Most requisitions for a lined reactor say "PTFE lining" and stop. Five fluoropolymers are in routine use for chemical process vessels in China — PFA, PTFE (F4), ETFE (F40), ECTFE (F30) and FEP (F46) — and they are not interchangeable. We are KAVORTE, an independent sourcing and engineering office in Zibo, Shandong. We specify, audit and ship glass-lined, stainless steel and PTFE-lined reactors from 50 to 30,000 L, and we do not own a factory. Here is how we separate these five on a live enquiry.
1. The five names, and what separates them
Two labels are chemical names, three are trade codes, so start with chemistry. The F-numbers are the Chinese convention: F4 is PTFE, F46 is FEP, F40 is ETFE, F30 is ECTFE.
The real divider is fluorine content. PTFE, PFA and FEP are fully fluorinated — every carbon in the backbone carries fluorine. ETFE and ECTFE are partially fluorinated copolymers: ethylene co-polymerised with a fluoromonomer, which buys mechanical strength and barrier performance at the cost of chemical breadth.
That single difference explains most of the decisions below. Chemically aggressive duty at high temperature points to the fully fluorinated three. Abrasion, or vapour permeating through the liner, is where the partially fluorinated two earn their place.
The crossover with glass lining is worth knowing too. Fluoride-bearing media, and strong alkali above pH 12 at 100 °C, are outside what a glass-lined vessel will tolerate, and those enquiries usually arrive as fluoropolymer jobs. That is a question of material family, not of which of the five.
2. Temperature: the first cut
The figures below are published continuous-service limits for the resin itself. They are not the limit for a lining inside a vessel, and the gap is large enough to matter.
- PTFE (F4): about 260 °C continuous.
- PFA: about 260 °C continuous, with better creep resistance and low-temperature toughness than PTFE.
- FEP (F46): about 200 °C continuous.
- ETFE (F40): about 150 °C continuous.
- ECTFE (F30): about 150 °C continuous.
Treat that list as a screen only. A fluoropolymer lining in a steel vessel is a composite, and the composite fails before the resin does. PTFE expands roughly ten times as much as carbon steel per degree, so every temperature swing works the bond or the mechanical retention, and flange faces and nozzle necks take the strain. In practice the service ceiling for a lined vessel can sit 20–40 °C below the resin figure, and the governing number comes from the lining process and the bond, not from the polymer.
Thermal shock is the harder test. A steam-out at 130 °C followed by a cold charge stresses the lining more than steady operation at a higher temperature. If your CIP cycle is aggressive, say so at enquiry stage — it changes the answer more than the name of the medium does.
3. Chemical resistance: where the five actually differ
PTFE and PFA are the same chemistry, and for corrosion purposes you should treat them as equivalent. What separates them is processability. PTFE is sintered rather than melt-processed, so lining it onto a complex vessel usually means sheet, mechanical retention or a loose lining. PFA is melt-processable and weldable, which is why it is the default where the geometry is intricate or the lining has to be seam-free. PFA also resists creep at temperature far better, and creep is what opens a seam or thins a liner at a gasket face over years of service.
FEP (F46) is fully fluorinated as well: smooth, non-stick and easy to weld. Its liabilities are temperature and softness. Serviceable below roughly 200 °C, but easier to score and erode than PFA.
ETFE (F40) is the tough one. High impact and abrasion resistance, good against acids and bases, and a lower temperature ceiling. Its gaps are real: hot concentrated sulphuric and nitric acid, ketones, esters, amines and some chlorinated solvents attack or swell it. Right answer for an abrasive, moderately aggressive duty; wrong answer as a generic substitute for PTFE.
ECTFE (F30) is the barrier material. It has the lowest permeability to hydrochloric acid, chlorine and water vapour of the five, which is why it is routinely specified for HCl, hypochlorite and wet chlorine service. Where a liner would otherwise fail by vapour passing through the wall, condensing behind it and blistering off the steel, ECTFE holds longer. Its gaps are organic: amines, hot polar solvents and some organics at temperature.
4. Permeation, vacuum, and the failure nobody tests for
The most common lined-vessel failure we see is not chemical attack; it is permeation. Every fluoropolymer passes a small quantity of vapour through the wall, driven by temperature and concentration. Behind a bonded lining that vapour has nowhere to go, so it condenses, builds pressure and lifts the liner. Once it lifts, the steel underneath corrodes, and the failure presents as a hole in a lining that looked intact.
Vacuum attacks the same weak point from the other side: a liner that is neither bonded nor mechanically retained can be pulled off the wall. This is where the application method matters as much as the resin. Spray coating, rotational coating and sheet lining give different seams, different thickness control and different bond quality on the same polymer.
Rule of thumb: pick the resin on temperature and chemistry, then pick the application method on vacuum, geometry and permeation risk.
5. Cost: what the money actually buys
On resin price alone, PFA is highest, FEP below it, ETFE and ECTFE lower again, and PTFE resin is the cheapest of the five. Fabricated price does not follow that order. Surface preparation, application method, thickness, the number of nozzles and baffles, the agitator shaft, flange facings and inspection carry more of the cost than the granules do.
- PFA earns its premium where temperature is high, the vessel cycles thermally, vacuum is involved, or the geometry is complex enough that a weldable seam-free lining is the only way to build it.
- PTFE remains correct for many duties: simple geometry, loose lining, no vacuum, at the top of the temperature range.
- ETFE (F40) is the abrasion answer and often the cheaper one, provided the medium sits inside its chemical envelope and the temperature stays moderate.
- ECTFE (F30) is the permeation answer, and is routinely cheaper than PFA in HCl service at moderate temperature.
- FEP (F46) covers moderate-temperature duties where smoothness and release behaviour matter more than creep resistance.
Honest trade-off: on a 60 °C dilute acid duty with no vacuum, no solids and simple geometry, the cheaper lining is usually the right one. PFA buys nothing you will notice there. The logic reverses at 150 °C with a steam-out cycle and vacuum distillation on the same vessel, where saving money on the lining is a false economy — that failure mode is not graceful.
6. What we need before quoting a lining
- Full medium list — process fluids plus cleaning agents, solvent traces, chloride and fluoride content.
- Temperature range — normal, maximum, and the steam-out or CIP peak rather than the nominal figure.
- Pressure and vacuum — including how often the vessel cycles between them.
- Solids and abrasion — catalyst, slurry or crystal content, and whether the agitator runs inside the lined vessel.
- Lining process, thickness and test — spray or rotational, bonded or loose, and the acceptance criterion for the holiday test. These belong on the numbered specification sheet, not in an assumption.
Takeaway
Stop specifying "PTFE lining" as shorthand. Name the resin, then state the duty that justifies it: operating temperature and the CIP peak, vacuum, abrasion, and permeation risk. Send those five facts and we will come back with the lining that survives the duty rather than the one that was easiest to quote. Confirm every figure — resin limits, lining thickness, test criterion and application method — on the approved drawing before fabrication starts, because that drawing is what you inspect against.