Pickling

The group of chemical surface pretreatment methods also includes pickling. Here, thinned acids are applied, which remove layers on the metal surfaces via chemical reactions resulting in metallically clean surfaces. The respective application regulations apply, too. 

The speed of the pickle reaction is also dependent on the concentration and temperature of the pickle, the degree of agitation of either the metal part or the pickle solution, the alloy being pickled, and the acid used. Pickling solutions may be appHed by either spray or immersion techniques. However, because of the noxious fumes emitted, there must be adequate ventilation. Sometimes, particularly when spraying techniques are used, an enclosure to contain the fumes and mist is employed. 

Copper and Copper-Containing Alloys. Either sulfuric or hydrochloric acid may be used effectively to remove the oxide film on copper (qv) or copper-containing alloys. Mixtures of chromic and sulfuric acids not only remove oxides, but also brighten the metal surface. However, health and safety issues related to chromium(VT) make chromic acid less than desirable. 

Zinc and Zinc Alloys. Zinc metal is highly reactive in acid solutions such as sulfuric, hydrochloric, and nitric dissolving rapidly at acid concentrations normally used to pickle steel and aluminum. Dilute (1—4%) solutions of these acids can be used with caution to remove zinc oxides. 

Sulfamic acid at concentrations of 2—6%, in conjunction with the proper proprietary inhibitor, can be effective in removing zinc oxides and corrosion by-products without attacking the zinc metal. 

Acids such as sulfuric, hydrochloric, nitric, and especially hydrofluoric as well as strong alkaUes such as caustic soda and caustic potash are extremely corrosive to animal and vegetable tissue. Extreme caution must be taken to prevent skin contact, inhalation, or ingestion. Violent reactions may occur when dissolving or diluting many of these chemicals with water. 

The purpose of the preflush is to remove organic or inorganic scale from the wellbore tubulars prior to injection of the acid stage. An aromatic solvent, such as xylene, can be used to remove hydrocarbon deposits. For asphaltene deposits, specifically, terpene-based solvent solutions can be quite effective. Circulation of 5%-7.5% HCl downhole is adequate to remove rust and other inorganic scale for rust removal in particular, non-add (nearneutral) removal solutions exist and may be preferable at temperatures of MOT (60°C) and higher. 

Weaker, formic or acetic acid mixtures are acceptable alternatives, especially at high temperatures. The preflush may also serve to displace oil from the near-wellbore area to prevent emulsion or sludge formation. Use of xylene or fresh water containing surfactants is adequate. 

The purpose of the acid stage is to remove or bypass formation damage. The acid stage is usually 15%-28% HCl. Treatment volumes are usually in the range of 10-300 gal/ft most treatments require 25-150 gal/ft, depending on the anticipated depth of damage and formation porosity. With a formation porosity of 10%, a 60 gal volume of acid per foot of zone is required in order to fill the porosity to a distance of five feet from the wellbore. 

However, penetration of acid in a carbonate formation is not uniform. In most formations, the pores are different sizes and shapes. The porosity maybe present in the form ofvugs, natural fractures or fissures, or tortuous, capillarylike pores. Such heterogeneities in the porous structure cause channeling or wormholing of acid through the formation. The effect of wormholing is the penetration of acid much deeper than expected into isolated portions of the matrix, which may be sufficient to overcome skin damage. 

High-strength HCl (28%) has use in the removal of deeper damage, but for most cases, 15% HCl is adequate. For fracture acidizing applications. 

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Acid phosphatase Acid phosphatases Acid pickling Acid rain... 

Metal passivation Metal pickling Metal powders Metal recovery... 

Pickling agent Pickling of steel Pickling solutions Pick s disease Pidoram [1918-02-1]... 

Uses. Propargyl alcohol is a component of oil-well acidizing compositions, inhibiting the attack of mineral acids on steel (see Corrosion and CORROSION control). It is also employed in the pickling and plating of metals. 

Butynediol is principally used in pickling and plating baths. Smak amounts are used in the manufacture of brominated derivatives, useful as flame retardants. Itwas formerly used in awkd oat herbicide, Carbyne (Barban), 4-chloro-2-butynyl-A/-(3-chlorophenyl)carbamate [101-27-9] C H Cl2N02 (77). 

The depressed prices of most metals in world markets in the 1980s and early 1990s have slowed the development of new metal extraction processes, although the search for improved extractants continues. There is a growing interest in the use of extraction for recovery of metals from effluent streams, for example the wastes from pickling plants and electroplating (qv) plants (276). Recovery of metals from Hquid effluent has been reviewed (277), and an AM-MAR concept for metal waste recovery has recentiy been reported (278). Possible appHcations exist in this area for Hquid membrane extraction (88) as weU as conventional extraction. Other schemes proposed for effluent treatment are a wetted fiber extraction process (279) and the use of two-phase aqueous extraction (280). 

Celery Seed. Celery spice is the dried ripe fmit of y piumgraveolens L. (UmbeUiferae) a biennial, sometimes aimual, herb native to southern Europe and grown extensively in India, China, Mexico, and the United States. The seed is 0.42 cm long and brown. The odor of the seed is characteristic and warm and the taste somewhat bitter. It is used in tomato ketchup, sauces, soups, pickles, pastries, salads, and certain cheeses. 

Cumin Seed. Cumin spice is the dried ripe fmit of Cuminum cyminum L. (UmbeUiferae). The seed-Uke fmit is elongated about 0.31 to 0.63 cm and is yeUowish brown. It is native to upper Egypt and the eastern Mediterranean, but is now cultivated in Pakistan, Turkey, India, China, and Syria. It has a strong pecuhar aroma and flavor, pleasing to some and offensive to others. Cumin seed is used in chutney and curry, chili powders, chili con came, cheeses, and the pickling of cabbage. 

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