C H EM I CA L
& M E T A L L U R G I C A L
E N G I N E E R I N G
v o l u m e 40 Es t a b l i s h e d 19 0 2 n u m b e r 2
1 ? M C G R A W -H IL L PUBLISHING C O M P A N Y , INC.
S. D. KIRKPATRICK, Editor
FEBRUARY, 1933
SOCIAL CHANGES A ND IMPLICATIONS
O 0 C I A L C R I T I C I S M flourishes most in
^ times of depression. Dissatisfied w ith the existing order, many men begin to question the soundness of established institutions. W ith most of the world in such a frame of mind, it is only n atural that science and engineering should come in for their share of questioning. T h is in itself is not to our discredit, but it explains best, perhaps, w hy such a futile movement as tech
nocracy should spread like wildfire across the prairies only to leave behind the ashes of even greater discontent. D raw n unw illingly into this maelstrom, the engineer was caught off his guard and found himself unprepared to meet this dis
torted and destructive picture of his work. He needed badly the real facts and figures that would refute the gloomy portents of his self appointed representatives.
Fortunately, but in no sense a consequence of the squabble over technocracy, there appeared in the very midst of the excitement the calm and considered report of the President’s research committee on social trends. W h en history records in true perspective the lasting m erit of this w ork of more than five hundred specialists who directly or indirectly contributed to its two volumes, technocracy and those who exploited its cause will have long since been forgotten. T h is report is so comprehensive and so fundam ental to all of our social and industrial problems as to w arran t careful study and use not alone by those w ho are interested in the social sciences,-but by engineers and technologists in every field. Here, if one looks for it, is the answ er to most of the questions and criticisms that have been leveled so dram atically against technology and invention.
H ere we find w ithout the help of higher mathematics and the jargon of the technocrat, an im partial appraisal of the social consequences of the work of the engineer and the scientist. No effort is made to minimize labor displacement and technological unemployment, but on the other side of the ledger are cataloged the many great contributions w ith which technology has increased the w ealth of the w orld, broadened our mental horizon, provided comforts and convenience, shortened our working day, built innumerable new industries and thereby created millions of new jobs. “ Social changes of today are con
nected w ith inventions of the past and inventions of tom orrow will, no doubt, foreshadow the social changes of the future. . . . M ore and more inven
tions are made every year, and there is no reason to think that technological developments w ill ever stop. On the contrary there is every reason to expect that more new inventions w ill be made in the future than in the past . . . . and many new and unheard-of inventions are now in exist
ence that will have wide use in the future.”
Since 1900, while the population of the country has increased 61.5 per cent, the num ber of en
gineers has mounted by 445 per cent, the number of designers, draftsmen and inventors has in
creased 442 per cent, and the number of chemists and metallurgists, 420 per cent. In this period of greatest technological progress, the American people have made their most striking advances both in the cultural and m aterial phases of our development. I t is futile to believe th at progress is at an end. T h an k s to technocracy, the engineer is only beginning to sense the full potentiality in the social effects and implications of his work.
E D I T O R I A L S
T lie P re sid en t-E le ct D ream s—
W ill th e T e n n e ssee V a lle y B o o m ?
F
A R M O R E th a n M uscle Shoals, the N o rris-sp o n sored public ow nership p rogram , an d the th re a t of increased com petition fo r the fe rtiliz e r and electrochemical in d u stries are involved in the fireside dream credited by the daily press to P resid en t-E lect Roosevelt.
N ew spaper m en p resen t a t th a t interview state w ith all candor th a t they w ere m erely rep o rtin g th e fireside conversation in w hich perhaps the rad ia n t energy o f the crackling logs had w arm ed an d enlarged the im agination o f the speaker quite as effectively as it had cheered and w arm ed his anatom y. A nd yet, w hether dream or not, this T ennessee R iv er p ro ject cannot be ignored.
M r. R oosevelt proposes th a t this v en tu re be som ething o f an experim ent to see w h eth er th e plight of ag ricu ltu re m ay n o t be relieved, pow er needs of a com m unity better served, and a real econom ic advance achieved. I f m an
aged on a basis o f sane engineering and sound economics, b u t w ith o u t d estro y in g the im aginative effo rt of one keen to accom plish social advance, such a p ro g ram m ight well contribute m aterially to the natio n ’s good. A n d yet there are m any technologic pitfalls th a t m ust be avoided.
N o sane engineer will question the desirability fo r fu rth e r developm ent upstream from M uscle Shoals of w ater storage and pow er en terp rises. W h e th e r the G overnm ent can afford to strain fu rth e r its credit a t a tim e like this to accom plish such developm ent, is quite a n o th er question. T h en , too, as to re fo re sta tio n th ere is no sim ple answ er. U nquestionably m uch m arginal ag ricu ltu ral land w ould be b etter u n d e r fo rest control th an w hen farm ed as now. Such a principle is easy to e n u n c ia te ; b u t to accom plish the changes involved in its application will be extrem ely difficult.
F ro m the stan d p o in t of the fo re st in d u stries th ere will be still o ther questions. A t the present tim e, as d em onstrated in the pages of Chem . & M e t. last O ctober, we do not need m ore hardw ood developm ent. A n d in the T ennessee V alley one finds th e g re a te st o p p ortunity fo r re fo restatio n w ith hardw ood, ra th e r th an the m uch- needed softw oods fo r pulp an d paper m an u factu re. O nly as w e m ay encourage reg ro w th a n d reclaim ing of so ft
w ood lands can a genuine public service be expected fro m this colossal adventure.
T h en one m u st settle m any fund am en tal policy ques
tions as to in d u strial pow er if he is to an sw er w ith finality the basic idea proposed by the P resident-elect.
F u n d am en tal, too, is the m a tte r of using th e public credit to build up increased com petition in com m odities already over-produced in o th e r ag ricu ltu ral and industrial areas. H ow will the fa rm e rs of the M ississippi V alley react to plans fo r reclam ation and increased fertilizatio n o f farm lands in o rd er to produce a la rg e r co rn crop ? H ow will the electrochem ical m a n u fa c tu rers of the K an aw h a o r the N ia g a ra and S t. L aw rence valleys a d ju s t them selves to in d u strial decentralization sponsored, if not financed, by o u r ow n govern m en t? V erily, the path ahead is full of pitfalls w hich can be easily avoided—
only in a dream .
B ut the process in d u stries are m ore concerned in these m atters of pow er supply, G overnm ent com petition, refo restatio n , and b etter land utilization, than any o ther like group, save perhaps the public utilities. T h e re fo re chemical engineers m ust study the T ennessee p ro ject carefully. W e m ust recognize in th a t p ro ject w hat appears to be a sincere effort at social betterm en t o f a backw ard region. W e m u st oppose unsound engineer
ing and unreasonable econom ics; b u t still we m ust cooperate, even w ith some self-sacrifice a t tim es, it the long-run over-all benefit can be proved to be real fo r the public as a whole.
