CATHODIC PROTECTION IN HIGH CONSEQUENCES AREAS: CHALLENGES AND SOLUTIONS IN EASTERN ECUADOR OIL PRODUCTION FIELDS Jorge J. Cantó Ibáñez Corrosión y Protección Ingeniería S.C.
Edgar JaimeMaya Cervantes Calvo Corrosión Corrosión yy Protección Protección Ingeniería Ingeniería S.C. S.C.
Lorenzo Martínez Martínez de la Escalera Corrosión y Protección Ingeniería S.C.
Hernán JaimeRivera Cervantes Ramos Corrosión Corrosión yy Protección Protección Ingeniería Ingeniería S.C. S.C.
Fernando Eguiguren G Repsol Ecuador
Lorenzo Martínez Gómez Corrosión y Protección Ingeniería S.C. Lorenzo Martínez Gómez Corrosión y Protección Ingeniería S.C.
1
SUMMARY
hydrocarbons in Ecuador, a Mexican company highly specialized in pipeline integrity technologies, has made direct assessment of cathodic protection systems with special emphasis on the mapping of the current flow and the development of alternatives to the problems found. The study was conducted with the participation of three leaders of the highest international certification in the field of corrosion control. This panel has been supported in the field with full equipment and technology for the diagnosis and numerical modeling of cathodic protection installations.
With the continuous growth in oil production, the Ecuadorian economy is betting it’s development in the medium and long term exploitation of new and tested reserves. This new operation will occur in regions with the world’s most biodiverse and Waorani communities, which remain in limited contact with the rest of the Ecuadorian population, and sub groups identified as Tagaeri and Taromenane are kept in complete isolation. The region’s oil production has been in a unique symbiosis between industrial activity, the environment and the native population. In this delicate environment, the implementation of more stringent standards in the industry becomes a commitment. Maintaining the integrity of the pipeline, through the cathodic protection becomes a crucial line of defense to ensure continuous and reliable operation in a high consequence area due to ecology and business.
WORK DEVELOPMENT In general, field the field work was based on the measurement of performance indicators of the cathodic protection systems. The diagnose is based on readings such as pipe to soil and current mapping using high diameter ammeters as well as the operation of rectifiers, anode beds and variables associated with electrical isolation structures. In total 109 measurements were performed of current flow with the use of large diameter ammeters, completing the measurement at all point that coverage and diverge at the facilities as well as the interconnections and waypoints. The result was a complete mapping of the CP current flow, telling the operators of the system the magnitude and direction of the current in all its pipelines and flows and losses that may be deleterious to the integrity of the pipelines.
We report the diagnosis and solution approach for the reengineering of cathodic protection systems for pipelines, as well as a first experience in the application of numerical modeling of a complete oil field where high soil conductivity cause the interaction of distant systems. Also the discharge of cathodic protection to the water inside the pipelines is reported as a major problem since only a limited percentage of the total current is utilized to polarize the pipeline. As the defect increases water production and its presence as a secondary phase within the pipeline exceeds ninety percent from oil, electrical insulation systems stop working when a discharge of current through the electrolyte and across the isolation joint. We describe the design of a cathodic protection system for internal protection of the pipelines at the discharge points.
Figure 1. Current measurement with large diameter ammeters
INTRODUCTION In response to the initiative of industry production, extraction and transportation of
The current mapping has indicated that there are significant losses of current
2
facilities that should be isolated, quantifying a total of 57.2% of the total current being captured mainly by wells and returning to the rectifiers by two main paths.
components that will reduce the leakage current to the facilities and wells and mitigate the effects of accelerated corrosion that could presented. We present a description of the problem of internal corrosion being caused by the cathodic protection system as well as its alternative solution.
The first, are pipe fittings and chemical injection or measurement equipment that bypass the isolation joints.
Case Description The phenomenon of corrosion in metallic materials is supported in the formation of a galvanic cell between two dissimilar metals or electrical potential difference which produces an electromotive force and current flow through these elements as long as they are electrically connected and submerged in a common electrolyte. In the simplest case, a corrosion cell is formed when two metals are electrically connected and immersed in the same electrolyte medium. Figure 3 shows a schematic of a cell where the electromotive force is produced by the natural potential difference between both metals, this can occur even between two sections of the same structure, which is the most common corrosion process in buried metal structures or submerged.
