Acid pickling process

Laser cutting, welding, and hot working leave a discolored oxidized layer or scale on the surface of the worked steel. This must be removed in order to perform many of the surface finishing processes. The acid pickling process is used to remove the oxide or scale of metals and corrosion products, in which acids or acid mixtures are used. 

The roughened ends of the pipe are manually deburred with an air grinder. Then the pipes are straightened as necessary and transported to the acid pickling process. 

In the hydrochloric acid pickling process, ferrous chloride can also be recovered as a by-product. 

Table 1 Comparison of various chromic-sulphuric acid pickling processes.

This is a process to remove heavy black scale and rust from the surface. Hot-rolled sheets that may have such scale formation need only be acid pickled. Cold-rolled sheets, which may carry no such scales, need not be acid pickled. Depending upon the type of surface, one of the following methods may be adopted. 

Mildly scaled and mildly rusted surfaces Now the process of acid pickling may be eliminated if desired. Instead, only the de-rusting process can be used, as indicated in column 2 of Table A13.3. Alternatively acid pickling may be carried out as before, but at a lower concentration and temperature, as noted in column I. Since one cannot always be certain of the quality of sheet surfaces it is advisable to follow the process of acid pickling. 

The corrosive effects to be considered (mainly simple corrosion of metals) are, as would be expected from the edible nature of foodstuffs which are not excessively either acidic or basic but which may contain sulphur, less severe than those often encountered with inedible materials containing reactive substances. The importance of corrosive efiects where foodstuffs are concerned lies not so much in the action of the foodstuffs on the metal involved as in the resultant metal contamination of the foodstuff itself, which may give rise to off-flavours, in the acceleration of other undesirable changes (by the Maillard reaction for example), and in the possible formation of toxic metallic salts. Metal ions generally have threshold values of content for incipient taste effect in different liquid foodstuffs. Except in the case of the manufacture of fruit juices and pickles, process plant failure through corrosion must be rare. Nevertheless all foodstuffs, particularly liquid ones, should be regarded as potentially corrosive and capable of metal pick-up which may be undesirable. 

Acid Pickling This process is widely used for removing rust and millscale from steel, or for removing internal scales from boilers. The objective of the process is the dissolution of iron oxides or hydroxides or hardness scales, but at the same time the iron will also tend to corrode in the acid, with hydrogen... 

Before steel strip or rod can be cold rolled, tinned, galvanised, or enamelled, etc. any scale formed on it by previous heat treatment must be removed. This can be done by mechanical and other special methods, but if a perfectly clean surface is to be produced, acid pickling is preferred, either alone or in conjunction with other pretreatment processes. 

Probably the major use of inhibitors in acid solutions is in pickling processes. The chief requirements of the inhibitor are that it should not decompose during the life of the pickle, not increase hydrogen absorption by the metal... 

When dry material or a slurry has been filled, "pickling" is required, which means that the plate is stored in sulfuric acid for a short time. The material is soaked by the acid and transformed, at least partly, into lead sulfate (PbS04), as in the pastemixing process (Section 4.4.2.1). When minium is used, during the "pickling" process lead dioxide is also formed according to Eq. (4). 

Without the addition of corrosion inhibitors, acid cleaning or pickling processes to remove oxides and scales would result in severe corrosion of exposed metal surfaces. Acid corrosion is an electrochemical or redox process, and raising cleaning temperatures or acid strength (lowering the pH) increases the hydrogen ion concentration and consequently the rate of corrosion. 

About 3 billion kilograms of hydrochloric acid are produced each year, mostly as a by-product of the plastics industry. The largest single use of hydrochloric acid is the pickling of steel. The pickling process removes iron(III) oxide (FC2 O3, rust) from the surface of the metal. About a third of all hydrochloric acid is used to produce other chemicals, mostly ionic compounds. Other strong acids have specialized applications in indushy and research laboratories, but none approaches the importance of sulfuric, nitric, and hydrochloric acids. 

Effluent-Free Pickling Process with Fluid Bed Hydrochloric Acid Regeneration... 

This pickling process is operated such that no wastewater is discharged from a hydrochloric acid... 

Water rinses are used in surface preparation operations such as acid pickling, alkaline cleaning, and nickel deposition to remove any process solution film left from the previous bath. A water rinse may also follow the neutralization step. Another common water use is in the ball milling process, which uses water as the vehicle for the enamel ingredients, as a cooling medium, and for cleaning the equipment. Coating application processes normally use wet spray booths to capture oversprayed enamel particles. Water wash spray booths use a water curtain into which the enamel particles are blown and captured. 

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