Hybrid CP I System for an Airport Jet Fuel Pipeline L.M. Martinez-de la Escalera and J. Canto, Corrosion y Proteccion Ingeneria, Cuernavaca, Morelos, Mexico A. Rios, Aeropuertos y Servicios Auxiliares, Distrito Federal, Mexico H. Carrillo Calvet, Proteccion y Corrosion S.A., Cuernavaca, Morelos, Mexico H.C. Albaya, Sistemas de Protección Catódica S.A. Tronador, Buenos Aires, Argentina J.A. Ascencio and L. Martínez-Gomez, Instituto de Ciencias Físicas, Universidad Nacional Autonoma de Mexico, Morelos, Mexico
The Mexico City International Airport underwent a major expansion that included a new jet fuel pipeline. The new terminal was built on concrete decks above wet clay soils. Much of the new jet fuel pipeline was located within this structure. The cathodic protection system comprises a continuous galvanic anode configuration and a remote, deep, three-anode array.
ncreasing needs at the Mexico City International Airport (MCIA) led to the construction of a new terminal and the modernization and expansion of the original one. A new jet fuel pipeline and hydrants now provide a supply of over 3.5 million L/day. The airport is located in the former Lake of Texcoco. The high saline content of the clays is directly related to the very low resistivity (300 to 600 Ω{cm) and high corrosiveness of the soil. This article describes the design and installation of the cathodic protection (CP) system for the new jet fuel pipeline. Several particularities made this CP project interesting and challenging. Two generations of materials, pipeline steels, coating types, and conditions, as well as construction techniques, were involved in the final jet fuel configuration and had to be addressed in the CP design.1-2 Also, security issues established a fixed framework for the CP design work. No power devices were to be installed inside the terminal areas; rectifiers could be installed only in the tank farm. In the terminal fields, all connections had to be housed in flame-proof boxes and only underground test stations were allowed. There were many casings on the pipeline, which, in the long term, may not remain isolated. We originally targeted this CP system for the –100 mV criterion,3-5 but test results showed the system worked well using the polarized potential of 0.850 V to copper/copper sulfate (Cu/ CuSO4) electrode (CSE).
Site and Conditions Piping, Cathodic Protection, and Soil Factors The jet fuel pipeline consists of two networks. One was constructed ~25 years ago using API B2 type steel and coal tar coating to fuel ~40 hydrants existing before the expansion project. An API
2 MATERIALS PERFORMANCE August 2009 Ascencio.indd 2
6/29/09 12:30 PM
C AT H O D I C P R O T E C T I O N
FIGURE 1
X65 steel and fusion-bonded epoxy (FBE)-coated new pipeline was constructed to fuel the new Terminal 2, and a portion of the old pipeline went into Terminal 1. Figure 1 shows the runways (marked with red arrows), the services area, the older terminal, and the new one (marked as A, B, and C, respectively). The jet fuel pipeline network consists of three pipeline segments. Segment A is 25 years old, 18 in (0.46 m) in diameter, coal tar-coated B2 type of steel (green), to be decommissioned, but still electrically connected to Segment B. Segment B consists of a similar 25-year-old coal tarcoated B2 type of steel (blue), which feeds the set of hydrants of Terminal 1 (isolation joints are used and shown as orange circles). The largest is the new pipeline segment (magenta), which is 14 in (0.36 m) in diameter, is coated with a threelayered system of FBE, polyolefin adhesive, and polyvinyl chloride (PVC). This segment connects to Segment B through an isolating joint and has another isolating joint at the entrance to the tank farm. Segments A and B also have isolation joints at the tank farm. The current demand for the older pipeline (including the decommissioned one) was measured at 60 A by field tests; theoretical current demand calculations (described in Table 1) show that the current requirement to achieve acceptable CP potentials would be ~46 A. The difference between the 60 and 47 A can be explained as a consumption of CP system current due to pipeline electrical contact with fittings and foreign undetected structures. Three deep anode beds were designed and are identified by red circles in Area A (Figure 1). Each anode bed can produce 50 A; two of them are for the old pipelines and the third one is for the new pipeline. The terrain of the old lake bed is of very low shear strength, particularly in the zone of the last section of the jet fuel
Scheme of MCIA with the different jet fuel pipelines. Orange arrows show the points for pipeline isolation, the red ones correspond to the runways, and deep anode beds are illustrated with red circles. The yellow rectangle outlines the anti-sinking platform area.
