Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F13/00—Inhibiting corrosion of metals by anodic or cathodic protection

Definitions

• the invention relates to a device for compensation of an alternating voltage which occurs between a medium and a metallic pipeline disposed in the medium, the pipeline being surrounded by a layer (mantle) of electrically insulating material.
• the normal operating current of the transmission line induces a voltage in the metal pipe.
• a voltage in the metal pipe For example, from a 400 kv line with an operating current of 1000 A at a distance of 50 m from the pipeline, an induced voltage of about 20 V/km can be obtained.
• a metal pipe of the above kind may, for example, constitute part of a long gas conduit, which is disposed in the ground and possibly partially also in water.
• a conduit of this kind is usually divided into sections with the aid of electri ⁇ cally insulating joints. The length of one section may vary from several kilometres up to several tens of kilometres. If a transmission line runs parallel to such a line for a distance of some length, induced voltages of a considerable magnitude may therefore occur.
• the invention aims to provide a device which, in a simple and advantageous manner, provides good protection against the risks of corrosion which, in pipelines of the kind mentioned in the introduction, are caused by alternating voltages induced in the pipelines.
• Figure 1 shows an example of a device according to the invention, wherein Figure la shows a general diagram of the device, Figure lb shows the transformer included in the device and the location of the transformer around the pipeline, and Figure lc illustrates the reduction of the voltage between the pipeline and the surrounding medium which can be obtained with the aid of the device shown in Figure la and Figure lb,
• Figure 2a shows how, in equipment according to the inven ⁇ tion, several transformers can be arranged along a section of the pipeline
• Figure 2b shows the reduction of the voltage between the pipeline and ground which can be obtained in this way
• FIG. 3 shows an alternative embodiment in which the trans ⁇ former included in the device is supplied from a power amplifier
• Figure 4 shows how a controllable transformer coupling can be used as an alternative for supply of the transformer of the equipment
• Figures 5a and 5b show an alternative method for sensing the voltage induced in the pipeline and for controlling the supply voltage to the transformer included in the equipment.
• Figure la shows an elementary diagram of a piece of equip- ment according to the invention.
• the figure shows a section 1 of a metallic natural gas conduit 1 disposed in the ground, the conduit being provided with an electrically insulating coating and being electrically insulated from adjoining pipe sections with the aid of electrically insu- lating joints 11 and 12.
• a measuring conductor 2 insulated from ground is arranged. This conductor may be arranged in the ground, on the ground or above the ground.
• the measuring conductor 2 is suitably arranged parallel to the pipeline and close to this.
• the length of the measuring conductor may be small in relation to the length of the section 1, but if desirable for obtaining a sufficient magnitude of the measured signal from the conductor, the length of the conductor may constitute a considerable part of the length of the section.
• the conduc ⁇ tor 2 may be grounded at a suitable point.
• the voltage u s induced in the conductor 2 is supplied to an instrumentation amplifier 3, the output signal of which is designated u' g . Due to the location of the measuring conductor 2 parallel to and close to the pipe section 1, the signals u g and u' become a good measure of the voltage induced in the pipe section by the operating current of the transmission line.
• the signal u' from the instrumentation amplifier 3 is supplied to an absolute value generator 4 and a phase detector 5.
• the absolute value generator 4 delivers a signal U which is proportional to the amplitude of the voltage u tract induced in the measuring conductor 2.
• the phase detector 5 delivers a signal ⁇ which is proportional to the phase difference between the signal u' and a reference voltage u ref *
• the reference signal is an alternating signal with the same frequency as the frequency in the transmission line which causes the voltages induced in the pipeline.
• the reference voltage can be obtained in the simplest manner from a local network 6, which belongs to the same power network as the above-mentioned transmission line and therefore has the same frequency as this.
• the signals U and ⁇ are supplied to a controller 7, which is adapted to supply an alternating voltage U ⁇ with controll ⁇ able amplitude and with controllable phase position.
• the controller 7 may consist of an alternating voltage converter, for example an intermediate link converter with a controllable rectifier supplied from the network 6, a direct voltage intermediate link, and a self-commutated inverter adapted to supply an alternating voltage with controllable frequency and hence with controll ⁇ able phase position.
