BI3CKEI%-TYPECOKE 01 PHIL .ADELPHIA COIKE PApiIY, w'ITH PUSHER MAC IN THE FOREGRO UND OF
Courtesu, Koppers Construction Company
Carbonization of Coal Effects of Variation of Rate of Heating during the Carbonization of a Typical Coking Coal
QR
ESULTS obtained in a
could be obtained. The gear shift was manually operated a t Coal Research Laboratory, predetermined temperatures. study of the Carnegie Institute Of Technology~ Pa. I n all the work to be reDorted. effects of change of rate of heating during carbonization of a combinations of these two rates typical coking coal from the Pittsburgh seam, Edenborn mine, were used to a maximum temperature of 700" C. which was to a maximum temperature of 700" C. are reported in this maintained for one hour a t the end of each run. paper. Carbonization of the same coal a t constant rates of Detailed analyses of the carbonization products were not heating between 0.7" and 21.8" C. per minute to 540", 700", made for this study, and only a general separation into solids and 1000" C. gave data which showed that tar yield increases, (coke), liquid (tar and liquor), and gas is reported. For comcoke yield decreases, and in general gas yield decreases in proparison with the data given in the previous paper: Solids portion to the logarithm of the rate of heating, as reported in a include coke and residue; gas includes free ammonia and previous paper (0). However, when the maximum temperahydrogen sulfide; and liquids include liquor, neutrals, acids, ture was 700" C., the yield of gas was essentially independent bases, and combined ammonia. The method used for calcuof the rate of heating. The purpose of this investigation was lating the yields obtained in individual carbonizations to a to determine whether the effects noted in the previous work "loss-free" basis is identical with the method previously were due to the rate of heating over some limited temperature described. In the earlier constant-rate work to 700" C. range. Three series of carbonizations were made to a maxithe yield of total liquids was 22 per cent greater a t a rate of mum temperature of 700" C. in which runs were made with heating of 21.8' C. per minute than a t 1.4" per minute, and different heating rates through various temperature ranges to 40 per cent of this increase was due to increased yield of liquor test hypotheses suggested by the data obtained. and 60 per cent to other tar constituents; thus the trend of the summation of liquor and tar in the present work should Apparatus and Procedure be applicable to either one without serious error. Since the yield of gas was relatively independent of rate with a maxiThe apparatus and procedure were substantially the mum temperature of 700" C., as mentioned in a preceding same as were used previously, except for the temperature paragraph, the effect of nonuniform rates of heating should program controller (7). A single rate control record giving a be found mainly in the yields of solid and liquid products. rate of temperature rise of 21.8" C. per minute was used with The probable errors of a single observation of the yields of a simple sliding gear transmission so that either a direct drive solid, liquid, and gaseous carbonization products were deteror a 16 to 1 reduction, giving a rate of 1.4" C. per minute, WILLIAM B. WARREN
-
1350
NOVEMBER, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
mined by analysis of the data reported in the earlier paper (6) to be *0.3 per cent, which should be borne in mind in considering the data obtained in the present investigation.
Carbonization Data
SERIESI. Separate carbonizations were made in which each of the hundred-degree intervals, 200" to 300", 300" t o 400", 400" t o 500", and 500" t o 600" C., were traversed a t a rate of 21.8" per minute, and the balance of the total range from room temperature to '700" C. was traversed a t a rate of 1.4" per minute. The average yields of solid, liquid, and gaseous products, in percentage of the original coal, for each condition are given in Table I; the average of several runs is also given for each constituent a t constant rates of heating of 1.4" and 21.8" C. per minute. Examination of the data in Table I s h o w that the yields of solid for each combination of rates is higher than when a constant rate of 21.8" C. per minute was used and, where the intervals 400 " t o 500 " and 500 " to 600 " were a t the rapid rate, the yields are equal, within the experimental error, to those obtained with a constant rate of 1.4" per minute. With the possible exception of the single experiment in which the temperature interval 200" to 300 O was traversed rapidly, the yields of gas are constant. The yields of liquid carbonization products are intermediate between those obtained a t constant rates of 1.4" and 21.8" per minute. For the runs where the
m Results are reported on a series of experiments on the carbonization of a typical coking coal in which the rate of heating has been changed at various temperatures during each run. The object of the work was to determine whether the effects noted in previous studies-i. e., increase in yield of tar and decrease in yield of coke as rate of heating over the whole range was increased-could be related directly to the rate of heating through any particular temperature interval. Three series of carbonizations were made to a maximum temperature of 700' C. in which two rates of heating-1.4' and 21.8' C. per minute-were used in several combinations. It was concluded that the thermal history up to and after the plastic range is important, since no direct correlation could be made between effects found and rate of heating through the plastic range alone. The data show that the rate of heating through the preplastic range is of prime importance in determining the yields of carbonization products and gas composition. Coke hardness, on the other hand, is determined largely by the rate of heating through the plastic range. In general, it was concluded that theories to explain the processes of carbonization cannot be built up about the plastic range alone, since quite as important events occur both below and above it.
