[0001] This invention relates to improvements in hot water steel tanks having corrosion
inhibiting coatings on interior surfaces.
[0002] Typically a ceramic or glass lined hot water tank includes a cylindrical side wall
with a cylindrical top having a concave interior surface to define a "plus" head for
the tank. The bottom of the tank has a convex interior surface to define a "minus"
bottom for the tank. This arrangement has been manufactured for a considerable number
of years where the technique is normally to weld the top to the cylindrical side wall
rolled from a flat rectangular blank and to coat the interior of the bottom open ended
tank. A precoated bottom having the convex interior surface is then welded to the
base of the tank.
[0003] Although such construction is acceptable for hot water tanks, it has been found that
tank failure is a problem in the industry normally due to the hot water at the top
of the tank which increases the corrosion at the joint between the tank top and the
side wall. Such failure is normally caused by interruption in the glazing or coating
applied to this area during the coating process. An additional drawback of this construction
is that the "minus" bottom for the tank requires a material thickness considerably
thicker than the side wall of the tank to ensure that under pressure the tank bottom,
at least in its central area, does not flex which could crack or in one way or another
disrupt the coating. An additional drawback with the "minus" head construction is
that it subtracts considerably from the assembled tank volume, hence the overall height
of the hot water tank must be greater. The hot water at the top of the tank increases
any corrosive reaction because released gases, which includes oxygen, are free to
chemically react with and corrode any bare metal exposed by poor glazing or coatings.
It is also appreciated that the speed of chemical reaction doubles with every l0°C
increase in temperature. In addition the abutting nature of the fit of the tank top
with the tank side is not necessarily perfect because of nicks or other imperfections
in the outer periphery of the cylindrical portion of the tank side wall and the top.
Hence it is quite possible, even with the greatest of care in applying the glazing
material that some uncoated areas exist at the joint between the tank top and the
tank side wall.
[0004] To increase the tank volume, it would be beneficial to provide not only a "plus"
head portion for the hot water tank but also a "plus" bottom portion. This would increase
capacity of the tank for a given diameter with possible reduction in tank height depending
on the shape of the "plus" head. However with the existing technology, there is no
known approach to connect the "plus" bottom to the tank after the tank with welded
"plus" top has been coated with ceramic material. If a "plus" bottom end for the tank
as precoated were welded to the tank side wall in the manner in which the top is welded,
the coating would be severely degraded or damaged due to the heat of welding. Such
degradation would result in uncoated portions of steel which would be corroded by
the hot water.
[0005] Considering prior art tank constructions which provide "plus" heads and bottoms for
cylindrical tank construction, U.S. Patent 3,l99,7ll discloses a fire extinguishing
tank which may contain pressurized materials. The tank is constructed of materials
which are not corroded by the contents hence no protective or corrosion inhibiting
coating is applied to the tank interior. For example in containing fire extinguishing
liquids, the tank may be formed of copper or the like where the components are soldered
together. A similar system is provided in U.S. Patent 3,952,904 wherein again the
material of construction is not corroded by its contents. The plastic bottom of concave
interior shape is sonic w elded to the plastic side walls of the barrier where a seal
is provided at the connection to prevent leakage. No protective coating is required
in the system nor is any welding used in making the connection where the heat of the
weld could in any way affect an interior protective coating.
[0006] Other types of containers having "plus" end portions on cylindrical tank side walls
are disclosed in U.S. Patents 3,098,577 and 3,l32,6l8. Neither patent contemplates
interior coating of the tank surfaces to inhibit corrosion caused by its contents.
The considerations given above to the prior form of hot water tank construction is
not solved by the tank construction disclosed in these patents.
[0007] According to an aspect of the invention, a tank for containing a corrosive medium
has a corrosion inhibiting coating on interior surfaces thereof. The tank comprises
a cylindrical steel side wall and first and second ends for securement to and closure
of the tank. At least the first end is concave-shaped and projects outwardly of the
tank interior. At least the first end is secured to the tank by a connecting means
having an annular body portion for controlling effect of welding heat on the corrosion
inhibiting coating as previously applied to the tank side wall interior surface and
the first end interior surface. A first portion of the annular body portion is connected
at a first connection peripherally of the first end. A second portion of the annular
body portion is connected at a second connection to a cylindrical end portion of the
side wall. One of the first and second portions and corresponding first or second
connection is coated with the corrosion inhibiting coating. The other of the first
and second portions is a welded connection. The annular body portion controls temperature
to which the coating is heated by spacing the welded connection a predetermined extent
from the corrosion inhibiting coating.
