304 SS electric storage water heaters are developing leaks

A. I suspected is mainly caused by chlorine in water was attacked the SS material and caused the holes problem after few months used.

A. I agree with TEChuah -- chlorine (as chloride) plus temperature is a very common cause of 304 SS corrosion. If all SS areas exposed to the hot water are corroded, a more chloride-resistant alloy is needed. 316 SS is the next step up, a 'duplex SS' such as 2205 is better. The 2B refers to the surface finish, not a grade of 304 SS.

If only localized corrosion occurs, 304 may be usable with modified techniques:
If only areas contacted by steel forming tools and clamps are corroding, chemical passivation to remove iron contamination will help.
If only severely bent areas corrode, residual tensile stress is contributing to the corrosion. After forming, the SS should be cleaned and then stress relieved (heat treatment).
If only welds are corroding, there are many possible problems -- weld contamination, residual stress, chromium depleted zone, etc. Best to have a metallurgist examine. It may help to use the low carbon grade of 304: 304L, and an extra low carbon (ELC) filler metal to avoid chromium depletion (as carbides in the welds).

A. Mr Adrian Yeo

The phenomenon of SS tanks corroding is controllable by Passivating the SS after Manufacture before assembly.

We have similar examples here in India using SS passivation on welded SS tanks of both 304 and 316 grades. The life extends considerably.

Removal of free iron on un welded surfaces and restoration of the Chrome rich Surface layer is the mechanism which works to extend the corrosion resistance of SS surfaces.

Inorganic acids do not provide satisfactory results because thy extent the corrosion prone sites, and re deposit free iron.

Proprietary solutions work in service and deliver results.

Regards,

A. Hi Chaitanya. I'd say 304 stainless steel is the safest bet. Not necessarily because it is actually better, but it at least demonstrates that the vendor is open to spending money trying.

My own personal experience for what it's worth, as a mechanical engineer with 50 years metal finishing experience, is that a consumer, no matter how experienced, cannot evaluate a product based on sales pap specifications :-(

Regards,

A. Dear Mr Sirsat,

If you are planning on Solar Water system in your area, and there is only hard water supply; the fins will choke up with Calcium salts. Since you asked about corrosion I suspect that is your problem. Unless running a solar water heater for commercial purposes with an online RO system, dont waste your money. Around 80 % of all Solar systems are junked within 6 months all over India.

A. It is factually incorrect to say
"Around 80 % of all Solar systems are junked within 6 months all over India". I know people using solar water heaters for more than two decades in individual homes as well as in hotels etc. ( what is the probability that they fall in the 20% slab?!) We used to boil water for drinking in the same stainless steel vessel. Scales do build up over a period of time at the bottom and sides of the vessel though we use water supplied by the corporation which is not expected to be hard. Generally,in solar collectors, water flows through copper tubes to which fins/sheets are attached. Since these have been working for several years scale formation does not seem to be a major problem. Probably scale formation is less on copper or flowing water minimises scale formation. Experts may throw some light.
These days we get two types of solar collectors- one with fins/sheets attached to copper tubes and the other with tubes with special solar selective coating imported from china. Both are popular.