WO1995011124A1

WO1995011124A1 - Butt welding of pipes

Info

Publication number: WO1995011124A1
Application number: PCT/GB1994/002267
Authority: WO
Inventors: Eric Bridgstock; Roy Cartwright; David Michael Anthony Kenworthy
Original assignee: Fusion Group Plc
Priority date: 1993-10-19
Filing date: 1994-10-17
Publication date: 1995-04-27
Also published as: JPH09503713A; GB9321675D0; AU7941894A

Abstract

The invention relates to butt welding and is particularly concerned with the provision of self-determined cooling times during which pipe ends must remain clamped in the machine to ensure the creation of an effective weld. Most effective butt welding machines are already known such as are described in British Patent No. 2191976, but even machines of this sophistication leave largely to the discretion of an operative the degree of time that the machine must be left after the welding stage and before the clamps can safely be removed. Almost inevitably this results in the pipes being clamped in the machine far longer than is actually necessary and the object of the invention is to provide for shortened cooling times that are self-determined by the machine and by ambient temperature conditions. The invention involves the provision of control means employing parameters sensed and/or measured to limit the cooling stage to a duration no more than is required having due regard to ambient temperature conditions and the amount of heat input to the pipe ends during the heating and/or bead-up stage.

Description

BUTT WELDING OF PIPES

This invention relates to butt welding of pipes. There are numerous applications where successive lengths of plastics pipes in a pipeline must be in sealed engaging relationship, either for the safe transport of fluids through the pipeline or to prevent the ingress of fluid into the pipeline at a joint between successive lengths.

It is already known to provide equipment for the butt welding of adjacent pipe length ends. Thus, there is equipment such as is described in British Patent No. 2191976 that offers substantial guarantees in connection with the provision of an effective butt welded connection between pipe length ends. In such equipment, there is the need for a sufficient heat input to the pipe ends as they are pressed against a heater to melt the pipe ends and allow the formation of a bead of a required size on the pipe ends, and the need to hold the pipe ends against the heater plate for a soak period sufficient to guarantee that at the subsequent weld stage a sufficient degree of heat is maintained in the pipe ends and beads to ensure that effective welding can take place. Butt welding equipment must function correctly in extremes of ambient temperature conditions, and hitherto, the soak period has tended to be set to ensure that there is sufficient heat in the pipe ends under the coldest predictable conditions, with an allowance to guard against any delay from the point that the pipe ends are retracted from the heater plate to the point that the pipe ends are brought into contact for welding. As a direct consequence, in the majority of instances of usage of the equipment more heat than is actually required to ensure welding is provided in the pipe ends, and as a direct consequence, the pipe ends must be left for a longer period than is necessary to allow them to cool down following the welding stage. In addition to this, with some butt weldding machines of the prior art, the cooling period following welding is left to the discretion of the operative, with the frequent result of the operative deciding on a cooling period that is longer than is necessary. In terms of the efficient employment of such equipment and the efficient laying of a pipeline, the relatively long period of time that the equipment must be left holding the pipe ends in place after welding to allow the pipe ends to cool to a degree when it will be safe to remove the equipment from the pipe ends is an important parameter. Obviously, the length of time that the equipment must be left iri place after welding is a major factor in governing the number of butt welds that can be effected in unit time, and which of itself is a major factor in the total costs of laying a complete pipeline. It is the object of the present invention to provide equipment and a method of control that can shorten considerably the time required for pipe ends to be left clamped and to cool, without sacrificing the effectiveness of the weld between the pipe ends. According to the present invention, a butt welding machine comprises a control means to provide a self-determined cooling period for the pipe ends at the weld stage, said control means employing parameters sensed and/or measured during the operation of the machine by sensing and/or measuring means on the machine.

In one form of construction, a butt welding machine, such as, for example, of the type fully described in British Patent No. 2191976 is, in accordance with the invention, provided with an ambient temperature sensing means, a timing device, and a linear transducer. Thus, at the weld stage, the ambient temperature is sensed and the sensed temperature employed to set the duration of the timer, the timer being activated at the point that the linear transducer senses that the pipe ends have completed a required movement to cause a required degree of penetration of the pipe ends to ensure the formation of an effective weld. The duration of the cooling period is thereby set as a direct function of ambient temperature and kept to a minimum for any particular ambient temperature. At the end of the self-determined cooling period an appropriate signal is provided to advise the operative that the pipe ends can be safely removed from the clamps. A separate possibility is the provision of a temperature sensing means to sense the temperature of the pipes at the position of the weld, the sensed temperature being employed to terminate the cooling stage when the temperature has reduced to a predetermined level.

A further and important consideration that influences the final cooling period at the weld stage is the degree of heat put into the pipe ends at the heating stage with the pipe ends in contact with a heater plate. In accordance with a second aspect of the present invention a butt welding machine coraprises a control means to provide a self-determining degree of heating of the pipe ends against a heater plate, said control means employing parameters sensed and/or measured during the operation of the machine by sensing and/or measuring means on the machine.

