June, 1923
I X D USTRIAL AND ENGINEERING CHEMISTRY
555
LMATERIALS OF CHEMICAL-EQlJIPMENT CONSTRUCTION SYil/IPOSBUIM ~~
Papers presented before t h e Division of Industrial and Engineering Chemistry a t the 65th Meeting of t h e American Chemical Society, New Haven, Conn., April 2 t o 7, 1923. Some of the papers in this symposium were printed in the M a y issue, a n d others will appear in July.
Nickel and Mo'nel Metal in CorrosionResisting Machinery By Robert J. McKay INTERNATIOZAL
~SICKEI. Co., 67 WALLS T . , h'Ew YORK, N. Y.
r\'THE MODERN chemical plant for quantity production suitable machinery for handling active chemicals is a most important problem. .The material of which it is made and which is exposed to the action of the chemicals should be metal to assure mechanical efficiency.
I
FACTORS INFLUENCING EFFICIENCYOF A CORROSIONRESISTINGMATERIAL In selecting a particular metal for corrosion-resisting machinery, several complementary factors must be considered. In any special case one may require more careful thought and attention than another, but all are essential. At no time can any of them be disregarded without the danger of serious mistakes in equipment. STRENGTH-The first to consider is the strength. The relatively high strength of metals as compared with other materials is the reason metallic machinery is mechanically more efficient. The tensile strength or ultimate breaking strength is of evident importance, but for most machinery the yield point is even more important. I n addition, the resistance to fatigue and particularly the impact resistance deserve consideration. Much machinery is subjected to sudden shock a t some time in its life and a good deal of machinery is eventually destroyed or worn out by such shocks. AMEXABILITYTO WoRKING-Another important consideration is the amenability of the metal to various types of working. It should be reasonably easy to machine, forge, weld, solder, cast, etc. Ease of working not only makes it possible to build the machine originally in the most efficient shape, but it greatly facilitates repair. Cheap and rapid repair in machines handling corroding chemicals may be more important than original efficiency. CORROSION RESISTANCE-The true rate of the attack of the chemicals to be handled on the metals of the machine is of fundamental importance, It should be noted, however, that determining the loss of weight or change in appearance of a sample of the metal standing in contact with the material in question for a period of time does not determine this rate. The right kind of a laboratory test may furnish data of practical importance, but unless especial care is taken to duplicate practice in the test, the results are liable to be misleading and the conclusions worse than useless. The rate of agitation, amount of aeration, and amount of abrasion must have even more accurate and quantitative control than the temperature and concentration. Even when true results are determined they are not the only criteria on which the use of the metal should be based. A greater rate of corrosion may be overshadowed by a difference, for instance, in the tensile strength or in the working qualities of the metal. There are two effects to be considered in interpreting corrosion tests-first, the rate of wear of the metal as it affects its length of life; and second, the amount of material absorbed as it affects the purity or appearance of the product being handled. Processes often stand or fall on one of these to the exclusion of the other, and laboratory tests should be directed accordingly. EXTENT OF KNOWLEDGE-The extent to which the properties of a metal are known should affect its choice for machinery. Often machinery built for one purpose will later be required on a special job for another purpose or even used entirely on another process. If it is a metal of little known properties, pre-
diction cannot be made as to what it will do when subjected to new conditions. This holds for physical properties, but more especially for chemical corrosion. Efficient repair, for instance, depends on the possibility of forging, machining, etc., but it also depends on whether the man in charge of the machine knows they are possible and whether the methods are known to the repair man. I n regard to resistance to corrosion it may be desired to subject the machinery to entirely different classes of corroding chemicals from time to time. Thorough knowledge and experience in the effect of various chemicals may make the machine useful in different processes. If this knowledge is lacking an expensive machine may be uselessly ruined in attempting changes. STANDARD SUPPLY AND PROPERTIES-It is O f considerable advantage to use metal which is standard-that is, metal which is used by a large number of manufacturers and whose supply is therefore constant-and which is available in a large variety of forms. Obviously, this condition makes the purchase of new machines, and of replacement parts for old machines, simple, while in using a special metal every eventuality must be anticipated well in advance in order to keep machines running. The composition of the alloy should be permanent. Changes in composition interfere with the standardization of manufacturefor. instance, they may cause unlooked-for galvanic effects of serious consequence.