F le x ib le T ariff G ets C ou rt S u p p ort
T
A R I F F rates affecting sodium n itrite have been a subject o f c o u rt contest fo r nearly ten years. O n Feb. 6 the S uprem e C o u rt ap parently closed the contro v ersy w ith a decision th a t vigorously su p p o rts the p resen t practice in ad m in istratio n of th e flexible tariff law. In its decision the co u rt unequivocally concludes th a t w here a dom estic concern fu rn ish es confidential cost d ata to the T a riff Com m ission, these need n o t be dis
closed to a foreign com pany w hich has refu sed to give sim ilar d ata fo r the guidance of the Com m ission. T h is b road principle will be of c o m fo rt to A m erican e n te r
prises seeking relief u n d e r this p a rt of the law. I t will m aterially aid th e C om m ission in its inquiries. I t greatly stren g th en s the force o f the law u n d e r p resen t procedure.
Chem ical in d u stry will welcome the decision and hope th a t it will accelerate effective action w here differences in costs of production abroad and in the U n ited States a re subjects o f inquiry.
W h a t’s H a p p e n in g in E n g in ee rin g E d u ca tio n ?
C
A N A C O L L E G E E D U C A T IO N , aside fro m its cultural an d social benefits, be justified on a m oneta ry basis? I f so, are financially successful g rad u ates above o r below the average in scholarship? W hich courses a re best designed to give early indication of later success? Is participation in fra te rn ity life and e x tra cu rricu lu m activities a w aste of tim e o r a valuable p a rt of an u n d e rg ra d u a te ’s c areer? A n d finally, w h at is the tre n d o f g rad u ates into executive positions and w hat in d u stries an d w h at type of jobs w ithin these industries offer g re a te st o p p o rtu n ity fo r self-im provem ent and financial rew ard ?
Q uestions such as these have m ore th an academ ic in terest to m ost of us as we look back over o u r own experience or plan fo r those who a re to follow us in o u r jo b s and professions. T h e y a re p articu larly tim ely rig h t now because o u r engineering colleges are facing new problem s, dem anding m ore th a n evolutionary changes in th eir educational plans and pro g ram s. A recent survey by E n gineering N e w s-R e c o rd reveals a serious situation. Incom e in practically all institutions
58 Chemical & M etallurgical E n g in e e r in g—V o l.4 0 ,N o .2
has fallen w hile enrollm ent stays practically the same, th ere being m ore upper-classm en b u t few er entering students. R ecent graduates have found it difficult to obtain em ploym ent and m any have entered non-engineer
ing w ork. R esearch has had to be curtailed because of inability to purchase equipm ent o r provide adequate supervision. T h e survey concludes w ith the surm ise
“ th at c u rre n t events will lead to a re-appraisal of the functions of the engineering college and to the develop
m ent of a modified educational p ro g ram .” I f such fundam ental changes are in prospect, especially in the older branches of engineering, we can well afford to exam ine the records of a thousand g rad u ates of the course in business and engineering adm inistration at the M assachusetts In stitu te of Technology. A s reported in the article by M r. A nthony A nable, elsew here in this issue, these records not only answ er the questions asked in o u r opening p arag rap h , b u t indicate some basic con
siderations of policy th at m ay have a determ ining influ
ence on the fu tu re of engineering education.
A fter T ech n o cra cy — What?
T
E C H N O C R A C Y ’S m illennium has been postponed, indefinitely. Doom , then U topia, w hich w ere ju st around the co rn er a few weeks ago, have slipped into the limbo of m añana and the w orld has retu rn e d to its b rass tacks and its lim ping but still useful economic system. F ro m fellow -chem ical-m anufacturer H o w ard Scott we have had ou r glim pse of the happy never-never land w ith its w ealthy m illions, its leisure, its unflagging em ploym ent— not to m ention its energy determ inants and
“ m etrical” society. H e has perm itted us a brief but glam orous view of a paradise w here, w ith the Golden R ule in one h and and the E n e rg y S ta n d a rd in the other, the engineer would be king, ad infinitum — ad nauseum .
W h ere has it gone, this vision? B orn o f hard tim es, it seized on the public im agination as no o ther economic nostrum has since the days of B ryan and bim etallism . It battened on re fu ta tio n and fed on the ills of a depres
sion-sick w orld. Its fallacies scarcely noticed, its tru th s seem ingly new and startling, backed ap parently by the same science th a t had discovered the equivalence of in ertia and gravitation and had built the autom obile, the m ovem ent gained such headw ay in a m atter of a few m onths th a t bankers and business men hesitated, orders w ere cancelled and recovery all b u t lost its way. . . . B ut pow er is a heady thing and the organization col
lapsed, its m ore responsible m em bers re tu rn in g to their statistical research, the others to th eir soap boxes. T h e co u n try settled back to reflect on the so rry trick and recall th a t hum an nature, fo r all o u r increasing energy consum ption, is very m uch today as it w as d u rin g those 6,000 “static” years from which we had been led to believe we had graduated.
I t w as all p re tty taw d ry w hile it lasted ; and yet som e
thing valuable is left. T h ere w as nothing previously unknow n about its legitim ate revelations but now they
have been dram atized and th u s brought into sharper focus. W e can no longer ignore the uncontrolled grow th o f o u r internal debt, nor perm it surpluses to close the vicious circle w hich prevents norm al and reasonable consum ption. W e cannot continue to dodge the fact th a t increasing productivity, u n d er o u r p resent system carries in itself the g erm o f reduced consum ption and th a t a too generous technology can breed w ant. I t seems m ore and m ore evident th a t to restore purchasing pow er and m aintain it, our living stan d ard s m ust be raised and our leisure increased.
T hese things are n o t incom patible w ith capitalism , p ro vided th a t they are handled intelligently. U nbridled individualism can and m ust be curbed and production held w ithin the bounds of possible consum ption. T his m eans not m ore b u t b e tter governm ent, n o t m ore but m ore intelligent com petition. I t m eans reduced hours and, very possibly, higher wages. B u t above all, it dem ands full recognition of the fact th a t producers are likewise consum ers and th a t real w ages which lag fa r behind production m ust inevitably lead to hard sh ip and underconsum ption. O nce these sim ple principles are fully appreciated, we shall no longer need to fe a r the inroads of technology, n o r the increase o f energy con
sum ption. F a r fro m the calam ity it would be today, the eventual unlocking of atom ic energy will som etim e be a boon, com pared to w hich the first two centuries of the industrial revolution will be negligible. In the m eantim e, we m ust learn to live sanely. B ut, in spite o f hum an natu re, those 6,000 “ static” y ears w ere fa r fro m static.
Change has alw ays been in the air, and today it is m ore hopeful than ever.
