GB2187294A - Sensor unit for attachment to a structure - Google Patents

Abstract

A device for measuring/monitoring changes in condition or material qualities of underwater and on shore structures comprises a movable sensor holder carrying one or more sensors 3 and equipped with a locking mechanism 11, 12, 13, 14, 15 for releasably fixing the holder to a projecting coupling device e.g. a stud or bolt 4 mounted on the structure. The locking mechanism has a split cone 12 forced by springs 14 and conical surrounding casing 13 into engagement with the stud 4. Operating handle 11 causes piston 15 to descend and release the spring biased split cone 12 from the stud so that the device may be located manually or by a remote control vehicle on another stud provided on the structure. The device shown measures strain and comprises two fixed pointed probes 17 engaging the structure surface and a probe 16 engaging the structure surface and connected by a hinged portion 18 to the fixed probes 17. Other measuring devices specified are accelerometers, acoustic emission sensors and electrical field sensors. The locking mechanism may be replaced by a spring, washer and nut mounted on the threaded stud 4. <IMAGE>

Description

SPECIFICATION Censor unit The application concerns a device for measuring/monitoring of changes in condition or material qualities of structures.

Offshore steel structures today are equipped with apparatus for measuring and monitoring to an extent which depends upon the demand of the authorities or the needs of the operating company and whether it is a new type of construction or if the construction is installed in a very exposed area. For production of oil/gas at greater depths it is also necessary to find solutions which make divers redundant, and this is possible when the structures can be automatically monitored. New installations can have an estimated working life up to 40 years, and it can therefore be necessary to replace measuring equipment during this time period. It is also of importance that the equipment can be operated by remote operated vehicles (ROV).

The measuring methods of today demand installation of equipment in the course of construction (before launching) by gluing, welding or fixing by magnets below the water surface.

The equipment on the market today contains many parts and complicated work is needed both in advance and during the installation.

A known movable censor holder is ''GOS- CONVICE" marketed by the firm AV Technology Ltd. The holder is composed of a hinged bracelet of steel straps for fastening around steel pipes. Censors are glued to the holder after the fastening. The installation of such a holder must be done by a diver. The use is therefore limited to small diameter pipes because it is difficult for the diver to handle equipment for pipes of greater dimensions.

Great ocean depths are also a restricting factor.

The object of the invention is therefore to develop a device for measuring/monitoring changes in the condition or material qualities of the structures by use of a movable censor holder which can be adapted for different types of censors. The holder must be compact and have a simple construction which also makes possible use of remote operated vehicles for mounting and demounting. By using a simple way of mounting and demounting inspection, maintenance and calibration of the censor unit can be done on deck.

Further it is an object of the invention to develop a system giving fixed measuring positions on the structure to make periodic measurements.

These and other objects are obtained by the device described below, and the invention is characterised and defined by the enclosed patent claims.

By this invention a device is produced for measuring/monitoring of changes in condition or material qualities of structures which in the first place is movable. It can be used both in periodical measurements with a duration of days/weeks and for measuring over periods of many years. It is well suited for measuring/monitoring of structures both on shore and offshore. The censor holder is equipped with a handle, is small and relatively light and can be operated both by a diver and by a remote operated manipulator. Essentially the holder is adapted for mounting all kinds of censors where there is a need for contact with the material or for fixed measuring positions. Because it is movable, it can also be taken up on the deck of offshore structures for surveillance and calibration. New and better types of censors are developed all the time which can be installed as required.Another important feature of the invention is the simple mechanism for fixing the holder to the structure. The structure which shall be monitored, is preferentially equipped with small cylindrically smooth bolts which can be fixed to the structure in different ways, and if desired fixed to a base (double plate) welded to the structure.

The censor holder itself is equipped with a locking mechanism which comes into force by turning a release handle after the holder is located over the bolt. This is a very rapid and simple operation. By this operation contact points located apart from each other will come in good contact with the structure/measuring surface. An important feature of the invention is that signals from contact points with the measuring surface can be transmitted to a censor without any influence on the measurements from the fixing mechanism (bolt).

By measurement of the structural strain in the material the censor holder will be equipped with two fixed reference probes (measuring probes) and also a probe at a distance from the two others which will follow movement in the surface (measuring surface).

The structural strain will then be measured between these probes and signals are transmitted to a censor. The bolts can also be used as reference points for position measurements.

Other features of the invention are described more in detail below and also shown in the figures 1-4, where Figure 1 A shows a principal sketch of the censor holder.

Figure 1B shows a fixing bolt for the holder.

Figure 1C shows the fixing bolt fixed to the structure by magnets.

Figure 2 shows a side view of the holder and bolt, especially adapted for strain measurements.

Figure 3A shows the holder adapted for strain measurements seen from the one short side.

Figure 3B shows an alternative way of fixing the holder to the structure.

Figure 4 shows a system for mobile moni toring.

Figure 1 A shows a principal sketch of the device 1 with a measuring censor. One unit comprises a censor holder 2, a measuring censor or another type of censor 3 and a fixing bolt 4. The bolt 4 is preferably cyíindri- cal and is mounted at the measuring point (platform leg, stay or other structure) by welding or mounted on a belt which is fastened to the measuring point or fastened by a magnetic sheet as shown by 5 in Figure 1C. The size of the bolt can typically be 8-10 mm in diameter and 40mm high and normally projects out from the measuring point. The censor holder can be mounted to the bolt manually or by help of remote operated equipment (manipulator).

The censor holder 2 can be used to mount an acceleration meter, an accoustic emission censor, electrical field-censors or other censors to the structure as shown in figure 1 A.

