INDUSTRIAL AYD ENGINEERING CHEMISTRY
May, 1929
not be laid a t the door of the machine itself until it is definitely determined that the mill is being correctly used, and that the factors of hydrogen-ion concentration, temperature, and protective-colloid action have been carefully studied. It
425
should be reiterated in conclusion that the mechanism is only one-fifth of the problem and the knowledge and correct application of physical chemistry is the important four-fifths of the utilization of the colloid mill.
Welding in the Chemical and Process Industries’ W. Spraragen AMERICAN BUREAUOF
WELDING.
ITHIN the last ten or twelve years welding has been accepted by industry as one of its most important production and repair processes. Formerly welding was employed principally to repah broken parts of machinery and other metal parts, but until comparatively recent years its value as a standard method of joining metal pieces in general manufacturing was not fully appreciated. During the World War, however, the various welding processes came into their own rapidly because speed of production in every metal-using and metal-fabricating industry became a vital matter. At first welding was limited to use on small or less important parts, but as favorable experience soon showed the desirability its field of application was gradually extended to heavier and more important construction and repair work. Many
Design of Flued Outlets with Reinforcing Pads Oxyacetylene Welded
practical demonstrations of the utility of welding focused attention on its marked economic advantages, with the result that now all melding processes are widely used in all branches of manufacturing. Welding is employed for an almost limitless number of applications, from the manufacture of such small articles as watch stems to the largest metal-fabricated structures-ships, locomotives, trunk oil and gas pipe lines, gas tanks, and the largest turbine electric generators. Before considering the applications of welding a brief description will be given of the various methods by which it is accomplished. This will be followed by a discussion of the fundamentals of welding which are more or less common to all its applications in important construction work, and finally with problems that are peculiar to the chemical arid process industries.
29 WE5T 3 9 T H ST., N E W Y O R K , N. k’
Metal Arc Welding with Bare Electrodes. In this method an arc is struck between the wire or rod of suitable composition, called the electrode, and the parts to be welded. The parts to be joined are made one side of an electric circuit, the other being the electrode. The parts to be melded should be prop erly shaped and are usually beveled on both edges in the case of plates to be joined in the same plane by a “butt” weld. The metal is fused a t both ends of the arc and the fused electrode deposited in the joint until the latter is properly filled. The power is usually supplied by a suitable transformer or by an arc-welding generator which delivers an open-circuit voltage ranging from 35 to 75 volts. The arc should be as short as possible in order to avoid oxidation of the metal and the inclusion of harmful gases and to secure the proper penetration. Metal Arc Welding with Coated Electrodes. These have been used in some form almost from the beginning of arc welding. I n general, the coatings serve as a fluxing or deoxidizing medium, or provide a protective vapor around the arc. Arc Welding in a Reducing Flame. I n this method a cylindrical jet of gas surrounds the electrode and burns around the arc. Pure hydrogen, water gas, alcohol vapor, and a number of other gas combinations have been tried with considerable success. These welds are, in general, superior to the bare electrode welds, particularly as regards ductility. The reducing flame generally serves the same purpose as the electrode coatings and apparently with somewhat better results, although this method is still in the experimental stage. Atomic Hydrogen Arc Welding. A fine jet of hydrogen is forced through an arc formed between two tungsten electrcdes. The high temperature of the arc breaks up the hydrogen molecules into hydrogen atoms, which recombine into
t!
’PIT.
\
Welding Processes
FORGE WELDING-~Tkil about forty years ago this was the only available method, and it has been in use to some extent for centuries. After properly shaping the two surfaces to be joined, the parts are heated to welding temperature in a forge or furnace and then hammered, rolled, or pressed together, usually with the aid of some fluxing material. ARCWELDING-There are several divisions in this method, as w ill be indicated below. Several of these divisions may be further subdivided as to whether the current is direct or alternating and whether the operation is manual, semi-automatic, or automatic. 1
Received March 5 , 1929.
