WO1989003513A1

WO1989003513A1 - Process and apparatus for measurement of a curvature of an annular plate in a pipe

Info

Publication number: WO1989003513A1
Application number: PCT/NO1988/000076
Authority: WO
Inventors: Audun Haugs
Original assignee: Chr. Michelsens Institutt
Priority date: 1987-10-12
Filing date: 1988-10-12
Publication date: 1989-04-20
Also published as: NO874245D0; NO874245L; NO162831B; NO162831C; AU2539388A

Abstract

A process for measuring the degree of curvature of an opening-defining, annular plate (27) which projects radially inwards into a medium flow pipe (15), comprises measuring by varying differential pressures over said annular plate. The measurement is conducted at differential pressures which vary in the region between 0 and 1000 mbar, in that the flow of medium is limited to a narrow annular gap, which is localised to the region radially just within the inner periphery of the annular plate. An apparatus (10) for measuring the degree of curvature of the annular plate comprises a full scale medium flow pipe (15) with associated annular plate (27), wherein there is coaxially installed a flow cross-section-defining, longitudinal body (51). Between the inner periphery of the annular plate (27) and said longitudinal body (51) there is defined a narrow annular gap, which constitutes a small fraction of the cross-sectional area of an opening which is defined radially within the inner periphery of the annular plate.

Description

PROCESS AND APPARATUS FOR MEASUREMENT OF A CURVATURE OF AN ANNULAR PLATE IN A PIPE.

The present invention relates to a process for measurement of the degree of curvature of an opening-defining, annular plate which projects radially inwards into a medium flow pipe. The degree of curvature is measured by varying differential pressures over said annular plate.

According to the system of rules (in Norway as well as in GB) for the fiscal measurement of quantities of gas there is established the boundary region for differential pressures for opening-defining, annular plates in fiscal gas-measuring appara¬ tuses, to up to 500 mbar (and 0.6 Beta Ratio, that is to say the ratio between internal and external plate diameters) . Within the system of rules in GB however there are given instructions so that said limit of 500 mbar can be allowed to be exceeded, if the total deflection of the opening-defining annular plate is less than 1% and the errors in the measurement of the flow of medium is less than 0.1%.

It has been problematical to be able to clarify the technical conditions in practice, on exceeding the limit of differential pressure of 500 mbar, as a consequence of defective methods of measurement and defective measuring equipment. Hitherto deflections of the annular opening-defining plates have been estimated on the basis of a formula which is displayed by Jepson and Chipchase .in the publication "Journal of Mechanical Engineering", from 1975. Said formula from Jepson and Chipchase makes it possible to estimate both deflections and associated flow aults for various Beta Ratio plates. In this connection tests were conducted in Killingworth in the North East of England where the work was at differential pressures of from 0 to 120 mbar. In practice it has proved difficult to carry out tests at higher differential pressures, and then especially at differen¬ tial pressures above 500 mbar.

For example on the Statfjord installation in the North Sea there is employed a type of opening-limiting, annular plate, which forms a part of a replaceable carrier which is designated as "DANIEL Senior Carriers" and "DANIEL Junior Carriers". The sealing rings, which are used in such plates, are made of rust- free steel and are in accordance with ISO 5167, Rev. 80. But such sealing rings do not have the same rigid set up as obtained in flange-mounted plates, which have been tested by Jepson and Chip¬ chase. It is therefore of great practical significance to be able to corroborate that the formula of Jepson and Chipchase also applies to this type of sealing ring, which is in use on-sea- based installations and which is to be employable at differential pressures of up to or above 1000 mbar.

With the present invention the objective is to be able to simulate the working conditions as far as possible for a sea- based measuring station which is in operation, for example on a gas field at sea. In particular the aim is to be able to carry out tests with full scale measuring equipment and full scale pressure medium pipes with associated full scale annular plates, so that as far as possible practical and realistic results of the tests can be achieved. It is of special interest to be able to conduct such tests at prevailing differential pressures of from 0 to 1000 mbar. However it can also be of interest to employ differential pressures which substantially exceed 1000 mbar. The aim is a solution where the measurements can be effected in a simple manner in a laboratory environment independently of having access to the large volumes of gas which such full scale appara¬ tuses normally work with. The process according to the invention is characterised in that the measurement is effected at partial pressures, which vary in the region between 0 and 1000 mbar (or to a higher pressure level) , during the application of full scale equipment in a full scale medium flow pipe with associated full scale annular plate, in that the flow of medium is limited to a narrow annular gap which is localised to the region radially just at or radially just within the annular plate.