In v estin g In M an-P ow er
R
I G H T N O W is n o t an easy tim e to raise new capital,■especially if y o u r business happens to be a small or little know n enterprise. B u t we have recently learned o f one com pany th a t raises the equivalent of $100,000 of fresh w orking capital every y ear o r two. I t does it by the sim ple expedient of adding a new $5,000 m an to its production o r sales staff. “W h en we need a new m an,” w rites D r. A rth u r R . M aas of L os A ngeles in S o u th ern C alifornia B usiness, “ we proceed by setting aside m oney fo r an investm ent som ew hat like th a t fo r a new m achine. W e figure it will cost so m uch to locate a prom ising m an and te st him fo r six m onths, tra in him, let him dem onstrate w hat is in him fo r our business, and if he does not m easure up, let him go w ith th e feeling th a t we have m ade a fa ir tria l all around. . . . U ntil he has m ade his place we reg ard him as a research p ro ject and do n o t charge his initial salary to expenses.
A f te r the test period, he soon becomes a producer and an asset. W e have had very few failu res.” B uilding on m anpow er is n o t exactly a “secret of success” b u t th ere is plenty of evidence to prove th a t organizations so built can exhibit g reater stren g th and stability th an certain large aggregations o f capital.
February, 1 9 3 3 — Chemical & M etallurgical E ngineering 59
By KENNETH A . KOBE Department of Chemical Engineering
University of Washington Seattle, Wash.
C H E M IC A L W A R F A R E
In M o b and Crime Control
Tear gas foils a bank holdup
( P hoto b v F ederal L ab orato ries, I n c .)
I
N T R O D U C T IO N of chemical w a rfa re du rin g the W o rld W a r, and its rapid rise to im portance as an offensive and defensive arm , b ro u g h t to the a tten tion of the country a new w eapon. U nlike the rifle and pistol which possessed num erous peace-time uses, chem ical agents had been the object o f so m uch adverse propaganda th at people looked upon them w ith ho rro r.T h a t m uch of this ignorance concerning chemical agents still exists is shown by the cry th a t arose w hen tear gas w as used to cause evacuation of the B onus A rm y camp in W ashington, D. C. T h e train in g o f a large num ber of m en during the W o rld W a r in the use of chemical agents, retu rn ed to civilian life a group of m en fully aw are o f the potential value of chemical agents fo r offensive and defensive use against the crim inal. T hese m en have changed chemical w a rfa re m aterial to meet the needs o f police forces, devised new kinds o f equip
m ent which can be used by the individual fo r the p ro tection o f his p ro p erty o r person, and continually car
ried out an educational cam paign to show th a t the use o f chemical agents is the hum ane m ethod of handling not only crim inals, but also mobs. I t m ust be rem em bered th a t the individuals in mobs— lynchers, fo r exam ple—
m ay be responsible citizens who should be handled firmly b u t w ithout casualties. F o r this purpose chemical agents are id e a l F o r the protection of p ro p erty chemical agents are proving th eir m erits fo r they are quick acting and th eir persistent n a tu re gives protection even a fte r the device has discharged. Such a device can well be ad v er
tised as one th a t “ fights back.”
J u s t as chemical w a rfa re has a history p red atin g the W o rld W a r, devices and chemicals to p rotect safes and vaults from illegal entry w ere patented at an early date.
U n ited S tates patents of 1871 and 1872, fo r instance, disclose chemical m eans fo r this purpose. M any other devices and m ethods have since been devised, differing only in the mechanical details or chemical agents used.
Chemical devices on the m ark et a t the present tim e fo r protecting safes against b u rg lars m ay be divided into tw o classes. T h e first consists o f a frangible container w hich is broken to release a volatile chemical a g e n t; the
o ther is a m echanical o r electrical device w hich will detonate a grenade to volatilize a chem ical ag en t by a b u rn in g charge. T h e first type em ploys a glass container w hich is placed on the inside of the sa fe door behind the com bination tum blers. W h en the spindle is d riven back it breaks the container and allows the volatile chemical agent to escape. T h e use o f explosives w ould likewise break the container and liberate the chemical. P resen t- day devices of this sort contain chemical ag en ts such as chloropicrin, brom acetone and o th er lach ry m ato rs which will readily volatilize w ithout th e application o f heat.
T he second type contains a lachrym ator such as chlor- acetophenone which, being a solid a t room tem p eratu re, m ust be volatilized by the application o f heat. T he chloracetophenone is m ixed w ith nitrocellulose and the charge ignited w ith a detonator, the heat o f com bustion o f the nitrocellulose sublim ing the chem ical as a cloud of tear gas. T h e safe protector is placed on the inside of the safe door and a firing plunger is held up by a tension w ire w hich passes th ro u g h a shearing block connected to the re a r o f the com bination spindle. A n y attem p t to drive in the spindle puts pressu re on the sh earin g block and severs the tension w ire. T h e firing p lu n g er then hits a percussion cap, ignites the b u rn in g charge and volatilizes the lachrym ator. T o extend this pro tectio n to the entire safe door it is m erely necessary to w ind the tension w ire back and fo rth over pulleys until it g u ard s the entire surface, and if desired, o th er sides o f the safe as well. A lthough it is exceedingly effective w hen ignited, the sublim ed chloracetophenone is quite p er
sistent and ra th e r difficult to rem ove fro m the prem ises.
T h is safe protector is m erely a m odified h an d grenade and by changing the m anner o f detonating, the grenade m ay be modified fo r m any o th er purposes. O n e form is the gas lock ’ w hich is being used to p rev en t th e forcing o f doors. T o com bat daylight holdup of banks a gas sys
tem has been developed w hich can be op erated fro m the tellers cage or lobby desk. A gas cartrid g e is fired elec
trically and the lachrym atory vapors conducted th ro u g h a sh o rt length o f tubing to escape into the room th ro u g h inconspicuous outlets.
60 Chemical & M etallurgical E n g in e e rin g—V o l.4 0 ,N o .2
Chemical equipm ent has become an im portant p a rt of every police d epartm ent and its use and m isuse, as re p o rted in the daily press, has m ade the public conscious o f th e effectiveness of tear gas. M ost of this equipm ent is a m odification o f th a t used d u rin g th e W a r o r de
veloped by the Chemical W a rfa re Service since th a t time. U sually sm aller quantities o f chemical are em ployed since the agent is m ore o ften used indoors. T oo sparing use of the sm aller grenades in outdoor rio ts has sometimes been ineffective, as in the D earborn riot.
H a n d grenades are of several types. T h e strik e r type (sketch 1) is a m odification of th e rifle grenade an d re quires the w ithdraw al o f the pin and the strik in g o f the plunger against some h ard object b efo re the grenade is throw n. T h e autom atic type ( 2 ) requires the w ithdraw al of the pin, but w hen the grenade is th ro w n from the hand a sp rin g throw s out the lever on the side and de
tonates the grenade. T h e success of mobs in h u rling grenades back at the police has brought out a type which im m ediately produces a te a r gas cloud w hen the side lever is th ro w n out. T e a r gas, sm oke o r irrita n t smoke m ay be used in these grenades. C hloracetophenone m ixed w ith nitrocellulose is em ployed in the usual te a r gas grenade. H exachlorethane, zinc pow der and zinc oxide produce a dense w hite sm oke fo r screening p u r
poses, o r to sim ulate gas clouds fo r tra in in g purposes.
