3rd World Petroleum Congress

170 PROCEEDINGS THIRD WORLD PETROLElTM CONGRESS-SECTION VI11 management and engineers in the petroleum in- dustry. In his forty-six years of construction-engi- neering experience and beginning with riveted pres- sure vessels prior to 1920, the writer has devoted a considerable part of his time, during at least twönty- five years, to the design, fabrication, and inspection practices pertaining to unfired pressure vessels and oil storage tanks, particularly in the use of the most economical, commercially availabile steels including some of the newer high tensile steels where the need for such was indicated. This concentration of in- terest was predicated as much on a full measure of safety in plant operation ar for the economies that must be realized to keep costs within reasonable bounds, and, incidentally, to maintain a high load factor for production. Although the writer feels the honor conferred on him in being asked to prepare this paper, he also believes it quite likely that most of those attending this sectional meeting of the World Petroleum Congress who have been directly interested in unfired pressure vessels, and including those who will take the time to read it if it be later published, already know more than he does about the theories on which the practices in design and construction of such vessels for use in the petroleum industry have developed. Consequently, no attempt has been made in this paper to expound those theories, but merely to suggest some thoughts that have occurred to the writer on the basis of his own experience and the much greater direct contact with certain phases of the problems by those with whom he has been fortunate enough to be associated, largely through technical committees on reseach, and construction code rules, specifications and interpretations. In connection with construction codes for unfired pressure vessels, the rapid growth of the art has practically dictated the inclusion of much more detailed design information than is required for what are presently classed as routine types of vessels. It is because of the wider demand and the growth in the welding industry, with constantly in- creasing personnel and number of shops engaged in the business, that so many graduate engineers, draftsmen and foremen as well1 as fabricating rhop superintendents and inspectors need this greater fund of information for ready reference and to af- ford control of new developments. Early Developments The early history of unfired pressure vessels for processing in the petroleum industry, at least in America, is somewhat obscured by lack of good re- cords. It is not the author's intent to dwell on that early development. His own recollection is that horizontal $hell type fired stills 8 by 40 feet in series flow operation at 50 psig. were built as early as 1908, and there were naturally some auxiliary pres- sure tanks in connection with this battery of stills. The materials used were mild steel except for the lo

LARGE-DIAMETER HIGH-STRENGTH PIPE FOR OIL AND GAS TRANSMISSION BY PAUL E. NOLL * Synopsis The development of large-diameter high-strength pipe, together with progress in welding and laying techniques, has made feasible the installation of pipe lines of great length and capacity. In this paper, the characteristics of availab!e high- strength pipe and their relation to pipe line design are reviewed. The means of increasing strength are enumerated, and the characteristics and processes of manufacture of the most common type of high- strength pipe, namely expanded or cold-worked pipe, are described. The effect of expansion is examined, both as af- fected by amount of deformation and by chemical composition of the steel. The effect of heat on the tensile properties of expanded pipe is shown. An effective yield strength test of a section of pipe is described, in which incidental observations were made by means of brittle coating. Although impact tests indicate that the type of steel used is not critically notch-sensitive, the im- portance of avoiding surface damage is emphasized. Résumé La mise en oeuvre de tuyauteries de gros diamè- tre à haute résistance, jointe aux progrès simultanés réalisés dans les techniques de soudage et de mon- tage, a rendu possible l'installation de très longs pipelines de grande capacité. Cette communication examine les caractéristiques des tuyauteries à haute résistance utilisées dans la construction des pipelines. Puis elle indique les moyens d'augmenter leur résistance et décrit les caractéristiques et les procédés de fabrication du Consolidated Western Steel Co., Los Angeles, Califor- nia. type le plus usuel de tubes à haute résistance, les tubes mandrinés ou travaillés à froid. Le mandrinage est fonction du pouvoir de défor- mation et de la composition chimique de l'acier, et la résistance à la fraction des