Classifications

• • C—CHEMISTRY; METALLURGY
  • C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
  • C11D—DETERGENT COMPOSITIONS; USE OF SINGLE SUBSTANCES AS DETERGENTS; SOAP OR SOAP-MAKING; RESIN SOAPS; RECOVERY OF GLYCEROL
  • C11D7/00—Compositions of detergents based essentially on non-surface-active compounds
  • C11D7/02—Inorganic compounds
  • C11D7/04—Water-soluble compounds
  • C11D7/08—Acids
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
  • C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
  • C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
  • C23G1/04—Cleaning or pickling metallic material with solutions or molten salts with acid solutions using inhibitors
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28G—CLEANING OF INTERNAL OR EXTERNAL SURFACES OF HEAT-EXCHANGE OR HEAT-TRANSFER CONDUITS, e.g. WATER TUBES OR BOILERS
  • F28G9/00—Cleaning by flushing or washing, e.g. with chemical solvents

Definitions

• the invention relates to a process for the cleaning of equipment consisting wholly or partially of metal.
• the liquid cleaning agents used for this purpose are' usually inorganic or organic acids. According to the nature of the contamination and of the metal to be cleaned use is made in the chemical cleaning process of inhibited or uninhibited acids, such as citric acid, sulphamic acid, phosphoric acid, nitric acid, sulphuric acid and hydrochloric acid. For this purpose the use of hydrochloric acid is usually preferred especially due to its low cost, ease of handling and great capacity for dissolving many deposits and corrosion products.
• An inhibitor is usually added to the acid in order to counteract as far as possible the corrosive effect of these acids on the equipment to be cleaned. Examples of such inhibitors include hexamethylene tetra.- mine, alkaloids and quaternary ammonium bases.
• the invention therefore relates to a process for the cleaning of equipment consisting wholly or partially of metal which comprises treating the equipment with a cleaning fluid comprising an aqueous solution of an inhibited inorganic or organic acid which, in addition, contains a stannous salt soluble in this solution.
• Stannous chloride is preferably used as stannous salt soluble in the cleaning acid and therefore the source of stannous ion and inhibited hydrochloric acid as cleaning acid.
• concentrations of the hydrochloric acid of between 0.25% by weight and 15% by weight, appear to be very satisfactory.
• quantities of between 1 and 30 g. per litre of cleaning acid which therefore corresponds to a stannous ion concentration of between 0.53 and 15.8 grams per liter of against corrosion-can now be wholly omitted.
• the flow rate of the cleaning acid can be raised to high values without the corrosive attack exceeding acceptable limits.
• flow rates for the cleaning acid of at least 0.2 m./sec., and preferably of between 0.5 and 3 m./ sec. will be used, so that a rapid and effective cleaning can be obtained while avoiding a degree of corrosion of any substance.
• the process according to the invention also provides protection against corrosive attack in equipment which contains combinations of noble and less noble metals, a protection which formerly could be only obtained by removing or blanking off the nobler metal concerned before the cleaning operation. It was thus established that by the use of the cleaning acid according to the invention the corrosive attack on the following metals or combinations of metals was wholly or substantially wholly suppressed.
• a special aspect of the present invention is the possibility of maintaining the composition of the cleaning acid, by a simple continuous electrometric control of the cleaning fluid, at such a level that throughout the entire cleaning process the certainty exists that no corrosion, or substantially no corrosion, will occur.
• the redox potential in the presence of a corrosive quantity of ferric ions in inhibited hydrochloric acid of 10% concentration amounts to 200 to 400 mv., de ending upon the quantity of ferric ions; in the presence'of a quantitiy of stannous ions, su cient to counteract corrosion, the redox potential is below 280 mv.
• the cleaning fluid used according to the invention is characterized in that also at elevated temperatures there is no corrosive attack.
• the upper limit of the temperature to be used is only determined by the stability of the inhibitor in the inhibited acid, and this limit generally lies around 70 C.
• the present invention therefore, now provides for the first time the possibility of carrying out the cleaning operation conveniently with a cleaning fluid at an elevated temperature, i.e. at a temperature of up to 70 C.
• a cleaning fluid which in addition to an inhibited inorganic or organic acid and a soluble stannous salt, contains a complexing agent specific for ferric ions. It has been found that in that case the amount of stannous salt to be used can be considerably reduced; amounts of less than of the amount of stannous salt originally applied have been found to be suflicient for suppressing or substantially reducing the corrosive attack of the metal control of the redox potential as explained above and illustrated for the combination stannous chlorideammoniumbifluoride in Example IV.
• Test plates from unalloyed steel (dimensions 60 x x 1.5 mm.), from which plates the grease had been removed and which had been scoured bright, were exposed in duplicate in beakers containing 0.5 l. of inhibited ironfree hydrochloric acid.
