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LIA2 4462 ..... . --^ _-n-. 1 LEAD INDUSTRIES ASSOCIATION tot MADIOON AVCNUC NEW YORK 17, H. V. February 23# 1961 CHERTCAL BUULETDf WO. 16 SUBJECT: "HOW TO CHOOSE tEAD LDHB03 FOR PROCESS VESSELS'1 To Kecberi of the Lead Industrie* Association: Attached It a reprint of an article vith the subject title which appeared in the January 23 issue of "Chemical Engineering" uagaziDe, We believe that it provides a useful round-up of information on the methods of using lead linings under the vary ing conditions to be found in the chemical process industries. It will also be used for distribution at our booth at the Rational Chemical Exposition next fall and in answering in Q quiries co chemical construction received by the Association. Additional copies in quantities up to 25 are available free of charge as long as our supply lasts, and larger quan tities at five cents per copy. Very truly yours, RLZtJRD Att. Secretary 0 Corrosion Forum <**4 m iwpi|y^fe]g|l^mMy LIA24463 nrwin m )iil> iMirtlm iXinm r, rT, tfli dn *1 There are .five ways to line a vessel with lead--each Caged Lead--Cage construction has advantages and limitations. Choice is made based on consists of an open exterior frame work of steel flats and angles lead's properties and operating conditions in the vessel. welded together to support the lead lining. Supporting members are spaced closet together toward the tOIECT L ZIEGFE10 tsnd /wrfw*fnVs A t*w. covered steel; as sheets of lead and bottom to accommodate increased stefd or lead and copper continu hydrostatic pressure. (Expanding ously bondeo u,*.4**** face to face and contracting lead lining is free Lead {a an obvious choice for lin (commonly referred to a* homo to slip into stress-free posture with ing many reaction and storage ves genously bonded); as a lining shell in i 'are.) Open construc sels, particularly where severe cor of sheet lead externally supported tion allows for exci_z! hast *t - rosives must be contained. Hut bv a cage construction; or as a rhange, w hile leaks are readily seen specifying the correct type of lead membrane that envelopes an acid- and repairs easily made. Cost is for an application U only part of brick lining. low-, comparable to that of loos* the job. To avoid costly and prema Loose lead-sheet construction is sheet lining. ture failures, the type of lining con the least expensive but it is limited An ingenious example of cage struction should also be selected by in practical application to vessels of construction that makes the most the design engineer. moderate size and condition* that of heat-transfer possibilities is the This selection must be based on do not impose extremes of tempera Milb-Packard tower, designed as a an understanding of lead's chemical ture, abrasion, pressure or vacuum. reaction chamber for manufacture and physical properties--and how The theoretical maximum length of sulfuric acid by the chamber they relate to the corrosive and to of a lead sheet, of unifurm cross process The tower Is tapered so stresses that will develop in the op m*ct ion supported only from the top, that excess heat generated Inside erating vessel is 40 ft., at 6ft F. In practice, how- is dissipated by a film of water that Type* of Construction--There .-er, it is seldom feasible to sus flow's down the exterior surface. are five basic typos of construction pend lead sheet more than about 10 Bond for Vacuum--Homogene u*ed for installing lead linings in ft without strapping, And exces ously bonded sheets are usually lead chemical-processing vessels.* sive strapping requirements tend to on steel or lead on copper, although !*ead lining may be loose sheets offset the economies of this method. other combinations are possible. of lead drnped inside a shell of steel, However, new methods for fast Steel provides strength; copper has wood, or concrete, w ith lead burned ening strappings reduce time and desirable thermal properties along the cams that are with or cost for this operation by 70%. Steel is cleaned by shot blasting without internal supports of lead- Studs may ho driven home with a or sometimes by pickling in 10% o * PTv'lo abnv 1*ad'1ln*4 f**M Suri. Kh**t If ad atrip rovfra at*t ttw<1 faatfm-d in th* vra*f| ahfll Strip la brM4 to Um Ia4 lining. power tool, which eliminates drill sulfuric acid. Copper Is also ing and lining up bolt holes prior chemically cleaned. Lead is then ap to fastening. plied by s burning bar or, for larger IJmiiiSu h J hy HAD IM>t MKIIS AsMXiAHS Aw , \< Ywt I*, s. V. LIA24464 -- - t`- -v" - - -- C01R0SI0N flOWM . . . Cost*, conditions, requirements for five types of lead linings--Table 1 Cost fsctsfi InHiol Inspection Repair Hostile coadltioae High remperotvr* Thermo! ihoch High pmwr Vocwia flhyvcol >hock Crowe* Corrowo* toese Sheet Steel leaded Copper leaded Cage Irkk Low Uw tow foir *k DrceHe* ho Coer Poor Itcole* faWy high fairly high low buette* fecelle* CxceBe* Dwelt* liceHe* fair CaceOe* folrfy Wgh fo*ty high Low IxseHeat herbs) Good Good lacet!