Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED TANK COLLAR
Field of the Invention
The present invention relates to the construction of underground tanks. It is
particularly applicable, but in no way limited, to collar assemblies used to
form fluid
tight connections between containment or access chambers or containment sumps
and a tank. The invention includes methods of manufacturing such collars, to
tanks
incorporating them, and to chambers adapted to interface with the new tank
collar
assemblies.
Background to the Invention
In typical underground storage and distribution systems for hazardous fluids
such as
hydrocarbon fuels, the fuels are usually stored in a large storage tank buried
in the
ground and delivered through underground piping to delivery pumps or the like.
In
order to ensure that the fuels cannot leak into the ground surrounding the
tanks and
pipework, so-called secondary containment systems are used which essentially
provide a second barrier of protection around the primary fluid supply storage
and
delivery systems.
Typically, secondary containment systems have included containment sumps or
access chambers, which are an offshoot from the so-called back fill retainer.
There
are a variety of chambers now on the market usually comprising a body defining
an
enlarged chamber, a riser connected to the body, where the riser is generally
of
smaller diameter than the body, and a cover fitting over the top end of the
riser.
The containment or access chamber is installed below ground to provide a means
of
access to the manway, underground piping connections, submersible pumps, leak
detection sensors, fire extinguisher and other plumbing components usually
found
connected to the top of underground storage tanks or under fuel dispensing
units.
Access or containment chambers are multi-purpose in function:
1. They provide a means of surface access to equipment, plumbing and
miscellaneous devices installed underground.
2. They provide a means of ground isolation for contained components
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to prevent corrosion and decay.
3. They provide a means of secondary containment for those contained
components which handle hazardous liquids.
4. They act as a collection sump for double wall piping entering the
access chamber.
Underground storage tanks usually have an access hatch or manway on the top of
the tank to permit access into the interior of the tank if necessary. An
access
chamber is installed over the manway to facilitate access to the interior of
the tank
once it is underground. The access chamber is connected to the tank by means
of
a collar, which in turn is connected in a fluid tight manner to the outside of
the tank
around the manway. Where the tank is made of metal, a metal collar is normally
welded to the tank. These collars are typically circular or polygonal in cross-
section
but can be of any suitable cross-section as determined by the designer, and to
suit
the particular manway/access chamber combination.
Protruding through and connected to the top of the manway are various pipes,
elbows and connectors which are in turn connected to the underground pipework
system, whose pipe ends usually enter through the side of the access chamber
wall.
This enables the fuel stored within the tank to be distributed to the pumps.
Due to the limited space within the chamber and the necessary size of the
manway
to permit a person to enter the tank, the connections between the pipes
entering
through the side of the chamber wall and the pipes/fittings protruding through
the top
of the manway are usually made directly over the manway itself. Typically,
flanges
are used to connect together the underground pipework to the pipes/fittings
associated with the manway lid.
There are various methods by which an access chamber can be connected to the
collar around the manway. In one method the collar incorporates an upwardly
directed channel around its circumference, usually the outer circumference.
The
radius and profile of this channel is designed to accommodate a corresponding
downwardly depending skirt on the base of the access chamber, the skirt having
substantially the same cross-section as the collar channel. During
installation the
channel is filled with sealant, preferably a polyurethane sealant, before the
chamber
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skirt is pushed into the channel. Once set, the sealant forms a substantially
fluid
tight seal between the chamber and the collar.
However, these sealants can break down over time and this can lead to ground
water ingress into the chamber or escape of fuel from the chamber in the event
of a
fuel leak or spillage. Both these situations are serious and result in costly
maintenance work being required.
Because this seal is buried in the ground, excavation is necessary to expose
it, and
the whole assembly generally has to be dismantled. Not only is this expensive
in
both money and time, but the garage or operating unit has to be closed to
business
while repairs are carried out. This results in significant lost revenue.
