Flexible hose

A flexible hose comprising a main fluid retaining carcass and a secondary carcass enclosing at least part of the main carcass, said secondary carcass being constructed to expand radially relative to said main carcass on leakage of fluid from said main carcass. Said hose includes means to control the radial expansion of said secondary carcass in a predetermined manner; said means may comprise localized bonding of said main and secondary carcasses and/or localized circumferential reinforcement of the secondary carcass.

This invention concerns improvements in or relating to flexible hose and in 
particular to flexible hose of the type comprising a main fluid retaining 
carcass and a secondary fluid retaining carcass enclosing at least part of 
the length of the main carcass to prevent escape of fluid leaking from the 
main carcass. 
Flexible hose of the type referred to above is particularly useful for 
transporting fluids the escape of which would constitute a severe health 
or safety hazard and is especially suited to applications where the hose 
is required to withstand a considerable amount of flexing in use, rough 
handling during connecting operations and severe weathering, for example 
in the hose-line used to transport oil between a tanker moored offshore 
and an installation on shore. 
In assignee's earlier U K Patent No. 1 503 302 a flexible hose of the type 
referred to above is disclosed in which the secondary carcass is separate 
from the main carcass and constructed to expand radially under the 
pressure of fluid leaking through the main carcass which is retained by 
the secondary carcass. 
I have now found that under certain conditions excessive radial expansion 
of the secondary carcass may occur in the vicinity of the leak causing not 
only the reinforcement structure of the secondary carcass to become highly 
distorted but also the displacement and therefore the underwater weight of 
the hose to change significantly both of which are undesirable for the 
following reasons. The ability of the reinforcement structure to withstand 
the pressure of the leaked fluid is reduced by distortion of the 
reinforcement structure from its original configuration so that premature 
failure of the secondary carcass may occur. The delicate balance between 
added buoyancy and hose weight necessary to maintain an optimum 
configuration of successive hose lengths to minimize stresses in the hose 
line is disturbed by any significant change in the underwater weight of 
one of the hose lengths which may have a deleterious affect on all the 
hose lengths. 
According to the present invention there is provided a flexible hose 
comprising a main fluid retaining carcass, a secondary fluid retaining 
carcass which encloses at least part of the main carcass and is capable of 
expanding radially relative to the main carcass on leakage of fluid from 
the main carcass wherein radial expansion of the secondary carcass 
relative to the main carcass is controlled in a pre-determined manner. 
The extent of radial expansion of the secondary carcass relative to the 
main carcass may be controlled by bonding the secondary carcass to the 
main carcass at a plurality of positions spaced axially along the length 
of the hose. Bonding may be continuous in the circumferential direction 
but more preferably is discontinuous to allow fluid leaking from the main 
carcass to flow along the entire length of the enclosed part of the main 
carcass. 
Alternatively or in addition to the aforementioned bonding of the secondary 
carcass to the main carcass at selected axial positions the extent of 
radial expansion of the secondary carcass relative to the main carcass may 
be controlled by reinforcing the secondary carcass at a plurality of 
positions spaced axially along the length of the hose. For example the 
secondary carcass may be reinforced by circumferentially extending hoop 
plies. 
Where the secondary carcass is both bonded to the main carcass at selected 
axial positions and provided with circumferential hoop plies or similar 
the latter are preferably provided at the same axial positions as the 
bonding between the secondary and main carcasses to reinforce the bonds 
and control the extent of radial expansion in the event of any of the 
bonds failing. 
By controlling the extend to which the secondary carcass may expand 
radially relative to the main carcass excessive local radial expansion of 
the secondary carcass leading to high distortion thereof and consequent 
reduction in burst strength is prevented. In addition significant changes 
in the displacement and therefore underwater weight of the hose is 
avoided. 
Preferably the secondary carcass encloses the entire length of the main 
carcass and both the main and secondary carcasses are separately connected 
at each end to a respective end fitting. 
Preferably the main and secondary carcasses each include a respective 
reinforcement structure. Conveniently radial expansion of the secondary 
carcass relative to the main carcass is effected by forming the 
reinforcement structure of the secondary carcass from material having a 
substantially higher elongation than the reinforcement of the main carcass 
when subjected to the pressure of the fluid conducted therein, such that, 
at the designated working pressure of the hose, elongation of the 
secondary carcass reinforcement occurs on leakage from the main carcass 
allowing radial expansion of the secondary carcass. 
The reinforcement structure of the main and secondary carcasses may 
comprise one or more layers of woven or braided material or a helical 
winding or any combination of such layers. 
