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May 2009

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Rust is risk

Corrosion is no mystery: We know how to prevent it and how to control it

By Nicholas Sheble

In the U.S. alone, the loss number on corrosion is approaching $350 billion per year.

When InTech ran its corrosion article in 2007 (www.isa.org/intech/20071004), the number stood at $300 billion. The damage today is no less, but the market is certainly more, as are the opportunities.

“In the global process industries, the cost appears to be about $50 billion per year and is projected to climb still higher over the next five years. Real-time corrosion data brings the potential to implement more proactive corrosion control strategies before major problems occur,” declared Keith Briegel of Rohm and Haas and Russell Kane of Honeywell in their analysis.

Pipes, pipelines, and conduits of process materials are the primary victims of corrosion and its costly repercussions.

NACE International (originally National Association of Corrosion Engineers) concentrated solely on pipelines when it started in 1943. Like ISA and other engineering organizations, it grew and expanded its domain. Today, it is the largest organization in the world committed to the study of corrosion and is the keeper of corrosion prevention science and control standards.

Here is NACE’s most current information on corrosion detection, control, and management.

Testing the waters, the pipes

The pipeline industry is undergoing changes because of revisions to safety regulations. These changes include developing standards, recommended practices, and guidelines that operators can use to develop, implement, and validate pipeline-integrity verification programs.

Methods for verifying pipeline integrity include pressure testing, in-line inspection (ILI), and others, such as a method called Direct Assessment (DA). Each of these techniques has capabilities and limitations that need consideration in the developing and validating of a pipeline-integrity management program.

In the U.S., the Department of Transportation, Office of Pipeline Safety is changing pipeline safety regulations. These changes affect approximately 160,000 miles of hazardous liquid pipelines and 330,000 miles of natural gas transmission pipelines in high-consequence areas (HCA).

The new regulations will decrease the number pipeline failures affecting public safety and the environment.

The definition of an HCA is complex. For hazardous liquid pipelines, it includes unusually (environmentally) sensitive areas, highly populated areas, and commercially navigable waterways. The final rule for gas pipelines includes proximity to populated areas (including buildings such as schools and hospitals).

ILI tools, sometimes called pigs, are devices containing sensors designed to scan the pipe wall for defects. There is a wide range in type of tool and the defects they can detect.

A wider range of technologies is available to liquid operators than gas operators. The interpretation of signals is complicated, and the level of accuracy depends on the type of tool, how it operates, and the type of defect.

There are many advantages and disadvantage to ILI. However, ILI is impractical for many pipelines because the tools require construction of a launcher and receiver at the ends of an unobstructed pipe segment without changes in pipe size or bends.

Hydrotesting is a method where we take the pipeline out of service, fill it with water, and pressurize it to a value greater than the operating pressure. Any defects in the pipe wall that are near failure in a pipeline result in a release of water.

Hydrotesting is most often used for new pipelines (or those returned to service) to ensure construction defects are found. There are many advantages and disadvantage to hydrotesting. However, hydrotesting is not practical for many pipelines because the service interruption is not acceptable (e.g., a single pipeline feeding gas to a city or power plant).

DA methods are processes to assess the condition of pipelines with respect to external corrosion, internal corrosion, and stress corrosion cracking.

Each of the DA methods uses techniques to determine the most likely locations for corrosion. These locations are excavated and directly assessed. If these locations most likely to have suffered corrosion are not a threat to pipeline integrity, then we consider the remaining sections of pipe less likely to have suffered corrosion and that they are also not a threat.

Pipelines will deteriorate

Unprotected pipelines, whether buried in the ground, exposed to the atmosphere, or submerged in water, are susceptible to corrosion.

Without proper maintenance, every pipeline system will eventually deteriorate. Corrosion can weaken the structural integrity of a pipeline and make it an unsafe vehicle for transporting potentially hazardous materials.

However, technology exists to extend pipeline structural life indefinitely if we apply it correctly and maintained the pipeline consistently. Four common methods used to control corrosion on pipelines are protective coatings and linings, cathodic protection, materials selection, and inhibitors.

