Chemical Resistant Coatings

A chemical resistant coating is a fluoropolymer or composite barrier applied to metal equipment to protect the substrate from attack by aggressive chemicals — strong acids, strong bases, oxidisers, solvents and reactive process media. For industrial chemical service the most common coatings are PTFE, PFA, FEP, ETFE (Tefzel) and ECTFE (Halar). Each has a different chemical resistance envelope and maximum operating temperature.

PTFE and PFA share the broadest chemical resistance envelope of any industrial coatings — both are resistant to nearly every industrial chemical except molten alkali metals, elemental fluorine and highly reactive fluorinating agents. PFA adds a nonporous melt-flow film making it the best for combined chemical and permeation barrier service up to 260 °C. Halar (ECTFE) has narrower chemical resistance at ambient but is the best fluoropolymer for sodium hypochlorite service and offers 10–100× better permeation resistance than PTFE.

Choose Halar (ECTFE) when permeation resistance is critical, when you need thick-film barrier lining up to 2,000 µm, or when the service includes sodium hypochlorite (bleach) — Halar is the best fluoropolymer for NaOCl and rated to 150 °C. PTFE or PFA are the better choice for hot concentrated nitric acid (above 66 °C), methylene chloride, chloroform and hot amines, where Halar is not recommended.

Yes. AST recoats existing process equipment including tanks, vessels, valves, pipework, fittings, stirrers and fabricated assemblies. Existing coatings are removed by thermal burn-off and silica bead blasting, and a new fluoropolymer system is applied. For heavy-duty chemical barrier applications AST can build Halar or ETFE thick linings up to approximately 2,000 µm.

PTFE and PFA are rated to 260 °C continuous — the highest of the fluoropolymers. FEP is rated to 200 °C. Halar (ECTFE) and ETFE (Tefzel) are both rated to 150 °C continuous. For aggressive chemical service above 150 °C the coating choice is effectively PTFE or PFA only. Temperature de-rating also applies in specific chemicals — hot concentrated nitric, for example, limits ETFE and Halar far below their nominal maximum.

AST maintains manufacturer technical data from Chemours (PTFE, PFA, FEP, ETFE), Solvay (Halar ECTFE) and PPG/Whitford (Xylan) and can cross-check any specific chemical, concentration, temperature and exposure regime against the latest data sheets. Our public Chemical Compatibility Guide covers 30+ of the most commonly specified industrial chemicals. For critical or unusual media AST has direct access to Chemours technical support as a licensed Chemours applicator.