Q: We are having some issues with corrosion in a highly sensitive pharma application. I need a bolt that is corrosion resistant to both acids and organics, but is usable in a high purity situation. Temperatures can reach about 120F. Also, it would need to be a polymer screw available in a socket head style.

A: There are several options available but it does depend on the acids in use and the strength requirements of your application. For highly corrosive applications that does not have high strength requirements PTFE will be able to offer the best corrosion resistance and easily handle the temperatures as its good to 260C or ~500F. PTFE screws are nearly inert to most acids, bases and organic compounds. PTFE screws are also approved for use by the FDA.

If you require more strength in your application you should also consider PVDF screws. PVDF provides a good level of corrosion resistance and is approved by the FDA, USDA, and NSF. PVDF is usable to about 150C as well and is significantly stronger than PTFE (almost 2x stronger). Both PTFE and PVDF screws are offered in medical grades and can be made in the socket head style or any other head design or style.

I’m running some laboratory testing in a mixed acid environment and would like to use a corrosion resistant polymer as apposed to a metal. I’ve tried PEEK screws but am still struggling a bit with some acids. Is there anything better?

PEEK screws provide reasonable corrosion resistance to most acids but is more geared for high strength applications in moderately corrosive applications. For a polymer fastener that is more corrosion-focused, I would go with PTFE fasteners. PTFE screws will not provide the strength of PEEK, but they are much more corrosion resistant. If the strength of PTFE screws are good enough (approximately 3900psi at room temperature) for your application then you likely improve the corrosion resistance of your fasteners.