2009 cp survey mp

Pipeline Survey T in Mexico Reveals Need for 100-mV Polarization CP Criterion

he use of the 100-mV polarization criterion was thought to be a sound approach to maximize pipeline operational compliance with the integrity management programs in the Gulf and northern regions of Mexico. By integrating the 100-mV cathodic protection (CP) criterion and its procedures into the algorithms of integrity management and regular CP surveys, the present needs of investments in refurbishing the CP infrastructure may be reduced.1-3 In Southeast Mexico, leaks related to pipeline failures caused over 500 incidents in 2005. Personal losses, injuries, deleterious effects to property and products, and severe damages to the environment occurred. Other than third-party damage, external corrosion was the main cause of these failures.

As a region, Southeast Mexico is a major producer of oil and gas. Of the total Mexican oil and gas production, ~70% comes from Southeast Mexico.

Pipelines transport crude oil and gas from wells to refineries and into final consumption. Altogether more than 20,000 km of active pipelines from 4 to 48-in (102 to 1,219-mm) diameter are installed in over 60 rights of way (ROWs) just in this area (Figure 1[a]).

J. Canto, L.M. Martinez-delaEscalera, H. Rivera, and A. Godoy, Corrosion y Proteccion Ingeneria, CIICAp, Universidad Autonoma del Estado de Morelos, Morelos, Mexico E. Rodriguez Betancourt and C.G. Lopez-Andrade, Petroleos Mexicanos, Distrito Federal, Mexico H.C. Albaya, Sistemas de Protección Catódica, Buenos Aires, Argentina Field Procedures Norberto Pesce, Omnitronic S.A., Mendoza, Argentina This work was undertaken to assess the J.A. Ascencio and L. Martinez-Gomez, current status of CP performance in the Instituto de Ciencias Físicas, Morelos, Mexico northern and Gulf regions of Mexico. It

A survey of over 5,000 km of pipelines was made in 2006 to assess cathodic protection (CP) performance.

Historically, CP surveying has been done by measuring “on” potentials and using the –850-mV criterion. Using the 100-mV potential criterion was the best way to comply with integrity management programs.

employed six mobile CP laboratory units, all equipped with state-of-the-art CP assessment devices including power plants, rectifiers, global positioning systemdriven current interrupters, soil resistivity sets, isolation joint testers, clamp ammeters, several types of half cells, close interval survey (CIS), direct current voltage gradient (DCVG) equipment, pipe locators with Pipeline Current Mapper †

Trade name.

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FIGURE 1

(PCM†) and alternating current voltage gradient (ACVG) technology, ultrasonic and coating gauges, and pipe-sized clamp ammeters up to 48 in. Each team driving in two mobile laboratories was led by a NACE International CP Specialist, working together with a NACE CP 2 field engineer and two corrosion technicians.

The procedure focused on using visual inspection and direct field measurement techniques, searching for electrical isolation, detecting possible interference from other CP systems or dynamic sources, and evaluating the pipeline coatings.

These parameters were evaluated with the help of satellite synchronized current interrupters, up to five along the ROW. From literature and the professional experience of the personnel, assessment focused on the following parameters: • Rectifier performance • Pipe-to-soil (P/S) potential • Isolation • Anode bed performance (surface anodes and deep anodes) • Anode bed remoteness • Coating performance The specialized instrumentation in the mobile laboratories diagnosed the control systems with the highest possible precision and directly evaluated in situ over 5,000 km of ROW, something never done in Mexico by a single work group.

These ROWs are located in the States of Veracruz, Tamaulipas, Nuevo Leon, Coahuila, Durango, Chihuahua, and up to the U.S. border. The evaluated pipeline diameters range from 8 (203 mm) to 48 in; and the transported products are crude oil for the northern refineries, natural and liquefied petroleum gas, gasoline, diesel, and jet fuel for national and international consumption.

(a) A map of the northern and Gulf regions of Mexico shows where the studied ROWs lie. Every test point is marked with red/green points; (b) illustrates the no-compliance values of P/S polarization potential (red squares) and the ones that show potential in normative compliance (green squares); and (c) shows the location of a few rectifiers, identified (RPC), south of Coahuila and near to Gulf of Mexico in Tamaulipas.

different landscapes and weather conditions. Figure 1(b) shows an interesting point of study. The green “R”-marked squares indicate the operating rectifiers (with adequate P/S potentials) and the red squares show areas more positive than –850-mV P/S potentials. This ROW is shared by two 24-in (610-mm) lines that supply oil to the large Cadereyta refinery in Nuevo Leon, and a 12-in (305-mm) refined products pipeline. Rectifiers average an individual output of over 50 A. Two main factors were identified. First, the groundbeds were as close as 10 m to the ROW, and second, both the 12- and 24-in lines have aged, coal tar coating with conductance equivalent to bare steel. Attenuation causes P/S potential values to go more electropositive than –850 mV in <1 km.

Figure 1(c) shows rectifier locations near the Gulf of Mexico.

