November, 1941
INDUSTRIAL AND ENGINEERING CHEMISTRY
had indicated the results t o be expected under these conditions. Sulfate and silica deposition were also known to occw in plant operation] and consequently the presence of this type of deposit in the experimental system would establish the successful simulation of the plant scale-forming conditions. Results obtained in this study ate shown in Table V. The study was interrupted a t the end of 16 days when the solids concentration in the uncontrolled system reached a maximum and discoloration from the redwood interfered with control of the other two systems. The character of the scale formation, including sulfate and silica, and the quantities formed checked well with plant experience. We were satisfied from these tests that we could duplicate scale and corrosion occurring in operating systems and that individual factors could be successfully controlled for research purposes. Subsequent studies reported in the following paper (page 1365) established the fact that synthetic waters corresponding to raw water analyses would give comparable results in these systems, and after eliminating the difficulties previously mentioned, these systems became useful laboratory and research instruments for the study of cooling water problems.
1365
Acknowledgment The cooperation of the Eastern Engineering Company in solving the pumping problems of these systems and of E. H. Sargent & Company in obtaining suitable immersion heaters is gratefully acknowledged. I n addition] I wish to express my appreciation t o Douglas M. Considine of our company staff for patient assistance in conducting experiments and preparing the tables and charts used in this and the following paper.
Literature Cited (1) Badger, W. L.,McCabe, W. L., “Elements of Chemical Engineering’’, 1st ed., p. 118 (1931). (2) Ellis, David, “Iron Bacteria”, New York, Frederick A. Stokes Co. (3) Haering, D. W., IND.ENG.CHEM.,30, 1356-61 (1938). (4) Hammerschmidt, E. G., PetroEeum Engr., 9,44-8 (Nov., 1940). ( 5 ) Hatch, G. B., rtndRice, Owen, IND.ENG.CHFM.,32,1572-9(1940). (6) Holaday, K.M.,and Von Gontard, A., Ice and Refrig., 95,28696 (1940). (7) Wilson, J. H., and Groesbeck, E. C., J. Reeearch Natl. Bur. Standards, 24, 665-76 (1940). PRBIWNTED before the Division of Water, Sewage, and Sanitation Chemiett y at the IOlst Meeting of the Americsn Chemioal Society, St. Louis, Mo.
SCALE AND CORROSION STUDIES
T
Initial studies in laboratory-scale cooling tetraphosphoglucosate, the SYSHE fact that soluble consystems have demonstrated the effect of tems differing only in their concentration plays an important part in scale formation tent of dissolved solids. The critical dissolved-solids limits on scale consolids content of tower was in cooling system operation effectiveness Of both may appear trite, but it is trol, the allowed to approach a limit of frequently ignored by chemists and corrosion inhibitors, and the effects of 5000 p. p. m. as a maximum as well as engineers. There chloride ion concentrations on corrosion while the solids of tower 4 were controlled to a maximum of 3500 rates. The facts disclosed show the need are, necessarily, critical concenp. p. m. Tower 3 circulated trations in formafor more study in these directions and the make-up water carrying a retion which limit the effectiveness of preventive chemical limitations Of corrective being sidual of 2 p. p. m. hexametaphosphate with the upper limit treatments, and complete knowlemployed. of solids content set a t 3500 edge of these critical limits p. p. m. Make-up water for may be expected to increase tower 5 contained 10 p. p. m. &glucoside. The P-glucoside the usefulness of chemidals employed in this direction. was added in this amount directly to the make-up water because residuals of &glucoside cannot be determined with the Effect of Scale Inhibitors rapidity possible with other determinations. Since we are dealing with systems where mass reactions are Each cooling system evaporated from 6 to 8 quarts of water economically prohibitive, knowledge of this sort is particuper day. The systems were replenished with make-up water larly important. We undertook to determine the possibilihourly, and treatment residuals of towers 2, 3, and 4 were determined before each addition of make-up. An observation ties in this direction in our experimental cooling systems, described in the preceding paper (page 1360). Aside from deof