GB2073357A - A system for cleaning tube- type heat exchangers automatically during operation - Google Patents
A system for cleaning tube- type heat exchangers automatically during operation Download PDFInfo
- Publication number
- GB2073357A GB2073357A GB8110658A GB8110658A GB2073357A GB 2073357 A GB2073357 A GB 2073357A GB 8110658 A GB8110658 A GB 8110658A GB 8110658 A GB8110658 A GB 8110658A GB 2073357 A GB2073357 A GB 2073357A
- Authority
- GB
- United Kingdom
- Prior art keywords
- tube
- helix
- wire
- corrosion
- fluid
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 238000004140 cleaning Methods 0.000 title claims abstract description 10
- 239000012530 fluid Substances 0.000 claims abstract description 12
- 238000005260 corrosion Methods 0.000 claims abstract description 9
- 230000007797 corrosion Effects 0.000 claims abstract description 9
- 238000005299 abrasion Methods 0.000 claims abstract description 8
- 238000009825 accumulation Methods 0.000 claims abstract description 6
- 239000000463 material Substances 0.000 claims abstract description 6
- 238000011144 upstream manufacturing Methods 0.000 claims abstract description 5
- 230000000694 effects Effects 0.000 claims abstract description 4
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 6
- 229910052751 metal Inorganic materials 0.000 claims description 6
- 239000002184 metal Substances 0.000 claims description 6
- 239000010936 titanium Substances 0.000 claims description 3
- 229910052719 titanium Inorganic materials 0.000 claims description 3
- 238000009434 installation Methods 0.000 claims description 2
- 230000000712 assembly Effects 0.000 claims 1
- 238000000429 assembly Methods 0.000 claims 1
- 230000000750 progressive effect Effects 0.000 description 4
- 239000003208 petroleum Substances 0.000 description 3
- 238000013019 agitation Methods 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 239000010779 crude oil Substances 0.000 description 1
- 230000008030 elimination Effects 0.000 description 1
- 238000003379 elimination reaction Methods 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 238000009533 lab test Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
- F28F21/00—Constructions of heat-exchange apparatus characterised by the selection of particular materials
- F28F21/08—Constructions of heat-exchange apparatus characterised by the selection of particular materials of metal
- F28F21/081—Heat exchange elements made from metals or metal alloys
- F28F21/086—Heat exchange elements made from metals or metal alloys from titanium or titanium alloys
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B08—CLEANING
- B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
- B08B9/00—Cleaning hollow articles by methods or apparatus specially adapted thereto
- B08B9/02—Cleaning pipes or tubes or systems of pipes or tubes
- B08B9/027—Cleaning the internal surfaces; Removal of blockages
- B08B9/04—Cleaning the internal surfaces; Removal of blockages using cleaning devices introduced into and moved along the pipes
- B08B9/043—Cleaning the internal surfaces; Removal of blockages using cleaning devices introduced into and moved along the pipes moved by externally powered mechanical linkage, e.g. pushed or drawn through the pipes
- B08B9/0436—Cleaning the internal surfaces; Removal of blockages using cleaning devices introduced into and moved along the pipes moved by externally powered mechanical linkage, e.g. pushed or drawn through the pipes provided with mechanical cleaning tools, e.g. scrapers, with or without additional fluid jets
-
- E—FIXED CONSTRUCTIONS
- E03—WATER SUPPLY; SEWERAGE
- E03C—DOMESTIC PLUMBING INSTALLATIONS FOR FRESH WATER OR WASTE WATER; SINKS
- E03C1/00—Domestic plumbing installations for fresh water or waste water; Sinks
- E03C1/12—Plumbing installations for waste water; Basins or fountains connected thereto; Sinks
- E03C1/30—Devices to facilitate removing of obstructions in waste-pipes or sinks
- E03C1/304—Devices to facilitate removing of obstructions in waste-pipes or sinks using fluid under pressure
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
- F28F13/00—Arrangements for modifying heat-transfer, e.g. increasing, decreasing
- F28F13/06—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by affecting the pattern of flow of the heat-exchange media
- F28F13/12—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by affecting the pattern of flow of the heat-exchange media by creating turbulence, e.g. by stirring, by increasing the force of circulation
- F28F13/125—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by affecting the pattern of flow of the heat-exchange media by creating turbulence, e.g. by stirring, by increasing the force of circulation by stirring
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
