Some definitions assigned to corrosion monitoring have been wide ranging, essentially including any type of corrosion-related measurement or observation. For example, a glossary published by the National Corrosion Service of the National Physical Laboratory (NPL, UK) has defined corrosion monitoring as: "Any method used to observe or measure the progress of corrosion."

Such broad definitions highlight the multi-disciplinary nature of corrosion monitoring, covering a wide range of materials, measurement techniques, instrumentation, rules and regulations, standards, logistical support, data analysis, communication and information management. (For this reason, a wide range of topics and supporting information has been incorporated on corrosion-club.com under the corrosion monitoring umbrella.)

However, more distinctive characteristics have also been assigned to monitoring, to distinguish it from inspection activities and surveys. A useful differentiation can be made on the following basis [1]:

Inspection, survey: A "snapshot" of corrosion conditions at a specific point in time.

Monitoring: A series of surveys, planned and organized to obtain more comprehensive information on conditions over time (through time, as a function of time).

The above role of corrosion monitoring, in defining changes in corrosion conditions over time, represents a longer-term commitment compared with once-off corrosion inspections, surveys. Furthermore, it represents a deeper commitment to quantifying the rate of corrosion and determining underlying causes of corrosion damage ("understanding it all"). It has been noted that the rate of corrosion ultimately determines how long a process can be operated usefully and safely [2].

The measurement of corrosion condition changes over time obviously also falls in the domain of on-line corrosion monitoring, which facilitates "continuous" corrosion monitoring - as such on-line monitoring can be viewed as a continuous series of surveys (in relatively rapid succession). In this context, the term "corrosion surveillance" has been introduced. It refers to the possibility of using corrosion monitoring (with sufficiently sensitive sensors and instrumentation) as a form of process control - by linking corrosion "events" to process parameter changes; with process parameters being measured together with the corrosion sensor signals. The term "real-time monitoring" is also applicable to on-line monitoring with sufficiently senstive techniques.

The important concepts of obtaining "early warning" before serious corrosion damage sets in and avoiding process "upset windows" associated with excessive corrosion rates are all part of the corrosion monitoring philosophy of characterizing corrosion conditions over time.

Adding value: Most importantly, to generate real value from corrosion monitoring initiatives, the information gathered over time has to be translated into effective corrosion mitigation/control programs. "Making sense of it all", from a deeper understanding of information from corrosion monitoring and other sources is required. For effective corrosion control it is important to understand "where, when and why" corrosion damage takes place - corrosion monitoring can be helpful for these purposes.

Prepared and published March 4, 2003 on corrosion-club.com (updated March 23, 2003).