pipeline, marked with the yellow rectangle on Figure 1. The soil is typically clay saturated with water, and it produces the imminent risk of sinking. It was necessary, therefore, to design complex and hybrid solutions to reduce the sinking risks and to apply CP to the jet fuel pipelines.
the Mexican airport authority, to select a design for the new terminal taxi ways using a tailored construction methodology based on concrete decks above the wet clay soil. Structures are prone to sink with time in this type of soil; therefore, the decks were made of a low enough density to remain above the wet clay soil, but with high enough rigidity to support Anti-Sinking Platform the aircraft traffic of Terminal 2. The strategy to maximize the space The construction selected was a sandutilization in the current location led wich with three layers—two steel-reinAeropuertos y Servicios Auxiliares (ASA), forced concrete slabs with the in-between August 2009 MATERIALS PERFORMANCE 3
Ascencio.indd 3
6/29/09 12:30 PM
Hybrid CP System for an Airport Jet Fuel Pipeline
C AT H O D I C P R O T E C T I O N
table 1 Current demand values and parameters to consider Mexico City International Airport Jet Fuel Pipeline Current Demand
Description
Diameter (in)
Length (m)
Area (m2)
Coating Efficiency (%)
Current Demand (A/m2)
Actual Current Demand (A)
New pipeline natural ground
18.00
7,230
10,384.4
95
0.02
10.4
New pipeline sandwich area (Terminal 2)
18.00
3,724
5,348.8
95
0.02
5.3
Hydrant pipeline branches (Terminal 2)
6.00
797
381.6
95
0.02
0.4
Old pipeline (Terminal 1)
18.00
6,635
9,529.8
80
0.02
38.1
Old decommissioned pipeline (Terminal 1)
18.00
1,232
1,769.5
80
0.02
7.1
Old pipeline hydrant branches (Terminal 1)
6.00
488
233.6
80
0.02
0.9
Copper-coated groundrods
0.75
300
18.0
0
1.1
Total current demand
3.9 62.2
the first stage was the collocation of the steel-reinforced concrete, the Tezontle fill, and the sand bed for the pipeline. The final slab of reinforced concrete with an asphalt surface lies above the tezontle. Figure 2(c) also shows the space between the concrete layers and the pipeline (to be filled with tezontle and sand), which provides mechanical protection for the pipe supports.
FIGURE 2
Cathodic Protection Current Demand
Anti-sinking platform for Terminal 2. (a) longitudinal, (b) transverse view, and (c) photograph of the building process.
