Pipe tee

A pipe tee comprises a substrate having deposited thereon a reinforcing wrapping of a resin-impregnated filament.

BACKGROUND OF THE INVENTION 
In one aspect, the invention relates to a pipe tee. In another aspect, the 
invention relates to improvements to a pipe tee. In yet another aspect, 
the invention relates to a process for forming a plastic pipe tee. 
Plastic pipe has come into extensive use in recent years for handling 
corrosive materials, petrochemicals, and the like where metallic pipe is 
unsuitable; and other applications where metallic pipe is unduly 
expensive. The plastic pipe itself, which can be formed from a suitable 
thermoplastic material such as polyethylene, is usually extruded from high 
throughput machines. 
Plastic pipe fittings for such pipes up to a pipe diameter of about 8 
inches are usually injected molded. Such fittings are small and have good 
stress ratings and can be made economically on commercially available 
equipment. The larger pipe fittings, such as for pipes having a diameter 
from about 10 inches up to about 48 inches, are too expensive to made by 
injection molding since they require massive equipment and extremely high 
mold costs. Rotationally molded fittings can be made at considerably lower 
cost do to the less expensive equipment requirements. However, when pipe 
fittings are rotationally molded, it is extremely difficult to control the 
wall thickness of the fitting so as to provide sufficient strength at the 
areas of greatest stress. It is particularly difficult to rotationally 
mold large diameter pipe fittings to have long term hoop stress resistance 
equal to the long term hoop stress resistance of the plastic pipe to which 
it is to be attached. Additionally the heavy walls require extremely long 
cycle times and do not develop good gel on the inside surfaces. Further 
the heavy wall is difficult to mold without bubbles, which can lead to 
premature failure. 
It will be extremely desirable to solve these molding problems and provide 
long term hoop stress resistance in the fitting equal to the long term 
hoop stress resistance in the piping system; to mold thinner wall pipe 
fittings; and to reinforce pipe fittings by economical methods. 
OBJECTS OF THE INVENTION 
It is thus an object of this invention to provide a pipe fitting which is 
reinforced so as to require only small amounts of material in the walls, 
and to be suitable for fabrication by rotational molding. 
It is another object of this invention to provide a reinforced pipe fitting 
which utilizes only small amounts of the reinforcing material. 
It is a further object of this invention to provide a method for 
reinforcing of pipe fitting which is readily adapted for automation and 
provides economical results. 
SUMMARY OF THE INVENTION 
In one aspect of the present invention, there is provided a suitable 
suitable substrate defining a branched pipe fitting which was deposited 
thereon a reinforcing wrapping of resin impregnated filament rovings. The 
wrapping of resin impregnated filament rovings provides reinforcement to 
the pipe fitting and allows for the use of a thinner walled substrate. 
Additionally, the filament rovings can be deposited on selected pipe 
fittings when their end use is to be for relatively high pressure service. 
