WO2010002269A1

WO2010002269A1 - In-line weld seam heat treatment method and apparatus with internal selective heating of the welded joint

Info

Publication number: WO2010002269A1
Application number: PCT/NO2009/000244
Authority: WO
Inventors: Leif MARKEGÅRD.; John Inge Asperheim
Original assignee: Efd Induction As
Priority date: 2008-06-30
Filing date: 2009-06-29
Publication date: 2010-01-07
Also published as: NO20082936L

Abstract

The present application relates to a method and an apparatus for in a high frequency welding (HFW) or electrical resistance welding (ERW) line to perform in-line seam heat treatment of an established welded joint on a pipe (1) made from roll- formed plate material, the welded joint being heated inductively from the exterior side of the pipe (1) downstream of a welding location. The method provides for selective heating (7) of the welded joint from the interior of the pipe (1) downstream of the welding location at least one heating zone, such heating from the interior, when operative, being performed simultaneously and in addition to the external heating (4, 5, 6). The apparatus comprises in addition to exterior heating means (4, 5, 6) downstream of a welding location also induction heating means (7) located inside the pipe (1) for selective operation to heat the welded joint from the interior of the pipe (1) downstream of the welding location at least one heating zone, said operation when selected being additional and simultaneous with operation of the external heating means (4, 5, 6).

Description

IN-LINE WELD SEAM HEAT TREATMENT METHOD AND APPARATUS WITH INTERNAL SELECTIVE HEATING OF THE WELDED JOINT

The present invention relates a method for in a high frequency welding (HFW) or electrical resistance welding (ERW) line to perform in-line seam heat treatment of an established welded joint on a pipe made from roll-formed plate material, the welded joint being heated inductively from the exterior side of the pipe downstream of a pipe welding location, as defined in the preamble of claim 1.

Further, the present invention relates to an apparatus for in a welding line to perform in- line seam heat treatment of an established welded joint on a pipe made from roll-formed plate material, said apparatus having induction means located downstream of a welding location to heat the welded joint inductively from the exterior side of the pipe, as defined in the preamble of claim 16.

Pipes produced according to API, ISO or DnV standards require for higher grades of steel a heat treatment as to simulate a normalizing heat treatment. This means that the entire heat affected zone (HAZ) from welding shall be heated above the Ac₃ temperature.

This is today done in-line by induction heating using coils located above the welding zone, one after the other, in sufficient length to heat through the wall. For wall thicknesses up to about mm this works well with a relative small temperature difference from outside to inside of the pipe wall. As wall thickness increases, a bigger part of the temperature difference through the wall has to be equalized by heat conduction. Too high normalizing temperature on the outside gives unwanted impact on the micro- structure as it causes grain growth. Properties of the steel as regards its strength and toughness are influenced negatively by increased grain size. It is therefore a relative small temperature difference between the maximum temperature on the outside and the inside temperature at the end of heating that can be considered as acceptable.

To obtain this, induction coil width and heating time have to be increased as maximum wall thickness is increased. Heat zone width is a result of coil width and heating time as heat is spread by conduction from the heated zone. The wider the resulting heat zone, the slower it cools down after heat treatment as the cooling is very much dependant of the heat soaking into the colder body of the pipe. Fast cooling after heat treatment also promote fine grain size. Due to heat radiation from the inside surface of the pipe there will be a stationary heat difference between the outside and inside of the pipe and this difference is increasing with wall thickness and starts to be significant for wall thicknesses above 10-15 mm.

When summing up these aspects, it is observed that as wall thickness increases, some disadvantages with the present outside seam heat treatment system become more predominant:

1. A resulting wide heat zone width

2. A long heat treatment zone length

3. Bigger difference in time at maximum temperature between outside and inside part of the pipe wall

Wide resulting heat treatment zone causes high energy need and relative slow cooling after finished heating. Slow cooling influence seam heat treatment quality and line length.

Long heat treatment zone means that a long length of pipe is affected when a stop in production occurs with a potential of producing large amount of scrap pipe. This is indeed a most serious issue from point of view of production efficiency and overall production cost, when the amount of manufactured pipe to be scrapped is substantial.

The third disadvantage is another serious issue that has impact on the quality since there is a difference in heat treatment conditions between the outside and inside of the pipe wall.

With such drawbacks related to current pipe production of a type as mentioned in the introduction, it has been an object of the present invention to provide a method and an apparatus in a welding line in order to substantially improve in-line seam heat treatment of an established welded joint on a pipe made from roll-formed plate material.

According to the invention, such improved heat treatment is provided through heating 5 the pipe from both its outside and its inside to produce more equal heat treatment conditions for the outside and the inside part of the pipe wall.

According to the invention, the method mentioned in the introduction is characterised in that it further comprises selective heating of the welded joint from the interior of the io pipe downstream of the welding location at at least one heating zone, such heating from the interior, when operative, being performed simultaneously and in addition to the external heating.

Further embodiments of the method appear from the attached sub-claims 2 - 15.

I₅

According to the invention, the apparatus mentioned in the introduction is characterised in that it further comprises induction heating means located inside the pipe downstream of the welding location for selective operation to heat the welded joint from the interior of the pipe at at least one heating zone, said operation when selected being additional 20 and simultaneous with operation of the external heating means.

Further embodiments of the apparatus appear from the attached sub-claims 17 - 51.

These and other features of the invention will also appear from the following descriptive is portion of the application with reference to the attached drawings, showing non- limiting examples of aspects of the invention

Fig. 1 is a sub-divided view of a part of the apparatus of the invention being related to heating from the interior of the pipe.

30

Fig.2 is a schematic drawing of a prior art apparatus for external heating of a pipe. Fig. 3 is a first embodiment of the apparatus of the invention.

Fig. 4 is a second embodiment of the apparatus of the invention.

Fig. 5 shows axially mutually aligned exterior and interior heating means.

Fig. 6 shows axially mutually offset exterior and interior heating means.

Figs. 7 - 9 show alternative circuits for powering heating coils of the external and internal heating means.

Fig. 10 shows a system to control the speed during heat treatment of the weld located in the heat treatment zone at a halt in production.

Fig. 11 shows behaviour of the apparatus of fig. 3 upon in-line operational halt.

Fig. 12 is a modified behaviour of that on fig. 11.

Fig. 13 shows behaviour of the apparatus of fig. 4 upon in-line operational halt.

Fig. 14 and 15 illustrate alternative embodiments of a wagon assembly with heating coil and power supply cables inside a pipe.

Fig. 16 illustrates a typical heating means with basic associated suspension means.

Fig. 17 is a side view of the embodiment of fig. 16.

Fig. 18 illustrates how an axially movable heating means is suspended from a crane like support.

