NATIONAL BUREAU OF STANDARDS The program of research on building materials and structures vmdertaken by the National Bureau of Standards is planned with the assistance of the following advisory committee designated by the Subcommittee on Design and Construction of the Central Housing Committee.

TECHNICAL RESEARCH GROUP

Walter Junge, Federal Housing Administration, Acting Chairman

A. G. Bear, Vincent B. Phelan, Veterans' Administration. National Bureau of Standards. Pierre Blouke, E. A. POYNTON, Home Owners' Loan Corporation. Bureau of Lidian Affairs. C. W. Chamberlain, John H. Schaefer, Procurement Division. Procurement Division. Jos. M. DallaValle, A. C. Shire, Public Health Service. United States Housing Authority. Hugh L. Dryden, George W. Trayer, National Bureau of Standards. Forest Service. G. E. Knox, Elsmere J. Walters, Bureau of Yards and Docks, Navy Quartermaster Corps, War Department. Department. Sterling R. March, Charles E. Mayette, Secretary. United States Housing Authority.

The program is administered and coordinated by the following staff committee of the Bureau: Hugh L. Dryden, Chairman

P. H. Bates W. E. Emley A. S. McAllister H. C. Dickinson G. E. F. Lundell H. S. Rawdon

The Forest Products Laboratory of the Uniied States Department of Agriculture is cooperating with the National Bureau of Standards in studies of wood constructions.

How To Purchase BUILDING MATERIALS AND STRUCTURES REPORTS

On request, the Superintendent of Documents, U. S. Government Printing OflBce, Washington, D. C, will place your name on a special mailing list to receive notices of new reports in this series as soon as they are issued. There will be no charge for receiving such notices.

An alternative method is to deposit with the Superintendent of Documents the sum of $5.00, with the request that the reports be sent to you as soon as issued, and that the cost thereof be charged against your deposit. This will provide for the mailing of the publications without delay. You will be notified when the amount of your deposit has become exhausted.

If 100 copies or more of any report are ordered at one time, a discount of 25 percent is allowed.

Send all orders and remittances to the Superintendent of Documents, U. S. Government Printing Office, Washington, D. C. UNITED STATES DEPARTMENT OF COMMERCE • Daniel C. Roper, Secretary

NATIONAL BUREAU OF STANDARDS • Lyman J. Briggs, Director

BUILDING MATERIALS and STRUCTURES

REPORT BMS8

Methods of Investigation of

Surface Treatment for Corrosion

Protection of Steel

by ROLLA E. POLLARD and WILBUR C. PORTER

ISSUED OCTOBER 11, 1938

The National Bureau of Standards is a fact-finding organizat ion:

it does not "approve" any particular material or method of con-

struction. The technical findings in this series of reports are to

be construed accordingly.

• UNITED STATES GOVERNMENT PRINTING OFFICE • WASHINGTON 1938

FOR SALE BY THE SUPERINTENDENT OF DOCUMENTS, WASHINGTON, D. C. • PRICE 10 CENTS Foreword

The Present Paper describes the methods used in an investigation now under way of surface treatments for the protection of steel for low-cost housing construction against corrosion. Accelerated laboratory corrosion tests of various pretreatment processes and paints used for steel and galvanized surfaces form an important part of the inves- tigation. Because of wide variations in service conditions, these tests cannot be ex- pected to produce results directly measurable in terms of years of service. However, with the limitation of each type of tests in mind and with comparisons confined to the conditions of testing, such tests form a valuable means of studying the factors affecting the protective value of paints under particular conditions. In the present investigation special attention is being given to the study of conditions affecting corrosion by con- densed moisture, such as might occur in the enclosed areas between walls.