• the voltage U is adapted to control the intermediate link direct voltage and hence the amplitude of the voltage U-,
• the voltage U-, generated by the controller 7 is supplied to a transformer 8.
• this transformer has an iron core 81 with an annular or rectan ⁇ gular cross section, which surrounds the pipeline 1.
• the iron core is suitably made of oriented sheet metal and can be made wound from one single coherent strip of sheet.
• the core may consist of a number of composite sheets with their planes perpendicular to the longitudinal axis of the pipeline.
• a primary winding 82 is applied on the core, the voltage U- ⁇ from the controller 7 being connected to this primary win ⁇ ding.
• the winding 82 and the controller 7 are designed such that suitable current and voltage levels are obtained.
• the winding 82 may consist of ten turns, the vol- tage U ⁇ have a root-mean square (RMS) value of the order of magnitude of 100 V, and the current through the primary winding of the transformer have an RMS of about 13 A.
• RMS root-mean square
• this EMF is in phase opposition to the EMF induced in the pipeline by the transmission line.
• the constant k in the expression above is chosen and adjus ⁇ ted in the control system such that the desired degree of suppression is obtained of the voltage induced in the pipe ⁇ line.
• the constant k can be determined by calculation, measurement or by practical tests.
• the signal from the measuring conductor 2 can be filtered in a band-pass filter tuned to the frequency of the transmission line, this in order to eliminate the effect of voltages occurring in the measuring conductor and emanating from other sources than the trans ⁇ mission line.
• Figure lc shows the voltage in the pipeline in relation to ground plotted against the distance x from one end of the line section.
• the section is assumed to have the length 1 and be grounded at its centre, for example through damage to the electrical insulation of the line.
• the curve designated a in the figure shows the voltage which would be caused by a transmission line extending in parallel with the line section along the whole of its length.
• the voltage assumes a maximum value ⁇ u at the end points of the section. If a transformer 8 according to the invention is arranged at the centre of the line section and adapted to induce in the pipeline an EMF of the magnitude u , the voltage will have an appearance as shown by the curve b.
• the maximum voltage between the pipeline and ground is reduced by a factor 2.
• FIG. 2a shows such an example where three transformers 8a, 8b and 8c are arranged evenly distributed along the length of the section. The primary windings of the transformers are connected in parallel to the controller 7 and are thus supplied with the voltage U-, .
• the curve c shows the voltage which is obtained between the pipeline and ground. As is clear, in this case a reduction of the maximum voltage by a factor of 4 is obtained.
• Figure 3 shows an alternative embodiment of the equipment according to the invention.
• the signal u' from the instru ⁇ mentation amplifier 3 is supplied to a sign-reversing power amplifier 9, the output signal U-. of which is supplied to the transformer 8.
• the sign reversal in the amplifier 9, the signal U- will be in phase opposition to the signal u" and by a suitable adjustment of the amplification factor of the amplifier, in principle a complete suppression of the voltages induced in the pipeline 1 can be obtained.
• the amplifier 9 may, for example, be a switched power amplifier of a kind known per se.
• FIG 4 shows how, as an alternative, a transformer coupling can be used for generating the supply voltage to the transformer 8.
• the coupling comprises two single-phase transformers 22 and 23.
• the transformer 22 has its primary winding connected to the phases S and T of the local network 6, and the transformer 23 has its primary winding connected between the phase R and the neutral line 0 of the network.
• the amplitude of the output voltage of each transformer is controllable, continuously or in steps.
• the transformers may, for example, consist of servo-motor operated adjustable transformers or of transformers which are provided with tap changers.
• the output voltage U A from the transformer 23 will have a phase shift of 90° in rela ⁇ tion to the output voltage U ⁇ from the transformer 22.
• the output voltage of each transformer can be varied from maximum amplitude in one phase position to maximum amplitude in the opposite phase position, the output voltage U-. may in a known manner be controlled arbi ⁇ trarily both with respect to amplitude and phase position within all four quadrants.
• the signals U and ⁇ are supplied to a control unit 21, which delivers control signals si and s2 to the actuators of the transformers.
• the control device may, for example, deliver such control signals si and s2 to the transformers that the output voltages thereof become:
• the control of the equipment according to the invention can be carried out in other ways than the one described above.
• the voltage between the pipeline and ground may be sensed at one or a plurality of points distributed along the pipeline.
