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:  Hi, I need a 1.25” X 15” bolt that can operate in continuous temperatures of 1000F. Currently we are using a heat treated carbon based 4140 fabricated machined bolt. At these temps the bolts are “Stress Relaxing” and we are losing our clamping pressure. In addition, when we change the load to shear pressure, we are losing the bolts completely. Help!

A: For this situation, I think the most economical option for a high strength bolt that will maintain it’s strength at 1000F is A286 alloy. A286 stays strong to 1300F with an ultimate tensile strength of 167 ksi. A286 bolts will be oxidation resistant and will be a lot more creep resistant under loads.