Making a Butt Weld in Pipe
molecules after passing through the arc, giving up the heat absorbed during dissociation in the arc. The welding wire is fused in this flame and deposited in the joint exactly as in the case of gas welding, described elsewhere. The intensely reducing character of this hydrogen flame results in a nearly perfect weld. Carbon Arc Welding. I n this method, invented in 1881, an arc is struck between a carbon (or graphite) electrode and the parts to be welded. The welding wire is then fed into the arc and fused into the joint. For hand operation this
INDUSTRIAL A N D ENGJ!NEERING CHEMISTRY
426
requires two hands as in the case of gas welding or atomic hydrogen arc welding. In fact, i t differs from gas welding only in the source of the heat, the gas flame being replaced by the arc. In some cases the welding r d i s laid in the joint groove and the carbon arc passed slowly along the joint until the fusion is complete. Electronic Tornado Welding. This name is applied to a magnetically controlled carbon arc which produces welds with good ductility. Oxidation is largely prevented in this process, Great speeds are possible, although tho application is limited to "downward" welding. I
1
Fractlonaflne. Tower in Petroleum Refinery with Oxyacetyiene-Welded Joints Evident throueh Insuiatfan
Gas Wmnmo-This process of fusion welding is generally carried out by the heat produced by the burning of acetylene in the presence of commercially pure oxygen, the flame temperature so attained being probably about 5500" F., which, in view of the concentrated flame, is high enough to melt any metal locally, and so allows pieces to be easily fused together. It is necessary, when welding thick materials, to bevel the edges to bc joined so they form a V, which is filled u p by melting into it a rod of suitable composition, the weld metal also being fused to the base metal. T o d . An oxyacetylene welding torch is an instrument that thoroughly mixes the two gases, oxygen and acetylene, in the proper amounts and that permits easy adjustment and regulation of the &me and the application of the intense heat so produced to the edgcs of the metal parts to be joined so that they will be brought to the molten or fluid state quickly, caused to fuse or run together, and upon cooling result in a joint or union having strength and chemical qualities approximately t,he same as those of the original parts. The welder requires a small flame and little heat for welding thin-gage metals and a large flame and much heat when welding heavy sections. This is the reason for the separable interchangeable tips furnished by the torch manufacturers in several sizes ranging from the smallest to the largest practicable to use. RESISTANCE WErmhw-In this method, invented about forty years ago by Elihu Thomson, the parts to be joined, after proper shaping, are pressed together. A large current is then passed through the joint until it has reached welding tempera-
Vol. 21, No. 5
ture, when further pressure is applied, upsetting the joint and completing the weld. As the electrical resistance of the contact surface is much greater thsh that of the solid metal, most of the heat is generated a t the joint surface where it is desired. The larger the current the more rapid the heating, the less the heat extends back from the joint into the metal, and the less the upset. The voltage required is so low and the current so high that the only convenient source is an alternating-current transformer built into the welder and as close as possible to the jaws which hold the parts and transmit the current to them. Butt Welding. The simple type of resistance welding described above is usually known as butt welding, and has been applied to join sections of widely varying shapes up to 36 square inches in section. Parts to be welded are clamped in dies of welding machine giving equal or nearly equal projections to both parts, the primary circuit closed, and the ends of parts brought together slowly. When these ends actually touch each other, they is, minute particles of molten metal will wiU "flash"-that fly off; this flashing is continued until t.he entire faces of abutting ends have reached a welding heat, when rapid and heavy pressure is applied, forcing ends together and complee ing weld, a t the same time opeuing primary circuit. The above is, without doubt, the preferred method of welding, as the power and time consumptioil is considerably less and the personal equation of the operator enters to a much less degree than in any other type of weld, thus producing more uniform results. Spot WeZding. Where air-tightness is not required, a lap seam may be welded in spots hy clamping the seam overlap betwcen two (usually circular) electrodes and passing the necessary current between them and through the overlapping edges of the plates. As the electrical resistance of the surface contact is least in the region under pressure, most of the current, and therefore the weld, is confined to a spot of about the same area as that of the electrodes. For relatively thin metal this method is much more rapid and economical than any other known method of making a joint where mechanical strength alone is required. The me-