space filled with tezontle particulate, a very porous and light volcanic material, 2 to 4 in (51 to 102 mm) in diameter. Figures 2(a) through (c) illustrate the construction scheme. An asphalt cover on the upper concrete deck spreads the stress distribution and pressure over a wide area, where aircraft circulate and park at the passenger gates. The density of tezontle allows filling high volumes with
a relatively low weight. The lower density of the whole structure prevents it from sinking in the wet clay of the former lake. The jet fuel pipeline was located within the tezontle layer in a trench of sand. The three-layer structure contacts the wet clay soils at intervals, so the CP design included a solution for the pipeline in the middle of this structure. Figure 2(c) shows the construction process, denoting how
About 25% of the new jet fuel pipeline and hydrants are built inside the sandwich structure, which may act as an isolating cavity to the electrical field of an impressed current CP (ICCP) system. The rest of the pipeline and the hydrants of Terminal 2 are buried in natural soil where a remote bed ICCP system is indicated. The corrosion control system design considered these two different conditions. Consequently, remote and distributed anode beds, and sacrificial and IC anode beds were designed. Table 1 shows the current demand calculations. It is necessary to protect ~15,558 m of pipelines in natural ground. The segments that are inside the antisinking platform are 3,724 m of jet fuel pipeline and 797 m of associated connections and hydrants. We estimated the old
4 MATERIALS PERFORMANCE August 2009 Ascencio.indd 4
6/29/09 12:30 PM
C AT H O D I C P R O T E C T I O N
FIGURE 3
pipelines in the natural ground would have a coating efficiency of 80%, while the new pipelines in natural ground and inside the deck would show a value of 95% plus the hydrant connection branches. In this way, the exposed metal, having a unit demand of 0.020 A/m2, would have a given theoretical current demand. The total calculated current demand is 62 A (Table 1). The installed capacity for the CP system including IC and galvanic systems would be ~150 A. The proposed solution involved a hybrid system, utilizing ICCP with remote ground beds for the pipelines in natural ground, and galvanic anode CP for the pipeline that is inside the antisinking platform. The galvanic CP was designed to cathodically protect the pipeline when seasonal resistivity changes take Scheme of (a) three groundbed systems and (b) each anode configuration. place and also to have backup protection if a probable current blockage (shielding) from the IC system occurred in the space FIGURE 4 between the two connected decks.
Impressed Current Cathodic Protection System A set of three deep anode groundbeds were located in the tank farm area (Figure 3). That location made it possible to excavate and also to control, maintain, and operate the CP with no major logistical complications. The deep anode beds were located in soil of low resistivity and high humidity. The three deep anode beds are located 20 m apart, drilled to a depth of 100 m with an active zone of 35 m. The selected anodes were mixed metal oxide over titanium tubes, while the active column is embedded in low-resistivity carbon coke. The IC part of the CP system was targeted to provide corrosion protection to the jet fuel pipeline seg- Localization of Mg sacrificial anode beside the platform. ments buried in soil.
Galvanic Anode Cathodic Protection System
jet fuel pipeline is located within the sandwiched, water structured deck. The A galvanic anode was required in the water level in the former Lake of Texsandwich area. About 25% of the new coco reaches ground level most of the
year, especially in the rainy season that lasts about seven months. Water leakage into the sandwiched deck structure was considered unavoidable. The proposed August 2009  MATERIALS PERFORMANCE  5
Ascencio.indd 5
6/29/09 12:30 PM
C AT H O D I C P R O T E C T I O N
Hybrid CP System for an Airport Jet Fuel Pipeline
table 2 Evaluation of pipe/soil polarization potentials for positions in both terminals vs. CSE Terminal 1
Terminal 2
Position
Potential On (V)
Potential Off (V)
Position
Potential On (V)
Potential Off (V)
Tank farm
–2,060
–1,160
14
–2,040
–1,140
1
–1,800
–1,140
15
–1,923
–1,120
2
–1,800
–1,130
16
–1,700
–1,100
3
–1,790
–1,110
17
–1,826
–1,040
4
–2,400
–1,090
18
–1,840
–1,120
5
–2,870
–1,130
19
–1,200
–0,890
6
–2,220
–1,136
20
–1,340
–0,920
7
–1,460
–1,120
21
–1,310
–0,904
8
–1,456
–1,110
22
–1,170
–0,900
9
–1,550
–1,120
23
–1,120
–0,904
10
–1,100
–1,000
24
–1,120
–0,870
11
–1,382
–1,100
25
–1,170
–0,845
12
–1,259
–1,000
26
–0,985
–0,860
13
–0,940
–0,880
solution for the protection of the jet fuel pipelines and hydrants inside the antisinking platform was the use of a magnesium continuous ribbon anode following the same trajectory as the pipe at a distance short enough to present the effects of a distributed galvanic anode system. The ribbon anode is connected to the pipeline at 20 points to minimize IR drop from CP current in the core wire of the ribbon. This also permits appropriate behavior of the magnesium ribbon under the high gradients of humidity that occur in the sand. Figure 4 shows the placement of the anode and the sand backfill. The weight required for the magnesium anode was calculated for the worst-case scenario, where 5.3 A are required to protect the jet fuel pipeline. Considering a consumption rate of 18 kg/A-y, it was derived that the minimal weight requirement of Mg is 1,344 kg. The anode ribbon size is 0.0912-m wide and 0.36-kg/m linear density, and because the jet fuel pipeline length is 4 km (sacrificial anode is parallel and will have similar length), the total amount of mass is >1,440 kg, covering the established requirements.
