Caustic soda at temperature attacks stainless through caustic embrittlement and general corrosion. A filled-PTFE cladding seals the 316 from the caustic, because the PTFE matrix is inert to strong base. The glass filler is also stable.
The material-selection service specifies the caustic-service cladding, with a dense film. At each outage, the film is inspected for blistering. The controller holds the temperature. Procurement writes the caustic spec.
The smooth surface sheds the caustic. The dense film does not absorb. The result is a heater that handles hot caustic behind an inert film.
Plants that had caustic corrosion on 316 switched to the cladded heater and stopped the attack. The result is a heater that survives hot caustic, because the PTFE matrix resists the base and the dense film blocks the chemistry.
Hot caustic soda is a deceptively aggressive service. At temperature, concentrated caustic attacks stainless through both general corrosion and the risk of caustic embrittlement, and a bare 316 tube can fail surprisingly fast. A filled-PTFE cladding seals the 316 from the caustic, because the PTFE matrix is inert to strong base, and the glass filler is stable. The material-selection service specifies the caustic-service cladding with a dense film, because a porous coat would let the hot alkali through. At each outage, the film is inspected for blistering, and the controller holds the wall temperature within the safe range. Procurement writes the caustic spec, including the film density requirement, on the purchase order. The smooth surface sheds the caustic, and the dense film does not absorb it. Plants that had caustic corrosion on 316 switched to the cladded heater and stopped the attack, and they found the scheduled holiday test kept the barrier intact. The result is a heater that handles hot caustic behind an inert, dense film, because the PTFE matrix resists the base and the composite blocks the chemistry before it reaches the stainless.
At each outage, the film is inspected for blistering, and the controller holds the wall temperature. Procurement writes the caustic spec. The smooth surface sheds the alkali. Plants that had caustic corrosion on 316 switched to the cladded heater. The result is a heater that handles hot caustic, because the dense, inert film blocks the alkali before it reaches the stainless.
The dense film is verified on each batch by a thickness and density check. Procurement requires the certificate. The result is a caustic-resistant heater, because the inert PTFE matrix and the dense film block the hot alkali.
Safety drives the specification. In wet chlorine, a filled-PTFE liner seals the titanium from the chlorine and any hydrochloric acid film. The glass-fiber composite is inert to chlorine, and the dense pre-treated matrix blocks moisture. The liner wall is increased, because a breach in chlorine service is a safety event. Process monitors track gas moisture as a backup, but the liner is the last line of defense. At each outage, the liner is inspected with extra care. Plants handling chlorine now line their titanium heaters as standard risk reduction.
