tion of cast-iron gas mains in several cities yielded data of a similar nature.
Preliminary studies ... 301. I. INTRODUCTION. In April, 1928,the Bureau of
Standards issued its first Technologic. Paper 2 ...... igp-OO^r-H. © rH. I 00 00 © I.
© lOOt^NlO.
RP95
SOIL-CORROSION STUDIES,
1927-28
By K. H. Logan ABSTRACT This paper is the second progress report on the soil-corrosion studies, supplementing Technologic Paper No. 368 l which set forth the plan of the investigation, described the soils and materials under test, and gave the data obtained up to and including 1926. The present report supplements the earlier one, gives additional data on the chemical properties of the soils and materials, and records the results of the examination of specimens removed in 1928. These specimens include only ferrous pipe materials and cable sheaths, no specimens of nonferrous materials other than cable sheaths, pipe coatings, or galvanized sheet being removed. The results of "some laboratory and special field investigations are described. Soil characteristics, rather than differences in the composition of the ferrous pipe materials, appear to determine the type and extent of the corrosion Tables show the relative corrosiveness of soils based on rate of loss observed. of weight and rate of increase in depth of pits. Although it happened that the same soil was worst from both of these points of view, the soil that ranked next to the worst from the standpoint of pitting ranked twenty-eighth as to loss of weight.
As the specimens in the ground grew older the corrosion became more general, and in most soils there was a decrease in the rate of penetration. Field examination of cast-iron gas mains in several cities yielded data of a similar nature. Preliminary studies indicated that, in addition to the highly localized galvanic by mill scale, oxygen concentration cells, differences in soil contacts, etc., there are on long pipe lines galvanic currents that are the result of the line passing through different soils. There appeared to be a relation between the discharge of these galvanic currents and the corrosion observed on the pipe line. Considerable work has been done recently on methods of predetermining the corrosiveness of soils. The problem has not been solved. Additional specimens of pipe materials and coatings will probably be removed action caused
in 1930. »
B.
S.
Tech. Papers,
32,
pp. 447-554, 1929.
275
Bureau of Standards Journal of Research
276
[vol. s
CONTENTS 276 278 280 280 281 284 284 287 291
Introduction Additional data on soils III. Results of analyses of ferrous pipe materials IV. Tread of the results of field tests of pipe specimens 1. Rates of corrosion I.
II.
2.
Rates of pitting (a) (b)
"
Method of determining rates Limitations of the data
3.
Pitting factors
4.
Comparison of soils (a) With respect to rates of corrosion (b) With respect to rates of pitting With respect to soil texture (c) Comparison of materials
5.
291 291
,
Application of results to specific corrosion problems V. Results of supplementary research on pipe lines Inspection of gas mains 1 2. Corrosion accompanied by galvanic action VI. Results of tests of other materials used underground 6.
1.
2. 3.
VII.
:
Corrosion of high-silicon cast iron Corrosion of lead cable sheath Corrosion of parkway cable
Summary
_
I.
—
293 294 295 296 296 296 297 300 300 300 301 301
INTRODUCTION
In April, 1928, the Bureau of Standards issued its first Technologic Paper 2 on its soil-corrosion investigation. That paper outlined the purpose and scope of the work then under way and gave such data concerning the soils, materials, and results of the work as were then The present paper is intended to supplement the earlier available. The work now under way report and bring the results up to date. will not be completed before 1935, and until then it is expected that progress reports will be issued from time to time as results become available. With respect to time, the investigation is now half completed, although but a little over a third of the 15,000 buried specimens have been removed. The data discussed in the first technologic paper on soil-corrosion were obtained prior to 1927. Since that time considerable progress has been made. The Cast-iron Pipe Kesearch Association has employed an associate to assist in the study of soil corrosion, and the bureau has increased the number of men on this work. Assistance has also been secured from outside organizations, as will be noted in
more
detail later.
ress has 2
B.
S.
As
a result of this assistance, considerable prog-
been made along several
Tech. Paper No.
