In this article I will touch a sensitive but extremely important point with the aim of making you, my reader, start questioning the notion we all have taken for granted for so many years “rating for corrosion resistance”. I will encourage you to ask yourself this simple question: “Is rating an accurate form for the evaluation of corrosion performance/resistance?”
We all know that in the hydraulics business there are few aspects more important or more spoken off than that of the rods corrosion rating. In order to evaluate the potential of a producer or that of its product, we have taught ourselves to ask questions such as “how long it will last in NSS?” or “what do you guarantee for corrosion resistance?”. The answer inevitably will be the blunt and totally unsatisfactory standard phrase that will hit you: “R9 at 200 hours”. This has become the standard answer received from every single chrome product supplier (big or small, good or bad) – it has become a “benchmark or a trademark” answer, as everybody is marketing their products as per this rating.
During these past few years, I have tried to find the answer to this question by trying to understand aspects such as: what does R9 means? Is this satisfactory for my particular application? Does R9 mean that from the start I accept a rod that is not fully corrosion resistant for the given time? Can an accelerated test performed under controlled and unlike real world conditions, that give me a number as a result, is cause for reassuring me that the bar is good or bad? What is the real world condition test rating that corresponds to a rating 9, result obtained in laboratory conditions?
After carefully assessing various test performed on production batches as well as test runs spread over many years, I have come to the understanding that giving a “number” value (even the highest one found on a fix values scale), does not provide guarantees as per what I need, thus making me to realize envision the idea that the “RATING IS DEAD!”.
I know what you think as this has been also my first thought when I first envisioned this…….how can this be?
Well, let’s check out some of the facts that made me challenge the “rating 9” myth being the benchmark of the industry:
- salt spray test performed and interpreted in according to EN ISO9227 and EN ISO10289, lacks real world conditions of cycling between wet and dry conditions, heat and cold, various UV radiations to which the rods are exposed during its life span. To this end many OEM’s have started to ask for SCAB (Simulated Corrosion Atmospheric Breakdown) tests according with EN ISO11474, and while slower and more difficult to achieve, this sort of testing is more suited to mimic the conditions that rods will face in real world applications, thus providing a somewhat more reassuring result;
- limited sampling of the test specimens. A typical production batch can run for thousands of meters but you only test 0,00..% out of that production run;
- results interpretation by the lab technician;
- lack of ability to compare actual results over a spread of time (results incidents – how many R8, how many R9, how many R10; at what intervals and with what frequency for each one).
Does this mean that all ratings are useless?
YES because as already pointed out, you can’t place the equal sign in between. An R9 obtained under controlled laboratory conditions (accelerated conditions, true), and an R9 obtained in real world conditions.
NO because these tests can still be used to compare fast and with relative ease, different types of rods (either of different steel grades, chrome plating techniques and or thickness).
In my opinion the only evaluation/guarantee that needs be requested from any hard chrome plated supplier is the one that does not allow for any interpretation, any argument or any negotiation, and that notion is simply “NO RUST AFTER ‘X’ HOURS”.
If you have any comments, input or observations, feel free to share them here. I’d be happy to know your thoughts.
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