US 2888161 A
Description (OCR text may contain errors)
May 26, 1959 c. w. SPRINGER STATIC DRAIN ARRANGEMENT Filed Sept. 11, 1957 2 Sheets-Sheet 1 y 1959 c. w. SPRINGER 2,888,161
sTATIc DRAIN ARRANGEMENT Filed Sept. 11, 1957 2 Sheets-Sheet 2 INVENT OR.
i A m United States Patent STATIC DRAIN ARRANGEMENT Charles W. Springer, Chicago, Ill., assignor, by mesne assignments, to Union Tank Car Company, Chicago, 111., a corporation of New Jersey Application September 11, 1957, Serial No. 683,413
3 Claims. (Cl. 220-26) The invention relates to field storage tanks of the floating roof variety and particularly to seal arrangements incorporating means to avoid static electrical discharge and thereby reduce fire incidence in this type of structure.
It is well known in the art that floating roof field storage tanks are frequently used to store products having highly volatile and inflammable characteristics. These products are poor electrical conductors and subject to a high degree of'fire incidence. Concern over such fire incidence in storage facilities has increased in recent years due to an apparent increase in the number of fires reflecting factors other than a total increase in storage facilities. Analysis of these occurances has led those skilled in the art to the conclusion that static discharge of electricity was a responsible cause of fires in a great many instances. Investigation of these fires brought recognition to the fact that certain conditions must exist to establish this causal relationship, said conditions being a sufficient potential must be present so that sparking discharge will result and that such sparking must occur in an area where product vapor concentration is in an explosive range. This vapor concentration usually occurs, of course, in the seal space peripherally surrounding the floating roof, the seal being primarily provided to avoid extensive vapor loss of stored product.
Turning to the build up of static electrical charges,
it must reasonably be stated that the reasons therefore are not all clearly understood at this time. However, that such potentials exist is well known and can be measured using well known techniques. Investigations have shown that static charges can be acquired by a tank as a result of the motion of product, such as, for example, during filling or evacuation of the tank. It has also been found that the passage of clouds over the tank can result in impressing of an electric potential on the tank. Remembering that the roof is peripherally spaced from the tank shell, it will be understood that it can act in the manner of a capacitor and hold an electrical charge until such time that the potential reaches a level that under certain conditions and at certain points it will discharge to ground by sparking through the peripheral space to the grounded shell.
Upon careful investigation, I have discovered that the seal arrangements heretofore employed in floating roofs have not been designed to effectively avoid electrical sparking in the seal space where a critical vapor composition condition exists.
Accordingly, it is a primary object of the invention to provide an arrangement of the type described which provides an effective static drain path from the roof to ground in a location where the critical vapor concentration cannot exist.
It is a further specific object of the invention to provide such a path below the normal product surface in the tank.
These and other objects of the invention will become apparent in the course of the following description and from an examination of the concerned drawings, wherein:
H 2,888,161 Patented May 26, 1.959
Figure 1 is a sectional, fragmentary, side elevational view of a preferred embodiment of my invention;
Figure 2 is a fragmentary view taken along line 2-2 of Figure 1;
Figure 3 is another fragmentary side elevational view, similar in certain respects to Figure 1, of a slightly modified embodiment of the invention;
Figure 4 is a fragmentary sectional view taken along lines 44 of Figure 3; and
Figure 5 is a fragmentary sectional view taken along lines 55 of Figure 1 illustrating a further slight modification .of the invention.
Describing the invention in detail and directing attention first to Figure 1, it will be understood that'the arrangement comprises a cylindrical shell 2 of a field storage tank, said tank having a roof, indicated generally at 4, arranged to float on product 6 stored in the tank. The roof comprises a deck 8 having a peripherally arranged upstanding rim 10, it being noted that the surface 12 of the product 6 normally extends part way up the rim 10. The roof is so arranged in the shell 2 so that a space 14 is provided between the rim 10 and the shell 2. This .space, of course, extends around the entire roof.
