Paper quetzal 04 version 01

DIAGNOSIS, NUMERICAL MODELING AND DEVELOPMENT OF THE CATHODIC PROTECTION REFURBISHING OF THE METAL SHEET PILING OF THE DOCKS OF QUETZAL MARINE TERMINAL IN GUATEMALA

Lorenzo M. Martinez_dela_Escalera*1, Oscar Alvarez1, Jorge Canto1, Hernan Rivera1, Arturo Godoy1, Hugo E. Ventura1

(1)Corrosi贸n y Protecci贸n Ingenier铆a, S.C;

Jorge A. Ascencio2, and Lorenzo Mart铆nez1,2 (2) Universidad Nacional Autonoma de Mexico.

We report the experience in refurbishing the near 1200 A cathodic protection system of the 2 mile and 100ft deep steel wall made of sheet piling after 30 years service. We report the diagnosis of the sheet piling including underwater ultrasonic measurements, the analysis of the performance of the array of MMO anodes along the docks, the effects of Cable defects creating cupper exposition to aggressive corrosion environments on the anodic side of the circuit and is rapid detriment, and the performance of the high current rectifiers. We also report the experience of the replacement of the MMO anodes, the redesign of the anode mountings, the wiring works of the anodic cables and rectifier modifications. We report the results of the tests of the CP current distribution both in the wirings as well as the returns of current from the protected structure to the rectifier.

The status of the CP system performance after the refurbishing is presented. We also developed numerical modeling of the CP system as designed, and we discuss the limitations of the original design when considering all the metallic structures involved, other than the steel sheet pilings facing all electrolytes other than the main dock sea front.

INTRODUCTION Quetzal Marine Terminal was built after a requirement of the Guatemala government in the 1979 year, inaugurating the Quetzal Port during the year 1983. Its localization is latitude 13o 55’’ N/ longitude 90o 47’’. Quetzal port is considered one of the main ports in the Republic of Guatemala, because the considering the amount of imported/exported products and it is administrated by the “Empresa Portuaria Quetzal”. The port complex involves 835.15 hectares, divided into 10 zones, which are used with commercial goals that are at the disposal of the interested entities in developing projects related with related international products exchange. Its strategic geographic localization allows serving mainly to the Pacific Basin and the West Coast of the American Continent, and because its nearness to the Panama channel, it can be accessed from any place around the world (see figure 1a and 1b). The port has modern infrastructure, machinery, equipment and specialized installations, which allow offering complete port services, with competitive costs, big area for commercial and industrial development and access to touristic richness of the country.[1]

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c

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Figure 1. Generalities of Quetzal port. a) Satellite image to identify the localization of the port (marked with the arrow), b) aerial view of the Quetzal port, c) mechanisms of physical inspection of the dock and d) identification of the site with metal structure to be protected.

In the search of solutions to preserve the optimal conditions of the docks the “Empresa Portuaria Quetzal”, contracted “Corrosion y Protection Ingenieria” to develop a set of tasks to accomplish a new cathodic protection system for docks of Quetzal Port. This project involved diagnostic, identification of particular corrosion problems and the implementation of solutions to enhance the cathodic protection system. Our group was contracted implement a project concerning the “renovation of the cathodic protection for the docks of the Port Quetzal, which becomes and interesting goal particularly because these metallic structures are part of the main dock, which receives ships

basically of the next types: solid in bulk, containers, tanks, gas transporters, specialists in refrigeration, general chargers, roll on - roll off, cruisers, among others.

GOALS AND METHODOLOGY. In order to develop the tasks related to the renoval of the cathodic protection system, several tasks were identified to follow a complete methodology; the procedure on the following goals: •

• • • • •

General evaluation of the components of the cathodic protection: rectifiers, impressed current anodes set, connections network, anodic connections network, test stations, electrolyte-structure potential performance, cathodic protection current distribution and evaluation of structure isolation.

Physical dimensional survey of the metallic structure of docks in Quetzal port that are protected with cathodic protection.

Physical trace and diagnostic of continuity for electric networks of anodes and cathodes connections with help of global positioning system with a differential precision by satellite.

