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
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F11/00—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent
  • C23F11/08—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent in other liquids
  • C23F11/18—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent in other liquids using inorganic inhibitors
  • C23F11/187—Mixtures of inorganic inhibitors
  • C23F11/188—Mixtures of inorganic inhibitors containing phosphates
• • 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
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F11/00—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent
  • C23F11/08—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent in other liquids

Definitions

• This invention relates to compositions for inhibiting the corrosion of metal surfaces in contact with water, especially flowing water. More particularly, this invention relates to the prevention of corrosion of metal surfaces of equipment and piping employed in the purification and distribution of potable water supplies. This invention especially relates to a method and composition for the prevention of pitting and corrosion of metal particularly piping employed in water distribution systems.
• compositions containing of about 2:1 to 3:1 by weight of phosphate to zinc in a concentration of a few parts per million is surprisingly successful in limiting corrosion.
• the satisfaction concentration range based on zinc ion content is about 0.2 to 5 ppm at the point of metering into the system.
• the corrosion inhibitor of this invention is further preferably injected as a liquid at the raw water intake and further it is preferred that the pH of the raw water be between 6.5 to 8, although the inhibitor is effective in waters having a pH of 5-9.
• the liquid corrosion inhibitor composition comprises divalent zinc and trivalent phosphate (so- called orthophosphate P04 3).
• the source of the zinc can be any non-toxic zinc salt, soluble in an aqueous carrier fluid, such as zinc oxide, zinc phosphate, zinc chloride, zinc carbonate, zinc sulfate.
• the phosphate is best obtained from orthophosphoric acid.
• Solid sources of the orthophosphate ion may be supplied by any soluble orthophosphate salt, i.e., mono- and di-sodium acid phosphate (NaH 2 P0 4 , Na 2 HP0 4 ), zinc orthophosphate, monopotassium phosphate, dipotassium phosphate and tripotassium phosphate and the like.
• the requisite quantities of salt comprising a source of zinc and phosphate to provide the necessary 2:1 to 3:1 ratio of phosphate to zinc is dissolved in water and the pH of the solution adjusted with a non-toxic acid such as phosphoric acid, sulfuric acid, or hydrochloric acid to solubilize the components.
• a non-toxic acid such as phosphoric acid, sulfuric acid, or hydrochloric acid
• the phosphate to zinc ratio should not depart from the critical ratio set forth herein.
• the inhibitor content should preferably be as high as possible (40%-60%) so that shipping costs can be minimized and pumping costs reduced.
• composition need not be liquid but can comprise a mixture of dry salts, although the handling of this composition and its metering into the raw water intake or other suitable point is the distribution system is not believed as advantageous as a liquid.
• the zinc content should be controlled so that it preferably is within the range of 0.5-2 parts per million when measured at a point remote from the injection point.
• the composition is metered by any suitable equipment into the raw water immediately at the start of the treatment process.
• the inhibitor composition is injected into the system subsequent to the flocculation step. It is, however, desirable to inject the inhibitor composition as soon as practical so as to protect the downstream metals.
• the steel corrosion rate data were obtained in a test unit which utilized 8 liters of Pittsburgh tap water (22 mg./l Ca +2 , 6 mg./l Mg +2 , 18 mg./l Cl -1 , 82 mg./l SO 4 -2 , 10 mg./l HCO 3 -1 at 30°C. (86°F.). The water was circulated, aerated and its temperature and pH maintained essentially constant.
• test panels were AISI 1010 steel with two 1 x 1" panels exposed in each test unit. These panels were cleaned and degreased by cleansing with a commercial detergent and rinsing in xylene and distilled water. The panels were dried, weighed on an analytical balance, and then rinsed with acetone and distilled water to yield a uniformly wetted surface. At the completion of the test, the steel panels were cleaned with inhibited acid, reweighed and the corrosion rate calculated in mils per year (mpy).
• the corrosion test cycle used to evaluate the several corrosion inhibitors in the first series of investigations was a five-day laboratory test in which new inhibited Pittsburgh water was present at the beginning of the No. 1 and No. 2 days of testing while the fresh inhibited water used on the No. 3 day was not replaced during the remaining No. 4 and No. 5 days of testing.
• This test cycle will be referred to as the 1-1-3 cycle.
• a liquid containing 49.2% active components (2.9 P0 4 :1 Zn +2 ) with a specific gravity of 1.56 (at 25°C.), and a freeze point below -50°F. was prepared.
• the material of this example is made by mixing soft water, zinc chloride and phosphoric acid. For 1000 lbs. of product, 472 lbs. of 80% phosphoric acid are added slowly and with agitation to a mixture of 384 lbs. of ZnCl 2 (68.5%) and 144 lbs. of deionized water.
• Another liquid inhibitor composition was similarly prepared but adjusted in quantities of material so that a 2:1 weight ratio of PO 4 ⁇ :Zn was obtained.
• the following table shows the steel corrosion rates for the two methods when the three inhibitors were evaluated at 6 mg./l of active Zn/ phosphate and at a pH 6.5. Note that 0.9:1 composition performed slightly better than the others in the 1 x 4 cycle while the 2.9:1 composition appeared slightly more effective in the 1-1-3 cycle. The 2:1 composition peformed in a similar manner in both test cycles. In all cases, the experimental steel corrosion rates are in the 92.6%-95.5% inhibition range and both test methods would seem to give similar and useful corrosion rate data.
• the corrosion rate data at the several pH levels indicate that the 0.9:1 composition is a considerably less effective corrosion inhibitor for steel in the pH 7.5 range as compared to the pH 6.5 range.
• the 2.9:1 and 2:1 compositions appear effective over the pH 6.5-7.5 range.
• the 8 liter system (Pittsburgh 1X water) was continually aerated and agitated at 30°C. (86°F.) and pH 6.5.
• the lead panels were 1 1/2 x 3" and were cleaned in 5% glacial acetic (15 min. at boil) and scrubbed lightly prior to weighing and testing.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)

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Cited By (7)

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• 1979
  • 1979-06-01 EP EP79400353A patent/EP0006065A3/fr not_active Withdrawn
  • 1979-06-01 DK DK231879A patent/DK231879A/da unknown
  • 1979-06-05 JP JP6953579A patent/JPS54159350A/ja active Pending
  • 1979-08-08 IE IE103279A patent/IE791032L/xx unknown

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