2008 design and construction of the hibrid cp system for the mexico city airport jet fuel pipeline u

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Paper No.

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CORROSION 2008 CONFERENCE& EXPO

DESIGN AND CONSTRUCTION OF THE HYBRID CP SYSTEM FOR THE MEXICO CITY

AIRPORT JET FUEL PIPELINE UNDER THE lOOMV POLARIZATION CRITERION.

L. M. Martinez de la Escalera* and J. Canto*

Corrosion y Proteccion Ingeneria, S.e.

Rio Nazas 6.

Cuernavaca, Morelos. Mexico. 62290 .

A. Rios

Aeropuertos y Servicios Auxiliares

Avenida 602 No. 161.

México, Distrito Federal. Mexico. 62290.

H . Carrillo

Facultad de Ciencias, Universidad Nacional Autonoma de Mexico.

Circuito Interior. Ciudad Universitaria.

México, D.F. CP 04500.

H. e. Albaya

Sistemas de Protección Catódica S.A.

Tronador 1126, piso 5° A.

Buenos Aires . Capital Federal. Argentina. C1427CRX.

J. A. Ascencio and L. Martínez-Gomez

Instituto de Ciencias Físicas, Universidad Nacional Autonoma de Mexico.

Avenida Universidad s/n, Colonia Chamilpa

Cuernavaca, Morelos . 62210, Mexico.

*Also at Facultad de Ciencias Quimicas e Ingeniería, Universidad Autonoma del Estado de Morelos.

Avenida Universidad 1001, Colonia Chamilpa

Cuemavaca, Morelos. 62210, Mexico.

ABSTRACT The Mexico City international airport underwent a rnajor expansionltransformation in the 1ast few years, which included the growth or renewal of sorne segrnents of the jet fuel network of pípelines and hydrants. A strategy to maxirnize the space utilization in the current location forced to Copyright © 2008 by NACE Internati ona l. Reque sts for permission 10 publish th, s manuscript in any fonn , in pa n or 10 whole must be in writing 10 NACE Jnternati ona l, Copyright Di visio n. 1440 South creek Orive, HOtlSlOn, Texas 777084. Th e material p resented and (he views express ed in thi s paper are solely (hose of (he author(s) and are not necessarily endorsed by the Associ alion. Print ed in the USA .

build the new tennÍnal's method010gy based on concrete decks the wet clay s011s characteristic of the former of Texcoco. Structures are prone to with time of soíl; therefore the decks were made of a low enough density to hold aboye wet clay soil. this of reinforced concrete layers, with a selected construction for the apron was a Tezontle in middle. A of the new 2 meter layer of a porous volcanic fuel pipeline was located within thís sandwiched structured deck. of The CP system was a hybrid design so that the pipel into the hydrant Tennínal within the sandwiched deck structure, could a continuous configuratíon, and the jet fuel pipeline network would be protected by a remote three anode of the fuel pipeline network due to the combinatíon of a very old coated coated as well as the many associated to the hydrants, obliged a design of RP 0169 2002. the compliance to the 100mV

Keywords: Cathodic protection, airport, hybrid

system, continuous

deep anode, jet júel

INTRODUCTION. UU"','~L'",""'l S flow at Mexico City lnternational Airport, MCIA motivated a new tenninal and modernizatíon and and parcel company expansion the fonner single tenninal, both ín new years the aírport a near 100% growth in pipelíne Ultímately in the last and hydrants. Presently the million liters per day.

External corrosion control ís a very task for the proper íntegrity of the fuel supply of the aírport. soil ís very this part of Mexico City. is located in of The high ine content of the c1ays of once bottom and now soil of the to the very Jow the soil and ultimately to the high corrosivíty of pipelines are buried.

In this paper we the m fuel pipelínes motivated by the recent fuel pipelines in airports is usually a complicated constraints are nonnal in but entrance and the difficulty is and

and the cathodic protection system for the MCIA. Control of the external corrosíon of jet Multiple requirements about and logistic Mexican main port to the location of this project and conditions as had to be addressed

and therefore technically no negotiable for the design work. No devices were to instaJled inside the terminal areas, could only flame-proof installed in the tank fann. AIso in the tenninal fields all connections should and only underground test stations were allowed in the tenninals. We could convínce airport mainly to divide authority in charge of construction to install isolatíng joints where in order to treat separately the old and new jet fue I pipelines. However we could not what we thought was an number of casíngs that in the convince constructors ofnot middle or long term not ísolated from pipeline.