368,
Results of Early Observations.
Bureau
of
lines,
but
much remains
Standards Soil-Corrosion Studies.
I.
to
Soils,
be done.
Materials,
and
— 277
Soil-Corrosion Studies
Logan]
The first conference on bituminous protective coatings for pipes 3 not only brought out the inadequacy of most of the coatings under test, but showed also the difficulty of determining the quality of a It became apparent that a satisfactory coating under consideration. study of protective coatings would involve extensive work in the laboratory to develop methods of testing coatings, as well as a large amount of field work to determine the character of coatings suitable for the varied conditions to
which pipe
A
lines are exposed.
little
methods for testing protective coatings, and it is expected that this work will be continued during the coming year. Arrangements have been made for studies of protective coatings by research associates employed by the American Petroleum Institute and the American Gas Association.
work has been done on the development
Table
1.
of
Results of soil analyses
Lin per cent of weight of dry
Loss
No.
Description
by
ig-
S
nition
soil]
Insol-
Fe:0 3 -!-
uble
AI2O3
CaO
MgO
Per cent Per cent Per cent Per cent Per cent Per Allis silt
loam
Bell clay Cecil clay
loam Chester loam Dublin clay adobe Everett gravelly sandy loam..
loam Fargo clay loam Genesee silt loam Hanford fine sandy loam Fairmount
silt
Hanford very
sandy loam loam
fine
Hempstead silt Houston black clay Kalmia fine sandy loam Knox silt loam Lindley silt loam Mahoning silt loam Marshall silt loam Memphis silt loam Miami clay loam
Miami
silt
loam
Miller clay
Montezuma
clay adobe
Muck Muscatine
silt
loam
Norfolk sand Ontario loam Peat
Penn
silt
loam
Ramona loam Ruston sand3r loam St. Johns fine sand Sassafras gravelly sandy loam. Sassafras silt loam Sharkey clay Summit silt loam Susquehanna clay Tidal marsh Wabash silt loam Alkali
soil
Sandy loam Silt loam
m
7.06 10.40 12.00 4.44 7.14
o.os .05 .04 .03 .01
3.40 11.72 18.70 7.26 3.48
.03 .04
4.74 2.74 15.00 3.60
83.8 82.6 60. 46 79.5 85.5
cent.
PH
Per cent
8.4 4.6 23.6 14.4 5.7
0.32 .54 .30 .30 .24
0.08 .32 .40 .69 .50
7.0 7.4 7.2
.04
87.6 83.5 64.2 88.4 87.8
7.1 4.1 8.4 3.1 5.9
.40 .30 6.80 .30 .40
.58 .29 2.68 .40 .94
6.9 7.0 8.4 8.6 7.4
83.5 89.8 74.0 90.4 86.4
8.0 4.46 5.40 3.20 6.5
1.10 1.53 3.58 .34 .30
1.16 .83 1.00 .33 .50
7.6 8.4 7.0
4.60
.03 .05 .08 .11 .07
5.80 6.00 6.60 5.00 20.40
.07 .06 .15 .06 .08
84.3 81.6 89.2 8S.0 49.3
7.9 10.80 3.20 4.80 14.80
.30 .30 .30 .30 11.80
.80 .72 .43 .47 2.82
7.2 6.8 8.0
19.34 12.98 3.60 28.40 6.80
.09 .08 .08 .24 .03
51.24 81.40 93.0 62.0 82.4
17.30 2.00 2.80 7.50 7.90
10.96 1.80 .20 .80 .80
1.52 1.30 .29 .69 .76
8.2 8.4 7.4 7.0 7.6
.76 4.60 63.22 4.40 6.30
.03 .06 .04 .03 .03
98.6 85.3 22.1 84.8 90.1
1.00 6.40 4.40 9.10 2.46
.20 2.00 6.80 .40 .78
.14 1.21 2.30 .62 .80
6.9 8.4 8.6 7.4 8.0
4.86 4.54 .20 7.00
.04 .03 .05 .04
81.9 93.0 96.7 92.8
10.20 2.00 3.20 1.70
.40 .30 .10 .30
.40 .10 .12 .40
7.0 6.9 7.0 7.0
7.90 8.56 7.60 15.80
.06 .21 .34 2.21
83.6 84.62 79.90 71.22
6.70 4.68 10.70
.59 .65 .56 1.07
8.0 7.4
9. .46
.40 .30 .34 .56
8.20 6.80 .64 21.52
.42 1.00 .18 .24
87.58 86.00 95.22 44. 70
2.40 1.20 1.40 9.16
.34 2.54 .30 22. 00
.70 .33 .00 2.27
.11 .03
7.8
8.4 8.6 8.6
Note.— Leaders figure columns indicate that determination was impossible. Slight inaccuracies in of the water analyses are due to the extremely small amount of solution available for some determinations. some 3
See B. S. Tech. Paper No. 368, p. 521.