Evaluation of the physical conditions and electrical conductance of the electrolyte-structure interface.

Physical and chemical properties measuring of soil and marine media, which are quite relevant for the design of the cathodic protection.

Evaluation of corrosion damages in vertical metallic constructive elements of the dock.

Besides the tasks for the system enhancing that are: • • • • • • • •

Cathodic protection engineering to verify the design validity and the adequacy of the current distribution for the corrosion control over the metallic surface of docks in the Quetzal port under the metallic structure actual physical conditions.

Reposition of anodic and cathodic wires network of the cathodic protection system, in order to improve the control over the administration energy.

Reposition of the 100% of mixed oxides anodes for the impressed current network.

Reparation and activation of the automatic control systems of rectifiers.

Rehabilitation and sustenance of rectifiers including the reserve rectifier.

Polarization tests and commissioning of cathodic protection rehabilitation.

Elaboration of planes (as-built) of the cathodic protection system with the rehabilitation related installations.

Delivery of installations and training about cathodic protection systems operation to technicians of Quetzal port

SITE AND PREVIOUS CONDITIONS. Dock diagnostic.The dock of the Quetzal port use a stake-board of 1,773 meters approximately as mechanical element for the ships tie up, this is divided into four sections; the Roll OnOff dock, the East dock, the South dock and the Fishing dock. Additional at the sea

exposed side, the stake-board has a face in contact with the soil below docks, which is also joined to another stake-board (localized at 30 m. approximately) by using steel ties.

So, if we consider a cathodic protection for the whole electrically linked structure to the strake-board, we must consider the four sections that represent a total of 87,090 square meters as is illustrated in table 1.

External face of external plate External face of internal plate External face of internal plate External face of external plate

Longitude [m] 1773 1773 1130 1130 Total area

Area [m2] 26595 26595 16950 16950 87090

Table 1. Area of the stake-board for the different sections.

Using a differential correction system the dimensioning of installation and metal structure were verified, whereas the depth of the structure to study, as well as the location using submeter localization laboratory for infrastructure. The measurement of the dimensions of the anodes elevation and placing of the anodes and the clear of water, provided a clear picture of the area of the stake-board that must be protected. This sizing was accomplished by the work of specialized diving and cabinet calculations (see figure 1c). The total metal surface that had to be considered for the design of the cathodic protection systems was established as 26,595 m2 of uncoated stake-board along the dock as it is illustrated in figure 1d. The structure dimensional data were reproduced in geographic information system (GIS) for conveyance to modeling programs. Registered findings included also cathodic protection relevant parameters.

Cathodic protection evaluation.Originally (before this project), the external face of the external plate was the only one with a cathodic protection system. Its design was based on a system of impressed current administrated by 8 rectifiers with a capacity of delivering 300 amperes of direct current, and with 50 Volts of tension each. The rectifiers were Universal equipments model OSOI with 3-phase power of 230/450 Volts at 60 Hz AC the current input ranges from 18.8 and 8.9 amps. Teams are immersed in 110 gallons of dielectric oil which comply with the regulations ANSI7ASTM D-3487 and NEMA TR - PB - 1975.

The 8 installed rectifiers are of single output. The main anode cables conducts of Rerouting to “mojoneras� called cash anode, where is the connection to secondary cables between anodes, which are called to turn are connected in separate 6 m in series of anodes wired records. The cathode cables are connected to the masses (contacting points for the negative cable to the rectifier) independent to close circuit with the stakeboard as shown in figure 2a. It is worth mentioning that all the connections to mass inspected were considerably sulphated, so the circuit resistance was significantly increased before cp renovation Project took place. Besides, the 8 rectifiers are capable to operate manually, with the capability of measure the structure/soil potential on an own screen, although at the time of the inspection those were found working manually, because that the automatic control cards were damaged. It was identified also the original instrumentations that belonged to the system of automatic control, which used

to its operation a fix reference cell of silver-silver chloride that is was covered by marine life reducing its capacity of monitoring, as shown in figure 2b.