- F28F19/00—Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28G—CLEANING OF INTERNAL OR EXTERNAL SURFACES OF HEAT-EXCHANGE OR HEAT-TRANSFER CONDUITS, e.g. WATER TUBES OR BOILERS
- F28G1/00—Non-rotary, e.g. reciprocated, appliances
- F28G1/06—Non-rotary, e.g. reciprocated, appliances having coiled wire tools, i.e. basket type
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
- F28D21/00—Heat-exchange apparatus not covered by any of the groups F28D1/00 - F28D20/00
- F28D2021/0019—Other heat exchangers for particular applications; Heat exchange systems not otherwise provided for
- F28D2021/0059—Other heat exchangers for particular applications; Heat exchange systems not otherwise provided for for petrochemical plants
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Health & Medical Sciences (AREA)
- Environmental & Geological Engineering (AREA)
- Life Sciences & Earth Sciences (AREA)
- Hydrology & Water Resources (AREA)
- Public Health (AREA)
- Water Supply & Treatment (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Heat-Exchange Devices With Radiators And Conduit Assemblies (AREA)
- Cleaning In General (AREA)
Abstract
A tube assembly through which a fluid is to flow and containing a device for cleaning the tube and/or preventing the accumulation of deposits therein, the device consisting of a helix 2 of a material which is resistant to corrosion and abrasion, which can be constantly agitated and thus repeatedly brought into contact with the internal walls of the tube 1 under the effect of the fluid stream, the helix 2 being held in position against longitudinal movement by a hook 4 disposed at the upstream end of the helix 2 which hook permits rotation of the helix 2 within the tube 1. <IMAGE>
Description
SPECIFICATION
A system for cleaning tube-type heat exchangers automatically during operation
The accumulation of dirt and the like in a heat exchanger, for example in oil refineries, entails various drawbacks, such as: -a progressive fall in thermal exchange performance, giving rise to a greater consumption of energy, -a progressive increase in the loss of pressure, and sometimes a limitation on throughput, -the necessity of stopping a plant in order to clean one of its exchangers if it is not fitted with a bypass, which involves a production loss which has to be made up and various expenses inherent in all stopping and restarting operations, such as the expense of fuel, flaring, etc.
Investment in the provision of a bypass involves other expenses, e.g. those of installing isolating valves for the bypass and its valve, as well as those related to the loss of heat during the period when the bypassed exchanger is being cleaned.
In any case, the cleaning of the assembly of heat exchanger tubes is laborious and the dirty tubes are sometimes found to be corroded under the deposit of dirt.
The subject of the invention is a simple, relatively inexpensive device for providing permanent automatic cleaning of the inside of tubes when the exchanger is in use. This device is placed in each tube in the apparatus.
According to one aspect of the invention there is provided a tube assembly through which a fluid is to flow and containing a device for cleaning the tube and/or preventing the accumulation of deposits therein, the device consisting of a helix of a material which is resistant to corrosion and abrasion, which can be constantly agitated and thus repeatedly brought into contact with the internal walls of the tubes under the effect of the fluid stream the helix being held in position against longitudinal movement by a hooking means disposed at the upstream end of the helix, which permits rotation of the helix within the tube.
According to another aspect of the invention there is provided a device for installation within a tube through which a fluid is to flow to clean the tube or to prevent the accumulation of deposits within the tube, the device comprising a helix of corrosion and abrasion resistant wire having means enabling it to be attached to the tube to prevent longitudinal movement but to allow rotation, relative to the tube.
According to a first embodiment, a metal wire in an elongated spiral shape, having a specific pitch varying from 1 to 7 times the diameter of the tube and possibly obtained by stretching a helical spring, is threaded by suction, for example, into a slightly longer tube, to allow for the lengthening of the helical wire during use.
The helix is formed from a metal wire with a diameter of from 0.3 to 1 mm which is resistant to corrosion and abrasion, such as a spring wire made of a suitable metal or alloy such as cold-rolled titanium, for example, or any other suitable material. The choice of the characteristics of the helix-its pitch, diameter, elasticity, the diameter of the wire from which the helix is formed, and the construction material-is basically determined by the vibration frequency desired under the operating conditions of the exchanger.