[0008] According to another aspect of the invention, a process is provided for connecting
a steel end to a corresponding end portion of a steel tank for containing a corrosive
medium. The tank has a cylindrical side wall with an interior surface, the end being
circular and having a concave shape extending outwardly of tank interior and connecting
means for connecting the end to the tank side wall end portions. The process comprises
connecting the connecting means to either of the end or the tank side wall. The interior
surface of the tank, interior concave surface of the end and an exposed portion of
the connecting means are coated with a corrosion inhibiting coating. The connecting
means is welded to the end or the tank side wall. To complete connection of the end
to the tank side wall, the coated exposed portion of the connecting means abuts the
coating on the end interior surface of the tank side wall interior surface to form
a coating juncture. Temperature to which the coating juncture is heated is controlled
by predetermining an extent to which the connecting means spaces the welding of the
connecting means from the coating juncture.
[0009] Preferred embodiments of the invention are shown in the drawings wherein:
Figure l is a perspective view of a hot water tank characteristic of the prior art
devices;
Figure 2 is a section through the bottom and top end portions of a tank of Figure
l;
Figure 3 is a section through the hot water tank bottom incorporating the method of
connection of the "plus" bottom to the tank in accordance with an embodiment of this
invention;
Figures 4 through 9 illustrate different embodiments of the invention for connecting
the "plus" bottom of the hot water tank to the side wall of the tank in accordance
with this invention; and
Figure l0 is a section through the hot water tank base showing an alternative arrangement
for supporting the hot water tank with a "plus" bottom.
[0010] This invention is applicable to many forms of tank construction which contain
mediums corrosive to the tank material; for example, steel tanks for containing water,
gas cylinders for acidic gases, fire extinguishers and beer kegs. The preferred embodiments
of this invention will be demonstrated in a hot water steel tank construction. However,
it is appreciated that such embodiments are equally applicable in other tank constructions.
[0011] Hot water tanks are used in residential and commercial establishments to heat and
store water, normally at temperatures in the range of l20°F to l60°F, where the source
of heat is normally by electrical heating elements or gas fired heating devices. A
typical tank used in electrical type of water heater is shown in Figures l and 2.
The tank l0 consists of a cylindrical side wall l2 with a first or bottom end l4 and
a second or top end l6. The ends of the tank are welded to the cylindrical side wall
to seal the tank and provide a compartment in which water is heated and stored as
hot water. It is understood that the water inlet and apertures for electrical heating
elements, as provided in the side wall l2, are not shown. Usually the hot water is
taken from the top of the hot water heater via the outlet l8.
[0012] The assembly of the hot water heater of the prior art device is normally accomplished
by welding the end l6 to the side wall l2. With reference to Figure 2, the top end
l6 has a peripheral end portion 20 which is fitted within the side wall upper end
portion 22. The top end l6 is welded to the side wall end portion 22 by a fillet weld
24 which connects the upper edge 26 to the outer side wall 28 of the end l6. A bottom
open-ended tank is therefore provided where the tank interior with the end l6 in place
is coated with a corrosion inhibiting coating. This may be accomplished by cleaning
the inside of the tank and end by use of abrasives or acid pickling process to remove
the oxides and dirt from the steel interior surfaces and at the same time etch the
surface to provide for satisfactory bond of the corrosion inhibiting coating to the
interior of the tank. After cleaning, the tank interior is coated with a glazing slurry
which is commonly used in the art and consists of finely ground essentially ceramic
powder suspended in water. The coating is applied to all internal surfaces including
the interior concave surface 30 of the end l6 and also about the joint area 32 interior
of the tank along with the tank side wall interior surface 34. To facilitate welding
of the bottom end l4 to the tank side wall, the coating is wiped off the bottom edge
36 as well as a marginal interior portion of the tank side wall. The coated tank is
then passed through a drier to remove water from the glazing slurry, and placed into
a glazing furnace which operates normally at a temperature of about l600°F. This results
in a smooth corrosion resistant coating on the tank interior.
