Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.
Understanding the basic principles and causes of corrosion Corrosion Basics
Corrosion Testing and Monitoring in Manufacturing Plants
M
etals and their alloys are used in a multitude of
ch anging conditions, and
corrosion failures are not uncommon. The limited pre- dictability of metal perfor- mance is the main reason why corrosion tests and cor- rosion-monitoring programs are so important. Properly conducted, these tests can XZW^QLM [QOVQÅKIV\ [I^QVO[ 1V many cases, they are built-in
requirements. Corrosion can lead to failures in plant
infrastructure and machines that can be costly in terms of repair, lost or contami- nated product, environmental damage, and, ultimately, personnel safety. Deci- sions regarding the future integrity of a structure or its components depend entirely upon an accurate assessment of the conditions affecting corrosion and the rate of deterioration. Proper assessment of corrosion risk is
the foundation of material selection. This aspect of component design can avoid using materials under unsuitable condi- tions or using a more expensive material than is required. Accurate evaluation of environments and service conditions, together with corrosion resistance of al- loys, may also lead to the development of new materials that perform more eco-
80 MATERIALS PERFORMANCE March 2012
VWUQKITTa MNÅKQMV\Ta L]ZIJTa WZ [INMTa than commonly used materials. Quality- control corrosion tests are also a means of ensuring that the materials have the capabilities expected of them. Corrosion-testing programs can be relatively simple, able to be completed in a few minutes or hours; or they can be complex, requiring the combined work of a number of investigators over a period of weeks, months, or years. Because the process of corrosion is
highly time-dependent, the integration of corrosion-monitoring technology in exist- ing systems can also provide early warning of costly corrosion damage and provide information on locations where damage is occurring or possibly could occur.
Corrosion Testing Corrosion tests are divided into two
broad categories: a) tests made in the laboratory under controlled conditions and b) tests made in the field under natural or service conditions.
Laboratory Controlled Tests Tests in the laboratory are made with
X]ZM KPMUQKIT[ WZ [XMKQÅK KWUJQVI\QWV[ of chemicals, under closely controlled conditions. Each test should be reproduc- QJTM ]VLMZ I Å`ML [M\ WN KWVLQ\QWV[ IVL durations. An assessment of this repro- ducibility is especially important when a new test method is used or when a new alloy or fabricated item is evaluated. If reproducible conditions can be achieved, \PMV LQNNMZMVKM[ QV LI\I \Z]Ta ZMÆMK\ I difference in the resistance to corrosion of the materials being tested and the in- vestigator knows if an improvement has been made.
Laboratory tests provide indications of
what can happen in actual practice; how- ever, the time required for an "indica- tion" depends on the purpose and nature of the tests. Laboratory corrosion tests generally are conducted over a period of time ranging from a few minutes to as long as a year or more. Experimental ac- celerators, such as increased temperature or higher concentrations of chemicals, must be interpreted with great care be- cause they may change the fundamental corrosion behavior being investigated.
Field Tests Field tests can be much closer to end
use than the usual laboratory tests and normally range in duration from several months to many years. Some tests have been conducted for more than 50 years at well-established outdoor facilities. Field tests may consist of exposure to corrosive conditions in natural environments, particular industrial applications, and particular substances. Corrosion tests may be further sub-
divided according to their basic objec- tives, which in turn depend on the types of environments and test durations that interest an investigator. It is always criti- KIT \W NWTTW_ \PM [KQMV\QÅK UM\PWL _PQKP often requires a large series of tests with a single parameter varied in each one.
This article is adapted by MP Editorial Advisory Board Member Norm Moriber from Corrosion Basics—An Introduction, Second Edition, Pierre R. Roberge, ed. 0W][\WV <@" 6)+- 1V\MZVI\QWVIT 2006), p. 583-588.
NACE International, Vol. 51, No. 3