Heat resistant joining line seal system

A seal system comprising:

• a case defining a joint where two sections of the case join together, the case enveloping an internal space inside the case and separating the internal space from an external space outside the case;
• a seal disposed at the joint to seal the internal space from the external space;
• a case extension disposed at the joint and defining an expansion cavity on an outside of the seal, the case extension defining a nozzle opening that extends between the expansion cavity and the external space;
• and
• a lining of a heat responsive material coating an internal surface of the case extension in the expansion cavity in an unactivated state,
• wherein the heat responsive material is configured to expand to an activated state when exposed to heat above a threshold temperature and to pass through the nozzle opening encapsulating the case extension and insulating the seal from the external space.

A seal system for an auxiliary power unit of an aircraft, the seal system comprising:

• a duct of the auxiliary power unit defining a joint where two sections of the duct join together, the duct enveloping an internal space inside the duct and separating the internal space from an external space outside the duct;
• a seal disposed at the joint to seal the internal space from the external space;
• an extension of the duct disposed at the joint and defining an expansion cavity on an outside of the seal, the extension defining a nozzle opening that extends between the expansion cavity and the external space;
• and
• a lining of a heat responsive material coating an internal surface of the extension in the expansion cavity in an unactivated state,
• wherein the heat responsive material is configured to expand to an activated state when exposed to heat above a threshold temperature and to pass through the nozzle opening encapsulating the extension and insulating the seal from the external space.