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: I have a high temperature application which is exposed to sulfur and chloride gasses. We’re operating at between 1200° and 1400°F. Any suggestions on a bolt material to consider?

A: To deal with both sulfuric/chloride atmospheres as well as high temperatures, you may want to consider Incoloy 800HT bolts or an Inconel 600 bolts depending on the concentrations of the acid gasses. Incoloy is an ideal material for long-term exposure in high temperature environments due to its oxidation, carburization and creep resistance. Incoloy 800 series bolts are all similar and considering your temperature range, I would suggest the Incoloy 800HT since it will not become embrittled even after long periods of usage in the 1200-1600° F. However if you have more severe corrosion issues especially during shut downs or equipment cycling due to acid gasses or condensation formed by the sulfur and chlorine components combining with water, the Inconel fasteners will provide better corrosion resistance than Incoloy.

Q: Need help with specific needs regarding Polyimide fasteners and their high temperature capabilities

A:   This Italian company was developing a new client oven.  They were interested in Polyimide fasteners and their high temperature capabilities. In particular they needed:

• Usability to 300°C
• Capability with metal connections
• Heat and electric insulation
• Used in a hot box of steel

Polyimide materials like Vespel fasteners are a good thermal and electrical insulator for this application. It is heat resistant to 300°C (572°F) continuous use and 500°C (932°F) intermittent. Vespel fasteners also has a 3.55 dielectric constant at 1MHz. The only drawback for using Vespel fasteners is that it is an expensive option. Here is a great video by DuPont on the heat resistance of polyimide compared to other polymers: http://www.dupont.com/products-and-services/plastics-polymers-resins/parts-shapes/videos/polyimide-heat-resistance-vespel.html