To seal the space 14 a sealing arrangement is provided, said arrangement comprising a plurality of thin flexible metallic shoes 16 horizontally arranged around the inner surface of the tank shell 2. A plurality of hanger members 18 have their lower ends pivotally connected to the roof 4, as at 20, and their upper ends pivotally connected, as at 22, to brackets 24 which are in turn fixedly secured to the adjacent shoe 16. If desired, the hangers 18 may be longitudinally flexible by providing spring means 26 as is well known to those skilled in the art. The hangers 18 thus support the shoes 16 from the roof 4 and in proper horizontal relation thereto. A fabric seal 28 is positioned around the entire space 14, said fabric seal 28 having its inner edge continuously connected to the rim (10, as for example, by bolting as at 30. The outer edge of the fabric 28 is continuously connected to the shoe 16, as for example, by bolting as at 32 to the upper edges of said shoes.
In order to maintain the roof substantially in a central location within the shell 2 and to provide an outward pressure on the shoes 16 to maintain a proper seal between the shoes and the inner surface of the tank shell 2, aplurality of pusher arrangements 36 are provided. In the preferred embodiment an arcuate bar has its upper end pivotally connected as at 40 to a bracket 42 which in turn is secured to the roof by welding or the like to the .rim plate 10 at some point above the surface 12 of the product 6. The arcuate bar 38 extends downwardly and outward- ,ly to a variable point of contact with .the related shoe 16.
From the point of contact the bar 3-8 extends downwardly and inwardly under the roof 4 to a point whereat a weight 44 is provided, said weight being operative to bias the entire arrangement 38 outwardly and effectuate the mentioned centering action on the roof 4 and pushing and sealing action on the shoe 16.
It will be particularly noted that the pivots 22 and 42 as well as the central portion 26 of each hanger 18 are located in the space 14 above the surface 12 of the product. I have discovered that because of rough manufacture or the accumulation of foreign matter at these movable connections, sparking frequently can there occur during mechanism action should the proper potential be present on the floating roof 4. The incidence of fire resulting from such sparking is great because frequently at points within the space 14 where movable connections are present dirt and foreign material accumulate and therefore the conductivity characteristics at points of connection and operation can change. In orderto avoid such a condition I have provided, at the pivot 22 a jumper 46 which has its opposite ends positively connected at 48 to the hanger 18 as at 49 to bracket 44. Another jumper 50 is provided at the pivot 40 to interconnect the bar 38 and bracket 42 in a similar manner. A third jumper 52 may be provided to interconnect the longitudinally movable portions of the hanger 18, again in a similar manner.
To further provide a positive and effective drain path for any static electrical charge that may accumulate on the roof 4, I mount below the roof 8 a bracket 56, said bracket extending downwardly from the roof 4 and being provided with an aperture 58 having a long axis directed toward the shell 2. A drain arm 60 is telescopically received in the aperture 53 and extends therethrough to project from both sides of the bracket 56. A spring 62 may then be arranged to surround a portion of the drain arm 60 and be compressively interposed between the bracket 56 and a drain shoe 64 mounted upon the extremity of the arm 60 adjacent the shell 2. At the inner extremity of the arm 60 a jumper 66 may be provided to connect the arm 6%) and the floating roof 4 as at 68 and 70. The spring 62 is effective to tightly force the drain shoe 64 into firm physical contact with the shell 2 so that good electrical contact is provided at this point. It will be understood that the pressure of the spring 62 should be such as to avoid any product film built up between the shoe 64 and the shell 2 which might result in impeding current flow. The jumper 66, of course, provides a positive electrical path from the roof 4 to the drain arm 60. The presence of this drain arrangement below the product surface and below the shoe 16 offers a positive path to drain static electricity from the roof to the grounded tank shell in an area where vapor concentration in the explosive range cannot normally occur. Of course, a plurality of such drain arrangements 56, 60, 62 and 64 may be provided around the entire periphery of the floating roof if desired.
Turning to Figure 2, it will be noted that a further electrical jumper 74 may be provided to interconnect the adjacent edges of the shoe 16. Again, the jumper 74 is preferably located in the product 6 as is best seen in Figure 1.