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b

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Figure 2. Identified problems in the dock cathodic protection system. a) Installation of the electrical, sea life around elements and c) damages on the wires and metallic structure inside the seawater.

Electrolyte evaluation.To achieve the correct redesign of the cathodic protection system was to measure the resistivity of the water directly in contact with the stake-board. In the performed tests, the average of resistivity of 25 ohm-cm, this corresponds to a highly corrosive electrolyte and also a highly electrical conductor. The underwater inspections carried out that a considerable number of anodes were damaged in their mechanical integrity, also than some have ceased to operate by consumption integrity of the copper wire.

Also it was identified that the joints between anodes and conductor wires were realized in field with no formal procedure as it should be made because the sensibility of the process. The detected damage in some of the anodes corresponds to impacts of ships, losing the mixed oxides coating integrity and consequently reducing the useful life of the anodes. A series of evidences of the identified damages to the anodes are shown in figure 2c.

Besides the previous problems, some cables that were over the surface from the rectifier to the connection registries with the anodes showed fails on their isolation, so then it avoided the enough current flow of anodes that were interconnected to such principal wires. Using the current mapping systems with omni-directional antennas, it was possible to locate the exact location of these points failure of mechanical coating, even when those correspond to small pores of just a few millimeters.

Trace and electric network study.The physical trace of electrical networks by GPS technology was focused to the localization of the cables, the verification of electricity networks and continuities, as

well as their depth. We used a geo-positioning system with differential correction to generate an advanced diagnostic of electricity networks of anodic and cathodic connections. The location of the electricity network was carried out along the whole dock and based on the original drawings of the circuit of anodic and cathodic networks, efforts were made on raising the information of the trace of the networks generating a complete map including the circuits that were found non electrical continuous caused by the damages to the wires and the circuit bad conditions. Even when there was valid information about the localization of the cable conducts inside the cathodic protection electric circuit in the dock for the Quetzal port, it was important to have a record about the geo-referred position of each component of such structure, including their depth and relative position inside the dock. The trace study and localization of the electric circuit of the cathodic protection of the metallic structure for the Quetzal Port determined a total of 8 rectifiers, 209 anodes, 36 masses and 228 boxes that are distributed along the dock as it is shown in figure 3.

Metal structure potential evaluation.The control of the impressed current was reached with help of a portable direct current source and an incorporated current interrupter, which allowed to connect a temporal anode bed to be able of realize the current impression. Besides, the rectifiers were used to administrate the current, considering the iron extensions, with electric continuity, as monitoring stations that commonly are called cathodic masses. For the evaluation of this activity, it was needed to use devices for synchronization via satellite that allowed measuring the ON-OFF potentials in strategic points with the Ag/AgCl cell as reference.

The behavior was slightly different for each rectifier, so we can identify that the original structure potential in reference to the Ag/AgCl cell for them in table 2. The most important variation of data was recorded for rectifier 7; however it is clear the gradual reduction of potentials for several of the evaluated sites.

Rectifier 1 d (m) 0 12

Mass 1 ON -0.944 -0.874

d (m) 0 12

Mass 9 ON -0.997 -0.872

d (m) 0 12

Mass 17 ON -0.954 -0.876

d (m) 0 4

Mass 1 ON -0.818 -0.776

OFF d (m) -0.895 0 -0.867 12 Rectifier 3 OFF d (m) -0.920 0 -0.862 12 Rectifier 5 OFF d (m) -0.866 0 -0.858 12 Rectifier 7 OFF -0.786 -0.759

d (m) 0 4

Rectifier 2 Mass 2 ON -1.047 -0.912

OFF -0.957 -0.904

D (m) 0 12

Mass 6 ON -1.041 -0.900

Mass 10 ON -0.966 -0.852

OFF -0.897 -0.839

D (m) 0 12

Mass 13 ON -0.920 -0.856

Mass 18 ON -1.049 -0.860

OFF -0.932 -0.846

D (m) 0 12

Mass 22 ON -0.984 -0.884

Mass 2 ON -0.771 -0.750

OFF -0.758 -0.748

D (m) 0 9

OFF d (m) -0.925 0 -0.872 12 Rectifier 4 OFF d (m) -0.884 0 -0.841 12 Rectifier 6 OFF d (m) -0.910 0 -0.865 12 Rectifier 8