Welded Preesure Sfill Comlng Out of Anneailng Fvrnace
chanical strength obviously depends upon the number and size of the spots. With a double row of staggered spots it is easy to make the joint strength equal to that of the sheets themselves. Seam Welding. The overlapping edges of sheet metal are passed between two narrow roller electrodes, the speed, current, and pressure being so adjusted as to produce a continuous
May, 1929
INDUSTRIAL AND ENCI'NEERINC CBEMISTRY
seam weld. This method is usually limited to relatively thin sheets, but is readily applicable to either straight seams or to circular seams &s for the Aanged heads of cylinders. The employment of this method for the manufacture of hamels, moderate-sized transformer tanks, and numerous other similar containers has resulted in a very large saving in cost. Thousands of such welded containers are made every day. ALUMINO-THERXIC (THEREVIT) WEmrNc+-Thermit is a trade name for a mixture of finely divided aluminum and iron oxide, which when ignited reacts to produce a superheated
Sample8 Welded by Fhid Fusion Process
liquid steel a t 5000" F. The underlying principle of this process is the high chemical affinity of aluminum for oxygen. Up to a temperature of 2800' E'. thermit is an inert mixture. At that temperature, however, the aluminum unites with the oxygen of the iron oxide, and the iron is set free and comes down as a highly superheated liquid steel a t a temperature of approximately 5000" F., or about twice the temperature of ordinary molten steel. It is obvious that if steel at this temperature is poured around the sections to be united, especially if the sections have previously been preheated to a bright red heat, i t will melt those sections and amalgamate with them so that the whole will cool to form a single homogeneous mass or, in other words, a fusion weld. FundamentalElements of Welding
SELECTION OF PROPER MATERIALF+The Selection Of suitable materials is important in the application of welding to any industry, but is increasingly important in the chemical industry because we must have in mind the requirements of the specific application and we must have a material in which we can produce a sound, dependable weld. For example, in order to withstand the corrosive effect of acid or alkali solutions we would perhaps consider one of the newly developed corrosion-resisting alloys. Some of these corrosionresisting alloys are more readily weldable than others. In some cases where the corrosion-resisting property is dependent on special heat treatments, excellent welds can be produced from the standpoint of mechitnical strength, but the welds may not be able to withstand the corrosive action involved unless they are given special beat treatments or made in special ways. The economics of the situation must also be carefully considered, because it may be preferable to use thicker sections of low-carbon steel even though this steel may be less resistant to corrosive action, because it is cheaper, more readily weldable, and owing to the thicker section will last as long as vessels made from some more expensive alloy. The considerations given above apply in some cases with equal force to vesels that must resist elevated temperatures or vibratory stresses or a combination of these. For example,
427
