Some pipelines deteriorate slowly, and in certain cases pipeline life has been reliably targeted at 70 years or more. Other pipelines have been built which have exhausted their useful life after 1 year of operation. Apart from the quality of the construction, coatings, CP systems etc, the factors which affect pipeline life include nature of the product, nature of the external environment, operating conditions and quality of maintenance.
Regular inspections to assess the rate of change in physical condition give a more accurate idea of how much longer a pipeline can be expected to operate safely and productively and can also be used to plan for remedial action if this predicted life is below requirement. At the start of the 1990s there were concerns over the increasing threat of corrosion to pipeline integrity:
- Corrosion was the major cause of reportable incidents in North America.
- Corrosion was the major cause of pipeline failures in the Gulf of Mexico.
- Corrosion in one pipeline in North America required over $1 billion in repairs.
The corrosion-related cost to the transmission pipeline industry is approximately $5.4 to $8.6 billion annually. This can be divided into the cost of failures, capital, and operations and maintenance (O&M) at 10, 38, and 52 percent, respectively. Although data management, system quantification through the use of global positioning surveys, remote monitoring, and electronic equipment developments have provided significant improvement in several areas of pipeline corrosion maintenance, there have been few basic changes in the approach to the management of corrosion on pipelines until recently.
These changes have been in the development of risk assessment strategies and pipeline integrity management programs. In the past few years, a number of high-profile pipeline failures (both liquid and natural gas) have refocused concern on pipeline safety. Public safety concerns have provided the driving force for new regulations governing pipeline operations. The most significant of these, from a cost point of view, is the requirement for pipeline inspections. In-line inspection (i.e., “smart pigging”) is the one most often discussed. The ability of this technique to find corrosion flaws larger than a certain size (10 percent of pipe wall thickness) makes it extremely valuable for locating flaws before they become critical and cause pipeline failure (either leaks or rupture).
The major concern is that a “find it and fix it” mentality is pursued at the expense of corrosion prevention strategies. Both approaches are required to optimize the cost benefit of corrosion management programs. Operators may be tempted to adopt a “find it and fix it” attitude due to the significant cost of pipeline inspection, which is estimated to be as high as $35 billion over the next 5 to 7 years. If operators cut conventional corrosion O&M costs while pursuing pipeline inspection, corrosion prevention will suffer. Without a best practices corrosion prevention strategy, corrosion will continue and the cost of repairing a deteriorating pipeline will continue to escalate. Thus, a “find it and fix it” strategy utilizing in-line inspection at the expense of corrosion prevention may save money in the short term, but will greatly increase capital expenditures for pipeline replacement and major rehabilitation in the long-term.
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 applied correctly and maintained 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 are often applied in conjunction with cathodic protection systems to provide the most cost-effective protection for pipelines.
- Cathodic protection (CP) is a technology that uses direct electrical current to counteract the normal external corrosion of a metal pipeline. CP is used where all or part of a pipeline is buried 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 life span of a structure such as a pipeline. Materials selection personnel must consider the desired life span of the structure as well as the environment in which the structure will exist. Corrosion inhibitors are substances that, 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.
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.
So, 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.
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