Nace2008 08024 coatings mexico

COATINGS STRATEGY FOR FUEL STORAGE AND ENERGY FACILITIES IN MEXICO

L. M. Martinez de la Escalera* and M. Paredes Corrosion y Proteccion Ingenieria, S.C. Rio Nazas 6.

Cuernavaca, Morelos. Mexico. 62290.

A. Rios Aeropuertos y Servicios Auxiliares Avenida 602 No. 161.

México, Distrito Federal. Mexico. 62290.

J. A. Padilla López-Méndez Soluciones Para Mantenimiento, C.A. Av. 119, Torre Ejecutiva, Ofic. 10-4, Valles de Camoruco Valencia, Venezuela.

J. Genesca Facultad de Quimica, Universidad Nacional Autonoma de Mexico Edificio D, Circuito Exterior, México, Distrito Federal, CP 04500.

J. A. Ascencio and L. Martinez-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 Ingenieria, Universidad Autonoma del Estado de Morelos.

Avenida Universidad 1001, Colonia Chamilpa Cuernavaca, Morelos. 62210, Mexico.

ABSTRACT We report results of one-year field experience in monitoring atmospheric corrosion and developing field work of corrosion damages to assess the performance of the coatings that are currently used for the protection of tanks and structures in an industrial facility and four jet fuel storage stations. For this work, we selected sites located at representative climatic conditions of the Mexican territory. The sites included the industrial port of Altamira and the City of Villahermosa, near the coast of the north and southeast Gulf of Mexico, respectively; the city of Tapachula at the coast of the Pacific Ocean; and the inland cities of Mexicali, an extreme hot, dry and sunny location, and Guadalajara, a humid tempered city. Atmospheric conditions at the Gulf of Mexico were found to be very corrosive due to humidity, salinity and chemicals from industrial activity. An analysis of the coating systems and surface preparation that are currently used, as well as of historic records of the plant equipments revealed opportunities to improve the coating systems performance in the future. Modern coating systems and practices were discussed, benchmarked and a final selection was recommended, according to the atmospheric environments in the regions.

Keywords: Coatings, surface preparation, atmospheric corrosion, Gulf of Mexico, zinc epoxy, polyamide epoxy, polyurethane acrylic, siloxane epoxy.

INTRODUCTION It is well known that structural materials presently used in many of the locations have severely reduced serviceable life times, because of climate related variables. Atmospheric corrosion is a well known function of airborne components exhibiting significant variation in urban, arid and marine environments. This is especially true in developing regions in Mexico, along the Caribbean coastline and around the Gulf of MĂŠxico where industry and urban expansion are exposing building materials to prolonged humid, marine environments, as well as to high concentrations of industrial pollutants.1-7 The ratio of marine perimeter to land area is singularly large in the geography of Mexico. This singular geographic pattern contributes to the diversity of atmospheric conditions such as temperature, humidity, and salinity found presently in Mexico. The industrial activity is also diverse in the Mexican regions, and contributes to the atmospheric corrosion variability. The characterization of atmospheric corrosion in Mexico has been carried out in the past by a group of authors.5, 8. Previous work in the field has been reported and some regions were characterized by regional atmospheres in Mexico long term studies. The ISO 9223 standard has been used to perform a classification in several locations in Mexico5. C4 and C5 types of regions have been found, and in some marine and heavily polluted zones have led to the suggestion of incorporating a C6 level to the ISO standard to characterize the case of some extremely corrosive atmospheres found in Mexico5.

The present work was motivated by the needs to develop more successful strategies for the protection of structures from atmospheric corrosion. Modern coating systems are in great need in order to apply programs where performance and durability are improved. In this paper we comprise a set of case studies of industrial facilities where there was a need of a new strategy for coatings for corrosion control. Among the cases studied was a new two year old energy industrial facility in the Port of Altamira in the Mexican northern part of the Gulf of Mexico. Severe corrosion of atmospheric origin was found in several components of the plant including the electrical substation and towers, stairs and other metallic components of the combined cycle plant. Jet fuel storage tank farms were also studied in a variety of locations according the geographical and environmental conditions representing the Mexican national climates. These include the airport in Tapachula, in Chiapas at the Pacific southeast of Mexico, the airport in Villahermosa at the south Gulf of Mexico, the airport of Guadalajara

inland central Mexico, and the airport of Mexicali located in the driest and extreme hot, cold and dry climate.