Turning to Figure 5, it will be seen that the arm 60 may be provided with a corrugated shoe 76 which offers a plurality of contact points and lines between the shoe 76 and the tank shell 2 as a further aid in avoiding any product film impediment in the circuit provided.
Directing attention to Figures 3 and 4, a modified embodiment of the drain arrangement is here shown, it being understood that identical parts a shown in the previous embodiment are here indicated with identical numerals. The drain arrangement indicated generally at 82 is again below the product surface and comprises a housing 84 secured to the underside of the deck 8 and extending downwardly therefrom. The housing 84 is provided with opposed walls 86, 86 said walls having apertures 88, 88 located therein. A drain arm 90 is telescopically received within the apertures 88 and housing 84 and has its long axis directed in proper relation toward the shell 2. At the extremity of the arm adjacent the shell a drain shoe 98, similar to those previously described is provided for intimate contact with the inner surface of the shell 2 and below the seal shoes. A spring 1430 is again coinpressively interposed between the housing 34 and the shoe 98 to provide pressure for said intimate contact. In order to maintain the drain bar 96 in proper relation to the housing 84 and to provide close contact and adequate electrical path from the roof 4 to the shell 2, a leaf spring arrangement 102 is provided in the housing 84. The spring arrangement 102 is in pressured engagement with the arm 96 forcing same downwardly against the lower plate 104 of the housing 94. In this embodiment, it is desirable to provide a smooth and finished surface in the area of the contact between the arm 96 and the plate 104 as at 106. Both the spring arrangement 102 and the surface condition at the points of contact are such as to eliminate the possibility of film impediments being built up at the points of contact. If desired, a jumper may be provided between the roof and the arm 96 as earlier described.
Thus it will be seen that the disclosed invention provides both a positive path to drain static electrical charges to ground in locations where explosive concentration of the product cannot occur. Further, in those areas where explosive concentration of product can occur the invention again provides positive electrical paths between relative movable parts to substantially reduce or eliminate the possibility of sparking discharges at those movable connections. The desired result accruing from the arrangements disclosed is a substantial reduction in rim fires where the implementing cause of such fires is static electricity.
What is claimed is:
1. In a field storage tank arrangement, the combination of a grounded cylindrical shell, a roof arranged to float on product stored in the shell, said roof comprising a deck and a rim peripherally upstanding from the deck, the rim being in spaced relation to the shell, a sealing arrangement to close the space between the roof and the shell comprising shoe members arranged in abutting relationship with the shell and in end to end relationship with each other hanger arms having opposed ends thereof connected to the roof and the shoe members respectively, whereby the members are supported from the roof, pusher means operatively interposed and in pressured engagement between the roof and the members, a seal fabric covering the space between them connected to the roof and the shell respectively, and conducting means to provide a path between the roof and the shell to accommodate the discharge of static electrical potential from the roof, said last mentioned means comprising a bracket secured to the underside of the roof and below the normal level or product therein, a drain arm telescopically received by the bracket and movable therein, a coil spring interposed between the bracket and the drain arm and in pressured engagement with the latter to normally bias the drain arm into engagement with the shell, said drain arm including a drain shoe on one end thereof and engaging said shell, said drain shoe having a nonplanar face thereon providing a plurality of areas to engage said shell, and jumper means directly interconnecting the drain arm and the roof.
2. An arrangement according to claim 1, wherein a plurality of movable connections are provided between the hanger arms, the shoe members, the pusher means and the roof; and jumper means spanning the connections.
3. An arrangement according to claim 2, and including a leaf spring compressively interposed between the bracket and the drain aim to maintain the drain arm in pressureengagement with the bracket.
References Cited in the file of this patent UNITED STATES PATENTS 1,913,643 Smith June 13, 1933 1,945,531 Kramer Feb. 6, 1934 1,986,869 Welp Jan. 8, 1935 2,193,484 Jones Mar. 12, 1940 2,650,738 Ulrn Sept. 1, 1953 2,735,573 Fino Feb. 21, 1956 FOREIGN PATENTS 244,951 Germany Mar. 22, 1912