Control Mass ON OFF -0.950 -0.942 -0.930 -0.925

d (m) 0 6

Mass 7 ON -1.030 -0.910

OFF -0.931 -0.889

Mass 14 ON -1.019 -0.884

OFF -0.929 -0.867

Mass 23 ON -0.935 -0.842

OFF -0.872 -0.830

Mass 4 ON -1.140 -1.094

OFF -1.030 -0.986

Table 2. Structure potential original values for different points in reference to an Ag/Agul cell.

Corrosion damages evaluation.Besides, the main objectives of the evaluation of corrosion damages in the metallic building vertical elements of the Quetzal dock were the verification and the thickness

measurement for the stake-board, by means of ultrasonic inspection determining the thickness profile. In order to reach this goal, visual inspection of the stake-board was made by a cathodic protection systems certified engineer. Additional to visual inspection, photographic and submarine video, ultrasonic measurements of the walls were performed, since dock walls were subject to corrosion; i. e. the loss of material that is declining the thickness of the wall and that can reach critical conditions.

On the basis of the dock depth, a total of 52 points were selected, covering 1.9 km. distributed approximately every 30 m; for each point of sampling three measurements were obtained, with which we got a total of 156 collected records. In table 3, the averages based on their depth measurements, as well as a general average thickness found on the stake-board.

ID

DEPTH (m)

A B C D

0 4 8 12 GENERAL AVERAGE

AVERAGE VALUE OF STAKEBOARD THICKNESS (in) 0.788 0.785 0.887 0.961 0.825

Table 3. Average thickness measurements.

Based on the obtained results, we can determine that averages based on their depth measurements, as well as a general average thickness found on the stake-board. Here we could note that minor depth, there was a wall thickness smaller of 0.788’’ this because there is a greater exposure of the stake-board to factors such as great concentration of oxygen, creating depolarization of the cathode defects, related with increased movement of water in contact with the protected structure, as well as increased aeration among others, as well as various substances that could be in the sea, surface and that are crucial to induce the corrosion processes; also we must consider that that the area with the best structural integrity is found around 12m depth with 0.961’’ thickness, representing 18% more than the found value at 0 m. According to the above yields a general average of 0.825’’ that is acceptable as wall thickness for the stake-board.

Cathodic protection system modeling.Looking for a better understanding of the fundamental parameters that affect the operation of the cathodic protection system, and to identify the way to administrate enough electrical current for a electronegative polarization of the metallic structure, in order to fulfill the criteria of -900 mV instant off against a Cu/CuS reference cell, the use of modeling mechanisms are really useful; particularly the application of approaches where the different elements can be considered by using the frontier element method and the finite element method based on numerical analysis and empiric data, which allow adapting a particular calculation to real data and to use the computer as virtual lab; the utility of this system is identified mainly because this can illustrate how the potential is been distributed over the metallic structures in function of the elements that play a role, as rectifiers, anode configuration, soil resistance and the own conditions of the metal interface.

From the anodes behavior data we could generate a model of the original cathodic protection system behavior but also, in function of the proposed system we evaluated the optimal conditions to induce the operation of the new network.

Old system model.From the anodes behavior data, and the previously obtained values for geometry, structure, dimensions (sustained also by the submetric geopositioning), number and characteristics of anodes, impressed current by the anodes, polarization potential criteria, media resistivity for seawater and soils, and electric isolating, we reproduced the system as it was working before the rehabilitation activities in a model. We can identify with help of the calculated profile for the two sections of the stake-board in the seawater and the corresponding bury. It is clear that both sections have a common behavior with similar profiles for the calculation in seawater and bury conditions; however the potential values are very depending where the metal structure is, with lower potential values when the electrolyte is earth (Figure 3). From the profiles, the multiple sites with not enough potential to protect the dock are more in earth than in seawater, and for the first section the risk sites appear in the most are more but also because the own dimensions of the segment.

