US2327332A - Tank construction - Google Patents

Description

Aug. 17, 1943.

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ATTORN g- 17, 1943- J. w. PRocToR ET AL 2,327,332-

- TANK CONSTRUCTION Filed Sept. 3, 1941 2 Sheets-Sheet 2 ATTORNEY Patented Aug. 17, 1943 i UNITED i STATES PATENT TANK CONSTR''II James W. Proctor, Summit; NQ J., and Walter S.;

Allen, Flushing, N. Y., assgnors `,to General ChemicalKComlany, New York, N. Y., a coiil.

ration of NewYork VApfplcatron September 3, 1941, Serial No. 409,334'

final deterioration of the tank- I-n the' course' oiV investigations l'eading to development of the present invention., We fouind that the maj or'v cause" of liligh corrosion is the heatinge'ffectlof sun-light on the film of acid which remains onthe i-ri-side wail of a tankwhen the'A acid level is lowered or when the tank is emptied enti-rely. The alos'oiptionv of heat from sunlight sucllins'tances` isvsufficientito raise the temperature ef the' steel tank sides and' top many degrees inexcess 'of the outside atmospher-ictemnerature; Ou-rl tests' show that rate of steel corrosion is greatly ticceleated as the temperature of the-acid constituting the acid'tlm is increased. For example, we have found thatl steel-is corroded by 66? (931.19%) sulfuric' acidi ("ausuall strength at which sulfuricacid is stored or shpped'- about twice as fast attemperatureot about 150 Fles Y compared with say 1500?" Fl These temperatuxfes are* representativeof those'` existing on a stun-4 mer dayv when a body of acidi is beingunlia'aded from aitank car. @Af-ten the temperature of the acid beingf unload-ed is atout/1005 F., andi We have' observed that'the' temperature of the lmof acid onI the wallso'f the-tank for' some time'af'terunL' loading, maybe' as high as 150 F. The saine temperature differentials are found also in a storage` tank" on' a hot Summer day after acid Withdrawal. Another factor is the Contact ofmoist air, from any source, with the acid film. This moisture dilutes the acid and liberates heat locally. Further', heating and dilutionl of thesul` furie acdllm decreases viscosity, permittingythef residual lm to run down the sides of the tank around the rivet heads with increasing corrosion and formation of deep grooves. Tests sliow' that at all temperatures the' corrosion rate increases' rapdly'as 66 B. acid isdilutedto about 63 B.-

(831.34%) the latter` strength being taken: asian example of the H2SO4l Strength' resulting'whe-n a lm of acid adhering to the inner Wall ofthe tank becomes diluted by moisture in thea-ir er1-- tering. Vthruthe tank. domed during unloading.v

Taking- 1-as-a corrosionrate of 66 B. sulfur-'lc acid 'at-10G F.,.at weaker concentration'-andavaryf ing-y temperatures; tests show vthe following.V

ticular1yt'ne invention ais to c'cbf'plsl these ends by provision 4of tank' construction til'lcl functions to keep'tli'e' teifeatur f acid body inthe tankhas close to atr'os'blie'dtenpatef as. feasible, to minimize use' tn ikfiss df the' acid arming on the'1ak'wa11s-stt' and` l'vi fs lbwered. and to materially fence@ tfhe temperatu're ofthe. acid constituting" lri as 'cnipared witnmi' tempratures' nsngi standard constructions, The ooj'ect's" aridXV advantages" f the intention will' aipa from' cnsd'at i the follov'ving descriitior t'akel i c'o` iect'ioi With-the accompanying" 'datii'ng'si Wlnclr i'g.4 is va vertical', longitudinal section 'f a anim Fig. 2` is a .horizontal section t'liei oline" 2`2' ofFi-g. t y i* ig, 3 is a vertical" sectior tal'eno'n line 0fA l; Y i l Y l l lig-.4 is avert'cal section of avcylirdial storage tanli-taken--ontheline @-4 of lFigfl 5;- A Fig. 5 isfaliorizontabsection taken'on line 5-5 cfFigeQA-andn' Fig.` 6 isy avei'-tca1 seot-iontaken on thealine- E-+6f of *Figft A Fig. 1 iilustratesfai'tanlc carcornprising-'a hori- Zonta/l cylindricalVA steel shell I-BP,l end'heads Ill',- and-clome t2, all=ofiusuai construction.-Y Outside of shell lo, and suitably spaceizlI from-it for- 'exfample by Siorl inchesiis a. metallic hood-like shield M held in place, relative to the .tahkltr approximately' the f reiationshipshown' in*- Fig.J 3;: by? brackets Espot-welded or rivetedE atone= ni to'thefoitside'o the tank and Ttb thesiileld*aty length offene1 tank as shown mine; a, and the e'nd'- edges off'thefshieidiae'welded to" the ouder edges ofsemi-circular steei end' plates lf thef inner edges of which are welded to the circumference of the tank heads il. rIhus the shield ifi, the adjacent portion of the outside tank and end lates l2 ferm an air chamber 2! which, in the ernbo ent shown in Fig. 3, covers the upper half l the tank. rhe arrangement is such that the lower endsoi chamber '.li are open to the atmosphere at As shown in Figs. 1 and 3, thereiare provided at the top of chamber 2i, slots 23 and 2d extending from the dome to the ends of the tank. The cut-out portions of the shield immediately adjacent the outer surface of the dome i2 are spot-welded thereto as at so that any acid spilled during loading or unloading will run off the upper surface of the shield. Thus, air chamber 2li is open to the atmosphere at both lower edges and by way of longitudinal slots 2d at the top.

