IAD: ANK1-7

U. S, DEPARTMENT OF COMMERCENATIONAL BUREAU OF STANDARDS

WASHINGTON

MATERIALS IN THE NATIONAL BUREAU OF STANDARDS\/

SOIL-CORROSION TESTS *

LetterCircularLC-646

CONTENTS

I. IntroductionII. Ferrous materials,

1. Wrought materialsa. Carbon steels, wrought iron, and open hearth iron.b. Low-allov steels,c. 4-6 percent chromium steels.d. High-chromium stbels,e. High-chromium steels with nickel and other

alloying elements.2. Cast materials.

III. Copper and copper alloys.1. Copper2. Brasses3. Bronzes4. Copper-silicon alloys5. Cooper-nickel alloysb» Metallic coatings with copper as the base metal.

IV. Zinc and zinc coatings.

V. Lead and lead coatings,

VI. Asbestos-cement pipe.

VII. Nonmetallic coatings,1. Organic coatings2, Vitreous enamel

*r reoared by I, A. Denison,

2 ,lc-646 — 3/29/4-1,

I, INTRODUCTION

The soil-corrosion investigation of the National Bureau ofStandards, begun in 1922, was devised for the purpose of esti-mating the corrosive action of various soils toward the commonlyused ferrous pipe materials. For this study 4-7 test sites werecarefully selected to represent a wide range of soil conditions.Because of the severe corrosiveness shown by certain soils,corrosion-resistant materials, such as lead, copper, high andlow copper brasses, and a number of metallic and nonmetalliccoatings were later included in the field tests. The recentextensive development of low-alloy steels of high yield strengthmade available a large number of materials some of which mightbe selected for service underground if their resistance to cor-rosion in soils could be established. In 1932 specimens of avariety of these materials were buried at 15 additional testsites selected to represent different soil conditions and de-gree of corrosiveness. In 1937 and in 1939 additional speci-mens of newly developed materials were buried at these testsites. In order that the tests might be made as comprehensiveas possible, nonferrous metals, steels coated with experimentalprotective coatings, and miscellaneous materials were alsoburied on these occasions.

At approximately two-year intervals two specimens of eachmaterial are removed from each of the test sites, the corrosionproducts carefully removed, and except in the case of certainclasses of materials, the loss of weight is determined and thedepth of the deepest pit on each specimen is measured, S^Lnce

previous studies have shown that the corrosion- time relationis different for different materials and environments, it wasconsidered necessary to conduct the test for at least 10 yearsbefore drawing final conclusions relative to the merits of thematerials. Several progress reports on the conditions of thespecimens have been published, the latest report appearing in

1939. The reader is referred to these reports for details ofthe corrosion tests, for descriptions of the test sites, andfor data on the behavior of the materials in the varioussoils, Corrosion rates for materials which are seldomused in soils and for which limited data are available, suchas aluminum and its alloys, will be found in certain of thesereports.

For the majority of the materials to be considered, a dis-cussion of resistance to corrosion in the various soil environ-ments would be premature at this stage of the investigation.Nevertheless, it is desirable to indicate the behavior of thematerials toward those corrosive factors in the atmosphere, innatural waters, and in solutions, which are also present insoils, so far as these effects can be judged from the resultsof corrosion tests and experience in service. An advantage to

LC-646 — 3/29/41. 3 *

to be derived from such a consideration is that significanttrends in the effect of alloying elements on corrodibilitymay be utilized in the interpretation of the results of thefield tests. At the same time those interested in the pro-duction of alloys resistant to underground corrosion may beassisted in deciding whether specimens of their materialsshould be offered in the event of extension of the fieldtests in the future.

Although a discussion of the corrosion resistance ofmost of the specimens in the various soils must be deferreduntil more complete data are available, some information onthe behavior of the materials buried in 1932 may., be obtainedby referring to the most recent progress report. re-port' on the first and third inspections of the materialsburied in 1937 and in 1932

,respectively, is being prepared

for publication.