In another method, a collar is provided which incorporates a metal flange
designed
to engage with a corresponding flange on the bottom of the chamber. A gasket
is
provided between the two flanges during assembly and the metal flange is
bolted to
the bottom of the chamber. These gaskets degrade over time, resulting in
similar
consequences to those described above.
Modular access chambers made from plastics material are known, as for example
in
EP1,717,377 (NUPI S.p.A.). The modules of these modular chambers can be
connected to each other by electrofusion means using special electrofusion
beads.
However, the bottom of such modular chambers is still connected to a tank
collar by
way of bolts through a conventional flange and a gasket. Electrofusing bonding
tape
or beads are known from GB2,407,795 (PetroTechnik Ltd).
It is an object of the present invention to provide a collar assembly for a
tank which
overcomes or mitigates some or all of the above disadvantages, and to provide
tanks and access chambers incorporating improved collar assemblies.
Summary of the Invention
According to a first aspect of the invention there is provided a tank collar
assembly
according to Claim 1. In one embodiment the tank collar assembly comprises:-
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(i) a first portion adapted at a first end to be connected to a tank around a
manway or to a manway itself in a substantially fluid tight manner, said first
portion being adapted to extend substantially entirely around the manway on
the tank and to extend away from said tank or manway such that it forms an
annular flange surrounding the manway;
(ii) a second portion formed from a fusible material, said second portion
being
attached to the first portion in a substantially fluid-tight manner by a
securing
means;
wherein a surface of said second portion is adapted to contact a corresponding
fusible mating surface on the base of an access chamber.
This arrangement provides, for the first time, the ability to electrofuse a
chamber
onto the tank collar.
Preferably the first portion is formed from a metal, especially when the tank
is
formed from metal.
Preferably said securing means comprising swaging, such that a substantially
fluid
tight swaged joint is formed between the radially extending flange of the
first portion
and the second portion. The technique of swaging is known per se and is a
convenient method of forming a durable plastic to metal seal.
In an alternative preferred embodiment the second portion is secured to the
first
portion by moulding the second portion to, around or within the first portion.
In a further preferred embodiment the second portion is secured to the first
portion
by way of an adhesive or a sealant.
Preferably the second portion incorporates an energy transfer means adapted to
heat a first surface of the second portion in order to form a substantially
fluid tight
seal with a mating surface of an access chamber, and more preferably the
energy
transfer means comprises one or more electrofusion heating elements.
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Alternatively, the electrofusion heating element(s) may be incorporated into
the
mating surface of the access chamber.
Preferably the second portion rests on and is supported by the first portion
in use.
5
Preferably the assembly further comprises one or more support means, said
support
means being adapted to support the first portion. Struts, stays or brackets
may be
used to strengthen the flange.
Preferably the assembly is connected to the tank, wherein the first portion
comprises
two components, a first component connected in a substantially fluid-tight
manner to
the tank around the manway, and a second component is connected to the first
component in a substantially fluid-tight manner, said second component
extending
substantially entirely around the first component in the form of a radially
extending
flange, the first and second components being joined during manufacture.
Preferably the first component and the second component are both made of a
metal
and preferably the two components are welded together.
According to a second aspect of the invention there is provided a tank
incorporating
a tank collar assembly as claimed herein.
According to a third aspect of the invention there is provided an access
chamber
incorporating a fusible surface in its base said fusible surface being adapted
to mate
with a corresponding fusible surface in a tank collar assembly as claimed
herein.
Brief Description of the Drawings
The present invention will now be described by way of example only with
reference
to the accompanying drawings, wherein:
Figure 1 is a partially cut-away side view of part of a petroleum forecourt
installation,
which includes a tank having a containment chamber, and a pair of dispensing
pumps having sump chambers;
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Figure 2 illustrates a side view of a prior art containment chamber assembly
together with a storage tank;
Figure 3 illustrates a cut-away perspective view of the containment chamber in
Figure 2;
Figure 4 illustrates a cross-sectional view of the prior art containment
chamber of
Figure 2;
Figure 5 illustrates a cross-sectional view of a first embodiment of a collar
assembly
according to the present invention attached to a tank and in combination with
an
access chamber;
Figure 6 illustrates a flange component of the collar assembly in Figure 5;
Figure 7 illustrates a cross-section A-A of Figure 6;
Figure 8 illustrates a cross-sectional view of a second embodiment of a collar
assembly according to the present invention.
