Corrosion Monitoring Basics
Corrosion can lead to failures in plant infrastructure and machines which are usually costly to repair, costly in terms of lost or contaminated product, in terms of environmental damage, and ultimately it may be costly in terms of human safety. Decisions regarding the future integrity of a structure or its components depend entirely upon an accurate assessment of the conditions affecting its corrosion and rate of deterioration. With this information, an owner can make an informed decision as to the type, cost and urgency of remedial measures. Monitoring corrosion characteristics of a proposed or existing structure can lead to the proper selection of longer life materials, durable and protective coatings and corrosion control measures.
Modern corrosion monitoring technologies can emphasize the highly time-dependent nature of corrosion damage. The integration of corrosion monitoring technology in existing systems can also provide early warning of costly corrosion damage and provide information on where the damage is taking place.
Corrosion Inspection and Monitoring reference book
In a modern business environment, successful enterprises cannot tolerate major corrosion failures, especially when these involve personal injuries, fatalities, unscheduled shutdowns and environmental contamination. For this reason considerable effort must be expended in corrosion control at all stages of a system's life, from the design table to the last day of operation. Typically, once a system, a plant or any piece of equipment is put into service, maintenance is required to keep it operating safely and efficiently. This is particularly true for aging systems and structures that will be required to operate beyond their original design life.
Corrosion Inspection and Monitoring Glossary
Correct and effective corrosion monitoring strategies should be used as a proactive tool to assist with operating a plant more effectively, thereby prolonging its life and gaining optimum throughput. It also enables continuous monitoring of actual corrosion rates, allowing for timely preventative action if a variance is observed.
Current corrosion inspection and monitoring typically requires planned periodic shutdowns to inspect equipment. Scheduled shutdowns are costly in terms of productivity losses, restart energy and material costs. Unscheduled shutdowns are disruptive and often quite expensive. Internal corrosion failures result in costly cross contaminations of product and process streams. External corrosion leaks put process fluids into the plant environment and can create significant safety hazards.
Experience has shown that the potential cost savings resulting from the implementation of corrosion monitoring programs generally increase with the sophistication level (and cost) of the monitoring system.
It is therefore helpful to have previous history or even a rough estimate of the types of corrosion problems to be investigated. It is also advisable to use several complementary techniques rather than rely on a single monitoring method. Real time monitoring of pipelines, vessels and other static equipment enables a near instantaneous appraisal of the corrosivity of produced and transported fluids.
On-line nature monitoring means that corrosion information is immediately available to the operator. If corrosion activity increases as a result of process non-conformities, the corrosion information can be viewed alongside process variables (including chemical injection data) such that cause-and-effect can be determined and rapid action can be taken to overcome the problem. Effectiveness of remedial action or treatment can be similarly proven.
See how the following famous scientists were involved in corrosion monitoring:
André Marie Ampere
Ampere really established the foundations for quantifying electricity into its finite variables. One century after his death Ulick Evans gave us the basic model that relates electrical current to corrosion rates. (back to top)
Charles Augustin de Coulomb
What Ampere did to help us describe electric current Coulomb had done to characterize the electric charges involved. With Faraday's relations these electric charges can be converted into corrosion rates. (back to top)
Sir Humphrey Davy
As you probably know, Sir Humphrey Davy was Michael Faraday's supervisor. While he has not discovered any specific principle directly involved in corrosion monitoring, Sir Humphrey established the first principles of cathodic protection (CP). Modern impressed current CP systems have built in corrosion monitoring devices that feedback to the control box. (back to top)
Albert Einstein is surely one of the most recognized and maybe controversial scientific genius of modern times. What is much less known, however, is that Einstein started his scientific career as an electrochemist therefore providing us many basic equations governing the movement of ions in solution. One cannot study or monitor aqueous corrosion without invoking these important equations. (back to top)
Well, Michael Faraday established a solid foundation to relate the conversion of chemicals into electric current (batteries, fuel cells ...) or electric current into chemical quantities. What could we do without Faraday's constant? (back to top)
Galvani's discoveries and what we know of the galvanic series are fundamental building blocks of many technologies and design considerations in corrosion prevention and control. The use of galvanic couples to sense corrosion is well established as shown in previous examples. (back to top)
Otto von Guericke
Now we are going way back in time, when corrosion was a simple natural process and corrosion monitoring not a requirement. However, Otto von Guericke invention of steam power led to the industrial revolution that has forced humankind to use steel and other metallic materials as increasingly high temperatures and pressures. One can probably say that the demand for corrosion monitoring tools and techniques was in great part due to these difficult situations and the many catastrophic explosions they created mostly in the first part of the twentieth century. (back to top)
James Prescott Joule
All is a matter of energy, including of course corrosion and corrosion monitoring. The most corrodible locations will release the highest amount of energy. These locations can be observed with infrared thermography. Alternatively these locations should be the prime targets of a corrosion monitoring program. (back to top)
Mendeleev discovery of the periodicity amongst elements opened up up the road of modern chemistry. How could we do any useful corrosion monitoring without good old chemical knowledge? (back to top)
Walther Hermann Nernst
Nernst has provided us with a cornerstone equation with which an electrochemical signal can be related to a chemical concentration. Nernst equation is behind all kinds of useful measures of ionic activities, e.g. pH, dissolved oxygen, ionic make-up ... (back to top)
The most commonly used corrosion monitoring technique uses the very useful Ohm's law to evaluate the corrosive action on a simple wire. The electrical resistance technique has proven the need and possibilities for a great variety of other techniques described in the present module. (back to top)
Volta made the first practical use of metallic corrosion in devices that revolutionized mankind in an unprecedented fashion. (back to top)