II. FERROUS MATERIALS

1. Wrought Materials.

The compositions of the wrought ferrous materials whichhave been buried at the various test sites are given in table1, Where there is a possibility of confusion in referring tothese and other specimens which have been assigned the sameletter symbol, the symbol has been followed in the text bythe year of burial,

a. Carbon Steels, Wrought Iron, and Ooen-Hearth Iron.-Thc ordinary wrought materials represented in the tests areopen-hearth iron, hand-puddled and mechanically-puddledwrought iron (Roe process), open-hearth steel and Bessemersteel.

In the manufacture of open-hearth iron (known commer-cially as ingot iron), carbon, silicon, phosphorus andmanganese are held to the lowest possible point, the sum ofthese impurities usually not exceeding 0.15 percent. Therelatively high degree of purity so obtained has no markedadvantage with respect to corrosion in soils, however

,since

the potentials which result from differences in aeration,for example, ere usually much greater than those that mightarise from lack of homogeneity of the metal. Open-hearthiron is used largely in sheet form for galvanizing, tinning,enameling, etc. for wire and for other purposes.

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1-

COMPOSITION

OF

WROUOHT

FERROUS

MATERIALS

(continued)

J

LC646- - 3/29

A

1 7I

Wrought iron is distinguished from other irons by the fact

that in the process of manufacture a certain amount of slag is

incorporated" mechanically in the molten iron. It is the exist-

ence of this slag, intermingled and dispersed among the crystals

of iron which gives to wrought iron its characteristic properties.

The superior corrosion-resistance claimed for wrought iron is

often attributed to the action of the slag flakes in divertingattack which has started locally into the plane of rolling,obstructing it from advancing at right angles to the surface.

In other words, the slag flakes are considered to divert pitting

into general corrosion.

In the manufacture of wrought iron the slag is incorooratedand distributed in the metal by the process of puddling and bythe "work" that is performed in the later rolling operations.Fuddling is either by hand or machine. As the quality of wroughtiron depends largely on the puddling operation, it was considereddesirable to include in the soil-corrosion tests specimens ofboth hand- and machine-puddled wrought iron (materials A and B

( 1932 ), respectively).

The machine-puddled specimens were made by the Roe"^ process.In this process puddling is accomplished by a specially designedfurnace which is oscillated at different speeds as desired. Thisprocess, however, is no longer used commercially.

Comparison of the rates of corrosion of specimens of hand-puddled wrought iron, steel, and open-hearth iron in soils doesnot indicate significant differences j.n the behavior of thethree kinds of materials underground."" However, a number ofexamples of the superior performance of wrought iron pipe lineshave been reported in the literature. Possible explanations forthis behavior have been advanced by Ewing ,^2

b. Low-alloy Steels. - Low-alloy steels are characterizedby much greater resistance to atmospheric corrosion than is shownby ordinary steels. Although these steels corrode readily ini-tially, the rust coating formed is very adherent and relativelyimpermeable and thus serves as a protective coating. Certain ofthese steels are used extensively for general structural pur-poses, in the manufacture of railway equipment, and generallywhere high strength and resistance to corrosive atmospheres areespecially important. Corrosion resistance in these materialsis obtained mainly by the addition of small amounts of chromium,nickel, copper, silicon, phosphorus or molybdenum. To the extentthat the soil environment approaches the conditions of atmos-pheric corrosion,

.as in well aerated soils, certain low-alloy

steels might be expected to prove superior to ordinary steels.However, as local differences in potential are probably con-siderably greater in soils than in the atmosphere, the protec-

LC-646 — 3/29/41 S.

tive film on the alloy steels is likely to be subjected to moresevere attack when exposed to the soil.