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Due to the construction constraints described aboye, and the many fittings and groundings near the jet fuel hydrants, we targeted this ep system at least to provide external corrosion control under the 足 100m V cri terion. 3-5

SITE AND CONDITIONS The problem understanding requires determining the conditions for the construction, logistics, involved material s and conditions that derivate into bigger complications; so it is convenient to identify the site and installations distribution . MelA jet fuel pipelines distribution is illustrated on flgure 1, which corresponds to an air view of the MelA region. The jet fuel pipeline consists of two networks.

One was constructed about 30 years ago using APl B2 type of steel and coal tar coating to fuel about 40 hydrants existing before the expansion project. An APl X65 steel and FBE coated new pipeline was constructed to fuel the new Terminal 2, and a portion of the old pipeline going into Terminal l .

NEW PIPELINE SEGMENT OF OLD PIPELINE TO BE DECOMMISIONED NEW

ro OLD PIPELINE

J OINTS

Figure 1. Scheme of MC1A with th e two segm ents ofthe j et fuel pipelin e network

The scheme of figure 1 sho.ws the run ways (marked with red arrows), besides the services ar.ea, the older tenninal and the new one (marked as A, B and e respectively over the photograph) . The Jet fuel

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pipelines system (with more than 20 km) is schematized using three line sets, which denote the localization of the new pipe (pink), old one (green) and the both pipes joining sections (blue) in order to understand the complexity in the common consideration of them for the CP system. The current demand for the older pipeline was measured 60A. The soil electrical resistivity is too low, just 300 to 600 Ohm足 cm the is mainly because this airport is on the lands that used to be the Lake of Texcoco, The terrain is of very low shear strength, particularly in the zone of the las! section of the jet fuel pipeline (marked with the yellow rectangle), which is characterized by clays saturated with water and it produces the imminent risk of sinking. In this way, it was necessary to design complex and hybrid solutions in order to reduce the sinking risks and to apply a cathodic protection system for the corros ion control of the jet fuel pipelines.

ANTI-SINKING PLATFORM The strategy to maxlmlze the space utilization in the current location forced "Aeropuertos y Servicios Auxiliares (ASA)", the Mexican airport authority, to build the new terminal's taxi drives using a tailored construction methodology based on concrete decks aboye the wet clay soils characteristic of the former Lake of Texcoco . Structures are prone to sink with time in this type of soil; therefore the decks were made of a low enough density to hold aboye the wet clay soil. This must have a high rigidity in order to support the airplanes traffic that can be forwarded to the gates of the Terminal 2.

Figure 2. Anti-sinking platform for Terminal 2 ofMelA. Schemes in a) longitudinal and b) transversal views, and e) a photographic registry of {he building process.

The construction system that was selected for the taxi drives was a sandwich with three layers; two steel reinforced concrete layers and in between filled with Tezontle particulate a very porous and light volcanic material. Figures 2a, b and c illustrate the construction scheme. An asphalt cover on the upper concrete deck allows the stress distribution and pressure over a wide area, where airplanes circulate and park at the passenger's zones. As mentioned before in the middle of these concrete layers, a zone of red gravel (around 2" to 4" diameter) with large porosity called Tezontle was placed. The density of Tezontle allows filling high volumes with a relatively low weight. The lower density of the whole

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structure prevents it from sinking in the wet clays of the lake. The jet fuel pipeline was located within the Tezontle layer in a trench of sand. The three layer structure is not water insulated at laterals which contact the wet clay soils. Since humidity may thus reach the pipeline, the CP design included a solution for the pipeline in the middle of this structure. In figure 2c , the construction process is shown, denoting how the first stage was the collocation of the steel reinforced concrete, followed by the Tezontle refill and the sand bed for the pipeline. Above are to be the final slab of reinforced concrete with an asphalt surface. rn the photography can be also observed the space between the concrete plate and the pipeline (to be filled with Tezontle and sand), which allows a mechanical protection for the pipe supports .

CP CURRENT DEMAND As pointed out before around 30% of the new jet fuel pipeline and hydrants are built inside the described three layer structure, which may act as an isolating cavity to the electrical potential induction for a impressed-current CP system. The rest of the pipeline and the hydrants of Terminal 2 are buried in natural soil where a remote bed impressed current CP system is indicated. The corrosion control system must be designed considering two different conditions, and therefore of hybrid nature both beca use of the remote and distributed anode beds, and also sacrificial and impressed current anode beds.

TABLE 1.