Figure 9 shows a tank collar according to a further embodiment of the
invention with
an access chamber attached;
Figures 10 and 11 show enlargement of Detail A and Detail B of Figure 9
respectively;
Figure 12 illustrates in exploded diagram form the assembly of Figure 9.
Description of the Preferred Embodiments
The present embodiments represent currently the best ways known to the
applicant
of putting the invention into practice. But they are not the only ways in
which this
can be achieved. They are illustrated, and they will now be described, by way
of
example only. By way of terminology used in this document the following
definitions
apply:-
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Access chamber - any receptacle designed to keep a fluid in or out. This
includes,
but is not limited to, access, manhole and sump chambers as described herein.
It
also includes tanks in general.
Access chamber system - any part of the underground system, including the
access chamber, that is contained by, or attached to the access chamber. This
includes the access chamber itself, corbel, frame neck or lid together with
the
underground tank, collar, manway and associated pipework.
Energy transfer means - a generic term describing any form of energy source.
Typically it takes the form of a resistance winding which heats up when an
electrical
current is passed through it. The term also encompasses other welding
techniques
including ultrasonic welding and induction welding.
Flange - any collar suitable for attaching the tank collar assembly to an
access
chamber. In the examples given the surface of the flanges are substantially
planar.
However, it will be understood that the flange must conform to the profile of
the
section to which it is to be joined. Thus the flange can adopt any suitable
configuration or conformation to achieve the necessary contact with a flat or
curved
surface.
Fluid - whilst the examples provided relate mainly to liquids, the term fluid
refers to
liquids, vapours and gases. For example, should a leak occur in a secondarily
contained pipe in a garage forecourt installation then petrol or petrol vapour
will
collect in the access chamber. It is essential that this petrol vapour cannot
escape
through the tank collar assembly and into the surrounding ground.
Pipe - where pipes are referred to herein they are generally of circular cross-
section. However, the term also covers other cross-sections such as box
sections,
corrugated and the like and secondarily contained pipes of the "pipe-within-a-
pipe"
type.
Glass reinforced plastic (GRP) - The term GRP has a very broad meaning in this
context. It is intended to encompass any fibre-reinforced plastic wherein a
fibre of
any type is used to strengthen a thermosetting resin or other plastics
material.
Fusible material - The term fusible material has a very broad meaning in this
context. It is intended to encompass any polymeric material which when energy
is
applied to it can melt and fuse together with an adjacent material and is
intended to
cover thermoplastics, thermosets, elastomers and adhesives.
Plastics Material - The term has a very broad meaning in this context and is
intended to encompass any polymeric material including thermoplastics,
thermosets,
elastomeric or any other polymeric material.
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The petroleum forecourt installation shown in Figure 1 comprises a pair of
dispensing pumps 10 and 11 connected to a subterranean tank 12 through a
pipeline 13. The pipeline 13 is formed from contiguously arranged sections of
polyethylene pipe. The pipeline 13 extends from the pumps 10 and 11 through
the
sump chambers 14 and 15 having side walls 16 and bases 17 into a containment
or
access chamber 18 having a side wall 19 and a base 1 immediately above the
tank
12.
Figure 1 shows two lines extending from the pipeline 13 into the tank 12.
These
lines relate to two alternative forms of fuel supply system and are both shown
for the
sake of completeness. In practice, only one of the lines would extend from the
pipeline 13 into the access chamber 18. One of those lines is a suction line 2
which
is used where the dispensing pumps 10 and 11 are fitted with suction pumps.
