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Fla. Weathering Report: Getting up to Speed on Accelerated Testing

FRIDAY, FEBRUARY 3, 2012

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More items for Coatings Technology

We’ve all heard of the “Bermuda Triangle,” but the Commercial Coatings and Flooring Symposium at SSPC 2012 this week in Tampa added a different spin (or angle, you might say) with the term “The Impossible Triangle.”

And thanks to a clear, lucid explanation by the noted materials-testing authority Allen Zielnik, the audience at the symposium came away with very useful guidance to help them fathom the sometimes disorienting realm known as weathering testing of paint, coatings and other building materials.

 The “Impossible Triangle”
The “Impossible Triangle”: Accelerated weathering testing might deliver on two of the three objectives of the triangle, but not all three.

Allen, our good friend and Durability + Design technology editor, explained that “The Impossible Triangle” represents the dilemma faced by makers, specifiers and users of materials that are destined for use in exterior settings, and want to know how these materials will hold up without waiting some 10 years or so to get an answer from a test-site array in South Florida.

Accelerated testing methods, he said, can provide valuable information on what could happen in the real world of sunlight, rainfall, humidity, and temperature extremes. But if you’re looking for sure-fire results quickly and cheaply, you’re out of luck.

With The Impossible Triangle, he said, the customer can get two of the three—cheap and fast, for example, or good and fast. But he can’t get cheap, good and fast all in one perfect package.

Zielnik, senior weathering science consultant with Atlas Material Testing Technology, navigated the symposium audience through the science and technology of weathering performance testing in a discussion titled “Fundamentals of Making Good Decisions in Coatings Selection.”

The symposium, part of the SSPC 2012 convention program, featured an impressive lineup of topics and speakers. (Admittedly we’re slightly biased, as Durability + Design was the symposium sponsor). D+D assisted SSPC’s new Commercial Coating Committee and its chairman, Ken Trimber, in assembling the symposium program.

 The accompanying video offers a quick look at SSPC 2012.
 The accompanying video offers a quick look at SSPC 2012.

Weathering 101 Cheat Sheet

Zielnik covered a great deal of territory in this brief excursion through the world of weathering testing, but we’ll try to catch a wave or two of his drift.

Essentially, he provided a condensed version of “weathering 101,” touching briefly on the evolution of weathering testing from its humble beginnings on a “test fence” in 1906 in North Dakota to the current state of the art with instruments and apparatus that employ fluorescent UV lights or xenon arc lamps combined with varied temperature, humidity and salt sprays.

One high-tech approach relies on actual outdoor exposure, but the environmental effects are amplified by several multiples with the use of solar-concentrating “Fresnel mirrors.” A UV-intense desert location adds to the octane of this “outdoor accelerated” testing method which, Zielnik opined, has proven its mettle as a better predictor of what plays out in the reality show known as extended outdoor exposure.

 The Fresnel mirror solar concentrator amplifies the effects of sunlight.
The Fresnel mirror solar concentrator amplifies the effects of sunlight.

In the hands of “experienced practitioners,” accelerated weathering testing can be a valuable tool, Zielnik said. But there are hazards that make correlation with real-world conditions and effects a risky proposition. Use of fluorescent lamps that employ UV-B radiation can accelerate some degradation mechanisms, but might also initiate degradation that would not normally occur, or skew the mechanisms and mask or avoid degradation that might normally take place.

He cited the example of “catastrophic delamination failures” of some early basecoat-clearcoat automotive finishes that “passed” using UVB-313 fluorescent lamps.

(So, I can blame a lamp for the paint that peeled off of my old Pontiac?)

Chemistry can also come into play, Zielnik cautioned, noting that testing coatings of different resin chemistry “side by side” can be a formula for error. And there’s always the possibility that test conditions could be manipulated to favor one product over another.

Warning Signs and ‘Bogus’ Claims

Taking into account all the variables at work, Zielnik offered a number of general guidelines and “cautionary notes” for those with an interest in using weathering test data for selecting or specifying coatings, “but who lack the knowledge or inclination to do in depth research.”

• Performance data based on real-time outdoor testing in a recognized benchmark climate such as south Florida or a specified location is always preferable; however, specifications requiring it risk excluding many newer coatings with proven chemistries that are still under test.

• Outdoor exposure data of less that two years may be biased by seasonality or weather abnormalities.

• Benchmark climate results, e.g., south Florida, may be useful for comparison but do not predict or guarantee performance in other climates.

• Coatings information based on UVB-313 fluorescent-condensation test data should be suspect; standards specifically advise that these should not be used for weathering tests. Specifications should not be written using UVB-313 lamps for accelerated testing.

• Data based on UVA-340 fluorescent-condensation test data should specify the specific test cycle (e.g., 4-hour light/4-hour condensation) and the duration of the test expressed in exposure units of kJ/m2 @340nm, a.k.a. “Kilojoules,” or hours.

• Use of terms such as “equivalent to X years in Florida” should be highly suspect.

• In accelerated tests, performance should be treated as a qualitative relative ranking , e.g., A>B>C, rather than a quantitative difference.

• Only compare products tested under identical conditions and at the same exposure point.

• Practical limits of most weathering-test acceleration over real-time outdoor tests are typically no greater than 10:1. Claims of “400-hour testing is equivalent to 10 years” are usually bogus.

Summing up, Zielnik said accelerated weathering testing may be viewed as “voodoo magic, a necessary evil, or a valuable scientific tool, depending on perspective,” and all three positions can be justified. If used correctly by knowledgeable individuals, such testing can provide data and insight into coatings performance that would be “otherwise difficult or impossible to obtain,” while on the other hand it can result in “unjustified” findings.

And then there’s the chance it can be misused for commercial gain.

“However, given the accelerating pace of business today, it is unlikely that it can be ignored,” he said. “So when confronted with suspect weathering test data or claims, arm yourself with knowledge by seeking guidance from reputable coatings and equipment manufacturers and industry experts.”

I don’t know about anyone else, but I found Allen’s discussion of Fresnel mirrors, UV lamps and other high-tech weathering devices highly illuminating. You might say he brought us “up to speed” on accelerated weathering methods.

Lame wordplay aside, we look forward to seeing a more comprehensive discussion of the subject by Allen in Durability + Design.


   

Tagged categories: Laboratory testing; Performance testing; Site/field testing; Weathering

Comment from Glenn Summers, (2/13/2012, 8:46 AM)

Excellent article! Hopefully it may open some eyes to the advent of this type of science as it applies to the day to day workplace. I'm not certain that a number of people that refer to this testing as Voodoo Science, are not just disquising their ignorance and dismissing it all together, rather than devote some time to trying to understand and appreciate what they could learn from it. In my opinion there too many "We been doin it this way for Years" type decision makers in the Real World! I was fortunate enough in the late 90's, to get inside an accelerated testing group employed by NASA. It took me a Good six months, just to learn how to converse with these folks. Some real eye opening science is available for us! Operative Word is " Eye Opening".. Unfortunate that so much of this type of information is not Openly Shared with the general public, but then again, Who Cares ?


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