The beneficial effect of small amounts of copper on thecorrosion resistance of steel in the atmosphere has long beenknown. A few tenths of a percent of copper is sufficient todouble or triple the resistance to steel to atmospheric cor-rosion, However, if certain other elements are /Iso presentin the steel, the life of copper-bearing steel is greatly in-creased. For example, Kendall and Taylerson 1

-^, in theiranalysis of the A.S.T.M. tests of the corrosion of steel sheetsin the atmosphere, showed that at Pittsburgh the life of steelsheets containing from 0.15 to 0.4-0 percent Cu increased from1500 days with’ 0,01 to 0,03 percent P to over 2500 days with0,10 percent F, whereas the presence of phosphorus in non-copper steels had no beneficial effect on such material, atthis test site. The high copper contents of the low-alloysteels as a class (Table 1) indicate the extent to whichcopper is being used along with other alloying elements inenhancing the corrosion resistances of this class of materials.Copper either alone or combined with phosphorus apparently hasnot improved the performance of steels in submerged corrosiontests to date, d In the soil-corrosion tests carried out bythe National Bureau of Standards no benefit has resulted fromthe presence of 0,2 percent Cu in open-hearth steel.

Phosphorus either singly or combined with copper has beenshown to increasg the corrosion resistance of steels in variousatmospheres, While the benefit of small amounts of phos-phorus apparently does not apply to total immersion, Ewing1 ^

was able to correlate the phosphorus content of the eight kindsof wrought materials buried in 1922 at the Bureau soil-corrosiontest sites with the average depth of the deepest pits on thespecimens after 12 years' exposure, The shallowest pits wereobserved on the specimens containing the highest content ofphosphorus

.

For submerged conditions low-alloy steels as a class donot appear to offer any appreciable advantage over low-carbonsteels, although certain compositions are used to advantage inconnection with specific corrosives. For example, nickel-molybdenum steels are used to gain improved resistance tocorrosion and corrosion fatigue in oil well brines containinghydrogen sulfide. 4°

c, 4—6 Percent Chromium Steels .- Steels containing inter-mediate percentages of chromium are widely used in oil refin-eries to resist tfc>e corrosive action of sour crudes containinghydrogen sulfide, ^ However, as the operating temperatures arewell above the dew point, the behavior of these alloys gives

'

LC-646 — 3/29/41 9.

no indication of their probable behavior in poorly drained or-ganic soils in which hydrogen sulfide is present.

Molybdenum is incorporated in the 4-6 percent chromiumsteels principally to improve their mechanical properties atand after their exposure to elevated temperatures,

d. High-Chromium Steels .- The high resistance to corrosionby the high-chromium alloys results from the capacity of thesematerials to assume and maintain the passive state in many cor-rosive environments. With most metals a change in the intensityof a corrosive factor leads to a more or less proportionatechange in the rate of corrosion, but with the stainless steels,a slight change in environmental conditions may be sufficientto throw the material from the passive into the active condi-tion, An increase in the chromium content and the additionof certain alloying elements, such as nickel, broadens thepassivity range. Specimens containing 26 percent Cn (materialC) after exposure for 8 years, were pitted deeply in severalsoils which were extremely corrosive to ordinary steelA

High-chromium alloys are resistant to attack by sea water,many salts, and non-oxidizing acids. Molybdenum is commonlyused as an addition element in these alloys, and to a lesserextent silicon and copper.

High- Chromium Steels with Nick* 1 and Other AlloyingElements, - The principal contribution of nickel to the corro-sion resistance of the 18-8 alloy steels is its effect in ex-panding the passivity limits although nickel does have otherspecific effects on the corrosion resistance of the high nickelalloys A"'

7

Nickel itself has a very high resistance to neutralchloride solutions and to acid solutions of low oxidizing capa-city. These are conditions which for the 18-8 steels lie atthe passivity-activity boundary.

Manganese contributes to stainless steel ttje property ofresisting corrosive attack by sulfurous gases A° Whether thiseffect also applies to reducing acids in solution is uncertain.Material S is representative of the 18-S chromium-manganesesteels. Material T may be regarded as an 1S-S chromium-nickelsteel in which only a part of the nickel has been replaced bymanganese.