Where the secondary carcass is provided with hoop plies or similar these 
are applied after the reinforcement structure i.e. radially outwards 
thereof, and formed of a material having a lower elongation than the 
material forming the reinforcement structure. 
The hose may include low density buoyancy material to provide the desired 
degree of buoyancy for the use to which the hose is to be put i.e. 
underwater pipe lines, buoy to sea floor pipe lines or buoy to ship and/or 
shore pipe lines. Buoyancy material may be incorporated in the body of the 
main and/or secondary carcasses. Alternatively or in addition buoyancy 
material may be provided between the main and secondary carcasses. However 
irrespective of whether or not the hose includes buoyancy material the 
hose as formed does not have a pre-formed gap within the hose wall into 
which fluid leaking from the main carcass passes i.e. each layer forming 
the hose wall is applied directly over the preceding layer and a gap is 
produced within the hose wall as a result of leakage of fluid from the 
main carcass causing radial expansion of the secondary carcass. 
The hose may be of constant or varying bore diameter such as can be used to 
connect hose of one diameter to manifolds of different diameter such as 
may be present on a ship, buoy or onshore installation. 
Preferably means is provided to detect leakage of fluid from the main 
carcass. the leak detection means may rely on the radial expansion of the 
secondary carcass due to the pressure of leaked fluid, for example the 
hose may be provided with external surface markings which distort on 
expansion of the secondary carcass to give a visual warning or the hose 
may be provided with one or more devices extending circumferentially 
around the secondary carcass and operable on expansion of the secondary 
carcass to produce a warning signal. 
More preferably the leak detection means relies on a change in fluid 
pressure between the main and secondary carcasses and may be of the type 
disclosed in assignee's co-pending U K Patent application No. 8208403 
titled "Improvements in or relating to flexible hose".

The hose 1 shown in FIGS. 1 to 3 of the accompanying drawings comprises a 
main fluid retaining carcass 2 surrounded by and in contact with a 
secondary fluid retaining carcass 3, a respective end fitting 4 at each 
end of the hose to which the main and secondary fluid retaining carcasses 
2 and 3 are secured and a respective leak detector 5 for detecting fluid 
leaking from the main carcass 2 mounted on each end fitting. 
The main carcass 2 comprises an inner liner impermeable to the fluid to be 
transported, a reinforcement structure 2a and a cover. The reinforcement 
structure comprises several plies of steel wire cord helically wound at a 
lay angle of 50.degree. (.+-.5.degree.) to the longitudinal axis of the 
hose with successive plies being of opposite hand to provide a balanced 
constructions and a single coil of helically wound steel wire. The 
secondary carcass 3 comprises an inner liner of polymeric material, a 
reinforcement structure 3a and a cover which forms the outer cover of the 
hose and is capable of withstanding the conditions to which the hose is 
subjected in use. The reinforcement structure comprises several plies of 
high extension cord helically wound at a lay angle of 60.degree. 
(.+-.5.degree.) to the longitudinal axis of the hose with successive plies 
being of opposite hand to allow the secondary carcass to expand radially 
relative to the main carcass following leakage of fluid from the latter. 
As best shown in FIGS. 1 and 2 the liner of the secondary carcass is bonded 
to the cover of the main carcass at six axially spaced positions, 6 
through 11, along the length of the hose to control radial expansion of 
the secondary carcass relative to the main carcass with the bonding at 
each axial position being in four circumferentially spaced regions a, b, 
c, d, to allow leaked fluid to flow along the length of the hose to either 
end fitting. 
In addition the secondary carcass is provided with six circumferentially 
extending hoop plies 3b (see FIG. 7) one at each of the axially spaced 
positions 6 through 11, radially outwards of the reinforcement structure 
and formed from a low extension cord, e.g. wire cord, wrapped around the 
hose. The hoop plies reinforce the bonds between the main and secondary 
carcasses and, being formed from cords having a lower extension than the 
cords of the reinforcement structure, control radial expansion of the 
secondary carcass in the event of any of the bonds failing due to effects 
of fatigue or degradation following leakage of fluid, e.g. oil, from the 
main carcass. 
Each end fitting 4 is similar and, as shown more clearly in FIG. 3, 
comprises an axially extending nipple portion 12 to which corresponding 
one ends of the main and secondary carcasses 2 and 3 respectively are 
connected and a radially extending flange 13 for connection to a 
successive hose length (not shown) or to a fluid input/output (not shown). 
