PACKAGING AND TRANSPORTATION OF CHEMICALS
Linings for Steel Shipping Containers L. F.
MCKAY,
Vice President, Ohio Corrugating Co., Warren, Ohio
In order to be useful for shipping a variety of chemicals, steel containers must be corrosion resistant • . . And in order to be corrosion resistant they must have linings adequately fabricated and tested for proper surfaces O T E E L shipping container manufacturers are currently busy in developing lined containers to be used for the packaging of a wide variety of materials which are not now satisfactorily packed in steel because of contamination of the product or chemical attack and corrosion of the package. Your industry estimated that the potential market for containers with highly chemical- and corrosion-resistant linings might be as large as the present requirement for unlined containers. With this in mind the Steel Shipping Container Institute, Inc., is sponsoring a research program at the Battel le Memorial Institute, Columbus, Ohio, which is directed toward the improvement of corrosion-resistant linings for steel shipping containers. Battellc is now actively engaged in research work on this problem. T h e research committee of the industry desired that the program be directed toward improving the corrosion resistance of steel shipping containers by developing better coating methods or organic finishes or both. The collection of useful data on steel properties, corrosion, and testing or fabrication m e t h ods which will help improve production efficiency or quality of steel shipping containers was also considered to fall within the scope of this investigation. Answers Undertaken Since it was the opinion of this research group that the surface preparation of the steel used was very important and that currently available coatings are probably otherwise adequate for many requirements, first emphasis was placed on the study of surface conditions and pretreatments. Specifically, therefore, the work on this program was designed to answer the following questions in order: (1) What are the effects of metal surface conditions on organic coating performance? (2) What are the relative merits and cost of different methods of preparing steel surfaces for organic coatings? (3) What are the relative resistances of various coating systems t o me-
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chanical abuse and attack by specific products? For the evaluation of surface conditions, representative steels were supplied by several container plants. T h e hotrolled steel supplied by each plant was sorted into two groups, tightly scaled and scaly. The cold-rolled steel was sorted into good and marginal-quality groups. Procedure The effect of the surface conditions on coatings performance was investigated by automatically spraying measured thicknesses of representative and widely used commercial coatings to the varioussurfaces and then placing the coatingin contact with corrosive chemicals in test cells. The coatings selected were an unpigmcnted phenolic, a pigmented phenolic, and a pigmented vinyl. Test chemicals chosen were (a) 1% hydrochloric acid solution, (6) 1% detergent (Dreft) solution, (c) formaldehyde (3638% grade), and (d) carbon tetrachloride. These four were selected as being representative of some of the most difficult materials t o package. The cell was designed for evaluating coatings o n flat panels without the complications of edge effects. Instead of perfectly flat panels, dimpled panels* which simulate the curvature of the rolling hoop or beads in steel container bodies may be assembled at one or both ends of the cell. This cell has also been satisfactorily used to evaluate coatings on the slightly curved surface of drum bodies. The thickness of dry coating films on flat or slightly curved surfaces was measured with the General Electric type A plating thickness gage. Since the measurement of film thickness by the General Electric gage is limited t o flat or only slightly curved surfaces, cross sections of dimpled area> of test panels and rolling hoops from containers were examined under the microscope t o determine coating thickness. Specimens were prepared by
CHEMICAL
mounting in babbitt metal the sections cut from the dimple or rolling hoop and then cross-sectioning and polishing. The surface pretreatments are being evaluated b y applying the selected commercial coatings over them and testing for impact resistance and corrosion resistance of the systems i n test cells Reverse impact tests were conducted with an apparatus adapted from Interchemical Co.'s tester consisting of a two-pound weight which can be dropped through a measured height to strike a blow on a 0.75-inch-diameter hemispherically tipped form in contact with the uncoated side. In addition, coating continuity over the various pretreatments is being investigated by a method similar to that used by Shaw and Moore i n their work on paint films. Effectiveness of Treatment and Surface Roughness Surfaces representing each of the pretreatments have been measured for surface roughness with a physicist's research profilometer which measures in microinches the deviation from a theoretical mean. Tests have also been m a d e t o determine effectiveness of the treatments in removing scale and, in some cases, the type of surface roughness obtained. T h e kind of surface roughness of steels was shown by photomicrographs of tapered sections cut through representative panels a t a small angle with the plane of the surface to give an apparent magnification. The typical pretreatments selected for evaluation include ordinary cleaning systems such as solvent wiping, vapor degreasing, alkali cleaning, and emulsion cleaning. Several chemical treatments tire also being investigated. T h e y are phosphatizing, sulfuric acid pickling, and phosphoric acid pickling. Mechanical pretreatments being investigated include sand blasting, grit blasting, blasting with a slurry of ^and and water, and wire brushing. An evaluation of coatings available for the lining of shipping containers is progressing simultaneously with the evaluation of surface pretreatments. For the initial evaluation of coatings, a vaporblasted surface was chosen. This surface is clean and free of scale. I t offers