Fig. 19 illustrates how a heating means which is movable away from the pipe radially and/or sideways is supported from a crane like, transversely movable support. Fig. 20 is a non- limiting example of a device for detecting and measuring the displacement angle when a weld seam is displaced from a reference plane.

5 Fig. 21 shows an initial part of means for operating a heating means inside a pipe.

Figs. 22 and 23 show two examples of a wagon assembly with heating coils and power supply cables for use inside a pipe. o Figs. 24 - 26 illustrate typical heating coils for heating the pipe from its interior.

Fig. 27 is a typical set-up of in-phase heating of the exterior and interior heaters.

Fig. 28 is a multi-turn coil. s

Figs. 29 and 30 illustrate two examples of a combined transformer and heating coil configuration.

Fig. 31 illustrates schematically a high level current transformer of coaxial type for useo with an induction coil.

Figs. 32 and 33 show planar and profiled coil configurations, respectively.

The present invention relates to a method and an apparatus for in a high frequency$ welding (HFW) or electrical resistance welding (ERW) line to perform in-line seam heat treatment of an established welded joint on a pipe 1 made from roll-formed plate material 1', 1". The roll-formed plated material 1% 1" is also indicated schematically in cross-section on fig. 1 downstream of forming rollers and "fin pass" rollers 2; 2', respectively. The welded joint 1'" is created using an inductive welder 3 with 0 subsequent sqeeze rollers 2", thereby creating the pipe 1 having the welded joint, as indicated on fig. 1. Subsequently to the welding operation, it is common in the art to subject the pipe to heating from the exterior side of the pipe 1 using induction means 4 located downstream of a welding location to heat the welded joint inductively from the exterior side of the pipe, as indicated on fig. 2. Fig. 2 thus illustrates the prior art.

The main novelty of the present invention resides in that in addition to exterior induction heating means, indicated by 5 and 6 on fig. 3 and by 8 on fig. 4, there are also induction heating means, indicated by 7 on fig. 3 and by 9 on fig. 4, located inside the pipe 1. The interior induction heating means 7; 9 are configured for selective operation to heat the welded joint 1'" from the interior of the pipe 1 at at least one heating zone. The operation of the interior induction heating means 7; 9, when selected, is additional and simultaneous with operation of the external heating means 5 and/or 6, or 8.

The induction heating means 7; 9 inside the pipe is controllably positionable to face a heating zone which is radially opposite to a respective heating location on the exterior of the pipe where the exterior heating means 6; 8 is located, as clearly understood from inspection of figs. 3 and 4, as well as fig. 5.

However, as indicated on fig. 6, the expert in the art will, based on the teachings of the present invention, appreciate that the induction heating means 7; 9 inside the pipe 1 could just as well be controllably positionable to face a heating zone which is axially shifted relative to a respective heating location on the exterior of the pipe occupied by the exterior heating means 6; 8.

Within the concepts of the present invention heating from the interior and the exterior of the pipe 1 is preferably made as in-phase heating, which implies that the exterior and interior heating means receives power being in-phase. Although the both heating means

5 and 6 could perform heating in-phase with the heating provided by the interior heating means 7, it is considered within the concept of the invention that just the heating means

6 and 7 are in-phase. In-phase operation also applies to the heating means 8 and 9 on fig. 4.

hi some applications, the heating from the interior and the exterior of the pipe 1 at an initial part of a heating period is carried out as in-phase heating or as out-of-phase heating. Further, in these and/ or other applications, heating from the interior and exterior of the pipe is made as in-phase heating just during a final part of the heating operation. It will be appreciated, with reference to figs. 3 and 4 that such co-operation is preferably related to the heating means 6, 7 and 8, 9.

Approximate, exemplifying length Ll of the prior art heating assembly shown on fig. 2 is typically 28 meters, whereas the in-line seam heat treatment apparatus of fig. 3, which has internal heating assistance, in an exemplifying embodiment has a length L2 being approximately 19 meters. The full in-line double side seam heat treatment of fig. 4 has in an exemplifying embodiment a length L3 being approximately 4.5 meters. It is thus readily appreciated that the present invention enables to reduce the length of the heating assembly, dependent on the type of the inventive apparatus which is selected. The examples given as regards lengths Ll, L2 and L3 indicate typical set-up values for the welding and subsequent heating pipe wall thickness of 2.54 cm (1 inch) at typical welding speed using induction welding.

hi order to enable in-phase heating of the pipe from the inside and outside, the exterior heating means 6; 8 and the interior heating means 7; 9 need to have co-operative power supply, as shown on fig. 7. The exterior heating means 6; 8 and the interior heating means 7; 9 are provided by means of respective induction coils 6'; 8' and 7'; 9' powered from one common power supply 10 and via respective transformers 11; 12 which are connected in series. A single temperature sensor 13 located downstream of the last external heater 6; 8 is provided to deliver a temperature signal to a temperature controller 14. The temperature controller 14 also receives a set temperature at input 14', and the controller 14 thereby is able to control power output from the supply 10.

The embodiment shown on fig. 8 provides for powering the heating coils 6'; 8' and 7'; 9' of the exterior heating means 6; 8 and the interior heating means 7; 9 not in-phase by having separate power supplies 15; 16 via respective transformers 11; 12. A temperature sensor 17; 18 located downstream of the last external heating means 6; 8 and the last internal heating means 7; 9, respectively is provided to deliver a temperature signal to a respective temperature controller 19; 20. The temperature controllers 19; 20 also receives a respective set temperature at input 19', 20', and the controllers 19; 20 are thereby able to control power output from the supply 15; 16, respectively.

5 A further embodiment of power supply to the exterior and interior heating means is shown on fig. 9. The embodiment is based on the embodiment of fig. 8. Based on temperature feedback from the sensors 17; 18, the controllers 19; 20 are able to control power pulse width and thereby effective current amplitude to the coils 6'; 8' and 7'; 9', respectively. Compensation capacitors 15'; 16' in the power supplies 15; 16 should be io tuned to give approximately equal resonance frequency of the coil/capacitor circuits. A two-way control line 21 provides for mutually controlling frequency and phase of the two power supplies 15; 16, so that the power delivered to the coils outside and inside the pipe 1 are in-phase.

i₅ A further modification of the circuits of figs. 8 and 9 is represented by fig.lO. The circuit shown is related to both the exterior and interior heating means. The output from the controllers 19; 20 may pass through a respective additional amplifier 19"; 20", if not included in the controllers. The output from the amplifier 19"; 20" represents a power set point or required power, which is delivered to the power supply 15; 16, as

20 well as being branched off at 22"" to a speed controller 22. The speed controller receives as an input 22' a set power as a function of pipe wall thickness. Accordingly, the controller 22 delivers via an amplifier 22" a speed set point 23'" related to movement drive means 23; 23, 27; and 28, 28' as will be further described with reference to figs. 11, 12 and 13, respectively. 5

The embodiments of figs. 9 and will be able to let the exterior heating means 6; 8 and interior heating means operate in-phase or out-of-phase, by virtue of the two-way link 21.