The second, and more dangerous, can potentially cause accelerated metal loos. This is the current passage through the insulating joints that operate satisfactorily by means of the water present in the pipelines that for highly conductive properties work as a return path to the current. As shown in Figure 2 most power loss occurs in the pipelines carrying production water.
Figure 2. Power distribution to facilities used and lost. Despite current losses, the polarization potentials in most sites are in compliance with the values indicating the internationally accepted standards. Using the criterion of 850mV polarization was found that only 10% of the sampling carried out does not meet this criterion or even if the criterion of 950mV. Figure 3. corrosion cell.
It is generally accepted that there must be a change in the polarized potential up to -850 mVCSE. In this case the criteria for protection of pipelines and because high temperature conditions should be -950mV respect to copper/ copper sulfate electrode.
In this case, the oxidation reactions occurring at the interface between the anode and the electrolyte, where the surface metal atoms of the free ions react with the electrolyte to form oxides, metal matrix leaving the free electrons are conducted through the metal path to the cathodic
During fieldwork experts agreed on common elements that point to the recommendation of some engineering practices and
3
surface, which are reduction reactions.
consumed
in
the
anodes (represented by arrow yellow) is collected by the wells and other buried metal structures, this current flows through the metal structures (flow represented by red arrows) until the electrical insulation.
In some cases, the potential differences generated by external electric paths can cause corrosion cells generating alternating between two different structures even when these are not in electrical continuity.
When current reaches the isolation joint it discharges to the highly conductive electrolyte and it’s picked up on the other side of the joint. At the point of discharge, severe corrosion can occur.
This phenomenon is called interference and can occur in many different ways, in any of them, the result can be a rapid corrosion process at the interfered structure. The pipelines use cathodic protection systems for external corrosion control, since the system is isolated from the rest of the facility, the current can only be captured by sections that are electrically connected a direct current source. Even if the facility has a lot of grounding facilities like wells, foundations and earthling systems, the current preferential path is the one of least resistance. The electrical insulations have the function of increasing the resistance between these installations and the cathodic protection system to prevent current flow through them, in normal conditions, the potential differences between the protected pipe and the other structures within the facility, are not enough to break the dielectric strength of the insulation.
Figure 4. Current flow scheme within cathodic protection station.
However, pipelines currently transport a large volume of water rich in chlorides and other salts whose resistivity is very low to the point of behaving as a good ionic conductor. When the potential difference between the two sides of the insulation is enough current will be discharged to the electrolyte and it becomes a “ionic bond�. Figure 5. Current flow through the gasket Current flows from the station side (left) to the side of the protected product (right).
This interference is a phenomenon that occurs because an alternative route of unwanted current, and as already mentioned this phenomenon can lead to problems of corrosion of the pipeline at specific sites.
Since production wells have been drilled vertically, but in a directional way, the precise location of the wells on respect to the anodic beds is not known but it is
Figure 4 shows the origin of the phenomenon, the electric current leaving the
4
reasonable to expect that the distance will be lower than expected.
that relates the flow of electric current consumed by the metal mass to form metal oxides.
The most influential factor is the aforementioned low resistivity production water. When the potential difference between both sides of the insulation (one in electrical contact with the structures of the installation and the other with the protected pipeline) is sufficiently large, the current begins to flow through the water through which travels to reach the other side of the flange, and continued his way through the pipeline to the electrical connection to the negative terminal of the rectifier.
Where: Wt = Total mass loss in the anode metal n = Number of charges transferred in the oxidation Icorr = Corrosion current F = Faraday constant = 96,500 Coulomb M = Atomic weight of anode metal t = Time during which the cell is operating corrosion A new constant Km substitutes the value of M/nF. Where Km is the rate of consumption for each material. In the case of iron, its atomic weight is 55.85 g, and each iron atom transfers two loads during the oxidation reaction so that the consumption rate is:
The phenomenon can be hard to identify if you do not have the right tools. As shown in Figure 6 when you measure potentials on both sides of the isolation flange with a fixed reference electrode, you can observe significantly different values, and declare adequate isolation. Dispite this testing, and at the same place a radio frequency will show that the isolation joint is not working.
The result of the above equation means that a corrosion current of 1 A for one year, representing loss of 9.125 kg on an iron structure. Taking as example the current measured by ammeter large diameter in the isolation of a water pipeline 16 "was found to pass through it is 4.9 A. According to Faraday's law iron consumption corresponds to a mass of 44.7 kg per year.