[0013] The bottom end l4 which has a convex interior surface is cleaned and glazed in a
similar manner to the tank shell assembly. The glazing coating is wiped off in area
38 so as to be adjacent the cleaned end portion 36 of the side wall. The bottom l4
is inserted within the tank. The coating on the interior surface 40 of the tank bottom
abuts the coating on the interior surface 34 of the side wall. A weld 42 is applied
between surfaces 36 and 38. Usually the weld 42 is sufficiently remote from the area
generally designated 44, which is the juncture of the coatings on interior surfaces
34 and 40, that the heat from the welding process does not degrade the coatings. Normally
such welding is carried out by a type of submerged-arc process.
[0014] This type of tank construction has been used for many years in providing a "plus"
head on the top of the tank and a "minus" head on the bottom of the tank. The "minus"
head considerably reduces the volume for the tank considering its overall height.
The bottom portion with the convex interior surface must be formed of material which
is thicker than the side wall to withstand the pressures within the hot water t
ank. If the bottom were made of thinner material the bottom could flex resulting in
cracking of the coating and opening areas to corrosion causing tank failure. The material
thickness for the bottom is usually in the range of l.6 times thicker than the material
thickness for the "plus" head portion providing the dished shapes are similar, which
in turn is usually thicker than the material thickness for the side wall. This results
in considerable inventory problems and the need to carry at least three different
thicknesses of material depending on the parts made. An additional requirement is
the extra tooling and machine set ups in manufacturing the parts.
[0015] To increase volume of the tank for its diameter and to permit use of thinner material
thicknesses at least on the bottom of the tank, the provision of "plus" end at the
bottom of the tank is a desired embodiment of the invention. However, after assembly
of the tank side walls to the tank top and coating and subsequent welding of the tank
"plus" bottom to the tank side wall, the welding would be on the tank bottom portion
in a area which is coated. The heat from the weld would travel directly through the
tank bottom wall portion thereby degrading the ceramic coating. This even becomes
more of a problem if non-ceramic coatings are used such as polymeric coatings which
include various suitable polyamides; for example Nylon II (trademark). Such degradation
of the coating can result in its destruction and loss of corrosion inhibiting properties.
[0016] As already noted, another problem with existing tank construction is that several
of the tank failures are due to a breakdown in the coating of the top seam area of
the tank top to the side wall. Hence a construction which would avoid such breakdown
is desired for the top construction of the hot water tank.
[0017] According to this invention a connection is provided for either end of the tank cylindrical
side wall which can constitute either the top or bottom of the tank when in use. As
shown in Figure 3, the cylindrical tank side wall l2 has fitted to its bottom end
portion 36 a "plus" bottom end 46. The end 46 has a concave interior surface 48 which
extends outwardly of the interior of the tank. According to this embodiment the concave
interior surface 48 has a semi-ellipsoidal shape. However, it is appreciated that
the end may be torispherical in shape as defined in ASME Boiler and Pressure Vessel
Code, Section VIII, Division l, l977 Edition. Due to essentially constant material
thickness the exterior surface 52 of the end 46 approximates the same shape. To provide
for connection of the end 46 to the interior of the side wall l2, a connecting device
generally designated 54 having an annular boby portion is used. According to one aspect
of the invention, the connecting device 54 is secured to the peripheral edge portion
56 of the exterior of the end 46. Such connection may be by welding or other suitable
securing means.
[0018] Prior to assembly of the end 46 to the cylindrical side wall l2 of the tank, the
interior surface 34 of the tank is coated as well as the interior surface 48 and the
exterior portion of the connecting means 54. Any excess applied coating in region
57, which is to be subsequently welded to the tank wall is wiped off. The tank interior
end is also wiped off to leave opposing uncoated surfaces for welding. The end portion
46 is then inserted into the end 36 of the cylindrical side wall where the coatings
on the connecting means 54 and on the interior surface 34 of the tank overlap and
contact one another to seal the tank end. The connecting means is then welded to the
end 36 by a fillet weld 58. The connecting device 54 is arranged to control the temperature
to which the juncture of the overlapped coatings is heated by the process of welding
the connecting means to the end 36. Such control on temperature is exercised by predetermining
the extent to which the connecting device 54 spaces the fillet weld 58 from the juncture
of the overlapped coati ng and also from the coating on the interior
surface of the end and tank side wall. The connecting device 54 conducts heat from
the welding region of weld 58 towards the juncture of the coatings. By trial and error,
the extent to which the connecting device spaces the weld from the juncture of the
coatings can provide a control on the temperature to which the coatings are heated.
