WO2000079242A1

WO2000079242A1 - Device and method for measuring corrosion

Info

Publication number: WO2000079242A1
Application number: PCT/NO2000/000211
Authority: WO
Inventors: Per Olav Gartland
Original assignee: Per Olav Gartland
Priority date: 1999-06-18
Filing date: 2000-06-16
Publication date: 2000-12-28
Also published as: AU6740100A; NO993035D0; NO993035L; NO313022B1

Abstract

Method for measuring corrosion or erosion inside metal pipelines, wherein a material (weight loss coupon) (20) is placed at a measuring site for a time, to be exposed to the conditions at the measuring site. The coupon (20) is collected and the corrosion degree and/or corrosion rate will be determined. A transportation unit (1) is led through a pipeline, and one or more weight loss coupon(s) (20) united on a carrier (12) with one or more magnets (19), is (are) deposited from the transportation unit. The carriers are secured to the pipeline wall at defined positions. The invention further includes a device for carrying out the method for measuring corrosion inside metal pipelines. The device includes a transport unit (1) arranged to be led through a pipeline exposed to corrosion. The transport unit (1) is arranged to carry one or more carriers (12) for weight loss coupons, the carrier carrying one or more magnets, and includes a deposition unit (4), for depositing carriers (12) at defined positions along the pipeline. The unit further includes a collection unit (4) for collecting the weight loss coupons after a defined measuring period.

Description

Device and method for measuring corrosion.

The present invention concerns a method and a device for carrying out the method, according to the preamble of claim 1 and 2, respectively.

Background

Known pipelines, mostly used for transportation of fluids undersea, are made of carbon manganese steel. Fluids includes in this connection, gas or liquid, or a mixture of these. The fluids are in many cases corrosive, and therefore there is a need for measuring the amount of corrosion in a pipeline, or measuring the effect of it. Corrosiveness may either be measured by measuring the corrosion-rate more or less continuously, monitoring the corrosion, or by measuring the effect of corrosion, by measuring the remaining wall thickness by inspection.

Inspection is carried out by means of so-called "intelligent pigs", being technical equip- ment, that is to be sent through the pipe, to measure and record the wall thickness/corrosion attack through the whole length and circumference of the pipeline, by means of magnetic or acoustic methods. Examples of such pigs are given in US 4123847 and US 2338307. The problem with this method is that it is very expensive, and often, several years pass by between every inspection of this type, if it is used at all. The accuracy is also somewhat limited, so that it may be difficult to decide the development of corrosive attacks, even after several subsequent pig-inspections with years between.

Corrosion monitoring may be carried out by means of at least two methods, intrusive and non-intrusive. One method demands that a foreign body is brought in contact with the fluid in the pipe, through a port, this is intrusive. The foreign body may be, and/or comprise many possible devices, from weight loss coupons, to the most advanced electrochemical measuring devices. In this connection, a weight loss coupon means any element that may be used for measuring weight loss upon weighing or thickness reduction, alteration in ohmic resistance, or other well-known techniques. US 4603113 shows the use of weight loss coupons. The problem concerning some of these methods, is that they demand advanced electronics and stable electricity supply and signal transmission, while others demand frequent exchange of measuring units/weight loss coupons. The result is that these methods are not very useful for pipelines at sea or uncivilized regions, because it is problematic to get close to the pipe. The other method, none-intrusive, uses principles based on ohmic potential, for example the Felt Signature Method (FSM), ultrasound or methods based on radioactivity. These methods do not demand replacement of probes, but have requirements for stable electricity supply and signal transmission. This method will therefor also be problematic for use in pipelines at sea or outside of civilized regions. Some methods, specially FSM, are still used to a certain degree. The use has, however, been somewhat limited, due to high costs and technical complexity.

With all known methods for measuring corrosion in pipelines, it is a problem that choice of position and installation of equipment, must be performed before the pipeline is deposited. This equipment can not be moved, if it should be desirable to measure corrosion at another position of the pipe. In pipelines already placed at sea, or outside of civilized regions, there are presently no satisfactory methods for installing equipment for measuring corrosion.

