosion attacks in the oil and gas industry occurs at the production, extraction, refining and storage stages [5]. Based on data from NACE, a worldwide association of corrosion experts, it is stated that 3.7 billion dollars are spent annually to solve the problem of corrosion in the oil and gas industry [6]. Based on data from the American Society of Materials (ASM), almost 80% of the damage or failure in the oil and gas industry due to corrosion attacks. The value of losses due to corrosion attacks almost reaches 1-5% of national domestic income (GDP). The performance of a cathodic protection system is closely related to the reading "Structure to Electrolyte Potential" using a high impedance voltmeter based on the international standard DNVGL-RP-B401 [7][8][9][10]. A potential value of -805 mV or below relative to the Ag / AgCl reference electrode in the seawater environment is generally accepted as the protective potential value Ecº (V) for carbon steels and low alloy steels [7][8][9][10]. The reading criteria are based on the ISO-15589-2-2004 standard [9]. Meanwhile, for soil containing sulfatereducing bacteria (SRB), the minimum potential that must be given is -900 mV. The reason is, the bisulfide and sulfide ions generated by the activity of the SRB bacteria will modify the Pourbaix diagram to a minimum of 100 mV more negative [11]. In general a structure is said to be well corrosion protected, if potential range of steel structures is -805 mV to -1000 mV with the Ag/AgCl reference electrode [9][10][11][12].

Proceedings of the 13th AUN/SEED-NET Regional Conference on Materials (RCM 2020) and the 1st International Conference on Materials Engineering and Manufacturing (ICMEM 2020) AIP Conf. Proc. 2338, 040011-1–040011-7; https://doi.org/10.1063/5.0068079 Published by AIP Publishing. 978-0-7354-4144-6/$30.00

040011-1

Potential-pH diagram or so-called Pourbaix diagram maps the stable phases of metals and their compounds in a water solvent that is in thermodynamic equilibrium, as a function of the electrode potential and the pH of the solution [13]. The main use of the Pourbaix diagram is to estimate the direction of spontaneous reactions, the composition of corrosion products, and environmental changes that can prevent or reduce the rate of corrosion attack [14]. Cathodic protection can be done in two ways, namely by using Sacrificial Anode Cathodic Protection (SACP) and Impressed Current Cathodic Protection (ICCP) [15]. Cathodic protection is considered to be the most effective method of external protection of metal structures with applications of up to 75 percent [6]. The success of cathodic protection design is influenced by many factors including selection of anode, environmental state, current requirements for protection, protection zone identification, etc. Many studies have been carried out in the design of cathodic protection for structures in both sea and land environments [16][17][18][19][20][21]. The highest level of corrosion occurs in the steels that is in contact with land or electrolytes. Therefore, the ICCP design of the crude oil tank focuses on the bottom of the tank that continuously contact with soil as electrolytes. This research aims to make a cathodic protection plan using ICCP method for crude oil tank structures in onshore.

RESEARCH METHODOLOGY In this study, some data were obtained both from field data, and literature. These data are used by the ICCP design stage for onshore crude oil tanks and then design validation stage to prove that the design is correct and meets the corrosion protection criteria for crude oil tank structures.

Design ICCP for Crude Oil Tank C in Onshore Components of the crude oil tank structure that will be cathodically protected are those that are always in contact with the ground (electrolytes), including the bottom tank, grounding rod and copper ring. The dimension of Tank C section area is 3021.16 𝑚𝑚2 . The soil resistivity value that functions as an electrolyte is 10000 Ωcm. This value is categorized as slightly corrosive [17]. The ambient temperature in the crude oil tank area is determined to be 30 ℃ (70 ℉). The calculation of protection current requirements is obtained from the equation: 𝑖𝑖

𝐼𝐼𝐶𝐶 = 𝐴𝐴𝐶𝐶 . 𝐶𝐶 . 𝑓𝑓𝑐𝑐 . (1 + 𝑆𝑆𝑆𝑆) (1) 1000 The value of protection current requirements is influenced by the area of the structure to be cathodic protection (𝐴𝐴𝑐𝑐 ), paint damage factor (𝑓𝑓𝑐𝑐 ) and current density (𝑖𝑖𝑐𝑐 ). The value of (𝑓𝑓𝑐𝑐 ) is 100% because the structure is not painted and a safety factor of 25% is added as a safety factor if there is a change in operating parameters during the service life of the ICCP, which is 20 years. The anode chosen for this ICCP design is tubular MMO (mixed metal oxyde) titanium type with specifications as shown in Table 1. below. TABLE 1. ICCP Anode Specification (manufacture data)

