November, 1930
INDUSTRIAL AND ENGINEERING CHEMISTRY
quently desirable to use it at a slightly lower concentration for best economy and rapid pickling. To the above primary requirements for inhibitors must also be added the obvious requirement that there be no injurious effect Won the work pickled Or the operators. For example, a very slight residue from certain inhibitors makes it impossible to apply a satisfactory zinc coating by the hotdip process. Another important item is pickling time. In some cases it takes from 10 to 100 Der cent longer to tickle in the Dresence of an inhibitor. I n i h e picklini of wklded pipe, dowever, Where at the is much ‘lower to than that On the rest Of the pipe, the use Of inhibitors is not generally seriously handicapped by the additional time required.
1203
Summary
(1) The amount of pickling acid used in dissolving scale is approximately a constant, depending only on the weight of scale on the pipe, (2) The amount of acid used in dissolving steel is a variable, which can be controlled by an inhibitor. (3) A small amount of acid is wasted in spent pickle. (4) The practical efficiency of a commercial inhibitor may be estimated from a simple hydrogen evolution test, Literature Cited (1) Chappell, Roetheli, and McCarthy, IND.ENG.CHEM.,20, 682 (1928). (2) Speller and Chappell, Trans. A m . Ins;. Chem. Eng., 1 9 , 1 5 3 (1927); Chcm. M e t . Eng., 84, 421 (1927).
Chemical Characteristics of Cement Pipe Lining’ E. L. Chappell NATIONAL TUBECOMPANY, PITTSBURGH, PA.
No sand should be mixed The chemical compositions of cements used for pipe IPE lined with cement with the cement. Portland celining after one to two years’ exposure t o hot water and to protect against corment is not fit for this work, befive to sixty years’ exposure to cold water are given. I t rosion has been extening too heavy and liable to fall is found that the soluble lime salts have i n most cases sively used for many years from the sides of the pipe before setting. * * * Any good been replaced by iron hydroxide. This replacement has in the New England States. Americannaturalcement which not prevented the practical effectiveness of the corrosion This experience has been disdoes not set too rapidly and prevention of the cement lining. Cement linings are cussed by several writers in is freshly ground can be used particularly suitable for tuberculating waters. the water-works j o u r n a l s with confidence. over the l a s t t w e n t y or thirty years (5, 6, 7 ) . In recent years interest in cement- Analyses of these old linings as they exist after forty to sixty lined pipe has increased owing to the demand for purer years are given in Tables I1 and 111. water in larger quantities and the growth of industries Most modern cement-lined pipe has been made from Portmaking exacting demands upon their water supp!ies. Al- land cement alone or wit,h admixtures of natural cement or though the cement to be used for lining pipe is essentially a of sand. Table V gives the analyses of commercial cement chemically resistant covering of suitable physical qualities, linings manufactured in 1927. and to obtain such a cement is primarily a chemical problem, Theories of Protection by Cement Lining little investigative work has been done with this point of view. It is thought worth while to call attention to the chemiSome idea of the type of cement suitable for pipe lining cal aspects of the problem, and particularly to suggest the may be obtained from consideration of the way in which such essential characteristics of a suitable cement as indicated by linings are thought to protect against corrosion. The French past experience and recent investigation. Academy regarded cement as a protective layer whose effectivenem they had determined by experience. Phineas Ball in Composition of Cements Used for Water Pipe 1876 considered cement as a Drotection against carbon dioxide. The first cements used for water pipe were the Pozzuolano acting both as a protective iayer and as”a neutralizing alkali: cements, of which the Romans one thousand to fifteen hun- At that time most corrosion was ascribed to carbonic acid. dred years ago constructed aqueducts, some of which may Table I-Analyses of Raw Cements POZZUOLANO still be seen. These cements were made by grinding and CONSTITUSOUTHERNNORTHERNALUMINA BEFORE sometimes partly burning natural rock, and adding burnt ENT PORTLAND NATURAL NATURAL CEMENT ADDINGLIMB q” vn % % % lime to form a hydraulic mass. The rocks have approxi63.50 45.26 35.26 33’.b 1o:o mately the composition indicated in Table I. About one CaO 0 . 