The nipple portion 12 has five axially spaced circumferential ribs 12a, 
12b, 12c, 12d and 12e. Each end of the main carcass 2 passes over the 
ribs 12a, 12b and 12c and abuts the ribs 12d of the associated end 
fittings 14 and is connected thereto by four axially spaced inextensible 
beads 14a, 14b, 14c and 14d each consisting of two wire windings. The 
secondary carcass 3 is slightly longer than the main carcass 2 and each 
end of the secondary carcass 3 passes over the ribs 12d and 12e of the 
associated end fittings 4 and is connected thereto by two axially spaced 
inextensible beads 15a, 15b, each consisting of single wire winding. The 
rib 12d has a channel 16 formed in the radially outer surface thereof 
which is continuous in circumferential direction and an internal bore 17 
leading from the base of channel 16 and extending in the axial direction 
towards the flange 13 of the associated end fitting. An axially extending 
small bore tube 18 connected at one end to the bore 17 projects beyond the 
end of the secondary carcass 3 and is connected at the other end to the 
leak detector 5 attached via a mounting 19 to an outwardly flared body 
portion 20 at the associated end fitting. 
The leak detector 5 may be of any type capable of sensing variation in 
fluid pressure and activating a warning device, visual and/or audio, when 
the pressure of leaked fluid between the main and secondary carcass 
exceeds a predetermined level and is preferably of the type disclosed in 
assignee's co-pending U K Patent application No. 8208403 titled 
"Improvements in or relating to flexible hose". 
In one method of manufacture the hose is built on a mandrel with each 
individual layer of the hose being applied under tension so that no gap 
exists between the main and secondary carcasses in the finished hose. 
Bonding between the main and secondary carcasses is effected by applying 
an appropriate bonding agent to the outer surface of the cured main 
carcass cover at the appropriate positions and applying a masking agent 
e.g. a silicone and/or polymeric material to the remainder of the outer 
surface of the cured main carcass cover prior to application of the 
secondary carcass liner so that, on curing the secondary carcass, bonding 
between the main carcass cover and secondary carcass liner occurs only in 
the areas in which the bonding agent is applied. 
In use of the above described hose, fluid which leaks through main carcass 
2 is retained by the secondary carcass 3 which due to the reinforcement 
structure thereof being formed from high extension cords expands radially 
to generate a gap between the main and secondary carcasses. The degree of 
radial expansion that can occur is controlled by the bonding between the 
main and secondary carcasses reinforced by the circumferential hoop plies 
so that the leaked fluid is constrained to flow along the length of the 
hose to either end fitting where its presence is detected by the 
associated leak detector 5. As a result excessive local radial expansion 
of the hose in the region of main carcass failure is prevented and 
detection of a leak may be effected before a large volume of fluid has 
leaked between the main and secondary carcasses and therefore before a 
significant increase in underwater weight of the hose occurs. 
FIGS. 4 to 6 are schematic representations of three typical installations 
in which the flexible hose above described may be incorporated. In each 
installation several lengths of flexible hose are connected end to end to 
form a hose line 30 extending between a floating buoy 31 and a submerged 
pipeline 32. The floating buoy 31 may typically be connected to a tanker 
(not shown) and the submerged pipeline 32 connected to an on-shore 
installation for loading or unloading the tanker. In each installation at 
least one of the hoses in the pipeline or the end fitting(s) connecting 
successive lengths of hose is/are provided with external flotation collars 
33 whereby the hoseline is constrained to a particular configuration which 
minimises stresses in the hose line. It will be appreciated that any 
significant change in the underwater weight of any length of hose within 
such a hose-line will alter the buoyancy thereof which if significant can 
result in the optimum configuration of the hose line being altered leading 
to the generation of undesirable stresses in the hose line and possible 
failure thereof. The hose according to the present invention overcomes 
this problem by ensuring any leak from the main carcass is detected before 
a significant change in the underwater weight and hence buoyancy of the 
hose length occurs and therefore before the hose line is disturbed from 
the optimum configuration. 
The invention is not restricted to the above described embodiment which may 
be modified in a number of ways. For example the number and area of the 
axial and circumferential bonds between the main and secondary carcasses 
may be varied to suit the load requirements of differing sizes or 
constructions of hose while the circumferential bonding at a particular 
axial location may be discontinuous as described or continuous in the 
circumferential direction, especially where detection of leaked fluid is 
effected at positions other than the end fittings e.g. where a device is 
arranged to detect radial expansion of the secondary carcass. Furthermore 
radial expansion of the secondary carcass may be controlled by a 
combination of bonding and hoop plies as described or by the use of either 
separately. The hoop plies may be replaced by any other suitable annular 
reinforcement structure e.g. rings of metal of plastics material. The use 
of flotation collars may be avoided by incorporating one or more layers of 
buoyancy material in the hose.