Anode

Specification Tubular MMO Titanium 0.032 m 1.25 m 0.125 m2 99760 A/m2 12438 A Steel Pipe

Type Diameter Length Surface area Current density Output current Canister

The calculation of anode requirement is obtained from the equation: 𝑄𝑄𝐴𝐴 =

𝐼𝐼𝐶𝐶

𝐼𝐼𝐴𝐴

(2)

The number of anodes needed is the result of dividing the required structure protection current (𝐼𝐼𝑐𝑐 ) with the output current of the anode used (𝐼𝐼𝐴𝐴 ). Followed by the calculation of the need for a rectifier transformer for the needs of

040011-2

electric current supply in this ICCP system. The total DC circuit resistance value is obtained from the sum of the anode resistance to ground and the cable resistance of the system. The equation used is: 𝑅𝑅𝑔𝑔𝑔𝑔 =

1

𝑅𝑅𝑝𝑝

𝑆𝑆 = 1 + =

1

𝑅𝑅𝑔𝑔𝑔𝑔

+

𝜌𝜌

𝑅𝑅𝑎𝑎

𝜋𝜋.𝑆𝑆.𝑅𝑅𝑎𝑎

𝐹𝐹

𝑅𝑅𝑐𝑐𝑎𝑎𝑔𝑔𝑐𝑐𝑒𝑒 2

(3)

. ln 0.656 𝑁𝑁

𝑅𝑅𝑐𝑐𝑐𝑐𝑔𝑔𝑐𝑐𝑐𝑐 = 1

. 𝑁𝑁

+

𝐿𝐿𝑐𝑐 .𝑅𝑅𝑒𝑒 𝑁𝑁 1

𝑅𝑅𝑐𝑐𝑎𝑎𝑔𝑔𝑐𝑐𝑒𝑒 33

+

(4) (5) 1

𝑅𝑅𝑐𝑐𝑎𝑎𝑔𝑔𝑐𝑐𝑒𝑒 4

(6)

𝑅𝑅𝑛𝑛 = 𝑅𝑅𝑐𝑐𝑐𝑐𝑔𝑔𝑐𝑐𝑐𝑐 5 + 𝑅𝑅𝑐𝑐𝑐𝑐𝑔𝑔𝑐𝑐𝑐𝑐 6 (7) (8) 𝑅𝑅𝑡𝑡 = 𝑅𝑅𝑝𝑝 + 𝑅𝑅𝑛𝑛 Where 𝑅𝑅𝑔𝑔𝑔𝑔 = anode-ground resistance, 𝑅𝑅𝑝𝑝 = positive DC circuit resistance, 𝑅𝑅𝑛𝑛 = negative DC circuit resistance, 𝑅𝑅𝑇𝑇 = total DC circuit resistance, 𝑅𝑅𝑐𝑐 = one anode resistance, 𝑆𝑆= interference factor, N= number of anodes, 𝑆𝑆= multiple interference factor anode, 𝜌𝜌= soil resistivity (Ωcm), 𝑆𝑆= distance between anodes (m). The required rectifier transformer voltage is obtained from the equation: 𝐸𝐸𝑡𝑡 = 𝐼𝐼𝑇𝑇 . 𝑅𝑅𝑡𝑡 . (1 + 𝑆𝑆𝑆𝑆) + 𝐵𝐵𝐸𝐸𝐸𝐸𝐹𝐹 𝐸𝐸 .𝐼𝐼 𝐼𝐼𝐴𝐴𝐶𝐶 = 𝐷𝐷𝐶𝐶 𝐷𝐷𝐶𝐶 𝐸𝐸𝐴𝐴𝐶𝐶 .𝐸𝐸𝐸𝐸𝐸𝐸.√3

𝑃𝑃𝐴𝐴𝐶𝐶 = 𝐼𝐼𝐴𝐴𝐶𝐶 . 𝐸𝐸𝐴𝐴𝐶𝐶 . √3

(9) (10) (11)