Object

The main object of the present invention is to provide a system for measuring corrosion or erosion of pipelines, which is reliable, providing easily interpreted results, and that may be used at different random positions in a pipeline. Another object of the invention is that it should have reasonable cost for manufacturing and use, and that it should be used in both new and existing pipelines with minimal adjustments.

The invention

The object of the invention is achieved with a method according to the characterizing part of claim 1, and a device according to the characterizing part of claim 2. Further advantages are stated in the dependent claims.

The new measuring system comprises a transport unit, and at the least one carrier. The transport unit is a plug or "pig" which is familiar to a person skilled in the art, for cleaning pipelines. The plug or transport unit is sent into the pipeline through so-called plug-locks, which exist on most pipelines, at least in the petroleum industry. It has collars in the front and the back, so that it, at any time, fills the inside of the pipeline completely, and follows the flow through the pipeline. The carrier comprises weight loss coupons, used to record corrosion and erosion.

The whole device, comprising both transport unit and carrier can be manufactured in all nonmagnetic materials, for example plastic and nonmagnetic steel. Example

In the following, a preferred embodiment of the invention will be described with reference to the figures, where

Figure 1 shows a longitudinal section through a transportation unit according to the invention, moving to the right,

Figure 2 shows a section along line I-I in Figure 1 , facing the rear end with regard to the movement direction,

Figure 3 shows a carrier according to the invention, from above, and Figure 4 shows a section along line II-II in Figure 3.

The transportation unit 1 comprises 5 main parts. A housing 2 at the leading end, containing different measuring instruments, a device 3 measuring distance, a deposition / collection unit 4, and a housing 5 at the back, comprising a rotating magazine 6. The housings 2, 5 are connected with each other through poles or bolts 7. The transport unit 1 is additionally provided with three collars, one in the front 8, and two in the back, 9, 10. The collars bear closely against the inside of a pipeline, where the corrosion is to be recorded. They are sufficiently flexible to slide over carriers 12, without damaging these.

As area of corrosion will not necessarily be consistent along the whole of the circumference of the pipeline, it is important to control where the carriers 12 are deposited. There- fore it is an advantage that the transportation unit 1 is shaped to have the same orientation along the longitudinal axis, during the whole transportation, with regard to the carriers 12. This may be solved simply by having a sufficiently low centre of gravity, but it may also be necessary for monitoring and active correction of variance. In most cases, the corrosion is greatest close to the bottom of the pipeline and the unit, for stable orientation along the longitudinal axis, should therefore make sure that the carriers 12 are deposited there. In other cases, it might also be desirable to measure corrosion at other given parts of, or the whole circumference of, the pipeline, and the unit for stable orientation will in this case, make it possible. In the illustrated embodiment of Figure 1, the unit for stable orientation is electronic, and placed in the housing 2 in the front, behind the foremost collar 8. The device 3 for measuring distance is necessary in order to decide where along the pipeline a carrier 12 should be deposited. The speed of the flow in the pipe is not always stable, and if the carriers 12 are deposited at defined times, it may be difficult to decide where they where deposited, afterwards. The device 3 for measuring distance is normally placed against the wall of the pipeline as a measuring wheel, but other methods for longitudinal orientation may also be used. If the topography of the route is known, the placement in the pipeline may be calculated from the number of recorded peaks and troughs, or from the number of recorded seam welds.

When the transport unit 1 is sent thought the pipeline, it is an advantage that it carries several carriers 12. Therefore it is provided with at the least one storage magazine 6. The magazine may be localized between the housings 2 and 5, or as shown in Figure 1 , in the rear housing 5. The rear housing 5 is hollow, and open at both ends. The magazine 6 protrudes longitudinally through the whole housing 5, and is directly accessible from both sides. It has a number of pockets 13 for carriers 12, and can be rotated. The opening towards the foremost housing 2, is shown in Figure 2.

