IE902018A1 - "A process for lining a metal pipe" - Google Patents

Abstract

A process for lining a metal pipe is disclosed. The process involves initially cleaning the internal surface of the pipe using a honing device (15) having three abrasive blocks (18) 5 mounted on radially extending arms (17) at 120°C separation. The honing device is rotated and moved along the length of the pipe (10) to ensure that all rough surfaces are smoothed and that the internal dimensions of the pipe 10 are consistent along the length of the pipe. The debris is removed using a 10 wire brush (25) and then a liner (30) is pulled through the pipe, the liner being interference fitted within the pipe. An excess length of liner (30) is left at each end of the pipe for formation of a flare at each end. The flare is formed in two stages using a pre-flaring die and a final-flaring die. 15 The action of deforming the liner using the dies is carried out slowly with intermediate pauses in the pressing action. At the end of the pressing action of each die, both the liner and the die are cooled using liquid coolant.

Description

The present invention relates to a process for lining a metal pipe. More particularly, the invention relates to the lining of a metal pipe with a corrosion-resistant plastics material for protection of the pipe from corrosive fluids. At present, plastics materials used for lining include Polytetrafluoroethylene (PTFE), Perfluoro Alkoxyalkane (PFA), Perfluoro Ethylene-Propylene (FEP), Poly Vinylidene Fluoride (PVDF), or Polypropylene (PP). Of these materials, PTFE is generally preferred, mainly because it has a relatively wide temperature operating range of -29°C to 260°C.

The process for lining pipes with such materials is of critical importance because the lining will often be required to provide protection in aggressive environments, for example, for storage or distribution of corrosive chemicals such as Sulphuric Acid, possibly under vacuum. Further, there may be both thermal and pressure cycling. The process must ensure that there is continuity in the lining with no weaknesses or potential weakness and further, the lining should not collapse under vacuum conditions.

At present, processes for the lining of pipes generally involve adhering a lining material to the internal surface of - 2 the pipe. In United Kingdom Patent specification No. 2,077,179, a pressurised membrane and heat are used to adhere a PTFE lining. In United Kingdom Patent specification No. 2,193,289, the process involves treating the internal surface with an inhibitor and adhering a flexible sleeve to the internal surface. Because of the complexity of these processes, they are quite expensive and time-consuming. There is thus a need for a simpler and less expensive process for the lining of pipes for protection from aggressive chemicals in conditions of thermal and pressure cycling.

The present invention is directed towards providing such a process.

According to the invention there is provided a process for lining a metal pipe, the process comprising the steps of:15 clamping the pipe in position; honing the internal surface of the pipe by inserting a honing device on an elongate rod into the pipe, rotating the honing device and moving it along the length of the pipe as it is rotated, the honing device comprising at least two opposed abrasive blocks, each block being mounted on an arm which is spring-biased outwardly in a radial direction from a central support; - 3 brushing the internal surface of the pipe by moving a wire brush along the interior of the pipe, the wire brush having radially arranged bristles and having a diameter greater than the internal diameter of the pipe; clamping an end of a plastics liner which forms an interference fit within the pipe and pulling the liner through the pipe until there is an excess length of liner protruding from each end of the pipe, the excess lengths of liner each being sufficient to form a flare; pressing the liner against the internal surface of the pipe with a rawl expanding device; forming each excess length of liner into a flare by initially pre-flaring the liner by directing a preflaring die in co-axial alignment with the liner against the liner, pausing at an intermediate position of the pre-flaring die, at a final position cooling the preflaring die and the liner with liquid coolant, and removing the pre-flaring die; subsequently final-flaring the liner by directing a final-flaring die in co-axial alignment with the liner against the liner, pausing at an intermediate position of a final-flaring die and at a final position, cooling the liner and the final-flaring die with liquid coolant. - 4 Ideally the abrasive block is of stone composition.

In one embodiment, there are three abrasive blocks separated approximately 120°C apart in end view.

Preferably the steps of pre-flaring and final-flaring include 5 temporarily halting movement of the die at at least two intermediate positions of the die to avoid stress cracking of the liner.