Molybdenum added to lS-o tends to expand the p&ssivity rangewith respect to salt water. It also is stated to be notablysuccessful in resisting the effects of sulfur compounds. '

Material CM resembles closely in composition the material knownas 16-13-3, (nominal composition 15-17 percent Cr, 12-l4 percentNi and 2. 5-3*5 percent Mo), This steel shows a somewhat lesser

(

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LC-646 — 3/29/4-1 10 .

tendency toward pitting and contact corrgsign in brines and seawater than the usual varieties of 12-S. °> -'-9

With increase in the number and amount of alloyingin stainless steel, increased corrosion resistance to avariety of soil conditions is to be expected.

element s

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2. Cast Materials.

Specimens of cast iron pipe made by sand casting (materialsL and Z 1922) and by the de Lavaud centrifugal process (materialC, 1922; were included in the field tests. The compositions ofthese and other cast materials are given in table 2. In the deLavaud process the metal is cast in a rotating horizontal metalmold. The material has a dense, fine-grained structure.

Corrosion-resistant cast irons have been developed in muchthe same way as corrosion-resistant steels, that is, by the addi-tion of such elements as chromium, nickel, molybdenum, manganeseand copper. However, in the group of low-alloy cast irons theinfluence of the alloying elements seerrP to consist rather inimprovement in the structure of the iron rather than in specificeffects on corrosion resistance. The indirect effects of thealloying elements are greater uniformity, denser structure ofthe casting and t n finer subdivision of the graphite flakes.

The specific effect of silicon on the corrodibility of castiron in soils is exhibited by the behavior in the field tests ofspecimens of a cast iron containing about 13 percent of silicon(material D) . After S years' exposure the loss in weight ofthe specimens was significant at only three of the 4-7 locationsand oply one of these specimens showed definite evidence of pit-ting, ^ High-silicon cast irons are hard, brittle, and non-machinable

.

Improvement in the structure of cast iron brought about byalloy additions or by other modifications in the manufacturingprocess apparently has the effect of reducing graphitic corro-sion, 20 a type of corrosion to which cast iron is subject. Bygraphitic corrosion is understood that form of corrosion whichresults from electrolytic action between ferrite and graphite,the former constituting the anode and the latter the cathodeof galvanic cells within the corroding iron. Graph! tizationmay decrease or accelerate the normal rate of corrosion depend-ing upon the tendency of corrosion products to deposit withinthe pores ofpthe casting as determined by the nature of theenvironment. " Donoho and Mackenzie^ 1 in correlating the be-havior of cast iron specimens in the National Bureau of Stand-ards soil-corrosion tests with the properties of the soils at thetest sites, pointed out that in poorly drained acid soils, and

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neutral and alkaline soils high in soluble salts, cast iron maycorrode at a somewhat higher rate than rolled ferrous productsbecause of graphitic corrosion. On the other hand, in wellaerated soils low in soluble salts, cast iron is less severelyattacked, according to these investigators, than are rolledmaterials. It would seem, therefore, that improvement in castiron from the standpoint of corrosion resistance is largelya matter of producing castings resistant to graphiti zation,However, in those soil environments where alloying elementsare able to exert their specific effects in reducing corrod-ibility, it would be reasonable to expect that the presenceof alloying elements in cast iron would be at least as bene-ficial as in steel.

Although a large variety of special cast irons are avail-able, relatively few have been included for study in the fieldtests. Cast irons of compositions other than those given intable 2 are in use for types of service which suggest that theseirons might be successfully employed for underground service.For example, Dief

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enbach.22 has reported that a copper-molybdenumcast iron has shown no noticeable corrosion in more than twoyears' service as lock gate valves under conditions for whichprotective coatings w^ere unsuitable. Cast irons containingsmall percentages of nickel, chromium, and molybdenum are under-stood to be used also for similar purposes,