1351
TABLE I. AVERAGE YIELDSOF SOLID,LIQUID,AKD GASEOUS PRODUCTS OBTAINED ON CARBONIZATION OF EDENBORN COAL AT 1.4" PER MINUTEWITH 100' C. INTERVALS TRAVERSED AT 21.8" PER MINUTE
Run
KO.
157, 158, 175, 176 156, 159, 168, 177 140 142, 143 179 145, 150
( M a x i m u m temperature, 700' C.) Temp. Range N~ Yield in Per Cent Traversed a t : of of Original Coal 1.4' C./min. 21.8' C./min. Detns. Solid Liquid G a s
c.
c.
25-700
.....
26-700 200-300
4 4 1
.. .. . 13ziI$:/ {4i:1;:g)
{5gk!g:] {6ik!:g}
76.2 73.0 73.8
12.5 14.8 13.4
12.3 12.2 12.8
300-400
2
74.2
13.7
12.1
400-500
1
75.5
12.4
12.1
500-600
2
75.2
12.7
12.1
TABLE 11. AVERAGE YIELDSOF SOLID,LIQUID,AND GASEOUS PRODUCTS OBTAINED ON CARBONIZATION OF EDENBORN COAL AT 1.4" C . PER MINUTE AS A FUNCTION OF THE PERCENTAGE OF THE RANGE 25" TO 700" C. TRAVERSED AT 21.8" PER MINUTE Temp. Range Per Traversed a t : N, Yield in Per Cent 1.4: C./ 21.8" C./ Range of Of Original Coal min. min. Rapid Detns. Solid Liquid Gas
"$:t$'
Run No.
c.
c.
.... .
25-700 248-700 473-700} 25-248
25-248 248-473
33 33
0
4 1 1
7 5 . 2 12.5 12.3 74.0 14.0 12.0 73.6 13.9 12.5
155
25-473
473-700
151, 160 152, 161, 16la 156, 159, 168. 177
Average of r u n s a t : 25-335 335-700 525-700 25-525 .. 25-700
33 33 53 75 100
1 3 2 3 4
75.7 13.3 74.t; 1 3 . 7 73.0 15.2 73.4 14.6 73.0 14.8
157, 158, 175, 176 154 153
{
...
11.0 11.8 11.8 12.0 12.2
interval traversed rapidly was below 400°, the yields of solid and liquid products are approximately equal but are significantly different from the yields for the runs where the interval traversed rapidly was above 400" C:. SERIES11. Since it may be concluded from the results of the first series of carbonizations a t nonuniform rates of heating that no one of the single hundred-degree intervals covers the entire temperature range within which rapid heating gives lower coke and higher liquid yields, a second series was made to test the hypothesis that the effect of increased rate is proportional to the percentage of the total range 25" to 700" C. traversed rapidly. The data obtained are summarized in Table I1 for 0, 33, 53, 7 5 , and 100 per cent of the range covered a t a rate of 21.8" C. per minute, the balance being a t 1.4" per minute; the data appear to support the hypothesis proposed. A numerical estimate of the significance of the observed differences between the averages of yields obtained in the different carbonizations prepared may be obtained by calculating the probability, P, of these differences occurring by chance-that is, due to random errors of sampling (4).If this probability is very small, it may be concluded that the observed difference is significant; if it is large, the measurements do not prove the difference to be significant. It is usual to take 0.05 as the largest probability for which we can conclude that the observed difference is significant. The calculated probabilities, Pa and P I , that the differences between the average yields of solids and liquids for the slow rate and for the given percentages a t the rapid rate are due to chance, are: 33 per cent, P, = 0.25, PI = 0.008; 53 per cent, P, = 0.006, PI = 0.003; 7 5 per cent, P, = 0.005, PI = 0.003; and 100 per cent, P, = 0.0002, PZ= 0,0001. The difference in the average yield of solid for 33 per cent of the range traversed a t the rapid rate is not significant, but the other differences appear to be increasingly significant as the percentage of the range covered a t the rapid rate becomes greater.
