The present invention concerns a device for measuring corrosion in metal structures in accordance with the preamble of claim 1, and a method of assembling the device to a metal structure in accordance with the preamble of claim 6.

Background

When using the Field Signature Method (FSM) in monitoring corrosion development in metal structures, such as pipelines or process equipment in processing plants, an array of electrically conductive pins are attached to the surface of the metal structure to be monitored. The pins are typically arranged in mutual distance of two to three times the wall thickness of the metal structure to be monitored. During corrosion monitoring, a measurement is performed by applying an induced current to the respective pins in the array, whereupon the voltage response is measured and compared to a reference voltage response, e.g. a voltage response pattern taken from an initial state without any corrosion. The corrosion monitoring is performed by taking measurements at selected intervals for a prolonged period of time, e.g. daily or weekly measurements during several months or years. An increased voltage response at a certain point in time indicates increased electrical resistance, e.g. caused by surface corrosion in the metal structure. The rate of change in voltage response between consecutive measurements can provide information about how fast the corrosion is developing. Moreover, the location of the corrosion can be determined from voltage response changes in one or more parts of the pin array. The accuracy or resolution of the measurements is determined by the distance between adjacent pins, and the resolution decreases by increasing distance between the pins.

However, the FSM principle is subject to certain drawbacks. Firstly, the assembly is typically performed on site, e.g. on the outer surface of a pipe in a refinery, and requires about two days to complete. Secondly, every single pin in the array, e.g. of 128 pins, is welded to the pipe wall and connected to the source of current. This manual assembly is prone to errors and there is a risk that one or more pins are not properly connected electrically conductive to the pipe surface, thus producing an incomplete monitoring of the pipe. WO 00/50907 Al describes a sensor device for monitoring of defects such as erosion and corrosion on metal structures. An articulated support means is provided with a row of pins in contact with the metal structure to be monitored and connected to a cable terminal via electric conductors. Voltage is applied to electrodes on the surface of the metal structure, whereupon voltage drop is measured between respective pins. The articulated support means allows monitoring of curved metal surfaces and other non-flat surfaces. Object

Accordingly, there is a need for a device of this kind that enables a faster assembly on site at the structure to be monitored. There is also a need for a device that enables a more reliable monitoring of the metal structure.

The invention The objects above are obtained by a device in accordance with the characterizing part of claim 1, and a method in accordance with the characterizing part of 6. Further advantageous features appear from the respective dependent claims.

Definitions

The term "stud" is in this context meant to define an electrical connection between the metal surface to be monitored and the electrical connection to a control and measuring device. Accordingly, the term "stud" includes, but is not limited to, electrically conductive pins or similar.

The term "array" is in this context meant to describe a pattern of objects (including studs) arranged in a predetermined layout, regular, partly regular as well as irregular. With respect to the apertures in the respective sheets, the term "array" is meant to identify the general layout of the apertures.

The term "sub array" is in this context meant to define a predetermined arrangement of a subset of studs with regard to the total number of studs in an assembly, such as 8 studs out of 128. Each stud in the sub array is arranged electrically conductive to a common electrical interface with respect to the sub array. The term "modular array" is meant to include all sub arrays of studs within the array as a whole.

In a first embodiment, the device according to the present invention comprises two flexible sheets, a first electrically insulating sheet provided with numerous through apertures in a desired calculated pattern, and a second flexible sheet provided with electrically conductive studs, arranged in a similar patterns as the apertures in the first flexible sheet, and in electrical connection with individual electrically conductive wires. The wires are arranged to be connected to a controller and to a voltage source.

In a second embodiment, the studs are not included in the second flexible sheet but are attached to the metal surface separately after the first flexible electrically insulating sheet has been applied to the metal structure to be monitored, whereupon the flexible modular array second sheet including electrically conductive wires can be applied upon the first sheet with the respective apertures in alignment with the affixed studs.

In a third embodiment, the second sheet is omitted, wherein the wiring is provided by a separate wiring assembly, where individual wires can be attached in an electrically conductive manner to the respective studs.

The first sheet is made of an electrically insulating flexible sheet material which is sustainable at temperatures ruling at the assembly site, for example a rubber material. The second sheet is made of a flexible material which per se is electrically insulating. Non-limiting examples of a flexible sheet substrate are polychlorinated biphenyls (PCB), glass fibre and carbon fibre. The components described in general above can be designed and prefabricated, ready for fast assembly at the metal structure to be monitored. The present invention allows reduction of assembly time from several days as with the prior art devices, down to a few hours. The stud and controller arrangement also enables corrosion monitoring with a high reliability which heretofore as not been possible. The invention is described in further details below with reference to several embodiments.

