Isaiah's call vision, at the opening of the sixth chapter, is the only place in the Hebrew Bible where seraphim stand above a throne. The prophet sees the Lord seated, high and lifted up, with the train filling the temple, and above him the seraphim, each with six wings: two covering the face, two covering the feet, and two for flight. They call to one another, holy, holy, holy, and the doorposts shake at the voice while the house fills with smoke. One of them takes a live coal from the altar with tongs and touches it to the prophet's mouth.
The name comes from a root meaning to burn. The same word is used elsewhere in the Hebrew Bible for the fiery serpents of the wilderness narratives and for a flying saraph in Isaiah's own oracles, so the noun does not by itself mean a winged attendant of a throne. It means a burning thing, and the sixth chapter is what gives it the form later tradition remembers.
The detail the ranked lists keep is the coal rather than the wings. Purification by fire, applied to one named person, at one moment, in order to make speech possible, is a narrower and stranger act than praise, and it is the only thing in the whole passage that the seraphim are described as doing. Everything else they are said to be is posture and voice.