CURRENT DEMAND VALUES AND PARAMETERS TO CONSIDER. MEXICO CITY AIRPORT JET FUEL PIPE COATING.s

OtAMETER

lENGHT

TOTAlAREAOF PIPE

UNir

INCH

METER

SOUARE METER

%

BURIED JET FUEL PIPE

18

10,000

14,363

JET FUEL PIPE IN SANDWICH

18

4,000

HYDRAHT CONNECTIONS

6

COPPER COATED GROUNOINGS

0.75

TOTAL

UNir CURR.fNT

CURRENT OEMMO

oEMAHO

PRESENT

CURRENT DEMAND IN lO YWlS

SQUARE ME TER

AMPEREJ SO METER

,AMPERE

AMPERE

80

2,873

0.020

57.5

100.5

5,745

95

287

0.020

5.7

10.1

600

287

90

29

0.020

0.6

1.0

300

18

O

18

0.060

1.1

19

14,9

113.5

EFFICIENCV

NET ME TALAREATC PROTECT

3,160

20,109

The current demand calculations are resumed in table l. There is shown that it is necessary to protect about 14,400 m 2 of pipelines in natural ground. The segments that are inside the anti-sinking platform, 2 which totalize 5,750 m 2 of jet fuel pipeline, associated to connections and hydrants that sum 287 m .

From these amounts of pipe surfaces exposed to ground, and considering extreme conditions, where the pipelines in the natural ground (including old and new ones) would have a coating minimal efficiency of 80%, while the pipelines inside the deck would show a value of 95% and the hydrants 90% in the worst scenery (used for the extreme requirements of security). In this way, the bare metal considered amount is 2,873, 287 and 29 m2 respec.tively for the mentioned sections, which present a unit demand of 0.020 Alm2 (characteristic to steel). A Iso to the copper coated groundings that correspond to 18m2 with a unit

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current demand of 0.060 Nm 2 . So the total current demand present is 64.9 A, and the total current demand in 30 years is 113.5 A.

PROPOSED SOLUTION. Under the current demand considerations, the mechanism for administrate the required current was deterrnined. Based on the complication of the sandwich deck, which acts as isolating cavity, the proposed solution in vol ves a hybrid system. With an impressed-current CP system based on remote ground beds for the pipelines in the natural ground, and using a galvanic anode CP system for the pipeline that is inside the anti-sinking platforrn.

A. IMPRESSED-CURRENT CP SYSTEM.The selection of the impressed-current CP system was based on the proposal of a set of three deep anodes, localized in the tarrk farm area , where it was possible to make the excavations, but al so can be used for the control, maintenance and operation of the CP system with no major logistic complications.

It was measured the maximum distance and because of the soil properties of low resistivity and high humidity, it was concluded this as the optimal solution.

RECTIFIER RECTIFIER

lIQUID CARBON

CATHODIC PROTECTION SYSTEMWITH THREEDEEP ANODES ARRAY

25cm

Figure 3. Scheme 01 a) three deep ground bed system and b) each deep anode configura/ion.

Figure 3a shows the configuration of the three deep anodes, it can be observed that the distance between the ano des of 20 m, while the established deep was 100m and the active zone (defined by the liquid carbon) is 35m. The systeĂ­TI of three ground beds is regulated with independent controls of two rectifiers, one of 100A X 100Y OC .output and the other with 50A X 50Y OC output. Each deep anode is considered a structure as shown in figure 3b, where the dimensions of the anode body are illustrated.

The selected anodes were mixed metal oxides deposited over titanium tubes, while the active column is

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immersed in low resistivity carbon coke. For each anode there is an independent wire attached to a shunt box, where they are all connected by a single wire to the rectifier. Ihis system provides enough current to keep the jet fuel pipelines with enough electronegative potential to control the corrosion behavior. It is important to establish that the impressed current part of the CP system was targeted to provide corrosion protection mainly to the jet fuel pipeline segments buried in soil. Ihe CP of the segments of the jet fuel pipeline in the two concrete slabs of the anti-sinking deck was designed by employing the reinforcement of a magnesium (Mg) continuous ribbon anode parallei to the pipeline due to the plausible blockage of the CP current coming from the impressed current configuration.