Ideally, the pre-flaring die and the final-flaring die and the liner are each cooled by the liquid coolant for at least fifteen minutes.

The invention will be more clearly understood from the following description of some preferred embodiments thereof, given by way of example only with reference to the accompanying drawings in which:15 Figs. 1(a) and 1(b) are side and plan views, respectively of a pipe honing station for carrying out part of a process of the invention, and Figs. 1(c) and 1(d) are end and front, cross-sectional views, respectively of portions of the honing station 1 in use; - 5 Fig. 2(a) is a side view of a winch station and Figs. 2(b) and 2(c) are perspective and cross-sectional views respectively of portion of the winch station in use; Fig. 3(a) is a side view of a flare forming station and 5 Figs. 3(b) to 3(d) are side views showing portions of the flare forming station in use.

Referring to the drawings, and initially to Figs. 1(a) to 1(d), there are illustrated the initial steps of a process of the invention for lining a metal pipe. A pipe honing station 1 is illustrated in Fig. 1(a), the honing station 1 comprising an elongate rectangular support frame 2 on one end of which there is mounted a pipe clamp 3. Referring specifically to Fig. 1(c), the pipe clamp 3 comprises a rotary handle 4 controlling vertical movement of a V-Shaped jaw 5 at the end of a spindle 6 which engages a through-hole in a cross-bar 7. The winch station 1 also comprises a motorised chuck assembly 8 mounted for longitudinal sliding movement on rails 9 on the support frame 2.

The pipe honing station 1 is illustrated in use for honing or abrading the internal surface of a pipe 10. The pipe 10 has a fixed flange 11 at one end thereof, the other end having a stop ring 12. A loose flange 13 is shown adjacent the stop ring 12. The loose flange 13 is provided for ease of - 6 alignment of bolt-holes for installation of the pipe 10 onsite .

A rod 14 is engaged in the motorised chuck 8 and is illustrated supporting a honing device 15 for cleaning by abrasion the internal surface of the pipe 10. Referring specifically to Fig. 1(d), the honing device 15 comprises a central spring housing 16 secured to the end of the rod 14. Three rearwardly and outwardly directed spring-biased arms 17 at 120°C apart each support an abrasive block 18 of grinding stone composition.

To clean the internal surface, the pipe 10 is mounted on the support frame 2 and is clamped in position by the pipe clamp 3. The rod 14 is engaged in the motorised chuck 8 which is moved into a position on the rails 9 whereby the honing device is within the pipe 10 at the opposite extremity thereof.

The abrasive blocks 18 are spring-biased outwardly in a radial direction against the internal surface of the pipe by the spring arrangement in the central spring housing 16. The motorised chuck 8 is activated to rotate the rod 14 and thereby the honing device 15 so that the abrasive blocks 18 abrade the internal surface of the pipe 10. For carbon steel in most situations a rotation speed of 2,800 rpm is preferable. The motorised chuck 8 is moved longitudinally by a control mechanism, not shown, along the rail 9 so that the honing device 15 moves along the length of the pipe 10 until - 7 it reaches the near extremity to clean the entire internal surface of the pipe 10.

This part of the process of the invention is critical as it is absolutely essential that the internal surface of the pipe 10 is smooth and does not include any burrs, rust or foreign bodies. It is also very important that the internal diameter of the pipe 10 is consistent for the whole length of the pipe. It has been found that cleaning or abrading the internal surface of the pipe 10 in this manner is particularly effective and reliable.

When the internal surface of the pipe 10 has been cleaned with the honing device 15, it is mounted on a winch station 20, operation of which is illustrated in Figs. 2(a) to 2(c). Parts similar to those described with reference to the previous drawings are identified by the same reference numerals. The winch station 20 comprises an elongate rectangular support frame 21, on one end of which is mounted a motorised winch 22 for a steel cable 23. The steel cable 23 is supported on a transverse guide roller 24. A threaded rod 23(a) is secured to the end of the steel cable 23.

The pipe 10 is mounted on the winch station 20 in a similar fashion to the pipe honing station 1. When mounted, a wire brush 25 is secured to the end of the rod 23(a) within the pipe 10 at the opposite extremity from the motorised winch 22. - 8 The wire brush 25 has radially arranged bristles and has a diameter greater than the internal diameter of the pipe 10.