Here again and in accordance with a preferred embodiment of the invention an ambient temperature sensing means, a timing device and a linear transducer may be provided on the machine, such as is described in British Patent No. 2191976. Thus, when the linear transducer has sensed that the pipe ends have been brought into contact with the heater plate or have been brought against the heater plate to a required degree, the ambient temperature sensing means is caused to sense ambient temperature, the sensed temperature setting the duration of the timing device and hence limiting the duration of the heating phase to no more than is required by ambient temperature. Alternatively, the sensed ambient temperature can be employed to set the temperature of the heater plate with the timer pre-set to a fixed duration. By limiting the heat input to the pipe ends to the minimum degree of itself has a major influence over the cooling period following the subsequent weld stage, and the duration of the heating phase can be employed to dictate the duration of the cooling period. The cooling period may be further curtailed as has been discussed above by the presence of a timing device set as a function of sensed ambient temperature.

The effectiveness of the trimming stage of butt welding machines as are currently available is such that substantial guarantees can be offered that after trimming opposed pipe ends will be square and with guaranteed all-round contact. It therefore does not necessarily follow that a bead needs to be formed on the pipe ends during the soaking period with the pipe ends against the heater plate. However, in those circumstances where it is thought to be desirable that a bead is formed, the bead can be formed by holding the pipe ends against the heater plate and when heat input into the pipe end causes an expansion of the plastics material with the attendant formation of a bead, or the pipe ends can be urged against the heater plate to provide a physical deformation of the pipe ends to create a bead of a required size. In these latter instances, ambient temperature conditions of themselves determine the temperature of pipe ends, and the temperature of the pipe ends prior to contact with a heater plate is a dominant factor over the rate of deformation of pipe ends such as during the formation of a bead on the pipe ends in contact with the heater plate. Therefore, and in accordance with a further aspect of the invention, a means of measuring a formed bead and a timing device are provided on the machine, and whereby the time taken to form a bead of required size can be measured, and the measured time employed to set the duration of the heating phase of the pipe ends against the heater plate. Here it may be the same timing device that is reset for the required duration of the heating phase or it may be a second timing device provided for that purpose. The result is the same, the limiting of the degree of heat input into the pipe ends at the heating phase with its influence over the duration of the final cooling stage following the formation of a weld.

The measurement of the time taken to form a bead of a required size can be by way of a sensor to sense that a required bead height has been reached, or can be by the measurement of the time taken for the movement of the pipe ends/clamps by a predetermined degree sensed by a linear transducer, to form a bead of a predetermined size.

At the end of the heating phase, there is the need to withdraw the pipe ends from the heater plate, to remove the heater plate, and to bring the pipe ends into contact (the dwell period). Heat loss from the pipe ends commences immediately. Consequently, a further parameter that can be taken into account at the cooling stage is the duration of the dwell period that can be measured by the timing device primarily provided for controlling the cooling and/or the heating phase, or can be a separate timing device for the purpose. The measured duration of the dwell period is employed to shorten commensurately the cooling period. To provide effective control over butt welding machines of the invention, microprocessor means may be provided, provided with predetermined parameters such as required degrees of linear movement of the pipe ends/clamps at the heating phase and/or at the weld stage and to which all sensed or measured parameters such as ambient temperature and measured time can be passed, the microprocessor being programmed to calculate a required duration of the heating phase and required duration of the cooling period. As a result either of effective control over the cooling period or effective control over the heating phase, and more particularly in a machine where control over both phases is employed, a noticeable reduction in the overall time taken from the onset of operations to the point that the clamps can safely be removed from the pipes without affecting the integrity of the weld, is achieved, and with the substantial avoidance of operator error. As a direct consequence, a greater number of welds between successive pipe ends can be achieved in unit time with its consequent reduction in the costs of laying pipelines.

To illustrate the various methods of control over butt welding machines reference is imported here to butt welding machines as are described in British Patent No. 2191976, by way of example only. To such machines, a control means can be attached that operate in accordance with the following brief examples. Example A i Linear displacement control to form a bead of predetermined size. ii Record displacement time. iii Employ recorded time to set duration of heating phase. iv Determine dwell time. v Control final joint by linear displacement, vi Consider time taken to form joint, vii Employ cooling time determined by time to form a bead and duration of heating phase. Example B i Sense ambient temperature ii Allow bead to form based upon a function of time related to ambient temperature. iii Duration of heating phase based upon a function of time to form bead. iv Record linear movement to create a bead of required size. v Determine dwell time. vi Linear movement at weld determined as a function of linear movement at bead up. vii Cooling time determined as a function of ambient temperature and heating phase duration.