The
alternative line, reference 3, is a pressure line connected to the pipeline 13
via a
pump 4 which is operable to propel fuel from the tank 12 to the pumps 10 and
11.
It can be seen from Figure 1 that the walls 16 and 19 have to be apertured in
order
to allow the pipeline 13 to pass into the chambers. In order to prevent water
leaking
from the surrounding ground (here denoted by reference numeral 5) into the
chambers 14, 15 and 18 through the aperture, the pipe is sealed to the walls
16 and
19 by means of a fitting. In the event of a spillage or a leak in a supply
pipe the seal
also prevents fuel from escaping into the environment.
Figures 2 to 4 show various views of a prior art containment or access chamber
mounted on a tank. The chamber arrangement can be seen more clearly in Figure
3, which shows a cut-away view of the chamber in place on a storage tank. It
can
be seen that the incoming pipework and its associated fittings are outside the
vertical footprint of the manway and that the lower aperture and the upper
aperture
are concentric. This can be seen by line 51 in Figure 4. Detail B shows a
detailed
view of a channel that contains a polyurethane sealant 50. The sealant is used
to
form a fluid tight seal between the chamber and the upstanding collar and
holds the
chamber in place.
Figure 3 shows a cut away perspective view of a containment chamber and shows
the upper aperture 52, access cover 53, access cover skirt 54, chamber corbel
55,
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chamber body 56 and chamber base 57. It also shows manway 58 and incoming
pipework 59, together with tank 60.
The prior art containment chamber of Figures 2 to 4 is a decagonal (10 sided)
shape, which means that it is extremely rigid and is compatible with all entry
fitting
design criteria. The asymmetrical offset design means that the chamber has one
large side for the 90mm-110mm secondary contained fill lines. Therefore, the 4-
inch
fill line flange fittings can be located outside the manway lid footprint
allowing easy
removal of the tank manway lid when required.
Underground storage tanks, particularly those used for storing petroleum
products,
are generally made of metal. The tank collars associated with such tanks are
also
usually made of metal, and welded to the top of the tank around a manway.
Access
chambers on the other hand are usually made from a plastics material such as
polyethylene. This is much lighter and more durable than metal, easier to form
into
the desired shape, and is compatible with the polyethylene pipework widely
used to
convey petroleum products. This therefore presents the problem of how to bond
a
plastic chamber to a metal tank collar in a substantially permanent and
substantially
fluid-tight manner, in a way which improves on the methods already known in
the
art.
The direct sealing method shown in detail B of Figure 4 means that the chamber
base fits into a groove on the tank collar filled with GRP (or some other)
resin and
the two surfaces bond to become one. If required, the chamber base can be
bonded onto the tank collar in the factory before delivery, dramatically
reducing site
installation time.
It should be noted that the term "access chamber" is analogous to the term
"containment chamber" and both terms can be used interchangeably. The present
invention provides an improved tank collar assembly and an improved sealing
method for sealing the base of an access chamber to a tank collar assembly.
The access chamber assembly can be manufactured from a variety of materials as
selected by the materials specialist. Preferably the base section and the
riser
section are formed from the same material. By way of examples only, suitable
plastics materials may be selected from the group comprising:-
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polyethylene;
polypropylene;
polyvinyl chloride;
polybutylene
5 polyurethanes;
polyamides, including polyamides 6, 6.6, 6.10, 6.12, 11 and 12;
polyethylene terphthalate;
polybutylene terephthalate;
polyphenylene sulphide;
10 polyoxymethylene (acetal);
ethylene/vinyl alcohol copolymers;
polyvinylidene fluoride (PVDF) and copolymers;
polyvinyl fluoride (PVF);
tetrafluoroethylene-ethylene copolymer (ETFE);
tetrafluoroethylene-hexafluroethylene copolymers (FEP)
ethylene tetrafluoroethylene hexafluropropylene terpolymers (EFEP)
terpolymers of tetrafluoroethylene, hexafluoropropylene and vinylidene
fluoride (THV);
polyhexafluoropropylene;
polytetrafluoroethylene (PTFE);
polychlorotrifluoroethylene;
polychlorotrifluoroethylene (PCTFE);
fluorinated polyethylene;
fluorinated polypropylene;
and blends and co-polymers thereof. Furthermore, it is known to use blends of
two
or more polymers and this invention extends to cover known and yet to be
developed blends of plastics material. The plastics used to construct access
chambers are generally electrofusible.