ADVANTAGES OF NICKELAND NICKELALLOYS Nickel and various nickel alloys have long been known to chemists as valuable metals for certain purposes in the laboratory and plant. Their strength, amenability to work, and resistance to corrosion are in many cases well and widely known. However, the supply of nickel and nickel alloys has a t times been irregular enough to discourage their use by chemists and engineers. Recent progress in the difficult metallurgy of nickel has, however, stabilized the supply, and this has been accompanied in many cases by parallel progress in the metallurgy of alloys. Several large new plants, modern in design and equipment, have gone into production during the last few years. They not only produce virgin metal by up-to-date processes with research and technical control, but also many forms of material which formerly were only available through shipment of the raw material abroad, and reshipment of finished products to America or through cooperative arrangement between several metal producers, which delayed the manufacture and interfered with the supply. Naturally, this progress is accompanied by a closer control and better quality of the product of the furnaces, as well as a more dependable supply of the more finished products. It has also resulted in important price decreases and in redoubled efforts by other producers of nickel and nickel products to increase the efficiency of their operations in proportion. Quantity production of hot-rolled, pure nickel sheets is a part of this progress. These sheets are taking the place, in many cases, of the more expensive, imported, cold-rolled product. Cold-drawn, seamless, pure nickel tubing in pipe and tubing sizes is another important product being introduced as a n addition to the former production of all the common forms, as bars, rods, etc. Pure nickel and nickel alloys are therefore of more interest for the construction of chemical machinery than ever before. Research laboratories which during the World War were interested in production problems are now studying the properties of the finished metals and the innumerable problems which occur in their use. The Mellon Institute is
556
IhTDUSTRIAI, A N D ENGINEERING CHEMISTRY
carrying on researches on the resistaiice to corrosion of nickel and monel metal, and their application to various chemical processes. The Bureau of Standards is making determinations of interesting physical properties of various wades of nickel. i n d laboratories or the large manufacturers are studyi n g commercial problems, tabulating the properties, and standardizing the rating and production of n i c k e l and its alloys. Monel metal is probably the most interesting nickel alloy to the chemFIG.~-CAST-NICKELFUSION POT ical engineer. It is produced, by smelting the ore of the Creighton Mine, Sudbury District, Ontario, and refining as though it were pure nickel, but without separating the copper from the nickel as it occurs in the ores. The resulting alloy is a solid solution of nickel and copper containing 2.3 parts nickel to 1 of copper. The solution pressure is comparatively low, being, as far as has been determined, but slightly higher than copper. This and the properties due to the high percentage of nickel make it appropriate for corrosion-resisting machinery. Therefore, some of the places in industrial chemical practice where monel metal and pure nickel have been tried and proved successful by prolonged experience will be discussed briefly. Such instances should bring to mind many of the other possibilities not yet proved in service.
SERVICEAPPLICATIOKS One typical use in corrosion-resisting machinery is in pumps handling corroding liquids, as pump rods and shafts in various centrifugal pumps. If the materials to be handled are more corrosive, impellers, plungers, and, in extreme cases, all parts may be made of monel. Another considerable use is filter cloth. Such cloth has been manufactured from monel-metal wire for several years.