30 Thus, it will be possible for the interior heating means and the exterior heating means to cause the heating from the interior and the exterior of the pipe at an initial part of a heating period to be in-phase or as out-of-phase, dependent on set preferences. The exterior heating means 6; 8 is preferably configured to apply to the exterior side of the pipe 1 a heating power which is equal to or larger than heating power capable of being applied to the pipe by interior heating means 7; 9. hi case of larger power to the exterior heating means 6; 8, suitable heating power applied to the pipe by the interior heating means is in the range of 5% - 75% of heating power applied to the pipe by the exterior heating means.

Fig. 11 is provided to illustrate a situation when there is an operational halt at the welding station 3 or in the welding line. As seen from fig. 3, there is a plurality of heating means 5, 6 located one after the other exterior of the welded pipe 1 downstream of the pipe welding station 3 of the apparatus. The most downstream one of the heating means 6 or two or more of the most downstream ones of the heating means 6 are linked to drive means 23. The drive means is, upon an operational halt of the welding station, configured to be activated to move said one or more of the most downstream heating means 6 as a movable heater unit to an upstream location 24. The movable heater 6 is configured to heat while simultaneously being moved to said upstream location 24, and the movable heater unit will thereby perform a slow heat treatment of a specific length of the pipe which at said halt was below said plurality of heating means 5, 6.

Reciprocal movement means 25, 25' will upon said operational halt, before the operation and movement of the drive means 23 and thereby movement of said movable heater unit 6, pull the remaining heating means 5 radially away from a production line of the pipe 1, in order that the heating unit represented by the heating means 6 may pass by without being obstructed by the heating means 5. Said remaining heating means 5 are thereby disabled from heating the pipe. The drive means 23 is configured to return the movable heater unit 6 to its downstream normal position 26 upon completion of movement along said specific length (from position 26 to position 24). The reciprocal movement means 25, 25' will upon the return of the heater unit 6 to position 26 cause said remainder of the external heating means 6 to be moved radially back into heating position exterior of the pipe, as shown on fig. 3. The interior heating means 7 should be inoperative (power off) and stationary upon said operational halt. The drive means 23 is set to move the movable heater unit 6 upstream at a speed controlled to give a power being an inverse function of the square of the wall thickness or limited to 90% of the maximum deliverable heating power from the movable heater unit 6.

Although the preferred embodiment of this aspect of the invention leaves the interior heating means 7 stationary and without providing any heating, it may in another embodiment be considered to let the interior heating means 7 being configured to be moved upstream to the upstream location, and then back to the downstream normal position and during such movement aligned with said movable heater unit 6, as indicated on fig. 12. hi this context the interior heating means 7 is suitably mounted on a wagon or other supportive means, so as to be reciprocally movable inside the pipe, and this is symbolically represented by reference numeral 27 indicating means for moving the heating means 7.

The heater unit 6 and the interior heating means 7 are suitably moved upstream at a speed controlled to give a heating power being an inverse function of the square of the wall thickness or limited to 90% of the maximum deliverable heating power from the movable heater unit/ heating means 6; 7.

hi another embodiment, related to figs. 4 and 13 there is a plurality of inductive heating means 8; 9 located one after the other both on the outside and inside of the welded pipe 1 downstream of a welding station 3. In the fig. 13 embodiment it is intended to modify the heat treatment upon an operational halt in a welding process of the pipe or the welding line. Drive means 28; 28' will upon an operational halt of the welding line after power shut-down to the heating means 8; 9 be configured to move all heating means both outside and inside the welded pipe 1 downstream from a position 29 one full length of a set heat treatment zone to a downstream position 30. The drive means 28; 28' will upon restarted welding process and power-on to the heating means 8; 9 being configured to return the heating means outside and inside the pipe 1 to their respective upstream normal position 29 at a fraction of the welding speed. The interior heating means 7; 9 will suitably be located on at least one supportive wagon 31, e.g. as shown on fig. 14, or on a supportive beam, hi case of the wagon 31, it is configured to move said interior heating means inside the pipe, e.g. between positions as depicted on fig. 12 or fig. 13. In the embodiment of fig. 13, the distance of 5 movements will be far less than for the embodiment of fig. 12. hi fig. 14 references 7'; 9' denote the induction coils of the interior heating means 7; 9. A return conductor is indicated by 32, and a coaxial high current transformer is denoted by 33. A water cooled supply cable 34 is provided for delivery of power to the coil 7'; 9' downstream. A mechanical support 35 for the coil, any rollers and the transformer 33 is provided. 36 io denotes a pipe (like pipe 1) of the smallest cross-sectional dimension, and 36' denotes a pipe (like pipe 1) of the largest cross-sectional dimension, hi case of the large- dimension pipes 36', the wagon 31 is suitably provided with legs 37 having spring means 38 to be spring-loaded or lifting means 38 in order to keep the coils close to the inside wall of the pipe. The legs 37 are suitably provided with wheels 39 at their lower is end. 40 is representative of a space below the wagon where cuts cut off from the internal bead present after the welding process can lie without causing trouble for the passing of the wagon.

Fig. 15 is a variant of the embodiment shown on fig. 14. A bottom wagon is denoted by 20 41 in which cables 42 can be supported. Cables 43 are supportable by a support 44 and so is also the transformer 33.

As shown on fig. 16, the exterior heating means 5; 6; 8 are installed on wagons 45 which have a quick-lift drive means 46. The wagon 45 is attached to a frame 47 via its

2₅ upper part 45"', and two pairs of pivotable arms 45" link the upper and lower parts. The wagon 45 is in addition to be provided with the means 45'" having the possibility of transverse (sideways) movability by means of motorized drive means 48 relative to the fixing frame 47. The pipe 1 has limited sideways movability by means of rollers 49, 49'. The heating unit 5; 6; 8 with its coils 5'; 6'; 8' is tiltable relative to the lower part

30 45' of the frame 45 by means of a rotary drive 50, as shown on fig. 17, enabling a sideways tilt of ± α°. The value of the angle α is suitably 10°, although a higher value could apply, e.g. 20°, or even a smaller value than 10°. The wagon 45 also supports a coaxial high current transformer 51. Upstream and downstream rollers 52; 53 are provided to enable the heating means 5; 6; 8 to have a rolling contact with the pipe 1, instead of a damaging abrasive contact. A temperature sensor 54 of infra-red type is suitable located at the downstream end of the wagon. The temperature sensor is thus associated with the exterior heating means downstream thereof to enable control of delivered heating power from the respective heating means. Reference numeral 55 denotes a power cable.