it has been found in the oil-cracking industry that the best steels are the plain carbon steels, because the strength increase obtained in using the ordinary alloy steels a t elevated temperatures is not sufficient to cover the higher costs of the steel and increased costs in fabrication. The advantages gained in corrosion resistance for such alloy steels do not become apparent until very expensive alloys are used. Some of these have very high chromium content, which have the disadvantage of becoming exceedingly brittle a t the high temperatures involved. In some alloy steels, however, this difficulty of brittleness is overcome by certain additions of nickel. I n some cases ordinary carbon steels are coated electrically with a deposit of chromium or with inert siliceous materials. The problems of a suitable material therefore possess a great deal of ramification and can only be considered in detail for specific applications. The selection of a suitable welding rod is equally as important, for the resultant welds are expected to have certain chemical and physical properties. Specifications have been prepared by the American Welding Society for welding ordinary materials. Special wires, however, may in some instances give better results. All materials are suitable for welding, although by special technic and welding wire difficulties a t first considered insurmountable may sometimes be overcome. Low-carbon steela and a great many alloys its well as nou-ferrous metals can be satisfactorily welded by one or more of the fusion welding processes. It is generally agreed that a carbon cont.ent of not over 0.25 per cent lends itself most readily to welding. The greater ductility of this material minimizes distortion and the development of local stresses due to the heat of welding. Steel plate of fire-box quality should be specified for all important work. This steel is generally free from impurities of various kinds that are harmful to welding. Defects in steel plates, such as segreg a t i o n s and lamiuations, must be avoided. PROPER DESIGN-It
is a wrong basic principle to substitute welding for riveting in a structure originally designed forriveting. Although such a course can sometimes be justified as a temporary expedient, it is not fair to judge welding from results obtained in such cases. The structures that will be fabricated
ample of the need for special designs which recognize the fundamentally different bases of the two methods of joining metals, i t may be noted that, whereas for riveted joints it is necessary to overlap the plates or employ straps, the use of welding often permits butt joints to be used. This effects a considerable saving beyond that which could be made if the overlap necessary with riveting were retained. The Carnegie Institute of Technology bas made some tests for the Westinghouse Electric and Manufacturing Company in order t o determine the various types of connections required in the steel frames of buildings to be fabricated by arc welding, among which are some comparative tests on three specimens,
INDUSTRI.4L AND ENGINEERING CHEMISTEY
428
fabricated as girders on comparable materials. The results were as follows: LBNcra W n i r e r VISLD *r: Feel Pomdr Pounds Riveted girder
Welded sirder of riveted design Welded girder of welded design
15 15 15
798
785
798
55,000 85,000 60,000
Ulm)b*TE srnsss A T
FAiLVRE
Pounds
68,900 77.2M) 110,350
The girder designed especially for welding was made up entirely of Rat plates. A suitable web plate was rrwlded to two flange plates with small flat plates used as stiffeners and a suitable cover plate was also welded to the fiange plate. No angle irons were used. It can be seen, therefore, that welding in many cases requires special designs and not merely a svb stitution in a riveted design. The use of clip angles, gusset plates, brackets, and angle iron may sometimes be eliminated entirely in welded structures. Vessels made with riveted joints cannot be satisfactorily tested at hydrostatic pressures exceeding about one and onchalf times the working pressure because of the serious leakage at the joint. The welded joint,, on the other hand, may be tested up to its breaking point. In experiments carried out in the laboratories of one or two companies, it was l o u d that there were several weak spots in vessels fabricated according to previously accepted principles of design. Zones of unexpected weakness were found at several important pointsnotably a t the knuckle of t.he dished heads, at the manhole openings, and at nozzles. Investigations show that the correct design for eliminating high local stresses is an ellipsoid with a ratio of 2 to 1 between the major and minor axes. Design fiber stresses of 8000 to 9000 pounds may be used if qualified welders are available. The higher figure should only be used with special materials or methods. Where the size of the vessel permits, it is desirable to construct the shell in one course. Where girth seams are necessary, the longitudinal welds should be staggered an equal number of degrees. Several approved methods have been developed for welding nozzles and nipples. An unreenforced manhole open40 per ing decreases the strength of a thick-walled vessel by ~. cent. The minimum thickness of head should be at least equal to the thickness of the cylinder. An ordinary dished head requires a thickness about one and
