A few design improvement notes:
- PTFE is not Nylon. I'll assume from here on out you really mean PTFE here, but it's better known as Teflon. Nylon would be done entirely differently.
- You can't just snap these two parts together for an airtight seal. You can get mostly air tight, but you will not make an airtight seal between stainless and PTFE with just a snapped connection.
- PTFE is slippery stuff. It's well known for this property. You will need some kind of mechanical way to keep it on (such as end flanges that can be screwed onto the ends of the SST parts). Otherwise most mechanical stresses will break the very fragile airtight seal of the passive method, and up the power requirements of the active method.
There are two methods for joining these two materials.
In the passive method, you would roughen the stainless steel's surface to a white metal blast finish (SSPC.SP5 standard or NACE #1). Then the steel would be coated with a powder coat of PFA (or PFA/FEP combination), then baked in a powder coating application. Additional layers of PFA could be added, and baked on. A minimum of three would be recommended. Finally, heat both the stainless and PTFE to 260 Celsius, and join together at that temperature. The parts will have a fairly weak bond, but so long as the stress around the joint can be mitigated mechanically as discussed above, it will be workable.
This is more for robust applications and with thin, relatively flexible PTFE linings. In this method, you still treat the steel surface as mentioned above, but instead of all the thermal work, there is a manifold that would supply active compressed air to a thin layer of PTFE surrounding the joint. So long as the air pressure does not exceed the compressed air pressure, the mechanical push forces will maintain an active seal.
You should make samples ahead of time between the proposed materials and test them with a mechanical peel test (Such as an ASTM D1781 climbing drum test). A 50 lb/in peel is a bare minimum for pass/fail, 100 lb/in is more suitable.