Where the heater tube rests on a support, the contact point is a crevice. Water and chloride sit in the gap between tube and support, and bare 316 corrodes there. A cladding that stops at the support leaves the contact point exposed. The cladding must cover the tube through the support.
The filled-PTFE film covers the tube and the support saddle. The glass-fiber composite is non-absorbent. The smooth surface prevents crevice chemistry. Material-selection service specifies the coated support length on the drawing. At each outage, the support saddle is inspected for wear.
The support is also lined or coated, so no metal touches the cladded tube. The result is a heater that does not crevice at its supports. Procurement buys the coated supports. The dense film resists fretting.
Plants that had support-point corrosion found the cladding stopped it. The smooth, non-absorbent film prevents the crevice. The result is a heater that is protected at every contact point, because the cladding extends over the supports.
The support saddle is a hidden crevice. Where the tube rests on a steel support, water and chloride sit in the narrow gap between the tube and the saddle, and bare 316 corrodes there in a sheltered spot the inspector rarely sees. A cladding that stops at the support leaves that contact point exposed. The film must cover the tube through the saddle, and the saddle itself must be lined. The filled-PTFE composite is non-absorbent, so it does not wick water into the gap, and the smooth surface prevents the crevice chemistry from starting. Material-selection service specifies the coated support length on the drawing, and the saddle is lined or coated so no bare metal touches the cladded tube. At each outage, the support saddle is inspected for wear, because the tube can flex on its saddle and fretting can wear the film. The dense film resists fretting. Procurement buys the coated supports as matched parts. Plants that had support-point corrosion found the cladding stopped it, because the non-absorbent film prevented the crevice. The result is a heater that is protected at every contact point, because the cladding extends over the supports rather than ending just short of them.
The saddle is lined so no bare metal touches the cladded tube. At each outage, the saddle is inspected for fretting wear. Procurement buys the lined saddle. The result is a heater that does not crevice at its supports, because the non-absorbent film prevents the sheltered chemistry from starting and the lined saddle prevents metal-to-metal contact.
The support length is coated on the drawing, and the saddle is lined. At each outage, the saddle is checked for fretting. The result is a heater that is protected at its contacts, because the non-absorbent film prevents the sheltered crevice chemistry and the lined saddle prevents fretting wear.
The filler choice is not cosmetic. Glass-fiber filler gives chemical resistance and electrical insulation, while carbon filler gives wear, conductivity and anti-static drainage. The pre-treated filler is twin-screw dispersed. Material-selection service analyzes the chemistry and area classification: glass for ordinary chloride, carbon where static must drain. At commissioning, the gasket or cladding resistance is measured. Procurement buys the specified filler grade. The result is a heater with the right filler for the duty.