It may be desired to control the temperature to an extent which minimizes or avoids
any effect of welding heat on the coatings at the juncture. Alternatively, it may
be desirable to control temperature to the extent that the coatings at least at the
juncture are fused during the welding process. It is appreciated that, when it is
desired to increase the temperature at the coating juncture, a shorter height for
the connecting device is provided, or the mass of the connecting device is reduced,
or is made from material which conducts heat at a faster rate to the juncture area.
Further detail of the overlap of and formation of a juncture of the coatings and the
welding technique will be discussed with respect to the various embodiments of the
invention as shown in Figures 4 through 9.
[0019] To complete the assembly of the bottom of the hot water tank a cylindrical base or
stand 60 is provided. The stand 60 has a inwardly stepped portion 62 which is secured
to the interior surface 64 of the connecting device. The stand has a peripheral bottom
edge 66 which extends below the lowermost portion 68 of the end 46 to act as the support
feet for the hot water tank when it is stood upright for use.
[0020] The coating for the connecting device 54 for the end 46 and also for the interior
34 of the tank side wall l2 is shown in more detail in Figure 4. The connecting device
54 comprises an annular skirt portion having exterior surface 76 which is welded at
74 to the exterior surface 56 of the end portion. The skirt extends outwardly of the
end portion and is stepped in area 84 to facilitate insertion of the end 46 into the
tank. The coating 70 as applied to the interior surface 34 may be of a fired ceramic
composition or of some polymeric composition, such as "Nylon". As already discussed
in providing a ceramic or glass lined coating, a slurry including ceramic particles
is coated onto the interior surface 34 of the tank side wall. The lower circumferential
end portion of the shell interior 72 does not include coating material hence this
area is left uncoated after the tank side wall has been dried and fired. The end 46
and the connecting device 54 also have the slurried ceramic coating applied thereto
over the entire interior surface 48 of the end, and overlapping the welded area 74
which includes the connection of the connecting device 54 to the external edge portion
56 of the end. The exterior surface 76 of the connecting device is also coated with
the slurried material to provide thereby an essentially continuous coating 78. The
lower portion 80 is left uncoated to provide an uncoated peripheral area 80 about
the perimeter of the connecting device 54.
[0021] The coatings, which have been applied to the tank side wall interior surface and
to the end 46, are then glazed, cured or fused. The end is then inserted into the
tank end until the coated surfaces 70 and 78 contact in the region designated 82 on
the connecting device exterior surface 76 and also on the lower portion of the coating
70 of the tank side wall. Such contacting of the coatings forms a seal about the periphery
of the tank bottom end to prevent water leakage and thereby form effectively a continuous
coating from the side wall onto the end 46. In providing parallel coated surfaces
which form the juncture of coatings, a significant circumferential band of contact
area is provided for the contacting coatings. Such band area of contact ensures a
seal about the peripheral juncture of coatings, because of the band height over which
contact between the coatings can be established. If there is difficulty in providing
a seal about the peripheral junctu re of the coatings, as discussed, it
is possible by way of the connecting device to control the temperature to which the
juncture of coatings is heated to fuse coatings in that area without totally degrading
the coatings and losing any potential for a seal at this juncture. This is particularly
applicable when the coatings are of a polymeric material, such as "Nylon" which can
be fused when heated to the proper temperatures. It is appreciated that a sealant,
such as an epoxy coating or gasket, may be applied to the juncture before welding.
The heat of welding is then controlled by the connecting device to ensure that the
epoxy sealant or gasket is not degraded.
[0022] The end portion is now in a position to be secured to the tank side wall l2. The
connecting device 54 extends a sufficient distance outwardly of the juncture 82 of
the coatings such that when the uncoated portion 80 is welded to the uncoated portion
72 of the tank side wall, the heat of the welding does not in any way degrade the
non-corrosive characteristic of the coatings at least in the area of juncture 82 and
inwardly thereof. Such connecting device 54 serves to space the welded area away from
the coating not only on the connecting device 54 but also on the interior surface
of the end 46 such that when the weld is completed a continuous coating remains on
the bottom surface and side wall area of the tank. The welding which may be used to
connect the connecting device 54 to the outer peripheral edge portion 56 of the end
is done before the coating is applied to the end and connecting device hence the heat
of the weld of that connection has no effect on the subsequent coating process. In
actual fact, the coating overlaps the seamed area and any weld which may be present
to coat and protect that area from corrosion by the contained liquid which is normally
water.