An improved tank collar assembly according to a first embodiment of the
present
invention is illustrated in Figures 5 and 6. Figure 5 shows a tank 70 which
incorporates a manway 68. Encircling the manway is a first portion 69,71 of
the tank
collar assembly. A first component of this first portion comprises an
upstanding
collar 69 which extends substantially entirely around the manway 68 and is
spaced
radially away from it. In this example the tank is made of steel and the
lowermost-
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in-use edge of this first component is welded to the tank to form a
substantially
permanent, substantially fluid tight seal to prevent ingress of water or
egress of fuel
in the event of a leak or spillage.
Instead of carrying a channel around its uppermost in use edge, the first
component
69 is attached to a second component 71. This second component 71 takes the
form of an annular ring or flange extending radially away from the first
component
and secured to the outside of the first component around the inner radius of
the
second component in a substantially fluid tight manner. In this example the
second
component is also made from steel and the first and second components are
welded
together.
Whilst in this example the first and second components are shown as separate
components, welded together to become an integral unit, it is perfectly
possible that
the first and second components could be formed by or during manufacture as an
integral unit.
The outer region of the annular flange 71 is attached to a second portion 73
in a
substantially fluid tight manner by securing means, the second portion being
formed
from a fusible material. In this example the securing means is a swaged joint
74.
Some suitable fusible plastics materials are listed above. Chambers are often
made
from polyethylene and in this example the annular flange 71 is also made of
polyethylene (see below).
Provision is made in the outwardly projecting radially extending annular
flange 71 for
electrofusion heating element(s) 75. These heating element(s) are located on
the
uppermost-in-use face of flange 71 and are used to fuse the top of the annular
flange 71 to the bottom of a correspondingly sized and shaped annular flange
67 on
the base of chamber 65. The heating element(s) may take the form of a wire or
wires embedded in the surface of the flange, with the ends of the wire(s)
being
connected to electric terminals (not shown). This arrangement of heating wires
75 is
shown in more detail in Figure 7, together with the swaged joint between the
first
and second portions.
In an alternative embodiment the electrofusion heating elements may take the
form
of a pre-formed tape or a pre-formed core of heating elements. An indentation
or
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channel can be formed to accommodate such a tape or core and the tape or core
can be secured in such a channel during manufacture, such that the tank collar
arrives at site with the electrofusion tape or core already in position for
the
electrofusion process. For example, the tape/core may be tack welded in place.
Plastic chambers are traditionally formed by rotomolding and are often formed
from
Linear Low Density Polyethylene (LLDPE). As such it is therefore preferable
that
the fusible flange on the tank collar assembly is formed from a Polyethylene
of
similar density. Alternatively, the flange could be formed from Medium Density
Polyethylene (MDPE) or from High Density Polyethylene (HDPE). It has
unexpectedly been discovered that all three grades of Polyethylene form
adequate
electrofusion bonds with chambers made from LLDPE, and vice versa.
If a different plastics material is used for the chamber, such as
Polypropylene, then
a compatible polymer is used in the fusible flange collar. A materials
specialist will
select a suitable compatible plastics material for this use.
In summary, this embodiment of a tank collar assembly comprises an annular
collar,
flange or disc made from a fusible material and attached by a securing means
in a
substantially fluid tight manner to an upstanding collar adapted to be
attached to a
tank around a manway. This arrangement provides, for the first time, the
ability to
electrofuse the base of an access chamber, formed from a fusible plastics
material
such as polyethylene, to a tank collar. There may, or may not, be some
intermediate portion between the upstanding collar and the flange or disc.