It should be observed, with reference to the embodiments of figs. 11 and 12 that it is important to be able to move the heating means 5 radially away from the pipe 1 in order to let the heating means 6 pass unobstructed below. This will be further explained with reference to fig. 19.

However, the axially movable heating unit 6 will now first be briefly explained with reference to fig. 18. The dotted line 56 on fig 18, as well as on fig. 19 denotes the location of the wagon and quick-lift assembly shown on fig. 16 and represented by the reference XVI. The assembly XVI is hanging down from a crane like, fixed support 57 having an upright member 57' and a horizontal member 57". A bracket member 58 links the fixing frame 47 with the member 57" via supportive, axially extending beam 59 attached to the member 57" and rollers 60 which are rotary mounted on the bracket member 58. In order to move the assembly XVI with the bracket 58 and rollers 60 along the length of the beam 59, an underside of the beam 59 is provided with a gear rack 61 which engages a rotary gear 62 driven by a motor 63. It will be appreciated that the structure of fig. 18 applies also to the embodiment of fig. 13, thus to move the heating unit or means 8. Although just one support 57 is shown, it will be recognized that there will be a plurality of mutually spaced supports along the axial length of the beam 59.

On fig. 19 there is shown the same assembly XVI as just referred to above and with reference to fig. 16. Again, the dotted line 56 denotes the location of the wagon and quick-lift assembly shown on fig. 16 and represented by the reference XVI. The assembly XVI is hanging down from a crane like, fixed support 64 having an upright member 64' and a horizontal member 64". The fixing frame 47 is attached to the member 64". In order to move the assembly XVI away from the movement path of the axially movable heating device 6, it is necessary to lift the assembly XVI off the pipe 1 in radial direction, and then subsequently move the crane 64 and thereby the assembly XVI in a further radial direction or more precisely in a horizontal direction transversely s of the pipe, the upright member 64' thereby moving to a position denoted by 64"'. The upright member 64' of the support 64 is at a lower end fixedly attached to a wagon 65 which is movable on rails 66 via supportive wheels 67, 67'. In the example shown, the wheel 67' is a drive wheel driven by a motor 68 which has a gear 68' engaging a gear 67" on the wheel 67' via a drive chain 68". Other drive means may of course be io visualized. The rails 66 are suitably provided with an end stop 66'. The reference numeral 69 denotes a frequency converter/ power supply for the heating means 6, and also provides added weight to the wagon 65 to keep it on the rails 66. Although just one support or crane 64 is shown for simplicity, at least a pair of supports 64 will be required to support the heating means 5 and the related structure XVI.

I₅

Another aspect of the present invention is now to be explained with reference to attached fig. 20.

In order to be able to properly heat the weld seam 1'" if the weld seam 1'" is shifted 20 sideways from a reference plane 70 , the exterior heating means 5; 6; 8 should be tillable sideways by e.g. ± α° relative to the reference plane 70 in order to positionally adjust position the exterior heating means 5; 6; 8 relative to a default heating zone. The value of angle α is suitably 10° , although a larger angle value, e.g. 20°, or a smaller angle value than 10° is conceivable. The interior heating means would be able to be 2₅ controlled once any deviation from said reference plane is detected on the outside of pipe 1. In order to provide a simple means for detecting such deviation of the weld seam from a reference plane, the welding station is suitably provided with a paint spray unit or a paint roller unit (not shown) which is shifted e.g. 90° off the weld joint (weld seam). As indicated on fig. 30 the pipe 1 has a weld seam 1'" which is shifted an angle 30 α away from the reference plane 70. A support 71 is provided, the support having an upright member 71' and a horizontal member 71". The member 71" carries a roller 72 which is horizontal and is transverse to the pipe 1 and tangent to the top thereof. In the course of the welding of the pipe, a line of paint 73 is continuously applied to a side of the pipe 1 by said paint spray unit or paint roller, and the line is always applied at a fixed angle shift away from the weld seam, suitably 90°. The support 71 has an optical detector, suitably a camera 74 which views the side of the pipe 1 along a viewing plane 75.

In order to determine the angle by which the weld seam is offset from the reference plane 70, the optical unit 74 is movable in vertical direction by means of e.g. a screw drive 76 powered by a motor 77 from a level position of the diameter of the pipe to where the painted line is present, or vice versa. As an alternative to the embodiment shown, and as a currently preferred embodiment, it could be visualized that the camera 74 is stationary and has a centre viewing axis in plane 75 and with e.g. a viewing angle of 30 - 45°. Circuitry associated with the camera could then be able to determine where in a detected image the line appears and thereby determine the deviation angle α. However, it should be appreciated that in the apparatus of fig. 30 the optical unit or camera 74 should have its optical axis substantially coaxial with the diameter of the pipe to be measured. Therefore, downward or upward adjustability of the position of the camera by means of the screw 76 is important in order to have, as an outset, the optical axis of the camera or unit 74 coaxial with the diameter of the pipe to measures, irrespective of whether that diameter is large or small.

The description is now again finally focusing on the pipe interior heating aspects with reference to figures 1 and figs. 21 - 23. Initially, only a small part of fig. 1 was explained. As a repetition, 1' denotes a forming section , i.e. when a plate member is initially formed into a preliminary pipe shape, and 2 thereby represents forming rollers to create a last fin pass, and 2' denotes additional rollers or an alternative location of last fin pass, in particular if internal heating means are to be used. 78 denotes an impeder and 3 represents an induction coil to bring the walls of the weld "Vee" of the pipe 1 to welding temperature, and 79 denotes weld point at welding squeeze rolls 2". Fig. 21 shows part of an insert device to be introduced at least partly into the interior of the welded pipe, both upstream and downstream of the weld point 79. The device of fig. 21 comprises a bent pipe 80 of copper, water cooled power cables 81, one for each heating coil 7'; 9' inside the pipe 1, and further a umbilical which contains signal cables, auxiliary power cables, pressurized air hose etc. The cables have suitably a heat resistant textile sleeve to enable low frictional movement thereof inside the pipe 80. A support beam for the impeder and an internal bead cutter is denoted by 82. A space 83 is provided for the impeder, as well as a space 84 for an internal bead cutter 85 with a downstream scarfing tool 85'. An optional weight support wheel device 86 can also be provided. 87 denotes a telescopic tube which can be lengthened by a substantial length, e.g. 4.5 meters for the length example presented in fig. 4. Fixing points for cables are labelled 88, 89, and a tear-off connection or link for the power cables is labelled 90. Further, there is a provided a force sensor 91 and a spring loaded tear-off mechanism 92. The reference numeral 93 denotes a shaft pipe.

