Inhibited Acid Composition for Cleaning Water Systems

A pipe cleaning composition was made up of the following materials:

The pipe cleaning composition was produced by first mixing the hydrochloric acid with the diethylthiourea. This was then diluted with the given quantity of water and the furfural was added to this solution.

Two control solutions were made up in accordance with the above-described procedure. Control A included all of the components except the diethylthiourea. Control B included all of the components except furfural.

Three pieces of one-half inch galvanized pipe nipples, approximately 3 inches long, were partially submerged in each of the three solutions for 20 minutes, whereafter they were removed and washed with clear water. The nipple which had been placed in the composition of the present invention showed no noticeable removal of the galvanizing from the pipe and showed only slight rust-like corrosion on the threaded area. The pipes which had been submerged in the two control solutions showed complete removal of the galvanizing and substantial oxidation of the threaded portion of the pipe. The pipe which had been in control B, which contained no furfural, showed relatively severe oxidation of the threaded portion of the pipe.

A series of solutions were prepared, within the scope of the present invention, to determine the effect of varying the concentration of inhibitors of the present invention. The solutions described in Table I were made up using 37% hydrochloric acid by first mixing the hydrochloric acid with the diethylthiourea. This was then diluted with the given quantity of water and the furfural was added to this solution. Finally the benzyl thiocyanate was added with vigorous mixing.

A galvanized nipple was submerged for approximately 30 minutes in each of these solutions. The amount of corrosion, as visually determined, is reported in Table I.

The data reported in Table I demonstrates that reducing the amount of either diethylthiourea or the amount of furfural in the acid solution significantly increases the tendency of the solution to attack galvanized steel pipe. Table I also demonstrates that the benzyl thiocyanate is not essential to provide protection against corrosion of galvanized or steel pipe. Table I further demonstrates that increasing the quantities of these materials above the preferred ranges does not significantly reduce the corrosion of the pipe cleaning composition.

A pipe cleaning composition was made up of the following materials:

The pipe cleaning composition was produced by first mixing the hydrochloric acid with the diethylthiourea. This was then diluted with the given quantity of water and the furfural was added to this solution. Finally the benzyl thiocyanate was added with vigorous mixing.

A control solution was made up, which contained the same ingredients as shown above, but the benzyl thiocyanate was omitted.

The purpose of this test was to determine the relative ability of the two compositions to dissolve the scale, and for this purpose a small piece of flag stone was submerged in each solution. In order to eliminate the possibility that one piece of flag stone was more soluble than the others, the pieces of stone were reversed after 20 minutes.

In each case, 112 grams of the solution of the present invention or the control solution were placed in a small beaker. To each solution was added a piece of flag stone weighing about 100 grams, and after 20 minutes the flag stones were removed, and the weight loss, in grams, was recorded. The flag stone pieces were then placed in the opposite solution, for 15 minutes, and the loss in weight was again recorded. The results of the test are shown in Table II.

Using the same solutions as are described in Example 11A, above, the flag stone pieces remaining from the test shown in Example 11A were submerged in fresh solutions (115 grams) for 20 minutes, in the same order as the second phase of the test described in Example 11A. It is believed the weight loss of test 11B can be added to the weight loss in the first portion of test 11A to give a total weight loss based on the use of fresh solutions only. The results of this test are set forth in Table III below.

Table III suggests that the pipe cleaning solution of the present invention is about as quick to attack certain types of lime stone or scale as is a similar solution containing no benzyl thiocyanate. It has been found in practical operations that the action of the pipe cleaning solution of the present invention is sufficiently rapid and complete for practical usage, whether or not the solution includes benzyl thiocyanate.

A pipe cleaning composition as is set forth in Example 11 was made up. This was compared against a composition containing an equivalent amount of hydrochloric acid in water, but with no stabilizers or inhibitors being present. In this case two pieces of flag stone were used, one for each test solution. A piece of flag stone was submerged in one of the compositions being tested for 5 minutes and then removed, its weight loss being recorded. The flag stone was then placed in the other composition, and again the weight loss after 5 minutes was recorded. Finally, the flag stone pieces were returned to the composition they had been placed in initially, and left for 9 hours. Resulting weight losses are shown below in Table IV.

