304 stainless steel material, in theory, there is no welding, and after passivation of corrosion case, most can stand 30 days 35 degrees Celsius brine spray.
But the thermos bottle are welded, surface passivation treatment will have some damage, can withstand corrosion concentration of 1% saline for 24 hours, no rust has been good.
If it is 304 stainless steel, for a long time (at least for more than 30 days), light brine (the concentration is estimated to be less than 1%), it must be rusty. May the 316 or 4XX label be possible? But civilian products do not use such expensive materials.