This part of the invention is now to be further explained with reference to figure 1, where 94 represents rotating brushes for centric bead parts location. Cables are labelled by 95 and a towing wire is labelled by 96. A telescopic connection is also provided, labelled 97. Further, in order to provide a pulling means, a winch 98 is provided. Interior heating coils have been labelled 7'; 9' in harmony with previous notations. It is noted that the interior heating means are supported by wheels 99 and that beams 101, 102 are associated with pivotable arms 100 and a cylinder/piston unit 103 in order to enable said coils 7'; 9' to be movable towards and away from the interior wall of the pipe 1. Rollers 104 are provided upstream and downstream of the heating units 7; 9, i.e. their coils 7'; 9' in order to avoid that the coils 7'; 9' will engage in abrasive contact with the inside wall of the pipe 1. Further telescopic connections 105 and 106 may be provided and a spring 107 may be provided to press a pair of wheels against the interior side walls of the pipe 1. Finally, a brake 108 is provided.

Figs. 22 and 23 are related to aspects of the interior heating means 7; 9, and may be reviewed in context of figs. 14 and 15. Details of the embodiment shown on fig. 22 are also shown on fig. 1, however substantially as a variant embodiment. On fig. 22 the interior heating coils have been labelled 7'; 9' in harmony with previous notations. It is noted that the interior heating means are supported by wheels 109, 109' and that beams 111, 112 are associated with pivotable arms 1 and a cylinder/piston unit 113 in order to enable said coils 7'; 9' to be movable towards and away from the interior wall of the pipe 1. Rollers 114 are provided upstream and downstream of the heating units 7; 9, i.e. their coils 7'; 9', in order to avoid that the coils 7'; 9' will engage in abrasive contact with the inside wall of the pipe 1. The wheels 109; 109' will be in pairs, so that a total of four wheels should be used. The wagon carrying the coils is effectively supported by structure related to reference numerals 109 - 114. The wheels 109; 109' should, in order to have the centre of gravity of the overall wagon structure (including the coils) well below a centre-line through the pipe 1, in particular a pipe 1 of the largest diameter, have a weight of at least 60% of the weight of the overall wagon structure. Springs 115 are suitably provided so that the rollers 114 will have a firm abutment against the inside wall of the pipe 1 even when the pipe bends due to heating of a small zone on at least one side thereof. As indicated on fig. 22, the downstream wheels 109' to the right on the drawing are suitably provided with a steering mechanism (not shown) which is so constructed that it will automatically keep the wagon structure at the detected angle reference within ± α° of the vertical reference plane 70 (see fig. 20) . The wagon structure for use inside the pipe is suitably equipped with a measuring device (not shown) capable of measuring the default or current value of the angle relative to the reference plane. Such measurement could e.g. be based on a gyro or pendulum principle. Further, the measuring device could make use of the measurements provided by the camera 74 on the outside of the pipe 1 and which are transferable to proper angular position control means inside the pipe. As described in connection with figs. 1, 14 and 15, the coils 7'; 9' are caused to be lifted using the device 113, which is suitably a pneumatic jack, although it could be electrically or hydraulically operated. Rotating brushes 94, as also shown on fig.l are present upstream of the upstream set of wheels 109 (99 on fig 1), i.e. the set of wheels to the left on the drawing in order to move possible pieces and fragments cut off from the pipe 1 by the internal bead cutter 85' into bottom centre of the pipe interior.

A further variant of the embodiments of figs. 1 and 22 is shown on fig. 23. The shaft pipe 93 (see fig. 21) is pivotally linked at 93' to a longitudinal beam 116. The beam has upstream and downstream legs 117; 117' depending from the beam with wheels 8; 118' at the lower end resting against the bottom interior of the pipe 1. An arm 119; 119' extends from said wheels 119; 119' to a lower end of a jack 120; 120', and the upper end of the jack is pivotally attached to the beam 116. In order to press rollers 121; 121' into contact with the top interior region of the pipe 1, a further arm 122; 122' extends between the lower end of the jack 120; 120' and a bracket 123; 123' and will push the rollers 121; 121' upwards if the jack 120; 120' contracts. Further brackets 124, 125 are provided carrying rollers 126, 127 which are spring biased by means of springs 128, 129 on the beam in order to let the rollers bear against the top inside of the pipe 1. The coils 7'; 9' and their related power supplies, denoted by 7"; 9" are linked to the roller supports 123, 123', 124, 125, respectively and as shown. Thereby, a defined gap between the top inside wall region of the pipe 1 and the coils 7'; 9' is created. By virtue of its structure, the wagon which includes and also carries the heating mean 7; 9 will be rotationally stiff and with said pivotable link 93' to the shaft pipe 93.

The internal heating means 7; 9 being located on at least one wagon inside the pipe is movable inside the pipe by enabling movement of the wagon(s) relative to the welded pipe. A force sensor could be provided, e.g. at location 91, to detect when a pulling force by the wagon(s) on a support beam 82 for the impeder 78 and scarfing tool 85' inside the pipe reaches a threshold level. Alarm means are suitably connected to said sensor means to trigger the welding line to stop at such a situation.

In the case as shown on figs. 11 - 13 where the internal heating means are located on wagon(s) so that the wagons(s) and the pipe are mutually movable upon an operational fault, the power cables will normally pass to the internal heating means 7; 9 from an upstream end of the pipe through or along the support beam 82 for the impeder 78 and scarfing tool 85' inside the pipe. The cables at a downstream end of the beam 82 may form a disconnectable power, water and signal link 90 with the heating means located on the wagon.

Finally, some aspects related to coil configuration will be briefly presented in order to visualize possible alternatives. The interior heating means 7; 9 will suitably comprise coil structure of planar type (as indicated on fig. 32 or of profiled type as indicated on fig. 33, selected from the group of: a) heating coil 130 with core 130', and with return conductor 131, the coil 130 being located between the welded seam 132 and the return conductor 131 as shown on fig. 24, b) heating coil 130 with core 130' and with parallel return conductors 133, 134 through secondary heating coils 135, 136 being located on either side of the welded seam 132 inside the pipe 1, as shown on fig. 25, and c) hair-needle type coil with heating pair coils 137, 138 with respective cores 137% 138 along each side of the welded seam 132, as shown on fig. 26.

Fig. 27, being a variant of the embodiment shown on fig. 25, and depicting heating both from the inside and outside of the pipe 1 is a typical configuration of induction heating coils with current through the coil 139 (corresponding to 6'; 8') and coil 140 (corresponding to 7'; 9') being synchronized and in-phase, as also depicted on fig. 7. The core is denoted by 139'; 140', respectively. Return conductor is denoted by 139"; 140" , respectively.

