Pipe joints

A method of joining pipes in which a sleeve is placed over the adjacent ends of the pipes so as to overlap each pipe. The sleeve fits with clearance around the pipe ends. The ends of the clearance space are closed by inflating hollow sealing rings and then epoxy resin is injected into the clearance space to fill the space. The pressure of the epoxy resin composition is then raised to a pressure substantially greater than atmospheric and the pressure is maintained until the resin composition is set.

The present invention relates to a pipe joint and to a method of joining 
pipes, and is concerned particularly, but not exclusively with pipe joints 
for oil or gas pipelines. 
According to the present invention in one aspect, a method of forming a 
joint between a pipe end and a coupling sleeve which fits with clearance 
around the pipe end, comprises placing the coupling sleeve around the pipe 
end, closing the ends of the clearance space between the coupling sleeve 
and the pipe end, injecting a hardenable composition into the space 
between the coupling and the pipe end to fill the space, and maintaining 
the pressure in the hardenable composition at a pressure substantially 
greater than atmosphere pressure until set. Preferably the pressure should 
be of the order of the working pressure of the pipe. 
The hardenable composition may be portland cement but of preference it is 
an epoxy resin composition, such as that sold under the trademark 
"Araldite". The epoxy resin composition may include a filler such as 
carborundum powder which increases the coefficient of friction and 
crushing strength of the composition when set. Such a composition is sold 
under the trademark "Araldite SW 404". 
In the case of epoxy resin composition, the setting time for the joint may 
be substantially reduced by including a resistive heating wire in the 
clearance space and passing a current through the wire when the resin 
composition has been injected into the space. The current through the wire 
should be controlled so that the composition is raised to a temperature at 
which curing is accelerated, but not so high that it causes the 
composition to disintegrate. 
The sleeve may have a helical screw thread in its bore for increasing the 
surface area in contact with the resin layer and thus improving the grip 
between the layer and the sleeve. For convenience the resistive heating 
wire may be located in the root of the screw thread, for example by 
gluing, prior to the sleeve being fitted around the pipe end. 
To improve the grip between the pipe end and the resin layer, the end of 
the pipe may be roughened, for example by forming a helical groove using a 
rotary chipping hammer. 
The invention may be used to form a joint between two pipe sections by 
placing the sleeve over the adjacent ends of pipe sections each pipe 
section being overlapped by half the sleeve. 
In another aspect the present invention comprises a joint between a 
coupling sleeve and a pipe end, the coupling sleeve fitting with clearance 
around the pipe end, means for closing the ends of the clearance space 
between the pipe end and the sleeve, and a layer of a hardenable 
composition set under pressure greater than atmospheric filling the 
clearance space, so that when the interior of the pipe is at atmospheric 
pressure the pipe ends are pre-loaded inwardly. 
The means for closing the ends of the clearance space may conveniently be 
hollow rubber rings located in grooves in the sleeve at each end of the 
clearance space. The rubber rings may be inflated by injecting with 
hydraulic fluid or preferably by injecting with a hardenable composition, 
so as to span the space between the sleeve and the pipe end. 
The pipe joint of the present invention can be applied to pipes of any size 
up to the largest used in the petroleum off-shore or gas industry. The 
joint can be effected without welding and can be completed in a matter of 
15 seconds, which makes it most attractive for very rapid undersea or land 
pipe laying operations. The joint is very compact and light to handle and 
cheap to produce -- yet can have a strength equal to twice the strength of 
the pipe.

