NEWc

---T E C H N I Q U ES GUARANTEEIN6 THE LIFE AND SAFE OPERATION OF

PROCESS PRESSURE EQUIPMENT R d e. s*

The Travelers Insurance Company, Hartford, Corn.

Safety in chemical processing demands that vessels subject to pressure be comctly designed, properly installed, safely operated, and periodfully in- spected. The material in process bean an impor- tant relationship to the suitability of the vessel, its loution, appurknanar, and control.

Continuous safe operation n q u i m a definite in- spection routine conducted by a competent teat engineer, who will apply all required tests after proper preparation of the vessel with respect to

RFBBuRE vessels are in reality magazines of energy and, P unless correctly designed and constructed, properly in- stdled, eafely operated, and constantly ioepected, may con- stitute a serious hasard. While operating experience 88 a whole with un6red preasure vessels has beem relatively good, constant watchfuineas is eesmtd. There are nnmerous hazards which should be guarded against if workmen are to be protected from injury and property from damage. One has only to consider the numerous types of vessels used to- day in the chemical inaustrp to a p p h t e that each must be looked upon 811 a eeparata entity, and operated and inspected sccording to the circ&m surrounding that psrtiaular object. Thia procedure should be based upon common prac- tice for such v d , but ahodd be changed slightly to take cam of the special situation surrounding the individual unit.

necessary cleaning and ventilating. Such inspec- tions will provide opportunity for checking cor- rosion of internal surfaces and clogging or render- ing inoperative d pmsure release valves, pressure gages, or reducing valves.

The result will be longer life of equipment, better efficiency of process, accurate lonusting of the life of objects, and freedom horn interruptions and shutdowns. The actual cost of such procedure i s surprisingly moderate.

There is no Merence in the energy stored in a ateam-jacketd vessel at the m e preasure 88 the steam in the boiler supplying it except in 80 far aa rdse and contents are concerned. The wide variation of mstari$e of construction and the mnltitude of substances handled make the problem one requiring strict supervision in every chemical plant.

There is a dehite relation between the vessels under preb 8nre and the materisl in pmceas. Such a relation must be established prior to the Salection of the v d , for without a clear understanding of what ie to be done under a given Bet of processing conditions, the material for the vessel or for the king cannot be properly selected. While it ia true that car- tain unlired v d do not fall within the scope of common p- vessel codes, these codee am guides to Batisfaototy m a h a k and meth& of constructing p m u e v d . Ob-

I N D U S T R I A L A N D E N G I N F m m ' N G C H E M I S T R Y Vd 33, No. 9

k M 0 N U C O M m O a EXPLOSrON

Note the front of the rampressor blown out in the right-hand photo-

Braph

ample space must be allowed for all appurtg nancea, connectiom, and control& Room is required to operate, to repair, and to inspwt, and the location of any veseel within any pop tion of a plant should consider these items before the installation is actually made. The cmwding of Y d too C l d y is hardous and not only prevents proper control but may be a factor in the incream of loaaes during an emergenay. V 4 equipped with stjning appliances require service and power plat-

I

vioudy, if the design and theoonetruction of t h e 4 are not good in thebeejnning, ite operation is bound to be more or less b a d o u a . The plant owrating ocgmhtion can pro- duce the ultimate in eafety if they pmvide the builder with au5cient inetruction% or references. Any d o n preaaure vessel should be jnat as carefulIy built as if it were a steam produm'.

Most veesele in the chemical induatty are subjeoted to one primary haaard--meabanical failure of nome portion as a rfr d t of corroeion or conditiom incident to continued use. This may include exceaive pmaure. The heet remedy for this situation is to &ot matmiah for comtruation which are not afiected by thematerial to beprooessed. This is often a di65cult problem to solve, but m h haa produced many e.p3pecial d 0 ~ and the material known to give the beet resise ance to cornxion should be considered the proper one to use.. If such a material is not available for the vessel iteelf, then the aame conaideratian ahodd be given to the selection of a lining whicb will &t deterioration. Thin warning is emphssised becaw it in of utmost importance in producing safe wor!dng conditions.