V01. 21, No.15
one-half times tlic tiiickncss of the main cylinder in order to approximate the strength of the vessel cylinder. This is a disadvantage because of the stress effect of the joint between the plating and tho tliieker head. QUALIFIED Wmnms-It is now generally recognized that on important work only qualified welding operators should be used. It is not suficient. to judge a man by experience alone, but he must he required to make up test coupons using the same materials and thicknesses that he will be called upon to weld in service. A skilled operator on thin work may not be able t,o do satisfactory work on thicker materials, or if he is skilled in welding in a downward position lie may not be able to make an equally strong weld in a vertical or some other position without additional t.raining. Test coupons taken from welds in mild steel made by a welder with wire conforming to the A. W. S. specifications should average 45,000 pounds per square inch and with this combination a design pressure of SO00 pounds may be used. With some smrial weldine wires an averaee of 50.000 oounds per square inch may be ogtaioed, in whicccase a desi& pressure of 9000 pounds may be used. Very skilled welders can also obtain this strength with good grades of wires conforming to the A W. S. specifications. SUITABLE ArP.4n~Tus-A great deal may be said on this subject. There are a number of reliable manufacturers of apparatus used in the several welding processes. Special automatic apparatus has been developed for some cla.;ses of work. Other methods and technic are designed to give welds of extreme ductility. Manufacturers who contemplate the use of welding should make a thorough study of this phase and adopt types of apparatus most suitable for their specific needs. I'ROPER TEciINrc-Proper welding technic should be developed after the most careful study by competent experts. In complicated struclures, by the adoption of a suitable order
Jacketed Avtoctaae of 800 C a l l ~ nCapaacitY for pToce88 Imlustries, Welded by the A. 0. Smith Corporafion
of welding, trouble due to stresses and distortions may often be completely avoided. Number of layers, use of jigs, proper current, proper-sized tips, gas pressures, methods of assembling the work are all important factors which may determine the success or failure of a specific application. I n general, exceDt for automatic work the lonxzitudinal seam should be of a double-V construction, the oute;V being welded first. Before welding the inner V, burrs, globules, or oxide formations should be removed by a chisel. It is recognized that
May, 1929
INDUSTRIAL AND ENG.INEERING CHEMISTRY
for heavy vessels 1 inch in thickness or over it is desirable to anneal the structure. This is not necessary on thinner walled vessels. COMPETENT SuPEnvIslox AND INsPEcnoN-There must be a competent supervising and inspecting force to see that all the e1ement.s which enter into the making of a successful meld are carried out. This involves inspection of the material and its preparation for welding. For example, the edges must be free and dean from dirt, oil, or grease. Inspectors must also see that the proper currents or gas pressures are employed and that all the details entering into the correct technic of welding are carefully followed. TESTIXG OF THE FINISHED PnonncT-It is customary to test the welded vessel hydrostatically to three t,imes the working pressure with the application of a hammer test at one and one-half times the workin3 pressure. Exact procedure has been worked out for the weight of the hammer and method of application of the test.
429
a bibliography of articles on corrosion would occupy a goodsized volume in itself. Problems involving corrosion must be studied individually. It is possible to weld most of the corrosion-resisting alloys satisfactorily, although special teclinic and materials are sometimes needed. Welding apparently has t,he advanbage as a method of fabrication in most applications i~ivolvi-ingcorrosion. The problem is somew-hat coinplicated if t,empcrnturcs and repeated st,ressesarc involved, as high t,cmperatores in m:my instances increase the rate of corrosion, whercas corrosion oiten lowers the e.ndursnce limit. As pointed out elsewhere in this article, i t is sometimes advantageous to iise ordinary carbon steels with a deposit of chromium. This is sometimes done in the oil-cracking industry.