In another aspect of the present invention, a plastic pipe tee is provided 
having a straight run with the straight run having a back side, a front 
side opposite from the back side, a first hand side between the back side 
and the front side, and a second hand side opposite to the first hand 
side, the first hand side bearing a branch which divides the straight run 
into a first end portion and a second end portion with the intersection 
between the branch and the straight run passing through a first apex point 
on the first hand side and a second apex point on the second hand side, 
each of the first apex point and the second apex point being a point at 
which a line following the exterior surface of the straight run is tangent 
to the intersection of the branch and the straight run, the back side of 
the run have a center point on its surface which is coaxial to the axis of 
the branch. Onto the run of this pipe tee, there is deposited one or more 
circuits of a wrapping characterized by a combination of six helical 
wraps. The first wrap extends from the front side of the first end portion 
across the first hand side, the center point of the back side, the second 
hand side and to the front side of the second end portion. The second wrap 
extends from the front side of the second end portion, across the first 
hand side, the center point of the back side, the second hand side and to 
the front side of the first end portion. The third wrap extends from the 
front side of the first end portion across the first apex point on the 
first hand side and to the back side of the second hand portion. The 
fourth wrap extends from the back side of the second end portion, across 
the second apex point on the second hand side, and to the front side of 
the first end portion. The fifth wrap extends from the back side of the 
first end portion, across the second apex point of the second hand side, 
and to the front side of the second end portion. The sixth wrap extends 
from the front side of the second end portion, across the apex point of 
the first hand side, and to the back side of the first end portion. Where 
the wrapping has a relatively narrow width relative to the width of the 
branch, reinforcement will require minimal amounts of material while 
adequate reinforcement will be provided to the areas of the pipe most 
prone to pressure induced failure. This reinforced pipe tee can be 
produced by continuously winding one or more circuits of the wrapping 
following a path beginning on the front side of the first end portion and 
extending from the front side of the first end portion angularly across 
the first hand side, the center point of the back side, the second hand 
side, angularly crossing to the front side of the second end portion and 
circumferentially around the second end portion at least once, then 
continuing along a second wrap extending from the front side of the second 
end portion, angularly across the first hand side, the center point of the 
back side, the second hand side and angularly crossing to the front side 
of the first end portion and circumferentially around the first end 
portion at least once; then continuing along a third wrap extending from 
the front side of the first end portion angularly across the apex point of 
the first hand side to the back side of the second end portion and around 
the second end portion at least once; then continuing along a fourth wrap 
extending from the back side of the second end portion angularly across 
the apex point of the second hand side, to the front side of the first end 
portion and circumferentially around the first end portion at least once; 
then continuing along a fifth wrap extending from the back side of the 
first end portion, across the apex point of the second hand side, to the 
front side of the second end portion and circumferentially around the 
second end portion at least once; then continuing along a sixth wrap 
extending from the front side of the second end portion angularly across 
the apex point of the first hand side to the back side of the first end 
portion. The method is readily automated since the wrapping can be formed 
from continuous filament rovings and thus can be utilized to provide 
extremely economical results.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIGS. 12 and 13, the preferred embdiment of the invention is 
broadly a branched pipe fitting 2, the wall of which is formed from a 
suitable substrate encased in one or more layers of resin impreganted 
fabric, hereinafter described and having deposited thereon a reinforcing 
wrapping 4 of a resin impregnated filament roving 6. The fitting 2 can be 
formed from any suitable substrate. Preferably, the branched pipe fitting 
2 is formed from a thermoplastic material, such as crosslinkable 
polyethylene. More preferably, the branched pipe fitting 2 is in the form 
of a pipe tee where the branch intersects the run at an angle of about 
90.degree. because pipe tees have been tested with good results. Other 
branched pipe fittings, such as Y-shaped fittings, can also be 
strengthened according to the invention. Generally the pipe tee will be 
formed by a rotational molding process because rotational molding is the 
most economical way to form pipe tees having a large diameter such as in 
the range from about 10 inches to about 48 inches. 
The reinforcing wrapping of filament preferably contains fiberglass 
rovings. A suitable filament roving is PPG Glass Roving No. 1062T250. This 
glass roving has a weight of about 247 yards per pound and contains four 
rovings. The resin with which the filament is impregnated is generally 
selected from resins which use a curing agent, such as epoxy resins, 
polyester resins, or polyurethane resins. Epoxy resin is preferred, such 
as Shell Epon 828, which has been used with good results. This resin can 
be cured with Apco 2170 amine-type hardner and optionally oven cured at an 
elevated temperature such as about 300.degree. F. for a few hours to 
complete curing. 
FIGS. 1 and 2 illustrate a branched pipe fitting in the form of a pipe tee 
2 which is preferably formed from a plastic substrate. The pipe tee 2 has 
a straight run 8, and a branch 18 which intersects the run at an angle of 
about 90.degree. and divides the straight run into a first end portion 20 
and a second end portion 22. Each end portion has a back side 10, a front 
side 12 opposite from the back side 10, a first hand side 14 between the 
back side 10 and the front side 12 and a second hand side 16 opposite to 
the first hand side 14. 
