Whenever the joint involves stainless steel, whenever copper is prohibited by specification, and whenever service temperatures exceed the ceiling of a copper product. Stainless is the most common trigger: copper forms a galvanic couple with it and drives corrosion, while nickel does not. Nuclear, chemical, refinery and many marine specifications also exclude copper outright, in which case nickel is the standard substitute and the choice is made for you.

Products are commonly rated to around 1,400 °C, the highest of the widely available metallic anti-seize compounds, with the graphite content contributing lubricity as the carrier burns away. As always the figure describes the compound in isolation. Confirm it against the specific product data, and check that the fastener material, the joint and any coating on it are themselves suitable for the service temperature you are designing to.

Nuclear specifications restrict copper, lead, zinc and other low-melting-point metals because of their effect on stainless and nickel alloys at temperature, and they impose tight limits on halides and sulphur, which can promote stress corrosion cracking. Nickel-based compounds are produced to nuclear-grade formulations meeting those limits and are supplied with the certification to prove it. Where a job calls for nuclear grade, the certificate is part of the product and should be obtained with it.

Yes, and it is the usual recommendation. Stainless fasteners are highly prone to galling, where the mating threads cold-weld under load and seize during tightening, sometimes destroying the fastener before it is even in service. A nickel compound separates the thread flanks and prevents that, without the galvanic penalty that copper carries. Apply a thin film to the male thread and reduce the tightening torque as the manufacturer specifies.

Yes. Anti-seize is a lubricant and reduces thread friction substantially, so a fastener tightened to its dry torque figure will carry considerably more tension than intended and may yield or fail. This applies to nickel compounds exactly as it does to copper and aluminium. Use the manufacturer's stated reduction factor for the product, and where a joint is critical, consider tightening by bolt tension or angle rather than torque alone.

Nickel compounds contain metallic solids and are excluded wherever any metal contamination matters, such as food and pharmaceutical production or joints later inspected by dye penetrant. Metal-free compounds use graphite, PTFE or ceramic solids instead and cover those cases. Nickel generally offers higher load capacity and a higher ceiling than most metal-free products, so the choice turns on whether metal content is permitted rather than on performance alone.

Apply a thin, even film to the male thread only, keeping it out of blind holes in quantity where trapped compound can crack a casting. Keep the container closed so the carrier does not dry out, and stir if the solids have settled. Use gloves and eye protection and a dedicated brush, since sharing a brush between compounds cross-contaminates and can introduce copper into an assembly deliberately specified copper-free.