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F OL. 2;. NO. 11
INDUSTRIAL A\D ENGIKEERING CHEMISTRY
However, the yields obtained in the individual carbonizations where the position of the 33 per cent interval was shifted from 25-248' C. to 248-473" C., and to 473700' C. indicate that the actual temperature interval traversed rapidly is of as much importance as the percentage of the total range. While the data do not in themselves warrant any definite conclusion, they suggest that the middle third of the temperature range is of more significance from the standpoint of possible influence of rate of heating on yields of carbonization products than either the low or high end of the interval. SERIES111. Since this intermediate temperature range includes the plastic range, determined in work of the U.S. Bureau of Mines (3)t o be 392" to 455" C. for Edenborn coal, a third series of carbonixations was made in which the rate of heating through the plastic range was varied. For this purpose the temperature range 25" to 700" C. was divided into three intervals, 25" to 390°, 390" to 460", and 460" to 700" C. Pairs of runs involving all combinations of these three ranges and the two rates, 1.4' and 21.8' per minute, were made. If S be used to signify heating a t a rate of 1.4" per minute, and R, heating a t a rate of 21.8' per minute, the conditions of heating in a run may be stated by a combination of letters in the order in which the rates of heating ITere applied; for instance, SRS indicates heating a t a rate of 1.4" per minute from 25" t o 390' and from 460" to 700", and a t a rate of 21.8" per minute from 390" to 460'. The data obtained in this series are presented in Table 111. For determining the importance of the rate of heating through the plastic range, there are four pairs of rate combinations which differ from each other only in the rate of heating from 390" to 460" C.-namely, (1) SSS and SRS, (2) SSR and SRR, (3) RSS and R R S , and (4) RSR and RRR. The average difference is an increase of 0.25 per cent in the yield of solid and a decrease of 0.3 per cent in liquid when the plastic range is traversed rapidly. The probability that these differences are due to chance is about 0.6 for each, and they are therefore not significant. If the average yields, when the plastic range is traversed slowly are compared with the average yields when it is traversed rapidly, instead of comparing the pairs, a similar result is obtained; the differences are 0.26 and 0.28 and could occur by chance seven times out of ten. The data, therefore, indicate that the rate of heating through the plastic range is a relatively unimportant factor in determining the yields of solid, liquid, and gaseous products obtained in the carbonization of Edenborn coal.
T-4BLE Iv. CARBONIZATION T I E L D s ASD C O K E HARDNESS INDICES ( H ) OBT-4INED ON HEATING EDESBORN C O A L TO 700" C, WITH VARIOUS COMBIN.4TIONS O F THE HEATING RATES(1.4" .4ND 21.8' PER MINUTE) GROUPEDACCORDISG TO RATE THROUGH THE PREPL4STIC R.4SGE
c.
Run No.
Rates
145 150 155 157 158 169 169a 170 171 172 173 175 176 179
SSr SSr SSr SSS SSS SRR SRR SSR SRS SSR SRS
Yield in Per C e n t of Original Coal Snlid Liquid Gas
Gas Comon. in Per Ce'nt by Vol.
--H-
on 100
on
200
H2
47.4
43.8 42.3 52.1 40.7 39.3 29.4 22.9 34.6 19.2
CHd
+
C2Hs
Group 1, SXX
sss SSS
Srr
AV.
