Double wall piping system

A double wall pipeline is provided for a pumping system for fluid products, such as gasoline, diesel fuel and chemicals, and including a pump for pumping such products from a storage tank through the pipeline to a product dispenser. The double wall pipeline comprises a double wall, an inner primary pipe, an outer secondary pipe spaced from and surrounding the primary pipe, and integral spokes or spacers for supporting the secondary pipe in spaced relation to the primary pipe so as to create an annular space therebetween. The ends of some of the secondary pipe sections are stripped or cut back so as to terminate short of the corresponding end of the primary pipe and thereby permit testing and inspection of the primary pipe prior to completion of a secondary piping system in which the secondary pipe is incorporated. Unique primary and secondary fittings are provided as well as an air test clamp assembly for testing the integrity of the primary pipe and a collection sump fitting incorprated in the pipeline to permit the location of a leak to be visually determined.

FIELD OF THE INVENTION 
The present invention relates to a double wall piping system particularly 
adapted for use in subterranean applications involving dispensing of 
hazardous liquids such as gasoline, diesel fuel and chemicals. 
BACKGROUND OF THE INVENTION 
Subterranean piping systems such as gasoline and diesel fuel pipelines are 
typically found at service stations are installed and connected to fuel 
dispensing pumps so as to provide dispensing of fuels from a fuel storage 
tank or tanks, usually installed below ground, to fuel dispensers, which 
are located above ground. 
Conventionally, such undergound piping systems comprise single wall pipes 
which are connected together on the site using standard straight pipes and 
associated fittings such as tees, 90.degree. elbows, 45.degree. elbows, 
and unions. 
The underground storage tanks, the associated piping systems, and the fuel 
dispensers have all been determined to be sources of environmental 
pollution, as well as safety hazards because of leakage into the 
surrounding earth. Fire, explosions, and pollution of ground water have 
occurred because of these leakages. 
With respect to the problem of leakage from underground fuel storage tanks, 
one solution has been to use double wall tanks, rather than conventional 
single wall tanks. Double wall steel tanks and double wall fiberglass 
tanks which are used to remedy this problem (together with a secondary 
containment and corrosion protection for the tanks) are disclosed in U.S. 
Pat. Nos. 4,568,925 (Butts) and 4,672,366 (Butts). The secondary 
containment system disclosed in these patents is applied to a conventional 
steel tank and creates a unique double wall tank referred to as a 
"jacketed steel tank". In the event of a leak in the inner primary tank, 
the leak is contained in the outer secondary tank. Most such double wall 
tanks are equipped with a leak detection device for signalling an alarm, 
in the event that a leak should occur. 
While such tanks provide a partial solution, it has been determined that a 
substantial percentage of leakage which occurs at a typical service 
station site is due to leakage from the underground piping system. Various 
attempts have been made to deal with this problem. One approach is to 
install the piping in a trench line with a fuel impervious membrane liner 
or semi-rigid trough. This technique, if carefully installed, can provide 
a measure of containment of leakage from the piping system. However, such 
an approach does not offer truly effective leak detection. In particular, 
this technique does not permit a determination of when the leak occurred, 
or of the pipeline in which the leak is located, or of where in a specific 
pipeline the leak occurred. With such a system, should a leak occur, it 
may be required that all of the backfill contained within the trench or 
liner be removed. Further, integrity testing of such a system, by means of 
air pressure testing, is not possible. Further, in general, such systems 
do not provide 360.degree. containment and thus fill with water, thereby 
eventually becoming ineffective. 
A further solution to the problem of leakage from piping systems involves 
the use of fiberglass primary piping from the pump of the underground 
storage tank to the above ground fuel dispenser, this piping being 
encapsulated with an outer secondary fiberglass pipe and with fittings 
that are installed simultaneously with the primary pipe. The secondary 
pipe is, of necessity, of a larger diameter than the primary pipe so as to 
enable the secondary pipe to slide over the smaller primary pipe. The 
secondary fittings are of a clam shell design adapted to fit over primary 
fittings after the primary pipe has been bonded together, integrity tested 
and inspected. Secondary fittings are bonded to the secondary pipe by a 
combination of nuts and bolts, and through the use of fiberglass resins or 
a fuel resistant sealant. Such a solution does not permit a complete 
inspection of the entire primary piping system during an air pressure 
integrity test. Due to the construction and design of this system, the 
limited components available, and the bonding techniques used, it is 
difficult to install a system of this type which is air pressure testable. 