As between FIGS. 1 and 2, the pipe tee has been rotated about the axis of 
branch 18 by an angle of about 90.degree. in the counterclockwise 
direction. In FIG. 1, second hand side 16 of straight run 8 is 
illustrated, while in FIG. 2, first hand side 14 of straight run 8 is 
illustrated. This relationship is repeated as between FIGS. 3 and 4, FIGS. 
5 and 6, FIGS. 7 and 8, and FIGS. 14 and 15. 
The branch 18 and the run 8 intersect at a saddle shaped intersection 24. 
The intersection 24 passes through a first apex point 26 on the first hand 
side 14 of the straight run 8 and a second apex point 28 on the second 
hand side 16 of the straight run 8. The apex point on each of the first 
side 14 and the second side 16 is the point at which a line following the 
surface of the straight run 8 is tangent to the intersection 24 of the 
branch 18 and the straight run 8. The back side 10 of the straight run 8 
has a center point 30 which is opposite to the branch 18. This is most 
clearly shown in FIG. 13. 
In accordance with one embodiment of the invention, the plastic pipe tee 2 
has deposited on it one or more circuits of a wrapping 4 comprising a 
combination of six helical wraps extending between the first end portion 
20 and the second end portion 22. 
As shown best in FIGS. 3 and 4, the first wrap 32 extends from the front 
side 12 of the first end portion 20 across the first hand side 14, the 
center point 30 of the back side 10, the second hand side 16 and to the 
front side 20 of the second end portion 22. If desired, the wrapping 4 can 
then extend around the second end portion 22 at least once 
circumferentially. 
As shown best in FIG. 5, a second wrap 33 extends from the front side 12 of 
the second end portion 22, across the first hand side 14, the center point 
30 of the back side 10, the second hand side 16 and to the front side 12 
of the first end portion 20. If desired, the wrapping can then extend 
circumferentially around the first end portion 20 at least once. 
In FIGS. 6 and 7, a third wrap 34 extends from the front side 12 of the 
first end portion 20, across the first apex point 26 on the first hand 
side 14, and to the back side 10 of the second end portion 22 as best 
shown in FIG. 7. If desired, the wrapping can then extend at least once 
circumferentially around the second end portion 22 as illustrated in FIG. 
8 for example. 
Referring to FIG. 9, a fourth wrap 36 extends from the back side 10 of the 
second end portion 22, across the second apex point 28 on the second hand 
side 16, and to the front side 12 of the first end portion 20. The 
wrapping can then, if desired, extend at least once circumferentially 
around the first end portion 20 and preferably extends around the first 
end portion 20 one and one-half times. 
Referring to FIG. 10, a fifth wrap 38 extends from the back side 10 of the 
first end portion 20, across the second apex point 28 of the second hand 
side 16, and to the front side 12 of the second end portion 22. The 
wrapping can then extend at least once circumferentially around the second 
end portion 22. 
Referring to FIG. 11, a sixth wrap 40 extends from the front side 12 of the 
second end portion 22, across the first apex point 26 of the first hand 
side 14 and to the back side 10 of the first end portion 20. The wrapping 
can then extend partially or fully around the first end portion 20. 
Referring to FIGS. 12 and 15, a circular wrap 50 comprising six circuits 
extends around the branch 18 of the tee. Preferably the wrap 50 is 
comprised of the same material as wrap 4. End portions 20 and 22 can be 
provided with a similar circular wrap if desired. 