W h e re the situation is m ore serious th an the usual riot a grenade using diphenylam inechlorarsine m ay be em
ployed. T h is substance is one of the irrita n t sm okes or
“ sneeze gases” used du rin g the W a r, and though it is odorless it soon causes nausea and vom iting, headache and a sense o f suffocation. W h ereas the effects from te a r gas soon disappear w hen the person leaves the gas cloud, the effects from the irrita n t sm oke last fro m sev
eral hours to an entire day, b u t leave no perm anent in ju ry . T h ere is also a grenade (3 ) in w hich a liquid te a r gas, such as chloropicrin, is sealed in a glass container and surrounded by a so ft copper shield. W h e n it is throw n against a surface the glass is broken and a l l o t s the liquid to volatilize w ithout explosion.
T he te a r gas pistol ( 4 ) is a developm ent of the old V ery signal-light pistol. I t uses a cartrid g e 1 in. in diam eter, sim ilar to a shot gun shell, in w hich th e shot and p a rt of th e pow der charge are rem oved and replaced by a nitrocellulose container filled w ith chloracetophenone dissolved in ethyl brom acetate. T he spread of gas on dis
charge gives a 9 -ft. circle at the m axim um range of 30 ft.
Tear-gas weapons for personal protection and mob control: (1-3) grenades; (4, 5) gas pistol and gun; (6) riot tube; (7) pocket-size gas projector
A barrel and trig g er in the form of a police billy is made to discharge a 12-gage shell. F o r longer range w ork the gas field gun (5 ) is employed. T h is weapon uses a cartrid g e in. in diam eter and 8 o r 10 in. long. V arious kinds of cartrid g e charges m ay be employed, as tear gas shells, sm oke screen shells, illum inating sta r shells w ith p arachute and colored sta r signal shells. T h e 10-in.
shell discharges a projectile w hich detonates on striking a h ard su rface or by a tim e fuse eight seconds a fte r firing. Such a projectile is especially adapted fo r forcing evacuation of a barricaded space, as its range is 450 ft.
T h e 8-in. shell fires a gas cloud w ith a spread o f 15 ft.
at its range o f 35 ft., so is suitable fo r rio t use.
T h e latest developm ent in police equipm ent is the
“ rio t tu b e” (6) fo r use against mobs. T h is is a steel cylinder w ith a valve a t the end. I t contains a liquid te a r gas, o r te a r gas and a smoke producer such as stannic chloride, u nder high gas pressure. W h en the valve is opened th e liquid is sprayed o u t and im m ediately vaporizes to form a cloud. T h is tube has several advan
tages over the gun type o f equipm ent, since its discharge can be controlled in am ount and direction and will last over a period of tim e. A sm aller size is m ade in the form of a police billy.
F o r individual protection, the fountain-pen type of gas gun is ra th e r well know n as num erous styles have ap
peared, fo r sale to the public. T hey use a .38 caliber ex tra-lo n g pistol shell or a .405 caliber rifle shell. The la tter contains about 4 c.c. of liquid gas in a nitrocellulose container and has a spread of 3 ft. a t m axim um range of 12 ft. A ccurate shooting a t sh o rt range is necessary to secure results. T h e pocket size gas p ro jecto r (7 ) is a larg er w eapon, using a 20-gage shot-gun shell w ith chem ical. T h e spread of gas on discharge gives a 4 -ft. circle at the m axim um range of 15 ft.
T e a r gas still rem ains very m uch of a m ystery to the general public. T h e fear o f the unknow n m akes chem ical agents exceedingly effective in riot duty, but the same ignorance prevents responsible people from m aking use of chemical equipm ent in the protection of th eir persons and property. O nly dem onstrations will convince the uninitiated of the m any advantages of such equipm ent.
U n fo rtu n a te ly a skeptical attitu d e is taken by m any police officers who prev en t th eir departm ents from ob
taining and using te a r gas. T hose fam iliar w ith the m any advantages should aid in educating the public th a t tear gas is a useful servant as well as a dreaded enemy.
February, 19 3 3 — Chemical & M etallurgical E ngineering 61
W h a t the School of Exp erience
Has Taught a Dye-Plant O p e ra to r
A b o u t Construction Materials
By A POST GRADUATE
R
A W M A T E R IA L S used in dye plants include a large assortm ent of chemicals and interm ediate -products, which m ust be handled in all physical stages, gaseous, liquid and solid, a t high tem peratures and pressures. N um erous corrosion problem s are thus encountered, and the equipm ent is subject to a wide range of conditions, so wide, in fact, th at alm ost every known m aterial of construction finds application. A s a full discussion of the m aterials used necessarily would include m any data w ithout particular interest, the following review will be confined to the m ore outstanding applications.
Generally, association w ith conditions in a dye plant quickly develops a tendency and ability to consider all construction m aterials and plant products in view of their relation to c o rro sio n ; this is the gage by which a m ate
rial is found suitable o r of no value. T he lasting quali
ties are the prim ary co n sid eratio n ; closely connected w ith these is the question of first cost, as available funds generally impose certain limits which prevent the selec
tion of a m aterial otherw ise m ost suitable. Conserva
tism on the p a rt of the official w ho signs appropriations o ften creates some unexpected, often enlightening inci
dents when substitutes m ust be resorted to. T o illus
trate this point, an appropriation fo r a certain installation had become exhausted, w ith no funds rem aining fo r equipm ent needed fo r dissolving iron in hydrochloric acid. A s a tem porary expedient tw o cast-iron pots, salvaged from the scrap yard, w ere im bedded in cinders, an acid hose was lowered from an upper window, and a
“ tw o-by-four” w as donated fo r use as an agitator. N ot a scientific installation, but a suitable one for, a fte r eight years of operation, the pots are still good, the two-by- fo u r has been replaced only twice, and no one has ever thought of asking fo r a change.
Selection o f M aterials
Selection of the basic m aterials fo r equipm ent is gov
erned by general conditions pertain in g to corrosion, tem p eratu re, and physical properties. C ertain general fac
to rs soon dem and attention. A caustic process suggests iron, steel, nickel alloys, o r pure nickel. S trong inorganic acids— except hydrochloric— suggest iron and steel in the early stages, w ith lead, bronze, or wood as dilution proceeds. H ydrochloric-acid processes suggest glass, special alloys, rubber, and earthenw are. A nitric- acid process involves chrom ium steel, alum inum , or high- silicon cast iron. Follow ing this line of reasoning the
“ don’ts ” should be of equal im portance. Zinc alloys, or
alum inum m ust not be used w ith caustic liq u o rs; copper alloys should be kept away fro m n itric a c id ; s o ft rubber m ust never be exposed to hydrochloric-acid fum es, nor brass to am m onia. In spite of th e corrosion com plex cast iron and steel still rem ain the m ainstays of the equipm ent d esig n er; this is largely d ue to th eir low er price.