tubes ainsi mandrinés est modifiée par la chaleur. Suit la description d'un essai efficace de résis- tance d'un tronçon de tube, qui a permis d'autres observations en enduisant le tube d'une couche friable. Bien que les essais au choc montrent que le type d'acier utilisé ne soit pas trop sensible aux fissures, il faut éviter au maximum des endommagements de surface. Introduction The use of pipe for the transmission of fluids is an ancient art and one which has been fundamental in the development of our civilization. Historically, pipe has evolved through many phases, from the bamboo pipe of the Chinese and lead pipe of the Romans, to the countless types of pipe and tubing that today are vital to our economic life. One of the most significant phases has been the development in the last twenty years of large-diameter high-strength pipe for oil and gas transmission. This, together with concurrent progress in electric welding for field con- nection and development of proportionate laying equipment and techniques, has made practicable the installation of long-distan

(SICAL AND THERMODYNAMIC PROPERTIES USED IN PETROLEUM TECHNOLOGY BY [ALD F. OTHMER * AND ROGER GILMONT ** data by means of f a substance against P reference substance been applied to many sign and operation of he use of petroleum c in graphical plots of permit ready extra- data; moreover, the i with thermodynamic tency of the data may of the physical prop- orresponding thermo- t ternis. i are the basis of this ipply for such diverse as solubility, gas ab- miposition constant, constant, density of Tases, surface tension, iêmes conditions des physique d'une sub- ristique de même na- rice peut se faire par nombreuses courbes ides pétrolières (mise des installations - Lrs). On obtient pres- que l'on peut extra- ultés. ln les caractéristiques iques thermodynami- * Polytechnic Iiistitute of Brooklyn, Brooklyn 2, New ** Present address: The Emil Greiner Co., N.Y.C., U.S.A. York. Proceedings 3rd W.P.C., Section III qua, généralement exprimées en unités calorifiques. On peut en déduire des fonctions et examiner le sens de leurs variations. Ces cprbes s'appliquent à toutes sortes de caracté- ristiques : tension de vapeur, etc. Introduction The methods described in this article for the cor- relation of physical chemical data used in Petroleum Technology depend on the comparison of the prop- erties of one substance with those of another sub- stance under the same conditions, both by algebraic methods based on sound thermodynamic equations, and geometric plotting. While the methods have been developed generally and have many applications in other branches of chemical engineering and physical chemistry, many are particularly useful in the petro- leum% industry. No substance is a "perfect" gas, liquid, or solid, and the deviations from "perfection" (i.e., the exact following of physical laws) of many properties of different real substances tend in the same direction. Thus, if instead of deriving equations or plotting abwlute values of properties of one substance against temperature, these are considered and plotted against properties of another substance always taken at ehe same temperature, an opportunity is given for smoothing the irregularities of the properties of the substance by balancing them against those of the other. A second major attempt has been the derivation of cquations and the development of them graphically so as to give straight line plots which will take ad- vantage of the simplicity and precision of extra- polating and interpolating data as well as minim'izing the amount of experimental data required. The classic example of a plot which balances rela- tive values of properties of two different substances rather than plotting absolute values of one is that of I 2 rKuc.CCuinb> i nliKu WVKLU r&TROLEUM CONGRESS-SECTION III Diihring, wherein approximately straight lines are obtained by plotmting temperatures at which aqueous solutions boil against the temperature at which water boils at the same pressure. P

1 Le contrôle de d'une machine à i fonctionnant hydi The testing of jecting them to specially devised, machine. L'EPREUVE DE TRACTION DES TIGES DE FORAC PAR F. PEYSSART* Résumé l'état des tiges de forage au moyen raction mobile, spécialement conçue, rauliquement. Synopsis the condition of drillpipes by sub- a longitudinal pulling force in a hydraulically operated, tensioning C'est pourquoi, et sur í'initiatii Directeur de la Société Natic d'Aquitaine, a été étudié et réalii permette de soumettre les tiges épreuve de traction. Cette machine de traction horiz conçue et réalisée d`une façon ti constituée par 2 vérins hydrauliq s'appuyant chacun sur un tube -...:-"..