The elongated helix is bounded by an imaginary cylinder with a diameter which is equal to at least half the diameter of the tube, and it is preferably bounded by an imaginary cylinder with a diameter of between 0.50 and 0.90 times the internal diameter of the tube.
The helix is fixed in the tube in a flexible manner by one of its ends, on the upstream side relative to the flow of fluid, via a hooking system which may be of the same kind as the spring, or of a different kind. Thus this hooking system may be an inserted part, such as a metal hook in the shape of a "U" made of the same material as the spring or any other material which is resistant to corrosion and abrasion. Again, it may be formed by the interlocking connection of the ends of two adjacent wires.
Under the effect of a turbulent stream of fluid, the helix is permanently agitated; it regularly strikes and rubs all the points of the internal wall of the tube as it turns, thus providing repeated contact with the internal wall. A variation in the throughput of the conducted fluid brings about a variation in the length of the arrangement and consequently changes the striking and rubbing points on the interior of the tube.
The invention is illustrated by the following drawings and Examples which are given as an indication, but are not limitative.
Figure 1 shows part of a plate in which the heat exchanger tubes are inserted, shown by their cross-section.
Figure 2 shows a section through the layout of the laboratory test arrangement.
Figure 3 is a schematic section through a heat exchanger in a plant.
Example 1
As shown in Fig. 2, the test was carried out in the laboratory on a glass tube 1 with an internal diameter of 1 5 mm. The helix 2 is formed from a titanium wire with a diameter of 0.5 mm to avoid any risk of corrosion in use. The pitch 3 of the helix is 30 mm.
The diameter of the helix is 11 mm, and it is attached by a hook 4 to the upstream end of the tube.
The fluid chosen is water, so as to enable the behaviour of the stretched spring to be observed in a transparent medium, and it is circulating in the direction indicated by the arrows.
It was thus possible to confirm that at a flow speed of 20 I/minute, analogous to that of the crude oil in the tubes of a specific heat exchanger which regularly becomes soiled, the metal wire is endowed with a permanent agitation motion which brings it into contact with the walls of the tube.
Example 2
An industrial test on a hundred tubes 10 arranged as shown in Fig. 1, with an internal diameter of 1 5 mm, was carried out with a spiralled titanium wire with a diameter of 0.5 mm. The diameter of the helix was 8 mm, and its pitch was 30 mm. These wires were attached at one end either by a hook or by twisting them together in pairs. The crude petroleum circulates at a flow speed of approximately 0.40 m/sec in the tubes.
After operating for approximately 240 days, some of the tubes equipped with helical wires and some other tubes which were not so equipped were removed.
After having cut a certain number of these tubes in half lengthwise, it was possible to observe that the tubes which were equipped with a helix displayed a clean internal wall, while the other tubes were soiled internally.
Example 3
An industrial test on a complete heat exchanger with 2 sets of tubes with an internal diameter of 1 5 mm was carried out with helical titanium wire with a wire diameter of 0.6 mm, a helix diameter of 8 mm and pitch of 30 mm. These wires were attached at the end where the petroleum enters, by a hook, also made of titanium. The crude petroleum circulates in the tubes at a flow speed of approximately 0.40 m/sec.
After an operatihg time of approximately 140 days, the soiling in the tubes of this exchanger was compared with that in an identical exchanger with the same use. The tubes of the exchanger which was not equipped displayed marked internal soiling. A series of comparative measurements of the levels of heat transfer of these two exchangers shows the advantage of the helical device.
It was confirmed that the thermal exchanger equipped with the automatic cleaning device according to the invention maintained its thermal performance, while the exchanger without the arrangement displayed a progressive reduction in its performance, due to progressive soiling.
The device according to the invention therefore makes it possible to avoid the loss of calorific energy and to maintain a maximum and constant level of thermal transfer over a period of time. Another economic advantage is afforded by the fact that the price of supplying and fitting the device is of the same order of magnitude as the cost of cleaning the exchanger, and the investment may be recouped very rapidly by savings in energy and the elimination of cleaning costs.
Claims (7)
1. A tube assembly through which a fluid is to flow and containing a device for cleaning the tube and/or preventing the accumulation of deposits therein, the device consisting of a helix of a material which is resistant to corrosion and abrasion, which can be constantly agitated and thus repeatedly brought into contact with the internal walls of the tube under the effect of the fluid stream, the helix being held in position against longitudinal movement by a hooking means disposed at the upstream end of the helix, which means permits rotation of the helix within the tube.
