Corrosion has plagued process plants since the chemical industry began. After all, many sites handle materials that are inherently corrosive to steel or can become so under conditions that might occur. Acids, bases and salts all can harm hardware and equipment, as, of course, can water.
Corrosion causes product contamination, leaks, and equipment malfunctions, which, in turn, can lead to quality, environmental and safety issues. Some major accidents have stemmed from corrosion. Even if a site doesn't suffer overt mishaps, corrosion shortens the service life of assets. NACE International, formerly the National Association of Corrosion Engineers, (www.nace.org) puts the annual cost of corrosion in the chemical and pharmaceutical manufacturing and petroleum refining at over $5 billion in the U.S. alone.
Sometimes, corrosion itself doesn't create a hazard but ill-thought-out or simplistic responses may get plants into trouble, as Dirk Willard relates his Field Notes column "Solve the Real Problem." He cites a situation in which an engineer decided to replace carbon-steel bolts on a vessel with type 316 stainless steel ones. He didn't realize this would require de-rating the pressure limit of the vessel by about 15%. If no one else had realized it either, the plant might have put itself at risk.
Yet, historically, engineers have learned little, if anything, about materials' compatibility and corrosion while in college. NACE International is working to expand and improve university corrosion programs but more still needs to be done.
Exacerbating the problem, too many plants lack a specialist with in-depth knowledge on the subject.
So, perhaps not surprisingly, corrosion-related questions account for a large portion of inputs to our online "Ask the Experts" feature — nearly on par with queries about mixing. Our corrosion guru, Brian Dalder, an engineering consultant at Eli Lilly & Company, recently provided guidance on the material of construction for a vessel for a clean-in-place tank (www.chemicalprocessing.com/experts/answers/2012/060.html), which material is suitable for throttling control valve trim for molten sulfur (www.chemicalprocessing.com/experts/answers/2012/059.html) and what is causing damage to the rubber lining in a scrubber tank (www.chemicalprocessing.com/experts/answers/2012/058.html). If you have a corrosion concern, take advantage of his expertise. However, when posing a question, remember the more specific you can be (e.g., about the composition of streams, including minor constituents, temperature, pressure and material of construction currently in use) the better the answer Brian likely can provide.
We, of course, also publish articles about dealing with corrosion, such as this issue's "Successfully Combat Pipeline Corrosion."
NACE International provides a variety of resources, including publications and conferences. Among local events coming up are the NACE Central Area Conference in Chicago in August and the NACE Eastern Area Conference in New York City in October. The "Corrosion 2013" conference and exposition will take place in Orlando, Fla., next March.
The organization offers training programs, e.g., on cathodic protection and coatings. It also is developing standards on many specific aspects of corrosion protection — for instance, on installation and inspection criteria for external pipe coatings, on-line monitoring of cooling water, steam generating systems' lay-up and start-up, and materials for storing concentrated sulfuric acid at ambient temperatures.
Raising staff skills is important, but so too is an effective corrosion-monitoring program. Unfortunately, our April online poll on ChemicalProcessing.com provides troubling data. We asked, "How do you rate your site's corrosion monitoring practices?" and fully half of respondents termed the efforts "marginal" (for fuller details, see www.chemicalprocessing.com/articles/2012/survey-corrosion-monitoring-practices.html). Maybe this testifies to the dearth of expertise available at plants and thus a lack of knowledge of what to do. But reacting to the consequences of corrosion rather than addressing issues before they become problems directly conflicts with the quest of many operating companies to achieve predictive maintenance.
Some techniques to assess corrosion, such as the use of coupons, have proven their effectiveness for decades. Now, in addition, instruments can provide online real-time monitoring of generalized corrosion, i.e., uniform loss of material from a surface, and even localized corrosion such as pitting ("Plants Pit New Tools Against Corrosion"). Such instruments enable treating corrosion as a process variable that can be related to other variables and specific upset or transient conditions — potentially providing insights that can help avoid or minimize future corrosion.
Consider this a wake-up call to start combating corrosion correctly.
MARK ROSENZWEIG is Chemical Processing's Editor in Chief. You can e-mail him at Mrosenzweig@putman.net
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