-& ^^- 1>:-c :2:..:-- 17.. " II sur un élévateur mobile, un deuxi daire des tubes de compression, CO de la tige à éprouver. La plaque d'appui de I'élévateu :xploitation du pétrole, dans des a conduit à utiliser du matériel nllic In3,T.J C'il nct C?AlP A'?,*-- A',*- ;"A,, nrr; rn A`Ll,,,.n A,.,..,r La recherche et l'i gisements profonds de forage de plus en yiu;i IVUIu. .,II LaL LaL`LL uauo menter la puissance de l'équipement de surface, il n'en est pas de m travaillent d`autant que l'on approche de 20.000 pieds en exemple. Ceci a conduit à tiges de forage. . Ce contrôle est un ensemble pius ou moins complet d`opérations qui ont pour but, suivant le cas: soit de vérifier si les tiges neuves répondent aux conditions de l'A.P.I., soit d`évaluer par des procédés non destructifs le degré d`usure des tiges en service. Un certain nombre de méthodes d'inspection `ont été imaginées et sont utilisées couramment aux Etats- Unis, et même en France: magnafluxage, examen détaillé de l'extérieur et de l'intérieur des tiges, épreuve hydraulique, etc.. Mais ces contrôles ne ren- seignent nullement sur les efforts que l'on peut appli- quer à des tiges neuves, et à fortiori à des tiges usagées. . re de Mr. Chapelet, male des Pétroles sé une machine qui de forage à me ontale et mobile est -ès simple. Elle est ues de 100 Tonnes, de compression et dXlbbdllL. Ud1 I IIILTIIIICUldilT U une plaque d`appui, ème élévateur, soli- nstitue le point fixe ême pour les tiges de forage qui plus près de leur limite élastique d'une profondeur limite qui est viron, pour les tiges grade E par faire un contrôle systématique des Les 2 vérins, solidement fixé: sont alimentés par une pompe d' 2 manomètres. Un petit treuil à m; gauche des vérins, permet de r, retour de l'eau dans le bac de la F assuré par un flexible reliant le. Pour éviter toute flexion des .. . ., * Ingénieur de la Société Nationale des Pétroles d`Aqui- taine, Pau, France. Lr mobile est munie u u11 ~~~UL~ yu1 aL uLyiaLL ucvaiiL une règle graduée permettant ainsi la lecture directe des allongements. ; sur des supports, épreuve équipée de ain, placé à l'a

FUNDAMENTAL GEOLOGICAL CHARACTERISTICS OF THE VENEZUELAN OIL BASINS BY CLEMENTE GONZALEZ DE JUANA * AND LUIS PONTE RODRIGUEZ ** Synopsis The paper reviews the fundamental character of the Venezuelan sedimentary basins, in relation with the genesis and control of petroleum accumulation. Only the northern half of Venezuela is consid- ered potential oil land. Within this area are all the known petroliferous basins i.e.: Maracaibo, Falcón, Maturin, and Barinas-Apure. In the Maracaibo basin, Cretaceous accumulations of structural type Co-exist with Eocene fields show- ing stratigraphic as well as structural control, and Miocene deposits basically controlled by stratig- raphy. The Cretaceous and Eocene oils are con- sidered genetically autochthonous whereas the Mio- cene oil is fundamentally migratory. The Falcón basin produces indigenous Miocene oil from structural and stratigraphic accumulations. The Maturin basin presents a rim of fields along the borders of ,the Miocene basin development. The accumulation is both structural and stratigraphic and, with the exception of Quiriquire, most of the oil appears to be indigenous in the producing for- mations. The Barinas-Apure basin, still exploratory, pro- duces to date from Cretaceous formations, apparent- ly under structural control. Résumé La communication passe en revue les caractères fondamentaux des bassins sédimentaires du Vene- zuela en ce qui concerne la formation et les facteurs gouvernant l'accumulation du pétrole. La moitié nord seulement du Venezuela est con- sidérée comme un pays pétrolifère possible. Tous les * Professor of Geolo y, Univers. Central de Venezuela. ** Instituto Nacionaf de Minería y Geología. bassins de pétrole bien connus, savoir ceux de: Ma- racaïbo, Falcon, Maturin et Barinas-Apure se trou- vent dans cette région. Dans le bassin de Maracaïbo, des accumulations crétacées du type structural coexistent avec des champs éocènes présentant des caractères strati- graphiques et structuraux, et des gisements miocè- nes dont la formation a été déterminée principale- ment par la stratigraphie. On considère les pétroles du Crétacé et de l'Eocène comme génétiquement autochtones, tandis que celui du Miocène est dU essentiellement à une migration. Le bassin de Falcon produit du pétrole miocène indigène à partir d'accumulations structurales et stratigraphiques. Le bassin de Maturin présente des gisements en bordure des limites de développement du bassin miocène. L'accumulation est à la fois structurale et stratigra hique et à l'exception de Quiriquire, la plupart zu pétrole se révèle être indigène dans les formations productives. Le bassin de Barinas-Apure, encore en explora- tion, produit aujourd'hui à partir de formations cré- tacées, l'accumulation étant déterminée, semble-t-il, par des facteurs structuraux. Introduction Approximately the southern one-half of Venezu- ela rests upon ancient rocks of the Guayana shield whose nor