• this is done by connecting instrumentation ampli ⁇ bombs 31, 32, 33 between ground and the points P12, P2, P3 on the pipeline.
• the output signals u' s ⁇ , U ' S 2' u 's3 °" ⁇ t * ⁇ e instrumentation amplifier are supplied to an optimization unit 34 (Fig. 5b) .
• This delivers a control signal s3 to the controller 7.
• the control signal s3 influences the amplitude and phase position of the voltage U-> generated by the controller, which voltage is supplied to the transformer 8.
• the optimization unit 34 may, for example, consist of a suitably programmed computer adapted to influence the vol- tage U- ⁇ via the control signal s3 in such a way in depen ⁇ dence on the measured signals that the risk of corrosion of the pipeline is minimized.
• the optimization unit may, for example, form the mean value of the measured signals and by successive attempts vary the amplitude and phase position of the voltage U until this mean value reaches a minimum.
• the quantity which is minimized can consist of that of the measured signals which has the greatest absolute value.
• the input signal or signals to the optimization unit 34 in Figure 5b need not, of course, be formed in the manner shown in Figure 5a.
• the input signals to the optimization unit may consist of the measured signal or signals from one or more measuring con ⁇ ductors 2 of the kind shown in Figure 1.
• Figure 2a shows how several transformers, supplied from a common voltage source, can be disposed along the pipeline section in question to achieve a greater reduction of the induced voltages.
• the same effect can be attained by placing several complete pieces of equipment of the kind shown in Figure la along the pipeline section.
• the measuring conductors 2 shown in Figures 1 and 3 con ⁇ stitute one way of forming a quantity which is a measure of the voltage induced in the pipeline. Also other ways are feasible. As mentioned, the voltage induced in the pipeline is, with respect to magnitude and phase position, directly dependent on the load current of the transmission line. Where it is possible and suitable to measure this current, it can be used directly as a measure of the voltage induced in the pipeline.
• the load current in the transmission line and hence the voltage induced in the pipeline, is a pure sine wave current without harmonics.
• harmonics may occur in the load current and induce alternating voltages of corresponding frequencies in the pipeline, which voltages, in the same way as the fundamental component, may cause risks of corrosion.
• the embodiment of the invention shown in Figure 3 will automatically entail a compensation also of induced harmonics, since the voltage U-, applied to the transformer constitutes a sign-reversed reproduction of the measured signal u g obtained from the measuring conductor 2. Harmonics in the induced voltage may, of course, be compen ⁇ sated for also in other ways.
• both the fundamental component and the harmonics in question may be separated out of the measured signal with the aid of the band-pass filter and be determined individually in amplitude and phase position, whereupon the desired voltage U-. for suppressing all the sensed components are synthetized in a suitable way with the aid of suitable electronic circuits.
• a cascade connection of an induction regulator and an adjustable transformer can be used, the induction regulator being used for controlling the phase position of the supply voltage to the transformer 8 and the adjustable transformer being used for controlling the amplitude of the voltage.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Pipeline Systems (AREA)
• Investigating Or Analyzing Materials By The Use Of Magnetic Means (AREA)
• Water Treatment By Electricity Or Magnetism (AREA)
• Testing Resistance To Weather, Investigating Materials By Mechanical Methods (AREA)
• Pinball Game Machines (AREA)
• Surgical Instruments (AREA)
• Massaging Devices (AREA)
• General Induction Heating (AREA)

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• 1992
  • 1992-03-05 SE SE9200671A patent/SE469987B/sv not_active IP Right Cessation
• 1993
  • 1993-03-04 CZ CZ942109A patent/CZ284713B6/cs not_active IP Right Cessation
  • 1993-03-04 DE DE69315858T patent/DE69315858T2/de not_active Expired - Fee Related
  • 1993-03-04 US US08/290,924 patent/US5541459A/en not_active Expired - Fee Related
  • 1993-03-04 AT AT93905736T patent/ATE161295T1/de not_active IP Right Cessation
  • 1993-03-04 EP EP93905736A patent/EP0728227B1/en not_active Expired - Lifetime
  • 1993-03-04 WO PCT/SE1993/000187 patent/WO1993018204A1/en active IP Right Grant
  • 1993-03-04 DK DK93905736T patent/DK0728227T3/da active

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