Referring to the drawing two pipe sections 11 and 12 to be joined have ends 
that are free of any coating or other covering, and are prepared for 
joining by being brushed with wire brushes, their surfaces are roughened 
by high-speed rotary chipping hammers and they are then finally degreased 
before joining. 
A coupling sleeve 13 has a split distance ring 14 permanently secured 
within a centrally disposed circumferential groove 15 machined in the bore 
of the coupling sleeve 13. The coupling sleeve is first slid over the end 
of one pipe 11 until the end of the pipe abuts the distance ring 14. The 
end of the other pipe 12 is then slid into the coupling sleeve 13 until 
the end of this pipe abuts the split distance ring 14. 
At each end of the clearance spaces 16 between the respective pipe ends and 
the sleeve is an annular groove 17 in the surface of the bore of the 
sleeve. Ports 18 connect the grooves through the wall of the sleeve with 
the exterior at the top and bottom of the sleeve. A hollow sealing ring 19 
of nitrile rubber is located in each groove 17. Injecting valves 20 (see 
FIG. 6) are located in the ports 18 at the bottom of the sleeve and air 
bleed valves 21 are located in the ports at the top of the sleeve, the 
valves 20 and 21 communicating with the interior of their respective 
sealing rings. 
Each clearance space 16 can communicate with the exterior through an inlet 
port 22 at the bottom of the sleeve and an outlet port 23 at the top of 
the sleeve. Each inlet port 22 holds an injection valve 24 similar to the 
valve (see FIG. 3) and each outlet port holds an air bleed valve 25 
similar to the valve 21 (see FIG. 5). 
The interior of the sleeve is grooved with a helical screw thread 26 to 
increase its surface area. A resistive heating wire 27 is contained within 
the screw thread 26, being secured at the root of the screw thread for 
example with adhesive. The ends of the resistive wire pass through bores 
28 in the wall of the sleeve to terminals 29 on the outside of the sleeve. 
After the sleeve has been located over the pipe ends as described above, 
the injection valves 20 and 24 are connected to injection manifolds (not 
shown) and the terminals 29 are connected to a supply of electric current 
with automatically controlled valves and switches (not shown). 
Epoxy resin composition automatically metered and thoroughly mixed with 
hardener is injected through the injection valves 20 into the seal rings 
19 which are at the terminations of each joint. Air is automatically bled 
out through air release valves 21 which shut firmly as soon as the epoxy 
composition follows the air through the valve. The pressure is then raised 
to the working pressure of the pipe. When this pressure reaches a pre-set 
value of say 15% of the maximum, resin injection automatically commences 
through injection valves 24, air being bled off through air bleed valves 
25. The pressure is raised until a predetermined pressure is reached which 
may be say 75% of the working pressure. As soon as the pressure injected 
through injection valves 24 reaches a predetermined amount -- indicating 
that the air bleed valves 25 have shut an electrical heating current is 
passed between the terminals 29 which are connected to the continuous 
heating wire 27 contained within the screw-thread groove 26 cut into the 
bore of the coupling sleeve 13. A controlled temperature is maintained for 
about 10 seconds which rapidly hardens off the epoxy trapped under 
pressure within the joint. So in a matter of seconds from start to finish 
a high strength joint is obtained. 
In the embodiment described the effective length of the joint is about 0.7 
.times. D where D is the pipe diameter. For a 20" diam pipe of 0.5" wall 
thickness the strength of the joint equals. 
.pi. .times. 20 .times. 0.7 .times. 20 .times. 3 = 2637 tons. 
Pipe strength = .pi. .times. 20 .times. 0.5 .times. 35 = 1099 tons 
.thrfore. Factor of safety = (2637/1099) = 2.4 
On a pipe laying barge for underwater pipe laying or on a pipe laying 
vehicle, a pipe harness connecting injection points 20 and 24 and the 
electrical heater terminals 29 is clipped on the joint sleeve and the 
injection heating and pressurizing process is automatically sequenced, and 
metered so that each joint is filled completely with a metered quantity of 
epoxy mixture before the heat is applied. This ensures that every joint is 
perfectly made. 
The joint may be broken by simply maintaining the heat until 200.degree. C. 
is reached when the epoxy resin composition disintegrates. 
To summarize the joint described above has the advantages that no welding 
is used, it is very simple, the jointing procedure is fully automated and 
the strength is guaranteed. The jointing efficiency is ensured by metering 
joint filling, the quality and strength of the Epoxy mixture may be 
checked for each batch of resin and hardener delivered to site. The speed 
of making the joint is about 200 times faster than conventional joints. 
The joint is light and compact in construction, it is cheap to produce and 
the joint may be made or broken in seconds.