HEAT AND POWER FROM PETROLEUM LE PETROLE, SOURCE DE CHALEUR ET D'ÉNERGIE BY~PAR J. J. BROEZE" Although the casual observer within the off ice precincts of a great oil concern, or even the esteemed guest at this Congress who is not an oil man, might be easily misled into thinking otherwise, oil is there primarily to be burnt. Or at least, since we should not profess to know the purposes of Nature, it is by burning most of it that we seem to profit most by its existence, and it is fitting that in such a Congress as this we should together devote some time to this sacrificial ending. Not that I would give this sitting an unduly ceremonial character, but in starting off on this line one's thoughts quite naturally take a philosophical turn. For as soon as our production friends have unearthed the precious stuff from its timeless resting place it is as good as done with; a few days' storage, a scalding run through furnaces and columns, possibly some seasickness, more storage, tank car travelling, a few more days' respite, until at one fateful moment it goes down that narrow tunnel that leads to the fuel pump, and it is all over in a matter of seconds. Yet in those fateful seconds, nay in the final flash alone, all the trouble taken is repaid. Mesdames, Messieurs, je viens d`indiquer en quel- ques mots le rôle important que joue, dans notre in- dustrie, le caractère éphémère de ses principaux pro- duits. Aussitôt que nos équipes de production ont tiré le pétrole de son repos souterrain, il ne reste que quelques jours jusqu'à l`explosion finale qui justifie et récompense toutes les peines prises. Or, il faut bien comprendre que cette justification sera plus complète et la récompense plus ample à mesure que l'effet de la combustion se rapproche davantage de l'idéal du client ou, plutôt - élégante simplification de notre monde actuel si compliqué - de ses conseillers qui sont, d'une part, le vendeur de sa voiture ou de son four de chauffage et, d'autre part, son fournisseur de combustible. Voici qui nous * Professor at the Technical University, Delft, Director, Royal Dutch/Shell Laboratory, Delft, The Netherlands. mène, en synthétisant, à notre thème d'aujourd'hui, car c'est précisément la maîtrise du génie humain sur la combustion dans ses formes multiples et propres aux nombreuses applications des divers produits du pétrole, qui a inséparablement accompagné notre in- dustrie dans son ascension en mûrissant et se dé- veloppant avec elle. Loin de moi de prétendre que nous sachions tout ce qu'on peut connaître sur la combustion, mais n'est- il pas vrai que dans toute activité humaine la maîtrise technique s'écarte souvent bien loin du savoir scien- tifique? - Voyez plutôt quelques aspects du ma- riage ! Indeed, control of combustion has accompanied the manifold applications of combustible oil products and helped ever-increasingly not only to

ECONOMIC AND FINANCIAL PROBLEMS OF ITALIAN HYDROCARBONS PAPER III. PRODUCTIVE POSSIBILITIES, REQUIREMENTS AND CONSUMP- TION OF NATURAL GASES BY LUIGI FALESCHINI * Synopsis In the following paper there are set out a few data regarding the production, transport and con- sumption of hydrocarbons in Italy, so as to give an over-all picture of the national gas-extraction in- dustry. As will be seen, these data essentially con- cern the Northern Regions (Liguria, Piedmont, Emilia, Lombardy, Veneto): for these only, up to now, have an assured large-scale reductive capac- ity, and, moreover, we have fair y detailed infor- mation about their energy requirements. Résumé La communication présente quelques données sur la production, le transport et la consommation d'hy- drocarbures en Italie afin de peindre à grands traits le tableau de l'industrie nationale d'extraction de gaz. Comme l'on verra, ces données concernent es- sentiellement les régions du nord (Ligurie, Piémont, Emilie, Lombardie, Vénétie), parce que jusqu'ici celles-ci seules ont une capacité assurée de produc- tion à grande échelle et que nous possédons de plus des renseignements assez détaillés sur leurs besoins d'énergie. " Production of Hydrocarbons in the past The beginning of hydrocarbon prospecting in Italy can be traced back to 1860, a year after the United States, and four years after Rumania began prospecting. Unfortunately, owing to a number of reasons which may be attributed both to the tech- nical difficulties of research caused by the consider- able depth of the deposits, and to the lack of funds available to prospectors, the production was always short of national consumption. In table I are given * Azienda Generale Italiana Petroli, Roma, Italy. the average yearly figures (in ten-year periods from 1860 to 1939) of Italian hydrocarbon production, and of the imports of oil and coal products. All figures have been reduced to bituminous coal equivalents with the following Co-efficients of