Design and Inct.llation Compliance in d& and iwtdation with ~ t i d and

local codes is eawmtiaL De&n and inntabtion go hand in hand. Not only mwt the vessel be Suitably located, but

forms to be installed to provide eafety for the operator. Any equipment may need repairs and alwaya repuirae fm- quent inspection. If such rapairs and +ctionn are to be adequately made, sdcient epsce must be provided for the workers to function properIy and with parsod safety. Rs- sotion wmla should alwaya be corredy placed in relation to

nection di5cultiea. Wen vessels are heated by &?am, pressure gages and d e @

valvee are essential. Readion vessels, where the maW manufactured may clog the eafety Y ~ Y E and render it uselesr, may repuire frangible diskn to proteot it. In the we of stesm, when the prooesa preseure is reduced below normal boiler pressure, a reduoing valve in required in the line leeding from the msin to the 4. Pressure gsges and d e t y v a l ~ Bhould be installed OR the l ~ ~ - p r a s s ~ r e side of the IW- ducing valve; CBSB should be that the d e t y valve in- side the reducing valve has a relief cape.city d c i e n t to taka the main line supply if the reduoiog valve &odd fail to func- tion. In general, it is preferable to install aapsrate set6 of ~and~~valvesforeeohvesselandnotrelyuponsinglp valw aupplying manifold In everg instsnce th~ dhbacge from d e t y valvea and other relied de.vim &odd be piped to a safe area. When v~cuum reIief devicas 818 uaed, @hilar pracautionn are eaeential. When speoial aum

th& pact in the pmoe~a, thus eliminsting ~tructursl and 00n-

&pt.mba. 1M1 IN DU 8 T R I A L A N 0 1Y QI I IlESBL# Q C H P Y I 8 T R Y

and diefdevieeumunt be made from theesmematdrid. Rupave dike, if used, may slso bsplatedor pmtestsd by the specisl alloy, snd where the relief demand is exoegiW, noh qui& outletsmaybeprmriaedinmultiph. The looation and marking of control vdvm is important

for the safe operation of prpssure vwnela. Vdm may be msrlrsdby numb or by the um of diehctive oolor systems When oolora IVB used and the d v m rn painted a oertain color, at tips^ of the sama color &odd indirate theline or vfe- sel upon whieh the valve is located and owrate. Buoh spatems will give proteotion to the operation of the equip men$. When veesela IVB shut down for rep&n or for inape0- tion, the dvea or lines should be m marlred, and dl control valves should belocLed in the cloead ponitionwith thekey in the paaaession of the department supervhor. &xiow in- juriea have wcurred through the inadvertent opening of d v e a while a vessel w ~ 8 being repaired or inspected.

1093

Inspection Personnel Thelifeandsafeopmthnof~premmequipmentm

mananted by four lelated Wm. The E& thrm- pope? conatruotion and design, proper lofation, sad propa iwtdhtion, including the poovision of relie$ and contml de- vi-prepste the way for the mod important item whioh is propet inspection routine. Given the fint three, thafaurtb in in &@ solely mapodble for tha d life of the VraSaL w h i l e t h e ~ o n o f i n d p s M i t y i n s u r a n c e ~ o n a M i r s with i t a certdu amount of inapeotion mrvice, inhmdiste mthefe&andinapactionamudbe.u.wbbyplantpermn- nel. When a plant is dieientdyb, it is preferable that the tent and inspeotion pewonnel be aeperste from manutactqring operation. The dirsction of such a stetl should be independ- ent of thw prhwily in charge of production or equipment, for free judgment o ~ n then be had conceaping the oondition of the equipment and tale ohmwter of the maintenance found. Such hdqmdenca eliminates possible irduerw from pmmm whom inteest oentm upon maximum production or mainte- mea at the lowe& possible ood. The inspsotion abfl must have sbsolute frasdom to steta oonditim exaotly IYI found and to comment c.mhuctively upon the data developed ~ t b i r ~ o n a n d b l i n g p m c e d u r e . Theisstelle- tion of Rloh a statr, or even of an illdividd Workmm, lhould

ti- of the Hsponsibillty for the d e opesstion or mainte- nuumofthseguipmsnt, but rhould augment suah pmcadum

h M Wag hthedspsrtmpmtaUpm”fh?B WplanteneOn-

to the end that safety is innessed and longer vessel life ex- peded

uulem the iwpedru hae a thoragh undmtmding of the ohsmid aspects of the prorm# carrisd on within a given VBB- sel. Thin is true whek ib he a b @ , openmkiyvat or.m e x t m d y large or d v e bemb capable of W Y ~ ~ ~ ~ U I B enonnow pressurecl. without aroh hrowledge the ilwwtor op~~tlot determine the eqwtwoy of linea, liniogs, control vdvea, relief de- sta; thinb true if during the procpasmstQisls areintaudu~into tale unit whioh may be M)rroLbvB, ermive, 5 m d J l e # pOinmOua, or otherwise in- juriow to hedth. It fquently b.ppeols that in developing new matariala theresepmh department fsils to realire the im- portauoe of the inspection p m b b and dom not give the in- spector such aential infomation until trouble hss h. All poesible riakn attgched b the p r o m should be considered jhtlyby the d deperhaemt with the inspeotoras tha Work prograaws, and appmpi& p W a ~ t i 0 1 ~ should be in- atitated.