278
Bureau Table
of Standards Journal of Research 2.
Results of analyses of solution [By parts per million
Soil
C0
No.
3
HC03
2 3
4 4 2
4 5
30
1
2
2
6 7 8 9 12
SO4
CI
20 12 10 8 60
2 14 24
8 12 60 8
4
6
4 10 4 16
6
13
14 15 16
18 19 20 21
2
4 4 2 12
.
22 25
;..
26
_.
10 12 11 4
27 28 29 30 31 32 33 34 35 36 37 38 39..
41 42 43
44 45 .. 46... 47
75 90 10
~"~50~ 20 50 2,120 80
of soil]
SiC-2
44
17 32 27 24 19
10
68
301
16
5 5
30 100 30 50 10
20 90 26 104 22
50 18 218
20
4 14
6
4
20 60
20
3
4 5 3
40 10 12 28 6
15
20
70 8 7 10
3
6
15 18
130 36 46 23 41
8 7 36
140 8
18
35 26 15
15
5
35
5 13 8 15
62 12 49 118 26
17 8 20
37 17 169 7
105 20
48
18 15 15 15
35"
484
5
35 2
8
6 6 4 9
Total solids
12 7
2
7 22
40
42
Na+K
Mg
Ca
7 8
13 145
4 12 12 6 8
195
+
fi
22 4 12
16 14
3
AI2O3
22 4
20 100 21
"loo"
Fe 2
35
95 40 3S5 40 40
6
---
3
188 216 50 110 370 105 248
2,907 268 230 4,755 126 630 256 157
15
2
11 13 7 9 15
8
2
105 255 115 232 122
16
2 344 298 6 4
180 455 955 395 107
46 20
134 186 4,062 106 815
39 25 13 20
4 6
14 49 28 17 14
9 16 118 10 24 18 8 6 2
38 3
6
.....
6
6
10
18
35 80
480
170
2
136 10 2 4
20 20 20 50
25 20 10 10
10 10 15 12
16
6
20 20 4 5,850
30 25 8 40
5 45
10 1,516
6 14 7
217
9 10 4 231
160 3,085 100 20
13
10
37
17
233
472
10 13
5
50
9
15
35
8 14
210 130
4 4 4
40
[Vol. S
10 2 4
4 6
4
8
14
14
20
6
11
10 5
7
9
265 85 60 98
9
2 13,
7
92 122 35 780
—
Note. Leaders in figure columns indicate that determination was impossible. Slight inaccuracies in some of the water analyses are due to the extremely small amount of solution available for some determinations.
II.
There
is
ADDITIONAL DATA ON SOILS
a belief on the part of
many
that
soil
We
corrosion
is
closely
were fortunate, therefore, in securing the cooperation of J. W. Kichards & Son, industrial chemists, who have made the analyses shown in Tables 1 and 2 of Their method of the soils in which specimens have been buried. preparing the water extract in which the salt content of the soil was determined, as described by Percy J. Kichards, was as follows: "Six oimces of the soil sample are mixed with 300 cc of boiled distilled water in a small bottle; the contents should be thoroughly related to the chemical nature of the
soil.
