Q: I’m running a high temperature ethylene process that will reach 750-850C. I need a fastener that is carburization and creep resistance. Also moderate corrosion can be an issue. Any suggestions on materials?

A: This process is ideal for Incoloy 800H or 800HT bolting. These materials are designed for long-term high temperature use. These specialty alloy fasteners are typically used in temperatures above 1500°F where creep and stress rupture protection required. Incoloy bolts also offer moderate corrosion resistance to seawater, brine, sour gas, chlorides and sulfur containing atmospheres as well as oxidation and carburization. However depending on the size you need Incoloy fasteners may have limited availability so Inconel 600 bolts would be a safe bet as well.

Q:

Hello, I currently have an application that requires high strength set screws. One of our machines uses air cylinders with threaded shaft ends made of alloy steel set screws. The set screws are actually shearing off in our application, causing damage to the cylinders and equipment. I am looking for high strength set screws to swap out the current alloy steel ones. I would rather choose “over-kill” screws than something that won’t be much stronger than what I have now.

A:
Its a little hard to make a recommendation without more specifics, but a good place to start would be 17-4PH. This material is heat treated and can be very strong depending on the heat treatment desired. For example, the H900 is strongest with a yield strength of 185ksi but more brittle than an H1150 at yield of 125 ksi. As a point of reference this is about 3x stronger than 316 stainless. The combination of increased yield strength and material ductility will likely solve your problem. Unless you know the material you are working with now, you might want to start with the H1150 heat treatment as this material gives a good blend of properties.