Skill o f Foundry M en
A s a rule the chemical engineer does not realize the skill which can be exercised by the average fo u n d ry man, w ho in tu rn has little conception of th e fo rm e r’s needs, all because they do not speak the sam e language. T he draw ings of some cast-iron equipm ent m ay be sent out fo r estim ates w ith the enlightening specification th a t a good grade of cast iron, free fro m im perfections, m ust be furnished. U n d e r these conditions the average foun
d ry m an usually quotes fo r a nice, clean-looking piece of gray iron, probably a w onderful tailstock fo r a 36-in.
engine lathe, but not at all suitable fo r the bowl of a caustic kettle. O n the o ther hand, little w ould be accom
plished by m erely telling the fo u n d ry th a t th e equipm ent is to be used fo r a certain chemical p ro d u ct as it gen
erally has no conception of w h at th a t m eans. Both parties m ust fo rg et th eir secrets tem p o rarily and discuss the problem.
A n illustration or two will em phasize th is fact. Caustic dehydration pots have been m a n u factu red fo r y ears and the fo u n d ry m an has had an o p p o rtu n ity to make observations a t close range w ith the resu lt th a t excellent pots are made. Subjected to this service any o th er cast- iron kettle in the plant would last b u t a sh o rt tim e. T he results so happily attained m ay be cred ited to the fact th at the foundry has become fully acquainted w ith the requirem ents.
A nother illustration, m ore specific, b u t equally out
standing, w as furnished by a b atte ry o f m achines used in reduction of nitro-benzene w ith pow dered iron and hydrochloric acid. T h e kettles used h ad in tern al liner plates and agitators of o rd in ary cast iron w hich wore out so rapidly, due to the scouring action of th e iron, th at not m ore than one-half of th e equipm ent could be used at one time. A verage life of the ag itato rs w as three m onths, of liner plates about eight m onths. T h is situa
tion had been accepted as one of th e necessary evils of the process. T hen appeared a m an who knew enough about both foundry w ork and chemical equipm ent to appreci
ate th at this did not have to be. T h e m a tte r w as taken to a foundry w ith fra n k discussion of the requirem ents. A s
62 Chemical & M etallurgical E n g in e e rin g—V o l.4 0 ,N o .2
a result an iron w as produced th a t was so hard, th a t no drill could dent it, yet tough enough to p erm it tra n s
p o rtatio n an d the pounding necessary to assem ble the equipm ent. A verage life of ag itato rs w ent up to 14 m o n th s; of liners to tw o years, and the whole b attery rem ained on production. T h e new iron cost lc. p e r lb.
less than the old, because of its large content of scrap.
N e x t to cast iron in general utility value are the bronzes, p articularly the alum inum and m anganese types.
N ow th a t the la tte r type can be purchased in plate and pipe form on short delivery, w hile rods and bolts m ay be obtained from stock, the troubles in dye plants are m ate
rially lessened. A s long as these alloys could be had in cast form only th eir field w as lim ited; w ith plates a n d pipe available bothersom e lead linings o r lead-covered coils need no longer be used in w eak sulphuric-acid solu
tions. A lum inum bronzes of one com position or ano th er give excellent service in both sulphuric and hydrochloric- acid processes. T hese alloys have g reat stren g th , high h eat conductivity, and rem arkable corrosion resistance.
B efo re going too fa r and creating the im pression th a t allocation of alloys and iron m ix tu res to p ro p er corrosion service is a sim ple m atter of laboratory test alone a solem n w arning should be sounded. T h is is n o t the case.
P la n t equipm ent involves m any facto rs w hich sim ply can
n o t be duplicated in the la b o ra to ry ; all decisions involv
in g fine points should be supported by observations in the plant. E ven then one is n o t justified in sitting back com placently, thinking th a t the problem is solved. A n exam ple o r tw o will illustrate this thought.
O p eratin g Experience
T he equipm ent of an old process w as being sh ifted to a n o th e r plant to effect consolidation into a small num ber o f large units. O ne step in the m an u factu re w as the production of aniline hy d ro ch lo rid e; the addition of hydrochloric acid to aniline had alw ays been done in small cast-iron kettles w ith ag itato rs o f the same m ate
rial. T h e large 1,500-gal. units w ere equipped in the sam e m anner, b u t operation disclosed th a t the agitators would last three batches only. T h is w as not surprising, a s 3,000 lb. of 22 deg. hydrochloric acid w as used.
Incidentally, no one quite understood why th e equipm ent in the old plant w ithstood the punishm ent so well, but as it did, the new plant had been p attern ed a fte r it. A s quick action w as necessary to rem edy this alarm ing situation, an a g itato r and sh a ft of 8 9 : 1 0 : 1 (copper, alum inum , iro n ) alum inum -bronze w as installed. T h is m etal lasted th ro u g h 12 batches (11 days p er b a tc h ).
A t each failu re everything w as m inutely exam ined fo r some clue th a t m ight reveal th e cause of the difficulty;
o n one of these occasions it w as noted th a t all of the square 1^-in. nu ts w ere in b etter shape th a n the other p a rts. P ersisten t inquiry eventually b rought to light the fact th a t the foundry, in filling one o rd er, fo rg o t to p o u r the n u ts of the 8 9 : 1 0 : 1 m ix tu re and a t the last m om ent cast them fro m a 9 0 : 10 m ix tu re fo r some o th er cus
tom er. Based upon this uncertain evidence the n ex t ag itato r was m ade of the 9 0 :1 0 m ix tu re and th e life im m ediately increased 50 p e r cent, or to 18 batches.
F u rth e r experim entation finally led to the adoption of a patented alum inum -bronze of the 8 8: 10: 2 composition.
T h e first one installed lasted 68 batches ( f o u r y e a rs ), before failure o c c u rre d ; th e o ther fo u r are still in opera
tion. A cast-iron ag itato r cost $76 installed, a bronze ag itato r $500. C onsidering the scrap value of bronze and disregarding tim e lost in repairs, bronze agitators saved $3,800 per year fo r the departm ent. T his is a ra th e r striking exam ple of the different action of varying com positions of the same alloy u nder otherw ise sim ilar conditions.
Cast Iro n K ettles
N ow , a w ord as to the cast-iron kettle itself, under the identical conditions. T hese vessels have 3-in. walls, which, if of u n ifo rm and clean com position, a re reduced to a thickness o f £ in. at the solution line before giving w ay to the 90-lb. jacket steam pressure. A t this stage from 75 to 80 batches have usually been completed, a t a cost of about one-seventh cent per pound of product.
