Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Teflon coating problems
Q. We are looking for a suitable coating to be applied to the inside surface of a quantity of 1" 150# flanged components to resist 98% sulfuric acid at ambient temperature. The flange component is constructed from all carbon steel A105.
Previously we have used a Teflon coating, however this was eaten away within 1 week of service. We are unsure why the Teflon coat was attacked so vigorously given that Teflon is supposed to be compatible with this acid concentration.? I do not know the specific type of Teflon, however I believe that the Teflon coating was a spray on type.
Are you able assist with general advice on why the Teflon is unsuitable and also offer an alternative coating recommendation?
Thanks and kind regards.
Industrial Valving - Sydney, NSW, Australia
2007
A. Particles of Teflon® are perhaps still floating around, unattacked, within the sulfuric acid.
Was the coating applied via a thermal spray process? Considerable expertise is required to achieve good bonding and minimal porosity.
PTFE application usually involves grit blasting, phosphating, baked-on fluorocarbon binder coating and then baked-on PTFE. A high temperature cure [e.g., 275-290°C for one Xylan® formulation] gives complete melt flow to minimize porosity. A supplier list, from the Fluoropolymers Division (FPD) of The Society of the Plastics Industry:
http://www.fluoropolymers.org/products/FPDMaterialSuppliers.pdf
Also, PVDF (e.g., KynarFlex® Elf Atochem) and some varieties of PFA (perfluoroalkoxy) cure at somewhat lower temperatures and can be used up to 65 °C in sulfuric acid up to 98%.
Coating is easier said than done. Consider pre-coated pipe and fittings: http://www.resistoflex.com/
(This site has lots of information on chemical resistance & sulfuric acid.)
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.
2007
Need 350 °C Teflon service temperature
Q. Hello. I am new here and just came across this forum. My company is specialized in supplying anti-corrosive coatings currently we have a customer inquiring into a teflon high temp coating - service temp up to 350 °C. Application on stainless substrate. I have hosted at company web of Dupont Teflon, the highest temperature industrial teflon coating is 315 °C. Would you please help telling us where we can get a Teflon coating of working temp up to 350 °C? Thank you for your assistance.
Jimmy Cahyadi- Jakarta Barat, Indonesia
June 30, 2015
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