Fig. 28 is an example of a multi-turn coils 141; 142 with cores 141'; 142' (the coils configuration being useable as exterior coils 6'; 8' and/ or interior coils 7'; 9'), such as a two-turn coil made as a split-return coil. In practise, multi-turn coils are not so preferred because they raise difficulties due requirements of electrical insulation and the environment in which the coil is to be used, such as in a hot zone, in a moist or water vapour atmosphere or in an atmosphere of oil fumes.

The coil or coils structure used have suitably a core structure of laminated iron or iron powder in an insulating matrix. The coil or coils may be of a one-turn coil or a multi- turn coil type.

The transformer which is used could be configured as an integrated part of the induction coil as shown on fig. 29, where there is provided a primary winding 143, a core 144 and a combined secondary winding and coil 145.

In an alternative, the transformer used with the coils of the invention is a high level current transformer configured with a transformer primary winding 146, a torodially shaped core 147 and a first secondary winding part 148, as shown on fig. 30. The second part of the secondary winding forming the active coil part (such as e.g. 5'; 6'; 7'; 8'; 9') is indicated as the coil conductor 149. The core of the active coil part is denoted 150.

5 Fig. 31 depicts an embodiment which makes use of a high-current type of coaxial transformer 151 which has a primary winding 152, a core 153 and a secondary winding 154, 154', the winding part 154 being the inner part and the winding part 154' being the outer part of the secondary winding. The winding part 154 functions as a return lead from an active induction coil 155, the coil 155 having a core 155'. The winding part I₀ 154' functions as an onward lead to the coil 155.

The general planar type of coil as shown on fig.32 is labelled as 156 with a core 156' and is the most common one, and such a planar type of coil is commonly in use for external heating of a welded pipe.

I₅

A profiled type of coil 157 with a core 157' and a recessed part 157" of the coil 157 to face a weld seam, and as shown on fig.33, is suitable to cause a more uniform heating zone and will thus be suitable not only for external heating, but also for heating of the pipe 1 from its interior. A reason why the profiled type of coil would in particular be

20 suitable for interior heating of the pipe is that scarfing inside a pipe (i.e. scarfing off excess or unwanted weld seam parts) is difficult to perform and also to control by means of visual inspection through use of e.g. camera. A suitably profiled type of the coil 157, i.e. having said recess 157", would therefore not risk colliding with any excess or unwanted weld seam parts that have not been properly removed through use

2₅ of the scarfing tool 85'.

Claims

1. A method for in a high frequency welding (HFW) or electrical resistance welding (ERW) line to perform in-line seam heat treatment of an established welded joint on a pipe (1) made from roll-formed plate material (1', 1"), the welded joint (1"') being heated inductively from the exterior side of the pipe downstream of a pipe welding location (3), the method further comprising selective heating of the welded joint (T") from the interior of the pipe (1) downstream of the pipe welding location (3) at at least one heating zone, such heating from the interior, when operative, being performed simultaneously and in addition to the external heating.

2. The method according to claim 1, wherein the heating internally of the pipe (1) is made at a heating zone which is radially opposite to a respective heating location on the exterior of the pipe (1).

3. The method according to claim 1, wherein the heating internally of the pipe (3) is made at a heating zone which is axially shifted relative to a respective heating location on the exterior of the pipe.

4. The method according to claim 1, 2 or 3, wherein heating from the interior and the exterior of the pipe (1) is made as in-phase heating.

5. The method according to claim 1, 2 or 3, wherein heating from the interior and exterior of the pipe (1) is made as in-phase heating during a final part of the heating.

6. The method according to claim 1, 2 or 3, wherein the heating from the interior and the exterior of the pipe (1) at an initial part of a heating period is carried out as in-phase heating or as out-of-phase heating.

7. The method according to any one of claims 1 - 5, wherein the heating from the exterior and from the interior of the pipe is provided through use of respective inductive coils (6'; 8'; and 7'; 9') powered from respective transformers (11; 12) connected in series.

8. The method according to any one of claims 1 - 6, wherein the heating from the exterior and from the interior of the pipe (1) is provided through use of respective inductive coils (6'; 8'; and 7'; 9') powered by respective and separate converter (15; 16) having associated transformer (11; 12).

9. The method according to any one of claims 1 - 8, wherein heating power applied to the pipe (1) from its exterior side is equal to or larger than heating power applied to the pipe from its interior side.

10. The method according to any one of claim 1 -8, wherein heating power applied to the pipe (1) from its interior side is in the range of 5% - 75% of heating power applied to the pipe from its exterior side.

11. The method according to any one of claims 1 - 10, wherein the downstream heat treatment of the welded joint comprises the use of a plurality of heating means located one after the other exterior of the welded pipe downstream of a pipe welding station (3), wherein the most downstream one (6) of the heating means or two or more of the most downstream ones (6) of the heating means upon an operational halt in the welding process continues to heat the pipe while simultaneously being moved to upstream location (24) downstream of the welding station (3) as a movable heater unit, wherein the remainder (15) of the heating means prior to such movement of said movable heater unit are moved away from a production line of the pipe (1) and thereby disabled from heating the pipe (1), said movable heater unit (6) thereby being enabled to carry out a slow heat treatment of a specific length of the pipe (1) which at said halt was below said plurality of heating means, wherein the movable heater unit (6) upon completion of said travelling of said specific length is caused to return to its downstream normal position, whereupon said remaining external heating means (5) are moved back into heating position exterior of the pipe, and wherein said heating means (7) located interior of the pipe being selected to be inoperative and stationary upon said operational halt.

12. The method according to any one of claims 1 - 10, wherein the downstream heat 5 treatment of the welded joint comprises the use of a plurality of heating means (5; 6) located one after the other exterior of the welded pipe (1), wherein the most downstream one (6) of the heating means or two or more of the most downstream ones (6) of the heating means upon an operational halt in the welding process continues to heat the pipe while simultaneously being moved to an upstream location (24)

I₀ downstreams of a pipe welding station (3) as a movable heater unit (6), wherein the remainder (5) of the heating means prior to such movement of said movable heater unit (6) are moved away from a production line of the pipe (1) and thereby disabled from heating the pipe, said movable heater unit (6) thereby being enabled to carry out a slow heat treatment of a specific length of the pipe which at said halt was below said plurality is of heating means, wherein the movable heater unit (6) upon completion of said travelling of said specific length is caused to return to its downstream normal position (26), whereupon said remaining external heating means (5) are moved back into heating position exterior of the pipe (1), and wherein said heating means (7) located interior of the pipe (1) being caused to move simultaneously and positionally aligned with said 0 movable outside heater unit (6) to the upstream location and then back to the downstream normal position.

13. The method according to claim 11 wherein said movable heater unit is moved upstream at a speed controlled to give a power being an inverse function of the square 5 of the wall thickness or limited to 90% of the maximum deliverable power from the movable heater unit (6).