6 0 3.0 2.57 9.75 17.39 15.6 13.10 2.90 2.04 5.15 hundred years ago the French Academy recommended the A1203 16.5 33.4 7.34 8.66 11 45 20.24 19.26 19.98 2.80 lining of pipe with cement, using probably a natural cement. Si02 46.0 ... c0 2 ... 11.75 ... , . About sixty years ago a considerable amount of pipe in New SO8 0.30 1.99 1.99 1 75 ., 4.4 1.27 12 18 6.40 England was lined with cement, using northern natural ce- Ignition 15.0 Insoluble , . ... ... 5:0 ments either alone or with some sand (Table I). Recent discussions of cement-lined pipe have pointed out Phineas Ball, in a report to the city of Springfield in 1876 quoted by Metcalf, gives as his third recommendation, two ways in which cement linings protect-(1) by reason of “that in applying the cement no admixture of sand should be the alkalinity of the lime in the cement next to the pipe wall, allowed.” The use of pure natural cements seems to have and (2) because of the blanketing action of the cement layer. been favored by most New England water-works superin- Carson (2) indicates that the protection by cement linings is tendents. For example, Forbes gives the following opinion dependent upon both these principles. The permanence of the linings, in either case, would be expected to be related (4: to the solubility of the constituents, including the calcium Presented before the Division of Industrial 1 Received July 22, 1930. compounds. and Engineering Chemistry at the 80th Meeting of the American Chemical Baylis (1) emphasizes the effect of the lime in the lining Society, Cincinnati, Ohio, September 8 to 12, 1930.
P
E%
,
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1204
decreasing corrosion, H~ suggeststhat cementlinings last three hundred years or more in waters which were not corrosive toward calcium carbonate. We mentions that the cement-lined pipe from Danvers, Mass., shows a high iron hydroxide film on the layer next to the water. Examination of the condition of cement linings after use, and also study of the action of inert layers on pipe surfaces, give considerable information in this regard, as discussed below, and indicate that over long periods of time the blanketing action is probably the more important.
Figure 1-Oid Cement-Llned Pipe Used In New England
Examination of Old Cement-Lined Pipe
T o determine the composition of old cement linings and the changes which have taken place in them with time, samples have been obtained from various sources. The appearance of those from Worcester, Mass., and one from a rather complete set from Danvers, Mass., is shown in Figure 1. The two samples from Worcester, obtained from George Bacheldor, formerly water commissioner, were lined with ahout inch of coarsesandand cement. Theliningsshowed two layers. Portions were removed, separating the twolajrers, and analyses made, with the results shown in Table 11. It will be noted that the iron hydroxide contents of the lining ranged from 15 to 47 per cent and that the calcium had all been removed. Microscopic examination showed that a considerable amount of the silica, sand, etc., was still present. The high content of magnesium oxide indicates that natural cenients were originally used. The linings had become comparatively soft, but were still intact, and the pipe wall had been completely protected. Table XI-Analvsea
4hO
Cementdined Service-PioeLlningo from Danvers, Maes. (I-inch pipe about 50 years old)
Table 111-Analyses
Of
APPARBNILY
NSTY
CDNC~MTRiC
cOBBTZTVBNT coNcssTnrc E
~
T~~~~ ~ E~~~~~~~~ = ~ Greenish Dark, greenirh black black
Reddish Yellow
ea0
yellow
%
%
%
%
4.32
4.53 22.4 a5.09
0.79 40.6
1.15 44.4 19.22
11.8 29.30
20.02
These data agree with the observation that cement linings as they have been applied gradually change in
in small glass dishes. A number of the samples were left hare and some were covered with layers of sand '/@a, and J/lsinch thick. Two kinds of sand were used, one averaging about 20 mesh and one about 100 mesh. The testa were first continued for periods of time ranging from 2 to 20 days, samples being taken out and cleaned and weighed at the end of the different periods. The results of the short tests are plotted in Fignre 2, which shows that the corrosion rates are much less even under the comparatively thin layers of
co,n,ora* .c SIrU " W W s r w mi/ Sirici F&ur
-
of Cement-Ltned P b e from Wercest~1.Mass.
