A refractory cover for steam tube yokes and hangers may be assembled or disassembled from parallel steam pipes or tubes circumferentially distributed around a cylindrical steam boiler furnace. The yoke and hanger assemblies that support such steam tubes are protected against deterioration and mechanical failure due to thermal and combustion gas interaction with the supports. The cover includes an open box and an end closure having interlocking U-shaped openings that fit around the pipe and cover one side of the yoke and hanger. A lid member includes an outer and inner interlocking U-shaped openings at 90 degrees to the box and enclosure openings which also fit around the pipe to cover the other side of the yoke and hanger. In a preferred form the box bottom includes a pair of parallel U-shaped openings to span a yoke and hanger which supports adjacent parallel steam pipes.