While this experiment shows that the inhibitors of the present invention reduce the speed with which flag stone (and scale) is dissolved, this experiment also demonstrates that the inhibitors do not prevent the acid from working.

In order to compare the corrosion tendency of hydrochloric acid solutions with the compositions of the present invention, a 1/2 -inch by 2 inches galvanized steel nipple was submerged in a hydrochloric acid solution for about one month and was compared against a similar nipple which had been submerged in the solution of Example 11 (both solutions had the same amount of hydrochloric acid) for one month. The nipple which had been submerged in the hydrochloric acid solution was badly rusted and both ends had been partially eaten away. The nipple which had been submerged in the composition of the present invention was discolored and showed a very small amount of rust, but the nipple was mechanically sound.

The compositions of the present invention are usable in the same manner as the various scale removal solutions of the prior art. This is generally accomplished by pumping the pipe cleaning solution through the pipes of the system being cleaned for an hour or more.

More particularly, in cleaning or descaling a residential water system, the water supply is shut off, and the water removed from the plumbing. A shower head is removed and capped at the highest point of the water system and by opening both the hot and cold valves on the capped shower, the pipe cleaning solution can be pumped up through the cold water system, whereupon it returns down through the hot water system or vice versa. The time of pumping will depend on the concentration of the acid in the pipe cleaning solution and is a function of the amount of scale actually present in the pipe. The actual technique by which this pipe cleaning solution is applied to the pipes is not critical with respect to the present invention although it is preferred to keep the time of contact as short as possible in order to minimize corrosion.

After the scale has been removed using the compositions of the present invention, it may be advisable to neutralize the cleaning pipe. After cleaning out domestic or residential water systems, it is necessary to thoroughly flush the acid and all inhibitors out of the system. In this regard, the present invention contemplates the use of neutralizing agents, baking soda, or the like to neutralize the acid.

In addition to cleaning out residential water systems, the pipe cleaning composition of the present invention is useful in cleaning out humidifiers, vaporizers, shower heads, tea kettles, steam tables, air conditioners and similar water handling apparatus which is susceptible to scale formation. In cleaning out systems which are not used for potable water, it may be desired to mix a small amount of the pipe cleaning solution of the present invention with the water therein in order to inhibit, reduce or eliminate the possibility of scale formation.

The solutions of the present invention may be diluted with water, if desired, for some purposes. It has been found that diluting the pipe cleaning solutions will increase the amount of cleaning solution to be pumped, which may be an advantage if insoluble scale is encountered. In such cases the pumping of the increased volume of pipe cleaning solution will tend to carry the insoluble materials through the pipes, where the solids may be removed by filtration or sedimentation from the pipe cleaning solution. Further, the present invention contemplates that auxiliary materials may be added to the pipe cleaning solutions, such as abrasives or odor absorbers. Still further, one or more organic solvents may be added to the pipe cleaning composition in order to keep one or more of the inhibitors in solution and to help remove or dissolve some of the scale residue.

The pipe cleaning compositions of the present invention are preferably used at ambient temperatures although they may be used at elevated temperatures, if desired. While the use of elevated temperatures increases the speed with which the pipe cleaning composition acts, the advantage of the increase in speed is offset by the cost and trouble involved heating the cleaning composition and the pipe through which it is pumped.

As used herein, the term "parts by weight" shall not necessarily equal the percent by weight, except wherein so stated. Due to the nature of the present invention, the compositions may be diluted to alter the inhibitors or acids outside of the specified ranges, if said ranges were construed as percentages. Since the amount of water used in connection with the pipe cleaning compositions of the present invention may vary considerably, the ratios are expressed in parts by weight.

The forms of invention herein shown and described are to be considered only as illustrative. It will be apparent to those skilled in the art that numerous modifications may be made therein without departure from the spirit of the invention or the scope of the appended claims.