[0023] It is appreciated that the principle of the invention may be accomplished in a variety
of configurations for connecting an end portion to the tank side wall. With reference
to Figure 5 through 9 such alternative arrangements are shown where it is understood
that the surfaces as exposed to the contained liquid are coated with the corrosion
inhibiting materials.
[0024] As shown in Figure 5, the end 46 has a concave interior surface 86 which may be of
the ellipsoidal, torispherical or hemispherical configuration as shown in Figure 3.
The connecting device 54 includes the annular skirt portion 88 which extends outwardly
of the interior of the tank. According to this embodiment the skirt portion 88 is
a continuation of the wall portion 90 of the end as provided for by a reverse bend
92. The end 46 as fabricated from an essentially constant material thickness of steel
is coated prior to insertion within the tank side wall l2 which has a coating on its
interior surface 34. The coatings are such to form a juncture in the region 94 which
effectively forms a seal about the bottom of the tank. Uncoated portions of the tank
side wall in region 72 and 96 of the skirt exterior are provided so that a fillet
weld 98 may be used to connect the end 46 to the tank side wall l2. The skirt of the
connecting device 54 extends outwardly of the tank interior a sufficient distance
so as to locate the fillet weld 98 at a region where the heat of the weld does not
degrade the non-corrosive properties of the coating at least in the area of juncture
94 about the perimeter of the connecting device 54. By providing this reverse bend
arrangement 92 for the end 46, the entire end portion may be fabricated from a single
blank of steel sheet material without requiring any welding operation in the reverse
bend region 92.
[0025] With reference to Figure 6, another embodiment is shown for the end 46 of the hot
water tank for installation and connection to the tank side wall l2. With this type
of assembly, the top and bottom ends can be of the same diameter. This approach considerably
reduces inventory costs in keeping separate tank ends for completing the tank construction
. The end 46 has a concave interior surface l00. The connecting device 54 comprises
a skirt portion l02 having its upper end which is angled towards the bottom portion
l04 of the end 46. A fillet weld at l06 connects the angle portion l08 of the skirt
to the end 46. The assembly of the connector device 54 and the end 46 are coated in
the manner similarly used in coating the other embodiments. The interior surface 34
of the side wall is coated, such that when the end 46 is inserted within the tank
side wall the coatings contact and form a seal in the juncture region ll0. With the
end portion assembled within the tank the uncoated portions of the tank end 72 and
the connector skirt portion ll2 are connected by fillet weld ll4, the heat of which
does not affect the coatings in the region ll0.
[0026] The embodiment of Figure 7 is an alternative to that of Figure 6, where an arrangement
is provided which permits the use of an end 46 which is the same as the other end
used in connecting to the top portion of the tank side wall in accordance with the
technique shown in Figure 2. To accommodate the thickness of the connecting device
54 the side wall l2 is stepped in region ll6. According to this embodiment the connecting
device 54 is a skirt portion ll8 which is welded at l20 to the peripheral edge portion
l22 of the end 46. The end 46 with the connecting device 54 is coated independently
of the side wall interior surface 34. In coating the end portion 46 the coating covers
the seam area which includes the weld l20. After the end 46 is inserted in the tank
end portion, the end is secured by way of a weld l24. The skirt ll8 extends sufficiently
outwardly of the tank so as to locate the weld l24 a sufficient distance from the
region l26 about which the coatings on the interior surface 34 of the tank and on
the connecting device ll8 contact one another. The heat of weld from welding l24 does
not degrade coatings in this area or interior thereof including the coating on the
interior l28 of the end 46.
[0027] Another arrangement is provided in Figure 8 for connecting the end portion 46 to
the tank side wall. The connecting device 54 includes a skirt portion l30 which is
welded at seam l32 to the peripheral edge l34 of the end 46. The welded assembly is
then curved inwardly to the extent shown in Figure 8 to provide for a lead in portion
in inserting the end 46 within the tank side wall l2. The tank side wall l2 is provided
with the coating 70 in the manner discussed with respect to Figure 4, the tank end
46 with connecting device 54 is coated with a coating l36 which extends over the seam
area l32 and downwardly of the outer wall portion l38 of the skirt l30. A fairly close
tolerance fit is provided between the uncoated portion of the outer surface l38 of
the skirt l30 and the corresponding uncoated portion 72 of the tank side wall. The
weld l40 is located a sufficient distance from the juncture l4l of the coating so
as to not degrade same. Similarly the skirt l30 spaces the weld l40 from the coating
l36 on the interior of the end 46.
