Electric urns with drinking water 1

[lovescroll]

Please help me to clarify this
why electric urns didn't crack when exposed to boiled drinking water around 80-100C, i heard that it will be contained with XX ppm of chloride.
Electric urns made from SS304 , that's all we know . and normally from manufacturing process it will definitely have a residual stress.

Thanks
N.

 

[EdStainless]

Typically drinking water does not have very high Cl levels, and in an urn the surfaces are always wet. The worst case is alternate wet/dry cycles where impurities can concentrate.
The other issue is that even though the urns have fairly high residual stress it mostly results from them being formed and stretched, so the residual stresses are in the opposite direction making them mostly compressive. Add to this the flexibility of the urns and you can see why cracking failures are rare. In commercial kitchens they do happen from time to time with larger heavier equipment.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[moltenmetal]

Think about cooking pots used with brine or salty food- they survive too, just fine. There is lots of plane jane 304 and 316 stainless steel used in food preparation equipment and it doesn't tend to crack automatically into sugar candy, and you can be guaranteed that it's not all fully stress relieved before being put into service.

Chloride SCC depends on a lot of things. It's not merely a matter of having chloride in solution, having residual stress and operating above 60 C.

Chloride stress cracks tend to start at chloride pits. You pretty much need pitting conditions for SCC to initiate.

If the surface is flushed and the passive layer allowed to "heal" between exposures, the likelihood of pitting and hence SCC reduces quite a bit, which may explain at least partially why the food equipment handles it so well. Food prep equipment also tends to have good surface prep, especially relative to ordinary stainless pipe.