Introduction
Corrosion, resulting in the severe degradation of materials, isone of the most expensive engineering problems in our industrialsociety; estimates have been made that the annual cost ofcorrosion in the U.S. exceeds 100 billion dollars. As you mightimagine with the financial stake so high, manufacturers and endusers expend significant amounts of engineering time and moneyavoiding, protecting against, or repairing damages from corrosion.A very large majority of industry must, or should, consider theenvironmental effects on its products or equipment and guardagainst premature failure due to corrosion.
Most of us are aware of a very common corrosion problem,corrosion of our automobiles. If you have lived near a coastalwater area, or in the snow belt areas that keep the roads clear ofice and snow by spreading salt on the highways each winter, you areprobably familiar with the rusted-out car bodies that occur quitequickly when exposed to the moist salt-air environment. Ourautomakers spend considerable effort to protect their products fromframe and body corrosion by these severe environments, but quiteoften, Mother Nature wins the battle.
Other common examples of items needing corrosion protectioninclude bridges, electrical connections in appliances andelectronic devices, chemical processing plants, water pipes, hotwater heaters, structural steel, welds; the list is endless.Suffice it to say that corrosion is a pervasive problem andindustry must first understand corrosion before they can take stepsto solve the unique problems it presents.
Welded structures are often subjected to corroding environments;in some cases, the weld and base metal corrode uniformly at thesame rate. In other cases, the results are accelerated corrosion ofthe weld compared to the base metal, or the base metal may corrodeat a much faster rate leaving the weld metal relatively intact.Welding, and its associated heat input, can also contribute toother corrosion problems; these will be discussed in greater detaillater.
A logical starting point for dealing with corrosion of welds isto define corrosion and then list the various types of corrosionthat can occur, with examples. Definitions used are those developedby Dr. Mars Fontana and/or NACE. There are many different forms ofcorrosion recognized that include the various corrosion mechanisms,and the most common are defined and discussed below. The nextlogical step after defining the various forms of corrosion is tothen develop methods for avoidance of each and these are alsolisted following each definition. Several case histories are alsonoted to demonstrate actual, practical solutions.
- Edition:
- 99
- Published:
- 01/01/1999
- Number of Pages:
- 29
- File Size:
- 1 file , 5.9 MB
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