[0028] It is also possible to provide for the connection of the tank side wall to a "plus"
end, bottom or top which has an internal diameter at its circumferential portion greater
than the external diameter of the tank shell. This type of connection is shown in
Figure 9, wherein the tank side wall l2 has the connecting device 54 secured at a
first portion l42 to the exterior l44 of the tank side wall. The inner surface 34
of the tank is coated with the corrosion inhibiting coating including the connection
area l46 and remaining exposed external surface l48 of the connecting device 54. The
"plus" end, which may be the bottom 46, has a coating on its interior surface 48 which
overlaps the coating on surface l48 of the connecting device in the region l50. The
second portion l52 of the connecting device is fillet welded at l54 to the end 46
to complete the assembly of the end to the tank side wall. The connecting device 54
spaces the fillet weld l54 a suffici ent distance from the overlapped region l50 to
control the temperature to which the overlapped region of coatings is heated during
the welding operation. By this technique, a larger end can be assembled to a smaller
tank shell.
[0029] An alternative stand assembly for the hot water tank is provided in Figure l0. The
end 46 is assembled to the tank side wall l2 in accordance with the structure generally
shown in Figure 8. For hot water tanks which are insulated with a foaming material
such as urethane foam a prefabricated foamed base l56 is provided which receives the
shape of the end 46. With the tank bottom on the foam base l56 a shell assembly l58
may be assembled around the base and the tank leaving a cavity l60 between the tank
exterior l58 and the tank side wall l2 and also about the top portion (not shown).
With the assembly complete, a foam material is introduced into the cavity l60 to fill
the cavity with an insulating foam material and solidify the structure once the foam
urethane composition has set. This provides for a quick assembly technique for the
hot water tank construction where the shell l58 including a platform l62 is now complete
and ready for use where the platform includes projecting feet portions l64.
[0030] As previously discussed with respect to Figure 2, the prior art technique of assembling
the top to the tank end has resulted in failures. This can be avoided in tanks having
a "minus" bottom by using the same technique for assembling the "plus" bottom end
of the tank, as discussed with respect to Figures 3 through l0, to similarly assemble
the "plus" top to the tank end. It is appreciated that in connecting a top end to
the tank a skirt extension or the like 60 as shown with respect to Figure 3 is not
required. In the case of foam insulating the tank the tank upper portion may be the
mirror image of that shown in Figure l0 without the use of feet or the like where
appropriate openings and piping arrangement are provided for the outlet of the hot
water tank.
[0031] By this method of assembly in isolating the welding for connecting a tank end to
the tank side wall so that the tank coatings are not degraded, one can provide "plus"
head configurations at each end of the tank to increase the tank volume and in addition
permit the use of thinner material thicknesses for the tank ends since the concave
shape for the tank end can accommodate considerably greater stresses without yielding.
By considerably reducing the material thickness of the end portions which may be equal
to or less than the thickness of the tank side wall, appreciable savings in tank construction
are achieved. For example, with a tank construction where the top is also used as
the bottom and assembled in the manner shown with respect to Figure 7, there is a
material saving of approximately 8%. With a tank end configuration having ends approximating
the ellipsoidal configuration of Figure 3 or a similar torispherical shape, there
can be a material saving of approximately 20%. When the tank ends approach a hemispherical
shape the material saving can be approximately 3l%. This is accomplished by the fact
that as the tank ends approach a hemispherical shape considerably thinner material
thickness for the tank ends may be used while still accommodating the tank pressures.
[0032] The relationship of the material thickness of the tank end compared to the thickness
of the tank side wall for resisting stresses created by pressures within the tank
are well understood in pressure tank design. This permits the use of thinner materials
in the tank ends to considerably reduce the amount of material used in manufacturing
the tanks knowing that the tank end can be designed to accommodate a predetermined
stress. Surprisingly with the prior art construction of Figure 2 even with the "plus"
head configuration for the tank top, the material thicknesses for the tank top is
usually l.6 times the tank side thickness and for the bottom "minus" head the thickness
usually averages more than l.9 times th e tank side wall thickness. In
accordance with this invention where the "plus" head arrangement is used at both the
tank top and bottom, it has been found that both ends may be of a thickness less than
the tank side wall thickness. This results in significant material savings, to upwards
of 28%, and considerably reduces failures of the tank in the region of the joint of
tank top to side wall. In addition the design provides for a significant glazing energy
saving which can be realized in the range of l0 to 30% depending upon the shape for
the tank ends. Another form of energy saving can be realized due to the overall reduction
in tank surface area for the volume of water contained. Due to the reduced tank surface
area, there is less heat loss so that less energy is required to maintain the water
at the desired temperature.