Between the housings 2, 5, there is a deposit / collection unit 4. In the foremost housing 2, the collection unit is connected to the device 3 for measuring distance, so that the carriers 12 are deposited at the right position in the pipeline. This function can be performed in many ways, both mechanical and electronic. The deposition unit 4 comprises, in the illustrated example, a piston 14 moving axially in and out of the foremost housing 2, and a flat shaft 15 connected parallel to the piston 14, by way of a second piston 16. When the piston 14 moves out of the foremost housing 2, the flat shaft 15 moves to the rear housing 5, in a pocket 13 in the magazine 6, and pushes out a measuring-element 12. When the piston 14 moves back into the foremost housing 2 again, the shaft 15 will be pulled out of the pocket 13 in the magazine 6, and the magazine can rotate.

There are many alternative embodiments of the deposit / collection unit 4, and the magazine 6. The transport unit 1 may for example be provided with separate units, one fetching the carriers 12 from the magazine 6, and another unit depositing them. In another conceivable embodiment, the magazine 6 and the deposit unit 4 is one unit. The carriers will be deposited in the pipeline for a time, and then collected. The transportation unit 1 can be provided with a collection unit, in order to both collect carriers 12 and deposit new ones at the same time. In the illustrated example, the collection and deposit unit 4 are combined in one unit. The transportation unit must in this case distinguish between new and used carriers 12, and in the illustrated example, the magazine can be rotated, so that it is possible to deposit a carrier 12, and a collect a new one, before rotation. The transportation unit 1 can also be performed with two separate storages, one for new carriers, and one for used. It is also possible to use two types of transport units 1, one for depositing carriers, and one for collection. The unit for collection will in this case be a simpler embodiment, and just comprise a magazine, a collection unit and a system for orientation along the longitudinal axis.

The technique for releasing and collection of deposited carriers 12 in the illustrated example is based on a protruding loop 17, of metal wire or another strong flexible material, on the carrier 12. The loop preferably has two anchorage points, so that it is bendable and does not constitute an obstacle to other pigs being sent through the pipeline, it is deposited, at the same time, as the opening of the loop is so wide, it is simpler to find the opening for the collection unit. The loop is preferably placed as shown in Figure 2, i.e. to the side of the middle with regard to the longitudinal direction. This is done in order to ease the release from the pipeline. Upon collection, the second piston 16 will be lowered radially, and the protruding loop 17 of the carrier 12 will be caught on the flat shaft 15 on the depositing unit 4. The second piston 16 will be moved upwards again, rotated 180°, and the first piston 14 of the depositing unit 4 will thereafter move into the foremost housing 2, so that the carrier 12 is placed in a free pocket 13 in the magazine 6. The piston 14 will move back into the housing 2 again, and the magazine may rotate.

An alternative collection unit requires that the loop 17 is replaced by a protruding shaft, and that the flat shaft 15 of the collection unit 4 preferably has a V-shape with the opening towards the movement direction, so that the carrier 12 is detached, and intercepted. The detachment can also be based on the fact that the transportation unit 1 provides a pressure centrally on the carrier 12, that makes it loosen from the surface by means of a mechanical release mechanism or a release based on pneumatics/hydraulics. The transportation unit is preferably provided with a platform 18 at the lower part of the rear housing 5, easing the release of the carriers 12 from the pipeline.

Figures 3 and 4 show the carrier 12 according to the invention. It comprises magnets 19 and metal slices / weight loss coupons 20, of the same material as the pipeline. It is important that the carrier 12 is designed with an even and smooth surface, and that it is as flat as possible, in order to avoid changing flows in the pipeline. The conosion measurement can be based upon weight loss or potential fall in the weight loss coupons 20. In the first case the coupons are weighed before and after depositing, and the weight loss provides basis for calculating average corrosion rate in the deposit period. In cases where potential fall are used, ohmic resistance in the sensor is measured before and after deposition, and the change provides basis for calculation of weight loss and thereby average corrosion rate. The carrier 12 also includes a means for holding the magnets 19 and the coupons 20 together, and in the right position. This holding means may principally be designed in many different ways, but it is important that the carrier 12 as a unit is relatively flat and bears close against the wall of the pipeline, in order to avoid being loosened or creating disturbing flows in the pipeline. It should also be possible to send other instruments, pigs or the like through the pipe, avoiding the carriers being loosened or inhibiting the instruments, pigs or the like. If the carrier protrudes too much into the pipeline, the corrosion of the weight loss coupons 20 will not provide a true picture of the conosion of the pipeline.