Further, the components of this system are expensive to make as well as 
expensive to install. 
General considerations, and both present and future regulatory requirements 
for primary piping, dictate that the piping possess a number of basic 
characteristics and meet a number of general design criteria. In this 
regard, the secondary containment system should be of such a design that 
the secondary system contains the primary system from the dispenser to the 
tank including the submersible pump housing and all swing joints. In 
addition, the secondary containment system should allow for complete 
inspection of the primary pipe fittings during an air pressure soap test, 
before the secondary pipe system is completed. Further, the secondary 
containment system should be compatible with the products to be stored. In 
addition, the secondary containment system should be non-corrosive, 
dielectric and non-degradable, and should be resistant to attack from 
microbial growth. Still further, the secondary containment system, the 
materials used therein and the design thereof, should be of sufficient 
strength to withstand the maximum underground burial loads. In addition, 
the secondary containment fitting should be capable of being installed 
over the primary fittings after completion, testing and inspection of the 
primary piping system is complete so as to allow inspection of the primary 
fittings during such testing. Further, the secondary containment system 
should have a monitored fuel collection sump at the low end of the system 
which provides a fitting for insertion of a continuous monitoring sensor 
for signaling an alarm should a leak occur in the primary piping. 
SUMMARY OF THE INVENTION 
Broadly speaking, the present invention concerns a double wall piping 
system which incorporates both the primary and secondary containment 
piping and which exhibits the characteristics set forth above. The primary 
pipe and secondary pipe are spaced by means of spacers or spokes so as to 
create an annular space between the two pipes and the entire double wall 
pipe including the primary and secondary pipes is fabricated of plastic 
and extruded as a single integral unit. The double wall piping system of 
the invention permits inspection of the primary fittings before the 
secondary fittings are put in place and, once installed, the piping system 
of the present invention performs as an air-tight guttering system, 
providing containment of the primary pipe from a location under the 
product dispensers to the pump of the tank, including all swing joints 
and/or flex connectors. Any leak in the primary pipe will flow from the 
high end of the system, i.e., under the fuel dispenser, to a collection 
sump which houses the pump for the tank and the associated fittings at the 
low end of the system. Leak detection can be accomplished at the 
collection sump by visual or electronic monitoring. 
In installing the piping system of the present invention, the secondary 
pipe and associated spoke members are cut back a predetermined distance 
(typically 2 to 21/2 inches) from the end of the primary pipe so as to 
permit testing and inspection of the primary pipe prior to the completion 
of the secondary piping system in which the secondary pipe is 
incorporated. 
In accordance with a further important feature of the invention, the pipe 
fittings for the primary pipe are provided in the form of "tees", 
45.degree. elbows, 90.degree. elbows, straight connectors and the like, 
which include a built-in fusion welding wire for bonding the corresponding 
fitting to the primary pipe. This approach provides excellent sealing 
between the primary pipe and the corresponding fitting, in a very 
expeditious manner. 
According to yet another important feature of the present invention, an air 
test clamp is provided for the double wall piping system which enables air 
pressure testing of the secondary piping system. The air test clamp 
assembly is disposed at a location at which the primary pipe extends 
beyond the secondary pipe and the test clamp assembly preferably comprises 
a fitting member, clamping means for releasably clamping one end of the 
fitting member to the exterior of the primary pipe and for clamping the 
other end of the fitting member externally of the secondary pipe, and 
valve means for permitting connection of the fitting member to a source of 
air under pressure so that such pressurized air can be supplied to the 
secondary piping system. This permits a soap test such as referred to 
above to be carried out in order to detect pin hole leaks in the seals 
between the secondary pipe and the associated fittings therefore. 