Frequent and unsuccessful previous coatings practices for the corrosion protection of tanks and other accessories of jet fuel storage facilities motivated the presently reported work. The final outcome of these studies was the classification of the atmospheric corrosion types in every location, and several systems of coatings designs appropriate for each type of climate.1-6 FIELD PROCEDURES From the basic meteorological climate parameters (Koeppen’s climate classification),7-8 the four main climatic zones in Mexico are shown in Figure1a, along with the location of the area in which atmospheric exposure sites are located. The climate of the Gulf of México is known as tropical humid, having a mean annual relative humidity greater than 75% and mean precipitation greater than about 1500 mm/yr.

Mexicali

a Mexico City Altamira Port Villahermosa

Guadalajara Tapachula

Figure 1. a) Koeppen’s climate classification of Mexico and The mean annual temperature is greater than 26°C which is about the same temperature as the Gulf waters in this region. The shoreline region surrounding the Gulf of México has been the location of significant economic development with the building of structures, ranging from industrial sites such as refineries and petrochemical processing plants, to homes and schools, and infrastructures including roads and bridges.

General Methodology In order to assess the atmospheric corrosion of the different environments around Mexico, 5 places were evaluated: Tapachula, Villahermosa, Guadalajara, Altamira, and Mexicali. The variables considered for classifying the different environments where as follows: (a) industrial or non industrial area; (b) closeness to the coast; and (c) weather parameters such as relative humidity, dew point, and average temperature.

Evaluation of critical conditions in the Port of Altamira In this work we report field work developed under two different approaches. One was applied to the investigation in the industrial port in Altamira, where a set of steel plates over threaded bolt monitors of atmospheric corrosion evaluation was performed at an electric power plant. Chloride deposition on plant structural components was also performed, as well as the recompilation of atmospheric meteorological parameters relevant to corrosion.

In the Port of Altamira, four exposure sites were located within 1 km of the Gulf shorelines, where it could be anticipated that the atmospheric marine corrosion in this tropical region will be high and due mainly to large amounts of chlorides and high time-of-wetness. However, it could also be anticipated that the chloride concentrations at different regions along the Gulf shoreline will vary as a result of different predominant wind directions, and therefore different site corrosivity classifications will result from geographical influences even though proximities to the shoreline are similar. In order to correlate the Mexican corrosivity data with other international studies, the standard exposure and environmental monitoring techniques and parameters measured were compared in the framework of the ISO standards.9 The plate test materials were 0.10 m x 0.15 m rectangular coupons of thickness 0.003 m for carbon steel SAE 1014. Samples were exposed between 1 and 1.5 m above the ground on insulated racks angled at 45o. The coupons faced the water in marine environments and north in non-coastal locations in accordance with the general requirements for field testing, ISO 8565.9 Following exposure the corrosion products were chemically removed from the coupons in order to determine weight loss according to ISO DIS 8467.9 Average mass loss was determined from triplicate coupons exposed for three, six, nine and twelve months.

Evaluation of jet fuel tank farms in four airport locations.

b

4

4

A different approach was performed for the evaluation of the atmospheric corrosion conditions in a set of four airport jet fuel farm tanks of airports distributed in representative climates of Mexico, where the evaluation included chlorides, nitrates and pH measurements on the surfaces, the atmospheric meteorological parameters as well as a direct evaluation of the performance of the coatings. We performed chemical surface tests in 4 representative areas of the evaluated jet fuel tank farms. The chemical tests included presence of nitrates, chlorides and pH of the coated structures. Since the airports are official sites of the Mexican National Meteorological System, we could use the database at each location including average relative humidity, and temperature.

After evaluating the different variables as well as the chemical tests on the coated structures we were able to classify the corrosive environments as coastal/marine, urban, and desert (Figure 1b). This classification applies for all fuel plants of Mexico’s airports.