the tower level, indicating the volume of water in the system, plus the residual determination enabled the operator to termining critical-solids limits and relative effectiveness of common treatments, we wished to establish the fact that syncalculate the required amount of treatment concentrate necesthetic waters provided identical results with natural waters in sary for the maintenance of proper treatment residuals. studying these conditions. The make-up water for this study was prepared by diluting Chloride Ion as an Index a definite volume of synthetic concentrate to provide a water The fact that little possibility existed of the chloride ion of constant composition and pH. The concentrate was based being precipitated in the form of scale or corrosion deposits on analyses of a natural water which plant knowledge and preprovided a factor indicative of the solids concentration of vious experiments had shown to produce scale of definite composition under certain circumstances. As our objective each system. Ratios of dissolved solids to chloride were calculated at the outset of this study and were checked frewas to demonstrate the effect of dissolved-solids limits and treatment chemicals]we ran experiments with solids controlled quently. These ratios served as an instantaneous index of the a t 5000 and 3500 p. p. m. and with various treating chemicals. dissolved solids content of each system. A rapid determinaMake-up water containing no treatment was circulated tion of chloride content enabled the operator to calculate the through tower 1. This cooling system served as the primary amount of dissolved solids present. Upon closely approachbasis of comparison for our third study. Towers 2 and 4 ciring the upper limits of solids concentration, a definite amount culated make-up water containing a residual of 2 p. p. m. of system water was dumped and an equivalent amount of
INDUSTRIAL AND ENGINEERING CHEMISTRY
1366
Vol. 33, No. 11
make-up was added. I n this manner solids concentrations were controlled within a reasonable range. I n addition to daily determinations of dissolved and total solids, the pH and alkalinity of each system water were determined. At the completion of operations for this study, the immersion heaters were removed with the utmost care to prevent any disturbance or loss of scale deposited upon the heater surfaces. After a microscopic and photographic study of each scale deposit was made, the scales were analyzed conipletely for their chemical contents. I n addition, the water from each tower was completely analyzed. The results of this study showed that solids concentrations were an important factor influencing the effectiveness of chemical treatment. The chemical conditions maintained in the systems are shown in Figure 1. The hexametaphosphatetreated system exhibited a marked tendency to rise in p H and required the adjustment. of pH of the other systems in order to maintain equivalent conditions. Table I shows the analysis of the make-up water and the cooling waters a t the conclusion of the test run. Some conclusions may be drawn from this analytical evidence. &Glucoside shows a marked superiority a t carrying silica in suspension while all of the treated systems are better in this respect than the untreated system. The calcium contents show that hexametaphosphate and tetraphosphoglucosate keep this element in solution to advantage.
TABLE I. ANALYSES AT CONCLUSION OF STUDY No. 3
Hydrate Carbonate Bicarbonate
co2
Chloride Sulfate Silica Calcium Magnesium Iron Hardness Calculated Soap AlkaLinity Acidity Solids Total Suspended Dissolved Volatileand organic Cas04 Si02 CaCOs MOCOI Fez08 Cas(PO4h Volatileand organic Moisture Undetermined
Make-up Water, P. P. R.1. None None 127.0 3.0 43.0 212.0 10.6 35.0 12.0 0.2
c
Tower la
None 48.0 243.0 None 337.0 1238.0 24.0 60.0 59.0 1.1
Cooling Waters, P. Tower Tower 2b 30 None None 126.0 120.0 372.0 390.0 None None 355.0 350.0 I.398.0 1367.0 34.0 29.0 108.0 102.0 65.0 65.0 1.2 1.7
P. M-.
Tower
ToTer
4d
6
None 132.0 418.0 None 334.0 1156.0 26.0 110.0 61.0 1.1
None 54.0 266.0 None 344.0 1174.0 40.0 61.0 58.0 1.8
135.0 95.0 127.0 2.0
392.0 320.0 291.0 None
521.0 365.0 510.0 None
537.0 390.0 498.0 None
525.0 360.0 550.0 None
391.0 320.0 320.0 None
539.0 None 539.0
3720.0 104.0 3616.0
4224.0 32.0 4192.0
4238.0 12.0 4226.0
4137.0 144.0 3993.0
3892.0 101.0 3791.0
365.0
477.0
528.0
541.0
634.0
46.0
... .. .. .. ... .... ..
