Abstract:
A method of hose construction comprises: providing a sacrificial layer on the surface of a hose former; constructing a hose on the sacrificial layer; forcing pressurised fluid between the sacrificial layer and the hose former to separate the hose former from the sacrificial layer; and separating the sacrificial layer from the hose.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a method of hose construction. In particular the invention relates to the final construction stage of removing a rough bore hose, such as a liquid natural gas hose, from a mandrel. 
       BACKGROUND TO THE INVENTION 
       [0002]    The construction of a Liquid Natural Gas (LNG) hose body involves the build up of stacks of multiple non-bonded film and fabric layers as well as internal and external helical wire structures onto a cylindrical mandrel. The internal helical wire structure is the first layer that is built onto the mandrel and it provides the core structural integrity of the LNG hose. The LNG hose is classified as rough-bore hose as a result of this internal helical wire structural characteristic. High frictional forces are generated between the internal helical wire structure and the mandrel over the length of the hose being built as a result of: forces associated with the tension in the wire from the forming of the internal helical wire structure; and load from the build up of the subsequent hose layers. These frictional forces are high enough to restrict the removal of the mandrel by axially pulling the mandrel following the completion of the hose construction as per the standard marine hose de-poling procedure. Using excessive forces to remove the mandrel can potentially result in dislocating the internal helical wire structure and therefore compromising the core structural integrity of the LNG hose. 
       SUMMARY OF THE INVENTION 
       [0003]    The present invention provides a method of hose construction comprising: providing a sacrificial layer on the surface of a hose former; constructing a hose on the sacrificial layer; separating the hose former from the sacrificial layer; and separating the sacrificial layer from the hose. 
         [0004]    The sacrificial layer may comprise a solid layer between the hose and the former, preventing the former coming into contact with the hose. The sacrificial layer may be made of rubber. 
         [0005]    The hose may define an internal channel and the sacrificial layer and the hose former may be located within the internal channel prior to the separating steps. The hose may be constructed on top of the sacrificial layer. 
         [0006]    The method of separating the hose former from the sacrificial layer may comprise forcing pressurised fluid between the sacrificial layer and the hose former. The pressurised fluid may comprise water, air or other liquid lubricants. The sacrificial layer may be impermeable to the pressurised fluid. 
         [0007]    The sacrificial layer may form a tube with two openings and the method of separating the sacrificial layer from the hose may comprise sealing the openings of the sacrificial layer to produce a sealed internal volume in the sacrificial layer and reducing the pressure in the sealed internal volume. The sacrificial layer may be impermeable to atmospheric air, preventing atmospheric air entering the sealed internal volume. The sacrificial layer may comprise an end fitting which defines one of the openings and the method of sealing the sacrificial layer may comprise fitting a sealing plate to the end fitting sealing the opening. The end fitting may define one or more channels, for example in its inner surface, to allow fluid to flow between the sacrificial layer and the former. 
         [0008]    The method of reducing the pressure in the sealed internal volume may comprise connecting a vacuum pump to the sealed internal volume. The vacuum pump may be connected to the sealed internal volume through a port in the sealing plate. The method of separating the sacrificial layer from the hose may comprise collapsing the sacrificial layer under atmospheric pressure. 
         [0009]    The hose may be a liquid natural gas hose. 
         [0010]    The method may comprise, in any combination, any one or more features of the preferred embodiments which will now be described by way of example only, and with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a flow diagram of a method of hose construction in accordance with an embodiment of the invention; 
           [0012]      FIG. 2  shows the step of building the sacrificial layer on the mandrel in accordance with an embodiment of the invention; 
           [0013]      FIG. 3  shows the step of constructing the hose on top of the sacrificial layer in accordance with an embodiment of the invention; 
           [0014]      FIG. 4  shows the step of applying pressurised fluid between the sacrificial layer and the mandrel in accordance with an embodiment of the invention; 
           [0015]      FIG. 5  shows the step of removing the mandrel while applying pressurised fluid between the sacrificial layer and the mandrel in accordance with an embodiment of the invention; 
           [0016]      FIG. 6  shows the step of sealing the sacrificial layer at both ends and attaching a vacuum pump in accordance with an embodiment of the invention; 
           [0017]      FIG. 7  shows the step of activating the vacuum pump and collapsing the sacrificial layer in accordance with an embodiment of the invention; 
           [0018]      FIG. 8  shows the step of removing the sacrificial layer from the hose in accordance with an embodiment of the invention; and 
           [0019]      FIG. 9  shows a section view through the wall of a LNG hose formed using the hose construction method of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    In this embodiment the method of hose construction is applied to a LNG hose. The structure of a completed LNG hose is shown in  FIG. 9 . The LNG hose has inner  901  and outer  902  helical wire support structures which are supported by layers of non-bonded film and fabric  903 . 