4

4

TIJ MXL CJS

4

NOG

CEN

4

4

CUU

4

4

REX

URBAN DESERT COAST / MARINE

4

MAM

4

4

CUL PA

4

CPE

4

4

4

4 4

TGZ

COP

TGM

4

4

4

LMB IZT PXM HUX

CTM

VSA

4

MTT

4

4

ACA

OAX

CME

CMZ

4

4

4

PAZ

4 4 4 4 4

ZIH

CUN

MID

TLCMEX VER PVC CVA TCN

4

4

UPN

4

4

4

4

QET

MLM

4

4

GDL ZLO

TAM

4 4 4

BJX

PVR

COL

SLP TMN

4

AGU

4

TNY

4

ZCL

4

4

CVM

4

DUR MZT

4 4 4

SJD

MTY

TRC

4

4

LAP

4

4

4

4

4

LMM

4

NLD

GYM LTO

4 4

4

4

HMO

TAP

Figure 1b) main different environments found for the considered installations.

Results The electric power plant of Altamira was included in the present study because the reported high corrosion damage during its early years in service, and because the results would provide important learning of the marine corrosion in the northern parts of the Gulf of Mexico. Consequently we focused on this site for the analysis of corrosion rates, which could refer to the perspectives of corrosion in the plant, obtaining values during a year period. Four different test sites were selected, where corrosion rates measured values between 43 and 58 microns per year (Table 1), which denote the presence of corrosion agents but in a relatively controlled region.

TABLE 1 MEASURED VALUES FOR CORROSION RATES IN THE PORT OF ALTAMIRA CORROSION RATES IN THE PORT OF ALTAMIRA TEST SITE

STEEL COUPONS, microns/year

ISO 9223 SCALE

1

58

C4

2

44

C3

3

43

C3

4

45

C3

In fact, the monthly analysis of these sites allows recognizing a stabilization process, with a high value for the bare test material, and constant values after the third month, matching form this month up to the annual measured average. This is most likely associated with the presence of the oxide layer over the surface of the carbon steel test material.

Even when this behavior can be generalized to similar conditions, we evaluated four more sites in order to clarify the effects of the temperature and humidity over the presence of corrosive agents in the atmosphere of each environment (Table 2). Even when it can be considered not as critical the conditions for the selected sites for the airport fuel farm tanks, it can be observed that certainly the Altamira environment shows a value of 14 Âľg/cm2 for chlorides, much higher than the other sites; for nitrates, Tapachula and Mexicali are higher than the Altamira measured data (10, 7 and 5 ppm respectively). These parameters, besides the high temperatures for most of the sites allow determining the wide region of parameters that the studied installations in Mexico involved. Besides the relative humidity is clearly the highest for Altamira and the lowest for Mexicali, then the coating selection has to consider these specific conditions. However it can be established that the chemical tests performed in the three fuel plants did not reveal an aggressive concentration of nitrates, chlorides, or neither an acidic or basic pH that could represent risks for the application or performance of the actual coating system.

Corrosion rate, m icrons/year

120.00 100.00 80.00

Site 1 Site 2

60.00

Site 3

40.00

site 4

20.00 0.00 1

2

3

4

Time, three months period

Figure 2. Corrosion rate of carbon steel coupons as a function of exposure time

TABLE 2.

CHEMICAL AND METEOROLOGICAL ANALYSIS FOR THE DIFFERENT EVALUATED SITES CHEMICAL ANALYSIS AND METEOROLOGICAL PARAMETERS OF ATMOSPHERES AVERAGES Site

Chorides (Âľg/cm2)

Nitrates p (ppm) H

Altamira

14

5

Tapachula

4

10

Villahermosa

2

2

Guadalajara

--

4

Mexicali

--

7

6 6, 1 6, 8 6, 7 6, 5

Temp. o C

Relative humidity, %

33

82

30

74

33

59

27

51

36

32

Evaluation of coating systems in the field.

Under a technical evaluation, we can identify several common problems with the coating systems, which are reported in a general view to establish the parameters for better and conclusive recommendations. The evaluated installations show coating systems based on a very thin red alkyd primer and one or two coats of a topcoat based on coumarone indene resin with leafing alluminum as the topcoat. The system thickness ranged from 6.6 to 22.9 mils. In many instances, there was no evidence of the presence of the red alkyd primer.

