Do You sell Pre-Passivated Corrosion Coupons?
Posted 04 October 2012 - 11:32 AM
No we don't.
I am sorry, but that is just nuts.
Early in my career there were rumors that one of our largest competitors was soaking all of their corrosion coupons in a sodium dichromate solution so they could achieve better corrosion rates on their water treatment programs than we could. First, that is just plain cheating. But secondarily, what good does it do you to be able to point to a pristine corrosion coupon when the cooling tower has been destroyed by corrosion?
I realize that it would be nice to have a corrosion coupon of the exact same alloy, with the exact same age, the exact same stress, and the exact same passivisation layer. But that is impossible.
I would offer that the second best thing is to have a non passivated corrosion coupon of the same alloy as the metal you are trying to protect. Here is why:
When you place a corrosion coupon into a system the greatest corrosion always occurs in the first few days. With time the coupon approaches the same passivisation as the rest of the system. Corrosion rates get better the longer the coupon is in the system. Generally accepted within our industry is a 90 day test period.
If you place a passivated corrosion coupon in the cooling tower, you would expect the lowest corrosion rates initially and for corrosion to get worse the longer the coupon were left in the system. Perhaps if both coupons were left in the system together for a long enough period of time, they would both come to rest at the same corrosion rate.
But ask yourself: What am I trying to achieve? Am I trying to study corrosion coupons or am I trying to determine the best water treatment program to apply to my system which will give me the lowest possible corrosion?
If you are trying to achieve the second objective, wouldn't it be smarter to use a corrosion coupon of the same material that is even more sensitive than the system metal itself? Wouldn't this give you an early warning of trouble? It is like the canary in the coal mine that gives an early warning of methane. If you know something early, you have time to react and correct the problem.
A corrosion coupon should always be a leading indicator of corrosion not a lagging indicator.
One last note. We recommend three station racks with one coupon coming out in 30 days, one coming out in 60 days, and one coming out in 90 days. The first two are early warnings of something going badly wrong before the 90 day period is over. This allows you to make mid course corrections.
Posted 18 April 2013 - 12:52 PM
What is the ASTM Method by which they passivate those coupons? What is the purpose in using them other that to try to make your corrosion rates look better than some one else's?
I just went to there site and could not find any such product. I did see that they sold test kits to test passivation which is interesting.
Can you provide a hyperlink to the passivated coupons?
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