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Figure 3. Calculation potential off profiles for the stake-board. First section a) inside seawater and b) bury; besides second section c) inside seawater and d) bury.

Model for the improved conditions.Following a similar procedure for the case of an analysis for candidates to improve the operation of the cathodic protection system, we show results of comparable profiles against the previous conditions of the stake-board. Figure 5 show the calculated profiles where the implementation of solutions allowed increasing the control on the polarization potentials and the protected sites are increased to fulfill the -850 mV criteria (let consider that this value corresponds to the Cu/CuSO4, while the use of silver reference cells involves a value of -900mV). This calculation was based on the

substitution of anodes, cables and related instrumentation, with the new design of the cathodic protection system but similar anodes localization, with the goal of determining the required current to protect the whole stake-board.

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b

c

d

Figure 4. Calculation potential off profiles for the stake-board. First section a) inside seawater and b) bury; besides second section c) inside seawater and d) bury.

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b

Figure 5. Gradient plot of potential distribution for the stake-board a) before and b) after restoration.

The real impact on the cathodic protection operation can be identified with help of the plots of figure 5, where the calculated potential distribution around the stake-board structure in the soil is shown for each case, the original and the modified conditions.

These plots allow comparing the potential distribution behavior, which denotes a better regularity of the enhanced system, while irregularities can be found for the original case.

Through the simulation of the cathodic protection system installed in the dock of Quetzal port, we found that the design is suitable, however, its Needs for maintenance created several deficiencies in the cathodic protection system. The reasons were associated to problems with part of the cabling system as well as several damaged, which had been affected by various factors over a period of time, impacting negatively it performance. The above could be determined form the original conditions model, which showed that the amount of drained current by anodes varies significantly in the stake-board; this means that while they were draining little more than 10 amps, there were several others who were just draining hundreds of milliamp and even some more outside of operation, the results show that this variation in the amount of current drained by the anodes caused different areas of the stake-board not be cathodically protected therefore the recommended potentials were no reached.

Thus, to achieve the proper performance of the cathodic protection system as is seen in the results for the modified model, it was recommended that damaged connections and anodes were restored or replaced in providing the current drainage performance of 6.5 amps per anode, even considering the same location than the original anodes distribution, achieving uniform dispersion and therefore the adequate potentials in order to comply with cathodic protection international regulations all along the stake-board optimal in both, the submerged area and the subsea buried area.

IMPROVEMENT OF CATHODIC PROTECTION SYSTEM.Corrective actions From the previously mentioned results concerning diagnostic and modeling efforts, the substitution of anodic and cathodic cable networks the needs of rectifiers mainteinance was determined and implemented. The anodic and cathodic networks replenishment was using a methodology cables by replacement of circuits and rectifiers enhancement (Fig. 6a). Replacement work took place by engineers Certified by NACE International cathodic protection within the primary considerations replacement networks were the primary integrity of cables, the dimensions established at levels originals, cleaning of accommodation for cable, cleansing routes records and points of monitoring of anode and cathode circuits.

Elimination of the existing boxed anodes type connection A:n with the mixed oxide anode tied to a guide to the diver to be it is submerged pull the guide and remove the cable to remove. Later is fixed to the new anode cable to the guide so that staff can climb the new anode cable (figure 6b). The new anode into PVC holders mounts. In this case the anodes are oxides mixed with a nominal capacity of 25 amp as shown in figure 6c. Withdrawal of the prisoner screw to subsequently remove the hydraulic PVC Stoppers as in figure 6d. To mount the new anode in PVC, brackets are used anodes of mixed oxide with a nominal capacity of 13 amp.

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Figure 6. Images of the correction actions of the cathodic protection; a) cables substitution, b) besides the submerged cables manipulation to allow the anode substitution, c) the new mixed oxide anode into PVC holders, extraction of the prisoner screw to subsequently remove the hydraulic PVC Stoppers, and e) maintenance and rehabilitation of rectifiers.

The rehabilitation of the protection rectifiers cathodic was performed by changing the dielectric oil extraction total used oil and oil Univolt N61-B replacements through pumping, cleaning the rectifier, rehabilitation and replacement of the physical rectifier such as electrical terminals, components connections, bases of fixation and hardware in general (illustrated in figure 6e). The appropriate cleaning and replenishment of anode and cathode cables of DC power was done.