Results The effects of this designed CP hybrid system were evaluated with current interrupters to determine the on-off soil/ pipeline potentials. The sites for the analyses were selected considering eight points over the old pipeline and eight more for the new one (Table 2). The criterion used is –0.850 V polarized to CSE. Field measurements showed that during the rainy season, the ICCP system would have influence over the whole pipeline, including the anti-sinking platform, as it can be observed from the sandwich area measurements (positions 22 to 26).
Conclusions The CP system was a hybrid design so that the pipeline transporting jet fuel into the hydrant pits of Terminal 2, within the sandwiched deck structure, could have a galvanic anode configuration, and the rest of the jet fuel pipeline network would be protected by a remote deep threeanode CP array. This hybrid system can be used in future cases where similar conditions are found. Most of the test stations read a polarization potential complying with the standard –850 mV
criterion. Natural potentials ranged between –500 and 625 mV; from Table 2, one can conclude that the hybrid system is applied successfully. References 1 D. Klotz, “Cathodic Protection of Fuel Pipelines Under Difficult Conditions at a Commercial Airport,” MP 43 (2004): p. 24. 2 M.F. Obrecht, W.E. Downes, “Ongoing Cathodic Protection Operations at Chicago Ohare International Airport,” MP 13, 6 (1974): p. 17. 3 R.C. Benson, “A Review of Soil Resistivity Measurements for Grounding, Corrosion Assessment, and Cathodic Protection,” MP 41, 1 (2002): p. 28. 4 G.K. Glass, “The 100-mV Potential Decay Cathodic Protection Criterion,” Corrosion 55, 3 (1999). 5 J. Didas, “Cathodic Protection Criteria and its Application to Mature Pipelines,” MP 39, 4 (2000): pp. 26-29. 6 S. Szabo, I. Bakos, “Cathodic Protection with Sacrificial Anodes,” Corr. Rev. 24, 3-4 (2006): p. 231. Lorenzo M. Martínez de la Escalera is the executive director of Corrosion y Proteccion Ingenieria, Rio Nazas #6 Col. Vista Hermosa, Cuernavaca, Morelos, 62290, Mexico, e-mail: lmm@corrosionyproteccion.com. His engineering
6 MATERIALS PERFORMANCE August 2009 Ascencio.indd 6
6/29/09 12:30 PM
C AT H O D I C P R O T E C T I O N
experience includes designing, installing, and surveying CP systems for 25 Mexican airports and 3,000 km of PEMEX rights-of-way (ROW). He has a bachelors degree in finance, and an M.S. degree and Ph.D. in materials technology. He is a NACE-certified CP Technician, Coating Inspector Level 2, and has conducted studies on pipeline integrity management and designing for corrosion control. He is a five-year member of NACE. Jorge Joaquín Cantó is the engineering director at Corrosion y Proteccion Ingenieria, e-mail: canto@corrosionyproteccion.com. During the last four years, Cantó has been involved in a nationwide survey to assess the status of all the corrosion control facilities for Mexico’s state oil company, PEMEX. He is a mechanical engineer and a Ph.D. in material science. He has been a NACE International member since 2006. ALEJANDRO RIOS is director, Fuel Services, at the Aeropuértos y Servicios Auxiliares, Av. 602 No. 161, Col. San Juan de Aragon, DF, 15620, Mexico, e-mail: ariosg@asa.gob.mx. He has worked as director of the Fuels Services division for the last seven years, managing a network of 63 fuel farms that supply close to 10 million L/day through 2,000+ service operations. He has a Ph.D. in civil and environmental engineering from Cornell University (2001). HUMBERTO CARRILLO CALVET is the director of industrial relations at Corrosion y Proteccion