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Pitting Corrosion in Domestic Hot Water Heaters in Greece

The domestic hot water system was affected fairly uniform with pitting corrosion. A Reverse osmosis plant is equipped (sea water) for preparation of desalinated water, which is then mixed with fresh water for domestic purposes.

Do you believe that the use of stainless steel 316 was the correct selection taking into consideration the following:

Temperature
PRE (pitting resistance equivalent)

iS IT POSSIBLE TO HAVE PITTING CORROSION EVEN AT NORMAL pH (7.5)

CHRYSANTHOS CHRYSANTHOU
LCL - Athens, Greece
2001

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Dear Crysanthos

For your first question I would say about the kind of SS 316 is the right choice but not the best, I recommended 316L(14435 german number)with his higher resistance against seawater. And second you have to passivate all surfaces that have bean treated with welding grinding etc. Because I know how my homeland fellows works and that is something they never do and I am 99% sure that this is the solution of your problem.

Athanassiadis Stelios
Passivation Greece SA - Thessaloniki
2001

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I experienced deep pitting corrosion on type304 stainless steel twice last year. One is under fresh water use, and another one is sea water use. Both cases were finally supposed being occurred by deposit formation on the surface of stainless steel. And I verified that reason was correct by lab testings. In the testings, 316 showed better resistance tendency than 304, and 316L showed better than 316L Although better materials are more expensive.

Any stainless steels should be susceptible for pitting by deposit formation. The important thing to use such materials sound in likely possible in deposit formation is to avoid stagnant region in the system. Of course, it is much better to eliminate debris in the stream.

Hiromi Kawaguchi
- Tokyo, Japan
2001

Perhaps you should consider using epoxy vinyl ester resin to be used in the construction of the inner tank.

Dawie Thirion
- Cape Town, RSA
2004