conversion: 1 kilo coal = 0.6 kilos oil products = 0.67 CU. metres methane. The table shows that the contribution of hydro- carbons towards covering energy requirements was inconsiderable until recent years during which the exploitation of the Po Plain fields was begun by AGIP. The present situation regarding production, and the prospects for the future are dealt with in the following section. Present and Estimated Production of Hydrocarbons The deposits now being worked by AGIP as at the end of 1950 are the following: San Giorgio, Ca- viaga, Ripalta, Cortemaggiore. To these will be ad- ded two new fields: Soresina and Cornegliano, where exploration has confirmed productive ca- pacity. Drilling is being carried out in other formations detected by geological surveys. The reserves of gas in the fields now being worked may be estimated at about 60 milliards of cubic metres, equivalent to a daily potential supply of 10 million cubic metres for 20

CATALYTIC REMOVAL OF OXYGEN FROM SOUR CRACKED GASES BY C. G. BERTIL HAMMAR * Synopsis In desulfurizing a Swedish shale gas containing 207% H2S and about 1% 02. by absorption in an alkaline amino acid solution it has been observed that the alkali consumption and the life time of the solution depend primarily upon the oxygen content of the gas. An apparatus has been developed for continuous analysis and recording of oxygen content. By this method the oxygen is catalytically hydro- genated and the water content of the gas determined by means of a recording Psychrometer. The simul- taneous reactions of other components in the gas and their influence on the accuracy of the method have been studied. The same reaction is suitable for treating gases on a commercia1 scale, and the adoption as a technical process is discussed. Résumé En désulfurant un gaz de schistes suédois conte- nant 20 % d'H2S et environ I % d'oxygène par absorption dans une solution alcaline d'amino-acide, on a observé que la consommation d'alcali et la durée de vie de la solution dépendent principalement de la teneur en oxygène du gaz. On a construit un ap- pareil permettant l'analyse continue et l'enregistre- ment de la teneur en oxygène. Par cette méthode, l'oxygène est hydrogéné catalytiquement, et l'on dé- termine la teneur en eau du gaz au moyen fluii psychromètre enregistreur, les réactions simultanées des autres composants dans le gaz et leur influence sur la précision de la méthode ont été étudiées. La même réaction convient pour le traitement des gaz à l'échelle commerciale, et on discute dans la communication l'adoption d'un procédé industriel. General Today the removal of hydrogen sulfide from cracked gases has become a very important process. * Swedish Shale Oil Co., Inc., Kvarntorp, Sweden. Even if the gases are only to be burnt at the flare or as fuel in the plant, in many areas it is impossible to burn a sour gas. Commercial methods to remove hydrogen sulfide by absorption and regeneration of the absorption solution are well-known and show excellent performance on oxygen-f ree gases. How- ever, in the presence of oxygen, thiosulfate and other oxidation products are formed and in order to main- tain a high absorption capacity, caustic must be added. After some time the concentration of the thio- sulfate has become so large that a part of the solution must be withdrawn and regenera:ed or replaced by fresh solution. Besides, oxygen causes several cor- rosion problems. By retorting Swedish shale at tl,e Kvarntorp plant in Sweden a gas is produced with approximately the following composition : Mol- 'j% o2 1.1 CO2 8.0 N2 28.9 CO 1.1 cos o. I CH4 13.0 H,S (and mercaptans) 20.0 H2 15.3 c2 5.7 c3 3 *o c4 1 -4 c5 + 2.4 100.0 This gas is desulfurised by the German "A1kazid"- method and pure Sulfur is recovered. Ten years of experience has shown that the life time of the "al- kazid"-solution d

DIESEL ELECTRIC DRILLING BY HOWARD L. CHATTO* Synopsis The first part of this paper is devoted to a some- what basic discussion of various adaptations of the Ward-Leonard electric transmission as applied to internal combustion engines for driving oil well drilling equipment. It is written with an effort to refresh the memories of those who years ago studied this method of obtaining speed control and to as- semble ansd bring up to date the more recent develop- ments in Ward-Leonard control as compared with present mechanical transmissions. Part two covers the writer's opinions as to the direction that should be taken in future electric rig power equipment layout in order to use the excellent transmission characteristics potentially available in Ward-Leonard control to fullest advantage. A sample electric transmission is developed and its cost is com- pared to that of an equivalent mechanical trans- mission. Throughout the report emphasis is placed on the ability of the electric transmission to replace