In this way the elements of uncertainty which otherwise can occur can be avoided, for example by simulated partial pressures or by simulated low scale models, by ensuring the direct testing of appropriate annular plates in appropriate surroundings with appropriate partial pressures, such as those occurring in practice. According to the invention it has thus been possible by means of severely limited amounts of pressure medium to imitate the working conditions in a simple and effective manner. Conse¬ quently there is the possibility of carrying out tests in a laboratory environment based on relatively simple experiments while utilising conventional equipment.

The present invention also relates to an apparatus for measuring the degree of curvature of an opening-defining, annular plate which projects radially inwards into a medium flow pipe, including equipment for measuring the degree of curvature and equipment for measuring differential pressures over said annular plate, including equipment for measuring partial pressures on opposite sides of the annular plate.

The apparatus according to the invention is characterised in that in the medium flow pipe, which is a full scale medium flow pipe, including a full scale annular plate, there is coaxially installed a flow cross-section-defining, longitudinal body, which has a uniform or essentially uniform external diameter d' over the whole or essentially the whole longitudinal dimension and which has a significant dimension axially on opposite sides of the annular plate, and in that there is defined between the inner periphery of the annular plate and said longitudinal body a narrow annular gap, the cross-sectional area of the annular gap constituting a small fraction of the cross-sectional area of an opening which is defined radially within the inner periphery of the annular plate.

Further features of the invention will be evident from the following description having regard to the accompanying drawings, in which:

Fig. 1 shows schematically an apparatus according to the invention.

Fig. 2 shows schematically a section of the apparatus according to Fig. 1.

Fig. 3-5 show three different constructions of the annular plate, which are to be subjected to tests by the process according to the invention.

In Fig. 1 there is shown an apparatus 10, according to the invention, which is supported at opposite ends on a pair of trestles 11 which rest on a floor 12. The apparatus has an air-(gas)- inlet end 13 and an outlet end 14 in alignment with the main section 15 of the apparatus which is illustrated in Fig. 1 with a reduced length.

The inlet end 13 of the apparatus is connected via a coϊttrol valve 16 to a pressure tank 17 having a pressure of 1-3 bar. Compressed air is supplied via an air feed conduit 18 to an expansion chamber 19a in a pressure tank 19 and via a branch conduit 18a with associated pressure regulator 20 to a pressure chamber 19 in the pressure tank 19.

The outlet end 14 of the apparatus is connected to the atmosphere, at the arrow 21, via a pressure control valve 22.

The apparatus 10 comprises a longitudinal pipe 15 in the form of two pipe members 15a, 15b which together form the main section or said pipe 15 of the apparatus. The pipe member 15a is flanged on to a conical portion 23 which in turn is flanged on to a pipe 24 of substantially less cross-section than the pipe members 15a and 15b. Said pipe 24 forms a part of the inlet end 13 of the apparatus. The pipe member 15b is correspondingly flanged on to a conical portion 25 which in turn is flanged on to a pipe 26 which forms a part of the outlet end 14 of the appara¬ tus . In the joint between the pipe members 15a, 15b, where these are flange connected to each other to form the pipe 15, there is installed an opening-defining, annular plate 27 which projects a distance radially inwards into the main section or the pipe 15. In the illustrated embodiment the main section consists of a full scale medium-(gas)- flow pipe 15 having an internal diameter D (Fig. 2) of 256 mm (10") and with a corresponding plate 27 (external diameter d" of 271 mm and internal diameter d¹ of 153 mm) . The plate 27 is of the type which forms a part of a carrier which is designated above as "DANIEL Junior Carrier". The carriers of this type are adapted to be replaceable in a ready manner in the apparatus according to the invention without this being further illustrated and described in detail.

The plate 27 is as shown in Fig. 2 inserted in a gap 28 between the pipe members 15a and 15b via an annular seal-forming holder member 29, which on its side facing radially outwards forms a support against an intermediate layer piece 30. Just outside the plate 27, that is to say radially just within the holder member 29 there is arranged a first curvature-sensing transducer 31 and just within the inner periphery of the plate 27 there is arranged a second curvature-sensing transducer 32. Similarly there is arranged on the diametrically opposite side of the plate a third transducer 33 radially innermost and a fourth transducer 34 radially outermost. The distance between each pair of curvature-sensing transducers 31, 32 and 33, 34 is 26 mm in the illustrated embodiment.

The transducers 31-34 are connected via connecting leads 35 and 36 (Fig. 1) to a common meter 37 for registering signals in accordance with sensed local deflections in the plate 27.

In Fig. 1 there is shown a first pressure gauge transducer 38 upstream just in front of the plate 27 and a second pressure gauge transducer 39 downstream just behind the plate 27. The transducers 38 and 39 are connected via leads 40 and 41 to a common pressure difference transducer 42. From the leads 35 and 36 there extend branch leads 43, 44 to a (16 piece) data log 45. Correspondingly a branch lead 46 extends from the transducer 42 and a branch lead 47 from the meter 37 via a common lead 48 to said data log 45. From the data log 45 extends a lead 49 to a recorder/plotter 50.