—
"
279
Soil-Corrosion Studies
Logan]
agitated at least 10 times a day for six days
*
*
*
then
filter
into a clean bottle and cork for analysis.
When
the rates of corrosion of the specimens have been
definitely established
by the examination
of
more specimens,
more these
may
be very helpful in the study of the relation of the chemical nature of the soil to corrosion. At the present time, such a relation It is not to be expected that a knowledge is not well established. tables
of the constituents of the soil will in itself
make
possible a prediction
oxygen and water be factors. The amounts of oxygen and water reaching the specimens depend upon the position of the trench in which specimens are buried, the type of soil, and the amount and distribution of rainfall.- The soil descriptions given in Technologic Paper No. 368 as to the rate of corrosion, since the supply of
may
include the soil characteristics and drainage, while the rainfall and
temperature can be judged in a general way by the location of the specimens, or more detailed data can be secured from the reports of the Weather Bureau. It has been suggested that weather conditions for the months immediately preceding and following the burial of the specimens may have affected the type of initial corrosion product formed and, consequently, the subsequent rate of corrosion. PI ans for a study of this question are under way. The amount of colloidal matter in a soil may have a bearing on corrosion because of the relation of colloids to the ability of the soil to absorb and hold water and because of the change in volume of soils containing large amounts of colloids with change in moisture Information on the colloid content, as determined by the content. method of Bouyoucos, 4 is given in Table 3. Table Soil
No.
1
2 3
4 5
__:._
6 7 8
.._
9..
10 11 12
» 4
Per cent
Soil
No.
3.
Soil colloids
Per cent
°
Soil IN o.
Per cent
Soil
No.
Per cent
63.6 46.6 43.3 25.3
13 14 15 16
17.8 32.0 63.1 20.8
25 26 27 28
31.0 50.1 91.4 29.1
37
44.8 11.1 70.3 66.0
17 18
76.0 28.8 38.9 43.6
29
24.5 41.6 1.1 22.7
41
42 43 44
44.0 44.6 51.0 31.5
35.9 15.9 52.5 8.9
21
20 4
45 46 47
7.0 53.6
19 20
42.8 33.2 17.9 7.2
22 .. 23 24___.
30 31 32.
.
33 34
35 36
Determinations by Dr. S. P. Ewing, Bureau of Standards. The Hydrometer as a New and Rapid Method for Determining
Bouyoucos, Soil Science, 23,'No.
4, p. 319.
41.9 20.0 37.9
39 40
6.6 5.5 15.5
49.8
the Colloidal Content of Soils, B.
J.
Bureau
280
of Standards Journal of Research
[Vols
RESULTS OF ANALYSES OF FERROUS PIPE MATERIALS
III.
Earlier reports have stated that the several kinds of ferrous pipe materials in any one soil showed similar corrosion patterns and that The indicafor any one material this pattern varied with the soil. tions were, therefore, that the initial corrosion
by
was determined
largely
soil characteristics.
There were, however, minor differences, which appeared to be caused by differences in the pipe materials, and these may become more pronounced on the specimens which are exposed longer. For this reason the character of the material under test is of interest. Since the specimens were selected from stock, not all of the specimens of any one material were necessarily produced at the same time, and, consequently, they may differ somewhat in composition. An attempt has been made to gain some idea of the character of the materials by Most of these analyses were furnished analysis of a few specimens. by the manufacturer at the time he furnished specimens. In a few places, as indicated in Table 4, the analyses were made by the A. O. Smith Corporation, who analyzed the other rolled specimens also. Table
4.
Results of chemical analyses of pipe materials in the Standards soil-corrosion investigation
Bureau
of
Num-
Diam-
ber of
eter of
Material
C
speci-
pipe,
mens
inches
tested
Mn
P
S
Si
Cu
Analysis
by—
Per cent Per cent Per cent Per cent Per cent Per cent Per cent I 1/?
pen-hear th iron
1'-
Wrought
V-A
Bessemer steel Bessemer steel treated Bessemer steel - - Open-hearth steel.-. Open-hearth steel+Cu
\M 3 3 3 3 6
6 6
0.02
2 4 16
iron..