         [0021]    Referring to  FIGS. 1 and 2 , step  1  involves applying rubber to a rotating mandrel  200  to build up a sacrificial layer  201  directly on the mandrel surface. Fabric reinforcing layers are also applied to the rubber to provide extra strength to resist stresses primarily in the axial direction during mandrel removal. The sacrificial layer  201  forms a sleeve over the mandrel which is joined and sealed to an end fitting  202 . The end fitting  202  has a cylindrical collar  204  and an annular flange  203 . The flange is joined to one end of the collar  204  and the collar is sized to slide over the mandrel. The sacrificial layer  201  runs up to and over the collar  204 . The sacrificial layer is allowed to cure which bonds the layer to the collar. The cured sacrificial layer  201  provides a base for the hose construction to follow. It is therefore important that the thickness of the sacrificial layer is consistent and the surface finish smooth along the complete length of the mandrel to ensure the bore of the finished hose is consistent as per LNG hose specifications. Although the sacrificial layer has been made from rubber in this embodiment it will be appreciated that other elastomeric materials would also be suitable. 
         [0022]    In step  2 , the hose carcass  300  is built up on top on the sacrificial layer  201 , as shown in  FIG. 3 . The sacrificial layer prevents the hose from coming into contact with the surface of the mandrel  200 . The construction of the hose is carried out in the normal way by coiling internal  901  and external  902  helical wire support structures with stacks of non-bonded film and fabric layers  903  built up in between. 
         [0023]    In step  3 , referring to  FIG. 4 , a hydraulic coupling  400  is bolted to the flange of the end fitting  202 . The coupling forms a water tight seal with the flange and directs high pressure water  401  between the sacrificial layer  201  and the surface of the mandrel  200 . Machines grooves on the inner surface of the collar  204  of the end fitting direct water on to the surface of the mandrel. Alternatively, the collar may just be sized so that it loosely fits over the mandrel allowing water to pass between the collar and the mandrel surface, so it can flow between the sacrificial layer and the mandrel surface. The high pressure water stretches the sacrificial layer and lifts the sacrificial layer  201  and the hose  300  off the surface of the mandrel  200 . It will be appreciated that other pressurised fluids may be used such as compressed air. It is important that the sacrificial layer  201  is impermeable to the pressurised fluid to maintain the pressurised fluid within the sleeve and to prevent fluid permeating through to the LNG hose. 
         [0024]    In step  4 , referring to  FIG. 5 , the mandrel  200  is removed using axial force  501  applied to the mandrel while the sacrificial layer  201  and the hose  300  are restrained by the flange of the end fitting  202 . The sacrificial layer is put under tension by the axial load, but the sacrificial layer does not stretch under the axial loading because of the fabric layer. High pressure water  502  is continuously supplied during extraction to help hold the sacrificial layer off the surface of the mandrel. The inner surface of the hose  300  and the inner helical wire support structure  901  are protected during this phase by the sacrificial layer which takes all the applied axial load allowing removal of the mandrel without damaging the hose structure. 
         [0025]    In step  5 , referring to  FIG. 6 , with the mandrel removed the sacrificial layer  201  is sealed at both ends, by fitting a vacuum plate  600  to the end fitting  202  and black vinyl tape is used close and seal the other end which forms an internal sealed volume within the sacrificial layer. The sacrificial layer therefore prevents external atmospheric air from entering the internal volume. The vacuum plate  600  is a solid plate with a seal which abuts the flange of the end fitting  202  sealing the opening in the cylindrical collar  204 . The vacuum plate has a port  602  for connecting a vacuum pump. Before a vacuum pump is connected the vacuum plate  600  is fitted to the flange  204  and held in position with clamps. A vacuum pump  601  is connected to the internal sealed volume through the port in the vacuum plate  600 . 
         [0026]    In step  6 , referring to  FIG. 7 , the vacuum pump is activated reducing the pressure in the internal volume of the sacrificial layer which collapses under the external atmospheric pressure. As the sacrificial layer collapses it separates from the internal wall of the hose  300 . While the sacrificial layer has strength in the axial direction, its thickness should be thin enough to allow it to collapse under vacuum. 
         [0027]    In step  7 , referring to  FIG. 8 , the collapsed sacrificial layer, including the end fitting  202  and vacuum plate  600 , can then be easily removed from the bore of the completed hose. 
         [0028]    Although this embodiment of the invention has been described in relation to LNG hoses it will be appreciated that the invention may also apply to other types of hose such as standard rubber marine rough bore hoses.