Electrofusion fitting methods

Abstract

The invention provides improvements to electrofusion fitting methods that allow for continuity and repeatability of welds between an electrofusion fitting and a pipe lining (or stand-alone pipe). An electrofusion fitting for joining sections of lined pipe has heating elements configured to create at least one weld between the electrofusion fitting and a pipe lining, however prior to the weld step taking place the electrofusion fitting is heated and expands accordingly to ensure contact with the pipe lining. Preheating the electrofusion fitting also provides a predetermined starting temperature for the fitting and the lining which results in improved fusion cycle reliability. Furthermore, the need for clamps or support frames to support the electrofusion fitting in situ is removed, with corresponding reductions in cycle times, complexity, and hence cost.

Claims

1. A method of compensating for misalignment between two plastic pipe linings comprised in host pipes during a welding process, the method comprising inserting an electrofusion fitting into corresponding recesses in the ends of the plastic pipe linings, aligning the host pipes relative to one another, and heating corresponding portions of the electrofusion fitting to a first temperature lower than a melting point of the material of the electrofusion fitting, while the host pipes are held in place, to cause the portions of the electrofusion fitting to expand to fill the recesses, wherein the electrofusion fitting, once expanded, retains and supports itself during welding to the pipe linings.

2. The method according to claim 1, further comprising heating corresponding portions of the electrofusion fitting to a second temperature higher than the melting point of the material of the electrofusion fitting to weld the fitting to the pipe linings.

3. The method according to claim 1, further comprising performing a leak test between the electrofusion fitting and one or both plastic pipes through a channel extending at least partially through the electrofusion fitting or one or both pipe linings.

4. The method according to claim 3, wherein the leak test is performed before welding the fitting to the pipe linings.

5. The method according to claim 1, wherein the host pipes are held in place using clamps.

6. The method according to claim 1, further comprising welding the host pipes together.

7. The method according to claim 6, wherein the host pipes are welded together prior to preheating the electrofusion fitting.

8. The method according to claim 1, wherein heating to the first temperature comprises supplying electrical current to one or more heating elements integral to the electrofusion fitting.

9. The method according to claim 8, wherein heating to the second temperature comprises supplying electrical current to the same one or more heating elements as when heating to the first temperature.

10. The method according to claim 8, wherein heating to the second temperature comprises supplying electrical current to a different heating element as when heating to the first temperature.

11. The method according to claim 1, wherein the method comprises monitoring a temperature of the portions of the electrofusion fitting being heated.

12. The method according to claim 11, wherein the method comprises controlling the supply of electrical current to one or more heating elements responsive to the temperature of the portions of the electrofusion fitting to control the temperature of the portions of the electrofusion fitting.

13. The method according to claim 1, comprising forming the recesses in the ends of the pipe linings.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Aspects and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the following drawings (like reference numerals referring to like features) in which:

(2) FIG. 1 is a partial reproduction of FIG. 1 of the Applicant's earlier International Application Publication Number WO 2010/041016, showing a schematic sectional view of an electrofusion fitting according to the prior art;

(3) FIG. 2 is a schematic sectional view of an electrofusion fitting inserted into the end of a lined pipe in a weld process carried out according to an embodiment of an aspect of the present invention; and

(4) FIG. 3 illustrates the energy coupling into heating coils of an electrofusion fitting during an electrofusion weld process (a) without preheating the electrofusion fitting and (b) with preheating.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(5) As discussed in the background to the invention above, it is difficult to ensure that an effective and consistent fusion process is carried out when connecting lined pipes or the like. An embodiment of the present invention is described below, with reference to the electrofusion fitting illustrated in FIG. 2, which overcomes this problem with the prior art.

(6) An electrofusion fitting 201 is formed by a cylindrical sleeve of a thermoplastic material having heating coils 207a,207b disposed toward either end of the fitting 201. The electrofusion fitting 201 is shaped and sized to be inserted into the end of a lined pipe section 203a/203b and received in a recess 206a/206b in the end of the pipe lining 205a/205b. The heating coils 207a/207b are embedded in the outer surface of the fitting 201, so as to be adjacent to and facing an inner surface of the pipe lining 205a/205b, such that when provided with sufficient electrical power the thermoplastic material of the fitting 201 and of the lining 205a/205b in the vicinity of the coils melts and fuses together, thus creating circumferential or annular welds between the fitting 201 and the pipe lining 205a/205b.

(7) FIG. 2 shows the electrofusion fitting 201 at two distinct stages that occur prior to this electrofusion process taking place; note that the scales have been exaggerated for the purposes of illustration. On the left-hand side, the electrofusion fitting 201 has just been inserted into the recess 206a in the pipe lining 205a and abuts against a shoulder formed by said recess 206a. The outer diameter of the electrofusion fitting 201 is less than the inner diameter of the recessed pipe lining 205a and as a result there is a gap between the outer surface of the electrofusion fitting 201 and the pipe lining 205a in the region where the weld will be formed.

(8) It will also be realised that a gap between the electrofusion fitting 201 and the pipe lining 205a may be due to a misalignment between the pipe linings 205a, 205b in adjacent pipe sections 203a,203b, or specifically between the recesses 206a,206b. The gap might not be continuous or circumferentialin fact the electrofusion fitting might be in partial contact with the pipe lining 205a in the recess 206a.

(9) The existence of a gap means that while a weld might still be formed (although it is more likely that only a partial weld will be formed) the efficiency of the weld can be compromised, and there can be significant uncertainty about the quality of the weld particularly if the gap is relatively large. Accordingly, prior to the electrofusion process being carried out and in accordance with the invention, the heating coil 207a is employed to heat the electrofusion fitting 201 to a first temperature, which is lower than a melting point of the material of the electrofusion fitting 201, at which the electrofusion fitting 201 expands and as a result reduces or removes the gapas shown on the right-hand side of FIG. 2. This preheating step can therefore ensure that the electrofusion fitting 201 fills the recess 206b and ensures the surfaces of the electrofusion fitting 201 and the pipe lining 205b are in contact before the material is melted to actually form the weld.