III. COFPER AND COPPER ALLOYS

Copper and alloys high in copper are generally resistant tocorrosion in soils. Although severe corrosion of copper has beenobserved, no actual failures have occurred in the Bureau of Standards soil corrosion tests. Like certain other metals, the resistance of copper to corrosion depends on the maintenance of a pro-tective oxide film. Wherever this film cannot be maintainedintact, as in alkali soils high in chlorides and carbonates,poorly drained organic soils, such as tidal marsh, peat, andmuck, and in cinders, corrosion results. The specimens ofcopper and copper alloys under test are listed in table 3*

1 . Copper

Tough-pitch copper (material C) normally contains from 0.03to 0.05 percent oxygen or 0,27 To 0.4-5 percent cuprous oxide.By treatment with phosphorus even this small amount of oxygenmay almost completely be removed, the resulting product havingsuperior ductility and toughness (material A. 1932). Copperspecimens with soldered fittings (material M) were included inthe test in order to determine the extent of galvanic action atthe point of contact of the copper with solder. Laboratorytests itfith circulating water have not shown evidence of gal-vanic corrosion on this type of fitting, 23

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2 . Brasses

Brasses containing high percentages of zinc are in generalmuch less resistant to corrosion in soils than copper or highcopper alloys. An exception, however, is to be noted in thecase of marsh soils in which 6o/4o brass (material L) corrodesat a considerably lower rate than copper. A probable explana-tion for this difference is the greater resistance of low-copperbrasses to sulfides. The corrosion resistance of low-copperbrasses to sulfur and sulfur compounds has been previouslyobserved. 2^

Corrosion of the higher zinc brasses under certain condi-tions results in dezincif ication. The addition, in small amounts,of several metals has been employed to inhibit this form of cor-rosion. Admiralty metal (material H)

,in which 1 percent of tin

is substituted for an equal amount of zinc in 70/32 brass, ap-pears to be effective in reducing dezincification under theconditions for which this alloy is generally used. Arsenic infractional percentages is also said to be effective in repressingor inhibiting dezincification. Material B ( 1939 ) which contains0.00 arsenic has been included in the test for comparison withthe same material without arsenic (material L) . Various investi-gators have found that antimony in amounts up to 0.10 percent isparticularly effective in combating de zincif ication . ^3 Brassesof this type have not as yet been included in the soil-corrosiontests. Recently, the addition of phosphorus has been advocatedas a means of preventing dezincification of Admiralty metal. 2

In general, soils which are corrosive to copper are rela-tively noncorrosive to lead. Hence it would be reasonable toexpect that an alloy of copper containing lead as an additionelement would be more resistant to corrosion than the same alloylow in lead. This has been confirmed in some degree by the re-sults obtained in the soil-corrosion tests. Material K, knownas two-and-one leaded brass, appears to corrode at a slightlyslower rate than material J which contains a smaller quantityof lead. On this basis, a brass having a relatively high leadcontent might prove considerably more corrosion-resistant thana brass of the same copper content but lowr in lead.

3. Bronzes .

The term, bronze, which primarily connotes an alloy of cop-per and tin, is also applied to alloys of copper with aluminum,nickel and silicon. In an early tesA an. aluminum bronze, con-taining S7 percent copper, 9*5 aluminum, and 3*5 percent iron(material N, 1926), corroded slightly sloi'/er than copper, Thealuminum bronze, however, showed evidence of attack similar todezincif ication in soils which were corrosive tOpCopper. Otherinvestigators have observed the same phenomenon, b

-

LC-646- - 3/29/41 16.

!

A recently developed alloy having the composition 96. percent

copper, 2.25 percent aluminum, and 1.75 percent tin is said to

have proved very resistant to the corrosive action of locomotive

fumes" salt fogs and spray and other corrosive conditions en-

countered along railroad rights-of-way. ' On this basis, some

of the new nickel-aluminum bronzes might prove highly resistant

to soil corrosion.

4. Copper-Silicon Alloys

Two oropper-ailicon alloys, materials N and D, containing.

1.49 and 3.19 percent silicon, respectively, are represented in

the field tests.