.. % None
None
.. % None
% None
17 46
17 68
%
MsO P*.O* Ah01
9.84 38.30 6.10 31.78 0.92
4.89 48.60 6.02 29.16 1.00
Combined HIO
13 80
11 64
sio, coz so2
Vol. 22, No. 11
15.44 24.Y0 7.56 30.90 1.04
9.44 14.70 10.56 40.14 1.7s
Several hundred feet of old cement-lined pipe were ohtained from Danvers, Mass., through the courtesy of MI. Esty, superintendent of water distribution. All of this pipe was said to be about fifty years old. The pieces varied considerably in appearance, however, and samples were selected ranging from almost white to quite dark shades. Analyses gave the results in Table 111. It will be noted that the maximum calcium content was ahout 4.5 per cent and that the calcium was practically gone from the darker linings, but that they contained as much as 45 per cent iron oxide. These linings had all been effective in protecting the pipe against corrosion. In a few cases, where the original linings were quite thin owing to eccentricity, tubercles had formed, but none were large enough to he considered as having impaired the usefulness of the pipe.
Flgure 2
coarse sand than on the hare steel, and drop off very rapidly with time under the thicker layers of fine sand. Tests of this nature were then rnn for periods as long as two years, at the end of which time thesand film had becomecemented together to a hard m a s which was difficult to remove. The results of such tests of corrosion in hot water up to a period of about 8 months are given in Table IV. At the end of this period the '/%-inch films had become so hard that they had to be cut from the samples with a knife. The decreasing corrosion rate under the thick film is notioeahle.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
November, 1930
Table 1%'-Corrosion under Silica-Sand 1 X '/a X %/s inch steel ~quares.exposed to hot 14 D A ~ S 67 D&YS (Average 3 runs) (Average 2 mns) Loss Rate Loss Rate MZ s* Mg.rrq. Gram cm./doj Gram cm./dov Bare n.1127 1.23 0.2~58 0 . 5 8 under vS2inchsilica n.291 0.32 0.0634 0.16 under v8. inchsilica 0.123 0.14 0.0669 0.15
Coverings water (170DF.)
221 DAYS (1 run) Loss Rate
ME
10
Cioms cm./d& 1.4926 1.06
0 . ~ 1 ~ 50.36
Florida, using somewhat harder water, the cement composition was practically unchanged after fifteen months, the lining and the pipe being as usual in excellentcondition. Similar results were obtained in a test in California water, which results are shown in Table VII. Table 7'11-Chsnee Y
Chemical Changes in Modern Cement-Lined Pipe Cement-lined pipe as now made contains somewhat more lime than much of the old pipe. Table V gives the analyses of linings taken in 1927 from four differentmakes of eommercia1 cement-lined pipe. When such pipe is exposed to water, the lime on the surface gradnally goes into solution, which a t first tends to harden the water. This was studied and discussed hy the New England Water Works Association (3'). I n their experiments a considerable difference in rates of solution between different commercial cement linings was noted, and their further results will he awaited with interest. Table V-Analyses
N
s
0.04s
0.06ez
1205
Original lining %
."
CaO
con
65.52 2.95 2.46 3~18 16.60 5.46
Ignition
17.96
MEO FexOi AIiOi
SiOr SO2
of Cement ComDosltIon In Natural Waters w Yon= CITYcompn. S*CR*M.NTO, JacasonvLLLB, After 20 of rust in C ~ P . FLA. moothr at gslv?nired After 15 After24 prpe monthsin monthsin 160'P. (71°C.) (same test) hot water hot wrfei 4 " 4 . 4 " 4 " ," ," ," ," 2.25 Trace 20.81 49.34
1.60
Table VIII-Teats
...
32.0
25:ZS ... ... ...
...
04.8
i:ie ... ... ...