** fair Earette* -i 1 tow Very low Uw hoor Hot Hoe Poor floor floor EeceHo* flobfy hifk fairly high Duetto* DiceUo* btrbsr . Good Good btrbn) Emo Ho* Design rHvksmssa kwviolfO* Heel Wonder Mr jte<W* ' . W . - - .r. fair farefie* floor MM floor httbo) lilllK floor w . - -x areas, simply poured over the other metal. The lining surface is smoothed by penning and/or scrap ing. Bonded linings are, of course, more expensive but are superior on almost all counts u4 wiy usually remain serviceable much longer man oiner types. Since there is no air gap between the two metals, uni form heat exchange is good. Rigid ity, particularly with a steel bark ing, permits operation under high vacuum. For lead bonded directly to steel, operating temperatures a high as 608 F. are permissible, and the lining won't creep or crawl up to 4SO F. Rapid temperature fluctua tions, mechanical shock, and vibra tion are tolerated. This type of con struction Is also recommended for very tall structures where heavy acid-brick lining would impone for midable stressta. Design engineers are advised not to skimp on the weight of lead specified in bonded linings: cost of such linings is essentially that of the bonding process. Modern techniques have largely overcome objections to the difficult job of locating imperfections In the bond. An unbonded area may be identified by a bubble that forms when the interna) temjarrature Is raised to 400-500 F. or. In a pres sure vessel, when the internal pres sure is raided to Gj *0 psia. and sud denly released. Efficient sonar and radiation methods of inspection are also available. brick (er Heat--?*utaineu op eration involving high temperature, erosive attack, and extremes of cor rosive attack and thermal shock are best withat<*J with acid-brvk con struction. The brick lining, usu ally one or two courses, inflates not only the system as a whole but the enveloping lead membrane as well, permitting operation at in terior temperatures well in excess of the melting point of lead. Arid-brick and lead art function ally complementary' to one another. Acid-brick is resistant to polar or ganic chemicals but is attacked by nonpolar organics, to which, how ever, lead Is resistant. The total system tolerates the most severe corrosive attack, as, for instance, both acids and alkalis In the same vessel. However, brick spalls due to rapid temperature changes, sus tained operation at extreme high temperature, or absorption of satu rated solutions that crystallize on cooling. Best grades of acid-brick are intentionally made 3 to 4'r por ous for increased resistance to ther mal shock. The impermeable lead membrane contains the seepage. If extreme high temperatures arc cxpci ied. a brick-lined vessel should be built <>n an elevation so air caa circulate freely beneath It Otberwl... r~"'..*#tive heat mar build up deep in the vessel. Sufficient brick must be used to prevent sur face temperature of the lead from exceeding 125 F. Bottom of the vessel should be dished if extreme pressure is a factor. Also, it la sometimes desirable to design the lining so elongation of the brick* will close the gap between brick work and lead membrane, holding the lead under compression for greater support. Asbestos paper la bonded to the lead with potassium silicate solu tion to prevent contact with sodium Ions in acidproof or furan-rcaia cements. While asbestos it not re quired with sulfur-base eemcnU, two or three layers of nonburn pa per should be used to form a pro tective cushion against abrasion. Some of the new inspection methods developed fur bonded lin ings have been equally elective (a simplifying maintenance of bricklined vessels. Table I provides a check list of the relative strung and weak pointa 165 )$nu*ty 2?, 1961- CittMiCAL Ek c imiu h c I v t r i i r\ i \ r .3 o iu mm' m < n: '.h i L1A2 4465 COitO&tON fOftUM . . . & Leads's resistance to va rious chemicals--Table II* fta ***<*<H Ai<aiaM svll*4 WS* 4*l4 l*t6M tt*Vr Attteas AkWJ Isattat T*4v*ta C ><<-- t**r yr>Sta l>**# 0*Kk ac* 0*U<'Motoric n M *>> fi< t>ry tHal( fta Oc t rfct*ri** C*rW 4--*>4* 7 W,1t SvHr lrita*4 Ltav- <Wta** *!