Results From our field study, the values of the This study covered 5,000 km of 5,205 P/S potential at the evaluated sites ROWs distributed in areas in the Gulf show an almost Gaussian distribution, as and northern regions of Mexico with very is clear in Figure 2(a), which shows the

P/S polarization potential vs. the frequency. This figure shows that most (54%) of the measured values (light gray columns) correspond to potentials with insufficient P/S polarization (based on the Mexican standard for CP) while 39% of the values (from –850 to –1,100 mV) match with the range established as effective for CP (dark grey columns). Finally, 6.4% of the values are evaluated as exceeded potentials (black columns). The potentials (black) are not recommended values, as they could damage the coating and possibly the steel. Most of these (black) cases are not polarized potentials because of the effect of IR drop associated with unidentified sacrificial anodes.

The causes for the CP insufficiency are indicated in the results obtained during the inspection of the CP system components for each ROW. Figure 2(b) shows a summary of the main factors in the studied installations. The dark grey fragment of each bar corresponds to the components working properly at satisfactory P/S polarization potential, and the April 2009 MATERIALS PERFORMANCE 33

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Pipeline Survey in Mexico Reveals Need for 100-mV Polarization CP Criterion

FIGURE 2

Statistical analysis of (a) P/S polarization potential distribution and (b) particular causes of CP failure evaluated during the 5,000-km survey of the main ROWs from the northern and Gulf regions of Mexico.

FIGURE 3

light gray fragment shows the components associated with failure or insufficiency. As previously mentioned, the evaluated components are rectifiers, P/S potentials, isolation joints, anode bed remoteness, test stations, and casings.

It is evident here that there is a direct correlation between the operating conditions of the CP system components and the resulting potential measurements.

Consequently, the CP insufficiency exists when rectifiers are not operating, there are no isolation joints or they fail, there are electrical bonds as shorts between pipelines and foreign structures, the coating systems are defective, or the anode beds have insufficient remoteness. Figure 2(b) shows that the most important problems causing insufficient potential are casings failures, omission of isolation joints, and undesired electrical interconnections.

Figure 3(a) illustrates a pipeline interconnected (shorted) to a compressor station. Figure 3(b) shows a deep anode bed in Monterrey with the vent tube blocked; the tube was apparently used to pump down the backfill. The groundbed resistance exceeded 10 Ω, greatly reducing current output and resultant P/S potentials. Many failures of these installations from construction and design faults have occurred. Figure 3(c) shows an old 36-in (914-mm) line with a coal tar enamel coating that is bonded to a new 12-in line with a fusion-bonded epoxy (FBE) coating. To avoid damage to the FBE coating, the rectifier output was reduced from 100 A to 670 mA, leaving the old 36-in line virtually unprotected. Buried and unidentified bonds were found to be common all along the ROW.

Conclusions Common problems with the isolation of pipelines that cause important local reductions of the P/S polarization potential: (a) absence of isolation, (b) poor deep anode construction technique, and (c) noncontrolled interconnections between poorly coated and well-coated pipelines.

This article reports the unique and innovative experience of performing a CP survey on a large number of pipelines in the northern and Gulf regions of Mexico.

The variety of problems encountered in

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the actual field conditions has provided an enormous amount of information, allowing the work team to identify the main areas of opportunity for the improvement of the CP coverage. Altogether, the problems lead to the fact that more than 50% of the P/S polarized potentials do not comply with the standard –850 mV criterion. The team has identified important areas for the improvement of the CP performance both in operational practices and the improvement of the infrastructure. These are described below.

1) Lack of electrical isolation of the pipelines in the ROWs is a major issue limiting the effectiveness of CP. Isolating pipelines from huge metallic structures such as refineries, gas processing units, and power plants is a high priority to accomplish protective P/S potentials in the ROW. Pipelines must be isolated from metallic bridges and other grounded structures in the thousands of kilometers of the ROWs in Mexico.

2) More CP current output is necessary from the currently installed rectifiers. The present Mexican CP regulations limit the “on” or “off” P/S potentials with the aim of protecting the coatings and minimizing other deleterious hydrogen effects.

Either the “on” potentials at drainage points are to be limited to –2,500 mV or the “off” potentials are limited to –1,100 mV. The conservative application of both limits often causes the rectifiers to operate at very low current output.

Because of considerably high IR drops, the –2,500 mV limit may cause the “off” potential to be significantly less electronegative than –1,100 mV, and current outputs are far below the capacity of the CP systems. Over 95% of the rectifiers found in the field have a capacity of 100 A, and actually were operated

with an output averaging 14 A. The team sees an area of opportunity in raising the average from 14 A output to 50 A per rectifier/anode bed.

3) Many of the lines inspected had no records of CIS, DCVG, or ACVG surveys. Others had records that were up to 10 years old. Very few coating failures were actually repaired. Coating quality is a major component for external corrosion control, and a very good partner in having a successful CP practice.

Coating surveys and repairs should be done on all active pipelines after five years. Inspection during pipeline coating repairs was also found to be lacking when field practices were observed during this survey.