Copper-silicon alloys are said to be highly resistant to

corrosion by sea water, corrosive natural and industrial waters,

a variety of salts, and to organic compounds and organic acids .

j

5. Copper-Nickel Alloys

Specimens of a copper-nickel alloy containing 75 percent Cu,

20 percent Ni,and 5 percent Zn were buried at the test sites in

193*

2 . The standard 70_ 3° copier-nickel alloy, in which the maxi-

mum zinc content is 1 percent 1- ^ has not as yet been included in

the field tests. While the beneficial effect of zinc is open to

question, there is no evidence that it has a deleterious effect. b

Copper-nickel alloys are used for condensers on ships and oilrefineries and for piping salt water on board ship.

6. Metallic Coatings with Copper as the Base Metal.

Since copper is corroded appreciably in certain soil environ-ments, the protection of copper by some type of metallic coatingdeserves consideration. Since tin is probably anodic to copperunder all soil conditions, corrosion of tin would be expected toprotect copper cathodically in the same manner that the corro-sion of zinc protects the underlying steel in galvanized mater-ials. Data on the thickness of the tin coating on the testspecimens, which is of course a very important consideration,are not available at present.

Aside from the question of the minimum thickness requiredfor protection, another possible cause of failure of tinnedcopper in soils is the formation of tin-copper alloys. Thesealloys have been shown under certain conditions to be morecathodic than copper . ^9

In considering the effect of zinc on the corrosion resist-ance of brasses in soils, it was noted that both copper and

LC-64-6 — 3/29/41. 17.

lead are apparently not appreciably corroded in the same environ-ment. Advantage might be taken of this observation by using incorrosive soils copper coated with lead. In soils corrosive tolead but not to copper, no protection of the copper is needed.However, in soils corrosive to copper but relatively noncorrosiveto lead, the copper would probably be protected cathcdically

.

Lead-coated copper sheet is used as a roofing material. Coppercan be coated with pure lead only with difficulty. A copperalloy containing a little tin gjives a good bond with lea.d andgreater freedom from pinholes. c4

IV. ZINC AND ZINC COATINGS

The chief use for zinc underground is in the form of coat-ings for iron and steel pipe. Results from an early study 3 haveshown that zinc coatings having a weight of 2.22 oz/sq ft of ex-posed area prevented the formation of pits in all but one of agroup of 47 soils over a period of 10 years. In order to testfurther the protective action of zinc coatings in soils, thisstudy was extended to include a second group of 15 corrosivesoils. For this purpose specimens of galvanized iron pipehaving a nominal weight of coating of 3 oz/sq ft were buriedin 1937 in the special group of soils.

The protective action of zinc as a coating on iron andsteel depends chiefly on the fact that it is anodic with respectto ferrous metals. However, as zinc is corroded relatively slow-ly under many soil conditions, it is difficult to determinewhether the protective action is chiefly electrolytic or whetherit results largely by shielding ferrous metals mechanically fromthe environment. In order to obtain experimental evidence onthis point, specimens of bare iron pipe and two varieties ofzinc were buried in 1937 in addition to the specimens of gal-vanized iron previously mentioned. The compositions of thezinc specimens are given in table 4.

The behavior of zinc in electrolytic contact with ferrousmetals in soils assumes special importance from the standpointof the cathodic protection of pipe lines. In one type of instal-lation the corrosion of zinc anodes distributed along a coatedpipe line to which the anodes are connected at intervals byinsulated wires provides the current required for protectionof the line cathodically . 3° In order to determine the conditionsunder which this type of protection is effective, plans are inprogress for the burial at the 15 test sites of zinc-iron couplesin various area ratios. These plans call for the use of zinc ofdifferent degrees of purity and for measurement at intervals ofthe electrode potentials and the galvanic current.

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V. LEAP and lead coatings

The compositions of the varieties of lead which are exposedat test sites are given in table 5* The samples of "chemicallead" contain 0.02 percent of bismuth, which is not presentexcept as a trace in the standard grade of chemical lead. Leadof this composition is claimed to have certain advantages inmechanical properties over the A.S.T.M. standard "chemical" lead.

