Setting - Heater

The heater casing, brickwork, refractory, and insulation, including the tiebacks or anchors.

Spoilers / Strakes

The metal stack attachments that prevent wind-induced vibration.

Slag

Non-metallic solid material entrapped in weld metal or between weld metal and base metal.

Sootblower

A mechanical device for discharging steam or air to clean heat-absorbing surfaces.

Stack

A vertical conduit used to discharge flue gas to the atmosphere.

Sagging of a tube

Excessive sagging is usually because of a decrease in the structural strength of the tube caused by overheating. It may also be caused by improper spacing of hangers, uneven metal temperatures, or failure of one or more tube supports or hangers.