Ex -ample C i Linear displacement control to form a bead of required size. ii Record time to form bead. iii Determine duration of heating phase as a function of recorded time. iv Determine dwell time.

V Predetermined linear displacement control to form a weld.

VI Cooling time determined as a function of the duration of the heating phase. Example D

1 Sense ambient temperature. ii Set heater plate temperature according to ambient temperature. iii Allow bead to form for predetermined time, iv Heating phase duration predetermined based on heater plate temperature, v Determine dwell. vi Weld determined by linear displacement. vii Cooling time determined as a function of heating phase duration. Example E i Sense ambient temperature. ii Form bead in a predetermined time. iii Determine heating phase duration as a function of ambient temperature, iv Dwell time determined, v Weld formed by predetermined linear displacement. vi Cooling time determined as a function of heating phase duration.

Claims

1. A butt welding machine comprising a control means to provide a self-determined cooling period for the pipe ends at the weld stage, said control means employing parameters sensed and/or measured during the operation of the machine by sensing and/or measuring means on the machine.

2. A butt welding machine as in Claim 1, wherein an ambient temperature sensing means, a timing device, and a linear transducer, are provided.

3. A butt welding machine as in Claim 2, wherein a microprocessor means is provided to receive signals from ambient temperature sensing means, the timing device, and the linear transducer.

4. A method of controlling a butt welding machine to provide a self-determined period of time for the cooling of the pipe ends subsequent to the weld stage comprising sensing the ambient temperature at the weld stage, employing the sensed temperature to set the duration of a timer and activating the timer at the point that a predetermined linear movement of the pipe ends at the weld stage has been completed.

5. A method as in Claim 4, wherein a signalling means is provided associated with the timer and whereby to provide a signal to confirm the completion of the self-determined cooling period.

6. A method of controlling a butt welding machine to provide a self-determined period of time for the cooling of the pipe ends subsequent to the weld stage comprising sensing -li¬

the temperature of the pipes at the point that linear transducer means sense the completion of a required degree of movement of the pipe ends towards each other at the weld stage, sensing the fall of temperature in the pipe ends until a predetermined lower level of temperature or a predetermined reduction in temperature has been reached and when an appropriate signal is generated to signal the completion of the cooling period.

7. A method as in Claim 6, wherein ambient temperature is sensed at the point that the temperature of the pipes is sensed at the commencement of the weld stage, the signals of ambient temperature and pipe temperature being combined by the processor to determine an acceptable lower temperature or an acceptable reduction from sensed temperature at which the cooling stage will have ended.

8. A butt welding machine as in any of Claims 1 to 3, comprising a control means to provide a self-determining degree of heating of the pipe ends in contact with a heater plate, said control means employing parameters sensed and/or measured during the operation of the machine by sensing and/or measuring machines on the. machine.

9. A butt welding machine as in Claim 8, wherein ambient temperature sensing means, a timing device, and a linear transducer are provided to control the degree of heat applied to the pipe ends against the heater plate.

10. A method of controlling a butt welding machine as in Claim 9, comprising sensing by the linear transducer that the pipe ends have been brought into contact with the heater plate or urged against the heater plate to a required degree, sensing ambient temperature at the point that the linear transducer has sensed the required movement of the pipe ends, signalling the timing device to set a duration that is a function of the sensed ambient temperature to limit the duration of the heating phase to no more than is required by ambient temperature.

11. A method as in Claim 9, comprising sensing ambient temperature, employing sensed ambient temperature to set the temperature of the heater plate, and setting the timing device to be of fixed duration governed by the set temperature of the heater plate.

12. A butt welding machine as in any of Claims 1 to 3 and 8 and 9, comprising a means of measuring a bead formed on a pipe end and an associated timing device.

13. A method of controlling a butt welding machine as in Claim 12, comprising measuring a bead, sensing when the bead is of a required size, measuring by the timing device the time taken for the bead to reach the required size, the measured time being employed to set the duration of the heating phase of the pipe ends against the heater plate.

14. A method of controlling a butt welding machine as in any of Claims 1 to 3, 8 and 9, and 12, comprising sensing the duration of the dwell time, i.e. the time taken to retract the pipe ends from the heater plate, remove the heater plate from between the pipe ends and bring the pipe ends into direct contact, signalling the control means with the dwell time to add to the other sensed and/or measured parameters, to limit the duration of the cooling stage to a self-determined degree.

15. A method of controlling a butt welding machine as in any of Claims 1 to 3, 8 and 9, and 12, comprising measuring the linear movement of pipe ends away from the heater plate and the subsequent movement of the pipe ends into contact following removal of the heater plate, signalling the control means with the combined sensed movement to add to the other sensed and/or measured parameters to limit the duration of the cooling stage to a self-determined degree.

16. A method of controlling a butt welding machine as is herein exemplified in Examples A, B, C, D, and E.