A metallurgical furnace cooling plate includes a cooling plate body with front and rear faces and at least one coolant channel inside the body, which communicates with a rear opening on the rear face; and a connection pipe connected to the body so that a pipe channel of the connection pipe communicates with the coolant channel, the connection pipe adapted for carrying coolant fluid to or from the channel. The body includes a receiving bore extending in a bore direction from the rear opening into the coolant channel, the channel being spaced in the bore direction from the rear face by a cover thickness of a cover portion and extends in the bore direction over a width. A connection pipe end portion extends into the receiving bore beyond the cover thickness and is form-fittingly received in the receiving bore along at least a portion of a width of the channel.

A method for detecting a fluctuation of a solidified layer, and a method for operating a blast furnace by employing the relevant method. In the method for detecting a fluctuation of a solidified layer, the fluctuation of the solidified layer in the lower part of a blast furnace is detected by using the amount of heat supplied to pig iron in the lower part of the blast furnace and the amount of heat in the pig iron tapped in a predetermined period.