Localized Corrosion in Complex Environments

Preface

Over the past millennium, significantly improved understanding of materials behavior and performance, extensively developed materials selection standards and software, as well as various engineering design tools have facilitated the avoidance of ‘short-term’ failure of engineering structures. However ‘long-term’ materials failure issues, in particular localized forms of corrosion and materials degradation, still remain tenacious threats to the integrity and safety of the huge network of civil and industrial infrastructure assets especially those exposed to complex and varying environmental conditions. Substantial progresses have also been made in corrosion science and engineering, facilitating the effective control of uniform and general corrosion in many industrial structures such as automobile body rusting and radiator corrosion, however the management and control of localized corrosion in complex engineering environments is still a significant challenge. It is evident by many publically reported catastrophic engineering structure failures and an enormous amount of unreported infrastructure incidents. This problem becomes even more acute when complex forms of localized corrosion occur on ‘invisible’ and highly variable engineering structures such as buried and submerged oil and gas pipelines.
Effective control and management of complex forms of localized corrosion are critical for maintaining the safety and integrity of industrial and civil infrastructures that are vital for the provision of the world’s essential services and the maintenance of its economic activities. Although localized corrosion has been widely studied over the past decades, it should be noted that most studies are typically limited to the investigation of specific forms of localized corrosion such as pitting of stainless steels in defined laboratory environments. Conventionally corrosion science research considers a corrosive environment uniform and stable, a simplification of complex and changing industrial environments. Corrosion prediction models, testing methods and protection measures are mostly developed under such simplification. Unfortunately most practical engineering structures can be subjected to highly non-uniform corrosion under multiple and dynamically changing environmental conditions. An example is localized corrosion of buried steel pipelines that are affected not only by seasonal changes in soil moisture and oxygen levels, inhomogeneous coating defects and coating disbondment, but also by fluctuating stray currents and oscillating mechanical stresses. Another example is localized corrosion and materials degradation on offshore structures such as wind turbines and oil platforms that are affected by multi-zone and dynamically changing marine environmental conditions. Variable and complex environmental conditions can not only lead to changes in corrosion rates, but also in corrosion patterns and mechanisms. Unexpected changes in environment and mechanism could also cause suddenly accelerated localized corrosion damages that are not predictable by conventional corrosion models. Currently corrosion engineering studies have not sufficiently considered these issues, leaving a major knowledge gap in corrosion science and engineering.
The ultimate goal of corrosion science and engineering would be to prevent the pre-mature failure of engineering materials and to extend the safe operational life of engineering structures through detecting, mitigating and minimizing corrosion damage. This could be compared with the protection of human health through detecting, diagnosing and preventing cancer and other diseases. Human body itself has many ‘sensors’, the eyes, ears, nose, skin and tongue, that provide disease information through vision, hearing, smell, touch and taste. Diseases can be further diagnosed and treated through medical testing, doctor’s analysis and the use of various medical treatment. For engineering structures, unfortunate