Preferably, as best shown by FIG. 14, for example, the plastic pipe tee 2 
further comprises one or more layers 42 of resin-impregnated fabric 42 
encasing the portion of the branch 18 adjacent the run 8 and the portions 
of the first end portion 20 of the run 8 and the second end portion 22 of 
the run 8 which are adjacent to the branch 18. Any desired number of 
layers of fabric 42 can be utilized. The resin-impregnated fabric will 
generally comprise about 30-50 wt.% fabric and about 50-70 wt.% resin. 
Preferably, where the pipe has a diameter in the range of from about 10 to 
about 48 inches, from about 1 to about 10 layers of fabric such as woven 
glass cloth will be used, usually from about 2 to about 6 layers of resin 
impregnated fiberglass fabric. A suitable fiberglass cloth is J. P. 
Stevens No. 7520, 8.70 oz./yds..sup.2, which is a 0.012 inches thick plain 
weave, 180 mesh plain weave glass cloth. Preferably the glass cloth is 
wrapped on the tee 2 so that the warp and weft yarns of the glass fabric 
will be substantially followed by the rovings in the third wrap, the 
fourth wrap, the fifth wrap, and the sixth wrap. For an 8 inch inside 
diameter flanged pipe tee formed of crosslinkable polyethylene having a 
diameter to wall thickness ratio of 15.5:1 and designed for 210 psig 
service, three layers of resin impregnated fiberglass cloth were used with 
good results. For an 8 inch flanged pipe tee formed from crosslinkable 
polyethylene with a diameter to side ratio of 11:1 designed for 320 psig 
service, five layers of the resin impregnated fiberglass cloth were with 
good results. The resin impregnated fiberglass cloth so used contained 
about 40% by weight glass and about 60% by weight polyester resin. The 
polyester resin tested with good results was formed from Shell Epon 828 
about 76% by weight, TETA (triethylene tetraamine) approximately 7% by 
weight, and Apco 2170, which is a cyanoethyl modified aliphatic amine, 
about 17% by weight. Apco 2170 is commercially available from Applied 
Plastics Company of El Segundo, Calif. 
Preferably, the wrapping comprises from about 1 to about 25 circuits of 
resin impregnated filament rovings. Each circuit is preferably formed from 
filament rovings because filament rovings are readily adapted for machine 
lay up. The wrapping preferably follows a path beginning on the front side 
4 of the first end portion 20 and extending around the first end portion 
20 at least once circumferentially then along the first wrap 
aforementioned from the front side 10 of the first end portion 20 
angularly across the first hand side 14 and the center point 30 of the 
back side 10 to the front side 12 of the second end portion 22. The 
wrapping then preferably extends circumferentially around the second end 
portion 22 at least once. From the front side 12 of the second end portion 
22, the wrapping then continues along the second wrap angularly across the 
first hand side 14 and center point 30 of the back side 10 to the front 
side 12 of the first end portion 20. The wrapping then extends preferably 
circumferentially around the first end portion 20 at least once. The path 
then continues along the third wrap from the front side 12 of the first 
end portion 20 angularly across the first apex point 26 of the first hand 
side 14 and to the back side 10 of the second end portion 22. Preferably, 
the wrapping then extends circumferentially at least once around the 
second end portion 22 then continues along the fourth wrap from the back 
side 10 of the second end portion 22 angularly across the second apex 
point 28 of the second hand side 16 and to the front side 12 of the first 
end portion 20. The wrapping then extends preferably circumferentially 
around the first end portion 20 at least once and then continues along the 
fifth wrap from the back side 10 of the first end portion 20 across the 
second apex point 28 of the second hand side 16 to the first side 10 of 
the second end portion 22 and then preferably circumferentially around the 
second end portion 22 at least once. The path then continues along the 
sixth wrap from the front side 12 of the second end portion 22 angularly 
across the first apex point 26 of the first hand side 14 to the back side 
10 of the first end portion 20 and then ending at a point partially or 
fully around the first end portion 20. 