Where 𝐸𝐸𝑡𝑡 = DC output voltage requirement (V), 𝐼𝐼𝑇𝑇 = current requirement (A), 𝑅𝑅𝑡𝑡 = DC total resistance (Ω), SF = safety factor (25%), 𝐵𝐵𝐸𝐸𝐸𝐸𝐹𝐹 = back electromotive voltage (2 volts), 𝐼𝐼𝐴𝐴𝐶𝐶 = current AC input (A), 𝑃𝑃𝐴𝐴𝐶𝐶 = TR capacity / rectifier transformer (kVA), 𝐸𝐸𝐴𝐴𝐶𝐶 = AC input voltage (volts), 𝐼𝐼𝐷𝐷𝐶𝐶 = DC input current (A), 𝐸𝐸= DC input voltage (volts), Eff = transformer efficiency (80 %).

FIGURE 1. Installation scheme of ICCP crude oil tank C

040011-3

Installation Design of ICCP After the ICCP design was completed, the ICCP installation work was continued in the field. The anode will be installed using a ground bed with a diameter of 6 in and a tube length of 2 meters. The ground bed anode is installed at a depth of one meter. This design is to ensure polarization of cathodic protection for both structures evenly distributed. The scheme of installation and installation location for anodes, rectifier transformers, junction boxes and other accessories can be seen in Figure 1 below.

RESULT AND DISCUSSION Design Result of ICCP for Crude Oil Tank in Onshore Measurement of the potential value of the oil tank using the Ag/AgCl reference electrode. The required corrosion protection criterion is less than -805 mV against Ag/AgCl [14]. The protection values are in accordance with recommended values from some literature and international standards commonly used as references for cathodic protection design [7] [19]. Measurements were made around the tank with a distance of 45 degrees to each measuring point. The measurement results of potential value of crude oil tank C can be seen in Figure 2 below. From the graph of the measurement results below, it can be seen that the potential value of tank C is above -805 mV at all measurement points. This indicates that the current C tanks are not well corrosion protected.

1000 805 805

805

415 412

401

805

805

805

805

438

431

805

Potential (-mV)

800 600

457 382

400

270

Tank C before Standart [8]

200 0 0

45

90

135

180

225

270

315

Circumference position (deg) FIGURE 2. Potential Measurement of Crude Oil Tank C before ICCP Installation

The areas to be protected by ICCP include the bottom of the tank in contact with the ground (tank bottoms), grounding rods and copper rings. The results of the calculation of the area and protection current requirements required for this ICCP system can be seen in Table 2. TABLE 2. Surface Area and Protection Current Requirement ICCP

Structure Steel Tank Bottom Grounding Rod Copper Ring

Length (m)

Diameter (m)

Surface area (m2)

Current requirement (A)

0.3

61.38

3014.34

30.14

3

0.02

0.18

0.0018

211.67

0.01

6.64

2.66 32.80 A

Tank (C)

We know from the calculation results, the total protection current requirement for the tank is 32.8 A. This protection current is added with a safety factor of 25% to anticipate changes in operating and environmental parameters during the 20-year service period, so that the total protection current required by this ICCP system is 41 A. This design refer to international standard code [22].

040011-4

The need for the number of anodes for the ICCP system is obtained from the calculation of Equation (2), which is four anodes. The anode will be installed using a groundbed with a diameter of 6 in and a tube length of 2 meters. The groundbed anode is installed at a depth of one meter. This design is to ensure polarization cathodic protection for both structures evenly distributed. The DC circuit total resistance value is the sum of the DC positive resistance and the DC negative resistance. The calculation result of DC positive resistance and DC negative resistance can be seen in Table 3 and Table 4. TABLE 3. DC Circuit Positive Resistance

Tank OD and Electrical Grounding System T-1306C

Cable

Anode + Ground bed

Anode Tail

3.173

0.002

Cable Anode Header to PJB 0.069

Positive Cable to TR 0.046

1/R Total DC Circuit Positive Resistance

Total 3.290 6.603 1.651

TABLE 4. DC Circuit Negative Resistance

Tank and Size Insulation Electrical Type Grounding System mm2 Structure Cable HMWPE 50 Resistance to NJB Cable Resistance HMWPE 50 NJB to trafo Total DC Negative Circuit Resistance