Probable error 140 rSS 142 rSS 143 rSS 151 rRR 152 RRr 153 rRR 154 rSS 156 RRR 159 RRR 160 rRR 161 RRr 161a RRr 163 RSR 164 RSR 165 RRS 166 RRS 167 RSS 168 RRR 174 RSS 177 RRR 178 rRR -4v. Probable error
75.6 74.8 75.7 75.0 74.6 75.6 76.7 75.1 76.6 75.7 76.7 75.8 75.4 75.5
7. 5 - 6-
0.3
73.8 74.2 74.1 72.8 73.9 73.6 74.0 73.3 73.0 73.2 72.9 73.3 73.1 73.3 72 5 72.9 73.2 72.9 74.4 72.8 73.0 73.3 0.2
12.3 13.0 13.3 11.9 12.7 12.4 11.8 13.2 12.4 12.8 11.6 12.6 12.7 12.4
-1-2 . -5
0.2
Group 2, 1314 13.8 13.6 15.8 15.2 13.9 14.0 14.8 14.7 14.8 14.8 13.9 15.6 15.2 15.7 15.4 14.9 14.9 13.9 14.6 14.7 14.7 0.4
12.1 12.2 11.0 13.1 12.7 12.0 11.5 11.7 11.0 11.5 11.7 11.6 11.9 12.1
-1 01- ..4.1,
R X X or 12.8 12.0 12.3 11.4 10.9 12.5 12.0 11.9 12.3 12.0 12.3 12.8 11.3 11.5 11.8 11.7 11.9 12.2 11.7 12.6 12.3 12.0 0.1
7.2 ,..
....
6.9 4.9 1.0
46.6 41.7 36.8
3.7 6.5 2.0 4.5 2.5 1.8 8.3
36.2 45.1 40.2 43.0 41.0 35.8 42.7
rS.Y 8.3 7.1 7.8 2.5 1.4 2.4 4.7 5.5 5.1 3.1 1.8 7.6 3.9 2.1 2.9 4.3 6.8 4.7 6.2
...
...
...
...
....
I
.
.
.
43.9 45.6 37.4 47.3 48.2 56.5 62.7 52.1 67.4
....
22.4 38.2 38.3 28.1
63.7 49.9 49.6 58.3
48.6 47.6 46.2 37.2 39.6 41.3 45.8 43.0 40.3 39.1 37.8
41.8 41.7 39.1 52.1 42.4 42.9 43.4 53.4 53.2 51.0
46.1 46.7 49.1 36 4 43.4 45.2 45.0 34.9 33.2 37.7
46.3 47.9 41.5 42.3 45.2 41.6 45.4 43.0
45.4 54.3 54.6 41.6 39.7 39.7 55.6 38.6 54.2 48.1
42.8 35.4 35.0 46.0 47.4 47.7 33.5 49.6 35.0 41.3
....
....
....
....
tion of the data in Table I11 suggests that the determining factor is the rate of heating through the preplactic range. The averages of the runs made with a rate of heating of 1.4" C. per minute through the preplastic range and their probable errors are 75.7 * 0 . l i per cent, 12.4 * 0.11, 11.9 * 0.11, for solids, liquids, and gases, respectively; with a rate of heating of 21.8" C. per minute through the preplastic range they are correspondingly 73.1 * 0.11 per cent, 15.0 =t0.12, 11.9 * 0.09. The differences between these averages are 2.6, 2.6, and 0.0 per cent; they could occur by chance only one time in a hundred for the solids and three times in a thouTABLE 111. AVERAGEYIELDSOF SOLID,LIQUID, AND GASEOVS PRODUCTS OBTAINEDos CARBONIZATION OF EDESBORS COAL sand for the liquids, and are, therefore, significant. AS A FUNCTION OF THE RATEO F HEATING THROUQH THE PL.4STIC R l N Q E Importance of Preplastic Range
Per R a t e of Heating, Cent Yield of C./min. of Per Cent of 25-0 390- 460390 4600 7000 original Coal R u n No. C. C. C. Code Rapid Detns. Solid Liquid G a s 7 5 . 2 12 5 12 3 0 157, 158, 175, 176 1 . 4 1.4 1 . 4 SSS 76.7 12.0 11.3 171, 173 1.4 21.8 1 . 4 SRS 10 75.4 13.0 11.6 170, 172 1.4 1 . 4 2 1 . 8 S S R 35 76.2 12 1 11.7 169, 169s 1 . 4 2 1 . 8 2 1 . 8 S R R 46 73.8 14.4 11.8 167, 174 21.8 1.4 1 . 4 RSS 54 7 2 . 7 1 5 . 5 11 8 165, 166 21.8 21.8 1 . 4 R R S 65 73 2 1 5 . 4 1 1 . 4 163, 164 21.8 1 . 4 2 1 . 8 R S R 90 73 0 1 4 . 8 1 2 . 2 1 5 6 , 1 5 9 , 168, 177 2 1 . 8 2 1 . 8 2 1 . 8 RRR 100
%'
Neither do the data presented in Table I11 support the hypothesis that the yields of solid and liquid are a simple function of the percentage of the total temperature interval traversed rapidly although the yields of solids are greater and liquids less where more than 50 per cent of the entire range is traversed rapidly in comparison with the yields where less than 50 per cent of this range is so traversed. Examina-
It does not appear reasonable that the increase or decrease in the rate of heating through different parts of the preplastic range will be equally effective in determining yields of carbonization products, but data are not available to define the important range more closely. If it is assumed that rapid heating over only part of the range from 25" to 390" C. will tend to give the same result as rapid heating over the entire preplastic range, all the data collected in this investigation as shon-n in Table IV may be divided into two groups: (1) SXX and (2) R X X or r X X , where X may be S, R, or r, and r represents rapid heating over only part of the indicated range. It may be mentioned that no study of the preplastic range below 200" C. is included, and that therefore an r in the first position refers only to the temperature interval 200" to 390". Except for the yield of gas, which is insensitive a t 700" to the rate of heating, the observed differences could occur by chance less than one time in a billion and are significant.