Surface preparation, environmental conditions, coating application procedures, and care of the coated surface before burying are the reasons for the critical need of enforcing the presence of certified coating inspection in the field.

4) The history of decades of vandalism has led to the loss of test stations. In many cases, the ROW has only one test station per kilometer, and all pipelines sharing the ROW are interconnected in between and only to this test station. For the proper control of the CP current demanded by each of the pipelines, the test stations should be reinstalled and the interconnections removed. The public needs to be informed about the role of test stations in the safe operation of the pipelines, and the hazards of destroying test stations and the penalties for vandalism.

The newest test stations are made of lightweight polymeric materials.

The present test stations are made of reinforced concrete; these are frequently vandalized for use as structural materials. The polymer type are much less attractive.

5) Many anode beds are too close to the pipelines, causing extensive potential attenuation and insufficient protection in long segments of the pipelines. Deep anode solutions may help on congested ROWs where lateral extensions of land are unavailable.

6) The use of the 100-mV criterion may also help in solving the problem of complying with pipeline integrity management programs. It is conceivable that the old and poorly coated pipelines may not meet the –850-mV criterion that has been the compliance target for decades in Mexico. Investments in new CP infrastructure for these pipelines may just be too costly. A recommended practice manual has been prepared covering the correct application and technical limitations of the 100-mV criterion. The 100mV criterion proved useful on a field test performed for 5 km of a 16-in pipeline where the –850-mV criterion has not been met for several years.

References 1 R.C. Benson, “A Review of Soil Resistivity Measurements for Grounding, Corrosion Assessment, and Cathodic Protection,” MP 41, 1 (2002): p. 28.

2 G.K. Glass, “The 100-mV Potential Decay Cathodic Protection Criterion,” Corrosion 55, 3 (1999): PBD. 3 J. Didas, “Cathodic Protection Criteria and Its Application to Mature Pipelines,” MP 39, 4 (2000): p. 26.

Jorge Joaquín Cantó is the engineering director at Corrosion y Proteccion Ingenieria, Rio Nazas 6 Vista Hermosa, Cuernavaca, Morelos, 62290, Mexico, e-mail: canto@corrosionyproteccion.com.

Corrosion y Proteccion Ingenieria is Mexico’s leading corrosion control organization. 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.

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Pipeline Survey in Mexico Reveals Need for 100-mV Polarization CP Criterion

Lorenzo M. Martínez de la Escalera is the executive director of Corrosion y Proteccion Ingenieria, e-mail: lmm@corrosionyproteccion. com. His engineering 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. Hernán Rivera is a project manager at Corrosion y Proteccion Ingenieria, e-mail: hrivera@ corrosionyproteccion.com.mx. He has worked on 10 CP diagnostic projects covering the north, center, southeast, and Gulf areas of Mexico, including major oil and gas pipelines. He has a mechanical engineering degree from the Universidad Nacional Autónoma de Mexico (UNAM) and is a NACE-certified CP Technician. He has been a NACE member for two years.

Arturo Godoy Simon is an engineer at Corrosion y Proteccion Ingenieria, e-mail: arturogodoy@ corrosionyproteccion.com. He is a CP Technician with experience in surveying, modeling, and diagnostics in several ROWs. He has conducted impressed current CP (ICCP) modeling at an oil field in the south of Mexico and has designed a hybrid ICCP/galvanic system for a major airport in Mexico.

A three-year member of NACE, he is a Ph.D. student in engineering and material science at Morelos State University (UAEM).

Enrique Rodriguez-Betancourt is a pipelines maintenance specialist at Petroleos Mexicanos, Marina Nacional Torre PEMEX Piso 23, Distrito Federal, 01000, Mexico. He has worked for PEMEX for more than 27 years, with various responsibilities and experience implementing multiple programs. He has worked on pipeline maintenance improvements using an automated CP system for the national transportation system for natural gas and liquid petroleum gas (~15,000 km), implemented new methodologies for pipeline evaluation and control, performed risk evaluations, and improved several methods used in Mexico for assuring pipeline integrity. He has made many presentations on CP, risk evaluation and administration, integrity, and geo-spatial systems related to pipeline risk evaluation.

Carlos G. Lopez-Andrade is a pipeline maintenance specialist at Petroleos Mexicanos. He specializes in pipeline maintenance and has participated in multiple program implementations at PEMEX. He is experienced with methodologies for evaluating maintenance and corrosion control systems for PEMEX pipelines, including CP, pipeline integrity, and risk administration.

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.

Norberto Pesce is the director of Omnitronic S.A., Avda. San Martin Sur 36, Godoy Cruz, Mendoza, 5501, Argentina, e-mail: npesce@omnitronic-sa. com. He has been an electrical-electronic engineer involved in the design, supply, installation, and maintenance of CP systems in oil and gas facilities since 1989. A 10-year member of NACE, he is a NACE-certified CP Specialist.

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 Price 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.

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