Detailed description

In the following, the present invention is described in further detail by reference to example embodiments illustrated by drawings, wherein

Fig. 1 is a perspective view of a part of the device in accordance with the invention assembled on a pipe,

Fig. 2 is a schematic illustration of the device in accordance with the invention assembled at a pipe,

Fig. 3 is a cross-section through a pipe showing a first embodiment of the present invention, Fig. 4 illustrates a cross-section of the framed upper part of Fig. 3 of the first embodiment, Fig. 5 is a drawing similar to Fig. 3 of a second embodiment,

Fig. 6 is a drawing similar to Fig. 4 of the framed upper part of Fig. 5 of the second embodiment. First embodiment

Now referring to Fig. 1, a first preferred embodiment is described. A pipe section is illustrated at reference numeral 100, and an electrically insulating first sheet material 200 is wrapped around a substantial part of the periphery of the pipe 100, leaving a gap 202 extending along the longitudinal axis of the pipe 100. The first sheet 200 is attached to the pipe 100 by a first attachment means (not illustrated). A second sheet material 300, denoted as conductive sheet, second sheet or modular array sheet 300, is wrapped around the pipe 100, on top of the electrically insulating first sheet material 200 and attached to the pipe 100 by a second attachment means (not illustrated). The modular array sheet 300 is provided with numerous studs 400, arranged in numerous sub arrays R (Fig. 1 and 2) in electrical connection with respective wires 500. The studs are arranged to be connected electrically conductive to the pipe 100. Accordingly, the studs 400 are arranged in a pattern comprising sub arrays R. Each sub array R of studs 400 comprises numerous studs 400 arranged at a mutual substantially equal distance. The respective studs in a sub array R are connected with electrically conductive wires (illustrated at 500 in Fig. 2). In the example embodiment shown in Fig. 1, each row or sub array R consists of a total of 8 studs. Further, the modular array sheet 300 comprises in the illustration about 20 rows or sub arrays R. The components comprising one modular array sheet provided with numerous sub arrays provided with electrically conductive wires is also denoted as a stud array module. An assembly may comprise one or more such stud array modules.

Figure 2 is a schematic representation of the device according to the present invention in an assembled state, as described in further detail below. One stud array module indicated in general by reference numeral 302 is wrapped around the electrically insulating first sheet 200. The stud array module 302 comprises numerous sub arrays R of studs. Each stud 400 is connected with a controller 600 via electrically conductive wires 500. The wiring of the remaining sub arrays R are omitted to simplify the illustration. The controller 600 and its function is in general known from the prior art and is not discussed in further detail here. However, in a preferred embodiment every single wire 500 in the arrangement is connected individually to individual interfaces within the controller, wherein the controller 600 is provided with executable algorithms that enables determination of the location of the respective studs. Now referring to Figure 3, a schematic cross-section of the assembly of Figure 2 is shown, where the wiring has been omitted for clarity sake. Accordingly, the arrangement illustrated in Figures 1- 3 shows numerous sub arrays R of studs arranged in a mutually equal distance about the periphery of the pipe 100, where each sub array R is arranged with their respective longitudinal axis coaxially with the pipe 100. It should be noted that this arrangement is not obligatory, and the respective sub arrays R can be arranged with their longitudinal axis at an angle with the longitudinal axis of the pipe 100. The respective sub array angles can be the same or different.

Figure 4 illustrates a cross-section of the framed part of Figure 4. A stud, indicated generally by reference numeral 400, is attached in an electrically conductive manner to the outer surface of the pipe 100. The stud 400 is welded into a contact area 101 with satisfactory electrical conductivity, formed in the pipe surface. The contact area 101 can be provided by grinding the outer surface of the pipe to remove rust or other deposits that may impair the electrical connection between the monitored pipe and the stud. Moreover, the stud 400 is extending through an aperture 201 formed in the electrically insulating first sheet 200 and through an aperture 301 formed in the modular array sheet 300, the latter being superimposed on the electrically insulating first sheet 200 with their respective apertures 201 and 301 formed in a similar arrangement and fixed in an aligned manner. An electrically conductive wire 500 provided on the modular array sheet 300 is arranged adjacent to the stem 401 of the stud 400, within the aperture 301 in the array sheet 300. A connection means is provided to ensure electrical connection between the stud 400 and the wire 500. Here, the connection means comprises a first nut 402 and a first washer 403 arranged about the stem 401, between the modular array sheet and the pipe 100, wherein the nut is in a threaded connection with the stem 401 (outer thread of the stem 401 is indicated by reference numeral 406 in Figure 4). Similarly, a second washer 404 and a second nut 405 are arranged in an electrically conductive manner about the stem 401 of the stud 400, but superimposed on the modular array sheet 300 and the wire 500. Accordingly, an electrical connection between the stud 400 and the wire 500 is in this embodiment obtained by tightening the nut 405 and establish electrical connection between the pipe 100, the first nut 402, the first washer 403 and finally the wire 500.