49
.03 .09 ""."08"
1
.12 .07 .72 3.56 3.40 3.45
6
.
?
High-silicon cast iron
1
Cast iron (northern)
2 3 2
1
A. O. Smith Corporation.
2
Manufacturer furnishing material. United States Cast-Iron Pipe & Foundry Co.
3
IV.
Trace. Trace. 0.39 .38 .40 .41 .24 .26 .73 .48 .56
0.010 .145 .088 .092 .098 .043 .008 .11 .77 .84 .55
050 .023 .040 .050 .038 .038 .032 .123 .083 .083 .075
0.
0.09 .15
0.014 .02
il 1
22 2 2
""."22" "l3."44" 2.34 1.61 1.55
2 2 2 2 2
TREND OF THE RESULTS OF FIELD TESTS OF PIPE SPECIMENS
The soil-corrosion specimens removed in 1928 were limited to specimens of pipe and cable sheath buried in 1922. The specimens have been cleaned and the depth of pits measured. Data on each individual specimen can be supplied to those needing these details, but for most purposes the average results presented in Tables 5, 6, and
7 are sufficient.
Space limitations make the soils in these tables.
it
impracticable to include the names of
The names and
locations of the soils cor-
281
Soil-Corrosion Studies
Logan]
responding to the soil numbers in Tables 5, 6, and 7 will be found in Table 8. It should be understood that the soil under test in or near a given city is not necessarily characteristic of the soil of that city; for example, there is little Cecil clay loam to be found in the built-up section of the city of Atlanta, Ga., and there is very little Susquehanna clay within the city limits of Meridian, Miss. Since the preparation of the progress reports presented at the meetings of the American Foundrymen's Association in 1925 and 1927, several soils have been reiden titled, and this has resulted in a rearrangement of the alphabetical list of soils. As these progress reports had rather wide circulation, it appears desirable to indicate the change in soil numbers, and this is done in Table 9.
Comparison
of the rates of corrosion
6 year periods are of interest. soils it
the
must be kept
first
country.
periods, are
and pitting
for the 2, 4,
and
In comparing results in different
mind that the periods of burial, especially somewhat different in different parts of the
in
In most cases, the rates of corrosion and pitting are
greatest for the
first
period. 1.
Since specimens of
RATES OF CORROSION
De Lavaud
cast iron were not buried in
all
of
the test locations until some time after the other specimens were in 1928 from some of the soils. Moreweight of the first specimens buried were based on corrosion on both the inside and the outside surfaces of the pipe, as was the case with all other specimens. While the two surfaces of the other specimens were substantially the same, the outer surface buried, they were not
over, the data
on
removed
loss of
De Lavaud cast iron differs materially from the inside surface, was evidenced from the appearance of the surfaces after corrosion. For these reasons we have not included the data on De Lavaud cast iron in summarizing the data. If we take the data on four or more of the six classes of material in Table 5 in any one soil (De Lavaud cast iron being disregarded) as of
as
indicative of the trend of the corrosion in that
soil,
17 out of the 45 soils from which specimens were
we
find that in
removed
in 1928
there has been a decrease in the rate of corrosion throughout the
In 5 other soils the rate for the 1928 than that for the specimens removed in 1926, and in 10 other soils the rate for the third period was less than that for the first period. In only 2 soils was there a progressive increase in the rate of corrosion. In 11 soils the rate for 1928 was greater than for 1926. In a considerable number of cases the variations in the apparent rates seemed due to accidental occurrences incident to conditions at time of burial. If we average the results in all soils, we find that for each material there was a continuous decrease in
period of the investigation.
specimens was
less
the rate of corrosion.
282
Bureau u
y
10
of Standards Journal of Research iCO
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