4.28 6.U6
... 2.70
...
6.83 16.67
2KE0
2i:i3
26.79 3.93
...
of High-Alumina Cement (33 Per Cent Sand1 Llnlnge In New York City Wafer OIUGENAL A ~ r a ~ MONTHS 29
CONSrrT"B"7
LWINO
of Modern Cement-Lined Pipe MODIliILLD
CONSIITUBNT
FoETLnao
,, O P
P O a r L A N o *ND
S*Nn
The Con content is roughly proportional to the time the pipe from which the samples were taken had been exposed t o the sir.
Some time ago a sample was obtained of pipe lined with natural cement, which had been exposed to fairly pure water for five years. The composition of the lining before and after this exposure is given in Table VI taking the original composition from other data. It will he noted that the calcium content decreased about 30 per cent in five years, and the iron and silica content increased somewhat. The lining was in good condition, and had completely protected the pipe. Table VI-Analy8es of Cement-Llned Pipe from Portland, Me. (Used from April, 1924. to Pebmary. 1929) CoXsrtrusNr OBLOINAL (Estd.) AXTEE 5 Y ~ R S
Plpe t h e Cement B d n g High lo Iron and SMca a i d Low In Lime
Figure 3-Cement-Lined
It should be emphasized that no noticeable corrosion of the pipe had occurred, for example, in the New York test, and only experience can tell how long such a pipe will be protected by the layer of iron oxide and silica which results from the changes in the cement lining. The effectiveness of linings of pure Portland cement in hot water has been tested over a period of two to six years, and, ES would he expected, the effect of the water upon the lining varies greatly with the water composition. Tahle VI1 shows the composition of a pure Portland cement lining and its composition after two years' exposure to New York Citywaterat 160'to 180°F. Itwillhenotedthatmuehofthe lime has been leached out, the action being similar to that noted in cold water after forty to sixty years. However, the pipe was still completely protected by the lining thus left, no evidence of corrosion of the metal being visible on removina. A similar test in the same water over a aeriod of two and one-half years waa carried out with a hightalumina cement plus 33 per cent sand. The results are shown in Table VIII. In this ease also, although much of the lime was removed, the lining was in excellent condition and the pipe perfectly protected. I n a third test, in a hot-water line in
Discussion The data presented above show that cement linings in use from forty to sixty years have gradually lost their lime content, which has been replaced by iron hydroxide. This change is found to take place much more rapidly in hot water. The replacement of the lime by iron hydroxide does not result in the disintegration of the lining, nor does it appear to impair the protectiveness of the lining. It is found that the old pipe as shown in Figure 1 is in excellent condition after many years of use. It is shown by laboratory experiments that thin films of pure silica sand greatly decrease the corrosion of cement and gradually become cemented into still more protective lavers bv the weeidtation of iron hvdroxide . from the steel beneath. One important implication from the obvious importance of the behavior of iron hydroxide in cement linings as they
1206
INDUSTRIAL AND ENGINEERING CHEMISTRY
have been made is that such linings should give protection under any condition where iron hydroxide tends to precipitate. Thus in tuberculating water such pipe is excellent. Cement-lined pipe has been found good in other water, however-as, for example, in salt water and sulfur water, where the tendency toward tuberculation is not so marked. At the same time it has been found that steam return lines high in carbon dioxide, which have a solvent action on both iron and calcium salts, attack and destroy some cement linings. Other steam return lines have little action, but the conditions of balance are evidently quite delicate. A cement for pipe lining based on the principles above has been developed, which is high in iron and silica and low in lime. Figure 3 shows the appearance of a lining of this type. The rate of solution of lime from the lining is also a sub-
Vol. 22, No. 11
ject of great interest, which has been carefully studied, but which will not be discussed in the present connection. It is expected later to present data on the solution rates of various compositions of cement in natural water of various kinds, and also to discuss the necessary conditions for obtaining satisfactory physical qualities, such as resistance to shrinkage and necessary physical strength. Literature Cited END.CABM.,19, 777 (1927). (1) Baylis, IND. (2) Carson, Ibid., 19, 781 (1927). (3) Committee on Cement-Lined Pipe, J . Naw Engl. Water Works Assoon., 42, 492 (1928). (4) (5)
Forbes, Ibid., 14, 44 (1900). Gibson, Engineering News, 89,378 (1922); J. Ant. Watn Workr A ~ J O C W . ,
(6) (7)
Metcalf, J. New Engl. Water Works Assocn., 13, 1 (1909). Sherman, Ibid., 40, 98 (1926).
