Methods and systems are provided for treating oxide scale on the surface of a metal object. In one embodiment, a system temperature control apparatus controls the temperature of metal object's surface to an application temperature below the Leidenfrost temperature point of an alkali metal hydroxide aqueous conditioning solution. An application apparatus wets the metal object's surface at the controlled temperature with a thin layer of the solution that engages the oxide scale, and a heating apparatus heats the wetted surface to a final conditioning temperature above a melting point of the alkali metal hydroxide by an additional value selected to effect conditioning of the oxide scale at a reasonable but not excessive rate by the melting alkali metal hydroxide reacting with the oxide scale. The system terminates additional conditioning to prevent creation of additional oxide scale beyond the conditioned depth.

A method for continuously cleaning a moving strip in a cleaning installation including a tank containing an aqueous solution, at least a roll immerged in the aqueous solution for guiding the strip into the tank, at least an ultrasound emitter a feed for feeding an aqueous solution inside the tank, a tank emptier for emptying the tank, an aqueous solution estimator for estimating the aqueous solution level in the tank, a distance calculator for calculating, for each ultrasound emitter, its distance to the aqueous solution level and a power controller for controlling the power of the at least one ultrasound emitter including the following steps, performed continuously: estimating the aqueous solution level in the tank, calculating for each ultrasound emitter its distance to the aqueous solution level, comparing for each ultrasound emitter its distance to the aqueous solution level to a determined threshold.

A cleaning plant for hot-rolled metal strips provided with a surface oxide layer, the plant comprising unwinding means for unwinding at least one coil of rolled strip and pickling means for pickling said rolled strip; wherein there are provided measuring means for measuring the thickness of the surface oxide layer, arranged between said unwinding means and said pickling means; and wherein gaseous hydrogen detection means are provided to detect the presence of gaseous hydrogen in fumes produced by said pickling means. A corresponding cleaning method is also claimed.

An acid solution preparation device is an acid solution preparation device for preparing an acid solution used for pickling of a steel plate, the device including a sealed tank for storing the acid solution, a gas supply part for supplying an oxygen-containing gas from outside of the sealed tank to the sealed tank, and a purge part for discharging a gas in the sealed tank to the outside.

A cushion tank device includes: a cushion tank configured to store pickling solution and sludge discharged from a pickling tank; a discharge pipe provided on a bottom of the cushion tank and configured to discharge the sludge to an outside of the cushion tank; and an opening/closing member configured to open and close the discharge pipe. The cushion tank device configure to guide the sludge to the discharge pipe, the inclined surface including an inclined surface part on a lower part of the cushion tank that is inclined to horizon at an angle greater than an angle of repose of the sludge with respect to an inner wall surface of the cushion tank.

A grain-oriented electrical steel sheet that can reduce iron loss and improve the adhesion of a secondary coating is provided. In a grain-oriented electrical steel sheet of the present embodiment, when a maximum emission intensity of Mg is defined as I.sub.Mg/Mg, and an emission intensity of Sn at a sputtering time at which Mg exhibits the maximum emission intensity is defined as I.sub.Sn/Mg, in glow emission spectroscopic spectra obtained by performing glow discharge optical emission spectroscopy in a thickness direction of a base steel sheet from a surface of a secondary coating, the glow emission spectroscopic spectra showing the relation of an emission intensity of Mg and an emission intensity of Sn with respect to a sputtering time, an intensity ratio I.sub.ref defined by Formula (1) is 0.0000 to 0.0006, and an iron loss W.sub.17/50 is less than 0.90 W/kg.

I.sub.ref=I.sub.Sn/Mg/I.sub.Mg/Mg(1)

A cleaning plant for hot-rolled metal strips provided with a surface oxide layer, the plant comprising unwinding means for unwinding at least one coil of rolled strip and pickling means for pickling said rolled strip; wherein there are provided measuring means for measuring the thickness of the surface oxide layer, arranged between said unwinding means and said pickling means; and wherein gaseous hydrogen detection means are provided to detect the presence of gaseous hydrogen in fumes produced by said pickling means. A corresponding cleaning method is also claimed.