The censor holder is thus suitable for use with all kinds of censors in contact with the surface or censors where fixed measuring positions are wanted. The censor holder has grooves 6 in each long side which allow space for mounting censors. Censors can also be mounted on the short side 7 or in a circular opening.

The censor holder is shown more in detail in figures 2 and 3A. These show a holder especially equipped for structural strain measurements. The holder 2 is equipped with a handle 9 which makes the placing of the holder easier. The censor holder 2 is pushed down on the bolt 4 and is held at the surface 10 where the measurements are to be made.

A release handle 11 is turned over to lock the holder to the bolt. The same handle will also release the holder from the bolt. The locking mechanism consists of a spring loaded grip casing with two conical parts 12, 13, in which the innermost part 12 is split and grips around the bolt 4. The spring package is initially stressed and by turning the handle 11 from the position "released" to "fixed", the piston will be lifted up, the external spring 14 and the casing 13 follow, and the split cone 12 is pressed towards the bolt 4. The release is done by turning the handle back to the position "released", the piston 15 will go down, the spring 14 is pressed down and the conical connection is loosened in such a way that the innermost split cone 12 is released from the bolt 4. The censor holder 2 can now easily be lifted off the bolt 4.

To measure the structural strain (material stress) the holder will have three probes 16, 17 having a pointed end in contact with the measuring point and will transfer strain in the material to for example an inductive censor 3 as shown in figure 2. The censors are fixed to the holder 2 by help of a screw-or clamp connection which must be adapted for the actual censor which will be used. Two of the reference probes 17 will be fixed and give a fixed position for the holder, while the third probe 16 will follow movements in the surface (measuring surface 10). This is achieved by weakening the end face 7 of the holder with a groove 18. The probes 16, 17 are formed in such a way that they will give good contact with the measuring surface even if the surface should be fouled or corroded. The probe will be forced through any coating by fixing the holder to the bolt.

The reference probes 16, 17 in contact with the measuring surface transfer the structural strain to the censor 3 without any influence on the measurement from the bolt. The spring package in which the grip casing is mounted, can be moved about 1 mm parallel with the measuring surface. The strain measured is 100--1000 times less than this.

In figure 2 the bolt 4 is shown mounted to a base 19. The base will often be necessary for welding a bolt on a structure with heavy load. The base 19 (or double plate) will be welded to the construction during building in a particular way to prevent damage or weakness of the structure when the bolt is welded to the structure.

Figure 3B shows an alternative way of fixing the censor holder to the structure. A threaded bolt 20 with a spring 21 is used with a washer 22 and a nut 23. This way of fixing is simple, but not suited for use underwater or for installation by help of a manipulator. Other ways of fixing the holder are also possible.

Figure 4 shows several censor holders 2 located around a nodal point. Transmission of signals from a censor to the deck can be done either by help of a cable up to the surface for collection/analysis of data or via a cable to an adjacent module for collection/reduction of data, either by storage of data locally or by help of a hydro accoustic link to a hydrophone below the wave zone with a cable to the surface. The choice of method for data collection depends upon the demand, the speed of transmission and the need for a fast availability of information. In figure 4 a system is used for underwater data collection 24 and a hydro accoustic link 25 to the surface. The size and weight of the censor unit must be such that it can be handled by a small ROV (remote operated vehicle). As an example of the size the length can be 210 mm, the width 50 mm, the height 100 mm and the weight about 2 kg.

The holder 2 and bolt 4 as described before, can also be used as a way of fixing underwater modules for collection/storage of data.

The equipment is especially being compact, it can be operated without extra loose parts, it can be mounted or demounted (friction mechanism against bolt), and it gives fixed measuring positions. Fixed measuring positions make it possible to make periodical measure ments to the same positon and for instance see alteration in a signal with time (difference in signature). The bolt 4 is easy to clean before mounting of the censor holder, and the bolt does not demand straightness of diameter tolerance, so that a distortion of about 5O or a reduced material thickness of about 1 mm because of corrosion or other things, can be tolerated.

By having many small bolts or many stays or several positions on one stay, it will be possible to measure local parameters, as an example for all stays, towards a local point of a steel structure.

By use of remote operations on a construction it is often difficult to locate and particularly to find the exact position for start of the operation. Fixed reference points will be of help in this situation. These small bolts will therefore fulfill this important requirement of reference points for position measurements by operation of ROV or robot.

The use of the censor holder is not restricted to use underwater on offshore structures-it also can be used for control of structures on deck, cranes and similar loaded equipment.

The range of uses is therefore much wider than only for underwater operations.

Claims (7)

1. Device for measuring/monitoring changes in condition or material qualities of structures, comprising a movable censor holder adapted to hold one or more censors and adapted to be fixed by help of a locking mechanism to a coupling device mounted at the measuring point.

2. Device according to claim 1, wherein the coupling device is in the form of a bolt.

3. Device according to claim 2, wherein the bolt is fixed to the measuring point by welding, by magnets or by a belt.

4. Device according to claim 2, wherein the bolt is welded to a double plate (base).

5. Device according to claim 1, wherein the locking mechanism consists of a spring loaded grip casing with two conical parts where the innermost is split and adapted for gripping around the bolt and, where the spring package is initially stressed, a handle which acts on a piston and adapted to be bent to fasten/unfasten the censor holder from the bolt.

6. Device according to clam 1, wherein the censor holder has at least two contact points at the measuring point at a distance from each other.

7. Device according to claim 1, especially adapted for measurement of the structural strain, wherein the censor holder is equipped with two reference probes in a fixed position and a third reference probe located at a distance from the two others which is adapted to follow movement in the measuring surface by being mounted at an end face of the holder which is weakened by a groove, and where the structural strain in the material measured between the probes can be transmitted to a censor.