Rating at 30 C Amp

Re

N

R

Ohm/m

pcs

ohm

185

0.000387

1

0.00774

240

0.000387

1

0.046 0.0534

The total resistance of the DC circuit is 1.704 Ohms. The need for a rectifier transformer is: 𝐸𝐸𝑡𝑡 = 140 𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉 𝐷𝐷𝐷𝐷, 𝐼𝐼𝐴𝐴𝐶𝐶 = 26 𝐴𝐴 and 𝑃𝑃𝐴𝐴𝐶𝐶 = 19 𝑘𝑘𝑉𝑉𝐴𝐴. The DC output voltage value is 𝐸𝐸𝑡𝑡 = 140 𝑣𝑣𝑉𝑉𝑉𝑉𝑉𝑉 and the AC output voltage value is 𝑃𝑃𝐴𝐴𝐶𝐶 = 19 𝑘𝑘𝑉𝑉𝐴𝐴. From the calculation of AC and DC voltages, the rectifier transformer is selected with a DC voltage of 150 volts and a current of 100 ampere DC with a transformer capacity of 19 kVA. In the ICCP protection system, the availability of electric current is a must, because the transfer of electrons from the anode to the cathode occurs due to an external electric current flowing in the system. If the current source is lost the structure will become unprotected. Therefore a UPS (Uninterruptable Power Supply) or battery is needed to anticipate if the electrical power supplying the ICCP system is lost. The selected UPS specifications are adjusted to the specifications of the battery and transformer used.

Validation and Measurement Result of ICCP Design for Tank C After the ICCP installation work for the crude oil tank has been completed in the field, then the design will be validated with the aim of seeing whether the ICCP design is appropriate to provide corrosion protection for crude oil tanks C. The main parameter of the success of this ICCP design is value of tank potential must be lower/negative than -805 mV. Apart from the potential value, there are several more parameters that are measured to see the effectiveness of the design, including the DC voltage value and the output current value of the system.

040011-5

2100

1791

1800 1500

Ptential (-mV)

1644

1605 1512 1309

1442

805

805

1455 1340

1200 805

900 600

805

805

805

805

805

135

180

225

270

315

Tank C after

300

Standart [8]

0 0

45

90

Circumference position (deg) FIGURE 3. Validation and Measurement Result of ICCP Design for Tank C

The validation of the ICCP design for crude oil tanks in the onshore environment was carried out by direct measurement of the installed installations. Measurements made include the potential value on tank C, transformer rectifier (TR) curent output, negative current output and positive current output for junction box. The main parameter of success of this ICCP system is that the potential value of the structure must be lower than -805 mV which indicates that the structure is well corrosion-protected [23]. The value of the potential measurement of the structure can be seen in the graph above.

CONCLUSION From the design of the ICCP for crude oil tank in onshore several conclusions can be drawn including: 1. Corrosion protection for crude oil tank C in onshore environment with a service life of 20 years, ICCP is used with 4 MMO (mixed metal oxide) tubular titanium type anodes. The diameter, length and surface area of MMO are 0.032 m, 1.25 m, and 0.125 m2, respectively. The current density and output current of the MMO are 99760 A/m2 and 12438 A, respectively. 2. External power sources require a DC voltage of 150 volts DC and a transformer capacity of 19 kVA. 3. Measurement of potential value of tank C after ICCP installation is drop below -805 mV at all measurement points. This indicates that the thank C is well corrosion-protected.

ACKNOWLEDGMENTS The authors would like to thank Hibah RTA and The Department of Mechanical and Industrial Engineering, Faculty of engineering, Gadjah Mada University, Yogyakarta, Indonesia.

REFERENCES 1. Lam, C., Statistical Analyses of Historical Pipeline Incident Data with Application to the Risk Assessment of Onshore Natural Gas Transmission Pipelines, Electronic Thesis and Dissertation Repository, The University of Western Ontario (2015). 2. Hopkins, P., Learning from Pipeline Failures. Penspen Integrity Virtual Library, Unit 7-8, United Kingdom. (2008). 3. Myers, J.R. and Cohen, A., Conditions Contributing to underground Copper Corrosion, American Water Works Association, Houston (1984).

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4. Cunha, S.B., Comparison and Analysis of Pipeline Failure Statistics, International Pipeline Conference, IPC201290186 (2012). 5. El-Lateef, A.H.M., Abbasov, V.M., Aliyeva, L.I., and Ismayilov, T.A., Corrosion Protection of Steel Pipelines Against CO2 Corrosion-A Review, Chemistry Journal, Vol. 02, Issue 02, pp. 52–63 (2012). 6. Cramer, S.D. an...