TECHNICAL INFORMATION ON BUILDING MATERIALS

TIBM - 10

FOR USE IN THE DESIGN OE LOW-COST HOUSING

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THE NATIONAL BUREAU OF STANDARDS

UNITED STATES DEPaRTS IENT OE COMMERCE

WjiSHUTGTON, D. 0.

March 20 , 1956 ,

CORROSION OE METALS USED IN HOUSE CONSTRUCTION

Atmospheric Corrosion of Ferrous Metals

The atmosphere may cause corrosion of metals either on the inside or

on the outside of a building. However, the active corroding agents, oxygen

and liquid water, must both be present on the metal. Inasmuch as air

inside and outside of a building has the same content of oxygen, metals

corrode at the same rate indoors and outdoors, providing the amount of

water reaching the metal in a given time is equal in each case. Normally,

however, the outside metal, being subjected to rain and snow, corrodes

more rapidly.

The lowest rate of atmospheric corrosion occurs in rural or suburban

locations, where the air is only slightly contaminated with smoke or oxides

of sulphur from the combustion of fuel. The highest corrosion rates are found in industrial centers where the degree of contamination is relatively

high. A high rate of corrosion is also common near the seacoast because of

salt in the atmosphere. Rain dissolves such contaminating substances in

the air and the resulting solution is much more corrosive to metals than is

pure water. Rain water may also dissolve some corrosive material present

in dust which is suspended in the air or has settled on a roof.

Atmospheric Corrosion Tests

Since 1916, The American Society for Testing Materials, has been

investigating the outdoor weathering of metals and has obtained important

data on the durability of ferrous metals exposed continuously to the

weather in rural, industrial, and seacoastal atmospheres. This investigation is being conducted by committees on which are represented producers

and consumers of metal. Before these tests were started, a mutually

acceptable program was agreed upon. The tests were carried out at

Pittsburgh, Pa. (industrial atmosphere), Annapolis, Md. (mild seacoastal

atmosphere) and Fort Sheridan, 111. (rural atmosphere somewhat contaminated)

04065S-Z

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. po _ aa rr e Sheets of steels and irons were exposed

a s^are"

1

" sheets i!e . , unpainted or without any applied protective metallic

, 3 t iT, « similar iuwstieation on galvanized iron and

steel^heet s^as^undertaken . Details or' the latter study, will be given in

a subsequent memorandum 01 this seiies.

Tn the test of bare metals, two general types of steel and iron were

used: (a) those containing the small amounts of copper r”01****?TM'

T.r'XlloTe fcS copper fc^ionafl? S during the

iS- -

' , T it' -mMrip twice a ^ea1’ bv committee members, a

sheet^was considered to have farted when perforated, by oorros on at one n„wn^ t ^ s i imma.r i z6 s the results oi this xeoi, or more places. Tabxe 1, page o, &uwlua± xz,cd oi __ . , J j D LUULiUJ. n. <cj w _ Annapolis but which could not do continued

X which is still in progress . -i-i.nl To /—» s~\ “f* o TTT o T* at

sheets were

at Pittsburgh and Port Sheridan until such time as all the sheets wor perforated^ as these sites had to be utilized for other purposes.

Results of Te sts

]?rom the data obtained, the following conclusions would seem justified

(1) Steel or iron with 0.15$ to 0,50$ copper was more durable at all

locations than companion material low in copper content.

(2) In heavy industrial atmospheres, such as found in the Pittsburgh

area, bare metel 'sheets should not be used; painting or galvanizing preferably both, is advisable, particularly for exterior parts of a house.

( 5 ) In atmospheres of the less corrosive type, such as in Annapolis

Tf nT. t SV-ridan

1 the life of steels without added copper is much longer

“an “ Pitisb^gh. The choice of metal in such cases should be governed

by the frequency or regularity with which the structure cun e pain
TABLE I

RESULTS OF OUTDOOR WEATHERING TESTS OF BaRE FERROUS SHALT .LLAiE

CONDUCTED BY TliL AMERICAN SOCIETY FOR TESTING ivATERIaLS

Material

Location Duration Gage Kind of Steel Number Number Percentof Tests of Test or Iron of of age

(Months

)

Sheets Sheets Failed

Tested Failed*

Pittsburgh, 78 22 With added copper 146 123 84.4

Pennsylvania (

. 0306"

( industrial

atmosphere ) thick) Without added copper 84 84 100.0

16 With added copper 132 none 0.0

( .0613”

thick) Without added copper 126 102 81.0

Fort Sheri- 152 22 With added copper 156 50 36 .8

dan, Illinois

(rural

atmosphere

,

Without added copper 85 77 92.8

somewhat

contaminated) 16 With added copper 156 none 0.0

without added copper 124 4 3.2

Annapolis

,

i.iaryland

216** 22 'With added copper 148 7 4.7

(mild

seacoastal

Without added copper 79 56 70.9

atmosphere)

16 With added copper 150 none 0.0

Without added copper 129 none 0.0

*a sheet was considered to have failed when perforated, by corrosion,

at one or more places.

**Last reported inspection, October 1935.

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