NOVEMBER, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
Gas Composition While the yield of gas as percentage by weight of the original coal is the same whether the carbonization rate was rapid or slow through the preplastic range, the composition is different for these two conditions: For the rapid heating through this range, using all the run- given in Table IV, the per cent hydrogen is 46.6 * 1.0 and the per cent methane and ethane IS 41.6 * 0.9; for the slow heating, the percentages are 34.1 * 2.0 and 53.1 * 1.8, respectively. The differences between the two groups arc in the same direction but not as great as reported in the previouc paper (6) for constant rates of heating of 1.4" and 21.8" C. per minute. The observed differences could occur by chance less than one time in ten thousand niid are therefore significant. If the same method of analysis of the data is applied to the gas analyses for only the carbonizations given in Table I11 to determine the possible significance of the rates of heating through the plastic and postplastic ranges, as well aq through the preplastic range, it may be concluded (1) that the rate of heating through the plastic range is not significant, ( 2 ) that the rate through the poetplastic range may have some significance, and (3) that the rate through the preplastic range is the predominant factor determining the coinpo~itionof the gas obtained.
Hardness of Coke I n the sixth and seventh columns of Table I T are given the hardness indices, H , for the cokes prepared in the several carbonizations. The first index represents the percentage of coke retained on a 100-mesh screen after a standardized grinding in a rod mill for 1.50 revolutions (6) and the second the percentage retained on ZOO-mesh. If the hardnv. data are regrouped into two classes differing in the rate of heating through the plastic r a n g e 4 e., XSX and SRX--the averages for the slow rate of heating are 5.6 * 0.4 and 44.4 * 0.6 for the first and second indices, respectively, and similarly are for the rapid rate of heating-3.4 * 0.3 and 40.2 * 0.4;
1353
the slow rate of heating gives the harder coke. The differences are significant since the probabilities that they could occur by chance are less than eight times in a thousand for the first indices and less than eight times in ten thousand for the second indices. A similar analysis of the data for the runs listed in Table I11 indicates that the hardness may be determined in part by the rates of heating through both the preand postplastic ranges, the rapid heating giving a harder coke.