Advantageously, the air test clamp assembly is affixed to a wall of a unit 
of the pumping system such as the collection sump in which the pump is 
located. This wall is provided with a hole therein through which a portion 
of the pipeline system extends and the test clamp assembly preferably 
comprises a coupling member including a flange attached (e.g. welded) to 
the wall and a base portion extending through the wall. The clamping means 
referred to above preferably comprises a first clamp for clamping the one 
end of the fitting member to the exterior of the primary pipe and a second 
clamp for clamping the other end of the fitting member to the exterior of 
the base portion of the coupling member. The fitting member is preferably 
fabricated of resilient material such as neoprene rubber and comprises 
first and second spaced end portions of different diameters and an 
intermediate portion in which the valve means is disposed. 
A further important feature of the present invention concerns the provision 
of leakage monitoring means for the double wall pipeline system which 
provides an indication of a leak in the primary line and serves in 
determining where in the line the leak has occurred. The leakage 
monitoring system preferably comprises a sump fitting having first and 
second spaced, aligned end portions through which a portion of the double 
wall pipeline system extends. This pipeline portion includes a hole in the 
secondary pipe and the sump fitting is welded to the pipeline portion so 
as to surround the hole. The sump fitting further comprises a sump portion 
in which leaking fluids can collect. Advantageously, the sump fitting is 
cross shaped and includes an upwardly extending observation portion, in 
alignment with the sump portion and the hole in the secondary pipe, for 
permitting observation of any fluid collected in the sump portion. 
Pumping systems of the type under consideration characteristically include 
at least one flexing connection such as a swing joint or a flex connector 
and, in accordance with a further important aspect of the present 
invention, the pipeline system includes a corrugated flexible pipe in 
which the flexing connection is contained, and clamping means for clamping 
the flexible pipe in place. 
Another important feature of the invention concerns the provision of 
secondary fittings for connecting adjacent portions of the secondary pipe 
of the pipe line system. These fittings can comprises tees, 45.degree. 
elbows, 90.degree. elbows, straight connectors and the like and basically 
comprises a split fitting member having a split therein in the top surface 
thereof. Advantageously, the split takes the form of a V-shaped groove and 
the opposed ends of the fitting which define the groove are joined 
together by fusion rod welding wherein triangular fusion welding rods 
received in the V-shaped groove. 
Pumping systems of the type under consideration typically include a metal 
(steel) primary line and in accordance with a further important feature of 
the invention, a connector member is provided for connecting the primary 
pipe to the steel primary line. The connector member preferably comprises 
a metal member having a connection end, advantageously in the form of a 
hex-headed nut, adapted to be connected to the steel primary line and a 
base portion which is serrated or barbed in cross section, and an 
injection molded, high density plastic end section which encapsulates the 
barbed base portion of the metal member. 
As will become apparent, the piping system of the present invention 
provides many benefits and advantages as compared with prior art systems 
More specifically, one major advantage is that the cost of the system is 
competitive with respect to both component costs and installation costs, 
while the system of the invention is much faster and easier to install 
than other primary or secondary containment systems of the type under 
consideration. In addition, as noted above, the system is able to be air 
pressure tested to insure containment integrity of both the primary and 
secondary pipes. Further, the system permits identification of which 
primary pipe is leaking and the approximate location of the leak. Still 
further, the system can be flushed out after a leak has occurred and 
repairs have been completed. Still further, the double wall piping system 
of the invention does not interfere with the assembly, testing and 
inspection of the primary pipe fittings Further, the fusion welding 
process used in bonding the components of the system together is highly 
advantageous, as was mentioned above and is discussed further below. 
Further, the system incorporates, or can incorporate, a large number of 
different components which can accommodate almost any pattern or layout of 
piping desired. Further, the system can be installed on both new 
installations as well as retrofit installations. 