chain drives, multi-speed mechanical ratios, counter- shafts, clutches, hydraulic couplings and torque con- verters. Résumé La: première partie de cette communication porte sur la discussion en quelque sorte fondamentale de plusieurs adaptations de la transmission électrique Ward-Leonard appliquée aux moteurs à combustion interne pour actionner l'outillage de forage des puits de pétrole. On l'a écrite en vue de rafraîchir la mé- moire de ceux qui ont étudié il y a des années cette méthode de commande de vitesse et mettre à jour les développements plus récents de la commande Ward- Leonard comparée aux transmissions mécaniques actuelles. La deuxième partie exprime l'opinion de l'auteur sur la route à suivre dans la disposition future des * Development engineer Shell Oil Company, New Orleans Area, Louis, U.S.A. éléments de force motrice électrique de l'installation de forage afin de profiter au plus haut degré des excellentes caractéristiques de transmission poten- tiellement disponibles dans la commande Ward- Leonard. On a conçu un prototype de transmission électrique dont le coût est comparé à celui d'une transmission mécanique équivalente. Partout dans le rapport on souligne la capacité de la transmission électrique à remplacer les commandes à chaîne, les rapports mécaniques à vitesses multi- ples, les renvois de mouvement, les embrayages, les accouplements hydrauliques et les convertisseurs de torsion. Foreword This report is divided into two parts. Part I is devoted to a somewhat basic discussion of various adaptations of the Ward-Leonard electric transmis- sion as applied to internal combustion engines. It is written with an effort to refresh the memories of those who studied the methods of electric speed control years ago and to assemble and bring up to date the more recent devdopments in Ward-Leonard control. Part II covers the writer's opinions, based on con- clusions from Part I, as to the di

THE SIZE AND SPEED OF TANKERS AND RECENT TMPROVEMENTS IN CONSTRUCTION BY JOHN LAMB * and R. L. BROWN ** Synopsis The paper entitled "The Size and Speed of Tank- ers and Recent Improvements in Construction" deals with the importance of tankers in the Shipping In- dustry, the factors which, from the Owner's point of view, make for efficiency, and the relationship of economy and tanker design and equipment. The paper also discusses the incentives to build larger tankers and the factors which limit the size of such ships. Size in relation to strength is also dealt with without becoming too involved in technicalities, while a comparison is made between rivetted and welded construction. The speed of tankers recently built and now being built is referred to and the fac- tors which should be considered when determining the most economical speed of a proposed ship are given. Résumé La communication intitulée: "Dimensions et Vi- tesse des Tankers et les derniers perfectionnements apportés à leur construction" traite de l'importance des tankers dans la navigation, des facteurs qui, du point de vue du propriétaire, contribuent au bon rendement et du rapport entre l'économie et la con- struction et l'armement des tankers. La communi- cation discute les motifs incitant à construire des ta%kers plus grands ainsi que les facteurs qui en limitent les dimensions. I1 y est également question des dimensions en fonction de la force de résistance sans qu'on ait trop insisté sur les détails techniques, et on y établit une comparaison entre la construc- * O. B.E., M. I. Mech. E., Manager of the Marine Re- search and Development Department of the Anglo-Saxon Petroleum Company, Ltd., London. ** M.I. N. A., Naval Architect of the Marine Research and Development Department of the Anglo-Saxon Petroleum Company, Ltd., London. tion rivée et la construction soudée. Mention est faite de la vitesse que peuvent déployer les tankers récemment construits et en voie de construction ainsi que des éléments à prendre en considération pour déterminer la vitesse la plus économique d'un navire donné. Introduction Never before have there been so many bulk oil carrying ships under construction, and in view of the constantly increasing application of petroleum and its many and varied products it is safe to say that this class of ship will form a larger proportion of the worlds future shipbuilding than has been the case hitherto, particularly as the average useful life of an oil tanker is considerably less than that of a dry cargo carrier. To illustrate the phenomenal growth of the world's oil tanker fleet during the past twenty years the number of shi s built or on order in January of 1,000 tons deadweight and under have not been in- cluded but it can be assumed that in the period reviewed there has been a great tonnage increase in this class of oil tanker also. the years 1930 an d 1950 is given below. Tankers of Number of tankers Deadweight t