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Old 12-01-2009, 04:19 PM   #22 (permalink)
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Originally Posted by DrAndy View Post
Originally Posted by watterinja View Post
Try to avoid stainless steel if you're using chlorinated tap water. It suffers from stress-corrosion cracking.
yes, that's why I mentioned I need a tank that can take pressure without cracking

so it is the chlorine that causes it rather than the pressure variations?
The chlorides cause cracks that develop along the grain boundaries. Under a low pressure situation, the crack depth may not be too much of an issue - but, it will be there. The issue comes when applied pressure plus chlorides act simultaneously.

If the system is thermal-current driven (tank-panel), with gravity feed to the house, or draw-off to a pump suction, then the problem may not really show up as a serious failure, within a reasonable time.

Above 65'C is where the cracking really accelerates, although for most solar panels, they probably don't get up quite as high as that in the tank (well-mixed) too often (could, though in principle, if not careful on a very hot day, with excellent solar panel & very slow water circulation rate).
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