The apparatus as described above is a full scale measuring apparatus for a full scale pipe 15 with associated full scale plate 27.

In the illustrated apparatus 10 there is centrally installed, that is to say coaxially in this, a flow area-defining body 51 which extends over the whole length of the main section or the pipe 15. The body 51 extends with a uniform diameter d over the whole length dimension with the exception of conically tapered end portions 52, 53 which project a distance inwards into the afore-mentioned conical portions 23, 25. The aim is an even cross-sectional flow from the inlet end 13 of the apparatus via the conical portion 23 to a longitudinal annular space 54a in front of the plate 27 and between the outer surface of the body 51 and the inner surface of the pipe 15, with a correspondingly even cross-sectional flow from the plate 27 via an equivalent annular space 54b and via the conical portion 25 to the outlet end 14 of the apparatus. The only constriction of practical significance in the cross-sectional flow is found at the plate 27 the degree of curvature of which is to be measured during prevailing, different that is to say varying differential pressures. There is shown between the body 51 and the inner periphery of the plate 27 a narrow annular gap 27' ((d'-d)/2 = 0.8 mm) which the pressure medium (the compressed air) shall pass through. The measurements shall for example be effected during tests where the differential pressure is varied upwards from 0 to 1000 mbar and is varied downwards from 1000 to 0 mbar. The annular gap 27' can generally have a somewhat larger or somewhat smaller radial dimension than shown, but is generally D/300 in size.

In the illustrated embodiment, where the pipe 15 has an internal diameter D equal to 256 mm, the pipe has upstream in front of the plate 27 a length equal to D x 16, that is to say equal to 4096 mm and downstream behind the plate 27 a length equal to D x 6, that is to say equal to 1536 mm. The plate 27 has a ratio d'/d" (Beta Ratio), that is to say a ratio between the internal diameter d' and external diameter d", equal to 0.6. Even and essentially uniform flow ratios have been found in front and behind the plate 27, so that to a large degree the flow ratios in a measuring apparatus which is in practical use for measuring gas or a similar medium can be imitated, for example in a sea-based rig on a gas field at sea.

In Fig. 3 there is shown a plate 27a (of a DANIEL-95685 type having a thickness of 6.465 mm) which is held in a holder 29a, which is made of Teflon and which consists of a first clamp member 29a¹ and a second clamp member 29a". In this instance the clamp members 29a' and 29a" form sealing abutments against associated stops 57a and 59a in the pipe 15.

In Fig. 4 there is shown a plate 27b (of a ESAS-M076 type with a thickness of 6.177 mm) which is held in a holder 29b, which is made of metal and which consists of a first clamp member 29b' and a second clamp member 29b". There is shown a first 0 ring 55b between the clamp members 29b¹ and 29b" on the back side of the clamp members and a second 0 ring 56b between the clamp member 29b' and a stop 57b in the pipe 15 together with a third 0 ring 58b between the clamp member 29b" and a stop 59b in the pipe 15. At 60b there is shown a common clamp means for the clamp members 29b' and 29b".

Correspondingly there is shown in Fig. 5 a plate 27c (of a ESAS-M075 type with a thickness of 6.197 mm) which is held in a holder 29c, which is made of metal and which consists of a first clamp member 29c' and a second clamp member 29c". Three 0 rings 55c, 56c and 58c and a common clamp means 60c are shown, similarly as in Fig. 4.

The plates 27a (Fig. 3) and 27c (Fig. 5) both have a holder (29a and 29c respectively) which projects a distance radially within the inner surface of the pipe 15, while the holder 29b (Fig. 4) is terminated flush with the inner surface of the pipe 15. There were carried out equivalent tests with the three said plates in order after there has been established a differential pressure of 1000 mbar over the annular plate (27a, 27b, 27c), with the pressure control valve 22 in the fully open position and with the data log 45 made ready for recording the test data.

Initially tests were conducted with rising pressure diffe¬ rences, that is to say rising from 0 to 1000 mbar. First the pressure control valve 22 was closed, while the air valve 16 between the pressure tank 17 and the pipe 15 was adjusted into a fully open position. Trigger signals were emitted to the data log 45 and to an arrangement (not shown further) for opening and closing the pressure control valve 22. The data log 45 was started for obtaining data, while the pressure control valve 22 was slowly adjusted to the fully open position. The sought pressure difference signals and associated deflection signals were stored in the data log memory for further treatment.

