A stainless steel intermediate bulk container costs roughly ten to fifteen times what an equivalent caged composite IBC costs. For some applications that math is obvious — the chemistry would eat plastic for breakfast, the temperature is too high, the pressure is too much, the regulatory environment requires it. For other applications, the customer is buying a stainless tote because somebody told them stainless is "better," and what they actually have is a more expensive way to do the same job.
I want to lay out the cases where the upgrade is worth it and the cases where it is not.
Worth it: chloride chemistry.
Anything containing chlorides — sodium hypochlorite, ferric chloride, brines, certain industrial cleaners — will eventually attack a plastic tote, and certainly attacks 304 stainless. The right answer for chloride chemistry is 316 stainless, which contains molybdenum that resists pitting corrosion. Do not try to substitute caged composite. Do not try to substitute 304. Pay for the 316.
Worth it: sanitary process work.
Dairy, brewing, distilling, and most pharmaceutical process applications need clean-in-place capability, which means tri-clamp fittings and a smooth interior surface that scrubs cleanly with food-spec CIP cycles. A caged composite IBC cannot do this — the seams in the bottle and the small features around the valve and bunghole will trap residue. 304 stainless is the right material here.
Worth it: high-temperature contents.
A standard caged composite IBC tops out at about 140°F (60°C) before the HDPE starts to deform and the cage starts to take more of the structural load than it was designed for. Stainless handles 250°F or higher comfortably. If you are storing anything above 140 — hot oils, certain process intermediates — stainless is not optional.
Worth it: any pressurized application above about 5 psi.
Caged composite IBCs are designed for atmospheric pressure with a small headspace allowance. They are not pressure vessels. If your contents have a vapor pressure that creates more than a couple of psi of internal pressure (think alcohols, certain solvents at elevated temperature), you need a stainless vessel that is rated to the pressure you are seeing.
Not worth it: water storage.
Water at ambient temperature is the gentlest possible cargo for a plastic IBC. Caged composite will store water indefinitely. Buying stainless to hold water is, with very rare exceptions (potable water for a hospital backup system, for example), simply lighting money on fire.
Not worth it: most fertilizers and aqueous nutrient solutions.
Liquid fertilizer, fish emulsion, hydroponics nutrient solutions, ag chemicals at typical concentrations — these all run fine in caged composite. The savings versus stainless is enough to fund a year of maintenance and replacement parts.
Not worth it: short-term storage of unknown contents.
If you are buying totes to hold "whatever we end up with this season," buying stainless first is a guess that the unknown content will turn out to be aggressive. Statistically, it usually does not. Buy the cheaper composite first, learn what you actually have, then upgrade to stainless on the specific applications that need it.
The honest summary
Stainless is not better. Stainless is different. It is the right answer for a specific list of applications and the wrong answer for everything else. We will sell you whichever you ask for, but if you ask us which you should buy, we are going to walk you through this list.
— Aldo Ramírez, IBC Denver