Steels continued pickling

Fume scrubber water recycle. The steel finishing industry uses fume scrubbers to capture acid gases from pickling tanks. Scrubber water, which may contain a dilute caustic solution, is neutralized and recirculated continuously to adsorb the acid. Makeup water is added to replace water lost through evaporation and water that is blown down to end-of-pipe metals treatment. 

Pickling is conducted by continuous, semicontinuous, or batch modes depending on the form of metal processed. In developing a National Emission Standard for the steel pickling industry, U.S. 

Steel sheets, widely used in thousands of products, are produced Irorn slabs from a slabbing mill, continuous casting machine, or pressure-poured molils. These pieces are hot-rolled in a hoi strip mill, descaled bv pickling in an acid solution, and then cold-rolled and tempered m a cold-reduction and temper mill. Tlte cold-tolled snip may he marketed in coil form, or carried to a side-trimming and sheet shearing line, where it is customized lor speeilie user needs. 

Bipolar membrane synthesis also holds promise for regenerating spent pickling liquors in stainless steel manufacture. As shown in Fig. 43(b), waste acid laden with metal ions can be continuously neutralized, filtered to remove the precipitated metal oxide, and the clarified salt solution split into its acid and base components in a bipolar membrane unit [Type (IV) shown in Table IX], As much as 95% of the hydrofluoric and nitric acid used are returned to the pickling bath, thereby solving a waste... 

With the war years, polyvinyl chloride (PVC) resins came under study, and plasticized PVC compounds, based on these resins, became available as calendered sheet lining materials-the material of choice for stainless steel pickling and for chrome plating and other exposure employing mixtures of chemicals including such strong oxidants as nitric and chromic acid which rapidly attack natural rubber. (A higher temperature limit modification now seldom seen is PVDC, for which the continuous temperature limit is said to be 170°-180°F.)... 

Granite is used to form tank liners (bottoms, walls and covers) and skid caps and skid bars in and between tanks in continuous acid pickling lines for the descaling of steel. The acid baths are commonly 10-15% solutions of HCI or H2SO4, and FeCIs or Fe2 S04>3 at temperatures of about 200°F. The granites selected for use as skid caps and tank liners are generally quartz-rich because they are resistant to the abrasive and impact wear of the sliding steel as well as the corrosion from the acid baths. 

Samples are taken from the melt and analyzed, and the chemical composition of the steel can, if necessary, be modified by the addition of alloying metals in the converter or in the ladle afterwards. Later, the desired molten metal is either cast into ingots or continually cast into a slab or billet form. Then the material is hot-rolled or forged into its final form. Some material receives cold rolling to further reduce the thickness as in sheets or drawn into smaller diameters as in rods and wire. Most stainless steels receive a final annealing and acid pickling in order to remove furnace scale from annealing, and they help to promote the passive surface film that naturally occurs. 

Steel pipes according to DIN EN 10255 which were pickled and scaled were tested in hard and partly softened drinking water (Table 4) at continuous flow rates of 0.5 and 1.5 m/s in field experiments [14]. 

Stainless steel wire brushing or light grinding with clean aluminum oxide abrasive disks or flapper wheels are helpful. Grinding or polishing with grinding wheels or continuous belt sanders tend to overheat the surface layers to the point where resistance cannot be fully restored even with subsequent pickling. Brief descriptions of hot- rolled, cold-rolled, and mechanical finishes are presented in Table 8.34. 

For structural steel designated for pickling, the geometry and fabrication techniques should provide homogeneous continuity of surface without crevices, ledges, cups, or recesses where the pickling liquid could penetrate and be retained. 

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