16, 427 (1926).
The Bulking Properties of Microscopic Particles* Paul S. Roller NONMETALLIC MINERALS EXPERIMENT STATION, U. S. BUREAU OF MINES,NEW BRUNSWICK, N. J
By means of an air analyzer for fine powders, a n anhydrite, gypsum, Portland cement, and chrome-yellow powder were separated into homogeneous fractions above 1 micron surface mean diameter. The bulkiness, or volume per unit weight, was found to increase with decrease in particle size below a critical diameter; for particle sizes greater than the critical diameter the bulkiness was constant. For all the powders the same functional relationship was found to hold between the voids per gram and the surface mean diameter. The differences'in the value of the constants for the different powders appear to depend chiefly on the particle shape, whether cubic, prismatic, basal, etc.
As would be expected from a consideration of packing of small particles in the voids of larger particles, the surface mean diameters of the Portland cement and chrome-yellow microscopic powders calculated from the bulkiness of the powder were found to average several tenths of a micron higher than the true mean diameters. With this correction in mind, for powders above 1 micron surface mean diameter, a rapid method presents itself of estimating the mean particle size of the microscopic powder from a knowledge of its curve of bulkiness vs. particle diameter, but no knowledge as to the distribution of the particle sizes in the powder is thus obtained.
K CONNECTION with the development of an air ana-
precipitation. I n this connection he devised a useful apparatus on the principle of a tilt hammer for automatically tapping the cylinder which contained the powder whose bulkiness was to be tested. Work (4) measured the bulkiness of silica powder by handtapping a cylinder containing the powder. He found that the weight per unit volume, which originally was 1.710, after 30 minutes' grinding reached a value of 1.805 and then dropped continuously until after 14 hours it was 1.205.
I
lyzer for fine powders (8) and for the determination of chemical reactivity as a function of particle size (S), a number of microscopic powders2were fractionated into homogeneous particle-size groups above 1 micron surface mean diameter. It was a t once noticed that the finest fractions bulked enormously and that the bulkiness, or space occupied by the unit mass of the powder, decreased rapidly as the mean particle size of the different fractions increased. To see if any relationship existed between the particle diameter and the bulkiness, the latter quantity was measured for various fractions of four different powders for which the mean diameter of each fraction had been accurately determined under the microscope. The powders studied were (1) a laboratory ground crystalline anhydrite, (2) a laboratory ground c. P. gypsum, (3) a commercial Portland cement, and (4)a commercial chrome-yellow pigment. Previous Results
It is known in an empirical way that the more finely ground a powder is the greater it bulks. Cocking (1) utilized this property in standardizing pharmaceutical products formed by Received July 30, 1930. Publis'hed by permission of the Director, U, S. Bureau of Mines. (Not subject to copyright.) 1 Here, as elsewhere, a microscopic powder is defined as a powder whose largest particles average 100 microns in size-i. e., that portion of a powder passing through t h e 200-mesh sieve. 1
Experimental Procedure The size of the particles of the well-defined fractions was determined microscopically as the mean of the length and width, or length, width, and depth in the case of the cement and pigment. From these measurements in duplicate the surface mean diameter of the fraction-i. e., the diameter of a sphere or cube of equal surface per gram-was calculated from the equation
a.
=
Zd3 Zd2
-
(1)
In Equation 1, d, the diameter of a particle, is summed for all the particles measured; d, is the surface mean diameter Of the fraction. The surface mean diameter, which is a measure Of the 'pcific surface of the powder, is of greater significance than the
