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Water Quality & Stainless Electric Boilers

Water Quality & Stainless Electric Boilers

Water Quality & Stainless Electric Boilers

(OP)
My company makes miniature electric boilers for both high and low purity water applications.  As per PEB 5.3 we require deionized water greater than 1 Mego-Ohm/cm if the boiler is constructed from austenitic stainless steel.  Conversely, we also require stainless steel if the water purity is greater than 1 Mego-Ohm/cm.  I understand that stainless steel boilers are susceptible to stress corrosion cracking therefore you must use treated water.  It is also my understanding that water with high resistivity will aggressively attack carbon steels like SA-53B or SA-516-70.  I have two questions:

1) What would be a safe water quality standard for miniature boilers constructed from SA-53B and SA-516-70?

2) Why does the requirement PEB 5.3 only apply to electric boilers of the immersion element type?  I would think that any boiler regardless of heat source should have this requirement however I did not find an analogous statement elsewhere in the code.  Is there some simple explanation here that I am missing?

As always, the help here is amazing and you guys (and gals) are great.  Thank you in advance for all of your help!!

-Steris

RE: Water Quality & Stainless Electric Boilers

(OP)
So I've been thinking about my second question and the only reason I can think of is that the elements in a stainless boiler will typically have a stainless sheath.  Since the sheaths are thin and get very hot, they are the most susceptible to SSC and failure.  This could explain why the code specifically singles out electric immersion boilers versus electrode type boilers.  Anyone have any thoughts on this?

-Steris

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