There are several problems in the coating system. The most common problems found were generalized corrosion in structure walls, joints between ladders and structures, presence of corrosion in non regular welded joints, corrosion in confined spaces such as valves, stairs, tank access doors, vent valves. There was also corrosion in supports of pipelines connecting tanks, corrosion as a result of welding splatter, and corrosion in fabrication defects and structure irregularities.

Poor adhesion of the coating system is also a recurrent problem. This problem is caused by poor surface preparation before the coating application. Adhesion destructive tests were performed in order to evaluate the existence or nonexistence of surface preparation. No surface preparation (i.e., surface profile or anchor pattern) was observed on none of the structures of the fuel plants evaluated.

During the survey, historic information of the coating systems was required from the airport fuel plants, but no records were available to determine the existence of a coating specification or if a coating inspector was able to evaluate the existing coating system application.

The main problem for the evaluated coating systems involved chalking and cracking as can be observed in the examples of Figure 3. Chalking is the formation of fine powder on the surface of the paint film due to weathering. Chalking can cause color fading. All paints chalk to some degree, it is a normal, desirable way for the paint film to wear away and provide a good surface for future repainting. Generally, alkyd paints chalk more quickly and to a greater degree than acrylic latex coatings. Medium and heavy chalking will cause tinted paint to lose its color and become lighter. Severe chalking makes repainting a problem because the extreme porosity of the surface powder will adversely affect adhesion and does not provide a sound surface the paint to bond to.

This is particularly true with water based paints which tend not to penetrate and therefore will bond only to the surface powder as it can be observed in Figure 3a. Quality paints may chalk mildly, but still maintain a sound surface that will not crack and retains good moisture and weather resistance for many years.

a

b

c

d

Figure 3. Main problems of evaluated coating systems. a) Chalking and leafing resulting from coating exposition to the UV light. Alkyd coatings tend to chalk and lose film thickness while they are exposed to the sun. b-d) Cracking evidences with different levels of severity.

One reason cracking occurs is when the topcoat of a paint system is unable to expand to the same degree as the previous coating. This occurs commonly when an undercoat has not been given sufficient time to dry, or indeed if a paint is encouraged to dry too quickly, for example by increasing the temperature in a room or if decorating exterior surfaces in excessive heat. Cracking will also occur if wallpaper adhesive is allowed to dry on new paintwork (Figure 3b). Different grades of cracking can be identified, from a few evidences (Figure 3c) to the whole lost of material (Figure 3d), and the consequences must be clearly associated to the level of the problem.

Evidences denote that corrosion was enhanced by abrasion processes and by poor surface preparation found in the evaluated plants, as it is illustrated in Figures 4 and 5. Corrosion on stairs and supports caused by coating failure assisted by abrasion produced physical damage. Alkyd and coumarone indene coatings systems have poor abrasion resistance and consequently this problem can be associated to the type of selected coating.

Because abrasion resistance is defined as the ability of a material to withstand mechanical action such as rubbing, scraping, or erosion, this tends progressively to remove material from its surface. Such ability helps to maintain the material's original appearance and structure. The evidences allows recognizing that the corrosion by abrasion is clearly present in regions where metal is plenty exposed after a mechanical process of degradation in zones with high use, such as stairs (Figure 4a) and supporting structures (Figure 4b), where mechanical contact induces to lose the coating material.

a

b

Figure 4. Coating failure in stairs and supports due to abrasion. Exposed metal surface in the environment creates general corrosion and localized as well as generalized metal loss.

Finally the foundation of any coating system is the surface preparation. It is the most important factor in developing a successful coating system. The purpose of surface preparation is to remove all contaminants that can interfere with adhesion and to develop a surface roughness to promote mechanical bond. Destructive tests as well as nondestructive tests were performed at the jet fuel tank farms of four Mexican airports. In none of the tanks or aboveground pipelines a surface preparation was found. There was no anchoring profile or available documented information that could prove that the applied system was applied after a surface preparation. Also, there was no available specification of the applied system that could show that a surface preparation was recommended. Evidences shown in Figure 5 determined the surface was poorly prepared, when the coating was being applied, inducing an early degradation of the coating system and the metal substrate.

