Iron is the most common material used in water transmission. Cast iron, cement-lined cast iron, and ductile iron are the types that have been widely used in the US. Some examples of galvanized iron are also reported. Failure rates for cast iron are about 5 times greater than for ductile iron, owing largely to differences in corrosion rate.

Timeline of Pipe Technology in the USA (EPA 2002)
  Decade ending
Pipe Material Lining 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Steel none                    
Steel cement                    
Cast Iron none                    
Cast Iron cement                    
Ductile Iron cement                    
Plastic                      
    available  
    widely used                

 

Heavily tuberculated unlined cast iron pipe, Utility 2a. Note about one-half the interior volume has been occluded.Newer pipes are cement-lined ductile iron to protect against this type of corrosion.

 

 

 

 

 

 

 

Composition of Scales in Iron Mains of Various Types

Information on scale compositions comes either as surveys of a few samples from many utilities or intensive study of many samples from one utility. An example of survey data is summarized in the paper by Peng and others (2010):

 

Survey of elements in iron scales of U.S. distribution systems (Peng et al. 2010)

mg/kg

n

Al

Ba

Ca

Cd

Cr

Mg

Fe

Mn

Ni

P

Pb

S

Si

V

Cast iron

22

1771

350

4702

1.5

14

1306

309091

1052

39

157

20

1.7

2172

29

ductile iron

5

5022

162

766

0.6

7.0

152

311200

866

9

132

5

1.1

1154

27

galvanized steel

4

938

80

6649

11

109

270

346500

1913

253

32

1199

0.4

1839

228
steel/iron  
0.28
0.31
2.4
11
10
0.37
1.1
2.0
11
0.22
96
0.26
1.1
8.1

 

 

Regulated elements (Cr, Pb, V) are quite low except in scales from galvanized pipes, although the sample set is small for that category.

Other elements strongly enriched in galvanized pipe scales are Cd and Ni, each about 10x enriched.

Note that Pb is nearly 100x enriched, which probably reflects the presence of appreciable Pb in the Zn coating on these pipes (see the galvanized iron page).

 

Detailed study of a single distribution system gave similar results as shown in the next table.

Illustrations of the textural types are shown on the tubercles page; discussion of the iron compounds on the minerals page.

 

Chemistry of tubercles from individual pipes and hydrants - Utility 2 (Jones, 2013)

Major elements by tubercle region (wt. %)

Trace elements (mg/kg)

 

Fe

Mn

Si

Al

Ca

P

S

Ba

Co

Cr

Cu

Pb

Sr

Zn

Cast Iron Mains (unlined)

FeOOH-rich textures (goethite or lepidocrocite)

Surface

44.3

0.19

6.63

3.50

5.18

0.22

1.31

2505

28

25

31

12

62

20

Core

59.1

0.03

1.27

1.32

0.56

0.17

1.82

2118

29

27

7

96

9

8

Fe3O4-rich textures (magnetite)

Shell

51.8

0.10

1.31

1.40

3.84

0.05

0.95

2287

31

17

7

19

31

9

Veins

56.5

0.04

1.13

1.26

0.81

0.12

1.79

2453

29

27

6

159

7

7

overall avg

52.9

0.09

2.59

1.87

2.60

0.14

1.47

2341

29

24

13

71

27

11

Cast Iron Connections to  Hydrants 

FeOOH-rich textures (goethite or lepidocrocite)

Surface

25.6

0.06

1.18

1.27

20.9

0.01

0.62

4560

12

46

11

12

391

9

Core

57.8

0.05

1.56

1.35

1.35

0.08

0.34

1622

34

40

3

11

21

6

Fe3O4-rich textures (magnetite)

Shell

34.8

0.07

1.55

1.40

15.8

0.04

0.68

3981

17

33

10

12

243

9

Veins

57.7

0.02

1.30

1.64

0.74

0.05

0.78

2919

36

50

14

9

15

8

overall avg

44.0

0.05

1.40

1.42

9.68

0.05

0.60

3271

25

42

9

11

168

8
hydrants/mains
0.83
0.59
0.54
0.76
3.73
0.34
0.41
1.40
0.85
1.77
0.75
0.15
6.13
0.73

 

 

Some enrichment of the surface layer in Si, Al, and Ca occurs. These elements are probably contained in quartz and clay that have come through the treatment filters plus some precipitated CaCO3.

Other textural components have about the same compositions. There is a distinct difference however between the open mains (mostly flowing water) and the fire hydrants (mostly stagnant water).

The hydrant scales are strongly enriched in Sr and, to a lesser extent, Ca. Both are probably present as carbonates. See Gerke et al (2013) for more on Sr in distribution systems.

Gerke, Tammie L., Brenda J. Little, Todd P. Luxton, k G. Scheckel, and J. Barry Maynard. (2013) "Strontium concentrations in corrosion products from residential drinking water distribution systems."  Environ. Sci. Technol., 47 (10), pp 5171–

Jones, M.A. (2013) Iron, from the water main to the tap [electronic resource] : iron corrosion scales as possible sources of regulated elements . MS thesis, University of Cincinnati. https://etd.ohiolink.edu/pg_10?0::NO:10:P10_ACCESSION_NUM:ucin1378109085

Peng, C-Y., Korshin, G., Valentine, R., and Hill, V., (2010) Characterization of Elemental and Structural Composition of Corrosion Scales and Deposits Formed in Drinking Water Distribution Systems. Water Research Foundation Report 8038.