Lyman J. Bkiggs, Director. Methods of Investigation of Surface Treatments for Corrosion Protection of Steel

by ROLLA E. POLLARD and WILBUR C. PORTER

CONTENTS

Page Page Foreword ii IV. Testing program—Continued 2. conditions for plain I. Introduction 1 Surface steel II. Factors affecting durability of paint sheet 8 on metal 2 3. Protective coatings 9 10 III. Methods of testing , 3 4. Status of investigation.-. IV. Testing program 5

1. Pretreatments for galvanized steel 5

ABSTRACT siderably. Structural members fabricated from such steel are often used as joists or studs in the Some of the factors affecting the protective value of framework of houses of conventional construc- paints for steel and galvanized surfaces are being tion. so-called "prefabricated" steel house studied by accelerated laboratory corrosion tests sup- The plemented by outdoor exposure tests. Short descrip- usually consists of wall, floor, ceiling, and roof tions are given of the various methods of testing. The sections of standard size prefabricated in the such tests as com- significance and the limitations of shop and joined together on the job by welding, pared with actual service tests are briefly discussed and bolting, or interlocking joints. The sections or the materials, pretreatment processes, and paints in- panels consist of a steel frame work fabri- cluded in the testing program are outlined. Special may attention is being given to the severity of corrosion cated from sheet steel and covered on either side which may result from condensed moisture. by other materials, or may be made entirely of sheet steel or galvanized sheet in cellular units. Sheet steel also is used in considerable amounts in window frames, metal cabinets, metal furni- I. INTRODUCTION ture, and the air ducts of air-conditioning equip- As PART of a general research program on ment. Among the newer uses of sheet steel in building materials, the National Bureau of house construction, may be mentioned bath- Standards is conducting an investigation on rooms made as a separate unit complete and the surface treatment for corrosion protection ready for installation in the desired location and of steel used in the construction of low-cost requiring only connections for light, water, and houses. sewer. The use of steel as a building material is not When used in the form of hght-gage sheet, the new, of course. Large amounts have been used protection of steel is a matter requiring serious for many years as heavy structural members in consideration. A corrosive attack that would large buildings. Used in this manner, in heavy be relatively insignificant in a heavy steel beam sections, covered and protected to some extent might perforate a light-gage sheet. In steel by other building materials, the deterioration of houses the initial protection of inaccessible sur- steel is not a serious problem, since small faces such as the interior of walls, is particularly amounts of corrosion do little damage, and ap- important since renewal after installation is not pearance is not a factor. practicable. Condensation within walls has In recent years the use of light-gage sheet been greatly increased in modern houses by liigh steel as a building material has increased con- humidity caused by the use of winter air-con-

90695°—38 [1] —

ditioning equipment. This is particularly true parts of the same house. Painted surfaces ex- in colder climates where parts of insulated walls posed outdoors, for instance, are affected by the may be cooled below the temperature of the ultraviolet rays of sunlight, moisture in the moist inside air for long periods. form of rain or dew, and the expansion and con- traction resulting from temperature changes. II. FACTORS AFFECTING DURABILITY OF PAINT ON METAL These factors vary according to climatic condi- ,tions. The corrosive action of rain or dew is Painting is one of the cheapest and most (determined largely by the amount of impuri-

widely used methods for protecting plain steel. • ties, such as sulfur dioxide, with which the air Galvanized steel surfaces are often painted also, may be polluted. The degree of pollution both for decoration and increased protection. varies considerably in different localities. An important part of the present investigation In the interior of a house, painted surfaces are is a laboratory study of the factors affecting the not exposed to ultraviolet radiation, but may be durability of paint films on steel and galvanized subjected to rather wide variations in tempera- surfaces under conditions somewhat similar to ture and to corrosion by condensed moisture. those which might be encountered in service. Recent tests at this Bureau have demonstrated The conditions under which house paints are the severity of this type of corrosion on unpro- expected to stand up vary considerably, not tected steel and even on galvanized sheet, and only in different localities, but also in different have served to emphasize the need for surface

. P'iGURE 1 AcceleraU'

The arc lamp has been raised out of the working position in the unit at the right. The cylindrical rack, with the specimens mounted thereon, makes a complete rotation once in 20 minutes. A fixed water spray (tap water) thoroughly wets each panel once every 20 minutes while the light is continually in operation.

