Aqueous (or wet) corrosion is a form of degradation resulting from electrochemical reactions associated with differences in the electrical potential of metals in a wet environment.  Essentially, the degradation process involves an electrochemical reaction in which ions from one metal are released and flow in an electrical current through an aqueous medium (the electrolyte) to join with another chemical or metal.  This process continues until the parent metal is consumed.  There are many forms of aqueous corrosion which vary with the types of metals and aqueous media involved, as well as operating conditions.

Aqueous corrosion can be controlled by modifying the aqueous environment, using different metals or changing their properties through treatment, applying protective coatings or films, or by providing cathodic protection.  Understanding the specifics of the corrosion mechanism and selecting the appropriate remedy may be complex and involve mathematical modelling of the corrosion, laboratory studies, metallurgical assessments, and root cause failure analysis, among other engineering evaluations.

Quest Reliability has expertise in all of the major aqueous corrosion mechanisms and has solved many hundreds of corrosion problems for our industrial clients.  We also have expertise in other forms of corrosion which involve aqueous corrosion processes.  For example:

• CO₂ corrosion – a major cause of corrosion damage experienced in oil and gas production.  Dissolved CO₂ in the produced liquids (in the form of carbonic acid) is very corrosive to carbon and low carbon steel pipelines and processing equipment. It is the cementite, which is also part of the corrosion layer, that is cathodic to ferrite and revealed by the ferrite corrosion.
• Crevice corrosion – linked to the existence of a narrow gap between two metal surfaces. These gaps often become filled with moisture via capillary action, and corrosion may be induced through liquid aeration differentials.  This form of corrosion represents a major problem and is part of the design consideration in fluid machinery, heat exchangers, and piping, among other systems.
• Intergranular corrosion – may occur in high strength aluminum alloys used in manufacturing of aircraft.  The presence of intermetallic precipitates (e.g., CuAl₂ and MgZn₃, which are cathodic and anodic to the base alloy, respectively) at the grain boundaries and within the volume of the grains, controls the alloys’ strength. However, under certain conditions, these intermetallic precipitates may also create short-lived localized galvanic cells, which subsequently result in either dissolution of anodic precipitates or surrounding metal.

Quest Reliability has extensive experience in corrosion consulting and in performing investigations where the root cause of failures was related to corrosion and/or poor design promoting corrosion.  Our staff’s expertise is a function of extensive fundamental scientific research, complemented by over 30 years experience in solving corrosion-related problems in commercial applications.

For further information about Aqueous Corrosion, please contact us.