14. The method according to claim 12 wherein said movable inside and outside heater units (7; 6) are moved upstream at a speed controlled to give a power being an inverse

30 function of the square of the pipe wall thickness or limited to 90% of the maximum deliverable power from the movable heater units.

15. The method according to any one of claims 1 - 9, wherein downstream heat treatment of an established welded joint further comprises the use of a plurality of heating means (8; 9) located one after the other exterior as well as interior of the welded pipe (1), and to modify the heat treatment upon an operational halt in the welding process of the pipe, wherein the method further comprises, after power to the heating means has been switched off, movement of all exterior (8) and interior (9) heating means downstream one full length of a heat treatment zone to a downstream position (30), and wherein the heating means exterior (8) as well as interior (9) of the pipe (1) after power-up to the heating means and restarted welding process being caused to return to an upstream normal position (29) at a fraction of the welding speed.

16. An apparatus for in a welding line to perform in-line seam heat treatment of an established welded joint on a pipe (1) made from roll-formed plate material, said apparatus having induction means (6; 8) located downstream of a welding location (3) to heat the welded joint inductively from the exterior side of the pipe (1), the apparatus further comprising

- induction heating means (7; 9) located inside the pipe (1) downstream of the welding location (3) for selective operation to heat the welded joint from the interior of the pipe (1) at at least one heating zone, said operation when selected being additional and simultaneous with operation of the external heating means (6;8).

17. The apparatus according to claim 16, wherein the induction heating means (7; 9) inside the pipe (1) is controllably positionable to face a heating zone which is radially opposite to a respective heating location on the exterior of the pipe (1).

18. The apparatus according to claim 16, wherein the induction heating means (7; 9) inside the pipe (1) is controllably positionable to face a heating zone which is axially shifted relative to a respective heating location on the exterior of the pipe (1).

19. The apparatus according to claim 16, 17 or 18, wherein the interior heating means (7; 9) and the exterior heating means (6; 8) are connected to co-operative power supply means (11; 12; 15; 16) enabling in-phase heating of the pipe (1) from the inside and outside.

20. The apparatus according to claim 16, 17 or 18, wherein the interior heating means (7; 9) and the exterior heating means (6; 8) are connected to co-operative power supply means (11; 12; 15; 16) configured to enable heating of the pipe (1) from the inside and outside in-phase during a final part of the heating.

21. The apparatus according to claim 16, 17 or 18, wherein the interior heating means (7; 9) and the exterior heating means (6; 8 are connected to co-operative power supply means (11; 12; 15; 16) configured to cause the heating from the interior and the exterior of the pipe (1) at an initial part of a heating period to be in-phase or as out-of-phase.

22. The apparatus according to any one of claims 16 - 20, wherein the exterior heating means (7; 9) and the interior heating means (6; 8) are provided by means of respective induction coils (7'; 9'; 6'; 8') powered from one common power supply (10) and via respective transformers (11; 12) which are connected in series.

23. The apparatus according to any one of claims 16 - 20, wherein the exterior heating means (7; 9) and the interior heating means (6; 8) are provided by respective induction coils (7'; 9'; 6'; 8') , the coils each powered by a respective and separate converter (15; 16) having associated transformer (11; 12).

24. The apparatus according to any one of claims 16 - 23, wherein the exterior heating means (7; 9) is configured to apply to the exterior side of the pipe (1) a heating power which is equal to or larger than heating power capable of being applied to the pipe (1) by interior heating means (6; 8).

25. The apparatus according to any one of claim 16 - 23, wherein heating power applied to the pipe by the interior heating means (7; 9) is in the range of 5% - 75% of heating power applied to the pipe by the exterior heating means (6; 8).

26. The apparatus according to any one of claims 16 - 25, wherein a plurality of heating means (5; 6) are located one after the other exterior of the welded pipe (1) downstream of a pipe welding station (3) of the apparatus, wherein a most downstream one (6) of the heating means or two or more of the most downstream ones (6) of the

5 heating means are linked to drive means (23), wherein said drive means (23) upon an operational halt of the welding station (3) is configured activated to move said one or more of the most downstream heating means (6) as a movable heater unit (6) from a downstream location (26) to an upstream location (24) downstream of the welding station (3), wherein said movable heater unit is configured to heat while simultaneouslyo being moved to said upstream location (24), said movable heater unit (6) thereby performing a slow heat treatment of a specific length of the pipe which at said halt was below said plurality of heating means (5; 6), wherein reciprocal movement means (25, 25') upon said operational halt is configured to pull the remaining heating means (5) prior to such movement of said movable heater unit (6) away from a production line ofs the pipe (1) and thereby disabling said remaining heating means (5) from heating the pipe (1), wherein the drive means (23) is configured to return the movable heater unit (6) to its downstream normal position (26) upon completion of movement along said specific length, wherein said reciprocal movement means (25, 25') thereupon is configured to move said remainder (5) of the external heating means (5, 6) back into0 heating position exterior of the pipe (1), and wherein said interior heating means (7) are inoperative and stationary upon said operational halt.

27. The apparatus according to claim 26, wherein said drive means (23) is set to move the movable heater unit (6) upstream at a speed controlled to give a power being ans inverse function of the square of the pipe wall thickness or limited to 90% of the maximum deliverable power from the movable heater unit (6).

28. The apparatus according to any one of claims 16 - 25, wherein a plurality of heating means (5; 6) are located one after the other exterior of the welded pipe (1)0 downstream of a pipe welding station (3) of the apparatus, wherein a most downstream one (6) of the heating means or two or more of the most downstream ones (6) of the heating means are linked to drive means (23), wherein said drive means (23) upon an operational halt of the welding station (3) is configured activated to move said one or more of the most downstream heating means (6) as a movable heater unit (6) from a downstream location (26) to an upstream location (24) downstream of the welding station, wherein said movable heater (6) is configured to heat while simultaneously 5 being moved to said upstream location (24), said movable heater unit (6) thereby performing a slow heat treatment of a specific length of the pipe (1) which at said halt was below said plurality of heating means (5; 6), wherein reciprocal movement means (25; 25') upon said operational halt is configured to pull the remaining heating means

(5) prior to such movement of said movable heater unit (6) away from a production lineo of the pipe and thereby disabling said remaining heating means (5) from heating the pipe (1), wherein the drive means (23) is configured to return the movable heater unit

(6) to its downstream normal location (26) upon completion of movement along said specific length, wherein said reciprocal movement means (25; 25') thereupon is configured to move said remainder (5) of the external heating means (5; 6) back intos heating position exterior of the pipe (1), and wherein said interior heating means (7) being configured to be moved upstream and then return to said downstream location (26) aligned with said movable heater unit (6) upon said operational halt.