>* Ca4< cwctawaN S*4** n^iearie <***! *<(** fU.'ktaJ Oueaitii {4iMt |4tM4 s*rt< <m Wn^H talS tsHimn *t>a Tarteri add CM*r{* MlW> Wl (hUari** W*( ** Crba MVwkltriA* 0*y Vy^Hea <Men< tLMrita ** awr.d* *-'M cfcMriS* 0 AaMi ^bfifMa fcr*w>4 <* H >C%t Ntetw** *rU*-M`S <** H %| WilrH taM (laatStirfMl H)aey<u< atid HyS-taMcr* 4 <* W % kw>< W* m^K* fta Cfc* * Sk 4mm> *iM towM*) l*d> SWm W*eia* <***) *** Ca^is t acid Asaniw ckan K# lCr*st| Cokwro b;a'.da *** fcre**Lta W-( d (*td Hydr>Ban< Kid **< *04 !t<0 A*#f* #f>4 |*Mc k S MrAevcM*#;* Kid WkU<*f iW***} cttrt4 SvHsdc Kid -****) Hy4c*<Marie *-W %d OMeda Mtact M4*viw<* pafKaagawM N>**y*ike UdKra VyyaeMarHa L. fame rhMri^a Niirk kek k iS jd'li<| *> tilled ar<^.ri4irv4 <,, w<, < .<, ..f (Mart l^aet ****** w Malta Arad. La>4 M c kafcWal grata. of each of the five major typed of 0 lead-lined construction. Composition Important FactorAside from construction method*, composition of the lead itaelf may he varied to enhance certain prop- ertie*. Chcmical-grade lead or arid-cop- per-grado lead, containing from 0.04 to 0.08 % copper and from 0.002 to 0.02*? silver, form* a pro tective film faster than pure k*a. The Aim adhere* firmly and resist* abrasion. Trace element* a1*o Increase lead's creep and fatigue strength. Maximum allowable fiber stress at room temperature U 200 pal. Use fulness it limited to temperatures up to about 446 F A 26 to 26% sulfuric acid solution win form a complete aulfate film on this grade In from 9 to 10 hr. at 70 F. Antimony-rb fw Valve*--lead contrining 4 to 12% antimony la preferred for valves, pumps and other component* requiring a cer tain degree of dimensional preci sion. This grade ha* greater hardnet.*, rigidity, mechanical atrength. and resistance to erosum and abra sion at ordinary temperatures In addition, it creep* and warps less than pure lead. However, aatimoniat lead is only advantageous up to about 248 F., because it soften* rapidly at higher temperatures. At these higher tea*- y^ratutcH, u .. length is only equal to that of chemicalgrade lead. Moreover, antimony lower* lead's chemical resistance. Antimonlal lead I* preferred for handling sul furic acid only in very low concen tration* (optimum resistance with 3% tntimauyy. Maximum allow able fiber stress of antlmonlal lead it 400 p*i. at room temperature. A complete sulfate film I* formed on antimonlal lead by 25 to SE% sul furic acid in from 1 to II hr., at 70 F, Resistance to metal fatigue Is promoted by addition of 0.04 to 005% tellurium to the lead. Tel lurium acts at an inhibitor of grain growth and also m*k*t the lead amenable to work hardening. Corrowlo* Resistance -- And, of course, lesd's corrosion resistance must be considered in any lining instillation. At with aluminum and stainless steel, lead's resistance to chemical attack la baaed cot oo It* chemical inertness but rather on it* chemical reactivity. Lead reacts very quickly with most corrosive agents to pro duce resistant, insoluble salts that form nonporout protective films over the pure rretal. It is this film, not the metal itself, that resists fur ther attack. Lead (a highly recommended for handling sulfuric acid under moat conditions. This acid reacts with the metal to form an adherent. Im permeable film of lead sulfate that guards the metal against further attack. In acid concentrations up to 96%, corrosion of lead Is neg ligible at room temperature. In stronger concentrations, acid ap parently reacts with the film. Nitric arid presents a more com plex situation. Dilute nitric com bines with lead to produce lead ni trate, which adheres poorly to the metallic surface and Is somewhat soluble in the dilute acid. Lead it, therefore, f*t recommended for handling dilute nitric. But concen trations from 52 to 70% by weight do little damage to lead vessels. This it, apparently, because solubil ity of lead nitrate In nitric arid decre*5cs a* concentration of the acid (Fig. 1), Dissolved ga*ea, particularly oxy.** miv affect rate of corrosion substantially. C:rr--'rates of lead in distilled water at 77 F, vary directly with the oxygen content of the atmosphere above the liquid. Arid Bath Protects--The corro sion pattern observed at a typical sulfurle arid plant illustrates the effect of oxygen in the vapor phase and suggest* a useful protective technique. Where the liquid acid was In con tact with a kad lining, the lining was perfectly protected by a film of sulfate salts formed by reaction of the metal and the arid. However, aerrre corrosion was observed higher on the waits of the vessel where the lining was In contact with the vapor phase. The reaction products formed in the presence of free oxygen In the vapor pha*e wer* unstable and formed an Inadequate film. One solutfon to this problem was to malnUin the liquid level at the top of the vessel or periodically to 163 /anu*ry 23, 1961--Ch e mic a l Fj s c w mx w o "anHP mmx--m r ,m ti.niuinn ifr HWW ll11 H'HfWHWiJi LIA2**466 Lead nitrate dissolve! in nitric add--Fig. 1 toll Pfc(NQ,),/!OQ f+fH taMiaa 0 to 20 >0 40 SO HNOi % Lead corrodes in mixed adds--Fig. 2 C*ee*t**o, h i./m. X K)'1 MO tMteal)tiM, % raise it to the top long c ik >u *I. tn renew the impermeable film. This suggests the following method of pretreating lead for use in contact with corrosives that do not form an impermeable protective film: fill the lead-lined vc.