Abstract:
A method of detecting excessive strain in an elongated flexible member comprising: (a) applying at least one strain-detecting strip to the flexible member in an area that will be subject to bending in installation or use; (b) installing the flexible member in place; and (c) after installation, inspecting the strain-detecting strip for signs of excessive strain in the flexible member.

Description:
[0001]    This invention relates to a method for detecting an excessive amount of stretch or strain in a metal flex hose or other flexible conduit. 
       BACKGROUND OF THE INVENTION 
       [0002]    Metal flex hoses are used in various applications, including gas turbine plants where they are used to route compressed air of various temperatures and pressures from point A to point B. Hose routing can be quite complex depending on the location and geometry of each attachment point or termination point. Such complex routing in typical field installations can lead to incorrectly installed hoses that are over-strained and/or over-stressed, leading to premature failure. 
         [0003]    There remains a need for a simple but rapid, reliable and quantifiable method for measuring the overall strain condition in a metal flex hose as installed. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    In one aspect, the present invention relates to a method of detecting excessive strain in an elongated flexible member comprising: (a) applying at least one strain-detecting strip to the flexible member in an area that will be subject to bending in installation or use; (b) installing the flexible member in place; and (c) after installation, inspecting the strain-detecting strip for signs of excessive strain in the flexible member. 
         [0005]    In another aspect, the invention relates to a method of detecting excessive strain in an elongated flexible member hose comprising: (a) before or after installation, installing a collar over the flexible member, the collar sized and shaped to slide over the flexible member in a substantially straight condition with a specified clearance; (b) after hose installation, sliding the collar along the flexible member to detect presence of bends or kinks of a magnitude such that the collar will not pass over such bends or kinks, thereby indicating improper installation. 
         [0006]    The invention will now be described in connection with the drawings identified below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0007]      FIG. 1  is a schematic illustration of a flex hose subject to stresses and strains resulting from a one-way bend in the hose; 
           [0008]      FIG. 2  is a schematic illustration similar to  FIG. 1 , but illustrating an S-bend in the flex hose; 
           [0009]      FIG. 3  is a schematic illustration of a flex hose having a reverse curvature, S-bend therein, but with a sensor strip applied thereto in accordance with an exemplary but nonlimiting implementation of the invention; 
           [0010]      FIG. 4  is a schematic illustration similar to  FIG. 3  but wherein the sensing strip is replaced by a split collar sized and shaped to detect excessive bends or kinks in the flex hose; 
           [0011]      FIG. 5  is a perspective view of a split collar of the type that may be used in the arrangement shown in  FIG. 4 ; 
           [0012]      FIG. 6  is a partial perspective view of a flex hose to which multiple sensor strips have been applied in accordance with another exemplary implementation of the invention; and 
           [0013]      FIG. 7  is a partial perspective view of a flex hose in which a sensing wire has been integrally woven in accordance with still another exemplary implementation of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]      FIGS. 1 and 2  illustrate a flexible hose mounted between two fixed points, demonstrating the types of potential bending that could occur during installation of the hose, and that could result in failure of the hose. In  FIG. 1 , the flex hose  10  is secured between fixed points  12  and  14 . The hose is shown in a position in which potentially damaging tension or compression in excessive amounts could result in rupture of the hose. 
         [0015]    In  FIG. 2 , the hose  10  is shown to incorporate a kink or reverse curvature, S-bend, which again, could result in rupture of the hose. 
         [0016]    In accordance with exemplary but nonlimiting implementations described herein, several alternative methods are provided for detecting and/or quantifying the amount of stretch or strain in flex hoses, including metal flex hoses of the type that are utilized to carry compressed air in gas turbine engine plants. The invention is applicable to other elongated flexible members such as tubes, conduits or the like. 