Specific Requirements of Chemical Industry
RELIABILITY OF WELDS-Reliikjility of wekls is important in construction work, where failure might result in loss of life or property. If all the elements enumerated above that enter int.0 the making of a successful weld are closely followed, the variation of the finished product should he no greater (perhaps less) than with other methods of fahricat~ion. Only experienced welding engineers should be responsible for t.he design and selection of materials and apparatus. Qualified welders and competent inspectors and supervisory force should be used. There are in existence today hundreds of vessels which are called upon to withstand the most drastic service conditions. Some are operating at extremely high temperatures at heavy pressures. Other vessels are undergoing constant reversal of stresses. Vessels made by reliable companies have vlithstood these tests and are in daily commercial use, as will be indicated by a number of the illustrations. HIGETEMPERATURES AND PRE8SURES-SOme chemical processes depend upon their success for high temperatures and pressures. Without the aid of welding i t has been difficult and sometimes impossible to construct vessels that are able to meet these very severe requiremenbs. For example, i t has become recognized that 900" F. is a temperature around which oil-crackinr operations can economically be carried out. The butt joint is geiierally considered t,he best for tlGs class of work, which can, of course, be readily made by one or more of the fusion eld ding processes but not so readily by other methods of Fabrication. At first great fears were expressed that the welds vl.ould not be able to withstand these high temperatures. Preliminary short-time investigations, made under the auspices of the American Bureau of Welding, indicated that good arc and gas n~eldsfollow very closely the properties of fire-box steel from room temperature to 1000" F. There seemed to be a gradual increase in st.rength in both the parent inet.al and the welded joint up to about 600" F., with a rapid fa.lling off in strength after that temperature, so that at 1000° F. the strength of the joint and of the parent, metal NBS about half of that at room temperature. Long-time tests have not yet been made by the Society, hut other experimenters have found that at high temperatures the falling off in strength of welded joints will be about the same as that of the lowcarbon steels. I n some tests reported by these investigators the decrease in strength nt about 900" F. it1 long-time tests was to 25 per cent of the ultimate strength a t room temperatures. There are hundreds of welded vessels made by one company alone for oil-cracking, which requires both high temperatures and pressures. CORROSION-RESISTING PRoPEaTIEeIt has been said that
225-Ton Kettle, Fabricated by Yefroleum Iron Works 14 feet inside di'metei by 0 Ieet Y inches deep. Thickness of plate, li/. inches. Weight. 11.3 ions fire-box steel.
ENDURANCE LIMn-'L'he endurance limit of materials is often affected by corrosion and temperature. Where these factors are not involved, the endurance limit of welds made in ordinary steels may he taken a t about 18,000 to 20,000 pounds. It is customary t,o use these figures with a design factor of safety of two. Several companies, however, claim to have hem able to produce welds with an endurance limit as high as the parent metals themselves, akhough these are special eases and in general these welds are quite superior in ductility, soundness, aud microstructure. PIPING-A piping system cannot be purchased all ready to install like a piece of machinery, but it must be fabricated in place. Lengths must be cut and connected to obtain a continuous line and outlets for branches and connections provided. Innumerable tests demonstrate that a properly welded joint is as strong as the pipe wall itself and to all intents and purposes becomes an integral part of tho pipe. Therefore, the joint will last without maintenance as long as the pipe. Thus, on Recount of the strength of the joint, higher pressures may be safely carried than would be permissible with screwed, flanged, or any other type of joint. Owing to its great tensile strength i t is largely able t o resist expansion and contraction stresses caused by changes in temperature. Economies effected by weldingarenot limited to the making of the joint itself, but begin at the pipe mill and extend beyond the installation, continuing throughout the entire life of the line. Savings due to welding of pipe start at the mill. Most mills formerly made pipe of approximately 20-foot lengths to facilitate handling, cutting, and threading. They are now responding to public demand and manufacturing pipe in 40-foot lengths, because welding has made i t possible to take advantage of the obvious economies of using the longer lengths.