Other features and advantages of the present invention will be set forth 
in, or apparent from, the detailed description of preferred embodiments of 
the invention which follows.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Before examining the overall pumping system of the invention, important 
individual components making up the system will be considered so that the 
function of these components in the overall system can be better 
understood. Thus, referring to FIGS. 1 and 2, a key component of the 
piping system of the present invention is, as discussed above, the double 
wall piping utilized therein, a section of this piping being indicated at 
10. The double wall piping 10 includes an inner primary pipe 12, an outer 
secondary pipe 14 and a plurality of intermediate spacer members or spokes 
16, (best seen at FIG. 1) which support pipes 12 and 14 in spaced 
relationship so as to create an annular space therebetween. The double 
wall pipe 10 is preferably plastic extruded out of high density 
polyethylene, with the primary pipe 12, secondary pipe 14 and spokes 16 
all being extruded in the same operation at the same time so as to create 
a one piece double wall pipe. The inner primary pipe 12 is, in a preferred 
embodiment, thicker than spokes 16. As will be discussed in more detail 
below, in order to make connection to corresponding primary fittings 
(which are described below in connection with FIGS. 3 to 7), the secondary 
pipe 14 and associated spokes 16 are stripped or cut back approximately 
two inches to permit assembly, sealing, inspection and observation of the 
primary fitting. 
Typical primary fittings are shown in FIGS. 3 to 6. In particular, FIG. 3 
shows primary 45.degree. elbow denoted 18, FIG. 4 shows a primary 
90.degree. elbow denoted 20, FIG. 5 shows a primary "tee" denoted 22 and 
FIG. 6 shows a primary straight connector denoted 24. Each of the primary 
fittings of FIG. 3 to 6 is prefereably injection molded of high density 
polyethylene. A key feature of these fittings is that a fusion wire, 
denoted 26 in each figure, is molded during the injection molding process 
into the corresponding fitting itself. More specifically, a fusion were 26 
is molded into the fitting at each opening thereof (so that three such 
fusion wires, one of which is not shown, are used in tee 22), and, at each 
of these openings, two lead wires 26a, 26b, connected to a corresponding 
fusion wire 26, extend or protrude outside that opening. The distance that 
these lead wires protrude is approximately four inches in an exemplary 
embodiment. Each fitting includes an internal built-in stop (not shown) so 
that the pipe can be precisely positioned inside the fitting. The inside 
diameter of each fitting, including the fusion wire 26, is designed to be 
slightly larger than the outside diameter of the primary pipe 12 so that 
the primary pipe 12 can slide smoothly into the fitting. Once an end of 
the primary pipe 12 has been slid into place within the fitting, the 
outside of the fitting is clamped with a steel clamp (not shown) so as to 
provide the necessary pressure to achieve fusion bonding of the primary 
pipe 12 to the corresponding primary fitting. This bonding process is 
described in more detail below. 
A further primary fitting 28 is shown in FIG. 7 which is used in connecting 
or joining the polyethylene primary pipe 12 to a length of steel primary 
pipe (not shown in FIG. 7) such as the swing joint described below in 
connection with FIGS. 16 and 17. Connector fitting 28 is designed to 
connect to a nipple extending from a steel swing joint, or to directly 
connect to the end of a flexible steel connector, in order to provide a 
transition in the piping system from high density polyethylene to steel. 
Connector 28 includes (i) a steel connector portion 30 comprising a 
hex-headed end portion 32 which connects to the steel pipe referred to 
above and a base portion 34 of reduced diameter have a serrated or barbed 
outer surface 36, as illustrated, and (ii) a plastic (polyethylene) 
portion 38 incorporating a fusion wire 40 and associated leads 40a, 40b, 
as described above. Connector 28 is injection molded so the polyethylene 
which forms portion 38 encapsulates the barbed base portion 34 of steel 
connector portion 30. After the injection molding process, at least one 
steel clamp (not shown) is clamped in place over the outside of the 
polythylene in the region of barbed base section 34 to ensure that the 
connection is air tight. The hex nut end portion 32 of connector 28 is 
used to tighten the connection to a corresponding steel pipe. 
Referring to FIGS. 8 to 11, a series of secondary fittings are shown which 
are used with the secondary pipe 14 of the double wall piping system 10. 
In particular, FIG. 8 shows a 45.degree. elbow 42, FIG. 9 a 90.degree. 
elbow 44, FIG. 10 a "tee" 46 and FIG. 11 a straight connector 48. The 
fittings of FIGS. 8 to 11 are each split at the top so as to allow them to 
be spread apart to fit over a corresponding, previously installed primary 
fitting and in particular, are provided with a V-shaped groove 50 which 
forms the split. These fittings are preferably made of high density 
polyethylene so that they are strong but flexible enough to accomodate the 
spreading apart required in installation. 