2. A tube assembly according to Claim 1, wherein the helix is bounded by a notional cylinder with a diameter lying from 50 to 90 percent of the internal diameter of the tube.
3. A tube assembly according to Claim 1, wherein the helix is formed of a metal wire which is resistant to corrosion and abrasion.
4. A tube assembly according to Claim 3, wherein the wire is spring wire of cold-rolled titanium.
5. A tube assembly according to any preceding claim wherein the hooking means is a
U-shaped hook.
6. A heat exchanger, including tube assemblies according to any preceding claim.
7. A device for installation within a tube through which a fluid is to flow to clean the tube or to prevent the accumulation of deposits within the tube, the device comprising a helix of corrosion and abrasion resistant wire having means enabling it to be attached to the tube to prevent longitudinal movement but to allow rotation, relative to the tube
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR8007856A FR2479964A1 (en) | 1980-04-08 | 1980-04-08 | SELF-CLEANING SYSTEM ON TUBE COIL EXCHANGERS |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2073357A true GB2073357A (en) | 1981-10-14 |
| GB2073357B GB2073357B (en) | 1984-06-06 |
Family
ID=9240629
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8110658A Expired GB2073357B (en) | 1980-04-08 | 1981-04-06 | System for cleaning tube-type heat exchangers automatically during operation |
Country Status (7)
| Country | Link |
|---|---|
| BE (1) | BE888308A (en) |
| DE (1) | DE8110199U1 (en) |
| ES (1) | ES264968Y (en) |
| FR (1) | FR2479964A1 (en) |
| GB (1) | GB2073357B (en) |
| IT (1) | IT1137667B (en) |
| LU (1) | LU83284A1 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2569829A1 (en) * | 1984-08-31 | 1986-03-07 | Raffinage Cie Francaise | METHOD AND MECHANICAL DEVICE FOR IMPROVING THERMAL TRANSFERS AND PREVENTING THE INJECTION OF HEAT EXCHANGERS |
| FR2592924A1 (en) * | 1986-01-10 | 1987-07-17 | Total France | DEVICE FOR HOLDING THE END OF A MOBILE ELEMENT IN A POSITION, ROTATING DRIVE IN A TUBE AND APPLICATION TO PREVENTING FOULING AND CLEANING OF THIS TUBE. |
| CN101210791B (en) * | 2006-12-29 | 2010-11-10 | 北京华夏英蓝科技发展有限公司 | Self-cleaning reinforcement heat transfer low flow resistance rotor in heat-transfer pipe |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19544185C2 (en) * | 1995-11-28 | 1998-08-13 | Renzmann Und Gruenewald Gmbh | Heat exchanger |
| FR2820197B1 (en) | 2001-01-30 | 2006-01-06 | Elf Antar France | DEVICE REDUCING THE ENCRASSMENT OF A TUBULAR THERMAL EXCHANGER |
| FR2940152B1 (en) | 2008-12-19 | 2011-01-21 | Total Raffinage Marketing | DEVICE FOR REDUCING ENCRASSMENT WITHIN A TUBE |
| CN102128560B (en) * | 2011-04-19 | 2012-10-17 | 北京化工大学 | Twisted belt type pendant in heat exchange pipe |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| BE389314A (en) * | ||||
| US3409470A (en) * | 1966-06-27 | 1968-11-05 | Dow Chemical Co | Cyclic water hammer method |
| JPS5535912A (en) * | 1978-09-06 | 1980-03-13 | Mitsui Toatsu Chemicals | Pipe inside scratchinggoff device |
-
1980
- 1980-04-08 FR FR8007856A patent/FR2479964A1/en active Granted
-
1981
- 1981-04-03 DE DE19818110199U patent/DE8110199U1/en not_active Expired
- 1981-04-06 GB GB8110658A patent/GB2073357B/en not_active Expired
- 1981-04-06 ES ES1981264968U patent/ES264968Y/en not_active Expired
- 1981-04-07 BE BE0/204394A patent/BE888308A/en not_active IP Right Cessation
- 1981-04-07 LU LU83284A patent/LU83284A1/en unknown
- 1981-04-08 IT IT20981/81A patent/IT1137667B/en active