[2] protection. The corrosive action of condensed produced by prolonged outdoor exposure. Tliis moisture, like that of rain, is influenced by the is particularly true for conditions of exposure in impurities in the air from which it is condensed. which the efi'ect of sunlight is the dominant Corrosion may also be greatly accelerated by factor in determining the life of the paint. An accumulations of dust or other dirt. accelerated weathering apparatus similar to that shown in figure 1 is being extensively used investigation. III. METHODS OF TESTING in the present Two other accel- erated laboratory tests in use are the moisture- Some of the conditions mentioned can be sim- condensation corrosion test and the salt-spray ulated to some extent and with more or less test. accurate control in laboratory tests. In order The condensation corrosion test was designed to get results within a reasonable length of time, to simulate as nearly as possible the conditions however, it is necessary to change the conditions that may occur within a house, particularly in considerably. In the accelerated weathering, enclosed spaces such as the interior of walls. for example, painted specimens are exposed The test consists in exposing steel panels which alternately wet and dry to the heat and the have been painted or otherwise treated to the ultraviolet light of a carbon-arc lamp. The corrosive action of moisture condensed from a accelerating factors of this test as compared controlled atmosphere. Photographs of the with ordinary outdoor exposure are (a) almost condensation corrosion cabinet are shown in constant exposure to light containing ultraviolet figures 2 and 3. The specimens rest in a nearly rays, (b) frequent wetting and drying, (c) fre- horizontal position on the cooling tank in the quent abrupt changes in temperature, and (d) bottom of the insulated box through which air liigh humidity. of controlled temperature and humidity is cir- The experience of this Bureau in conducting culated. The degree of purity of the air is also laboratory tests of painted metal panels extend- controlled, at least so far as the amount of ing over a period of years indicates that the dust and degree of pollution with sulfur dioxide accelerated-weathering test often produces with- are concerned. A test run consists in a series in a short time corrosion effects similar to those of cycles, each of which embraces a condensa- — - —

Figure 3. Interior view of chamber shoiving speci- mens in position.

Note how the specimens have been intentionally scratched for the test.

tion periotl, a poriotl in which the panels staiul The accelcratctl-weatheruig tests mentioned wet, and a drying period. Since tlie composi- above are being supplemented b,y ordinary out- tion of the air and the temperatures are such door exposure tests at Washmgton. Part of as might be encountered in service, the only the exposure test racks are shown in figure 5. accelerating factors involved in the test are the Special exposure tests are being made in which anu)unt of condensed moisture, the length of specimens are exposed in ventilated enclosures, time wet, and the comparative frequency and the specimens being shielded from the sun and suddenness of the temperature changes. direct rainfall but open to the aii" through The salt-spray test consists in conthuious louvres and exposed to the condensation of exposure to the fine mist or spray produced moisture. This test should be similar to the from a 20-percent solution of sodium chloride. SATURATING CLEANING of the testing- appa- The important principles TOWER.^ . TOWER. TO COUNTER WEIGHTS of 4. VENT ratus are shown in the drawhigs figure h- WATER. SEAL WATER.-N| SUSPENDED COVER.-^ its simplicity This type of test, because of and ^WINDOW speedy results, is witlely used in laboratory cor- rosion testing, although it has been repeatedly shown that the results are comparable to those produced in service only when the conditions of service include frequent wettuig by salt water or prolonged exposure to salt spray. Salt- spray tests were included in the present investi- gation not so nuich for direct comparison with DR-AlM the corrosive conditions of marine atmospheres, LONGITUDINAL SECTION THR.OUGH SALT- SPRAY 50X simple but more as a comparatively quick and Figure 4. Diagram showing the principle of flic salt- means of studymg some of the factors afiecting spraij test. the protective value of pamt films, such as A stream of air which has been cleaned and saturated with moisture "atomizes" the test solution (sodium chloride solution) and produces ]HM ineability to moisture and inhibitive action a mist which completely fills the interior of the cabinet where the speci- of pigments. mens are exposed. —