A second embodiment is illustrated in Figure 8. In this embodiment the annular
disc
or flange of fusible material 93 is supported by and accommodated
substantially on
the annular metal flange ring 91 extending away from the upstanding collar 89
or
manway. In this embodiment the annular ring 91 is also made of steel and is
spun
swaged at one edge, the edge furthest from the manway, over the fusible disc
93.
To add strength and support to the assembly, support means in the form of
brackets
96 support the steel plate 91 as it extends from the upright member or portion
89.
In an important feature of this invention, and because of the flexibility of
this
invention, it is possible to dispense with the separate upstanding collar
normally
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attached to the top of the tank around the manway. This can be achieved by
welding the radially extending plate or flange 91 directly to the outside of
the
manway. This limits the amount of construction needed on site, thus reducing
cost,
installation time and materials. The radially extending plate or flange 91 can
extend
away from and around the manway cover for a significant distance, sufficient
to give
the desired amount of room within the tank chamber or sump both for the
required
connections and to allow an operator access. The support means 96 can be of a
size, design and extent to give sufficient support to the flange 91 and to the
tank
sump 87 until the area under the sump has been back filled.
A further embodiment is shown in Figures 9 to 12 inclusive. These illustrate a
tank
190 with a manway 158 around which is formed a tank collar 169. The detail of
the
flange and sealing arrangement for sealing an access chamber body 156 to the
flange is shown in Detail A shown in Figure 10. This illustrates a
circumferential
flange 171 as an integral part of a tank collar ring 169. Held captive within
the
flange by a swaged joint is a polyethylene ring 174. this ring includes a
series of
heating elements 175, set into a matrix of polyethylene or some electrofusibly-
compatible plastics material. This is housed in a shallow channel set into the
polyethylene ring. This construction provides a PE tank transition collar with
an
integrated welding coil.
The base 157 of an access chamber body 156 is placed onto the ring and current
passed through the heating elements in a known fashion to electrofuse the
polyethylene ring to the chamber base in a fluid-tight fashion. These
components
are shown in exploded diagram format in Figure 12.
A similar integrated electrofusion heating coil is provided in the bottom of
chamber
riser.
This second integrated electrofusion coil enables the chamber riser to be
electrofusion welded to the chamber base 156.
Whilst the electrofusible ring on the tank collar is shown as being
substantially
horizontal, when the tank collar is in its usual installed configuration, it
will be
appreciated that this is not essential. For example, the flange of the tank
collar
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could be angled inward somewhat, at an angle of between 1 and 200 such that
the
chamber base will self-centre once placed onto the flange.
It will be appreciated that the materials used in each of the components or
portions
will be decided by materials specialist as appropriate, according to the
application
and to material from which the tank is constructed. Where the tank is made say
from GRP, then a first portion, preferably made of metal, is joined in a
substantially
fluid-tight manner to the GRP tank. This could be by way of a swaged
connection
incorporating an internal sealing means, such as a rubber ring or gasket, as
necessary. A second portion made from an electrofusible plastics material is
then
joined to the first portion in a substantially fluid-tight manner, again
possibly by
swaging. Or alternatively the plastics material could be moulded around or
into the
first portion with a fluid-tight seal therebetween.
In summary, an equivalent form of construction to that described elsewhere in
this
document is possible for a GRP tank, as well as for a metal tank.
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KEY TO FIGURES
FIGURE 5
70 Tank
5
FIGURE 7
71 Steel ring
73 PE disc
74 Spun swage
75 Electro fusion coil
FIGURE 8
85 Tank sump
90 Tank
91 Steel plate
93 PE ring
94 Spun swage
95 Electrofusion core
FIGURE 9
190 Deep burial chamber
FIGURE 12
153 PE water tight chamber lid
154 PE chamber riser with electrofusion coil - welds to chamber base
156 PE chamber base - welds to tank transition collar
158 Manway
169 Steel collar welded to tank
190 Storage tank
