Metal working – Method of mechanical manufacture – Repairing
Reexamination Certificate
1997-06-02
2001-06-05
Echols, P. W. (Department: 3726)
Metal working
Method of mechanical manufacture
Repairing
C029S402090, C029S451000, C029S234000, C138S097000
Reexamination Certificate
active
06240612
ABSTRACT:
This invention relates to a method of and apparatus for the lining of existing pipes. The invention will be described in relation to gas, oil and water supply pipes, but it will be appreciated that the invention is applicable to pipes of all kinds.
When lining installed pipes (which pipes when ground embedded are prone to crack due to ground movement) it is known to draw a heated liner of plastic tube through a die to reduce the diameter and then into a length of the existing pipe.
The present invention relates to an improved method of lining installed pipework when using a swaging die to reduce the diameter of the liner pipe prior to its being drawn into the existing pipework. By “installed” pipework is meant pipework that has already been installed in position to carry out its intended purpose, such as for example, ground embedded pipework for gas, oil, water or sewage, pipework forming part of a larger installation such as in oil or gas refinery or storage installation, or pipework resting on the ground and laid down to connect a source. of supply to the recipient such as an oil pipe connecting a well to a refinery or port.
In the case of ground embedded pipework it will be appreciated that the normal arrangement when such a process is being carried out will involve a winch adjacent to an excavation at one end of a length of pipe to be lined, whence a cable or similar flexible ligament passes through the length of pipe to a second excavation beyond which it is attached to the front end of a liner pipe of plastics material. Adjacent to the second excavation is a tube heating and compressing apparatus which has a heater and a size reduction die. At a downstream end of this apparatus there may be a reciprocatable “pusher” which can grip the pipe and draw it from the apparatus and urge it towards the pipe to be lined.
According to the present invention, there is provided a method of lining installed pipework which includes the steps of taking a length of liner pipe made from a memory retaining plastics material of external diameter greater than the internal diameter of the pipework to be lined, drawing the liner pipe through a swaging die which is attached directly or indirectly to the pipe t o be lined using pulling means under tension attached to the leading end of the liner pipe and threaded through the pipework to reduce the external diameter of the liner pipe by up to 15% the tension applied by the pulling means being such as partially to restrain the radial expansion of the outer surface of the liner pipe after it s emergence from the die, drawing the liner pipe through the installed pipework with its outer diameter reduced to and/or maintained at a dimension less than that of the inner diameter of the installed pipework and thereafter allowing the liner pipe to expand within the pipework by relaxation of the said tension followed by memory induced expansion at ordinary atmospheric pressure and at the ambient temperature of the pipework,
In one aspect of the present invention, the liner pipe may be heated by methods known per se prior to the swaging operation. Alternatively, or i n addition, the liner pipe may also be heated during its passage through the swaging die. In such a case, means are provided for heating the internal surface of the swaging die simultaneously with the passage of the liner pipe through it.
According to another aspect of the present invention, the swaging operation may be carried out at ambient temperatures. The choice of liner pipes suitable for swaging at ambient temperatures will depend upon, inter alia, the dimensions of the liner pipe, its SDR ratio and the particular characteristics of material from which the liner pipe is made. Whether in any particular circumstances a liner pipe may be successfully swaged at ambient temperatures is a matter which may easily be ascertained by the operator by way of trial and error.
The present invention envisages in a preferred aspect of its operation the employment of a swaging die that is provided with a surface which, or part of which, is inclined at an angle between 6 degrees and 32 degrees there being no part at an angle of more than 32 degrees to the die axis and which extends over an axial length that is at least 70% of the axial distance between the part where the liner pipe engages with such surface and the part where the liner pipe disengages from the die.
Dies used according to the prior art methods of pipe swaging as employed in practice have comprised two portions, the first being the inclined swaging surface reducing in diameter to a minimum value and the second being an axial continuation of the die interior having its walls parallel to the die axis and an internal diameter equal to such minimum value. We have found that in the carrying out of the present invention, it is advantageous to reduce the axial length of the said second portion relative to the axial length of the first portion, or else to dispense with the second portion altogether. In particular, by so designing the die that the first part extends over an axial distance that is at least 70%, and preferably over 80%, and advantageously over 85% of the axial distance between the part where the liner pipe engages with the inclined surface and the outlet orifice where the pipe emerges from the die, the pulling tension required to swage the liner pipe is substantially decreased. Another consequence of the use of such a die in the carrying out of the present invention is that, when using a liner pipe of synthetic hydrocarbon resins such as polyethylene or modified polyethylene as conventionally used in practice, the liner pipe on emerging from such outlet orifice manifests a greater tendency towards radial expansion relative to the degree of swaging exerted by the die than in the case where, as in the prior art, the swaging die was provided with a second portion as mentioned above of substantial length, typically in the order of 50% of the overall die length. On release of pulling tension such tendency will result in a greater proportional radial expansion in relation to the pulling tension employed than would have occurred using the prior art dies.
The process of the present invention relies both upon the expansion of the liner pipe within the pipework as a result of relaxation of the pulling tension and also as a result of the memory induced expansion of the swaged liner pipe. By the use of a die having a reduced axial length of its second portion relative to the axial length of its first portion as mentioned above the proportionate expansion resulting from the relaxation of the pulling tension may be significantly increased thus resulting in improved control over the pipe lining operation.
The arrangements described above furthermore provide a significant advantage in relation to the case where a “pusher” device as e.g. of the kind described in our co-pending Patent Application UK No. 8806926 is used. It is inherent in the operation of such a pusher that, when it grips the liner pipe and urges it towards the pipework to be lined, there is experienced a temporary reduction in the pulling tension exerted by the pulling device (such as a winch) at the far end of the pipework. Upon the pusher releasing its grip, the tension resorts back to its original value. In practice, this results in a continuous fluctuation in the tension. It is desirable that the changeover between maximum and minimum tensions in the course of the fluctuations be affected as smoothly as possible and with the minimum amount of sharp transitions or jerks.
We have found that as a result of the preferred use of the dies of the present invention which require substantially lower pulling tensions to effect a comparable degree of swaging as compared with prior art dies and which furthermore being about a greater “spring back” tendency on the part of the pipe emerging from the die orifice, the amplitudes of the fluctuations are reduced and the fluctuations themselves become smoother. Having regard to the very high forces involved in exerting the pulling tension, this again
British Gas plc
Echols P. W.
Larson & Taylor PLC
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