29. The apparatus according to claim 28 wherein said movable inside and outside0 heater units (7; 6) are moved upstream at a speed controlled to give a power being an inverse function of the square of the pipe wall thickness or limited to 90% of the maximum deliverable power from the movable heater units.

30. An apparatus according to any one of claims 16 - 25, wherein the apparatuss comprises a plurality of inductive heating means (8; 9) located one after the other both on the outside and inside of the welded pipe downstream of a welding station (3), and means to modify the heat treatment upon an operational halt in a welding process of the pipe, wherein drive means (28, 28') upon an operational halt of the welding line after power shut-down to the heating means are configured to move all heating means (9; 8)0 both inside and outside the welded pipe downstream one full length of a set heat treatment zone from an upstream position (29) downstream of the welding station (3) to a downstream position (30), and said drive means (28, 28') upon restarted welding process and power-on to the heating means being configured to return the heating units (9; 8) inside and outside the pipe (1) to their respective upstream normal positions (29) at a fraction of the welding speed.

5 31. The apparatus according to claim 30, wherein said internal heating means (9) are located on at least one supportive wagon (31) or supportive beam being configured to return said internal heating means (9) to its upstream normal positions (29) positionally aligned with said exterior movable heater unit (8) and at a fraction of the welding speed. Q

32. The apparatus according to claim 31 , wherein said wagon being axially movable inside the pipe (1; 36; 36'), and wherein the wagon is provided with a plurality of spring-loaded (38) legs (37) having wheels (39) or rollers for movable contact with the inside wall of the pipe (1). s

33. The apparatus according to any one of claims 16 - 29, wherein said internal heating means (7; 9) being located on at least one supportive wagon (31) or supportive beam.

34. The apparatus according to claim 33, wherein said wagon (31) is axially movable inside the pipe (1; 36; 36') or the pipe (1; 36; 36') is movable relative to the wagon (31),Q and wherein the wagon (31) is provided with a plurality of spring-loaded (38) legs (37) having wheels (39) or rollers for movable contact with the inside wall of the pipe (1; 36; 36').

35. The apparatus according to any one of claims 31 - 34, wherein the supportives wagon or beam of the interior heating means is provided with a rotational position tracking device to locate the heating means at the welded seam.

36. The apparatus according to any one of claims 16 - 35, wherein the interior heating means (7; 9) comprises an induction coil structure of profiled type having a weld seam0 adapted recessed portion.

37. The apparatus according to any one of claims 16 - 35, wherein the interior heating means comprises coil structure of planar or profiled type selected from the group of:

- heating coil (130, 130') with return conductors (131), the coil being located between the welded seam (132) and the return conductors (131),

5 - heating coil (130; 130') with return conductors (133, 134) through secondary heating coils (135, 136) being located on either side of the welded seam (132) inside the pipe (1), and

- hair-needle type coil with a heating pair (137, 138) along each side of the welded seam (132).

10

38. The apparatus of claim 36 or 37, wherein the coil has a core structure of laminated iron or iron powder in an insulating matrix.

39. The apparatus according to claim 36, 37 or 38, wherein the coil is a one-turn coil or is a multi-turn coil.

40. The apparatus according to any one of claims 22 or 23, wherein said transformer is high level current transformer configured as a coaxial transformer.

20 41. The apparatus according to any one of claims 22 or 23, wherein the induction coil is a part of the transformer secondary winding.

42. The apparatus according to any one of claims 16 - 41, wherein a temperature sensor (13; 17; 18) is associated with the exterior heating means (6; 8) downstream thereof to

2₅ enable control of delivered heating power from the respective heating means.

43. The apparatus according to any one of claims 16 - 42, wherein said internal heating (7; 9) means being located on at least one wagon (31; 41) so as to enable movement of the wagon(s) relative to the welded pipe, wherein a force sensor (91) is provided to

30 detect when a pulling force by the wagon(s) on a support beam (82) for an impeder (78) and scarfing tool (85') inside the pipe reaches a threshold level, and wherein alarm means are connected to said sensor means to trigger the welding line to stop.

44. The apparatus according to any one of claims 16 - 43, wherein the internal heating means are located on wagon(s) so that the wagons(s) and the pipe are mutually movable upon an operational fault, wherein power cables to the internal heating means pass from an upstream end of the pipe through or along a support beam (82) for an impeder (78) and scarfing tool (85') inside the pipe, and wherein said cables at a downstream end of the beam (82) form a disconnectable power, water and signal link (90) with the heating means located on the wagon.

45. The apparatus according to any one of claims 16 - 44, wherein the exterior heating (6; 8) means are installed on wagons which are tiltable ± α° relative to a reference plane in order to positionally adjust the exterior heating means relative to a default heating zone, and wherein any tilting is controlled by an angular position detector (74) which is configured to detect and adjust for angular deviations of the exterior heating means relative to a reference applied to the exterior wall of the pipe axially, near the welding point, e.g. a painted, longitudinal stripe .

46. The apparatus according to any one of claims 16 - 45, wherein the wagon is tiltable ± α° relative to a reference plane, e.g. a vertical plane, in order to positionally adjust the interior heating means (7; 9) relative to a default heating zone, and wherein any tilting is controlled by the said angular position detector (74) located on the outside of the pipe.

47. The apparatus according to claim 45 or 46, wherein the angle α is in the range of 5°- 20°, preferably having a value of 10°.

48. The apparatus according to any one of claims 16 - 47, wherein induction coils of the interior heating means are individually liftable by means of a spring device, and wherein each interior heating means is associated with at least one roller device (114; 121; 121'; 126; 127) to enable the heating means to have a rolling contact with the inside wall of the pipe, said roller device defining a fixed gap between the active coil (7'; 9') of a heating means (7; 9) and the inside of the pipe wall (1).

49. The apparatus according to any one of claims 16 - 48, wherein the interior heating means being supported by a wagon or wagons provided with a mechanism (46) for rapid movement of the interior heating means away from the inside wall of the pipe.

50. The apparatus according to any one of claims 16 - 49, wherein induction coils of the exterior heating means are individually pressed towards the exterior wall face of the pipe by means of a spring device, and wherein each exterior heating means is associated with at least two roller devices (52; 53) to enable the heating means (5; 6; 8) to have a rolling contact with the exterior surface of the pipe, said roller devices defining a fixed gap between the active coil (5'; 6'; 8') of a heating means (5; 6; 8) and the outside of the pipe wall (1)..

51. The apparatus according to any one of claims 16 - 50, wherein the plurality of exterior heating means each or jointly being provided with a mechanism (46) for rapid lifting of a respective one or all of the exterior heating means radially away from the exterior surface of the pipe.