B. GALVANIC ANODE CP SYSTEM. Considering that about a third part of the new jet fuel pipeline was located within this sandwiched stmctured deck. Ihe freatic level in the former Lake of Iexcoco reaches ground level most of the year, especially in the rainy season that lasts about 7 months. Water leakage into the sandwiched deck stmcture was considered unavoidable. In this way, the proposed solution for the protection ofthe jet fuel pipelines and hydrants inside the anti-sinking platform was the use of a magnesium sacrificial continuous ribbon anode following the same trajectory than the pipe at a distance sufficiently short enough to present the effects of a distributed galvanic anode system. Associated to this effect, the electrolyte must be considered, and then the zone between the pipeline and the magnesium ano de is filled with sand, which has the adequate resistivity and it also allows the mechanical manipulation for the sacrificial ribbon along the trajectory . Ihe placement of this anode and the sand electrolyte can be observed in figure 4, where the installation is registered .

Figure 4. Localizatiof1 ofMg sacriflcial anode besides the pipeline.

In order to determine the specifications of the magnesium ribbon to be used, the amount of mass required for the sacrificial anode must be calculated. Ihis analysis is resumed in table ll, which corresponds to the worst scenario, where it is necessary 5.6 A to protect the jet fuel pipeline during 30

7

years in extreme conditions. It ís derived from calculations that the mínimal mass requirement of 1,344

kg

Mg. TABLE H. MASS FOR GALVANIC

Following the condition in al1 the the solution of the galvanic continuous anode involved the selection with characteristics listed in table III, beca use the jet fuel pipeline length anode is parallel and will have similar length) is 5 the total amount is more than 1800 covering the established requirements.

SPECIFICA TlONS

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TABLE HI. CONS1DERED . . .• .

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A NODE.

of this designed CP hybrid system were evaluated with current interrupters to determine sod/pipeline potentials. The for analyses were points over old pipeline and 8 more for the new one. These values are shown in denoted for positions with va]ues than -0.850 V, ID criteria for steel structures. values are basicaUy for the terminal 1, whích has the poorest coating mainly the of TABLE IV.

EVALUATlON

8

Since we could not find any the ground conditions allow fuel pipelines. This would allow the the whole set structures.

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induced here it is important to notice that -100m V criteria with no detriment on the security of the jet system with less expenses and keeping the corrosion control for

it is important to notice that the ground conditions allow on security of jet pipelines. would allow and keeping the corrosion control for the whole set of structures.

LU,lL'>¡ULl

CONCLUSIONS CP system was a hybrid design so that the pipeline transporting jet fuel into the hydrant pits Terminal withín the sandwiched deck structure, could have a continuous anode configuratíon, and protected by a remote ano de the rest of the jet fuel pipeline network would complexity of the jet fuel pipeline to combination of a very old poorly the new coated as well as the to the hydrants, obliged a the compliance to the 100m V criterion of NACE 2002. We report the construction hybrid system. FuI! coverage of the pipeline and hydrant branches was achieved. tests during the commissioning provided valuable Mexico including mapping the CP current distribution in the complexity airport employing a clamp ammeter. configurations and systems for both; the continuous anode, and for the use the ground beds allow establíshíng a along period of 30 years. Thís was equivalent conditions are "'-'1\A.. C.... U

fue! pipeline in anti-sinkíng deck, where an current system, based on the use of three of the jet pipelines at least for a In cases where can be

Beyond our most test stations a polarizatíon potential complying with the standard mV criterion. Natural potentials -500 mV; at point where the potentíal read was mV, natural potential Then, we can conclude that the hybrid was applied successfully, and can applied directly to this jet fue! pipeline project provided a sound protection for the corrosíon control hybrid system helping for compliance of the current major airport in Mexico.

ACKNOWLEDGMENTS are grateful to Aeropuertos y Servicios for the valuable support while performíng ano de field work. We specíally thank Tom Lewís his valuable advice in of Joseph Tatum IlI. also thank the technical support as well as the of Arturo Godoy, Gonzalez, Maura Miguel Lobato and Osvaldo Flores; as well as

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3.

4.

5.

6.

D. protectíon of fuel pipelines under difficult conditions at a commercial airport." Mat. 43 (2004): p 24.

Obrecht, M. W. E. "Ongoing Cathodic Protection Operations at Ohare Airport." Mal. 13 (1974): p 17.

R. C. "A reyiew of soil resistiyity measurements for grounding, corrosion assessment, and cathodic protection". Mat. 41, 1 (2002): p. 28.

3 (1999): PBD. K. "The 1OO-m V potentíal decay cathodic protectíon cnteríon". Corros ion J. "Cathodic critería and its to mature Mal. Perf. 39 (4): 26-29 APR 2000 r. "Cathodic protection with sacrificíal auu'",,",,, . Corro Rey. 3-4 (2006): p. 231

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