... ... ...
--Immersion 3.20 3.22 3.66 1.48 42.31 49.49 16.86 19.75 7.62 4.50 None 2.77 23.30 2.03 1.02
16.01 1.82 0.86
Heater Deposits, yo3.35 3.53 3.36 1.70 1.58 1.35 48.15 44.51 41.40 21.88 23.66 15.15 4.80 4.61 7.40 2.58 2.77 None 13.90 2.30 1.34
15.77 2.15 1.42
28.25 2.45 0.64
a No treatment. b 2 p. p. m. tetraphosphoglucosate; dissolved solids controlled a t 5000 p. p. m. 0 2 p. p. m. hexametaphosphate; solids a t 3500 p. p. m. d 2 p. p. m. tetraphosphoglucosate. solids a t 3500 p. p. m. 6 10 p. p. m. @-glucoside; solids at k 0 0 p. p. m.
It is rather difficult to interpret results from the water analyses, but a study of the immersion heater deposits corrects this situation. Figure 2 shows these deposits. The uninch treated system at 5000 p. p. m. of solids deposited of crystalline scale, which checks well with plant data and establishes the fact that synthetic waters will produce the same results in laboratory studies as natural waters. The scale deposited in system No. 3 with hexametaphosphate was I/SZ to '/le inch, nm crystalline in nature, and
Time
FIGURE 1.
OPERdTINff CHARACTERISTICS
November, 1941
Untreated, 5000
Tetraphosphoglucosate, 5000
Hexametaphosphate, 3500
HEATERS AT ENDOF STUDY No. 3 FIGURE 2. IMMERSION
AND WEIGHT LOSSES, STUDY NO.5 TABLE 11. WATERANALYSES
Sulfate Silica Calcium Mraneaium Iron Total Dissolved Hardness Caloulated Soap Alkalinity Aoidity
solids
Dissolved Suspended Total Volatile. and organio
YLW,.
loss
1367
INDUSTRIAL AND ENGINEERING CHEMISTRY
Raw Water
d o o l i n g Waters System System System System io 2b 3c 4d
5.3 None None 119.0 1.0 17.0 5.7 34.0 9.2
None None 160.0 None 49.0 5.0 42.0 15.0
70.0
496.0 None None 128.0 None 54.0 6.2 39.0
0.2 0.2
32.0 0.3
120.0 100.0 119.0 2.0
System 5'
16.0
1518.0 None None 99.0 4.0 46.0 11.0 37.0 14.0
2484.0 None None 104.0 4.0 64.0 13.0 50.0 20.0
4964.0 None None 115.0 None 60.0 8.2 51.0 19.0
108.0 0.4
167.0 0.4
199.0 0.3
238.0 0.4
170.0 160.0 160.0 None
145.0 140.0 128.0 None
150.0 130.0 99.0 4.0
210.0 200.0 104.0 3.0
205.0 200.0 115.0 None
235.0 None 236.0
472.0 40.0 512.0
1147.0 148.0 1295.0
2644.0 203.0 2847.0
4389.0 361.0 4750.0
8661.0 584.0 9245.0
106.0
107.0
137.0
169.0
263.0
438.0
...
7.70
3.40 0.28
8.35 0.30
7.70 0.45
7.95 0.43
8.30 1.32
showed little improvement over untreated conditions. The tetraphosphoglucosate-treated systems at 5000 p. p. m. showed l/&nch and '/&-inch deposit at 3500 p. p. m., and indicated a decided beneficial result from controlled solids concentrations. Tower 5 with 0-glucoside-treated water exhibited a scale deposit of '/a inch of no mechanical adherence, equivalent by normal standards to perfect scale control. Table I also shows the analysis of the immersion heater deposits from this study. The presence of appreciable sulfate and silica deposits should be emphasized, as these check the plant experience using natural water and further establish the presence of this type of scale in cooling system operation. There may be some question as to whether calcium carbonate forms scale in the absence of other materials t o act as binder; if this is true, the presence of binding agents assumes added importance.
