A New Approach to Corrosion Monitoring

ost assets depreciate, losing value over time as a result of wear and tear, age, or obsolescence. Corrosion, like depreciation, results in the often hidden cost of a non-cash expense — measurable in terms of reduced operating life — that reduces the value of assets. Many engineers in the chemical process industries (CPI) see corrosion on a “straight-line basis” in terms of repair, maintenance and replacement during fixed-interval turnaround inspections. New technology, however, can assess corrosion deterioration in realtime, using the plant control-andautomation system. The latest technology links corrosion to process conditions more directly and immediately. It also allows corrosion depreciation to be assessed in much-shorter time intervals with the ability to control and mitigate the rate of damage, and more accurately factor-in its true economic impact on plant operations. Illustrating the importance of corrosion depreciation is the fact that corrosive attack leads to plant breakdowns with some very considerable costs. Consider these figures based on recent studies: • The annual cost of corrosion in the U.S. is estimated to be about $300 billion (about 4% of the gross domestic product) • For the petrochemical and pharmaceutical sectors, the annual cost is about $2.5 billion • The annual corrosion cost in the CPI is over 10% of the annual plant capital expenditures across these industrial sectors • Globally, the cost of corrosion in the CPI appears to be about $50 billion per year and is projected to climb still higher over the next five years Indeed, corrosion gives a whole new meaning to the term “depreciation,” particularly when both immediateand longer-term effects of corrosion are considered. Still, to many CPI engineers, corrosion is simply a routine part of plant operations and a cost of doing business. A corrosion specialist is called when a problem arises. Once the problem is solved, the plant operates more or less as before, until the next upset occurs. The major impact of corrosion to the business lies in costs associated with lost production, health, safety and environmental issues, and legal liabilities. New technology allows corrosion monitoring via the plant distributed control system (DCS), whereby corrosion measurement is coupled to a suite of key, realtime process variables. This process can lead to gains in many parts of the corporate balance sheet. Process optimization often brings an immediate reduction in direct costs and also helps increase plant productivity and revenues while minimizing corrosion damage. Ultimately, it can provide major gains through reduced “corrosion depreciation allowance” and increased plant asset life.