Buyers often approach this as a cost question. It is not. The material is decided by what is inside the vessel, and getting it wrong produces either a corroded shell or a cracked lining — both of which cost far more than the price difference.
Glass-lined wins when the medium is acidic
Glass lining is resistant to most inorganic and organic acids, organic solvents and weak bases at almost any concentration, and it does not contaminate the product with metal ions. Its surface is smooth and non-stick, which matters in crystallising and polymerising processes where material wants to adhere to the wall. For API synthesis and fine chemicals it is the default for good reason.
Glass-lined fails on three specific things
Hydrofluoric acid — at any concentration, any temperature — will destroy a glass lining. So will fluoride-bearing media. Strong alkali is a problem above roughly pH 12 and 100 °C. Phosphoric acid becomes aggressive at concentrations above about 30 % and temperatures above 180 °C. A buyer who does not know their fluoride content is buying blind.
Stainless steel wins on alkali, pressure and hygiene
Where the medium is caustic, or where pressures above the glass-lined range are needed, or where the process demands a polished hygienic surface with no possibility of a chipped lining, stainless steel takes over. Type 316L covers most pharmaceutical and food duty; titanium, duplex and Hastelloy handle the difficult cases, and clad plate keeps the cost of an exotic contact surface under control.
PTFE lining is the third answer
For media that defeat both — fluoride acids, strong oxidisers, ultra-high-purity work — a steel shell with a PFA, PTFE, ETFE or ECTFE lining covers the widest corrosion range of the three families, does not scale or foul, and sheds no ions. The trade-off is mechanical: fluoropolymer linings are less tolerant of local impact damage and of deep vacuum than either glass or steel.
How to make the decision quickly
- Write down the medium's exact composition, including trace fluoride and chloride.
- Write down the concentration and the maximum temperature, not the nominal one.
- Check whether the process runs under vacuum or pressure, and how much.
- Only then ask for quotations — and give every supplier the same brief.
If you can supply those four things, the correct material usually becomes obvious, and you will not be choosing between quotations that were never comparable.