As a general rule the lower half of car and truck tanks is cylindrical, and consequently the Y.:

lower half of the outer tank surface is protected from the direct rays of the sun during the hotter part of the day. As a result, the lower half is appreciably cooler and our observations showy that acid corrosion on the lower `half of the tank is small. Hence, in the embodiment of Fig. 3 the shield id is brought down far enough on either side to cover only approximately the upper half of the tank. In some instances, however, it may be desirable to extend the lower horizontal edges of the shield below the position shown in Fig. 3 sumcient, for example, to envelop say the upper two-thirds larea of the tank. Y If desired, the shield might'also be made to cover the vupper half or more of the tank end walls il.

A further feature of the invention comprises provision on the inside wall of the tank of deflecting plates such as 23, 29 and Sii. IThese plates (Figs. l and 3) extend horizontally the length ofthe side walls, the cross-sectional shape of the plates being such that the upper faces are inclined downwardly. Similar plates Si extend across the tank heads ll. As shown particularly in Fig. 3, the arrangement is such that the dripoff edge 3S of a plate projects into the tank beyond the drip-od edge of the immediately subjacent plate. The purpose of the deflecting plates is to shunt awayJ from the inner side and end walls ofthe tank, the acid film iiowing down the walls as the tank is emptied. Moisture drawn into the tank as it is being emptied results in a nlm of weaker acid which is more corrosive than the acid loaded into the tank. It is important to the service life of the tank that the quantity of this lm in Contact with the shell and rivet heads be kept at a minimum to prevent both corrosion and grooving. Shunting the descending film off the walls at suitable intervals, keeps the corrosive action at a minimum. Most of whatever corrosion does take place is thus transferred to the plates which may be readily replaced at small cost. In Fig. 3, reference numeral indicates a double horizontal row of rivets, and in this instance deflecting plates 30 are located directly abovethe line of riveting to minimize grooving around the rivet heads.

Figs. 4, 5 and 6 illustrate application of the invention to stationary storage tanks. In this modification, a cylindrical shield extends completely around the circumference of tank lil, the shield being held suitably spaced from the outer wall 43 ofthe tank by a series of brackets i4 preferably spot-welded to the tank and riveted to the shield at G5. The annular air chamber 43 formed by the outer wall of the Vtank and the inner wall of the shield Ml is open to the atmosphere at the top as at 5|, and at the bottom communicates with the atmosphere thru a series of ports 54.

In Fig. 4, 55 and 55 indicate horizontal and vertical series of rivets. To afford protection for the riveting from the corrosive action of the acid nlm left on the inner walls of the tank when the acid is withdrawn, a horizontal deecting plate 6! is xed to the inner tank wall just above the line of riveting 55. At suitably spaced vertical intervals, other deiiecting plates 6i are attached to the tank wall in the line of vertical riveting 55, as indicated in Fig. 6 which also shows that the drip-oil edge, e. g. 6ft, of a given plate overhangs the drip-off edge of the subjacent plate.

In the car construtcion of Figs. 1 3, shield i4 is extended all the way over the top of the tank because when loaded, such tanks are completely filled, the acid usually rising a few inches in the dome.` In the storage tank of Figs. 4-6, no shield is placed over the top since in practice it is not customary to entirely Yfill the tank, and there-is no acid in direct contact with the metallic upper end of the tank.

In both embodiments illustrated in the drawings, atmospheric air is drawn in at the bottom of the chamber, formed by the shield Yand the outside of the tank, circulates freely up thru the chamber, and is discharged at the top. The heat of the sun striking the shield is largely dissipated by the atmospheric air passed thru the chamber by the chimney effect, and when the tank is filled or partly so, the construction described effects maintenance of temperatures of the acid in the tank substantially the same as the average temperature of the surrounding atmosphere. Such temperature control results in marked lower corrosion. The following data show the difference in corrosion effected in shaded and non-shaded tanks. Four horizontal cylindrical steel tanks were filled with 66 B. sulfuric acid containing .0008% iron, temperature of the acid on filling being F. vDuring a period of four days two of the tanks were shaded and two were left in the open'exposed to the rays of the sun. Once a day, when temperature was maximum tempel'- atures (l) of the atmosphere immediately adjacent the tank surfaces, (2) of the acid directly in contact with the tank surfaces, and (3) of the acid in the center of the tanks were taken. After the third day the acid in each tankwas blown with air to miX the acid well and representative samples tested for iron, results being as follows:

In sun In sun lu'shade In shade i F. F. o F. If'.