Ingenieria and a faculty member at the Universidad Nacional Autonoma de Mexico (UNAM), e-mail: hcc@corrosionyprotection.com. His research interests include scientific modeling, analysis of complex dynamical systems, and mathematical and computational modeling of nonlinear electrochemical processes in natural sciences and engineering. A NACE member and Cathodic Protection Technologist, he has a Ph.D. in mathematics from UNAM, is a National Researcher of Mexico, has been a visiting scholar at the University of Utah, and was a postdoctoral visitor at Brown University. In 1986, he received a Fogarthy Fellowship Award from the National Institute of Health, and is a collaborator of the National Prize of Science 2002 of the Cuban Academy of Sciences. HéctOr César Albaya is with Sistemas de Proteccion Catodica S.A., Tronador 1126, Buenos Aires, Argentina, e-mail: halbaya@fibertel.com.ar. He has been involved in CP design for more than 25 years. He is a NACE CP Specialist and has been a NACE instructor since 2003 for CP Levels 1 through 4. He has been a NACE member for more than 35 years. Jorge A. Ascencio is a researcher at the Instituto de Ciencias Fisicas, Universidad Nacional Autónoma de Mexico, Avenida Universidad s/n, Col. Chamilpa,
Cuernavaca, Morelos, 62210, Mexico, e-mail: ascencio@fis.unam.mx. He specializes in materials science and solutions development, with experience in metals, characterization methods, new materials design, and particularly the application of nanotechnology to multiple fields. He is a member of the Materials Research Society, Mexican Academy of Sciences, and Mexican Academy of Materials Science. He received the Mexico State Award in Science and Technology in 2005. He has a Ph.D. in physical science and materials from UAEM and has a postdoctoral position at the Mexican Petroleum Institute. He has led groups in the National Institute of Nuclear Research and the Mexican Petroleum Institute and is the leader of the materials science group at the UNAM Institute of Physical Science. He is a member of NACE. Lorenzo Martínez-Gomez is a research leader and head of Corrosion Protection at Corrosion y Proteccion Ingenieria S.C. and the Instituto de Ciencias Fisicas, UNAM, e-mail: lmg@ corrosionyproteccion.com. He specializes in materials science, in particular steels and corrosion. He has contributed to solutions for the petroleum industry and several others associated with the use of steel structures. He received the Mexican National Prize of Science and Technology in 1992, received the Latin American Science and Technology Award in 1991, and received a J.S. Guggenheim Fellowship that year. He served as NACE Director of the Latin American Region from 2006 to 2009, was chair of the NACE Mexico Section from 1997 to 1998, and served as secretary of the Latin American Region (1999 to 2001) and chair of the region (2002 to 2006). He served on the NACE Education Committee and is a NACE-certified CP Specialist and Internal Corrosion Technologist. A NACE member, he has delivered numerous presentations at conferences and meetings.
Need reprints of MP ads, articles, or covers? REPRINTS ARE A GREAT INVESTMENT! Professionally printed reprints and photo copied reprints of all MP ads, articles, and covers are available for purchase. Reprints can be customized with your company’s logo, additional product information, or the magazine cover—with no limits on creativity!
Order your reprints today; it simply makes good business sense! For reprint information and rates, call +1 281-228-6219.
August 2009 MATERIALS PERFORMANCE 7
Ascencio.indd 7
6/29/09 12:30 PM