To improve the mechanical properties and to reduce corrosionof lead, it is commonly alloyed with small amounts of other metals,namely, antimony, tin, tellurium and calcium. Since these ele-ments, as well as those normally present as impurities, such asbismuth, are in certain environments cathodic to lead, possi-bility of the development of local corrosion cells must be con-sidered when lead is exposed to soils. In the corrosion testsextending over a 10-year period, lead containing 1 percent ofantimony corroded at a slightly higher rate than commercial lead.Pliers,^-*- on the other hand, has reported that lead containingup to 3 percent of tin has shown best resistance on exposure towet atmospheric conditions, water and some soils. Similarly,the introduction of approximately 0.05 percent of tellurium incommercially pure lead (material T) is said to result in a con-siderable increase in corrosion resistance, 32

Since lead in electrolytic contact with iron functions asa cathode, lead as a coating can not protect a ferrous metalelectrolytically in the manner that zinc does. Hence, the pro-tective value of a lead coating on steel is dependent entirelyon continuity of the coating. In the case of sheets pinholescan be removed by rolling after the coating has been applied.Lead applied as a coating to copper would of course functionanodically in an aqueous environment.

VI. ASBESTOS-CEMENT FIFE.

Specimens of asbestos-cement pressure pipe manufactured bydifferent processes were buried at 15 test sites in 1939*Specimens of flue pipe were buried in 1932.

In the manufacture of asbestos-cement pipe a mixture ofasbestos fiber and portland cement is built up by a continuousprocess on a revolving steel mandrel which is rotated underpressure until the required wall thickness is obtained. In atleast one process of manufacture the pipe is cured in waterfor 7 days and then cured in air for a minimum of 21 days.

Since cement-asbestos pipe is nonmetallic, it is of coursenot subject to soil corrosion, tuberculation or electrolysis.

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Whether it is subject to deterioration under certain soil condi-tions will be indicated by examination of specimens after removalfrom the test sites.

VII. NONMETALLIC COATINGS

1 . Organic Coatings.

Synthetic resins are used in the protection of steel struc-tures such as locks and dams subject to submerged corrosion, andin the protection of freight and refrigerator cars which are sub-ject to condensation of moisture containing dissolved sulfur com-pounds and to contact with brines and fruit acids. The resist-ance offered by synthetic resins to the rather severe conditionsmentioned suggested the possible use of these materials in theprotection of metal underground. The important classes of resinsor plastics proposed for use as protective coatings on metalswill be described briefly. However, not all of the classes tobe mentioned are represented as yet by specimens in the fieldtests

.

Phenolic Aldehyde Resins. - The basic materials in the manu-facture of this group of resins are phenol or cresol and formal-dehyde. One type of coating included in the field tests consistsof several coats of different resins with intermediate baking.In another type two coats of phenolic resin in which aluminumpowder had been incorporated were applied to the primed surface,each coat being air-dried. A third type consists of two layersof asbestos tape impregnated with phenolic resin. Phenoliccoatings are characterized by durability under conditions ofexposure in which resistance to high humidity, water, andstrong chemical reagents is necessary. The film has beendescribed as being smooth, glossy, non-porous, hard and toughenough to withstand distortion produced in railway tank carsin service. To

Hydroxy-carboxylic Resins. - The hydroxy-carboxylic type ofresin includes a wide variety of materials produced by the

^esterification of polytasic acids with polyhydric alcohols.

-

They are often called alkyd resins (from alkyl-acid). Theirprincipal use is as the resinous constituent of varnishes andlacquers. These finishes are said to be characterized by gooddurability out of doors, excellent flexibility, tenaciousadhesion, and good electrical insulating properties. Coatingsof this type are not at present under test.