The first cloths made in the infancy of monel-metal wire were rather crude, but have been improved until now the several grades of filter cloth available are efficient and dependable. These metal cloths form filter cakes well, are strong, and resistant to corrosion and abuse. They may be readily cleaned by scrapers, countercurrents of water or steam, or solvents. They may be used to replace duck cloths, but it is probably better practice to use presses with filter leaves designed for the purpose. The possibility of using metal cloth offers many advantages ili design. Various types of meters are more dependable owing to their judicious use of monel metal. In water meters for slightly corrosive liquids, gears or other rapidly wearing parts, or parts that may stick, are of this metal. If the meter is to handle more corrosive liquids, it can all be made of monel metal or nickel. Gas and oil meters use monel-metal parts. Flowmeters for high temperature steam use monel-metal disks because they are little eroded by steam. Many applications of monel metal hinge on this unique resistance to the action of steam at high temperatures and pressures. The high strength, resistance to wear, and the fact that monel metal does not usually depend on protective coatings for its corrosion resistance make it well adapted to conveying machinery in the form of buckets, and sprockets and
FIG 3-MONEL-METAL
PUXP
chains. Automatic weighing-machine parts in contact with corrosive materials, such as chutes, buckets, and latches; the supply tank, pipes, and nozzles of bottle-filling machines halidling liquids; and the valves and pistons for semiliquidfilling machines are monel or nickel if corroding material or foodstuffs which may be contaminated are handled. Pails, dippers, and all shapes of containers are readily formed of both metals by stamping, welding, and soldering; the use for fabricating linings and agitators in mixing machinery, autoclaves, and digesters, and all forms of tanks is therefore extensive. As seamless tubing, nickel is used for air agitators. In soldering and welding, ,corrosion by galvanic action must be taken into account. With half and half and high-tin solders, no trouble will usually be experienced. A weld may have no visible defects and still contain oxidized spots which will give way rapidly under galvanic corrosion. The way to prevent this is to have the welding done only by skilled and dependable men who have the foregoing facts in mind. In fabricating joints by bolting, riveting, or spot welding, corrosion by quasi-concentration cells1 should be guarded against. This may occur, for instance, at a place where two flat surfaces overlap each other, leaving a crack wide 1 McKav “Electrolvtic Concentration Cell Corrosion,” Trans. A m . Electlochem. Soc.. 4 1 (1922), 201. ~
FIG.Z-ALL MoNSL-METALFILTER
VOl. 15, N o . 6
-
I
INDUSTRIAL A N D ENGINEERING CHEMISTRY
June, 1923
enough to contain liquid but narrow enough to prevent free flow while adjacent to the crack free circulation goes on. Differences in concentration occur between the liquid in the crack and the free-flowing liquid. The magnitude and source
557
in construction that they can be economically operated, though built of metal of relatively high cost. Various types of drum, belt, and centrifugal machinery have thus been built for drying and filtering, using monel metal for screens, belts, centrifugal rotors, etc. These include drum driers and filters, combination belt filters and driers, centrifugal separators and centrifugal spray driers. These machines are, of course, of extended use without nickel or monel-metal parts, but are often applicable with these metals where they would not be otherwise. It is well aot to lose sight of the fact that the cost of a repair is not usually represented by the actual cost of materials and labor in the repair itself, but rather by the interference with production which it occasions. I n dyeing and bleaching it has been found economical t o manufacture rotary machinery entirely of monel metal, and to use tank linings and baskets made ,of monel. For job work on different colors in the same machine this is especially true, on account of the ease of cleaning monel.
PERTIXENT PROPERTIES
FIG &-FILTER
I N S T A L L A T I O N WITH
MONELCLOTH
of the electromotive force are the same as in concentration cells. The author has measured corrosion by such cells under service conditions proceeding a t fifty times the normal rate. The widespread damage from these cells has not been sufficiently recognized. They attack all metals under the ' described conditions. Often special parts of apparatus are subject to exceptionally severe service, owing to the rate of movement of the corroding medium or other special conditions. Rapid flow of the medium affects the rate of corrosion by changing the concentration in the contact film. This has been shown in recent papers by Speller2 and others on the corrosion of iron pipes. Rapid flow also removes protective films and particles of the mela1 itself by erosion, so that, in general, parts subjected to rapid flow corrode rapidly. It is often economical to manufacture them of nickel or monel metal, even though the rest of the niachine is made of cheaper metals. Thus, certain parts of valves, such as seats, rings, and stems for valves for compressed and liquefied gases including chlorine, blast gates for controlling the flow of various gases under low pressure, gas-exhaust fans, ventilators and stacks for destructive fumes, agitators of all kinds, and parts of centrifugal gas-scrubbers, are made of nickel or monel metal. 'L'aluable uses of nickel and monel metal for special parts due to conditions other than the velocity of the corroding medium are: plugs for oil stills, used to prevent sticking and unequal expansion; spuds for steel barrels, which prevent failure due to corrosion and wear of threads; scrapers and screens, where corrosion is combined with abrasion; gasburner tops subjected to hot gases; parts of recording instruments to resist heat, amalgamation, and other corrosion; molds for various molding and tablet-manufacturing machines; dipping baskets for pickling, plating, and heat-treating; and screens for crystallizing evaporators. Being of high strength, monel metal has been considerably used as a reinforcing material for less corrodible but physically weaker materials. Instances of this are monel reinforced pottery valves, asbestos monel filter cloth, and other asbestos cloth. For large production by a continuous, rapidly moving process, machines may be designed so small and compact I
2
Speller and Kendall, THISJOURNAL, 1 5 (1923), 134; Wilson, I b i d
(1923), 127.
, 15
The general properties of nickel and monel metal are available in several places in the l i t e r a t ~ r e . ~Some of the properties are especially pertinent to the present symposium, and are discussed here. The ultimate tensile strength of hot-rolled monel metal is about 90,000 lbs. per sq. in., and of hot-rolled nickel about 75,000 lbs. per sq. in. The yield point of monel is 50,000, and of nickel 25,000 lbs. per sq. in. The high strength of these metals as compared with other acid-resisting metals makes them exceptionally well adapted for machinery. Monel metal has practically the same strength as mild steel. These metals cannot be tempered in the ordinary sense, but considerable variation in ultimate strength, yield point, and hardness is obtained by proper forging and annealing. They may be machined, forged hot or cold, brazed, soldered, and welded with gas or electricity. They harden rapidly when worked cold, so that-as compared with copper, for instance-frequent annealing is required in spinning. Annealing must be done in a carefully controlled reducing atmosphere free from sulfur. I n hot forging the temperature
Fro.
~--MONEL
GEARS, PINIONS, ETC
IX
L I Q U ~METER D
of 1100" C. should not be exceeded. It is thus possible, in fabricating machinery from monel metal and nickel, to perform practically any desired operation except producing a high temper. 3 Bur S t a n d a i d s , Bull. 100; Chem. M e t E n g , 24 (1921), 17, 73, 261, 291, 375, 558, 649, Brown and Thompson, Trans. A m . Insl. M i n z n g M e t . Eng., 64 (1920), 417.
558
INDUSTRIAL A N D ENGI NEERIXG CHEMISTRY
When worked cold the strength and hardness of metals increase, and their ductility decreases. This condition is accompanied, of course, by a breaking u p of the large grains formed in annealing into small ones. Thus, under ordinary circumstances soft, ductile metal is accompanied by coarse grain. I n drawing or deformation, the metal gives in a direction determined by the axis of the grain, and when the grain is large this effect shows up as depressions in the surface which may open into cracks extending completely through sheet metal. This has been a drawback in drawing and other work, and has led to a research on the subject by the metallurgists of The International Nickel Company. The study has developed a method of combined working and heattreating by which nickel and FIG.6-MONEL AGITATOR A N D LIN- monel-metal sheet or rod are I N G I N M I X I N G KETTLE produced with a very high ductility and still with fine grain. The importance of resistance of apparatus to shocks and breakage has been emphasized. Impact resistance is the best measure of this and the following comparative tests are a p r ~ p o s : ~ IMPACT PROPERTIES O F I Z O D TEST
Cast iron Rolled brass rod
Forced - - - _ - - canner --==-Wrought iron
Mild steel Hot-rolled monel metal
Energy Absorbed Ft.-Lbs. 1 23 46
58 77 114
vARIOUS METALS Energy Absorbed CHARPYTEST Ft.-Lbs. Cast aluminium 9 Copper bars 35 Chrome nickel steel (annealed) 83 Hot-rolled monel metal (Average of 6 tests) 163
The corrosion of metals has been befogged with much data and experimentation of a doubtful character. At the present time attention is directe'd to the question by important research organizations and technical societies, and in the next few years many of the problems should show important progress. The data on monel metal and nickel have been kept as dependable as possible under the circumstances, and recent researches have thrown considerable light on their corrosion. Sickel owes a great deal of its corrosion resistance to its tendency to become passive under highly corrosive conditions. It is fairly high in the electromotive series of metals. Monel metal, on the contrary, is apparently low with reference to this series, being in nearly the same position as copper, or but little above it. The effect of nickel in producing passivity is also evident in monel metal. Thus, as would be expected, monel metal is very resistant to acid corrosion, because it cannot directly replace hydrogen in combination. It will successfulIy resist direct acid attack, even when the hydrogen-ion concentration is comparatively large, as in 10 per cent sulfuric acid. It is only attacked where a considerable hydrogen-ion concentration is accompanied by the presence of another radical which easily decomposes to combine with the metal. Thus, while monel metal will withstand the action of 10 per cent sulfuric acid somewhat better than nickel, due to the relatively high position of nickel in the electromotive series, in 10 per cent nitric acid the nickel is more passive and is less rapidly attacked. The presence 4 Values from Waltenburg, Chem. Met. Eng , 25 (1921),322; and from private communication from laboratory of G. & J. Weir, Ltd., Glasgow,
Scotland.
Vol. 15, No. 6
of an unstable, strong oxidizing agent in conjunction with strong acidity is the chief condition to guard against in the use of monel metal. It will resist the oxidizing agent b y itself, as shown by its resistance to the action of liquid chlorine and to alkaline bleach solution, such as peroxide and chlorine bleach, and will also resist the acid as shown by its extended use in pickling acids, but the combination produces rapid action. At the same time, if metallic apparatus is desired, monel metal may be used even under these conditions with proper precaution. An instance of this is the use of the metal in machine dyeing with developed colors. In this process a diazo reaction is carried out in the machine, which necessitates the presence of nitrous acid in excess of sulfuric. Such a mixture with the same hydrogen-ion concentration-say, as a 3 per cent nitric acid solution-will attack monel metal approximqtely fifty times as rapidly as the latter. Monel is not ordinarily recommended for use even with nitric acid, but by judicious adaptation of the process it has been found economical to diazotize in nionel-metal machines. Variations in the rates of the various reactions involved with differences in concentration and temperature make this possible with some modification of the accepted process. Another instance is in sodium peroxide bleaching. If, according to usual practice, the solution is made up in a monelmetal tank by adding sulfuric acid, then solid peroxide and then alkaline reagents to the proper alkalinity, the detrimental condition of an unstable oxidizing agent with high hydrogen-ion concentration is produced. If the solution is made up slowly the metal is noticeably corroded, the liquor turns green and at the neutral point copper and nickel hydrates contaminate it, the bleach is weakened and satisfactory bleaching impossible. If the additions are made rapidly, effects are lessened and successful bleaching may be carried out.
FIG.7-FILLING
M A C H I N EWITH MONBI. AND
FILLING HEADS
TANIC
Hon-ever, with a knowledge of the foregoing facts regarding corrosion, a thoroughly satisfactory solution is obvious. If the solid peroxide and other alkaline reagents are added first and the proper measured amount of acid last, with stirring EO that no part of the solution becomes acid, the detri-
June, 1923
IA-D USTRIAL A N D ENGINEERING CHEMISTRY
mental combination of oxidizing agent and high acidity is never present. Under these conditions there is no color in the liquor, no perceptible action on the metal, the liquor is full strength, and bleaching satisfactory. These instances and that of the quasi-concentration cell discussed above show how closely laboratory tests must be checked with practice in order to predict service, and how
Fro. ~ - - ~ . I o x E L ROTORS,E T C , IN SHARPLES CESTRIFCGAL
easily a wrong prediction may be made. Some other conditions that may be mentioned, which have been a t times neglected, are the effects of agitation, erosion, and oxidation by atmospheric oxygen. The author has found the rate of corrosion of certain met& in strong acid solutions multiplied seven times when the
559
solution was saturated with air. Duplicating practice in concentration of dissolved air is complicated by the small amount of oxygen which dissolves from air and its slow diffusion. The solution close to a metal is rapidly denuded of oxygen, and, unless agitation rate and air supply are duplicated closely, results are erroneous. The importance of agitation rate is thus apparent in furnishing oxygen. Erosion is intertwined with agitation, removing coatings, protective or accelerating, and directly attacking the metal. The author has drilled holes through I/&. plates of several acid-resisting alloys immersed in acid by the flow of air from a glass delivery tube under ordinary laboratory pressure. The holes were drilled so rapidly that metal in the immediate neighborhood was not perceptibly attacked. On the subject of erosion the following extract5 is given : The resistance of monel metal to erosion