The fittings of FIGS. 8 to 11 are preferably manufactured using plastic 
injection molding techniques. The split fitting design permits easy 
installation, testing and inspection of the corresponding primary fittings 
before the secondary containment system is installed. 
The split fittings of FIGS. 8 to 11 are bonded and sealed to the adjacent 
portions of the outer secondary containment pipe 14 of the double wall 
piping 10 by fusion wire welding, between an overlap joint. After the 
split fittings have been fusion wire welded to the secondary pipe 14, the 
V-groove split 50 in the top of the fitting is fusion rod welded to 
complete the seal of the fitting. In general, this is accomplished by 
laying a bead of triangular shaped welding rod down the groove 50, 
starting just over the edge. The welding rod is applied through the 
welding tip of a hot air gun to provide welding of the groove 50. The 
welding process is described in somewhat more detail below. 
Referring to FIG. 12, a secondary sump fitting 52 is shown which is, in 
use, disposed directly under an observation well in order to determine the 
approximate leak location should a leak occur in the primary system. 
Fitting 52 is not split and thus must be installed into the double wall 
piping system during assembly of the primary pipe system. Fitting 52 is 
generally cross shaped and includes aligned, open ended arms 54 and 56, a 
closed arm portion 58 which is directed downwardly and forms a sump, and 
an oppositely directed open arm portion 60 which, in use, points upwardly 
towards a corresponding monitoring access hole which, together with 
fitting 52 and an associated riser (not shown in FIG. 12) complete the 
observation well. Preferably, fitting 52 is plastic injection molded of 
high density polyethylene. 
The installation procedure for sump fitting 52 includes first installing 
the fitting over the secondary pipe 14 of the double wall pipe 10. At this 
time, the fitting 52 can be shifted back and forth along the pipe 14. At a 
predetermined location along the pipe 14 a hole (not shown) is cut 
therein, which, in the exemplary embodiment under consideration, is 
approximately 3 inches in diameter. The sump fitting 52 is then moved to a 
position over this hole and sealed permanently in place using fusion wire 
welding as described above. As stated, sump portion 58 points downwardly 
and the open end 60 points upwardly towards a future monitoring access 
hole (as described in more detail in connection with FIGS. 16 and 17). As 
is shown in FIG. 13, which is an end view of three fittings 52, in a 
situation where there are three closely spaced pipes 10, the open end 60 
of fitting 52 is then fitted with a riser pipe 62 that is sealed at the 
top with a cap 64, preferably fabricated of neoprene, so as to form an 
observation well. As illustrated in FIG. 13, when more than one 
observation well is located in a single area, it is advantageous to tip 
the outside wells toward the center so that the riser pipes 62 converge at 
the top, and thus fit within a small radius, so as to be accommodated 
underneath an observation manhole. 
When such an observation manhole is used, should a leak occur in the 
primary piping system 12 and thus be identified by fluid collecting in the 
sump portion 58 of fitting 52, a visual inspection of the observation well 
for that particular pipe will determine whether or not the leak is above 
or below that particular well. In other words, if the sump portion 58 of 
the observation well is free of product (fluid), the leak is downline from 
that well, whereas if the observation well sump 58 has product therein, 
the leak is above, i.e., upline or upstream, of that well. Thus, plural 
wells can be installed in order to more definitively isolate the location 
of a leak. 
Referring to FIG. 14, a flexible corrugated pipe section 66 is shown which 
is used for containment of multi-directional swing joints and/or flex 
connectors. The left end, which is the upper end in use, of flexible pipe 
section 66 includes a neoprene rubber reducer fitting 68, and associated, 
different diameter steel clamps 70 and 72, for closing off the secondary 
containment pipe underneath the product (fuel) dispenser (not shown in 
FIG. 14). The lower end 74 of pipe section 66 is adapted to be attached to 
the outer secondary pipe 14 by means of fusion welding, as described 
above. 