Vinyl Resins. - Vinyl resins made by the polymerization oforganic compounds having the vinyl group CH2=CH-. Dissolved insuitable solvent mixtures, these resins form lacquers which areclaimed to be resistant to water, acids, alkalies, oxidizingagents and corroding materials in general, A coating consisting

LC-646 — 3/29/41 22 .

of polyvinyl chloride is included in the field tests. Vinyl resincoatings are used in the chemical and electrochemical industries,as for example, as a lining material in chromium plating baths.A resin composed of a mixture of vinyl chloride and acetate isconsidered to have exceptional merit as a protective coating,but this type of coating has not yet been included in the fieldtests.

Acrylate Resins, - Acrylate resins are polymers of the estersof acrylic acid. This group includes the well-known methacrylateresins which are finding application as protective coatings.The polymeric ester coatings may be applied either as a solutionin a solvent or in the molten state by extrusion. High resist-ance to various chemicals and water and to other desirablephysical properties- 0 are claimed for them. Coatings of thistype are not under test at present,

Resins Derived from Rubber. - Chlorinated rubber is usuallymade by passing chlorine into a solution of rubber in chloroform,benzene or other solvent. The most important application ofcoatings of chlorinated rubber is in preventing corrosion ofindustrial equipment. These coatings are said to be character-ized by unusual resistance to acids and alkalies. Specimenscoated with chlorinated rubber are under test.

Another type of coating derived from rubber, which is in-cluded in the field tests, is made by reaction of rubber andchi oros tannic acid, r^SnClg, which gives a chloro derivativeof isomerized rubber. It is considered to have many potentialapplications as a protective coating.

Svn the t i c Rubb e

r

. - In addition to the synthetic resin coat-ings which have been described, coatings composed of severalvarieties of heard rubber and a variety of natural resins areunder test.

The particular synthetic rubber included both as a materialand as a protective coating in the field tests is made fromreaction of various dihalogenated organic compounds with alkalinepolysulfides. The product is cured at an elevated temperaturein a manner similar to the vulcanization of rubber, a rubber-like material being formed. Among its other applications,this material is used as a protective sheathing for electriccables.

2. Vitreous Enamel.

Vitreous enamel consists of a mixture of grit, clay, borax,feldspar, and water which is usually sprayed on the pickled orsand-blasted metal surface. The coating is then dried and heated

,

LC-646 — 3/29/41 23 .

until the material is fused. Although coatings of this type sub-mitted foff the field tests contained pinholes before burial,the specimens after five years' exposure showed no definiteevidence of rust in any of the soils to which they were exposed,nor was there evidence of pitting except where the coating hadbeen injured in handling.

LC-646 — 3/29/41.

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REFERENCES

Kirk H. Logan. Soil-corrcsion studies, 1937* Corrosion-resistant materials and special tests. J. Research NB322 , 515 (1939) EP 1250 .

Kirk H. Logan. Soil-corrosion studies, 1934-. Bituminouscoatings for underground service. J. Research N5S 12, 69 B

(1937) “RP105S.

Kirk H. Logan and Scott P. Ewing. Soil-corrosion studies,1934. Field tests of nonbi tuminous coatings for undergrounduse. J. Research NBS IS, 361 (1937) RP 9 S2/

Kirk R. Logan. Soil-corrcsion studies, 1934-. Rates of lossof weight and penetration of nonferrous materials. J. Re-search NBS 17/721 ( 1936 ) RP945.

K. H. Logan. Soil-corrosion studies, 1934-. Rates of lossof weight and pitting of ferrous specimens. J. Research NBS16

,432 ( 1936 )" RPSS 3 .

K. H. Logan and R. K. Taylor. Soil-corrosion studies, 1932.Rates of loss of weight and pitting of ferrous and nonferrousspecimens and metallic protective coatings. J. Research NBS12

,120 (1934).

K. H. Logan, Soil corrosion studies. Nonferrous metals andalloys, metallic coatings, and specially prepared ferrouspipes removed in 1930* J. Research NBS

]_ } 525 (1931) RP359*

K. H, Logan and V. A. G-rodsky. Soil-corrosion studies, 1930*Rentes of corrosion and pitting of bare ferrous specimens.J. Research NBS 7, 1 ( 1931 ).

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