Tetraphosphogluoosate, 3500
WITH
5000
AND
@-Gluooside,3500
3600 P. P. M. SOLIDS
The scale analyses show the hydrolysis of phosphate compounds, whether organic or inorganic, to be factors in scale formation. Other facts established by this experiment included the close relation of chloride concentrations t o dissolved solids, the effect of controlled solids in limiting scale formation, and the greater efficiency of the organic compounds over the inorganic chemical in inhibiting scale formation. An effort was made in the next study to determine the effect of chloride-ion concentration on corrosion rates in cooling systems. Study No. 4 was interrupted by mechanical difficulties with the systems and was rerun in study No. 5. I n this experiment chloride concentrations were controlled at 500, 1500, 2500, and 5000 p. p. m., respectively, and compared to the raw water with no concentration control made. Results are shown in Table 11. A concentration of 500 p. p. m. of chloride does not appreciably increase the corrosion rate over normal concentration, but an increase to 1500 p. p. m. causes a noticeable acceleration of the corrosion rate. Conditions between 1500 and 2500 p. p. m. of chloride appear to be relatively constant, but an increase to 5000 p. p. m. causes a sharp increase in corrosion rate The effect of the chloride ion is illustrated in Figure 3 and compares favorably with values determined by other investigators in independent corrosion research.
0.oJ
1000
,
,
2000 3000 4000 Chloride Concentration p.p.m.
5( 30
FIGURE 3. RELATION OF CHLORIDE TO CORROSION RATE
INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
1368
Vol. 33, No. 11
Effect of Corrosion Inhibitors TABLE 111. ANALYSES AT CONCLUSION OF STUDY6
Chloride Hydrate Carbonate Bioarbonate
coz Sulfate
Silica Calcium Magnesium Iron Total Dissolved Hardness Calculated Soap Alkalinity Aciditv Solids" Dissolved Suspended Total Volatile, and organic Treatment
Raw ,-Water System P. P. M. 15 493.0 5.3 None None None None 149.0 119.0 1.0 2.0 17.0 144.0 11.0 5.7 62.0 34.0 44.0 9.2 9.1 0.2
5.4 0.3
4.4 0.7
7.6 1.0
10.0 1.2
120.0 100.0
330.0 300.0 149.0 2.0
375.0 398.0 None
375.0 350.0 338.0 None
250.0 230.0 284.0 None
170.0 150.0 166.0 1.0
2.0
350.0
235.0 None 235.0
1117.0 12.0 1129.0
1462.0 8.0 1470.0
1107.0 7.0 1114.0
1569.0 11.0 1580.0
1075.0 31.0 1106 0
106.0 None
197.0 None
193.0 3.6
172,O 4.0
277.0 91.0
215.0 123.0
7.66
8.05 0.28
...
8.80 0 06
--Immersion 1.98 1.72 0.40 0.30 67.50 55.53 7.39 10.96 4.90 5.32 12.80 3.17 3.60
Cas01 SiOn CaCOa MgC03 FezOs Caa(PO4z Moisture Volatile and organic Undetermined a
Waters, P. P. M.-----System System System ac 4d 5e 489.0 496.0 496.0 None None None 34.0 None 62.0 250.0 156.0 276.0 None 1.0 None 180.0 116.0 98.0 20.0 14.0 11.0 30.0 69.0 46.0 33.0 24.0 47.0
0.2 0.2
119.0
g w t . loss
Cooling System 2b 504.0 None 62.0 336.0 None 130.0 10.0 70.0 49.0
...
9.35
4.40
10.00 0.62
8 75 0.11
8.65 0.05
Study No. 6 was undertaken to determine the effect of well-known corrosion inhibitors utilized in cooling system operation. Chloride concentrations were controlled at 500 p. p. m., and untreated systems were compared with tetraphosphoglucosate, hexametaphosphate, chrome glucosate, and cupric chrome glucosate in this study.
8.15 0.07
Heater Deposits, %----1.54 1.68 1.74 0.80 0.20 0.97 54.73 67.25 64.38 8.13 10.12 10.95 7.36 17.23 2.99 7.68 2.40 2.88 2.40 7.03 2.83
...
...
8.35 1.39
14.23 0.74
No treatment.
b Tetraphosphoglucosate. c
d e
Hexametaphosphate. Chrome glucosate. Cupric chrome glucosate.