The motorised winch 22 is operated to draw the wire brush 25 along the length of the pipe 20 at least three times to ensure that debris deposited after the honing process is removed. Again, this is an important step in the process as any loose foreign bodies remaining in the pipe 10 could damage a liner, with serious consequences. Effective cleaning is provided by the fact that the diameter of the brush 25 is greater than the internal diameter of the pipe 10. In some cases, it is also advisable to blow debris out using a compressed air supply.

After brushing, a liner 30 is selected for the pipe 10. The liner 30 has an external diameter such that it has an interference fit inside the pipe 10. The length of the liner is the length of the pipe 10 plus an allowance for an excess at each end sufficient to provide a flare at each end. The liner 30 is inserted in the pipe 10 by drawing one end of the liner through the pipe using the motorised winch 22. This is achieved by initially cutting short, longitudinal slots 31 in one end of the liner 30 and pushing this end over a tapered collar 32. The threaded rod 23(a) runs through a through-hole in the tapered collar 32 and supports a stop 33 which holds the tapered collar 32 in position. A metal clamping ring 34 is pushed over the tapered collar 32 and the liner 30 to clamp the liner 30. The motorised winch 22 is then activated to pull the tapered collar 32 and therefore the liner 30 through - 9 the pipe 10. The pulling action acts to more securely clamp the liner 30 between the clamping ring 34 and the tapered collar 32. The liner 30 is pulled quite slowly through the pipe 10 to avoid damage as it is an interference fit within the pipe 10. When the liner 30 has been pulled through, the end with the slots 31 is cut off to leave an excess at each end of the pipe 10 for forming a flare.

Referring now to Figs. 3(a) to 3(d), the steps for forming a flare at one end of the liner 30 are illustrated. The process 10 is simply repeated for the other end of the liner 30. Again, parts similar to those described with reference to the previous drawings are identified by the same reference numerals. The pipe 10 is mounted at a flare forming station 40 which has an elongate rectangular support frame 41 and a pipe clamp 3. The pipe 10 is clamped at the flare forming station 40 in a similar manner to the other work stations. As stated above, the liner 30 is an interference fit within the pipe 10, however, because of the longitudinal pressure on the liner 30 during the flare forming process (which pressure would not be present when the pipe is in use) the liner 30 is pressed outwardly against the internal surface of the pipe 10 by a rawl expanding device 42. For further support of the pipe 10, a fixed flange clamp 43 is engaged behind the fixed flange 11. The flare forming station 40 comprises a hydraulic ram 44 connected to a control device, not shown. The hydraulic ram 44 includes a piston 45 which is arranged to - 10 support a flaring die at the end thereof. In this embodiment, two flaring dies are used, namely, a pre-flaring die 46 and a final-flaring die 47. The flare forming station 40 also includes a coolant delivery system 48 for delivery of liquid coolant to the liner 30 and the dies 46 and 47.

The rawl expanding device 42 is illustrated more clearly in Fig. 3(c) in which it will be seen that it comprises a threaded spindle 49 engaging a pair of opposed tapered collars 50 surrounded by three sets of three sectors which may be pushed outwardly in a radial direction by longitudinal movement towards each other of the tapered collars 50. This outward movement causes the expanding sectors 51 to press the liner 30 evenly against the internal surface of the pipe 10.