Thereafter tests were conducted with falling pressure differences, that is to say falling from 1000 to 0 mbar. First the pressure control valve 22 was closed, while the air valve 16 between the pressure tank 17 and the pipe 15 was adjusted to the fully open position. Trigger signals were emitted to the data log 45 and to the arrangement for opening and closing the pressure control valve 22. The supply of air to the pressure tank 17 was shut off. In this instance the arrangement for opening and closing was adjusted to opening the valve 22 to the maximum discharge speed. When the pressure control valve 22 was in the fully open position the supply of air to the pressure tank 17 was shut off. The pressure began to fall in the pipe 15 and the pressure difference signals went down towards zero after a specific data logging period (approximately one minute) . The sought pressure difference signals and associated deflection signals were stored in the data log memory for further treatment.

As a result of the tests it was found that each unit of plate and holder (sealing ring) behaved in a varying manner. The following comments can be given for the three objects of the tests: Holder 29a of the plate 27a projected inwardly into the pipe 15 and gave introductory extra support to the plate 27a. On repeated tests this support was far less prominent as a result of plastic deformation of the Teflon material.

The tests showed that it was only the holder 29b which was adapted to the plate 27b.

Holder 29c of the plate 27c projected inwardly into the pipe 15 and gave extra support to the plate 27c. The results which were achieved by this holder 29c were reproducible, even if considerable movement of the seal was observed at low pressure differences, something which was due to the use of "old" O rings.

It could be concluded that even if the plates 27a and 27c were the most interesting test objects according to the tests conducted, such plates would not have been chosen in practical measuring stations as a result of the holders projecting inwardly into the pipe 15.

The following has been able to be established (especially when it concerns the plate 27b) : a) The formula of Jepson and Chipchase for deflection of the annular plate under high differential pressures will give as the result a "worst case" if the plate was employed with a holder of metal. In other words the outcome of the tests is more advan¬ tageous than feared and estimated by the afore-mentioned formula. b) The increase of the thickness of standard annular plates will not significantly reduce the deflection of the plate. c) Gradually as ^■ the differential pressure (maximum 1000 mbar) increases the formula of Jepson and Chipchase predicts a size of deflection which is greater than the size measured in practice. d) The use of holders of Teflon will generally give smaller total plate displacement (that is to say displacement of holder + plate) but can give a plate deflection which is 15% larger than that which is estimated by using the formula of Jepson and Chipchase.

It must be added that even if the tests carried out clarify certain working conditions for suitable plate and holder units, it is clear that the process and apparatus can also be utilised in connection with other conditions which shall be investigated in connection with deflection measurements in combination with pressure difference measurements.

Claims

CLAIMS ,

1. Process for the measurement of the degree of curvature of an opening-defining, annular plate (27a, 27b, 27c) which projects radially inwards into a medium flow pipe (15), measured by varying differential pressures over said annular plate, charac¬ terised in that the measurement is effected at differential pressures which vary for example in the region between 0 and 1000 mbar (or to a higher pressure level), during the application of full scale equipment in a full scale medium flow pipe (15) with associated annular plate (27a, 27b, 27c) in that the flow of medium is limited to a narrow angular gap (27'), which is localised to the region radially just at or radially just within the inner periphery of the annular plate.

2. Apparatus (10) for esuring the degree of curvature of an opening-defining, annular plate (27) which projects radially inwards into a medium flow pipe (15), including equipment (31, 32/ 33, 34) for measuring the degree of curvature and equipment for measuring differential pressures over said annular plate, including equipment (38, 39) for measuring partial pressures on opposite sides of the annular plate, characterised in that in the medium flow pipe (15), which is a full scale medium flow pipe with associated annular plate (27), there is coaxially installed a flow cross-section-defining, longitudinal body (51), which has a uniform or essentially uniform external diameter (d') over the whole or essentially the whole longitudinal dimension and which has a significant dimension axially on opposite sides of the annular plate (27), and that there is defined between the inner periphery of the annular plate (27) and said longitudinal body (51) a narrow annular gap (27'), the cross-sectional area of the annular gap (27") constituting a small fraction of the cross- sectional area of an opening which is defined radially within the inner periphery of the annular plate.

3. Apparatus in accordance with claim 2, where the medium flow pipe (15) has an internal diameter D with an annular plate (27) fastened therein having an internal diameter d, characterised in that the longitudinal body (51) has a dimension axially on the upstream side of the pipe of the annular plate (27) of a size

16 x D and a dimension axially on the downstream side of the pipe of the annular plate of a size 6 x D, and that the radial dimen¬ sion of the annular gap ((d'-d)/2) is D/300 in size.

4. Apparatus in accordance with claim 3, where the medium flow pipe has an internal diameter D of a size 256 mm (10"), charac¬ terised in that the radial dimension of the annular gap ((d'-d)/2) is 0.8 mm in size.