INDUSTRIAL AND E.VL ~INEERIAVD CHEMISTRY
430
Any special fitting can he fabricated hy cutting with a torch and welding with the torch or arc right on the job. No thought on the part of the designer need be given connections
Rivetlese Sfeel Hoppers Corn letely F a h l c s t e d by Arc Welding. Fabricated by Mississippi Sfructural Steel C o m p a n y
alley
between pipe lines if the pipe is to be welded. Welding can be used to advantage whether the job is to he completely welded or whether only specials such as headers are to he fabricated by this process. Tliere are no delays necessary in waiting for special fittings. No special expensive tools or dies used in threading are needed. The covering contractor will cover or lag a welded pipe line for a much lower price than he will an identical screwed pipe line, as the former does not require molded fittings. The finished job is also more efiicient. The American Society of Heating and Ventilating Engineers recently conducted uii investigation t.o determine the efficiency of pipe coveriiigs. Their tesbs indicated that a pipe line with hare flanges, hut insulated along the body of thc pipe, loses half as much heat as a completely uninsulated line. Circulation of gases or liquids through a welded pipe line is maintained with less friction thnn when fittings are used. Operating experience in pipc-line work has shown that welded lines have somewhat greater carrying capacity than other types of the same diameter, and the reason may he traced di-
Welded Structural Steel To Frame for 73,WO-Volt 0 1 1 CirwIt €Laker
reotly to reduced friction of the Bow. The factor of flow resistance becomes increasingly important as pipe size decreases. A further advantage of welded construction is evident when it is desired t o make changes in an existing line, to add a new outlet, or to extend the line to another department. Where the line can he conveniently shut down for a few minutes, a new branch connection is made simply by cutting a hole in the main line with the cutting blowpipe and the welding in a short length of pipe carrying a shut-off valve. As soon &s welding is hished, service may he resumed on the main line. There is thus a minimum loss of service. Perhaps of even
Vol. 11,No. 5
greater importance is the improved service which such procedure allows the contractor to give. If all piping must be fabricated to exact length, as is the case unless welding on the job is done, it means that measurements for a portion of the piping a t least cannot be taken unless the apparatus, such as boilers, turbine, and auxiliaries are in place and lined up. It is then necessary to order these materials, get them fabricated, and ship them often a t an extra added expense and with consequent actual delay in time of starting of the pipe plant. For the high-pressure and high-temperature lines where cast-steel fittings are usually required, another element which has an important bearing on service enters into the proposition. The manufacture of steel fittings and east-steel headers i s a somewhat speculative undertaking. The several fittings and headers of this kind required for a given job may be ordered meks and sometimes months in advance. When finally cast there is always the possibility that one or more castings will be found defective and will tie up the entire joh. Defects in the casting may not become apparent until machine operations are well along and often such defects do not show up until after the material is completely installed and tested. This feature often results in the discovering of defective material a t the last moment with delays caused hy reorders and remanufacturing running to weeks and months. The methods of welding of pipes and fittings have now become s t a n d a r d i z e d . Exact technic bas been developed for making joints, templets h a v c been prepared for fahrieating connections, and jigs have been worked out for f a c i l i t a t i n g welding. PRESSURE VESSELSThere is no application of welding that requires more complete control and closer adherence to the fundamental principles of welding than does t h e welding of pressnre vessels. It can now he said that vessels of almost any thickness of commerOxYacetYlene-Welded SfUls of NonFerrous Metal cialiy required can be satisfactorily welded although, of course, inaterials more than 1'/* inches thick as yet require special processes. IVithin the last few years more than two hundred pressure vessels, ranging in diameter from 3 t o 8 feet having wall thicknesses up to 1% inches, and carrying working pressures u p t o 300 pounds per square inch, havc been oxyacetylene-welded under the supervision of one company alone and have proved entirely satisfactory under service conditions. Another company, which has developed a special technic and method for arc-welding oil-cracking stills and other higfipressure vessels, has built seven hundred vessels using 45,000 tons of plate averaging close to 3 inches in thickness. This process is a fusion operation in a reducing atmosphere, which completely eliminates oxide inclusions and other impurities from the weld, leaving a metal of greater refinement than that of the plates joined. This company states that test bars, machined out of the deposited metal in a weld joining 0.2W.30 carbon steel plates, have regularly given the following results: Ultimate tensile strength Elastic limit Elongntion Reduction in area
B 6 . m pounds per aquere inch 50,WO pounds PCT s p u ~ r etnch a7 per cent 53 per cent
May, 1929
INDUSTRIAL AND ENGINEERING CHEMISTRY
431
Endurance tests reported by tbis company on joining 0.20-0.30 carbon-steel plates showed the endurance limit of the deposited metal to be at least 10 per cent above that of the plate material. The metal immediately adjacent to the
of the double-Y weld for the longitudinal seams and the d e sign of head mentioned elsewhere. Careful and rigid procedure has been worked out for the exact technic to he followed in the fabrication of vessels by gas and arc welding.