Figure 5. Part aj cxpusurc leslfi of painted metal panels on roof of Chemistii/ BuUduiy, National Bureau of Standards. condensation corrosion test previously de- inches are being used. After pretreatment the scribed, but probably considerably slower. panels are brushed with two coats of primer with The various tests described above should 1 week drying time between coats. One-half yield useful information on the protective of the surface is then given one topcoat of an value of various pretreatment processes and outside finish paint. Two diagonal scratches paints used for steel and galvanized surfaces. are made across the front of each specimen. In Some of the tests have been used for a number of most cases test panels are prepared in duplicate. years and their limitations, as compared with actual service conditions, are well understood. IV. TESTING PROGRAM Service conditions vary so widely that actual 1. Pretreatments for Galvanized Steel service tests in different localities may not produce comparable results. It is not to be Most of the tests to date have been made on expected, therefore, that laboratory tests in painted panels of galvanized steel. The paint- which similar conditions are changed to speed ing of a fresh galvanized surface has always up the action will produce results directly been a difficult problem because of the poor measurable in term of years of service. How- adherence of paint to the smooth surface and ever, in the laboratory the conditions of testing because of possible reactions between the zinc are under control and by varying the conditions and the pigment or veliicle of the paint. Both in different tests, it will be possible to study difficulties may be overcome to some extent the factors affecting the protective value of by preliminary weathering, which roughens paints under particular conditions. the surface and changes it chemically so that Most of the panels are 3 by 6 inches. In the reactions with the paint do not occur so readily. condensation chamber, larger panels 5 by 7 However, weathering takes at least 6 months

[5] —

in most cases, and numerous pretreatments (2) Zinc sulfate (8 oz per gal); have been proposed and used for modifying the (3) Alcohol (60%), toluol (30%), car- surface so that painting may be done at once. bon tetracliloride) (5%), hydro- The pretreatments so far included in the chloric acid (5%) by volume; present testing program are: (4) Saturated solution of nickel sulfate (a) Common hxboratory etching solutions, (10 parts by weight), antimony- including: potassium tartrate (0.5 parts by (1) Copper sulfate (8 oz per gal); weight), neutralized with ammo-

Panel A^. Panel B^.

Figure 6. Painted galvanized steel panels after the six-months' accelerated-weathering test.

Panel A^, no treatment prior to painting. Panel B2, surface-treated prior to painting. Two coats of the same primer were used on each panel; a single top coat was applied to the upper half of the panels.

[6] — ; ;

Panel A9. Panel B9.

Figure 7. Painted galvanized steel panels after the six-months' accelerated weathering test.

Panel A9, no treatment prior to painting. Panel B9, surface-treated prior to painting. Two coats of the same primer

were used on each panel; a single top coat was applied to the upper half of the panels.

nium hydroxide, made slightly (b) Proprietary pretreatment processes, in-

acid with hydrocliloric acid, cluding :

and then diluted to 100 parts by (1) Zinc phosphate (hot dip and cold weight with water wash)

(5) Phosphoric acid (1 part), alcohol (4 (2) Iron-zinc phosphate (hot dip); parts), by volume; and (3) Barium phosphate (hot dip); and (6) Dilute acetic acid (4 %) by volume. (4) Acid dichromate (hot dip).

[7] — ; ; ;

2. Surface Conditions for Plain Sheet (b) Acid pickle, including: Steel (1) Hot hydrochloric acid (20% by volume) The surface conditions of plain sheet steel (2) Hot sulfuric acid (10% by volume) prior to painting also has a considerable influ- and ence on the durability of the paint coatings (3) Hot phosphoric acid (20% by applied. Among the surface conditions in- volume). cluded in the testing program are the following: (c) Proprietary pretreatment processes, in- (a) As rolled (hot-rolled annealed sheet) cluding:

Panel B2.

Figure 8, Painted galvanized steel panels after the salt-spray test.

Panel AS (4 weeks in spray), no treatment prior to painting; panel BS (6 weeks in spray), surface-treated prior to painting. Two coats of the same primer were applied to each panel. — ;

Panel A5. Panel Bo.

Figure 9. Painted galvanized steel panels after 18 weeks in the salt-spray test.

Panel AS, no treatment prior to painting. Panel B5, surface-treated prior to painting. Two coats of the same primer were applied to each panel.

(1) Zinc phosphate (hot dip); 3. Protective Coatings (2) Iron-zinc phosphate (hot dip) A total of 60 priming paints for steel or gal- (3) Barium phosphate (hot dip); vanized surfaces are being included in the (4) Phosphate cold wash—inhibitive tests. A small number of different types of pigment—aluminum-paint top top coats are also being tested. coat; (a) Pigments used in the priming paints and (5) Phosphate-chromate cold wash; and top coats mclude the following:

(6) Hot dip chromic acid treatment. (1) Lead pigments (metaUic lead, lead

[9] ;

oxides, lead carbonate, chromate, 4. Status of Investigation and sulfate; A considerable number of accelerated-weath- (2) Zinc pigments (metallic zinc, zinc ering tests and salt-spray tests have been made oxide, zinc chromate) on painted galvanized panels. Outdoor ex- posure tests have been in progress for periods (3) Aluminum; ranging up to 8 months, while condensation (4) Litliopone (barium sulfate-zinc sul- tests have been running about 2 months. fide); Photographs of some of the panels after being

tested are shown in figures 6 to 9, inclusive. (5) Carbon pigments; and The test program has not been completed, and Iron oxide. (6) in the absence of completed results from all (b) Paint vehicles include representatives of types of tests it is not considered advisable to the following classes: draw definite conclusions at the present time. It may be stated, however, that some of the (1) Drying oils; pretreatment processes show considerable prom- Synthetic varnishes (mostly oleoresin- (2) ise of increasing the adherence of paints to ous, phenolic, and alkyd types); galvanized surfaces, and that some of the newer paints may, under favorable condition, give (3) Asphalt varnishes; and good protection even on imtreated surfaces. (4) Natural and chlorinated rubber ve- hicles. Washington, August 8, 1938. o

[10] The National Bureau of Standards was established by act of Congress, approved March 3, 1901, continuing the duties of the old Office of Standard Weights and Measures of the United States Coast and Geodetic Survey. In addition, new scientific functions were assigned to the new Bureau. Originally under the Treasury Department, the Bureau was transferred in 1903 to the Department of Commerce and Labor (now the United States Department of Commerce). It is charged with the development, con- struction, custody, and maintenance of reference and working standards, and their intercomparison, improvement, and application in science, engineering, industry, and commerce. SUBJECTS OF BUREAU ACTIVITIES

Eleciricity Chemistry—Continued Simplified Practice—Continued Resistance Measurements Organic Chemistry Containers and Miscellaneous Inductance and Capacitance Metal and Ore Analysis, and Products Electrical Instruments Standard Samples Materials-Handling Equip- Magnetic Measurements Reagents and Platinum Metals ment and Ceramics Photometry- Electrochemistry (Plating) Trade Standards Radio Gas Chemistry Underground Corrosion Physical Chemistry Wood, Wood Products, Paper, Leather, Electrochemistry Thermochemistry and Con- and Rubber Metal Telephone Standards stitution of Petroleum Products Textiles Weights and Measures Mechanics and Sound Apparel Length Engineering Instruments and Petroleum, Chemical, and Mis- Mass Mechanical Appliances cellaneous Products Time Sound Capacity and Density Aeronautic Instruments Codes and Specifications Gas Measuring Instruments Aerodynamics Safety Codes Thermal Expansivity, Dental Engineering Mechanics Building Codes Hydraulics Materials, and Identification Building Practice and Specifi- Weights and Measures Laws Organic and Fibrous Materials cations and Administration Rubber Producer Contacts and Certi- Large Capacity Scale Testing TextUes fication Limit Gages Paper Consumer Contacts and La- Heat and Power Leather beling Thermometry Testing and Specifications Pyrometry Fiber Structure Office Heat Measurements Organic Plastics Finance Personnel Heat Transfer Metallurgy Cryogenics Optical Metallurgy Purchase and Stores Fire Resistance Thermal Metallurgy Property and Transportation Automotive Power Plants Mechanical Metallurgy Mail and Files Lubrication and Liquid Fuels Chemical Metallurgy Library Information Optics Experimental Foundry Spectroscopy Clay and Silicate Products Shops Polarimetry Whiteware Instrument Colorimetry and Spectropho- Glass Woodworking tometry Refractories Glassblowing Optical Instruments Enameled Metals Construction Stores and Tool Radiometry Heavy Clay Products Room Atomic Physics, Radium, and Cement and Concreting Mate- X-Rays rials Operation of Plant Photographic Technology Masonry Construction Power Plant Interferometry Lime and Gypsum Electrical Chemistry Stone Piping Paints, Varnishes, and Bitu- Simplified Practice Grounds minous Materials Wood, Textiles, and Paper Construction Detergents, Cements, Corro- Metal Products and Construc- Guard sion, Etc. tion Materials Janitorial