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better adhesion under impact conditions to pure phenolic coatings than a clean but otherwise unchanged h o t - or cold-rolled surface but does not give such good adhesion tha-t possible i m provement in other coatings are unobservable. This surface c a n be reproduced with a fair degree of accuracy. T h e coatings applied over the vaporblasted surfaces are being evaluated for impact resistance and those which look promising are further evaluated for resistance to chemicals in test cells. Film continuity tests are being made on all panels for test cell evaluation and those showing any appreciable porosity are replaced with other panels. A wide variety of both proprietary and formulated coatings are being evaluated. Test Results Early in the test cell evaluation of coated panels representing the various types of steel received from a number of container manufacturers, it became evident that failures predominated in the dimpled areas of test panels. T h e cause of failure was investigated b y mounting sections of the dimple i n babbitt metal and examining the cross sections under a microscope. It was found that t h e application of coatings t o a measured thickness of about 0.4 mil o n the flat surfaces gave him thicknesses within the dimple as low as 0.1 mil or even less. Film continuity within the dimple was determined by a n electrographic printing method. It was proved that porosity or film discontinuity was the dominant cause of earl}- failure within the dimples. Since coating thickness and continuity obtained within the dimples had been so surprisingly low as compared to those obtained on the flat surfaces, it was surmised that thin and porous films were probably the cause of early failures in rolling hoops reported b y a number of lined container manufacturers. Therefore, the rolling hoops of several representative commercially lined containers were examined for coating thickness and continuity. It was found that t h e coating in the rolling hoop was generally extremely thin on one side of the hoop and in some cases almost nonexistent. Evidently this is the side of t h e hoop which is difficult to reach with a spray gun set at a 45° angle t o the horizontal steel container shell, which was general production spraying procedure. The examination of coatings in the rolling hoops disclosed the presence of sharp gouges within the hoop, which were caused b y the swedge dies. These sharp gouges cannot be satisfactorily coated. T h e weld section was also found t o possess many sharp edges which cannot be satisfactorily coated. T h e coating continuity on the walls
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of the several commercially lined drums was better than that within the rolling hoops. Nevertheless, considerable discontinuity was shown by all but the most heavily lined containers. Sections were cut from the walls of three commercially lined drums. These coated sections were tested in cells with \c/o hydrochloric acid and a 1% Dreft solution. The sections cut from two of the drums were severely corroded or blistered after less than 30 days' contact with the test chemicals while the third failed in less than 60 days. If the perfect coating from the standpoint of chemical resistance, adhesion, flexibility, and impact resistance, and the best possible surface conditions for application of that coating, wore now definitely known, they would be of little avail if the job of application is not thoroughly developed. It is the responsibility of each manufacturer of lined containers to develop his spraying technique to ensure adequate coverage over the entire interior surface of the container. Effect of Surface Conditions In a study of the effect of surface conditions on coatings performance, it was found that early test cell failures are apt t o occur in thin films of coatings applied over loose, rough scale. These early failures under static test cell conditions may be due to poor coverage because of the surface roughness. Under nonstatic conditions loosening of the scale with accompanying loosening of the coating would almost surely be an additional problem. I n a good many cases removal of the heavy, loose scale from the dimpled areas of panels- by the forming operation resulted in a better coated area within the dimples than was obtained on the flat areas around the dimples. In contrast, good hot-rolled steels with tight scale provide as good or better surface, on the average, for coating than "good quality" cold-rolled steels under the static test cell conditions. In fact, the best performance obtained seemed to be from a surface containing tightsmooth scale. However, under impact conditions, it is probable that there would be a loosening of scale and a t tached coating resulting in early failures. Impact tests on panels coated with pure phenolics over medium-scaled areas have shown that considerable scale is removed by only a slight amount of impact. For this reason it will be necessary to remove scale for satisfactory coatings performance. However, even if the smooth tight scale could be used without serious injury to reverse-impact resistance, the problem of securing sufficiently uniform hot-rolled steel is obvious. I t is difficult t o explain the apparently somewhat better test cell performance of coatings applied over hot-rolled steel
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with smooth, tight scale than of coatings applied over clean cold-rolled steel. Possible explanations may be somewhat better adhesion of the coatings to the hot-rolled steels under static conditions and protection offered by the scale itself. However, as previously mentioned, impact tests have shown that scale is undesirable for good adhesion under impact conditions. Other test cell work showed that early failures can be expected over heavily rusted areas on cold-rolled steel. H o w ever, over light rust or rust stain early failures may or may not develop. I n any case, it is necessary to remove rust before application of coatings to assure proper performance. Effect of Surface Pretreatments Rough surfaces obtained b y grit or sand blasting are difficult to cover completely with thin films of coating. It was necessary to apply approximately 50'4 more coating over these blasted surfaces to obtain a measured thickness of 0.4 mil than was necessary over ordinary cold- or hot-rolled surfaces. E v e n with this additional coating, coverage