What type of stainless rusts?

In welding, 304 is certainly going to rust along both sides of the weld in the HAZ unless the protective oxide layer is restored. This can be done with a pickling paste/heat tint remover.

Due to the high carbon content in 304, the rust problem is the most extreme of austenitic stainless steels.

You will need to neutralize the rust at this point before applying the chemical treatment. I can't see the tanks but if I could, I might even tell you they are too far gone.

If you can't find this chemical, we'll have it. The site is www.usalloysweld/tech.com and the phone is 1-800-325-1568.

• U.S. Alloys

The most common stainless steels are the 300 and 400 series. You can identify the 300 series easily because a magnet won't stick to them.

Chances are, if the steel is non-magnetic, it's probably 304. 304, also called "18-8" (18 percent nickel, 8 percent chromium) is a good tradeoff between cost, tensile strength and corrosion resistance. 316 is much stronger, more corrosion resistant, and more expensive. (The 400 series is used in applications where strength is more important than corrosion resistance. 440, for example, is commonly used for knife blades.)

Anyone who has run a boat on salt water will tell you that stainless just "stains less".

As for these sprayers, I'd use them till they leak then scrap them out and go buy new ones. I prefer the heavy duty commercial all plastic ones. They will run you $80+ each for a 3 or 4 gallon but are well worth the money. I have one I use with a caustic detergent used for cleaning engines and one with kerosene in for cleaning #6 oil from piping system parts. I have these about 5 years and both are holding up fine.

I used to get the epoxy coated steel ones but every one of them rusted out in a couple years. There is no real good way of stopping the rust on the stainless ones you have and you'll probably waste more time trying to save them than it is worth to just buy a couple new ones when these go bad completely.