In operation, the rawl expanding device 42 is inserted inside the liner 30 and the threaded spindle 49 is rotated to press the liner 30 against the internal surface of the pipe 10. As stated above, the pipe 10 is secured in position by the pipe clamp 3 and the fixed flange clamp 43. The pre-flaring die 46 is heated to 350°C and is mounted at the end of the hydraulic piston 45, the piston 45 and the pre-flaring die 43 being in co-axial alignment with the pipe 10. The hydraulic ram 44 is activated to move the pre-flaring die 46 against the liner 30 which has a gradual contour to cause slight outward deformation of the liner. When the liner has been deformed to an extent of approximately one-third of the full deformation - 11 caused by the pre-flaring die 46, movement of the hydraulic ram 44 is stopped to allow setting of the liner 30. This pause is for approximately one minute and there is a similar pause at approximately two-thirds of the extent of movement of the piston 45. At the full extent of movement of the piston 45, when the end of the liner 30 has taken up the full shape of the pre-flaring die 46, the hydraulic ram 44 is stopped and coolant, in this case water, is delivered from the coolant delivery system 48 onto the die 46 for at least fifteen minutes. The intermediate pauses in the action of the piston 45 avoid stress cracking in the liner 30, and cooling of the liner 30 and the die 46 avoids relaxation of the deformation of the liner 30. This procedure is repeated with the finalflaring die 47 (also heated to 350°C) which brings the end of the liner 30 into the shape of a completely transverse flare as illustrated in Fig. 3(d). The final-flaring action is more critical than the pre-flaring action because there is a greater chance of a weakness developing in the liner material at the bend, which is right-angled. Generally, the final20 flaring die and the liner are cooled for slightly longer and there are longer pauses in the action than for the pre-flaring action.

The above procedure is repeated for the other end of the liner . - 12 It will be appreciated that the process of flaring the ends of the liner 30 is critical, not only because the liner may be damaged where it is deformed, but also because the flare must be tight up against the end flange or stop ring, whichever is the case so that the liner is tightly fitted within the pipe 10. It has been found that the intermediate pauses in the flaring actions and the relatively long cooling period have achieved this and thus, problems of collapse of the liner under vacuum and/or thermal cycling conditions are avoided.

What has been achieved by the process of the invention is the lining of a metal pipe in a relatively simple, inexpensive manner but with equal if not better results than if relatively complex processes involving adhesives or pressure membranes were used. It has been found that careful carrying out of this process ensures that there is a low chance of there being a weakness or fault in the liner and that the liner is fitted with an extremely small tolerance so that collapse will not occur under vacuum conditions. The process is relatively simple primarily because of the action of the honing device at an early stage in the process which eliminates potential problems in the remainder of the process.

The invention is not limited to the embodiments hereinbefore described but may be varied in construction and detail.

Claims (6)

1. A process for lining a metal pipe, the process comprising the steps of:clamping the pipe in position; 5 honing the internal surface of the pipe by inserting a honing device on an elongate rod into the pipe, rotating the honing device and moving it along the length of the pipe as it is rotated, the honing device comprising at least two opposed abrasive 10 blocks, each block being mounted on an arm which is spring-biased outwardly in a radial direction from a central support; brushing the internal surface of the pipe by moving a wire brush along the interior of the pipe, the 15 wire brush having radially arranged bristles and having a diameter greater than the internal diameter of the pipe; clamping an end of a plastics liner which forms an interference fit within the pipe and pulling the 20 liner through the pipe until there is an excess length of liner protruding from each end of the - 14 pipe, the excess lengths of liner each being sufficient to form a flare; pressing the liner against the internal surface of the pipe with a rawl expanding device; 5 forming each excess length of liner into a flare by initially pre-flaring the liner by directing a preflaring die in co-axial alignment with the liner against the liner, pausing at an intermediate position of the pre-flaring die, at a final position 10 cooling the pre-flaring die and the liner with liquid coolant, and removing the pre-flaring die; subsequently final-flaring the liner by directing a final-flaring die in co-axial alignment with the liner against the liner, pausing at an intermediate 15 position of a final-flaring die and at a final position, cooling the liner and the final-flaring die with liquid coolant.

2. A process as claimed in claim 1, wherein the abrasive block is of stone composition. 20

3. A process as claimed in claims 1 or 2, wherein there are three abrasive blocks separated approximately 120°C apart in end view.

4. A process as claimed in any preceding claim, wherein the steps of pre-flaring and final-flaring include temporarily halting movement of the die at at least two intermediate positions of the die to avoid stress cracking of the liner.

5. A process as claimed in any preceding claim, wherein the pre-flaring die and the final-flaring die and the liner are each cooled by the liquid coolant for at least fifteen minutes .

6. A process substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings .