Monday, December 31, 2012

Practical Self-Study Guide to CORROSION CONTROL

WHY CONTROL CORROSION?
Corrosion of metals is a natural process. For the most part, corrosion is quiet, gradual, and unspectacular, unlike other forces of nature such as earthquakes and tornadoes. These natural, dramatic processes we can do very little about except to watch for them, but corrosion can be prevented or at least controlled so that the metals can perform their required tasks.
The Cost of Corrosion
Reliability and Cost
Estimates of the cost of corrosion have been made by several nations (Great Britain, United States, Australia, and others) and all have reached similar conclusions. The direct costs-replacement and costs of corrosion protection-come to roughly 4% of a developed nation's gross national product (GNP) value, which for the United States means about $270 billion annually lost to corrosion. To put that in more comprehendible numbers, the cost is over $1000 per person each year.

Indirect costs, such as costs of shutdowns, loss or contamination of products, loss of efficiency, and the costs of over-design, are much more difficult to estimate but they are believed to be at least as great as the direct costs.
Example: Speaking of downtime, Moroccan sugar beet plants probably hold the world record. They get about three months effective production per year; the rest of the year is spent on maintenance. Maximum sugar extraction is made under slightly acidic conditions (pH 5-5.5), but poor control allows acidity to increase until the steel equipment corrodes at over one millimetre per month.

Most corrosion costs are unpreventable. Metals must sometimes be used in corrosive environments such as acids, so the choice comes down to paying extra for very expensive materials, for inhibitor chemicals, for electrical protection, etc., or simply replacing the metal as it corrodes. But the best or most economical choice is often not made. It is estimated that of that $1000 per year that corrosion costs you, approximately one-fourth to one-third is entirely unnecessary. Knowledge of corrosion's causes, proper design, good materials selection, and all the other ways of controlling corrosion could make a considerable difference.