• test plates were placed vertically on their long sides in small glass racks in the beakers. Beside each exposure in a stationary medium test plates were exposed in a moving medium having a rate of 0.2 1111. per second, which movement was obtained by means of an electrically powered glass stirrer. The plates were exposed for four periods, viz 8, 8, 8 and 24 hours, in the same fluid, unless otherwise stated. After each exposure the plates were weighed and examined for signs of pitting.
• the complexing agent should be specific for ferric ions in that it should not form a complex with the ferrous ions. This is essential for the purpose of the invention and another essential feature of the present embodiment is that an amount of the soluble stannous saltbe it a considerably reduced amount-should always be present.
• Complexing agents which may be used include phosphoric acid or hydrofluoric acid or its salts of which ammoniumbifluoride '(NH HF has been found especially suitable.
• the relative amounts of stannous salt and complexing agent can easily be fixed at the desired level by When the inhibitor applied is replaced by other conventional inhibitors corresponding results were obtained, as also with the use of I-lCl in a 5% concentration.
• EXAMPLE III This example illustrates the cleaning of metal combinatrons with the process of the invention.
• Thest plates of difierent metals were combined with test plates of mild steel and the metal combination was exposed at 20 C. during 16 hours to cleaning acids of the composition and under the conditions set out in the following Table V.
• ⁇ Stee has greenish scale which can be easily removed 1 Do.
• the total consumption of SnCia-2Hz0 was 1.15 gram which is about 10% of the amount required in the absence of the ferric ion complexing agent.
• the average corrosive attack of the test plates is 0.24 cleaning method according to the present invention. mm. a year. None of the test plates showed pitting.
• fluoride B With fluoride 15 weight percent of an acid selected from the group consisting of citric, sulfamic, phosphoric, nitric, sulfuric and hydrochloric acids, and (b) stannous ion in a concentration of from 0.53 to 15.8 grams per liter, the stannous ion being derived from a soluble stannous salt, and
• the bath without fluoride is corrosive.
• the bath with fluoride is non-corrosive.
• suflicient soluble stannous salt is added to maintain the redox potential below 170 mv.
• the corrosion inhibitor is selected from the group consisting of hexamethylene tetramine, alkaloids, and quaternary ammonium bases and the inhibitor is present in an amount of from about 0.2 to 0.3 weight percent.
• the equipment is constructed of a metal selected from the group consisting of steel and steel alloys with at least one of the alloyed metals selected from the group consisting of chromium, nickel and molybdenum.
• a process for the cleaning of metallic equipment constructed essentially of iron containing metal by means of a recirculating aqueous corrosion inhibited acidic cleaning solution comprising the steps of (1) contacting the surfaces of the equipment to be cleaned with a circulating aqueous corrosion inhibited acidic cleaning solution comprising (a) from about 0.25 to 15 weight percent of an acid selected from the group consisting of citric, sulfamic, phosphoric, nitric, sulfuric and hydrochloric acids, (b) stannous ion in a concentration of from 0.053 to 15.8 grams per liter, the stannous ion being derived from a soluble stannous salt, and (c) a complexing agent for ferric ions selected from the group consisting of hydrofluoric acid and ammonium bifluoride, said complexing agent being present in an amount soluble in the acidic solution; and
• ferric ion complexing agent is ammonium bifluoride.
• An aqueous based cleaning composition for cleaning equipment consisting essentially of iron-containing metal consisting essentially of water, 0.25 to 15 weight percent of an acid selected from the group consisting of citric, sulfamic, phosphoric, nitric, sulfuric, and hydrochloric, from 0.053 to 15.8 grams per liter of stannous ion derived from a soluble stannous salt, from about 0.2 to 0.3 weight percent of a corrosion inhibitor selected from the group consisting of hexamethylene tetramine, alkaloids, and quaternary ammonium bases, and a ferric ion complexing agent selected from the group consisting of hydrofluoric acid and ammonium bifluoride present in an amount soluble in the cleaning solution.
• An aqueous based cleaning composition for cleaning equipment consisting essentially of iron-containing metal consisting essentially of water, 0.25 to 15 weight percent hydrochloric acid, from 0.1 to 30 grams per liter of stannous chloride, from about 0.2 to 0.3 weight percent of a corrosion inhibitor selected from the group consisting of hexamethylene tetramine; alkaloids, and quaternary ammoniumbass, and ammoninum bifiuoride as a ferric complexing agent in a concentration of from about 10 grams to 30 grams per liter.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Organic Chemistry (AREA)
• Mechanical Engineering (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Materials Engineering (AREA)
• General Chemical & Material Sciences (AREA)
• Metallurgy (AREA)
• Wood Science & Technology (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Life Sciences & Earth Sciences (AREA)
• Inorganic Chemistry (AREA)
• Combustion & Propulsion (AREA)
• General Engineering & Computer Science (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)

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Cited By (23)

Citations (5)

• 1965
  • 1965-02-08 NL NL656501527A patent/NL155315B/xx not_active IP Right Cessation
  • 1965-05-17 DK DK247665AA patent/DK120424B/da unknown
  • 1965-05-28 US US459942A patent/US3440170A/en not_active Expired - Lifetime

Patent Citations (5)

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