Figure 5. The steel surface under the applied coating system did not have adequate surface preparation, no anchoring profile was found. Coating system did not show good adhesion to the surface.

CONCLUSIONS The present work has been useful for the development of a new strategy of coatings for jet fuel tank farms and other industrial facilities based on field studies of atmospheric corrosion, as well as coating performance, specifications and application procedures considering a set of locations representative of the Mexican territory.

The general analysis involved multiple common problems that were summarized, and they allow identifying possible sources of problems. The conclusions are associated with requirement of a deeper knowledge of the sites, environment, which even though they are not considered critical corrosive, show particular conditions and the adequate coating system must consider them. We have found an important potential of improvement in the protection of metallic structures exposed to the atmosphere by evolving from a practice based mostly on standard alkyd and coumarone indene coating systems, and application procedures involving almost no surface preparation.

Recommended solutions.

Several coatings systems were proposed for discussing the best alternatives for corrosion control of the structures in the analyzed regions. Cost, durability and availability were among the criteria used for the selection. Alternative primers selected included: organic zinc epoxy, epoxy surface tolerant, and epoxy primer.

Epoxy polyamide, epoxy siloxane and epoxy polyamide HB were selected as alternative second layers or intermediate coats. Acrylic aliphatic polyurethane and aluminum epoxy were selected for alternate finish coats.

An organic zinc epoxy primer, a polyamide epoxy intermediate coat followed by an acrylic aliphatic polyurethane finish coat with a thickness of 2 to 3 mils was seen as an economic as well as durable option for both the marine and urban types of environment. In this case the surface preparation alternative was dry abrasive blast or water blast to near white metal grade.

For the dry, sunny and very hot region of Mexicali a two layer system consisting of organic zinc epoxy as a primer, followed by a 5 to 7 mils DFT of siloxirane epoxy was recommended, with a surface preparation similar to the considered in the previous mentioned case.

ACKNOWLEDGMENTS We are grateful to Aeropuertos y Servicios Auxiliares in Mexico City, Guadalajara, Tapachula, Villahermosa and Mexicali and to the Port of Altamira for the help in performing the field work. We also thank the technical support of Anselmo Gonzalez, Maura Casales, Vianey Torres and Osvaldo Flores in sample preparation and laboratory work; as well as Evelia Sandoval in project management.

REFERENCES 1. Lichtenstein, J. “Good specifications - The foundation of a successful coating job”, Mat. Perf. 40 (2001): p.

46.

2. Sedriks, A.J., Dudt, P.J. “Corrosion resistance, coating, and magnetic property issues of nonmagnetic austenitic stainless steels for ship hulls”. Corrosion 57 (2001): p. 84.

3. Martinez, L. “Unusually high lead and chrome contents of paints in Mexico”. Mat. Techn. 15 (2000): p. 80.

4. Torres-Mendoza, V., Rodriguez-Gomez, F.J., Garcia-Ochoa, E.M., Genesca, J. The assessment of natural atmosphere corrosivity by the use of electrochemical noise analysis. Anti.Corr. Met. Mat. 53 (2003); p. 231.

5. Munoz, S., Avila, J., Genesca, J. “Atmospheric corrosion in Mexico-City.” Abs. Pap. Am. Chem. Soc. 195 (1998): p. 254.

6. Garcia-Ochoa, E., Ramirez, R., Torres, V., Rodriguez, F.J., Genesca, J. “Comparison of electrochemical noise and wire-on-screw technique in simulated marine atmospheres” Corrosion 58 (2002): 756.

7. Roberge, P.R., Klassen, R.D., Haberecht, P. W. “Atmospheric corrosivity modeling - a review.” Mat. Des. 23 (2002): p. 321.

8. Castro, P. “The atmospheric corrosion performance of reinforced concrete in the peninsula of Yucatan, Mexico. A review.” Corrosion Rev. 17 (2002): p. 165.

9. International Standard, “Corrosion of Metals and Alloys-Corrosivity of Atmospheres Clasification, ISO 9223: 1992”. International Standard Oganization, Geneva, 1992.