Claims
- 1. A composition for cleaning galvanized and steel pipe which composition comprises an aqueous solution containing from about 7.5 to 25 parts by weight of hydrochloric acid, and a combination of inhibitors consisting essentially of 0.6 to 2.6 parts by weight of furfural, and 0.5 to 1.4 parts by weight of a dialkylthiourea.
- 2. A composition for cleaning galvanized and steel pipe as described in claim 1, wherein the dialkylthiourea is diethylthiourea.
- 3. A composition for cleaning galvanized and steel pipe cleaning which composition essentially consists of:
- ______________________________________ Parts by Weight______________________________________hydrochloric acid 7.5 to 25furfural 0.6 to 2.6dialkylthiourea 0.5 to 1.4______________________________________
- the balance consisting essentially of water.
- 4. A composition for cleaning galvanized and steel pipe as described in claim 3, wherein the dialkylthiourea is diethylthiourea.
- 5. A composition for cleaning galvanized and steel pipe as described in claim 4, which comprises:
- ______________________________________ Parts by Weight______________________________________ hydrochloric acid about 10furfural about 1.3diethylthiourea about 0.7______________________________________
- the balance being essentially water.
- 6. A composition for cleaning galvanized and steel pipe as described in claim 5, wherein the composition contains about 87.9 parts of water.
- 7. A method of removing a scale deposit from galvanized or steel surfaces normally in contact with water, which deposit includes at least one of alkaline earth metal carbonate, which method comprises contacting said scale deposit with an aqueous composition containing from about 7.5 to 25 parts by weight of hydrochloric acid, and a combination of inhibitors consisting essentially of about 0.6 to 2.6 parts by weight of furfural, and about 0.5 to 1.4 parts by weight of dialkylthiourea, whereby said deposit is dissolved and/or dispersed.
- 8. A method as described in claim 7, wherein said dialkylthiourea is diethylthiourea.
- 9. A method as described in claim 7, wherein said composition is continuously circulated in contact with said scale deposit.
- 10. A method as described in claim 9, wherein said dialkylthiourea is diethylthiourea.
- 11. A method of inhibiting scale formation in galvanized and steel water systems which comprises adding to the water of said water system an effective scale inhibiting amount of a composition containing from about 7.5 to 25 parts by weight of hydrochloric acid, and a combination of inhibitors consisting essentially of about 0.6 to 2.6 parts by weight of furfural, and about 0.5 to 1.4 parts by weight of dialkylthiourea, and circulating said water throughout said water system.
- 12. A method as described in claim 11, wherein said dialkylthiourea is diethylthiourea.
- 13. A method as described in claim 11, wherein said water system is a closed system.
Parent Case Info
The present invention is a continuation-in-part of copending application Ser. No. 456,468 filed Apr. 1, 1974 now U.S. Pat. No. 3,969,255.
The present invention relates to the removal of scale from metal surfaces, and especially to the removal of scale comprising metal oxides and carbonates from interior of galvanized pipes or steel pipes and other galvanized or steel vessels employed for the transport or storage of aqueous fluids. More particularly, the present invention relates to an improved composition for removing scale from such metal surfaces which composition has a reduced tendency to attack the zinc or steel, and is particularly adaptable to the cleaning of scale from the galvanized pipes of portable water systems.
Formation of scale on the interior surfaces of pipes, tubes, coils, tanks, heat exchangers, and other vessels has been a source of trouble where such pipes or vessels come in contact with aqueous liquid. The formation or deposition of scale markedly reduces the heat transfer through walls of such pipes or vessels and furthermore, the capacity of the pipes or vessels and the passage of fluids therethrough is restricted by the formation of such scale. Because of the scale formation on the inner surfaces of the pipes, particularly in the heat transfer appliances, pipes are subjected to excessive heat due to the loss in the heat transfer capacity. Further, greater pressures are required to overcome the restricting effect of the deposited scale. These disadvantages often lead to leaks and rupture which necessitate undesirable down time and maintenance cost. Still further, the reduced cross-section of pipes caused by the deposition of scale can cause increased pressure drop, wherein the water pressure at the top of a multi-story building will approach zero.
Numerous attempts have been made to remove scale containing metal oxides and carbonates from the interior of galvanized or steel pipes or fluid confining vessels. The more successful attempts have consisted of using aqueous solutions of known solvents for the compounds commonly found in the scale such as Fe.sub.2 O.sub.3 and FeS, in combination with acidic materials which can react with the calcium carbonate and calcium oxide which comprises the balance of the scale. The use of hydrochloric acid solutions in concentration from about 1 to 25%, the balance being water, have been proposed, but such aqueous solutions usually lead to serious corrosion problems with respect to the galvanized or steel pipes or water-confining vessels.
