Corrosion failure analysis

The analysis of corrosion-related damage is an essential link in the whole chain of optimizing plant and process operation. Determining the origin of damage can play a very important role, on the one hand, in protecting the safety of people and the environment, and, on the other, in maintaining a satisfactory level of plant performance. More and more frequently, it is also a means for the various organizations involved to determine who is responsible for what, and to share the costs of a claim.

Expertise is the focal point of two approaches. It is the culmination of investigative work, enabling us to reconstruct, as far as possible, the causes of the degradation of the analyzed part. It is also a starting point, since the analysis of the causes will lead to action in terms of repair and monitoring of installations, as well as improvements in the design and operation of installations.

Expert appraisal is most often called for when the damage occurs well within the expected service life of the plant. However, when damage occurs over a period compatible with the service life initially envisaged at the design stage, we may also want to check that it is indeed the factor identified as limiting the service life that has caused the failure. If this is not the case, the expert's conclusions are, of course, extremely instructive.

Corrosion plays an important role in processes leading to premature failure. By way of illustration, in an international journal (Engineering Failure Analysis) devoted to failure analyses of all origins, the keyword "corrosion" has appeared in around 50% of articles since 2011. Stress corrosion, corrosion fatigue and localized corrosion are the most widely cited (over 50%).

Taking into account the behavior of materials, or the evolution of their behavior, in a corrosive environment requires in-depth analysis upstream, when designing installations. Although some equipment design and manufacturing codes include informative appendices on the damage modes of metallic materials (CODAP's informative appendices MA3 and MA4, dealing respectively with the behavior of steels in the presence of pressurized hydrogen and the prevention of corrosion risks, are an example) and can alert designers, the codes are not intended to replace a precise analysis of a material's ability to withstand given operating conditions (type of fluid, temperature, etc.). This analysis is obviously carried out when the corrosion factor is an initial determining factor for the service life of the installation. On the other hand, when the environment is considered less aggressive, the choice of materials, processes and monitoring may prove unsuitable. This is what many expert reports reveal. In plants using...