It should be noted that swing joints or flex connectors may not be required 
with the system of the present invention, although code requirements may 
dictate their use in any event. The purpose of such flex connectors and 
swing joints is to absorb the shock exerted on other pipe systems, and the 
double wall pipe system of the invention is, as described above, made of 
flexible (semi-rigid), high density polyethylene and a system 
incorporating such piping need not include such shock absorbing fittings. 
Referring to FIG. 15, a test clamp assembly 76 is shown which enables 
testing of the integrity of the secondary pipe system. The test clamp 
assembly 76 include a high density polyethylene, rotationally molded 
bulkhead coupling member 78, a neoprene rubber reducer fitting 80 
including an air-valve stem 82 incorporated therein, and a pair of 
stainless steel clamps 84 and 86. Clamp assembly 76 is used to seal off a 
collection sump wall at a location where a contained primary pipe 12 
exists, as described below in connection with FIGS. 16 and 17. Once 
installed, the clamp assembly 76 permits the secondary pipe 14 connected 
thereto to be filled with air through valve stem 80 so as to permit 
performance of an air-pressure soap test to check the containment 
integrity of the secondary piping system. Installation of the testing 
clamp assembly 76 is described below in connection with FIGS. 16 and 17. 
Turning to FIGS. 16 and 17, which show two stages in the installation of 
the overall system, as is evident from the foregoing, the present 
invention, in one important aspect thereof, can be generally described as 
a double wall piping system including an inner primary pipe 12 (FIGS. 1 
and 2) for supplying product from a tank, a portion of which is indicated 
at 90 in FIGS. 16 and 17, to a dispenser, indicated at 92 in FIG. 17, and 
an outer secondary pipe 14 (FIGS. 1 and 2) which performs as an air tight 
guttering system, thereby providing containment of the primary pipe from 
under the dispenser 92 to the tank pump, indicated at 94 in FIGS. 16 and 
17. Any leak in the system will flow from the high end of the system, 
under the product dispenser 92, to a collection sump 96, which contains 
tank pump 94, at the low end of the system. Detection of any such leakage 
can be accomplished at the sump end, using conventional alarm and 
signalling devices (not shown). It will be appreciated that the overall 
system typically includes more than one collection sumps (and may include 
more than one tank) but the description here will be limited to a single 
sump 96 and a single tank 90. 
Referring to FIG. 16, which shows the primary pipe assembly stage of the 
double piping system, installation begins with mounting the collection 
sump 96 on the tank 90. Collection sump 96 serves to collect leaking 
product and to permit access for repairs or servicing of the associated 
tnak 90. As illustrated, sump 96 includes a lid 96a, an upper riser 96b 
and a sump housing 96c, although it will be appreciated that sumps of 
different designs and constructions can be used. Further, mounting of the 
collection sump 96 on tank 90 can be accomplished in a number of ways. For 
example, the collection sump 96 can be mounted directly onto a 
pre-installed saddle 90a, which is available on tanks fitted with a 
secondary containment system constructed in accordance with U.S. Pat. No. 
4,672,366 (Butts) referred to above. Saddles such as indicated at 90a are 
specifically designed to accommodate the collection sump housing or body 
96c, with a bottom rim of the collection sump body 96c fitting into a 
preformed retaining ring of the saddle 90a. 
After mounting the collection sump housing or body 96c on the tank 90, the 
pump 94 and an associated swing joint 98 and other miscellaneous 
components are mounted inside housing 96c. The swing joint piping 98 is 
connected to double wall pipe 10 by means of a connector fitting 28 
corresponding to that described above and shown in FIG. 7. A test clamp 
assembly 76, corresponding to that described above and shown in FIG. 15, 
is installed over the connector fitting 28 inside the collecton sump 90. 
To do this, a pipe exit hole is cut in the wall of sump housing or body 
96c and the bulkhead coupling 78 is installed into the hole to accommodate 
a first section of double wall pipe denoted 10a. The pipe section 10a is 
then cut to length and at each end, the secondary pipe 14 and spokes 16 
(FIGS. 1 and 2) are cut back two inches as illustrated in FIG. 2 to expose 
the primary pipe 12. The double wall pipe section 10a is then inserted 
through the bulkhead coupling 78 into housing 96c and attached to 
connector fitting 28. 