Strong acid solutions have been proposed by the prior art to dissolve scale, particularly calcium carbonate scale which is deposited on cooling towers and the metal surfaces of other systems and equipment for handling water. Such systems are designed to handle circulating water for cooling purposes, among other things, and in order to clean the systems the acid cleaning solutions generally must be circulated. The circulation causes aeration of the acid solutions which renders most prior art corrosion inhibitors virtually ineffective.
A common problem encountered in cleaning scale from pipes and small cooling towers and the like is that acid solutions, whether inhibited or not, tend to remove and dissolve copper from the copper surfaces of various elements of the system, and redeposit the copper on the steel surfaces. The presence of dissolved copper in the system is highly undesirable since it tends to plate out and cause severe galvanic attack of steel surfaces.
The present invention overcomes the disadvantages of the prior art through the use of an acid solution containing a combination of inhibitors which provide for reduced corrosion or reduced attack on galvanized and steel surfaces. Using the compositions of the present invention, water systems, and particularly residential water systems fabricated from either galvanized steel can be cleaned and descaled, with a minimum amount of corrosion. The present invention contemplates pipe cleaning compositions which are fundamentally aqueous hydrochloric acid solutions containing a blend of inhibitors including furfural, and diethylthiourea, and use of such compositions to remove scale of the type described above, while significantly minimizing the acid attack on either steel or galvanized steel pipe. In other words, the present invention provides for a composition which will remove scale from galvanized or steel pipes without undue attack on the metal of the pipe, through the use of the novel combination of inhibitors employed in the present invention.
The present invention contemplates pipe cleaning compositions which include hydrochloric acid, furfural, and a dialkylthiourea, the balance of the compositions being essentially water. More particularly, the present invention contemplates a pipe cleaning composition containing from about 7.5 to about 25 parts by weight of hydrochloric acid, 0.6 to 2.6 parts by weight of furfural, and 0.5 to 1.4 parts by weight of dialkylthiourea. In order to obtain the most effective inhibition of galvanized steel corrosion, it is essential to use these components in approximately the ratios set out above. Since the balance of the compositions is essentially water, those skilled in the art will be aware that various ratios of dilution can be used for different purposes, depending upon the type of pipe or water holding vessel which is being cleaned. While it may be desirable to manufacture the pipe cleaning compositions of the present invention at higher concentrations than those set out above, prior to use the compositions should be diluted to the specified levels for most effective use.
It has been found that the addition of inhibitors to levels higher than specified above tends to increase the cost of the pipe cleaning compositions without increasing the effectiveness of the composition. Further, furfural is oily and has a bad odor, and use of more than 2.6 parts by weight (on the basis given above) of furfural tends to cause a film insoluble material to be precipitated on the surface of the pipe being cleaned, which is particularly desirable in domestic water systems. For these reasons, the amount of furfural used in the pipe cleaning composition should be kept as low as possible.
The thioureas of various types are slow to dissolve under some conditions. Therefore the use of higher quantities of thiourea require larger mixing times in the manufacture of the pipe cleaning compositions, and add to the cost thereof without a measurable improvement in the compositions.
As is indicated above, the composition must include a dialkylthiourea. It has been found that diethylthiourea produces the best results, although useful results have been achieved using dimethylthiourea, dibutylthiourea, and diisopropylthiourea. Those skilled in the art will be aware that other dialkylthioureas, similar thioureas such as diphenylthiourea and ethylenethiourea or materials which form such dialkylthioureas in the presence of water and acid may be used.
The preferred composition contemplated by the present invention for use in cleaning or removing scale from residential water systems is as follows:
In making up the compositions of the present invention, hydrochloric acid of various concentrations can be used, as will be known to those skilled in the art. The commercially available 37% hydrochloric acid has been found to be convenient. In making up the preferred composition, about 26.8 parts by weight of 37% hydrochloric acid are used with the described quantities of furfural, and diethylthiourea, the balance being essentially water. It has been found that this composition not only rapidly removes scale from the galvanized pipe of residential water systems, but is greatly improved over the prior art systems insofar as corrosion inhibition is concerned.
The pipe cleaning compositions of the present invention may be produced by mixing the components in any desired order. It has been found advantageous to mix the acid first with dialkylthiourea, followed by the addition of water. While this mixing step usually gives a clear solution, some dialkyl thiocyanates produce a milky solution. The furfural is then added to the acid solution. The present invention contemplates the use of various mechanical devices for mixing, including high speed dispersers and the like.
The following examples will serve to illustrate the preparation of several pipe cleaning compositions within the scope of the present invention, but it is understood that these examples are set forth merely for illustrative purposes and many other pipe cleaning compositions are within the scope of the present invention.
US Referenced Citations (6)
Continuation in Parts (1)
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Number |
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456468 |
Jan 1974 |
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Patent Grant
4025359