The coupons 20 should be weighed in one way or another, prior to deposition, and after they are collected again. Therefore they should be relatively easy to release from the rest of the carrier 12. This can be solved simply by fastening the magnets 19 and the coupons 20 to an attachment frame or sheet 21 with fastening devices 22, for example screws. The attachment frame or sheet is covered by a material, for example plastic, before or after the magnets 19 and coupons 20 are attached to the frame 21, in order to give the carrier an even and smooth surface. The carrier should also bear close against the wall of the pipeline, so that it does not loosen, and does not create disturbing flows. The magnets 19 are placed in the underneath of carrier 12, and are strong enough that the carrier 12 is fastened immediately after release onto the pipeline, and held in a stable position even upon strong flows in the pipeline.

Weight loss coupons 20 are distributed on the surface of the carrier 12. It is important that the coupons 20 are distributed along the whole of the carrier 12, because minor effects of disturbing flows will be recorded.

The carriers 12 shall be deposited for a time (1-6 months) in the pipeline, and the effects of corrosion/erosion are recorded as weight loss upon weighing or change in ohmic resistance, as explained above. Upon use of especially thin weight loss coupons 20 and measurement of ohmic resistance, the deposit time may be reduced to a few days. The measurement elements / carriers can also measure different parameters such as conosion, erosion, temperature, pressure, shear stress and the like, and the values may be recorded and stored by means of electronics and microprocessor technology. In this latter case, the carriers must contain microchips or a microprocessor.

Claims

Claims:

1. Method for measuring corrosion or erosion inside metal pipelines, wherein a material (weight loss coupon) (20) is placed at a measuring site for a time, to be exposed to the conditions at the measuring site, after which the coupon (20) is removed, and the degree and/or rate of corrosion is determined, the method comprises leading a transportation unit (1) through a pipeline, characterized in that the transport unit deposits one or more weight loss coupons (20) united on a carrier (12) with one or more magnets (19), that is secured to the wall of the pipeline at defined positions, and that the weight loss coupons are collected after a defined period of time.

2. Device for carrying out the method according to patent claim 1, for measuring corrosion inside metal pipelines, comprising a transportation unit (1) arranged to be led through a pipeline exposed to corrosion, characterized in that

- the transportation unit (1) is arranged to carry one or more carriers (12) for weight loss coupons, as the carrier carrying one or more magnets, and including a deposition unit (4), for depositing carriers (12) at defined positions in the pipeline, and

- including a collection unit for collecting the weight loss coupons after a defined measuring period.

3. Device according to patent claim 2, characterized in that the deposit- and collection unit (4) are combined in one unit.

4. Device according to patent claim 2, characterized in that the carrier is provided with a protruding loop (17), which may constitute a fastening for a gripper on the collection unit (4), arranged to be led through the pipeline.

5. Device according to patent claim 2, characterized in that the carrier (12) is provided with a protruding arm, which may constitute a fastening for a gripper on the collection unit (4), arranged to be led through the pipeline.

6. Device according to any one of the patent claims 2-5, characterized in that the carrier (12) includes microchips for registration and storage of information.

7. Device according to patent claim 6, characterized in that the transport unit (1) includes a distance measurer (3) activating the deposition unit (4) at defined positions.

8. Device according to anyone of the proceeding patent claims 2-7, characterized in that the collection unit (4) comprises at the least one protruding, preferably flat, shaft (15).