C ast of bronze or lined w ith enam el these kettles would cost six or seven tim es as m uch as iro n ; they would, th erefo re, have to last at least 15 years. W ho can be su re th a t th e process will be in use at th a t tim e?
Q uite advantageous, b u t seldom practiced, is the use of rough cast-bronze n u ts on external steel bolts, w here these m ay have to be rem oved in a h u rry . T h is applies particularly to cover bolts and bolts used in rem ovable flanges. W h en undisturbed fo r long periods the bolt and n u t invariably ru st together, requiring sledge and chisel w ork, generally aw kw ard and dangerous around the crow ded piping of the apparatus. If the n u t is frequently rem oved, as in placing blow pipes, the threads become w orn. U se of bronze n u ts— the inexpensive type
— will overcome these troubles.
R ubber fo r hose and tan k lining is fam iliar to all, but the use of sections of acid hose w ith pinch cocks to reduce valve expense on corrosive w ork, w here no g reat pressure is involved is not com m only know n. T his device requires only a 24-in. standard acid hose pinched w ith a steel clamp. T h is ra th e r severe tre a tm e n t of the hose eventually leads to broken walls, but the p a rt is easily replaced and the whole cost is fa r less than th a t of a special valve.
V arious alloys such as copper-nickel, nickel-chrom ium , and nickel-m olybdenum all have th eir m erits in the p re vention of corrosion or of contam ination of product, but th e ir high cost often precludes a m ore general applica
tion.
D iscussion of m aterials fo r dye-plant equipm ent would be incom plete w ithout m ention of the pressed and molded phenolic com pounds, m aterials which come n earer than any o ther to being universal corrosion resistant. T h ey seem to be wholly unaffected by the m ajo rity of chemicals encountered in a dye plant and have physical characteristics suitable to construction p u r
poses. W ith such qualifications one would expect to find this m aterial in com m on use, b u t such is n o t the case. A pplication has n o t advanced beyond the stage of bolts, rods, an d a few sm aller appurtenances. C ypress wood, the only suitable m aterial fo r color vats, is becom ing m ore scarce each day and the thoughts o f substitutes constantly p resent them selves. A better m aterial than the phenolic com pounds fo r such equipm ent can hardly be visualized. B ut, even though vats in chemical plants are num bered by the thousands, only w ithin the past few m onths have the plastics m an u factu rers developed m aterials suitable fo r this use.
F ebruary, 1933 — Chemical & M etallurgical E ngineering 63
P r o c e s s i n g
P ro c ess D e p a r tm e n t
F illin g P a c k o g e s |
L a b o i
O r d in a r y a n d Heavy Bepoir^j
R epair Shop A d m in istrai«
P r o d u c tio n Kainłenance Deport mg nłj
M inor C o n s t r u c t io n S u perv isio n o f C ontractorsj
P a c k a g e R e p a ir | S t o r e h o u s e
U nloading Raw M a te ria ls Y a r d D e p a r t m e n t
L o a d in g F r e i g h t C a r s Y a r d C a r e
THE CHEMICAL PLANT EXAMINES ITS
M A I N T E N A N C E P O L IC Y
By FRED. D. HARTFORD Mcchanical Engineer
Denver, Colo.
Separation of functions in a chemical plant’s production set-up
I
N I I S E A R L Y H IS T O R Y the chemical plant, or any industrial plant fo r th a t m atter, is m arked by a unique characteristic. D u rin g the first few m onths, every m an connected w ith the plant, from the superintendent to the most unskilled laboring m an, is dedicated to these ideas, “get the plant going, get the kinks w orked out, bring it up to production.” A ny distinct lines of position or even of authority are not sharply m arked.
T he superintendent m ay lend a hand at tightening a belt, or a handy m an m ay be stationed at a pyrom eter.
A hard pressed operator m ay install a piece of pipe, o r a pipe fitter m ay be called on to muck.
A fte r the process has developed into a routine, how ever, the two functions, processing and repair, become distinct. T ru e enough, the superintendent sees them both as expense and, accordingly, strives to make the sum of their costs a m inim um , but he finds he can b etter control these costs when he m akes a clear differentiation between the functions themselves. T hus, he establishes either in
form ally, by w ord of m outh, or form ally, by m eans of bulletins, definite operating policies, so th at each dep art
m ent and all mem bers of departm ents m ay understand precisely th eir duties in forw arding the aims and p u r
poses of the plant.
B ut, as any plant superintendent knows, policies that a t once define briefly the best m ethods of doing things, and a t the same tim e cover every situation th a t arises, are difficult to form ulate. T h ere is a broad tw ilight zone w herein processing and m aintenance are so closely in ter
m ingled th a t any statem ent fixing a sharp line between th e duties o f these tw o departm ents m erits careful con
sideration.
Maintenance departments usually handle minor new construction in chemical plants—
f o r exam ple, some chemical plants m ay give their process men kits of tools, broom s, an d w indow -cleaning com pound, and instruct them to act accordingly. In such a plant, m aintenance m en are called on only w hen their special craftsm anship is indispensable. In one p lan t I knew, the process men even had th eir ow n lathe on which they refaced valves and fittings “ in betw een tim es.” Due to the exceptional skill of the process forem an in charge of this unit, this procedure succeeded in producing very low total production costs.
• A t the opposite extrem e, and I th in k this is the direc
tion in w hich chemical plant m anagem ent is tending, one plant m anager I know, becoming ex asp erated at th e little deviations from established optim um op eratin g conditions excused u nder the plea th a t certain “ch o res” had to be done, issued orders to his process m en th a t they should have no tools w hatsoever ; not a ham m er, n o r a w rench, noi a piece of waste. T h e sole duty o f process men, the order stated, was continually to patrol th eir stations, tak-
64 Chemical & M etallurgical E n g in e e rin g—V o l.4 0 ,N o .2
As well as general supervision and acceptance of new plant classed as major construction
ing pyrom eter and m anom eter readings, ad ju stin g valves, rheostats, speed controllers and d ra fts, to the end th a t the reactions, heat tra n sfe r, and absorption w ere each to be held a t the very pinnacle of efficiency. F o r any mechanical disarrangem ent w hatsoever, a t any hour of the day or night, they w ere to call the m aintenance de
partm ent and w ere to hold it responsible fo r m aking rapid and w orkm anlike repairs. O nly the gravest em er
gency could excuse any deviation from these directions.
T h e increasingly exacting standards to w hich both process efficiency and mechanical rep air are held, seem to indicate th at such operating policies will increase in vogue. I f such is the tendency, let us exam ine the m ainte
nance function critically 'so' th a t we m ay form ulate a policy th a t at once produces a m inim um of cost and a m axim um of desirable results.
