temperature data for a 2009 summer day in New Orleans, LA. The The majority of your spray package products will be stored and data for this graph were obtained from the U.S. National Oceanic used at room temperature. However, a fraction of the containers & Atmospheric Administration web site. produced each year will also be exposed to temperatures above Notice in Figure 1 that: and below room temperature. Thus, we recommend the follow- •The time for the peak indoor, non-air conditioned ware ing guidelines for storage stability testing above and below room house temperature lags the time for the peak for the outside temperature: temperature •Do not use higher temperature to accelerate the corrosion •The indoor temperatures are lower than the outdoor tem rate for metal and polymer spray package materials peratures •Use historical temperature-time data to determine maxi •Temperatures above 90°F (32°C) last only a few hours per mum and minimum temperatures to which your spray pack day age products might be exposed •Use this historical data to estimate how many days per year A survey I conducted on peak weather temperatures for several your spray package products are exposed to temperatures above cities around the world indicated that peak temperatures for most and below room temperature cities are typically below 105°F (41°C). Higher temperatures were, •Use your estimates to determine the test length for storage or course, observed in desert cities. temperatures above and below room temperature We can use the graph (previous page) to estimate approximate- •Use the majority of your test samples for room temperature ly how many days per year the outside air temperature is above storage, and a smaller number of test units for storage tempera 90°F (32°C) in Louisiana. First, let’s assume summer lasts approxi- tures above and below room temperature mately 5 months in this city (June through October—150 days). Next, use the graph to estimate the amount of time tempera- Following these guidelines will also increase the statistical confi- tures are above 90°F—typically around two hours. We then esti- dence in the storage-stability test results at room temperature— mate that spray products are exposed to temperatures above 90°F most likely the most common temperature where the majority of (32°C) for approximately 13 days each year (two hours per day x your spray package products are stored and used by consumers. 150 days). Please send your questions/comments/suggestions to Consequently, 39 days of storage testing at 90°F (or slightly rustdr@pairodocspro.com. Back issues of Corrosion Corner are above) would simulate three years. A similar estimation could be available on CD from ST&M. Thanks for your interest and I’ll see made for storage temperatures below room temperature. you in February. Spray January 2013 37
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