| Atmospheric Corrosion Monitoring: Atmospheric
corrosion accounts for the highest overall cost and metal loss of all the fundamental
corrosive environments. A defining feature of atmospheric corrosion is the thin aqueous
layer between the surface of the corroding material and the atmosphere. Three phases (solid
[corroding substrate], liquid [thin aqueous layer] and gaseous
[atmosphere]) and the interfaces between these phases are therefore important and can be
used in corrosion monitoring principles..
Corrosion monitoring in outdoor and indoor atmospheres poses specific challenges
related to characterizing corrosion damage (generally taking place at a low rate) in a
short (practical) time frame. Three basic approaches to corrosion monitoring are
available:
- Direct measurement/monitoring of corrosion damage.
(Examples include exposing actual components or coated coupons to corrosive atmospheres
and evaluating these for corrosion damage periodically)
- Indirect measurement/monitoring of corrosion damage with corrosion sensors.
(Examples include thin film electrochemical sensors embedded under paint coatings and smart coatings)
- Classification of atmospheric corrosivity
by categories and correlating such classifications to actual in-service performance and
corrosion rates.
| The main drawbacks of the direct measurement approach
are the lengthy exposure time period usually required and that only a "snapshot"
of cumulative damage is obtained when detailed analysis of corrosion damage is performed
periodically. The approach of atmospheric corrosivity classification is generally one of
a simple, low-cost measurement in a short time frame. Ultimately, such simplistic
measurements require correlation to actual long term service performance and therefore
need to be linked to the other measurement methodologies. |
Atmospheric corrosion monitoring is generally employed to quantify this
type of damage and corrosion risk, rather than merely resorting to broadly descriptive
atmospheric classifications such as "industrial", "rural", etc.
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