Polarization potentials values.

After the design of the cathodic protection system and the different corrective actions, the evaluation in-site of the polarization potentials generates the values of table 4, where it can be distinguished the benefic impact of the rehabilitation. The polarization potential values fulfill the -850mV criterion in al the cases, and there is an evident tendency of more negative values in the superficial evaluated sites, which can be expected because the effect of the seawater resistivity.

From the two main goals (diagnostic and rehabilitation), we can conclude that the impact to the dock protection with the new cathodic protection system is positive and the real capability to reduce the corrosion processes over the stake-board in the two

sections and the two conditions (seawater and buried) are achieved based on the fulfilling of the -850mV criterion.

Rectifier 1 Deep measurement Superficial measurement Anodes ON OFF Anodes ON OFF 1-2 -0.978 -0.914 1-2 -1.067 -0.990 18-19 -0.874 -0.867 18-19 -1.062 -0.979 Rectifier 3 Deep measurement Superficial measurement Anodes ON OFF Anodes ON OFF 50-51 -0.970 -0.945 50-51 -1.114 -0.982 64-65 -0.977 -0.937 64-65 -1.115 -0.990 Rectifier 5 Deep measurement Superficial measurement Anodes ON OFF Anodes ON OFF 98-99 -0.954 -0.920 98-99 -1.113 -1.079 112-113 112-113 -0.999 -0.942 -1.114 -1.078 Rectifier 7 Deep measurement Superficial measurement Anodes ON OFF Anodes ON OFF 1-2 -0.948 -0.925 1-2 -0.963 -0.922 41-42 -0.957 -0.916 41-42 -1.050 -1.001

Rectifier 2 Deep measurement Superficial measurement Anodes ON OFF Anodes ON OFF 26-27 -0.956 -0.917 26-27 -1.147 -1.051 42-43 -0.900 -0.872 42-43 -1.134 -1.023 Rectifier 4 Deep measurement Superficial measurement Anodes ON OFF Anodes ON OFF 73-74 -0.964 -0.938 73-74 -1.112 -1.009 89-90 -0.974 -0.931 89-90 -1.075 -1.011 Rectifier 6 Deep measurement Superficial measurement Anodes ON OFF Anodes ON OFF 123-124 123-124 -0.998 -0.935 -1.158 -1.076 141-142 141-142 -0.884 -0.865 -1.155 -1.046 Rectifier 8 Deep measurement Superficial measurement Anodes ON OFF Anodes ON OFF 1-2 -0.979 -0.932 1-2 -1.122 -1.042 12-13 -0.976 -0.910 12-13 -1.129 -1.062

Table 2. Structure potential enhanced values for different points in referent to an Ag/AguSO4 cell.

The contribution for this goal of the different techniques of site characterization, together the computer modeling of the original and the proposed conditions, and the solutions implementation focused to the cables, anodes and cathodes network, and existing rectifiers are showed in this work and the complete process allowed identifying the contribution of each particular task. The rehabilitation of the Quetzal port will allow the operation of this maritime terminal for a longer time and with the confidence even under the different conditions that affect the metallic structure of the dock.

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[3] Tinker, W. A. Cathodic Protection For Ssteel Bulkheads Under Relieving Platforms.

Materials Performance, 30 (11), 20-23, 1991.

[4] Canto, J., Martinez-Dela_Escalera, L. M., Rivera, H., Godoy, A., Rodriguez Betancourt, E., Lopez-Andrade, C. G., Albaya, H. C., Pesce, Norberto,Ascencio, J. A., Martinez-Gomez, L. Pipeline Survey in Mexico Reveals Need for 100-mV Polarization CP Criterion. Materials Performance, 48, (4), 32-36, 2009.

[5] Castro-Borges, P; Ordaz, JM. Corrosion Performance of Concrete Columns After Localized Repairs in a Tropical Coastal Environment. Corrosion, 65 (2), 118-125, 2009.