Classifications

• • 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
  • C23G1/08—Iron or steel

Definitions

• the invention relates to a method of removing from a ferrous metal surface iron oxide incrustations containing copper such as the coppercontaining iron oxide incrustations oftentimes found on the internal surfaces of steam generators operated in conjunction with condensing equipment having a condensing surface of a copper alloy.
• the incrustations can be removed by subjecting them first to the action of hydrochloric acid solution containing a corrosion inhibitor o owe y a wa er rinse; secondly tothc action of an a mpg oniacal sgl ution containing a strong oxidizing agent followed by aware. rinse; third to the action of dilute hydrochloric acid; and fourth to the action of a hot dilute aqueous alkaline solution.
• a copper-containing iron oxide incrustation on a ferrous metal surface e.g. the inside of a steam generator, condenser, heat exchanger and the like
• a suitable acid solut'on in which is dissolved one of the followin f urea: thiourea, 1,3- dimethyl thiourea, hylene thiour 1,3-diefiyl iIiiourea, and 1,3diisopropyl t iourea.
• the iron oxides and copper-conta'ning incrustations may be used, for example, hgrochloric acid jprefer ablyjn a concentration of 5 to 25 rcent y weight), s (preferably in a concentration of 5 ercen an phosphoric acid (preferably in a concentrationbf 10 to 25 rcent).
• Tests of the action of the solution on coppercontainin iron oxide incrustations indicate that the urea derivativ in the acid solution forms a precipitate or a complex with the copper which revents it from bein rede sited from the acid solution on the ferrous metal which redeposition occurs in he absgnce of the urea derivatiye.
• the amount of the urea derivative required depends upon the quantity of copper in the incrustations to be removed and which becomes dissolved in the acid solution in the incrustation removal operation.
• the amount of 2 the urea derivative, we have found, should be at least about 2.0 unds r ound of co er to be brought into solution from the incrustations by the acid. Greater amounts of the urea derivative may be used if desired,
• the preferred 3 opera mg amount of the urea derivative is between about 2.2 and 6 pounds per pound of copper to be removed. It is preferable to employ at least 0.01 percent of the thiourea derivative in the solution.
• Test data set forth in the table are illustrative of the ,action of various amounts of a derivative of urea (e.g.
• the urea derivative at the lower concentrations, forms a more or less i c cid d cuprous chloride 15 insoluble compound with the dissolved copper, the compound becoming a precipitate in the acid solution; and at higher concentrations the urea derivative retains the copper in solution in some form of urea-copper complex, since the copper-containing precipitate formed at lower concentrations of the urea derivative does not form at the higher concentrations of the urea derivative. In either case, that is -whether the copper is converted into a precipitate in the acid solution or completely solubilized as on being complexed with the urea derivative, complete removal of the incmstations including the copper is obtained.
• the urea derivative it is advantageous to use enough of the urea derivative to completely solubilize the copper as when the incrustations are on the inside of vessels of complex shape where the removal of a precipitate may be somewhat difiicult. In most instances, it is suflicient to employ but a few pounds of the urea derivative for each pound of copper to be removed.
• urea derivatives already mentioned may be similarly used as exemplified in the comparative tests including blanks tabulated in Table II.
• mild steel coupons 2.75" x 1" x 0.125" were immersed in 5 percent hydrochloric acid solutions containing 0.128 percent of cuprous chloride and 0.4 percent of pyridine for 6 hours at 150 F.
• the appearance of the coupons after the 6 hours immersion was observed for the effect of various thiourea derivatives added to the solution on controlling copper deposition on the coupons.
• the acid solution containin i tive may be us Wl ouifgEQQQlliflhi-fiQL e presenmcorrosiofinhi nor of the organic nitrogenbase type has been found desirable especially when operating await -8011
• Common orgamc m ogen bases which may be used as inhibitors are the well known coal tar bases produced in the distillation of coal tar. If desired the bases themselves may be separated from the crude coal tar base mixture and used as individual substances. These compounds are the aromatic and heterocyclic nitrogen bases soluble in the acid solution.