(10) Note that it is possible to check that the electrofusion fitting has filled the recess and ensure that the surfaces are in contact before the weld takes place. By providing a channel 208 extending at least partially through the electrofusion fitting 201 or the pipe lining 205b, fluid access can be provided to a test region there between. If there is a tight fitting between the electrofusion fitting 201 and the pipe lining 205b, a leak test performed on the test region via the channel will confirm this and the welding step can be performed with confidence. If the leak test fails, the fit up can be remade (by further preheating or by reworking or replacing the electrofusion fitting) until a leak test is completed successfully. The test can also be performed, via the same channel, after the weld has taken place to test the integrity of the weld.

(11) By way of example, the preheating step might involve heating the electrofusion fitting to 50 C. for two minutes, and subsequently the welding step might involve heating the electrofusion fitting to 200 C. for five minutes.

(12) Using an electrofusion fitting to connect two sections of lined pipe is typically carried out prior to welding together the host pipes themselvesalthough the steps may be performed in any order. In practice, the host pipes can be aligned ready for welding and held in place, for example using clamps 209, prior to (and during) preheating the electrofusion fitting. In this way, any internal misalignment between the electrofusion fitting and/or the pipe linings can be compensated without losing external alignment of the host pipes. This provides for an improved external weld in addition to the improved internal weld. (As noted above, the steps may be performed in any order, e.g. the host pipes may be welded together even prior to preheating the electrofusion fitting).

(13) Furthermore, by preheating the electrofusion fitting 201 in this way, the electrofusion process by which the fitting 201 is welded to the pipe lining 205a/205b can start from a pre-determined temperature which means that the electrofusion process can be predictably and reliably performed. Much of the concern surrounding reliability of electrofusion welds stems from uncertainty around various parameters than can vary greatly from one process to the next. By providing a consistent start point for all electrofusion welding processes, continuity between subsequent electrofusion processes can be ensured. To this end, the temperature may be monitored as part of the electrofusion process.

(14) In addition, the preheating step avoids the need to provide internal physical support to the electrofusion fitting during the subsequent electrofusion process (for example, using a clamp or support frame) because the expanded fitting can fill the recess and therefore retain and support itself. The use of clamps or support frames is known to add complexity and extend the process cycle time, and as a result increase expense, without the increase in confidence that a satisfactory (and consistent) weld has been performed that the present invention provides. In short, the present invention reduces cost and complexity while increasing confidence in both the joining of the linings and of the host pipes themselves.

(15) Typically, a fusion cycle will be developed for a known set of conditions. For example it may be determined that, at an ambient temperature of 20 C., supplying a known electrical current to the heating coils for six minutes is sufficient for the thermoplastic material of the fitting 201 and of the lining 205a/205b in the vicinity of the coils to melt and fuse together effectively. However, in the field, the ambient temperature may for example be 6 C. in which case it is possible that the weld will not be formed effectively with only a six minute fusion cycle. One solution would be to have a calibration table or the like to refer to. However, the present invention provides a more elegant solution in which a predetermined starting temperature is set by preheating the electrofusion fitting (and optionally the pipe lining) which means that the actual parameters that have been approved or qualified for a particular operation can be reliably and repeatably delivered in the field, with predictable results. However, a calibration table or look-up chart might still be employed.

(16) As described above, the Applicant has also discovered that preheating the electrofusion fitting prior to performing the electrofusion step results in improved energy coupling into the heating coils. While the energy requirements of a single electrofusion process might only be reduced by a modest amounta pipelay operation for example might involve several hundred electrofusion fittings and so the energy saving benefits will be cumulative.

(17) FIGS. 3(a) and 3(b) illustrate the power consumption during a fusion cycle (a) without a preheating step and (b) with a preheating step. In this particular example, the initial power consumption can be seen to be approx. 75 W lower in the fusion cycle comprising the preheating step. Based on models the Applicant anticipates that in low temperature operations (where the starting temperature without preheat may be significantly lower than with preheat) and/or when employing larger electrofusion fittings, the difference in power consumption will be significantly magnified.

(18) It will of course be understood that while the present invention has been illustrated with reference to electrofusion fittings for joining lined pipe sections, such an electrofusion fitting can be employed to join standalone plastic pipes, or indeed to provide a plug or to blank off the end of a lined pipe section or standalone plastic pipe. Furthermore, while heating elements are described as embedded in a surface of the electrofusion fitting, the heating elements may be disposed elsewhere in the electrofusion fitting or even applied externally.

(19) The invention provides improvements to electrofusion fitting methods that allow for continuity and repeatability of welds between an electrofusion fitting and a pipe lining (or stand-alone pipe). An electrofusion fitting for joining sections of lined pipe has heating elements configured to create at least one weld between the electrofusion fitting and a pipe lining, however prior to the weld step taking place the electrofusion fitting is heated and expands accordingly to ensure contact with the pipe lining. Preheating the electrofusion fitting also provides a predetermined starting temperature for the fitting and the lining which results in improved fusion cycle reliability. Furthermore, the need for clamps or support frames to support the electrofusion fitting in situ is removed, with corresponding reductions in cycle times, complexity, and hence cost.

(20) Throughout the specification, unless the context demands otherwise, the terms comprise or include, or variations such as comprises or comprising, includes or including will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers.

(21) The foregoing description of the invention has been presented for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed. The described embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilise the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, further modifications or improvements may be incorporated without departing from the scope of the invention as defined by the appended claims.