has recently been brought out in a test of which Messrs. G. & J. Weir,Ltd., of Glasgow, have sent us particulars. In this test a number of ’/8-in. nozzles of different makes were inserted in a pipe in an enclosed tank. Opposite each nozzle was arranged a disk of the same material. The pipe was coupled to a direct-acting pump which drew water from the bottom of the tank and sugplied i t to the pipe at a pressure of 250 lbs. per sq. in. Air was admitted to the pump cylinder by a valve to a n extent which caused the piston to pump 1 in. of its stroke. The water was maintained at a temperature of 150’ F. and analysis gave its quality as follows: calcium chloride, 14 g. per gal.; sodium nitrate, 5 g. per gal. ; sodium chloride, 20 g. per gal. ; magnesium chloride, 2.5 g. per gal.; gritty matter, 26 g. per gal.-thus representing a bad feed water. The pump was worked for 500 hrs., after which. . , . . .the appearance of the specimens enables them to be classified with rolled monel metal a t one end of the scale, and mild steel right at the bottom of the list. A monel bronze, formed by adding copper to monel, came second, a nickel bronze third. The nozzles tested included all the commonly used brasses and bronzes, nickel bronzes, also stainless steel and mild steel.
Emphasis should be placed on the fact that monel metal does not rely for its corrosion resistance on protective coatings. The combination of corrosion and wear is, therefore, more easily withstood than where such coatings are influential. 3
Engsneeusng. 114 (1922).
Metallographic Analysis in Criminal Jurisprudence It is said that “there is nothing new under the sun,” and undoubtedly there is much truth in the statement. Yet, life is made more interesting b y the fact that frequently we come across striking new applications of principles which are old. A case in point is the recent application of metallographic analysis to effect the conviction of a criminal charged with first-degree murder. So far as we know, this is the first application of metallographic analysis in criminal jurisprudence, and is therefore of considerable interest, not only to scientists, but even more to the legal profession. I n December, 1922, a cleverly constructed bomb was sent through the United States mail in Wisconsin, and exploded in the hands of the addressee, maiming him badly and killing his wife instantly. Suspicion fastened upon a farmer by the name of Magnuson, living in the vicinity, who was known to have considerable mechanical skill and who was alleged to have made indirect threats against the man to whom the bomb package was sent. Parts of the bomb and most of the equipment and odds and ends in Magnuson’s shop were collected by the district attorney, sheriff, and the United States postal inspector. A tripping device on a gasoline engine on the farm of the ac-
cused seemed to bear a superficial resemblance to the release mechanism used on the bomb. Metallographic analyses of the two pieces of metal were made by Professors J. H. Mathews and E. D. Fahlberg, of the University of Wisconsin, and they found the two pieces of metal to be identical. Each contained characteristic and unusual inclusions of slag, and each showed the same crystal structure. In addition, two other pieces of metal, one a section cut from a 3/4-in. pipe coupling, and the other a section of a 3/4-in. pipe, were identified positively as having been cut from pieces of coupling and pipe of the same size found in Magnuson’s shop. The evidence was presented t o the jury in the form of enlarged photomicrographs accompanied by detailed explanations by the expert witnesses, drawn out by the questions of the prosecuting attorney. The Magnuson case is attracting considerable attention among the members of the legal fraternity, as i t is now realized t h a t the profession has a method for solving many bomb mysteries, which has not heretofore been used. Verily, the path of the criminal becomes more and more difficult in proportion t o the extent t h a t science is called upon t o assist the legal profession.