C onsidered narrow ly, the m aintenance d epartm ent of the chemical plant has th ree distinct offices : ( 1 ) servic
ing or ro u tin e inspection, cleaning, oiling, packing, and a d ju stin g ; (2) o rd in ary ru n n in g repairs th a t can be h an dled by the norm al num ber of c ra ftsm e n ; and (3 ) heavy repairs and replacem ents, frequently req u irin g additional crew and tackle. Besides these, as indicated in the a d
jo in in g ch art, m ay be added rep air- shop adm inistration, m inor construc
tion, supervision of building and equipm ent contractors, and package m aking and repair.
T h e servicing function is frequently the m ost difficult to separate from the process personnel. O ftentim es, am ong the process m en are num bered those who have excellent mechanical skill and who p re fe r to do their own packing, oiling and ad ju stin g . M ore
over, they can dem onstrate th a t they know m ore about these duties than m ost m aintenance men. H ow ever, a carefu lly train ed m aintenance m an w ho m ay be detailed to servicing duties in the plant should soon be
come m ore skilled and resourceful
These functions, how
ever, the operation of power house and pur- chased-power substation, are definitely operating department perquisites
T
in this particular field than any process m an to whom such w ork can be only incidental.
If the process d epartm ent has taken on certain m ainte
nance functions, this seem ing appropriation m ay be traced back to occurrences norm al in any plant. P erhaps the entire m aintenance d epartm ent w as once d ra fte d else
w here onto an u rg en t job, w hile the process men did cer
tain required m aintenance w ork at no added cost, and it seemed expedient to continue the procedure. Vacations, o r sickness, o r accident m ay have made it advisable for the process m en to take care of certain m aintenance fo r a time, and the m atter became a habit. A process fo re
m an, eager fo r a better job, m ay have felt th a t the m ore tasks he could take on, the better his chances, and may have w illingly accepted some of the duties of an over
burdened m aintenance d epartm ent head. Such practices creep into plant routine alm ost unobserved and their w eakness is revealed only by emergencies.
Power a Process Function
B ut if the process departm ent tends to take on m ainte
nance functions, this tendency is equalled only by th a t of the m aintenance departm ent to encroach on process work.
T h is is particularly evident in the case of the pow er departm ent.
U n d er the heading of “ pow er,” the chemical plant usually includes the production of steam , electricity, com
pressed air, and w ater, and the distribution system s for these essentials. A lthough these item s are consum ed by the various plant units, yet they are operating or process functions ju s t as m uch as if they w ere interm ediate
F ebruary, 1933 — Chemical & M etallurgical E ngineering 65
chemicals or chemicals sold to custom ers. U n fo rtu n ately , I think, fo r the m aintenance departm ent, it is usually fo u n d operating as well as m aintaining the pow er de
partm en t. T h is is the result o f tw o conditions : the m aintenance m en, both supervisors and craftsm en, sta rte d th eir careers around the pow er house or m ade it th eir head q u arters w hen the p lan t w as small. T hen, as the plant grew , quite n atu rally they absorbed th e pow er function into th e ir ow n departm ent. O r, secondly, since pow er seem ed unrelated to th e production o f chemicals, it became a so rt of unw anted orphan, an d the m ainte
nance engineer, either because he w as an especially obliging chap o r because he w anted to “ see the wheels go ro u n d ” u n d er his ow n supervision, willingly, b u t to the detrim ent o f all concerned, took over th e pow er house.
P ro d u ctio n o f steam assuredly is n o t a m ore com pli
cated operation th an the production of purified sulphur dioxide from pyrite ; the treatm en t and pum ping o f w ater is n o t a w hit m ore com plicated th a n th e regulation and pum ping of sulphuric acid over an absorption tow er ; nor should the ru n n in g of a turbine require a h igher type of operative than the regulation of a m echanical m uriatic plant. Since the pow er function is directly connected w ith the other plant processes and since it requires no m ore skilled attention th an m any chemical processes, its a d m inistration logically falls to the process departm ent, thus relieving the m aintenance d epartm ent o f a responsi
bility th a t always ham pers its ow n p roper function. I t is axiom atic th a t the m ore tim e devoted to th e m aintenance planning and strategy', the low er will be m aintenance costs.
Servicing— "Stitch in T im e”
T h e service function o f the m aintenance departm ent—
routine inspection, oiling, and ad ju stin g o f p lan t m a
chinery, is little less im portant th an th at of p lan t repairs.
P ro p erly carried out, it should forestall m any large re p airs th a t would otherw ise bring about heartbreaking rep air costs. F o r exam ple, if a skilled electrician m akes a daily inspection of each m otor in the plant, checking its tem perature, lubrication, the p ro p er belt tension, its need o f shop cleaning, the clearance, and the like, then he may reduce the chance of its b u rn in g out alm ost to the vanish
ing point. M oreover, he m ay prevent serious in te rru p tions to production th a t would be fa r m ore costly than the rew inding o f the m otor.
S im ilar reasoning would apply to pum ps. C areful periodic lubrication, repacking, and m aintenance of clearance m ay increase the o rd in ary life o f a pum p sev
eral tim es and contribute to its efficiency considerably.
Likew ise, the regular cleaning of w indow s and electric lam ps and shades undoubtedly has m uch to do w ith a full re tu rn on th eir cost. T h is servicing has little direct connection w ith the repairs, yet th e m en w ho p erfo rm this w ork best have the m aintenance type o f m ind and m akeup, ra th e r th an the process type.
B u t even m aintenance men, as plant superintendents know, fall into tw o distinct classes. B oth a re indispensa
ble. yet th e ir full value can be obtained only w hen this difference betw een them is fully recognized. O ne type o f m aintenance m an, th e b e tter craftsm an, is irritated by the least deviation from p erfect operation. F o r instance, should this type o f m an see a blow er w ith bearings a trifle too w arm o r developing an om inous knock o r rattle, he is fo r im m ediately sh u ttin g dow n th e p lan t an d re
building or replacing the blow er, reg ard less o f p lan t p ro duction. M ind you, this type o i m an is indispensable in doing high-grade rep air w ork. T h e o th e r type of m aintenance m an, and this is th e so rt w ho should be given th e m aintenance service job, finding th e same blower, would by ad ju stin g , oiling, o r by h is m ysterious faculty fo r keeping things going, hold it to th e jo b until everything else w as set, so th a t d isturbance to production would be cut to th e m inim um . T h e su p erin ten d en t’s m aintenance policy will distinguish betw een these men.
M atching Jobs and T em peram ents
Chemical p lan t superintendents recognize th a t first- class process m en and first-class m aintenance m en differ fundam entally. R arely does a v ery adept craftsm an possess the tem peram ent necessary to a good operator.
T h e thorough-going process m an m u st visualize the in fluences, o ften concurrent, of tem p eratu re, pressure, specific gravity-, concentration, turbulence, and th e like, upon the reactions of m aterials som e o f w hich m ay be unstable gases o r com pounds having only a theoretical existence. A ided byr his control in stru m en ts, m anom eters, potentiom eters, and indicators o f v ario u s so rts, he in stantly tran slates cause and effect in his m aterials into the necessary regulation o f his plant.
