Introduction
In the constant battle against structural degradation induced by external corrosion, particularly in infrastructures operating in restricted access areas where inspections are difficult to perform, the standard NACE SP01691 on ‘External Corrosion Control in Underground or Submerged Metallic Piping Systems’ emerges as a valuable and comprehensive tool for those organizations involved in the design and operation of these complex industrial facilities.
NACE SP0169, a standard generated and published by the National Association of Corrosion Engineers (NACE), provides detailed guidelines and practical strategies to address and mitigate this aggressive phenomenon. It focuses primarily on metallic piping systems, which are widely used in the manufacture of the extensive systems that transport oil, gas, water and various fluids.
Initially published in early 1996 under the name NACE RP0169. It has been revised twice prior to the 2013 update, specifically in 2002 and 2007.
Analyzing the value of the need for external corrosion control
This standard explicitly recognizes that metallic structures, whether buried or submerged, are inherently susceptible to corrosion. However, it also points to the effectiveness of proper corrosion control procedures, which, when properly applied, minimize or even neutralize metal loss, ensuring safe and economical operation.
It details specific practices for evaluating whether a buried or submerged metallic pipeline needs thorough external corrosion control, performed using a systematic approach, based on data derived from inspections, operational records and comparisons with similar systems. It also highlights the importance of considering specific environmental and physical factors, such as corrosion rate, product type, operating conditions and pipeline location.
From an economic perspective, NACE SP0169 emphasizes the costs associated with maintenance and corrosion protection, and urges experts to consider direct and indirect expenses, from repairs, replacements and relocation of assets to civil liabilities and loss of revenue due to service interruptions.
Importance of the design of piping systems according to NACE SP0169
The standard is clear on the need for a robust and efficient piping system design that takes into account corrosion prevention from the early stages of development. It also highlights the importance of integrating corrosion management practices from design to implementation.
Corrosion control needs to be studied and evaluated by qualified experts during all phases of pipeline design and construction. This practice is entrenched with safety requirements to be considered the core of the design process and to certify the durability and operational efficiency of systems operating under these conditions.
The selection of materials and coatings is essential for the prevention of external corrosion. Cathodic Protection (CP) is used with coatings to provide a barrier to help reinforce cathodic control and ensure asset life. For the selection and use of PC systems, variables such as temperature, pressure, chemical, dielectric and mechanical resistance must be taken into account to ensure optimum and safe performance under various system operating conditions.
Importance of the selection of external coatings
This part is extremely important from the design and the standards focus their attention on the selection of appropriate external coatings, which optimize corrosion control in the systems, isolating the external surface from the corrosive environment, to ensure the implementation of the subsequent PC system.
It is essential to apply the best features and selection criteria for optimized coating performance to reduce PC current requirements and improve current distribution. To ensure their effectiveness, it is necessary to select and apply them considering chemical and physical compatibility, resistance to acidic or caustic electrolytes and durability.
Coatings must possess specific characteristics, such as being an electrical insulator, providing a moisture barrier, and resisting chemical and thermal degradation. Factors such as the type of environment, geographical and physical location, and operating temperature are also considered in the selection of the protective system.
In addition, it is important to consider the mechanical properties, i.e., that they are resistant to counteract mechanical damage that may be caused during storage and handling in the pipes or structures. The selected coatings must be non-toxic, non-degradable. It is important that inspections are performed by trained personnel to certify the quality of the coating.
Main criteria and considerations for PC selection
This section of NACE SP0169 provides details on the criteria and considerations for selecting the cathodic protection system. Parameters and criteria are specified during design to ensure that PC is selected effectively, reducing and controlling the corrosion rate of metallic piping systems to acceptable levels.
It is essential to consider the diverse nature of environments, where the effectiveness of systems varies depending on specific environmental and operational conditions. A single criterion cannot be applicable in all circumstances, which requires an adaptive approach to each specific case.
The type of material, the specifications of the protective coating and other special conditions are basic variables to take into account when designing the PC; also the criteria documented through empirical tests are a valuable variable to include in the design. The diversity in conditions requires careful and adaptive application of the basic criteria, with particular emphasis on ongoing documentation, measurement and evaluation to ensure adequate protection.
Proper design and installation of cathodic protection systems
These units address identifying hazardous conditions, specifying materials, safe installation practices, and complying with applicable standards. Strategic location selection is critical to reducing adverse currents or potential gradients and ensuring efficient operations. The major goal of PC design is to provide sufficient current to the protected structure, minimize eddy currents, and ensure long system life.
To install these systems, compliance with the installation methodology is essential, compliance with the specifications of construction plans is required, and the supervision of qualified personnel is mandatory. All materials and construction work are inspected for integrity. Galvanic anodes and impressed current systems have specific inspection, handling, and storage requirements.
The anodes and cables must be free of defects, with specific measurements to ensure their optimal condition. Connections between cables and protected structures need to be mechanically safe and electrically conductive. The integrity of the electrical insulation is essential; All buried or submerged connections require sealing to prevent the ingress of moisture and maintain electrical insulation from the environment.
Eddy current detection and control
Here the practices for the detection and control of this type of currents, which are called static or dynamic, are detailed; and are characterized by their electrolytic pathways and magnitudes. Originated from a source outside the affected structure. Factors such as the resistivity of the electrolyte, the quality of the external coating and the presence of mechanical joints with high electrical resistance influence eddy currents.
During external corrosion control studies, changes or fluctuations in line potential and current, as well as external coating failures and localized pitting, are required to be verified. For new construction, it is advisable to identify and plan the mitigation of these currents from the design, after completing construction, implement monitoring, testing and mitigation plans to control their effects.
Operation, maintenance and inspection of PC systems
Performing electrical inspections and measurements to determine that the PC is operating correctly is necessary, because the conditions that affect these systems are subject to change over time, therefore, improvements to the systems may be required to maintain protection.
The effectiveness of the Cathodic Protection system should be monitored annually, although the intervals may vary depending on various factors. When periodic inspections and tests indicate that the PC is no longer suitable, immediate corrective action is necessary; This includes repair, replacement or adjustment of components, or an attached installation where additional protection is needed.
Why are external corrosion control records important?
It is necessary to keep records of all stages of corrosion control. These files not only serve as a history, but facilitate the continuous and effective evaluation of the measures implemented. Every aspect, from detecting and documenting signs of corrosion and external coating condition, detailed PC system technical specifications, and interference mitigation measures, needs to be recorded clearly and concisely.
Regarding design and installation; It is important to document critical aspects such as coating types, layout of insulating devices, current test results and details of additional controls. Related records of PC installation and interference mitigation measures are equally relevant.
In reference to maintenance, repairs, replacements and continuous evaluations of the systems must be documented; to ensure and facilitate early identification and correction of problems. Records are maintained for an appropriate period according to the needs of each company, ensuring that information is available for evaluations, inspections and continuous improvements in the management of controlling external corrosion.
Conclusion
The NACE SP0169 standard is an important tool in the mitigation of external corrosion, providing guidelines and strategies for the design, installation and maintenance of underground or submerged metal piping systems. Through detailed specifications and rigorous documentation, the standard ensures effective implementation of cathodic protection, guaranteeing the integrity, safety and operational efficiency of these critical infrastructures.
References
- NACE SP0169 “Control of external corrosion in underground or submerged metal pipe systems.” Year 2013
Loading...