is extremly poor as compared with the ordinary cold- or hot-rolled surfaces. The extreme porosity in thin films of coating over those blasted surfaces, which we consider to be of medium roughness, resulted in rapid failure in test cells, as was expected. We can expect to improve the poor performance of coatings applied over medium blasted surfaces by applying thicker films to assure good continuity. Coating continuity obtained over a comparatively smooth sand-blasted surface (35-50 profilometer reading), which will be further discussed later, is about equal to that obtained over ordinary hot- and coldrolled surfaces. The test cell evaluation of the various surface pretreatments, with one, two, and three coat films of the three commercial coatings applied, was shortened by limiting tests to only one chemical: the V/o detergent (Dreft). Thus far, the work shows no appreciable difference in coatings performance whether over phosphated, pickled, or chemically cleaned surfaces. However, tests are not complete; consequently definite conclusions cannot be drawn. Those differences in performance which were so far observed seem to be a result of coating continuity rather than surface pretreatment. Obviously the effect of the pretreatment has had little effect on coating continuity, which is t o b e expected since surface roughness is not appreciably changed by any of the chemical treatments. The effect of the surface pretreatments on the reverse-impact resistance of the two commercial pure phenolic and the one vinyl coating used for this study has been rather definitely estab3699
lished. The reverse-impact tests were performed on one- and two-coat systems. Regardless of the type of surface pretreatment (including the blasted surfaces) the phenolic coatings cracked even under slight impact. T h e y are inherently poor in flexibility. With all except one of the chemical pretreatments, whether the surface was merely cleaned or chemically changed, the coating was loosened and removed from th surface by only slight impact. Thus no appreciable difference in reverse-impact resistance was obtained from the various chemical pretreatments aside from the one exception already mentioned. T h e one exception noted was a phosphoric acid pickle which gave appreciably improved adhesion under impact conditions, but only with hot-rolled steel. Impact Resistance under Various Conditions The better flexibility of the vinyl coating in films of less than 1 mil thickness generally resulted in its considerably better impact resistance. The type of chemical pretreatment seemed to have little effect on the impact resistance of the vinyl. However, more cracking of this coating occurred over hot-rolled steel than over cold-rolled steel, perhaps due to loose scale or surface roughness. I n thicker films (1.4-2.0 mils) this vinyl coating, like the phenolics, required some roughening of the cold-rolled steel for satisfactory adhesion under impact conditions. T h e thicker films were more susceptible t o cracking under reverseimpact, regardless of surface preparation. Medium rough (100-200 profilometer reading) and smooth (35-50 profilometer) blasted surfaces were both found t o give very substantial improvement in the impact resistance of pure phenolic coatings as well as thicker films of the vinyl coating. However, the smooth blasted surface is most desirable because of ease of covering. The surface roughness of panels representing all the various pretreatments under study were measured with the profilometer to correlate surface roughness with reverse-impact resistance. Untreated cold-rolled steel measured 5 t o 20. Hot-rolled steel measured 40 to 60. T h e chemical pretreatments, in general, gave comparatively slight change in the surface roughness of either hot- or coldrolled steels. T h e medium-rough grit and sand-blasted surfaces measured 100 t o 200 and the one smooth sand-blasted surface, which was specially prepared by one company, measured 35 to 50. T h e impact tests showed that good adhesion of pure phenolic coating under impact conditions was obtained over the blasted surfaces, even when roughness (35-50 profilometer) was only about equal t o the roughness of untreated hotrolled steel. Intermediate adhesion was obtained over the phosphoric acid-
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pickled panels, although surface roughness was also not greatly different than untreated hot-rolled steel. Thus it seems that the better impact resistance over blasted surfaces as compared with cold-rolled surfaces can b e explained by surface roughness. However, surface roughness alone does not explain the difference between the various other surfaces. Obviously factors other than surface roughness are important. Scale is one of the important factors in the adhesion of coatings under impact conditions. This was shown by examining the under side of the coating flakes which were loosened from the various pretreated surfaces by impact. The clean removal of the coating from all cold-rolled steel panels showed what was to be expected if no scale were present. The under surface nf the coating loosened from untreated hot-rolled steel was black with scale even though the scale had seemed to be tightly adherent. So were the flakes of coating removed from the phosphated surfaces showing as expected that phosphatizing alone had not removed scale. The flakes of coating removed from the acidpickled surfaces were clean, showing that scale had been removed by pickling. T h e loosening of scale from the hotrolled steels resulted in the poor adhesion of the phenolic under impact conditions. Phosphoric acid pickle, which removed the scale apparently without critically changing surface roughness, resulted in improved adhesion, but the improvement was considerably less than the adhesion obtained on the blasted surface of about equal roughness. The sulfuric acid-pickled surfaces, which are also of about equal roughness, showed poor adhesion. It was therefore evident that the kind as well as the degree of surface roughness is also an important factor in the mechanical bonding of the pure phenolic coatings to metal surfaces. The kind of surface roughness obtained b y some of the surface pretreatments was investigated by making photomicrographs of tapered sections of test panels which were prepared as previously described.