In contrast, the m aintenance m an visualizes a m achine as a substantial entity having precise dim ensions, w eights, conductivity, an d the like. T h e fine m echanical percep
tions of th e high-grade craftsm an d iffer n o t in degree but in kind from the intuitions of th e sk illfu l process m an. W h y m en should be th u s tem peram entally different need not concern us here. W e do know , how ever, th a t m aintenance w ork of the chemical p lan t given to men fundam entally suited to it is reflected in m inim um m aintenance costs. P recisely th e sam e reaso n in g holds fo r selecting process men.
In fine, the m aintenance policy of a chem ical plant m ight be sum m arized briefly th u s :
1. T h e m aintenance d ep artm en t is responsible fo r all repairs, replacem ents, and m inor construction, fo r servic
ing o f machinery7 and buildings, fo r th e acceptance of new construction by contractors, fo r re tu rn ab le package m aking and repair, an d fo r re p a ir shop ad m inistration.
2. T he m aintenance d ep artm en t is responsible fo r the m aintenance of th e pow er d ep artm en t in th e sam e m anner as fo r o ther process departm ents, b u t it shall n o t be re sponsible fo r pow er generation n o r th e o peration of pu r- chased-pow er equipm ent.
3. In selection o f m aintenance personnel, tem peram ent and craftsm anship shall be given equal consideration.
N ational S afety Council, Chicago, has inaugurated, experim entally, a new service called “ Safety' In stru ctio n Cards.^ T hese are 3x5-in. cards fo r d istrib u tio n to o perating executives, forem en an d w orkm en, each one of w hich carries^ a technical o r sem i-technical treatm en t of a specific accident hazard. Since th e y a re specific, it is felt th a t the subjects covered are unsuitable fo r poster treatm en t. O f the 14 cards a t p resen t available, several a re of p articu lar in terest to chem ical o p eratin g d e p a rt
m ents. O th ers should be valuable fo r m aintenance dis
tribution, A leaflet published by the Council gives com
plete inform ation.
66 Chemical & M etallurgical E n g in e e rin g—V o lA 0 ,N o .2
■ of ¡a m .—
R e s u lt a n t n u t p r e s s u r e
R é s u lta n t g a s k e t m p r e s s u r e
G a ske t m e d ia n t i n e —
Bolts and Flanges for T A N K S
AN D
H E A T E X C H A N G E R S
Fig. 1 — Gasket pres
sure in a 6-in. pipe flange
By C. O . SANDSTROM Thermal Engineering Co.
Los Angeles, Calif.
E d ito /s N o te — In an earlier article (D ec., 1932, pp.
668-672) the author presented a general discussion of the design of heads fo r tanks and heat exchangers, w ith p a r
ticular reference to the o rd in ary spherical dished head, and lesser attention to elliptical heads, flat, stayed heads and a plain spherical head w ithout knuckle curve. In a later issue he will take up special heads and an im prove
m ent on the older ones.
* S W I L L A P P E A R fro m w hat follows, the design A of bolts and flanges fo r attach in g the heads of f \ pressure vessels is fa r fro m a cut-and-dried busi
ness. M any assum ptions a re involved and designers are by no m eans in exact agreem ent as to procedure. A s a first step, it is necessary to determ ine th e total pressure acting on the head o r cover. T h e one un certain ty in this step is the area u n d er pressure. I t is recom m ended by som e authorities th a t this area be assum ed as bounded by th e outer circum ference of th e gasket. A lthough this e rrs on the side of safety I cannot agree w ith the recom m endation. I think it best, o r a t least m ore w orkm anlike in engineering design, to establish the d ata to the best of one’s ability and then allow fo r th e u nforeseen by so- called factors of safety. I t seems obvious th a t the full fluid pressure cannot be exerted to the outside edge of the gasket. T o say th a t it can im plies th a t all b u t the outer edge of the gasket is useless in resisting the pres- sure— an evident absurdity. T e sts m ay be m ade to de
term ine the area u nder fluid pressu re by drilling holes radially into the edge of the gasket and noting the depth a t which leaks occur.
W h e th e r the diagram of the fluid p ressu re on the gas
ket is a triangle w ith the ap ex a t the o u ter edge of the flasket as shown in F ig . 1, or a parabola (o r some other cu rv e) w ith the v e rte x som ew here inside the edge, the total pressure, it seems to me, does not exceed the u nit pressure tim es the area inscribed by the m edian line of the U s k e t fo r gaskets lying w ithin the bolt circle which, fo r practical purposes, m akes the p ressu re diagram th e tr i
angle a, b, c, show n in the figure.
A lthough the difference betw een the outside area and the m edian line area of gaskets in heat exchangers of
large diam eter m ay be a trifle, the difference in the case of some pipe flanges is large and would e x e rt consider
able influence on design, because of the com paratively large ratio of gasket area to p o rt area. H av in g estab
lished the to tal fluid pressure, the n e x t step is to find the additional pressure on the gasket necessary to insure tightness. T h e sum of the tw o is then the load carried by the flange and the bolts.
T h e pipe-flange bolting stan d ard s o f the A m erican S tan d ard s A ssociation call fo r bolts which im pose an ap
p aren t u nit com pression on the gasket of fro m 8 to 20 tim es the w orking pressu re w ith full w orking pressure in the pipe (assum ing th a t the com pression is uniform ly distributed, which it is n o t) ; the low er ratio being fo r raised face gaskets and the higher fo r the n arro w tongue- and-groove gaskets.
A n o th er question th a t has been m uch debated is the point of application of the p ressu re exerted by the nut on the flange. I f th is point is assum ed to be on the circle passing th rough the centers of the bolts then the calcu
lated results would certainly be on the safe side. I t seems obvious, how ever, w ith a rin g gasket lying entirely w ithin the circle bounding the inside o f the bolt holes, m aking a cantilever o f the flange, th at th ere is some deflection of the flange w hich, added to the deform ation of the o u ter edge of the gasket, produces enough deflection to m ove the line of pressure to the inside half of the nut. I t has been proposed to consider the line of pressure as acting on a circle tan g en t to the inside o f the bolt holes, b u t th is would introduce very high bending stresses in the bolts, w hich will be discussed later.
U n certain ties th u s fa r disclosed are only added to w hen we come to proportion the bolts. W h en we con
sider th a t th e efficiency of a bolt as a m achine elem ent lies betw een 10 and 20 per cent, dependent on the condi
tion of th e bearing surfaces and lu b ric a tio n ; and th e u n certainty of the force applied to the w rench in tig h ten in g the nut, together w ith the uncertainties attending the area u n d er fluid pressure, and the point of application o f th e tig h ten in g force on th e flange, w e are inclined to feel w ith H e rb e rt Spencer th at, “A definition of w hich th e term s are indefinite, is an ab su rd ity .” Y et th ere is no o th er pro-
F ebruary, 1933,— Chemical & M etallurgical E ngineering 67