A second length of double wall pipe, denoted 10b, is cut to length and 
"stepped back" on each end as described above, and thereafter is attached 
to first pipe section 10a using a primary straight connector 24 
corresponding to that described above in connection with FIG. 6. 
In the illustrated embodiment, an observation well is employed which 
corresponds to that described above in connection with FIGS. 12 and 13, 
and, accordingly, a sump fitting 52 (also shown in FIG. 12) is slipped 
over the double wall pipe section 10b for attachment at a later stage. 
At the first piping junction, the primary pipe 12 of the double wall pipe 
10b is inserted into a primary fitting. In the illustrated example, this 
primary fitting is a "tee" fitting 22 (see also FIG. 5) but it will be 
understood that depending on the piping path, this could also be a 
45.degree. elbow fitting 18 (FIG. 3) or a 90.degree. elbow fitting 20 
(FIG. 4). In fact, in the embodiment shown in FIG. 16, a 90.degree. elbow 
fitting 20 is used to connect a short length of piping 10c to a further 
length of piping 10d. The primary pipe 12 of the latter terminates in a 
further plastic pipe-to-metal pipe connector fitting 28' (see also FIG. 
7), corresponding to that at the pump end of the system. Fitting 28' is 
preinstalled at the end of a swing joint 102 (or flex connector) adapted 
to be connected to dispenser 92 (FIG. 17). 
After the entire primary piping system, including pipe 12 and the primary 
fittings described above, have been sealed by means of fusion wire welding 
as described previously, the primary line 12 is tested for air pressure 
integrity. This is preferably accomplished by capping off the riser pipe 
102a located underneath the dispenser 92 (as well as any other such riser 
pipes located downstream). 
Referring to FIG. 17, the double wall piping system of the invention is 
shown in this figure during the secondary pipe assembly stage. After all 
of the primary pipe has been sealed, tested and inspected, assembly and 
testing of the secondary containment system follows. Inside of the 
collection sump 96, the reducer test clamp assembly 76 is shifted onto and 
around the protruding bulkhead coupling 78, the large and small diameter 
clamps 84 and 86 are tightened to the pipe 10. On the outside of the wall 
of sumping housing 96c, the flange of the bulkhead coupling 78 is fusion 
rod welded to this wall. At the first junction, where a primary straight 
connector 24 (see FIG. 16) is installed, a secondary straight connector 48 
(see also FIG. 11) is installed to seal together the straight runs of the 
secondary pipes 14 of the double wall pipe sections 10a and 10b. 
The secondary sump fitting 52 is then installed as described above in 
connection with FIGS. 12 and 13. In brief review, with a sump fitting 52 
shifted aside, a hole (approximately 3 inches in diameter) is drilled into 
the secondary pipe 14 of double wall pipe section 10b. Thereafter, the 
fitting 52 is moved to a position over the hole with the sump portion 58 
pointing downwardly and the sump fitting 52 is then sealed to in place. A 
riser pipe 62 (see also FIG. 13) is installed into top portion 60 and the 
top of the observation well thus formed is sealed with a cap 64 to permit 
future access. 
Further down the line from pump 94, all pipe junctions are fitted with the 
proper secondary fittings. In the illustrated embodiment, these fittings 
comprise a tee fitting 46 (see also FIG. 10) and a 90.degree. elbow 44 
(see also FIG. 9). A corrugated flexible pipe 66 (see also FIG. 14) is 
installed at the end of the line down over the riser pipe 102a and around 
the swing pipe 102 and is attached to the secondary pipe 14 of pipe 
section 10d. At the upper end of the flexible corrugated pipe 66 a 
terminating clamp 70 (see also FIG. 14) is attached which is affixed to 
the riser pipe 102a just under the location of a shear valve (not shown) 
which is installed later. 
Once all of the pipes and fittings are in position, the secondary pipe 14 
is sealed to the secondary fittings described above by means of fusion 
wire welding, as described previously. After the entire secondary piping 
system has been sealed, an air pressure test of the type described 
previously in connection with FIG. 15 may be performed on the secondary 
system by inflating the air test clamp assembly 76 inside of the sump 
housing 96c to an air pressure level no higher than 5 psi. A conventional 
outside soap test can be used to determine if there are any pinhole leaks 
at any of the secondary joints. Once the secondary containment pipe has 
been tested and inspected, the reducer section 84 of air test clamp 
assembly 76 should be loosened and slid back away from the bulkhead 
coupling 78. 