Assembly of preferred embodiment The preparation and assembly of the preferred embodiment described above can be performed as described in the following. Array modules 302 are prefabricated at the production facility by determining the designed array pattern and number of studs, and providing through apertures 301 in a flexible modular array sheet 300, in the desired number and pattern. Electrically conductive wires 500 are arranged adjacent to the respective apertures 301. Then, studs 400 are arranged in the respective apertures 301 and attached to the array sheet 300 including the connection means 402, 403, 404, 405. This can be performed by inserting a stem 401, with the first nut 402 and first washer 403 attached to the stem as described above, through the respective apertures 301 in the array sheet 300, and then attaching the stud 400 to the modular array sheet 300 by tightening the second washer and nut 404, 405. Moreover, electrically insulating first sheets 200 are provided with apertures 201 in a similar number and pattern as the aperture arrangement in the second sheet 300.

In this manner, prefabricated array modules and insulating sheets can be provided in a large number of different patterns and array densities, ready for fast and simple assembly on site.

On the site where a metal structure, e.g. a pipe, is going to be monitored with respect to corrosion, the electrically insulating first sheet 200 is wrapped around an exemplary pipe 100 and fixed by a first attachment means (not illustrated). Then, a grinding tool is used to remove rust and deposits in the respective contact areas 101 in the pipe 100, in alignment with the apertures 201 in the electrically insulating first sheet 200. Alternatively, the metal surface is cleaned before applying the electrically insulating first sheet 200. Then, an array module 302 is wrapped around the electrically insulating sheet 200 and fixed by a second attachment means (not illustrated), with all of the apertures in the respective sheets aligned. Then, every single stud 400 is attached in an electrically conductive manner to the pipe 100 by welding with a welding tool known per se. Electrical connection between pipe 100 and wire 500 is secured by tightening the second nut 405 of the respective stud 400, whereupon the wires are connected to the controller 600. The assembled device may now be tested by applying current to the respective stud 400 from the controller 600. Since the studs 400 preferably are provided with an individual connection with the logics in the controller 600, the exact position of faulty studs can be provided from the test procedure. This testing can be performed at all times and can even produce an alarm to personnel to issue a warning about need for maintenance or repair of faulty studs. Technical effect

From the description above it should be evident to the person skilled in the art that the composition of the device in accordance with the present invention and its assembly and operation on the site being monitored enables a faster assembly on site: the assembly time can be reduced from about two working days down to a couple of hours. Moreover, the individual wiring arrangement enables assembly of a measurement device with high quality from reliability testing of every single stud after assembly. This reliability is even maintained through normal operation as well.

Accordingly, the novel device described above exhibits substantial technical effects that have not been obtained until now.

Second embodiment

A second embodiment (not part of the invention) is illustrated in Figures 5 and 6. While Figure 5 is similar to Figure 3, Figure 6 illustrates a partially assembled stud. In this embodiment the electrically insulating first sheet 200 as described in the first embodiment above is wrapped around the pipe 100 with the sheet apertures 201 aligned with clean contact areas 101 provided in the outer surface of the pipe 100 and fixed with an attachment means. Then, individual studs 400 are inserted trough the apertures 201 and welded to the respective contact areas 101 in the pipe surface.

After a desired number of studs 400 has been attached in an electrically conductive manner to the pipe 100, an array sheet 300 (second sheet) with a similar array of apertures 301 and wiring 500 is lowered and superimposed on the electrically insulating first sheet 200, whereupon electrical connection between pipe 100 and wiring 500 is obtained by tightening the attachment means as described above. Finally, the wiring is connected to the controller and the assembly is ready for testing as described above. This second embodiment can be applied when the array sheet material is sensitive to heat from the stud welding process or heat from the operated (monitored) pipe. Accordingly, the second embodiment allows for use of more expensive array sheet material but may require more time to complete the assembly process on site since the studs must be handled and attached individually during assembly. Third embodiment

In a third embodiment (not part of the invention), the electrically conductive second sheet 300 is omitted and replaced by a set of wires provided with apertures. The assembly of the electrically insulating sheet 200 and studs 400 is as described above for the second embodiment. However, instead of superimposing an array sheet 300 on the electrically insulating first sheet 200, an a wiring array having wire ends provided with apertures is superimposed on the electrically insulating first sheet 200, whereupon electrical connection between pipe 100 and wiring 500 is obtained as described for the second embodiment above.

Modifications In an assembly, the number of electrically insulating first sheets 200 does not necessarily correspond to the number of modular array sheets 300. Accordingly, an assembly can comprise more, equal to, or fewer modular array sheets 300 than electrically insulating first sheets 200. Moreover, the electrical connection means to secure electrical connection between wire 500 and stud 400 is not limited to the exemplified nuts and washers 402, 403, 404, 405, and the person skilled in the art may easily replace the nuts and washers by a clamping means or similar.