• Coatings and linings are principal tools for defending against corrosion. They often work in conjunction with cathodic protection systems to provide the most cost-effective protection for pipelines.
• Cathodic protection (CP) is a technology, which uses direct electrical current to counteract the normal external corrosion of a metal pipeline. CP plays and works where all or part of a pipeline is underground or submerged in water. On new pipelines, CP can help prevent corrosion from starting; on existing pipelines, CP can help stop existing corrosion from getting worse.
• Materials selection refers to the selection and use of corrosion-resistant materials such as stainless steels, plastics, and special alloys to enhance the lifespan of a structure such as a pipeline. Materials selection personnel must consider the desired lifespan of the structure as well as the environment in which the structure will exist. Corrosion inhibitors are substances, which, when added to a particular environment, decrease the rate of attack of that environment on a material such as metal or steel reinforced, concrete.
• Corrosion inhibitors can extend the life of pipelines, prevent system shutdowns and failures, and avoid product contamination.

Evaluating the environment in which a pipeline is or will be located is very important to corrosion control, no matter which method or combination of methods is used. Modifying the environment immediately surrounding a pipeline, such as reducing moisture or improving drainage, can be a simple and effective way to reduce the potential for corrosion.

Furthermore, using persons trained in corrosion control is crucial to the success of any corrosion mitigation program. When pipeline operators assess risk, corrosion control must be an integral part of their evaluation.

Corrosion control is an ongoing, dynamic process. The keys to effective corrosion control of pipelines are quality design and installation of equipment, use of proper technologies, and ongoing maintenance and monitoring by trained professionals. An effective maintenance and monitoring program can be an operator’s best insurance against preventable corrosion related problems.

Effective corrosion control can extend the useful life of all pipelines. The increased risk of pipeline failure far outweighs the costs associated with installing, monitoring, and maintaining corrosion control systems. Preventing pipelines from deteriorating and failing will save money, preserve the environment, and protect public safety.

Storage tank pollutes

Leaking storage tanks, whether above or belowground can pollute the environment, threaten public health, and lead to billions of dollars in direct and indirect costs.

The main reason for storage tank failure is corrosion. Fortunately, corrosion prevention technology exists, which can protect storage tanks and keep them structurally sound for years to come.

Government and the public understand the extent to which leaking tanks can damage the environment and threaten public health.

In order to prevent environmental contamination, U.S. federal regulations require those who own or operate underground tanks and the connected piping to have spill, overfill, and corrosion protection mechanisms in place, and many U.S. states have additional tank protection requirements. The owners/operators of tanks who fail to comply with these regulations can be subject to both civil and criminal penalties.

Corrosion is the deterioration of a material, usually a metal that results from a reaction with its environment. Without implementing appropriate corrosion control measures, storage tanks will deteriorate.

Most tanks are made of steel, a material highly susceptible to corrosion. Corrosion related damage gains speed and momentum from certain factors like: the tanks’ interaction with interconnected components, corrosive environmental conditions, and stray electric currents.

Over time, uncontrolled corrosion can weaken or destroy components of the tank system, resulting in holes or possible structural failure and release of stored products into the environment.

Modern corrosion control combines historically proven methods with state-of-the-art technology to prevent tanks from deteriorating. Corrosion control strategies work individually or in combination with one another.

Common strategies includes corrosion resistant materials, application of coatings and/or linings as a barrier to the environment, various forms of cathodic protection to prevent deterioration of tank components in contact with the soil, and use of inhibiting chemicals in stored substances to control corrosion of the tank interior.

Corrosion control can protect storage tanks, the environment, and the bottom line of owners and operators. It must be integral parts of a storage tank owner/operator’s long term planning.

Tank owner support of corrosion control is vital, but comprises only half of the solution. Long-term planning for corrosion control must include ongoing education and training for persons responsible for operating tank systems.

Those individuals must be able to recognize the early signs of corrosion and prevent it effectively. Owners and operators must also dedicate the resources required to monitor and maintain these corrosion protection systems to ensure the effective protection of the environment and their economic interests.

Above- and below-ground storage tanks could leak hazardous substances into the environment that contaminate our soil and water. Often, corrosion is to blame.

Corrosion is not a mystery, and we know how to prevent it and how to control it. Industry can effectively protect the environment while saving billions of dollars each year by implementing comprehensive corrosion control for storage tanks.

ABOUT THE AUTHOR

Nicholas Sheble (nsheble@isa.org) is senior technical editor for InTech. Visit http://www.nace.org for more comprehensive information on corrosion engineering and standards.