• the concentration or amount of the organic nitrogen-base inhibitor to employ depends upon its effectiveness and the extent to which it is desired to suppress the corrosiveness of the acid and the temperature at which the acid solution is to be used. Generally the amount effective to inhibit or reduce the corrosiveness of the acid is in the range of 0.1 to 1 percent of the weight of the acid solution.
• pyridine alpha-picoline, beta-picoline, gamma-picoline, 2-n-amylpyridine,- 4-n-amylpyridine, 2- hexyl-pyridine, 2,4-lutidine, 2,6-lutidine, 2,4,6-collidine, quinoline, lepidine, quinaldine.
• Other compatible organics rosin amines see US. Patent 2,510,063 and 2,510,284).
• nitrogen-base inhibitors are rosin amines and hydrogenated
• the following example is illustrative of the practice of the invention as applied to cleaning a steam generator (high pressure steam boiler) having an internal volume of about 20,000 gallons.
• examination of the interior of the generator revealed extensive in crustations of ferrosoferric oxide estimated to amount to about 2000 pounds.
• Occluded in the incrustations was an amount of copper and copper oxide estimated to be the equivalent of about pounds of metallic copper.
• the generator was filled with a water solution of hydrochloric acid containing 5 percent of HCl, 2400 pounds of thiourea in solution, and 0.4 percent of pyridine as a corrosion inhibitor.
• iron oxide Po o, or Fe O or ferric chloride as an oxidizing agent in amount sufficient to meet the stoichiometric requirements of the foregoing equation.
• the method of removing copper and iron oxide containing incrustation from a ferrous metal surface without redeposition of copper thereon which consists in bringing into contact with such surface an aqueous solution of a urea derivative selected from the group consisting of thiourea, 1,3dimethyl thiourea, ethylene thiourea, 1,3- diethyl thiourea, and 1,3-diisopropyl thiourea, said solution containing an acid capable of dissolving the iron oxides and copper, the amount of said urea derivative being from 2 to 20 pounds per pound of copper in the incrustation, said aqueous solution being maintained in contact with the incrustation for a time suflicient to substantially solubilize the said incrustation.
• a urea derivative selected from the group consisting of thiourea, 1,3dimethyl thiourea, ethylene thiourea, 1,3- diethyl thiourea, and 1,3-diiso
• aqueous solution also contains an amount of an organic nitrogen-base other than thiourea and the substituted thiourea compounds defined in claim 1 capable of inhibiting the corrosive action of the acid on ferrous metal.
• the method of removing a copper and iron oxide containing incrustation from a ferrous metal surface without redeposition of copper thereon which consists in bringing into contact with such surfaces an aqueous solution consisting of water in which is dissolved from 5 to 25 percent by weight of hydrochloric acid, thiourea, and from 0.1 to 1 percent of an organic nitrogen base other than thiourea capable of inhibiting the corrosive action of the acid on ferrous metal, the amount of the thiourea being in excess of 0.01 percent by weight of the solution and between 2 and 20 times the weight of the copper to be removed, the volume of the aqueous solution being sufiicient to remove the incrustations.
• a composition for removing copper containing iron oxide incrustations from a ferrous metal surface consisting of a solution in water of from 2 to 25 percent by weight of hydrochloric acid, a urea derivative selected from the group consisting of thiourea, 1,3-dimethyl 6 thiourea, ethylene thiourea, 1,3-diethyl thiourea, 1,3-di' isopropyl thiourea in the amount of at least 0.67 percent by weight, and from 0.1 to 1 percent of an organic nitrogen base soluble in the solution selected from the group 5 consisting of the aromatic and heterocyclic nitrogen bases capable of inhibiting the corrosive action of the acid on ferrous metal.

Landscapes

• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)

Priority Applications (5)

Applications Claiming Priority (2)

Publications (1)

Family

ID=600887

Family Applications (1)

Country Status (5)

Cited By (21)

Families Citing this family (3)

Citations (14)

Family Cites Families (2)

• 1957
  • 1957-05-23 US US660999A patent/US2959555A/en not_active Expired - Lifetime
  • 1957-08-08 GB GB25017/57A patent/GB836160A/en not_active Expired
  • 1957-08-26 DE DED26296A patent/DE1142488B/de active Pending
  • 1957-08-28 FR FR1187034D patent/FR1187034A/fr not_active Expired
• 1960
  • 1960-01-05 BE BE586275A patent/BE586275A/fr unknown

Patent Citations (14)

Also Published As

Similar Documents