These two test methods are internationally recognized and are valid independently determine whether or not isolation is achieved. It is only with the use of a large diameter ammeter that you can understand that although there is a perfectly operating isolation joint current is traveling through the electrolyte.
This loss of metal occurs within a small area in the vicinity of the insulation, corrosion rate at this point will depend on the extension of the metallic surface which occurs in the discharge current. This phenomenon can be seen in Figure 7 where the ultimate test is the current “jump� (A) and a repair done at 6 o'clock a few inches of an isolation joint (B).
Figure 6. Determination of effectiveness of the insulation‌ As mentioned above, the metal corrosion occurs when a flow of electrical current from the metal to the electrolyte surface, such damage can be quantified by Faraday's law
5
Additionally, it is necessary to implement the system with a reference electrode also immersed in the water so that the potential of the protected section can be monitored or even be used to regulate the current source automatically. Figure 7. Jump current (A) and repair leak (B) Alternative solutions, insulation wells.
Figure 8 shows a schematic of a system for cathodic protection of the pipeline inner surface, installing a rod-shaped anode and connected to a source of direct current is inserted further into the pipe also a reference electrode which allows monitoring the potential of the inner surface also use it for the automatic adjustment of the source.
electrical
The second electrical factor that can be manipulated to reduce the current through the insulation, is the increase in resistance interfered structures. Some of these structures are formed by the jackets of the wells that are large areas of uncoated steel pipelines buried in direct contact with the ground.
This alternative should be considered if after installing insulation in the discharge lines from wells, there is still a significant current flow through the insulation of pipelines. The design of this system will be based on the magnitude of the current remnant after installing insulation boards.
It is a common engineering practice for cathodic protection installation of electrical insulation in the discharge lines to prevent current collection. Cathodic protection inside the electrical insulation As mentioned, the process of corrosion resulting from a current flow from the metal surface into the electrolyte, this effect can be minimized if electrical current is applied in the opposite direction on the same surface, reducing the net current flow on the metal surface. This can be achieved through the application of cathodic protection current in the discharge area of electrical insulation.
Figure 8. Cathodic protection system for the interior surface of duct in an insulated flange. CONCLUSION Overall, we found an operating system wellmaintained and sufficient capacity to control the corrosion process. The main problem is being caused by the high conductivity of the water into the pipelines that allows current to cross the insulating joints. The problem is certainly a challenge that has not been studied in detail by the international scientific community and whose solution requires the development of advanced
The principle of operation is equivalent to that used for underground pipelines, consists in the installation of an anode immersed in the water transported in the vicinity of the area affected by corrosion and by a direct current source connected at its positive terminal to the anode and the negative terminal to the pipe insulated to process plant (corroding side).
6
U. R. Evans, the Corrosion and Oxidation of Metals (Edward Arnold Publishers, Ltd., 1960).
technology as it is not due to a problem studied or standardized solution. Acknowledgements Our greatest thanks to Juan Carlos Andrade legal representative of Corrosion and Protection Engineering company in Ecuador for their invaluable support in the efforts for the success of this project. REFERENCES Dr. Thomas J. Barlo, “Field Testing the Criteria for Cathodic Protection,” Research sponsored by Pipeline Research Committee of American Gas Association, SAIC Interim Report, Dec. 1987, Cat. No. L51546 (Hoffman Estates, IL: AGA) 1988. J. Cantó, E. Rodríguez Betancourt, C. G. Lopez Andrade, H. C. Albaya, Norberto Pece, L. M. MartínezdelaEscalera, H. Rivera, A. Godoy, J. A. Ascencio and L. MartínezGÓMEZ “5,000 km row cp survey analysis and the potential advantages of the 100 mV polarization criterion for the CP of aged coating oil and gas pipelines in Gulf and North of Mexico”. Lorenzo M. Martínez de la Escalera, Jorge Cantó Ibáñez, Hernán Rivera Ramos, Arturo Godoy Simón, Lorenzo Martínez Gómez. “Control de la corrosión exterior de tuberías de pozos para beneficio del medio ambiente y la productividad de la industria petrolera de México”. Consejo Consultivo de Ciencias Presidencia de la República (2011). W. W. von Baechmann and W. Schwenk, Handbook of Cathodic Protection, (Surrey, England: Portcullis Press Ltd., 1975).
7