FIGTTRE 5 . CORROSIOX TESTSECTIOXS FROM STUDY No. 6 1. Untreated
2. 3.
4. 5.
KumChryee3ucosate Tetra Phospho ucosate
I 23
4 5 6 7 8 9 IO I1 12131415 Days
OF STCDY No. 6 FIGURE 4. RESULTS
A . Iron contents of cooling system waters cannot be used to interpret corrosion rates E. Quantity. of treatment required in make-up t o maintain a, residual IS not entirely a function of the r a w water analysis
Tetraphosphoglucosate Hexametaphosphate Sodium chrome glucosate Cupric chrome glucosate
The systems were operated for 15 days xyith all factors controlled, and iron and residual treatment contents were determined daily. Clean, new, weighed, corrosion test sections were installed. Table 111 shows the analyses of the waters a t the conclusion of this experiment. Several interesting facts were disclosed by this study. Figure 4A shows the iron contents plotted against time with the corresponding weight losses indicated fer each curve. As might he expected in a system where oxidation by air contact causes precipitation of iron and suspension depends on colloidal phenomena, there is no apparent relation between iron contents and corrosion rates. This important fact should not be ignored in cooling system practice. Figure 4B plots the treatment required in the make-up to maintain residuals in the system against time This is a significanb group of curves, since i t shows that, regardless of the corrective chemical employed, there is no direct relation betveen residuals in the make-up and in the system. Thus it becomes difficult to prescribe corrective chemicals in terms of make-up dopage and emphasizes the complexity of cooling water problems. Moreover, there is no apparent relation between the chemicals employed for corrosion inhibition. Therefore the dosage is not only specific to the system, but to the chemical utilized. Study of the corrosion sections used in this study failed to disclose any pitting or grooving which might be used as a comparison of results obtained. Figure 5 shows the corrosion
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
November, 1941
Untreated
Tetraphosphoglucosate
Hexametaphosphate
Sodium chrome glucosate
1369
Cupric chrome glucosate
FIGURE 6. SCALED IMMERSION HEATERS FROM CORROSION STUDYNo. 6
test sections split for examination with no evident difference in the several specimens. The macroscopic examination of the corrosion test section is in contrast to the weight losses disclosed in Table IV, which show clearly that metaphosphate is performing poorly as a corrosion inhibitor while the glucosates (tetraphospho-, chrome, and cupric chrom-) have accomplished substantial reductions in corrosion rate.
The studies conducted to date in these systems may be considered preliminary to further researches into the fundamental causes of scale and corrosion in cooling system operation and optimum methods of control. Facts disclosed by the immediate studies indicate considerable ignorance of controlling factors in this field which must be corrected before substantial progress toward the elimination of the problems may be expected..
Scale Deposit
Conclusions
Removal of the immersion heaters a t the conclusion of this study revealed appreciable scale deposits (Figure 6). This illustrates the difficulty of divorcing one cooling water problem from another. The analysis of these deposits is represented in Table 111, and the presence of sulfate and silica deposits may once more be noted. Of more significance, however, is the fact that the inhibitor (hexametaphosphate) showing the least effectiveness as a corrosion inhibitor also shows the smallest iron content, and even the untreated system presents a deposit showing a smaller iron content than two systems which definitely inhibited corrosion. Accustomed as water chemists are to interpret corrosion in terms of iron contents, these figures may encourage a closer analysis of the facts than has been deemed necessary in many previous cases.
The studies completed to date permit the following conclusions: 1. Scale formation and control are influenced by dissolved solids concentrations. 2. Synthetic waters produce identical results in laboratory studies with natural waters. 3. The glucoside derivatives are more effective in inhibiting either scale or corrosion than hexametaphosphate. 4. Iron contents, either in water or in deposits, cannot be used for accurate interpretation of corrosion rates in recirculating cooling systems. 5 . Chloride concentrations accurately represent dissolved solids concentrations in cooling system practice. 6. Chloride concentrations directly affect the corrosion rate in cooling system practice. PREBBNTEID before the Division of Water, Sewage, and Sanitation Chemistry a t the IOlst Meeting of the American Chemical Society, St. Louis, Mo.
