Abstract: In the threaded joint for pipes, a coating having a Vickers hardness greater than or equal to 310 is formed on a threaded portion of the box and an inner face of the box corresponding to a seal portion. The seal interference amount ratio ?/D of the seal portion in a pipe circumferential direction is greater than or equal to 0.002, where D is a seal diameter defined as an outside diameter of the pin at a seal point that is a point on the outer peripheral face of the nose of the pin at which the outer peripheral face first comes into contact with the inner peripheral face of the nose of the box and ? is an interference amount defined as an amount by which the outside diameter at the seal point is reduced by the box when the pin and the box are threadedly connected with each other.

Abstract: In the threaded joint for pipes, a coating having a Vickers hardness greater than or equal to 310 is formed on a threaded portion of the box and an inner face of the box corresponding to a seal portion. The seal interference amount ratio ?/D of the seal portion in a pipe circumferential direction is greater than or equal to 0.002, where D is a seal diameter defined as an outside diameter of the pin at a seal point that is a point on the outer peripheral face of the nose of the pin at which the outer peripheral face first comes into contact with the inner peripheral face of the nose of the box and ? is an interference amount defined as an amount by which the outside diameter at the seal point is reduced by the box when the pin and the box are threadedly connected with each other.

Abstract: A method is disclosed for accurately detecting an outflow of a slag into a stream of a molten steel when the molten steel is poured from a first vessel such as a refining furnace or a ladle into an intermediate vessel such as a ladle or a tundish through a melt-discharging hole or a nozzle. At that time, an inert gas is fed into the stream of the molten steel in the nozzle through a side portion of the melt-discharging hole or the nozzle, and the detection is made based on a change in a flow rate of the inert gas sucked into the stream of the molten steel and/or in a back pressure.