of coatings applied over it and if rough and heavy may cause early failure in protection against corrosion, even undex static conditions. The elimination of oil, grease, and dirt from the metal surface will also be necessary. These conclusions are in accordance with our expectations. However, the tests were conducted to substantiate these expectations. Therefore, a pretreatment capable of removing scale if hot-rolled steel is used, or capable of removing surface rust if cold-rolled steel is used, will be necessary. In order to obtain the optimum impact resistance with the currently used phenolic coatings, which are among the best known in chemical resistance, a certain amount of surface roughness seems t o be necessary for mechanical bonding of the coating to the metal. Kind, as well as amount, of roughness is also important. However, the surface should not be so rough that coverage is difficult. The surface which best meets these conditions is the smooth blasted surface (35-50 profilometer reading). In addition to desirable roughness, this surface is clean and free of scale. The possibility of obtaining the smooth blasted surface may b e difficult undex actual production conditions. I t will probably not be desirable t o use sandblasting in the plants. T h e fine sand necessary could be used only with an air or suction blast. I t could not be used with a rotating wheel (centrifugal blast) because of rapid wear to equipment and deterioration of the sand particles. Blasting with a slurry of sand and water may be the answer. Mechanical wire-brushing is also beinp investigated . Evaluation of Commercial and Formulated Coatings Before final conclusions can be drawn regarding surface preparation it will be necessary to select definite coatings for container linings. Although the currently used phenolic coatings are resistant to many chemicals, t h e y are poor in flexibility and reverse-impact resistance, as previously mentioned. Vinyls are satisfactory for many applications but are not resistant t o many solvents A wide variety of commercial coatings is available which m a y find application as drum linings for specific products. They are based on the following resins. phenolics, vinyls, modified alkyds, furfuran, furfural, synthetic and natural rubbers, Epons, and numerous combinations of these and others, t o mention only a few. Obviously the most desirable coating would have good adhesion and impact resistance over smooth steel surfaces so that pretreatment of cold-rolled steel would be limited t o a simple cleaning operation, and pretreatment of hotrolled steel limited t o scale removal
Effects of Blasting Blasting resulted i n severe undercutting and general roughening of the surface*. Vapor blasting produced about the same general type of surface but much finer. The phosphoric acid pickle caused some roughening of the surface with little or no undercutting. I n the selection of the type surface which seems best for currently used coatings, as indicated b y the results of tests completed thus far, we feel that certain conditions can definitely b e ruled out. Surfaces which contain rust cannot be used with any degree of certainty of good performance. T h e presence of scale will impair the impact resistance r u c Hit i r
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without special operations to roughen these surfaces. Therefore, a coatings investigation now in progress is directed toward the development of coatings systems with substantially better reverse-impact resistance than the phenolics, yet retaining good chemical resistance. A number of coatings, some proprietary and some formulated, appear promising in initial tests. However, in most cases the chemical resistance tests have been under way only long enough to eliminate the very poor coatings. Additional time will be necessary to evaluate the more resistant ones. Among the first of the promising coatings systems was an unpigmented size coat (proprietary) topped with new purephenolic coatings of improved flexibility. However, the new phenolic coatings alone did not give good performance when subjected to reverse impact because of poor adhesion. Phenolic resins plasticized with polyvinyl butyral show some promise. Good resistance to reverse impact was ob-
tained with sufficiently high percentages of poylvinyl butyral. However, the higher percentages of polyvinyl butyral may result in insufficient chemical resistance for many products. An experimental hydrocarbon resin coating containing no oil looks as if it may be satisfactory for some products. I t showed good resistance t o reverse impact even over smooth cold-rolled steel. One Epon resin (pure epichlorhydrin-bisphenol modified with a catalyst to facilitate heat conversion) showed good resistance to reverse impact and is now being evaluated for chemical resistance. Some proprietary coatings of unknown composition and other experimental coatings also show promise in initial tests. Most of the- coatings which have been evaluated thus far are unpigmented. It is believed that considerable improvement may be obtained in some of them by proper pigmentation. The investigation of proprietary and formulated coatings is continuing. We feel that a great deal has been ac-
complished from the work that has been done on this research program. Much more should be accomplished i n t h e near future. Future Work A substantial improvement has been made in lined containers through the utilization of the information which has already been made available t o t h e members of the Steel Shipping Container Institute. I t has been shown that proper surface preparations and application procedures are of prime importance. The program of coatings evaluation now under way should materialize into the development of improved systems. Future work will be directed toward this improvement of organic coatings for drum linings. The properties obtainable in the coatings will have the final deciding effect on the selection of surface pretreatment—that is, if satisfactory adhesion under impact conditions can be made an inherent part of the coating, then roughening of the metal surface will not be necessary.