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2569829A1 (en) * | 1984-08-31 | 1986-03-07 | Raffinage Cie Francaise | METHOD AND MECHANICAL DEVICE FOR IMPROVING THERMAL TRANSFERS AND PREVENTING THE INJECTION OF HEAT EXCHANGERS |
| EP0174254A1 (en) * | 1984-08-31 | 1986-03-12 | Compagnie De Raffinage Et De Distribution Total France | Mechanical device to improve the transfer of heat and to prevent clogging of heat exchangers |
| FR2592924A1 (en) * | 1986-01-10 | 1987-07-17 | Total France | DEVICE FOR HOLDING THE END OF A MOBILE ELEMENT IN A POSITION, ROTATING DRIVE IN A TUBE AND APPLICATION TO PREVENTING FOULING AND CLEANING OF THIS TUBE. |
| EP0233092A1 (en) * | 1986-01-10 | 1987-08-19 | COMPAGNIE DE RAFFINAGE ET DE DISTRIBUTION TOTAL FRANCE: Société Anonyme dite | Device for maintaining in position one extremity of a mobile element, rotating in a tube, and application for this device |
| US4781245A (en) * | 1986-01-10 | 1988-11-01 | Compagnie De Raffinage Et De Distribution Total France | Device for positioning a rotatable element within a tube |
| CN101210791B (en) * | 2006-12-29 | 2010-11-10 | 北京华夏英蓝科技发展有限公司 | Self-cleaning reinforcement heat transfer low flow resistance rotor in heat-transfer pipe |
Also Published As
| Publication number | Publication date |
|---|---|
| FR2479964B1 (en) | 1982-05-14 |
| IT1137667B (en) | 1986-09-10 |
| BE888308A (en) | 1981-07-31 |
| GB2073357B (en) | 1984-06-06 |
| ES264968U (en) | 1983-01-01 |
| DE8110199U1 (en) | 1981-10-15 |
| ES264968Y (en) | 1983-07-01 |
| LU83284A1 (en) | 1981-07-23 |
| IT8120981A0 (en) | 1981-04-08 |
| FR2479964A1 (en) | 1981-10-09 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4583585A (en) | System for cleaning tube-type exchangers automatically during operation | |
| US3319710A (en) | Apparatus for cleaning surface condenser and heat exchanger tubes | |
| US8225848B2 (en) | Device for reducing fouling in a tubular heat exchanger | |
| US4102393A (en) | Heat exchange apparatus | |
| JP4937133B2 (en) | Tubular member cleaning scraper | |
| GB2073357A (en) | A system for cleaning tube- type heat exchangers automatically during operation | |
| CN1021080C (en) | Method of and apparatus for cleaning liquid circling-running tube and use of same in heat exchanger | |
| US7386908B2 (en) | Structured foam pig | |
| CN208520252U (en) | A kind of heat exchanger tube with self-cleaning and enhanced heat exchange function | |
| WO2006088432A1 (en) | Device for cleaning tubes | |
| US3135322A (en) | Liquid cooled condenser | |
| KR20230157562A (en) | Tube cleaning apparatus used in heat exchanger | |
| CS268801B2 (en) | Device for energy transfer in desulphurization system | |
| NO167327B (en) | PROCEDURE AND DEVICE FOR AUTOMATIC CLEANING OF A HEAT EXCHANGE FOR GASIC FLUIDS. | |
| US4545426A (en) | Reversing turbulators for heat exchangers | |
| IL35375A (en) | Heat exchanger and method of operation thereof | |
| CN1948887A (en) | Scale spiral line fluidization on line washing in horizontal pipe and heat transferring streng thening device thereof | |
| CN209109757U (en) | A kind of phosphoric acid pipeline transportation cleaning device | |
| US7275429B2 (en) | Mechanical self-cleaning probe via bi-metallic or shape memory | |
| DE19544185A1 (en) | Industrial heat exchanger with tube bundle inserts | |
| JPH0642893A (en) | Cleaner for heat exchanger | |
| ES2415908T3 (en) | Device for reducing fouling inside a tube | |
| SU1322064A1 (en) | Shell-and-tube heat exchanger | |
| SU817478A1 (en) | Apparatus for cleaning inner surfaces of straight-pipe heat exchanger pipe | |
| CN219798030U (en) | Tubular heat exchanger |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PE20 | Patent expired after termination of 20 years |
Effective date: 20010405 |