Theinap6otorehouldbeempdbclwdoantheo~ tion of any VPBBd failing to pna him test or found openting cantrary to insbuoted routine. On the other hand, he ahould be held mapomible for the appmvd of a 4 when it pasvv hieexaminstion. T b ~ ~ & ~ ~ l d b s ~ l a b b f f l k ~ l i ~ ~ g i ~ meh instrnas except throu& aonaultation with ewinedw expartainthepflekl iu-fold

Proper safety control, test, Md ilI@fdom 08IlUot be made

I W D U S T KIA L A N D E N Q 1 N E ER I N 0 C H E H IS TR Y V d 33, No. @

Installation Testing Probably the moet important inspeOtion is & one made

irpmedistely following inatsllation and prior to a test run to msLe nue there baa been striot wmplianm with original safety stsndards. &me of the more important iterms for such an inapeation mutine are as follows:

Y.%2%Zwording dsrioes' elements been so p~ m to show accurately the hl eat temperature liahle to be reached in the reaction, and are & rewrdera capable of varying over the rsngerequid?

4. Have the per relief vdvea, explosion dish, prpssure re- du*g and ms%~ d Evlw ' with necemav slarms been pro- Videdl

6. It any hedth basarda are involved thmngb the material k w y d, is proper ventilacinn installed? 6. f volatile solvent. or other Bammable materials are em-

ployed, is all electrical equipment installed rwrding M code? 7. Are outleta and inlet. of eu65ment capacity? a Have all of the 8pecScatiom oven the manufacturer for

building the 4 bean roanplied with and hsa the veseel been proprly installed by the countruetion engineer?

Wbib 801118 of the items W above may ~ e e m superfluous, eacb has a d a t a bearing upon the d e operation and life of the equipment. Numerous injuries and property 1- b v e been recorded through failure to comply with the sim-

usually hydrcetatio, in ex- of the normal operation require menta whioh am ordinarily one and a half timeu working prea am for riveted wmtruction and twice working prsawve for welded oonstruction to be within the factor of d e t y limita, is considered a test. The visual obearvation of any apparatus, either in operation, statio, or dismantled, together with a hammerkstof theequipment, wmtitutesavisuainopection. The actual t e e t i of the equipment can be waived when the p& service record or operating conditions are known to j u s tify this part of the procedure. The pttrpcw of routine in- spection h not only to reduce the possibility of acudenta but to reduce mechanioal failures and fire hacards, and at the eame time to in- plant &ciency and thereby rtmm wntinuity of production. Consequently, it is well to establish a oertain definite system that should be followed by the inapeotion stafl. An example of such a routine follows:

1. The inspection 8 tern should have the approval of the v e n t ; it ehoulfie ci6c in requiremenL and efficient UL operation. Reports c.hod??be made of all raplira m well M teas and inspeetiom and these reports become a permanent part of a record ~yeie.m. kvery piece of pressure equipment should he identi6e.d and tbe identi6cation remain a# lo M ths vm¶el in in edstenea in the plant. AU equipmvt sho3d be prepared for teat and inspeetion by the operatq departmsnt personneL Thin arrangement eliminates duplicahon of dorts and at ths Bame time re uires the personnel to be wmpletely familiar with the makeup 3 the - in their control. The v m ~ l must be thoroughly clegneb;' ventilated, or wsshed until no noxlous or

plat inetruaeioaa. Cnm connection of supply lines, r e v d electrid polarity, failme to remune ddp- flu@ fmm 014- E-, and 0th~~ similar items have owurred and do continue to pmdqce loss exmpt where the inapeation service w E&- Cimtly active to detect the situation prior to aatual operetion. It h the mspomibility of the inspeotor to discover suoh neg- ligenca.

Testing and Inspecting Routine

The mtine inspsotion of equipvmt inwlvea both t d h g inspection. The subjedion of a 4 to prm3tmj

-, 1941 I N D U S T R I A L A N D E N G I N E E R I N G CBBMISTRY logs

the exact condition of the uipment based on for pm%%%? where codes exint, the code%odd be followed.

6. Thems~-?A~ on shwld produce a detsiled analye of the t con& on of the equipment. This wiu permit the estab K ent of the rate of wnvaion or detezioration and Bstimation

. .