PUKAQING AND TRANSPORTATION OF CHEMICALS
T a n k Cars H RONEMEYER, E . ddu u PPont o n t dde e N emours & o . , IInc., nc H.. JJ.. G GRONEMEYER, E.. II. Nemours & CCo.,
T a n k c a r s w e r e initially u s e d a s o i l c a r r i e r s b u t h a v e b e c o m e a method o f transportation used t h r o u g h o u t t h e c h e m i c a l i n d u s t r y f o r bulk s h i p m e n t s • • • R a i l r o a d s , private owners, and regulatory agencies f u r t h e r their u s e J_ HE utility of the railroad* ha* been amplified by the tank car, a service that only an extensive study has revealed. It embodies a great idea of quick, safe, and economical transportation of liquids. The first tank car made its appearance in 1865. I t was simply a flat car with two iron-hooped wooden tanks, each tank having a capacity of about 1,500 gallons. The steel tank car. the first of which was built in 1871, quickly led to the modern tank cars which now carry anywhere from 3,000 gallons to 12,000 gallons per car. Lately new cars were built with a capacity of 16,000 gallons per car. With this progress must be coupled railroad progress in track mileage. The aggregate length of all American railroads in 1830 was only 40 miles. Ten years later the mileage count was 2,755 miles. I n 1900 it was 192,941 miles and last year the published total was 284,340 miles. Today the United States has the largest, best equipped railroad system in the world. Tank car progress has been in keeping with this expansion. Because of the specialized problems VOLUME
involved, railroads do not furnish tank cars. Therefore, industries needing tank cars have to provide their own rolling equipment, for which they are inadequately compensated, investment and upkeep-wise, by a mileage allowance which is at the present time 2 cents per mile, both loaded and empty over railroad lines. Should the aggregate empty mileage of any owner's cars at the close of a yearly period exceed the aggregate loaded mileage on the lines of such railroads, such excess empty must be paid for by the owner, either by an equivalent loaded mileage during the succeeding six months, or a t tariff rates on such excess empty mileage, now set at anywhere from 14 to 23 cents per mile, depending on territory. Ownership Definitions and Designations Cars of private ownership are denned as cars having other than common carrier (railroad) ownership—that is, cars owned by individuals, firms, corporations, are companies. The affix " X " to reporting marks is the symbol of private
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Wilmington, Del. ownership for tank cars, like "GATX," "SHPX," "DOWX," "GCX," etc. Railroad transportation and operation of privately owned tank cars, mechanically, is in accordance with Association of American Railroads Code of Rules governing the condition of and repairs to freight cars for the interchange of traffic. Each railroad is responsible for the condition of all cars on its line and must give to all equal care as to inspection and lubrication. The car owner is responsible and therefore chargeable with repairs to cars necessitated by ordinary wear and tear in fair service by the safety requirements and by the standards of the Association of American Railroads. Numerous Committees The Manufacturing Chemists' Association Tank Car Committee works with the many technical committees of the Association of American Railroads in working out improvements in car construction. The Association of American Railroads' Arbitration Committee has jurisdiction over the important issues of providing an equitable basis for railroad charges covering repairs, as well as means of settlement for damage to tank car through unfair usage or improper protection by the handling company. T o provide more equitable handling of tank 3697
