High-Temperature & Steam Service Packing

Steam and thermal cycling push temperature, oxidation and stress relaxation to their limit. Packing that is fine at 200 °C can fail quickly at 400 °C, so material ceiling — not just chemical fit — drives the choice.

Best materials for high heat

Temperature	Material
Up to ~260 °C	PTFE (limited)
~260–450 °C	Carbon fiber, reinforced graphite
~450–550 °C	Flexible (expanded) graphite, inconel-reinforced
Extreme / furnace	Ceramic fiber (high friction, non-lubricated)

Why graphite wins on steam

Stable near 500 °C; does not melt or burn.
Inconel-wire reinforcement resists oxidation and blow-out.
Supports fire-safe requirements (see API fire-test practices).

What to avoid

PTFE above ~260 °C — it softens, cold-flows and extrudes.
Organic- or oil-laden packings that carbonize and harden under heat.

See PTFE vs graphite for valves and valve stem packing for the valve-specific view.

Frequently Asked Questions

What packing is best for steam valves?

Flexible (expanded) graphite, ideally inconel-wire reinforced to resist oxidation and blow-out. It stays stable near 500 °C, far beyond PTFE's ~260 °C limit.

Why can't I use PTFE on hot steam?

PTFE begins to soften and cold-flow above about 260 °C, so it extrudes from the stuffing box and leaks as the steam heats the bonnet. Graphite remains stable.

How hot can graphite packing go?

Flexible graphite is typically rated to about 450–550 °C in oxidizing air (higher with metal-wire reinforcement and oxidation inhibitor). In non-oxidizing or inert atmospheres the ceiling is higher.

What about ceramic fiber for extreme heat?

Ceramic fiber handles very high temperatures but has high friction and little self-lubrication, so it is reserved for extreme or furnace-adjacent duties rather than general rotating shafts.