Mechanism of Coking The data obtained in the present investigation and presented in the preceding paragraphs are of particular interest in any attempt to formulate a mechanism of coking. It would appear that the coal undergoes certain changes before initial softening takes place. It may he suggested that coal existin an unstable molecular configuration and that raising the temperature even slightly increases the rate of molecular rearrangement which is always going on even at relatively low temperatures. These rearrangements, result in more stable forniq which, when decomposed a t 390" C. and above, yield %olid,liquid, and gaseous products. It is postulated that decomposition of the unstable form yields higher liquids and lower solids and that even a t 300" C. the rearrangement reactions require a substantial period of time for their completion. Hence, if we heat rapidly to the temperature of actual decomposition there will be less opportunity for completion of the rearrangements, and the molecules decomposed will break down in greater part to liquids, while slow heating up to 390" C. will allow time for rearrangement to be completed and the molecules decomposed subsequently will be in a more stable form to start with and mill yield lower liquidand higher solids. This hypothesis is not in disagreement with the data of other workers who have found similar effects in studies of solvent extraction of coal (I, 2 ) , and of vacuum distillation of coal ( 5 ) . Recognition of the importance of the rate of heating
Courtesy. K o p p e t s Construction Company
BY-PRODUCT COKEPLANTOF BROOKLYN USIONG.M COMPAVY
INDUSTRIAL AND ENGINEERING CHEMISTRY
1354
through the preplastic range may aid in the interpretation of the results obtained in certain previously proposed commercial carbonization processes which involve preheating below the initial softening temperature of the coal before coking. The data may also be of use to coke-oven operators in indicating possible methods of modifying present practice to alter the relative amounts of solid and liquid products obtained in coal carbonization. It must be recognized, however, that this and the preceding study of the effect of rate of heating on carbonization of coal has been made on only a single coal, a typical coking coal from the Pittsburgh seam, Edenborn mine, Fayette County, Pa. The hypothesis proposed and the relationships found will be tested on three other coals, including an Illinois coal and one from the Pocahontas field.
Acknowledgment The aid of H. G. Landau in mathematical analysis of the data, and the helpful guidance of H. H. Lowry during the
VOL. 27, NO. 11
course of this investigation and in the preparation of the manuscript are gratefully acknowledged.
Literature Cited R.S.,IND. EKG.CHEM.,26, 1301 (1934). (2) Bunte, K., Bruckner, H., and Simpson, H. G., Fuel, 12, 222 (1933). (3) Fieldner, -4. C., Davis, J. D., Thiessen, R., Kester. E. B., Selvig, W-.A., Reynolds, D. A., Jung, P. W., and Sprunk, G. C., Bur. Mines, Tech. Paper 525 (1932). (4) Fisher, R . A., “Statistical Methods for Research Workers,” Chap. V, Edinburgh, Oliver and Boyd, 1925. (5) Juettner, B., and Howard, H . C., Coal Research Lab., C. I. T., Contribution 8; Juettner, B., and Howard, H . C., IND. ENG. CHEM.,26, 1115 (1934). (6) Warren, W. B., Ibid., 27, 72 (1935). (7) Warren, W. B., IND. ENQ. CHEM.,4nal. Ed., 5, 285 (1933). (1) Asbury,
RECEIVED July 22, 1935. Presented before the Division of Gas and Fuel Chemistry at the 89th Meeting of the rlmerioan Chemical Society, New York. N. Y., April 22 to 26, 1935.
Development of Specifications for Protection of
Underground Pipes K. H. LOGAN National Bureau of Standards, Washington, D. C.
@E
STIMATES made in 1931 (6) indicate that there were approximately 450 thousand miles of pipe lines and twenty-seven million house services exposed to soil action a t that time. Assuming reasonable pipe diameters, this is roughly equivalent to the vertical surfaces of 1.6 million medium-size two-story houses. The value of the underground pipe systems was estimated at more than 5 billion dollars and the annual underground corrosion loss a t 142 million dollars. In addition to buried pipe there is a large and growing number of fuel oil and gasoline tanks exposed to soil action. The extent to which protective coatings can be applied economically to buried structures depends not only on the corrosiveness of the soils to which the structures are exposed but also on the degree of permanence desired, the cost of replacement, the effectiveness of the coating, and the cost of application. The study of these questions has been underway a t the National Bureau of Standards since 1922.
Work on Protective Coatings The results of the first study of protective coatings for underground pipes by the Bureau of Standards were published in 1914 (6). This paper dealt with the mitigation of corrosion caused by stray electric currents. In connection
AMERICAZI GAS AssoCIATION TESTOF PROTECTIVE COATINGS ON BURIEDPIPES
with a study of the effects of soils on pipes, an investigation of five types of protective coatings was started in 1922. Additional coatings were placed under observation in 1924. Partly as a consequence of the preliminary results of these tests, the American Petroleum Institute placed a research associate a t the bureau in 1928 to study pipe line protection, and the American Gas Association took similar actionin 1929. Both of these research associates have devoted most of their time to tests of proprietary protective coatings and to the examination of such coatings when applied to oil and gas lines. More than ten thousand tests of one hundred and seventy varieties of pipe coatings have been undertaken and approximately six hundred examinations of coatings applied to working lines have been made. With the exception of a single series of laboratory soil box
