Corrosion - It's Nature's Way
Many people fail to realize that corrosion of metal is a natural process that is the reaction of the man-made alloy with its environment in an attempt to return to its natural state - the oxide form of the metal.
In Water Treatment, we are actually trying to arrest the natural progression of things. It is never really true to say that a system is not subject to corrosion, but in a well passivated and treated system, the corrosion has been brought to a near standstill.
The fact is that the instant that metal is processed, it begins corroding (not a very settling thought when you consider that multi-thousand dollar boiler or cooling tower you just purchased). Once this is realized, there begins to be an added bit of respect shown for that water treatment guy who comes by regularly to check your systems and give you advice.
If the person you have knows the science of Water Treatment - and is not just there to sell you stuff- he can prevent (or at least delay - now that you know the nature of corrosion) a lot of corrosion-related problems from occurring in your facility.
Any rapid change in system parameters - chemical, mechanical, temperature - can upset his stability and start the natural process of corrosion that he is trying to delay. This is why regular on site testing should be done as well as in house testing. Any departure from stability can cause rapid and long lasting damage to the stability he is trying to achieve.