Tempoutsi-le 109 S0 SO m etal. Temp. acid S4 S4 73 7l n next metal. mm Temp. acid `77 77 70 70 at center. Tempoutside lf3 l2l 85 85 T metal.

next metal. o 7 I4 lo 1 P' M' Temp. acid 84 84 72 72 at center. Temp.outside 76 76 72 72 Tmetal.

em p a c id 77 77 '2 2 next metal. I 7 Non Temp. acid 74 74 72 72 l at center. Y

l l Percent Percent Percent Percent Fmicid after .0094 .0086 .0044 0048 The above tests show twice as much iron` ls dissolved when the tankis left in the sunlight. In the case of the tanks exposed to the sun,

the amount of iron dissolved corresponds with a corrosion rate of about .018 inch penetration per year.

A second and more important advantage of the construction of the invention is the cooperative result aflorded by the shield and the deflecting plates. Temperature differences in tanks which have been emptied ci acid and are in transit or in dead storage in the sunlight are much more pronounced than in the case of tanks which are lled. In numerous instances temperatures as high as 139 F. have been observed in empty acid tanks in the sunlight. Corrosion rate at 130 F. is approximately four times as great with 66 Be'. acid, as at temperature of about 70 F. This much higher rate of corrosion is caused first, by the much higher temperatures prevalent in an emptied tank and, second, by the lm of acid, usually diluted by atmospheric moisture, which adheres to the tank sides after emptying. In the construction illustrated, the deecting plates keep the thickness of the residual acid lm on the inner walls of the tank at a minimum, and this feature in combination with the low temperatures maintained by the chimney eect created by the shield hold corrosion at a low point.

The shielding aiorded by the invention should be distinguished from ordinary insulation. The latter tends to keep the contents of a tank at uniform temperature which will be approximately the temperature of the acid at the time of loading. invention aiiords a maximum cooling of the contents aiter the tank is loaded. Because of plant operating requirements, a car or storage tank is often loaded with warm acid, for example 66 Be'. sulfuric acid at temperature of about 120 F. Corrosion caused by acid of this strength and temperature is at a rate of about .026 inch per year. Insulation merely holds this temperature Vat about 120 F. andcorrosion proceeds at the `accelerated. rate indicated. By means of the chimney effect produced by the shielding of this invention, air currents are continually drawn up from the cooler layers of air on the ground, and cool the acid in the tank with resulting corrosion decrease. The construction of the invention provides active cooling at all seasons of the year, a phenomenon not aorded by the usual type of dead insulation. Further, the vigorous air movement up under the shield is effective in preventing temperature rise.

VI e claim:

1. A tank car comprising a horizontally disposed tank adapted to receive a corrosive liquid and made of material corrodible by said liquid and provided on top with a Centrally located dome, a hood-like shield extending the length of the tank and substantially covering the outer wall of at least the upper half of the tank, end plates connecting the end edges of said shield with the adjacent circumferences of the ends of the tank, said shield being spaced from such outer wall of said tank and forming, with said The shielding provided by the present end plates, an air chamber between such outer wall of said tank and the inner wall of said shield, contiguous portions of said shield and Said dome being associated in liquid-tight relation, elongated openings at the bottom of said chamber on either side 0f the tank for ingress of atmospheric air, and slots extending from said dome to either end of the tank at the top of said chamber for egress or such air after upward passage through said chamber.

2. A tank car comprising a horizontally disposed tank adapted to receive a corrosive liquid and made of material corrodible by said liquid and provided on the top with a centrally located dome, a hood-like shield extending the length of the tank and substantially covering the outer Wall of at least the upper half of the tank, end plates connecting the end edges of said shield with the adjacent circumferences of the ends of the tank, said shield being spaced from such outer wall of said tank and forming, with said end plates, an air chamber between such outer wall of said tank and the inner wall of said shield, contiguous portions of said shield and said dome being associated in liquid-tight relation, elongated openings at the bottom of said chamber on either side of the tank for ingress of atmospheric air, slots extending from said dome to either end of the tank at the top of said chamber for egress of such air after upward passage through saidy chamber, a plurality of vertically spaced, horizontally disposed and downwardly inclined dellecting plates extending substantially the length of said tank, said plates being xed to the inner wall of the upper half of said tank and arranged so that the drip-oir edge of one plate projects into the tank beyond the drip-off edge of the immediately subjacent plates, said plates thereby effecting shunting from said inner wall surface of corrosive liquid flowing down said inner tank wall surface after the level of liquid in said tank has been lowered below a plate by withdrawal of liquid from said tank.

3. A tank car comprising a horizontally disposed tank adapted to receive a corrosive liquid and made of material corrodible by said liquid and provided on top with a centrally located dome, a" hood-like shield extending the length of the tank and substantially covering the outer wall of at least the upper half of the tank, means connecting the end edges of said shield with the adjacent circumferences of the ends of the tank, said shield being spaced from such outer wall of said tank and forming an air chamber between such outer wall of said tank and the inner wall of said shield, elongated openingsat the bottom of said chamber on either side of the tank for ingress of atmospheric air, and slots extending from said dome to either end of the tank at the top of said chamber for egress of such air after upward passage through said chamber.

JAMES W. PROCTOR. WALTER S. ALLEN.

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