         [0017]    In one exemplary implementation, one or more calibrated, strain-indicating and substantially transparent polymer strips  24  are adhered to the exterior of the flex hose  18  (one shown in  FIG. 3 ) prior to installation. If the hose and applied polymer strip strain over a certain threshold level, the transparent polymer strip crazes and becomes opaque, giving an immediate visual indication of improper installation. 
         [0018]    In a variation of this implementation, a color change polymer is employed in the one or more strips  24 , so if the hose  18  and polymer strip(s)  24  strain over the threshold amount, the polymer strip(s)  24  will craze and change color, thereby also giving an immediate visual indication of improper installation. 
         [0019]    In another exemplary implementation, the calibrated strain-indicating polymer strip(s)  24  are adhered to the exterior of the hose  18  prior to installation, but in this instance, each of the one or more strips  24  is constructed of two chambers, separated by a strain sensitive membrane. The chambers are filled with reacting fluids. If the hose and applied polymer strip strain over the threshold level or amount, the membrane breaks and allows the fluid in the two chambers to mix and change color, again giving an immediate visual indication of improper installation. 
         [0020]    In another exemplary implementation, the calibrated strain-indicating polymer strip(s)  24  are also constructed of two chambers separated by a strain sensitive membrane, but with the chambers filled with reacting fluids. In this instance, however, due to the composition of the reacting fluids, if the hose and applied polymer strip strain over the threshold level, the membrane breaks and allows the fluids to mix and thereby generate light, again giving an immediate visual indication of improper installation. 
         [0021]    In yet another exemplary implementation, the transparent polymer strip(s)  24  craze when over-strained, and thus reduce the ability to transmit light. An external device may be used to measure the change in light transmission, giving an indication of improper installation. 
         [0022]    In still another exemplary implementation, calibrated strain-indicating, electrically-resistive strip(s)  24  is (are) adhered to the interior or exterior of the hose  18  prior to installation and wired in such a manner as to quantify the amount of strain present in the hose after installation. A resistive value over a certain threshold limit would indicate an improper hose installation. 
         [0023]    With reference to  FIG. 4 , in another exemplary implementation, one or more hinged split collars  26  of suitable length and ID or inside diameter (as determined by the hose diameter and the excessive strain threshold), are provided in kit form. Each collar can be installed over the flex hose  28  before or after installation and run along its length to check for bend radius. The length and ID of the collar are thus chosen such that only if the bend is excessive will there be interference in the sliding motion of the collar. For example, the inside diameter of the collar may be chosen to provide an acceptable clearance, based on permissible curvature in the hose. A typical range is 0.5 to 1.5%&gt;hose outer diameter. Threshold interference in this regard, may be defined as desired, and may include a complete stoppage of the collar, i.e., where the collar cannot pass over the bend or kink. Such interference, however defined, indicates improper installation. 
         [0024]      FIG. 5  illustrates the split collar  26  in enlarged form, with collar halves  28 ,  30  having complimentary flanges  32 ,  34  and  36 ,  38 , respectively, that may be used to hold the collar on the hose  28  via use of any suitable fasteners. 
         [0025]    In use, the collar is assembled on the hose after installation of the hose and moved along the length of the hose to detect impermissible kinks or bends as described above. 
         [0026]      FIG. 6  illustrates a hose  40  with a plurality of sensing strips  42  applied in both axially and circumferentially-spaced arrays. The strips  42  may be sized to crack visually or “electrically” when subjected to excessive curvature, and hence strain, in the hose. Visual indication, as mentioned above, may be based on color change, light emission or the like, and electrical indication may be based on resistivity increase due to the bend or kink. 
         [0027]      FIG. 7  illustrates another implementation where a wire, such as a fiber optic wire  44  is woven or braided integrally with the hose  46 . Wire  44  could also be an electrically resistive wire as described above. In either case, excessive strain in the hose will trigger an indicator of improper installation. 
         [0028]    In all cases, thresholds may be determined based on specific hose compositions, environments, and other criteria regarding what is considered excessive strain, and the various indicators calibrated accordingly. 
         [0029]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.