6. Autest‘ and I’epsirs, when remrded on suitable report forma f o r z f e r e n m , &odd be distributed to inter-

7. Through the correlation of tests and inspection data, the t&.blishment of design, comtruction, and meintenance stand- u d s f o r t u t u r e e q u i ~ t m a y b e ~ ~ , a n d t h r o u g h t h e c o n -

t of defective equipment the pmoees may be

8. The iaspeation pmnud should inveatigata all accidents involving perarms or e uipment. while this may ~ e e m post morttrm treatment, the lata obtsined ma h o m e important in devainping future construction and c o n t r o ~ p d u r e .

edted company executives.

%%E=ually new.

This outline msy appear to the nninitiated to be eskuwive, complex, and d y , but when auah a produre is made s definite part of the entire plant production progmm, it is readii ahsorbed and, according to published information, can be held well within 0.6 pm cent the totsl plant man-horn. It is a ranall price to pay for protecting plant and psnOnna and guarsnteeing the life and safe operation of prooese pres- sure equipment. There is Little new in this Buggested routine. It b the cor-

relation of many i d w , definitely attached to the operation of chemical proasae d. For t h m who desire to obtain sdditional information for guidsnoe in handling the problems in their own plant, I would draw attention to the d e s d e d o p d within the American Sooiety of Me chanid Engineers, the d e for d e d preeaure veaaels of the Mean PetruIe.um Institute and American sooiety of Mechanical Engineers, the National Wety Counoil’s publica- tion, “Prmre Vessels, Fired and Unlired”, Parts I and 11.

GETTING THE MOST FROM AUTOMATIC CONTROL a. e. P&

Leeds BE Northrup Company, Philadephia, Penoa.

in auionutic conbol it is the combined charutuirtics d w&oller and pronr that count. They may be suited to u c h &. UnuUdadwy mulb may mean h i eithn a mom “mlined‘ mode d conboi or additional conbol may be q u i d Amin some rimple change in the p w e a may solve (he problem.

ClVrKtrrhticr d conboi equipmrnt are gennrliy dmple and udly w i l e d . Charas(.risUo d pfocesws a n in- finitely vaded. They not only depend upon &e par- Uculrr application but en frequently subied tu wide *u*- Uon rl(h Ume, The UICI d autonutic eonbol equipment should be familiar with cehin general pdnciples which a n

UTOMATIC control has long heen applied to pressure, A flow, level, and temprature, and recently, to an in- ing axtent, to such variables as electrolytic conductivity and pH. The great majority of applications have been mc- d u l , and, besides freeing operators for other duties, have often paid for themnelvea many fold in in& production and i m p r o d product. An the um of instruments and automatic controllers has

i n c d , many plank have assigned s p c i d men to c ~ n t for them. These men have usually become very proficient, often understanding a mechanism just as well as the manufacturer who supplied it. Generdy they have had a leas complete picture of important relations between controller character- iatiw and p r o w characteristics. To get the most out of automatic control they should be provided with this knowl- edge, in EO far powile, and, what is just as important, should be given m5cient authority to apply it. Further, they ahould be consulted when new pmcesa equipment is being designed to avoid mistakea which may be dif6cuIt to correct later.

What special knowledge should the p h t automatic control expert have in addition to knowing the mechanisms employed? FW he should understand the modes of control whioh these

helpiui in padlcubr sonbol prcblemr The idul time to apply these to a pmcer is during the M o d of design whcn c ~ U y midaka can be avoided. A brief mview daubnrUc control theory is gira, with examples horn the fields d hmperatum and pH conboi.

The impohnce of a suitable relation &em (he con. bol-valve setling and the resultant llow is dmud. C u m am given showing the chanckdrtics d wme pmentday valves when bted at consbnt pam drop. The dkd 01 line dmp in ddormining durachhUo in tnrice i s shown by families of gmerrlly applicable cunes plotkd on a percentage bsir

meobanims produce. Then he should know how the results obtSinable with those mcdea depend upon process ahmmtw iatics. FinalIy, he should undmtand the particular prows under consideration well enough to anaIye it from the point of view of ohsracteristics favorahIe or unfavorable to control.

oenerslly speaking, a d c i e n t knowledge for moat prac- tical purpoees w q u i ~ ~ little or no mathermatics and is well within the grasp of the average instrument department head. A brief review of the general theory wil l be given, followed by a discussion of what is called “the &ective valve character- istic”, a subject of considerable practid importanm in both existing and projected &omastic control applications.

Examples of M A of Control An a basis for discuening the combined dwt of controller

characteristics and pmcass characteristics, three of the most important mcdea of control w i l l be considered: two-position control, proportional-position control, and p i - ~ p ~ i ~ ~ l - position plus proportional-aped-floating control.

For brevity the latter wil l be referred to 88 proportional- plusfloating control in further discussion.

In explanation of these mcdea, consider a furnace heated by gas to be controlld at about 600’ C. The temperature is