playing heavy currents, and keewing the metal in a molten state for an appreciable lengtii iftime has satisfact,orily demonstrated its ability to build vessels of almost any commercial size or thickness. The physical preperties of the welded joints approximate those given above. Both of these companies anneal the vessel after its completion. It should be noted that these are special methods and the ordinary arc welds made by hand operators do not possess these desirable characteristics, Several methods are, however, available for commercial use that give welds of good ductility. Particular attention is called to the desirability of the use
Welding probably received its first impetus in repair and maintenance work in railroad shops. The several welding processes are annually saving the railroads of the United States millions of dollars. Almost every modern industrial plant of large size is now equipped to do its own repair and maintenance work. The cost of routine maintenance and repairs can be substantially reduced by the intelligent use of welding and cutting. Innumerable cast-iron and steel parts, including large castings, which so often are scrapped, can he recovered, and in many instances welded right in place in the machine a t a very small fraction of the original installation cost. In the emergoncy job, welding and cutting equipment in the hands of a competent man can do work in minutes which would necessitate delays of weeks if new repair parts were not available. In repair work the welding engineer does not have the o p tiou of selecting materials best suited, but he must do his best on the “job” a t hand. Almost all metals and their alloys can nov be satisfactorily welded, but each requires its own technic. Some repair jobs call for gas welding, othcrs for arc, still others of large sections for thermit welding, and sometimes in repetitive work for resistance welding.
Welding in Maintenance and Repair
Elll@oidal &ads
Phenol Recovery and Treatment Works of the Hamilton Coke and Iron Company’
F
OR the past five years the attention of administrative
authorities has been constantly directed toward elimination of tastes and odors in public water supplies caused by phenol or other tar acids produced in the destructive distillation of coal. During thus period unceasing effort to solve this troublesome problem has been made by the byproduct coke industry in cooperation with health officials. Various methods of recovery and treatment have been attempted and, although a large measure of success has attended the effortsto protect public vater supplies, the result has been accomplished a t great cost in some instances and an operating burden of considerable magnitude has been placed on the industry as a whole. Consequently new methods of handling the problem are of especial interest to both health authorities and coke-plant officials. For this reason we present this paper describing the phenol recovery and treatment works recently placed in operation by the Koppers Company a t the by-product coke plant of the Hamilton Coke and Iron Company, of Hamilton, Ohio. Since the Koppers Company is fully protecting this process and apparatus by patents and further information may he obtained from that organization, no attempt will he made to explain minute details of design, but rather the information set forth at this time will be of general nature and as uontechnical as possible. Received February 16. 1929. Amststant engineer in charge Stream Pollution and Industrid Waste Invertisation..
This phenol recovery system has already excited considerable interest and inspections of it have been made by representatives of a large number of by-product coke companies. In addition, the works has been visited by the chief engineers of the departments of health of West Virginia and Indiana in company with the chief engineer and the writer of the Ohio Department of Health. On these inspection trips information regarding the coke plant and the phenol recovery works has been given by J. T. Whiting, geueral manager of the Ifamilton Coke and Iron Company, C. L. Haldeman, superintendent of the coke plant, and J. A. Shaw, research chemist of the Koppers Company. The cooperation and courtesy of these gentlemen in arranging for the inspection trips and in giving detailed information with regard to the coke plant and the phenol recovery process are gratefully acknowledged. Location of Coke Plant The blast furnace and by-product coke plant of the Hamilton Coke and Iron Company are located about 4 miles north of Hamilton, Ohio, on the west bank of Miami River. This stream is one of the larger tributaries of Ohio River and joins i t about 30 miles southwest of the coke plant. Phenolic wastes from this plant, if discharged to Miami River, would first affect the water supplies of two small municipalities in Indiana which are situated on Ohio River close to the OhioIndiana boundary line, then that of Louisville, Ky., and other cities iarther downstream.