-sel with 25 to SS'T sulfuric acid and main tain temperature at 70 F. This wit! form a complete sulfate film on chemical-grade lead in 9 to 10 hr. Only 1 to !j Hr. is required to achieve the same effect on 9% antimonlaJ lead. * Additive Effet ta--In general, while lead is highly resistant to cor rosives that form insoluble sulfates or phosphate*, it d<ea not perform too well under attack by solutions that form soluble nitrates, acetates or chlorides. Also, effect of attack by a mix ture of corrosives )* additive. For example, lead It protected by sul furic add, cornded by hydrochloric acid. Resistance varies linearly M the ratio of sulfuric to hydrochloric in a mixture of ccids (Fig. 2). This, of course, assumes no com plications involving products of the reaction between lead and the sepa rate solutions, or between one solu tion and another. In such cases, ef fects of the intermediate and final products must be considered inde pendently*. Table 21 classifies resistance of lead to many of the chemicals com monly handled in the chemical proc essing industry. Performance in a particular application will depend, in addition, on temperature, ero sion, and mechanical abuse. Jo most cases, corrosion increases with in crease in temperature. Watch Erosion Effect--Erosion may become an important factor when the solution Is agitated or flowing through the vessel While it is true that lead's corrosion resist ance is essentially "self healing,H it should be remembered that forma tion of the protective salt film con sumes lead, if the film is constantly eroded and replaced, lead will be consumed progressively. Factors that determine rate of erosion in clude imU of flow ozd of particulate matter. The relationship between rate of fl"w and rate of erosion may not be linear. For example, in laboratory tests, for 20% sulfuric acid at 77 F., the following is true for chem ical-grade lead. Flow Velocity (Ft./Min.) 8.4 97 155 300 Corrosion Rate (In./Mo,) 0.00055 0.00017 0.00016 0.00066 Mechanical abuse may, of course, contribute to corrosion more than erosive attack. Design and oper ating procedures should minimise any mechanical damage. Smooth as Glass--Due to Its mal leability, lead presents an uncom monly smooth surface--one reason why it Is often chosen for process equipment Smoothness of the In terior surface of extruded lead pipe is rated about even with glass. Aside from ita softness and mal leability, the more pertinent me chanical properties of lead are ita coefficient of expansion (about 1&3 x lO^/F.), Its melting point (620 F.) and Its density (0.410 IKfcn. In.). In absence of sti *sa-corrosion conditions, it is safe to use lead up to about 446 F. Related to these physical charac teristics are two factors thit should be kept In mind when making com parisons of lead versus other ma terials. Such comparisons usually are based either on mass lost to cor rosion per unit time, or depth of penetration of corrosion per unit time. But loss of material of a given maaa is relatively insignificant la the case of lead, since lead is so heavy. And a given depth of pene tration Is not as serious in a lead lining, as a rule, since lead linings are ordinarily much thicker than those of other materials. Finally, economic considerations favor Wad. It U inexpensive and easy to work. And scrap recovery usually rebates about 50% of orig inal material cost. Meet the Author ROBERT L riEGFELn < nn. Ury arid triamrtr tf Ms Lead/wdwsfriW .\V*r I'erl, .V. F. fit it Me M<rr tf many artiWrs, leM (*&*{. eoj ad rceRamir, v* the prtdm<*ita and epph>Qf* a/ (rad. From l9S,t It tt$i, kt mtf ttrrtd a* trrrctary ed iretttrtr tf Me ftrtot Powder Arta. Ht Is presently a mrmbtr *f A'.MF.. A STM, IM (Bntitk), A lies gredwafs tf Ms SkrfitU SfUnfifie Srkeot tf YtU (,'m'rrrn'fy, w-iM a BS. im Mtniftf eigiNeri"g, k* prtcUetd Mis pmfrttitn t* *M A/rice td Mimntttfm. Rcrwmlid ftortt Ok nn j| l ncu>rt tine, |jn 9, 1*>6I Cofrnsht (961 fo fVibiiuiini Co, Ik no Wo s*. s<m Vjft if,, s v 0 *-