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ABSTRACT
Industrial water system components are at increasing risk of damage due to corrosion and metal loss as they get close to the end of their design life or if the system exhibits any of the following: accelerated corrosion, perforation, deposit build up (plugging), discoloration, and excessive attack due to corrosive bacteria.
The purpose of this paper is to provide failure analysis case histories on corrosivity, pitting tendency and the risk associated with corrosion activity in industrial water systems. Failure analysis methods, failure mechanisms, primary cause and sources of corrosion attack with recommendations are described at the end of each case history. Corrosion mitigation recommendations and risk ranking is based on many years of experiences and water system studies in industrial water systems.
Keywords: corrosion risk, inspection, failure analysis, industrial water systems, corrosion mitigation, corrosivity, pitting corrosion.
INTRODUCTION
Corrosion is defined as degradation of materials due to reaction with environment. The corrosion of metals can be broken down into several simple processes that must occur in series, the anodic reaction, cathodic reaction, electron migration through the metal and ions leaving the metal surface and going into solution all occur simultaneously. At its root, corrosion protection of pipes, as with all corrosion protection, is aimed at suppressing one of these elements. Corrosion is accelerated by low pH, corrosive bacteria, dissolved oxygen, high flow rate, galvanic action, high water temperature, high corrosive ion concentrations (chlorides and sulfates...), stagnation, high carbon dioxide, high oxygen and high suspended solids.
In general, the steps and/or strategies for developing corrosion control program are: 1-5
1. Develop and understand water related corrosion concepts and mechanisms
2. Determine the severity of the corrosion
3. List possible causes of corrosion
4. Develop a list of possible corrosion control alternatives
5. Develop a corrosion control strategy or treatment
6. Implement the treatment or program
7. Monitor the effectiveness of the program
8. Modify and optimize the program based on corrosion monitoring
The most common techniques for corrosion control are: 6-13
1. Adequate system design and proper materials selection
2. Modification of water chemistry, removal of corrosive ions and adjusting hardness
3. Use of corrosion inhibitors
4. Application of protective coatings, linings and paints
5. Design and implement cathodic protection for tanks and vessels
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