As discussed above, fusion wire welding is used to make various connections 
in the system. Considering this process in more detail, the process uses a 
wire ribbon (denoted 26 in FIG. 3 to 6) which, in an exemplary embodiment 
is 1/2 inch in width and 50 mils in thickness and is made up of 28 guage 
resistive wire with a resistance of 0.75 ohms per linear foot. Four 
parallel strands of such ribbon or wire are coated with or otherwise 
incorporated in the polyethylene of the double wall pipe 10 and the 
primary and secondary fittings described above. The length of the wire 
ribbon is approximately thirty-six inches with the wire ends connected so 
as to create a single wire circuit with two four-inch connector wires 
located on the same end. 
The profile of the wire ribbon is designed with a female and male interlock 
snap (not shown) on opposite sides. This allows the wire ribbon to form a 
set coil when wrapped around the telescoping pipe. As the wire ribbon is 
being wrapped, the male (barbed) edge snaps itself as it meets the female 
edge. This design allows a tight and stable coil to be formed around the 
pipe 10 which can then be shifted down the pipe into and between the 
overlapped joint of the double-wall pipe and the secondary fittings. 
Once the wire ribbon is inserted into the overlapped joint, a steel clamp 
(not shown) is installed around the secondary fitting directly over the 
coiled wire ribbon inside the overlapped joint. Pressure is then applied 
to the overlapped joint by tightening the aforementioned steel clamp. The 
two conductor lead wires (denoted 26a, 26b in FIGS. 3 to 6) are then 
attached to a terminal block clamp (not shown) which snaps onto the pipe 
to prevent the wire leads from movement during the fusion welding process. 
The terminal block clamp is connected to a fusion power unit (not shown) 
by a long (six foot) cord. By pressing a start button (not shown) on the 
fusion power unit, current from a 24 volt supply is delivered to the 
fusion welding ribbon. The resistance thereof causes the wires to get hot 
and create sufficient heat to produce a fusion bond between both the 
double-wall pipe and the corresponding secondary fitting. The fusion power 
unit is designed so that the unit will deliver current for a set amount of 
time and then automatically cut off. 
This same fusion welding procedure can be duplicated at all overlapped 
joints where the double-wall pipe meets a secondary tee 46 (FIG. 10), a 
secondary 90.degree. elbow 44 (FIG. 9), a secondary 45.degree. elbow 42 
(FIG. 8), a secondary corrugated flexible pipe 66 (FIG. 14), a bulkhead 
coupling 78 (FIG. 15), a close-off coupling (not shown) or a cross shaped 
monitor fitting 52 of an observation well assembly (FIGS. 12 and 13). 
The fusion rod welding process described above involves the use of a hot 
air gun (not shown) which specially equipped with a nozzle tip having a 
shaft designed to accomodate a V-profiled plastic rod. This plastic rod is 
inserted into the shaft where the rod is heated and applied to the surface 
of a joint to be welded. The hot air gun pre-heats the joint as the 
semi-melted rod is being laid so as to produce a strong homogeneous weld. 
This fusion rod welding process is performed on the top groove 50 of all 
split fittings, around the flange of all bulkhead fittings (e.g. fitting 
78) and close-off couplings (not shown) and around the flanges of all 
riser mount collars. 
Both fusion wire welding and fusion rod welding are disclosed in somewhat 
more detail in my concurrently filed, copending Application Serial No. 
07/103,206, now U.S. Pat. No. 4,805,444, entitled "Secondary Containment 
System", the subject matter of which is hereby incorporated by reference. 
Further, it will be understood that other plastic welding techniques can 
be used including the use of "self welding" plastics which can be welded 
by the application of heat thereto. 
Although the invention has been described relative to preferred embodiments 
thereof, it will be understood by those skilled in this art that 
variations and modifications in these exemplary embodiments can be 
effected without departing from the scope and spirit of the invention.