More preferably from about 5 to about 20 circuits of the filament are 
utilized in forming the wrapping or girdle. The filament will generally 
comprise a plurality of substantially parallel fiberglass rovings and have 
a width in the range from about 5% to about 25% of the diameter of the 
branch 18 of the tee 2. Fiberglass tape can be used if desired. Sufficient 
resin, preferably of the aforementioned type, is utilized in conjunction 
with the fiberglass filament rovings to provide the resin impregnated 
filament rovings in the range of from about 60 to about 70% by weight 
glass and from about 40 to about 30% by weight resin. Shell Epon 828 resin 
has been used with good results. In a preferred embodiment, the wrapping 
or girdle comprises about 5 to 20 circuits of a filament having four 
rovings and about a 1/2 inch band width when deposited on the tee. A 
filament roving which has been used with good results is 1062T15 filament 
available from Pittsburgh Paint and Glass and has a weight of about 247 
yards per pound. 
In a preferred embodiment, the pipe tee 2 further comprises a plurality of 
circumferentially extending circular resin impregnated filament wraps on 
the branch 18, the first end portion 20, and the second end portion 22. 
These wraps provide the tee 2 with additional resistance to hoop stress 
and aesthetically improve its appearance. The filament rovings can be the 
same as utilized for the girdle. 
Preferably, the pipe tee having the winding deposited thereon is heated to 
a temperature in the range from about 250.degree. to about 350.degree. F. 
for a period of time of from about 1 to about 24 hours or more to 
accelerate the cure of the resin. The invention is illustrated by the 
following example: 
EXAMPLE 
Flanged pipe tees of 8" nominal diameter were made by rotational molding, a 
method known in the art, from Marlex CL-100 L618 which is a crosslinkable 
ethylene-hexene copolymer furnished by Phillips Chemical Co. of 
Bartlesville, Okla. The samples had a 0.75" sidewall thickness. Ten of the 
samples were wrapped as described in the specification with five layers of 
woven glass cloth, J. P. Stevens #7520, 8.70 oz/yd.sup.2, 0.12" thickness, 
plain weave and fifteen circuits of Pittsburgh Paint and Glass Co. 
#1062T15, 15 strand, 247 yield (yds/lb) fiberglass type saturated with 
resin comprised by weight of 76% Shell Epon 828, 7% trethylene tetra 
amine, and 17% Apco 2170 (cyanoethyl modified aliphatic amine), sold by 
Applied Plastics Co. of Segundo, Calif. Fifteen samples were not wrapped. 
All samples had steel blind flanges attached on the three openings and 
were hydrostatic tested at the pressures shown in the table. The samples 
were maintained at room temperature of about 73.degree. F. at the 
indicated pressure until failure or termination of the test. 
______________________________________ 
Wrapped Tees 
Gauge 
Sample # Pressure PSI 
Hours on Test.sup.1 
______________________________________ 
1 360 144*.sup.2 
2 360 26,000+ 
3 320 26,000+ 
4 320 26,000+ 
5 280 26,000+ 
6 280 26,000+ 
7 250 13,000+ 
8 250 13,000+ 
9 200 13,000+ 
10 200 13,000+ 
______________________________________ 
.sup.1 Test terminated without failure. 
*.sup.2 This sample was not molded properly. It failed @ 144 hours. 
______________________________________ 
Non-Wrapped Tees 
Hours to Failure 
______________________________________ 
11 360 14 
12 360 192 
12 360 96 
14 330 7 
15 330 528 
16 320 168 
17 320 1560 
18 300 408 
19 300 384 
20 300 672 
21 280 908 
22 280 672 
23 280 1532 
24 260 1152 
25 260 2184 
26 250 888 
27 250 1008 
28 250 3096 
29 230 1416 
30 230 960 
31 230 1152 
32 200 3144 
33 200 2616 
34 200 5208 
35 150 4056 
36 150 5928 
______________________________________ 
It can be seen from the preceding Table that the wrapping provided a 
considerable improvement in long term hoop stress.