[0033] The method, according to this invention, is conducted in the manner described where
the significant advantage with one of the embodiments of the invention is that the
tank side wall may be coated independently of the end portions. Hence the interior
of the side wall can be inspected for flaws before the ends are connected to the tank
side wall. In addition, the threads of the outlet l8 can be independently inspected.
This is particularly important when coatings of ceramic slurry are applied to the
tank interior. In addition, with coating the tank ends with ceramic slurry the effectiveness
of the coating can be inspected particularly about the seaming area of the connecting
device.
1. In a pressurized steel tank for containing a corrosive medium having a corrosion
inhibiting coating on interior surfaces of said tank, said tank comprising a cylindrical
steel side wall and first and second ends for securement to and closure of said tank,
at least said first end being concave shaped and projecting outwardly of tank interior,
the improvement being characterized in said first end being secured to said tank by
a connecting means having an annular body portion for controlling effect of welding
heat on said corrosion inhibiting coating as previously applied to said tank side
wall interior surface and said first end interior surface, a first portion of said
annular body portion being connected at a first connection peripherally of said first
end and a second portion of said annular body portion being connected at a second
connection to a cylindrical end portion of said side wall, one of said first and second
portions and corresponding first or second connection being coated with said corrosion
inhibiting coating, the other of said first and second portions being a welded connection,
said annular body portion controlling temperature to which said coating is heated
by spacing said welded connection a predetermined extent from said corrosion inhibiting
coating.
2. In a tank according to claim l, characterized in that said second connection is
coated with said second portion of said annular body portion being connected to an
exterior surface of said side wall cylindrical end portion, said first portion of
said annular body portion being welded to a circular interior surface of said first
end, said annular body portion being coated with said coating to circumferentially
abut said coating on said first end interior surface.
3. In a tank according to claim l or 2, characterized in that said annular body portion
controlling temperature of said abutting coatings during welding of said first connection
to fuse said abutting coatings.
4. In a tank according to claim l, 2 or 3 characterized in that said annular body
portion extends outwardly of said first end and being coated with said coating which
has been applied to said interior surfaces of said first end, said annular body portion
being slidably received by an interior cylindrical end portion of said side wall,
said coating on said side wall interior surface circumferentially abutting said coating
on said annular body portion to provide a se al at a juncture
of said side wall interior coating and said annular body portion coating, said side
wall interior surface and adjacent said portion of said annular body portion being
uncoated outwardly of said juncture of coatings, a weld connecting said uncoated side
wall and annular body portion together.
5. In a tank according to claim 4 characterized in that said second end is concave-shaped
and projecting outwardly of tank interior and being welded to said side wall to provide
a peripheral interior junction of said second end to a second end wall of said side
wall, said coating extending over said interior junction.
6. In a tank according to claim 4, characterized in that said annular body portion
is integral with said first end and being an extension of said end in a reverse direction
as provided for by a reverse bend in said first end around its periphery, said reverse
bend constituting said first connection.
7. In a tank according to any one of the preceding claims, characterized in that said
first end has an ellipsoidal, torispherical or hemispherical shape in cross-section
along a diameter of said first end.
8. In a tank according to any one of the preceding claims characterized in that said
first end has an essentially uniform thickness less than or equal to an essentially
uniform thickness for said side wall.
9. A process for connecting a steel end to a corresponding end portion of a steel
tank for containing a corrosive medium, said tank having a cylindrical side wall with
an interior surface, said end being circular and having a concave shape extending
outwardly of tank interior, connecting means for connecting said end to said tank
side wall end portion, said process being characterized in connecting said connecting
means to either of said end or said tank side wall, coating said interior surface
of said tank, interior concave surface of said end and an exposed portion of said
connecting means with a corrosion inhibiting coating, welding said connecting means
to said end or said tank side wall to complete connection of said end to said tank
side wall, said coated exposed portion of said connecting means abutting coating on
said end interior surface or said tank side wall interior surface to form a coating
juncture, controlling temperature to which said coating juncture is heated by predetermining
an extent to which said connecting means spaces said welding of said connecting means
from said coating juncture.