PT88473B - PROCESS FOR THE MANUFACTURE OF COPPER TUBES OR COPPER ALLOYS, INTENSELY STRETCHED, RESISTANT TO FISSURE FORMATION - Google Patents

PROCESS FOR THE MANUFACTURE OF COPPER TUBES OR COPPER ALLOYS, INTENSELY STRETCHED, RESISTANT TO FISSURE FORMATION Download PDF

Info

Publication number
PT88473B
PT88473B PT88473A PT8847388A PT88473B PT 88473 B PT88473 B PT 88473B PT 88473 A PT88473 A PT 88473A PT 8847388 A PT8847388 A PT 8847388A PT 88473 B PT88473 B PT 88473B
Authority
PT
Portugal
Prior art keywords
tubes
copper
process according
jet
treated
Prior art date
Application number
PT88473A
Other languages
Portuguese (pt)
Other versions
PT88473A (en
Inventor
Achim Baukloh
Ulrich Reiter
Original Assignee
Kabel Metallwerke Ghh
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Family has litigation
First worldwide family litigation filed litigation Critical https://patents.darts-ip.com/?family=6335681&utm_source=google_patent&utm_medium=platform_link&utm_campaign=public_patent_search&patent=PT88473(B) "Global patent litigation dataset” by Darts-ip is licensed under a Creative Commons Attribution 4.0 International License.
Application filed by Kabel Metallwerke Ghh filed Critical Kabel Metallwerke Ghh
Publication of PT88473A publication Critical patent/PT88473A/en
Publication of PT88473B publication Critical patent/PT88473B/en

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24C—ABRASIVE OR RELATED BLASTING WITH PARTICULATE MATERIAL
    • B24C3/00—Abrasive blasting machines or devices; Plants
    • B24C3/32—Abrasive blasting machines or devices; Plants designed for abrasive blasting of particular work, e.g. the internal surfaces of cylinder blocks
    • B24C3/325—Abrasive blasting machines or devices; Plants designed for abrasive blasting of particular work, e.g. the internal surfaces of cylinder blocks for internal surfaces, e.g. of tubes
    • B24C3/327—Abrasive blasting machines or devices; Plants designed for abrasive blasting of particular work, e.g. the internal surfaces of cylinder blocks for internal surfaces, e.g. of tubes by an axially-moving flow of abrasive particles without passing a blast gun, impeller or the like along the internal surface

Landscapes

  • Mechanical Engineering (AREA)
  • Engineering & Computer Science (AREA)
  • Metal Extraction Processes (AREA)
  • Heat Treatment Of Articles (AREA)
  • Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
  • ing And Chemical Polishing (AREA)
  • Processing Of Meat And Fish (AREA)
  • Meat, Egg Or Seafood Products (AREA)
  • Chemical Treatment Of Metals (AREA)
  • Rigid Pipes And Flexible Pipes (AREA)
  • Shaping Metal By Deep-Drawing, Or The Like (AREA)
  • Saccharide Compounds (AREA)
  • Control Of Steam Boilers And Waste-Gas Boilers (AREA)
  • Preventing Corrosion Or Incrustation Of Metals (AREA)
  • Cleaning In General (AREA)

Abstract

The corrosion damage, particularly that due to local pitting, which occurs on hard-drawn copper tubes used in the sanitary sector is generally caused by carbon-containing films but also by oxide films. A carbon film on the inside of the tube is formed, for example, if the drawing compound added when drawing the tube is subjected to excessive heat. To avoid these damaging films and to improve the pitting resistance of hard tubes made of copper or copper-based alloys, the tubes are first of all degreased. In a further process step, the inner surface of the tubes is then treated with a blasting abrasive in order to establish a minimum roughness. A mean roughness of 0.8 to 1.0 mu m has proven particularly advantageous. The hard-drawn tubes treated by the method according to the invention have none of the films which promote pitting, even after brazing and/or hot bending.

Description

a presente invenção diz respeito a um processo para a fabri cação de tubos de cobre ou de ligas de cobre, intensamente estirados, resistentes ã formação de fissuras. A invenção refere-se ainda ã utilização dos tubos fabricados de acordo com este proces so como tubos de instalações em comprimentos estendidos para o domínio dos esgotos sanitários.the present invention relates to a process for the manufacture of copper tubes or copper alloys, intensely stretched, resistant to the formation of cracks. The invention also relates to the use of pipes manufactured in accordance with this process as pipes of installations in extended lengths for the field of sanitary sewage.

Sabe-se que os tubos de cobre recozidos para maleabilização depois do último processo de estiramento são susceptíveis de corrosão em águas canalizadas agressivas. Uma forma de ataque corrosivo de aspecto especialmente característieo e causada pela corrosão com fissuras, na qual o làdo interior dos tubos é cheio de fissuras locais. A origem destes ataques corrosivos e atribuída a resíduos que contêm carbono que se formam por exemplo por decom posição térmica do agente de estiramento utilizado durante a ope ração de estiramento dos tubos.Copper tubes annealed for malleability after the last stretching process are known to be susceptible to corrosion in aggressive tap water. A form of corrosive attack with an especially characteristic aspect and caused by crack corrosion, in which the inside of the tubes is filled with local cracks. The origin of these corrosive attacks is attributed to carbon-containing residues that are formed, for example, by thermal decomposition of the drawing agent used during the drawing operation of the tubes.

Mas também nos tubos de cobre endurecidos por estiramento, que não são submetidos a um processo de recozimento, pode formar -se no lado interior dos tubos uma película de carbono mais ouBut also in the stretch-hardened copper tubes, which are not subjected to an annealing process, a carbon film more or less can form on the inside of the tubes.

menos coerente, se por exemplo os tubos forem ligados uns aos ou tros por meio de solda dura ou forem aquecidos para facilitar o encurvamento.less coherent if, for example, the tubes are connected to each other or by means of hard soldering or are heated to facilitate bending.

Verificou-se que a película de carbono obtida por aquecimento é quase inofensiva se se encontrar sobre a superfície interna do tubo de cobre menos do que 0,1 mg/dm^ de óleo de estira mento.The carbon film obtained by heating has been found to be almost harmless if less than 0.1 mg / dmm of stretching oil is found on the inner surface of the copper tube.

Para a eliminação da película de óleo de estiramento é já do conhecimento geral que se podem empregar agentes de desengorduramento, por exemplo dissolventes orgânicos tais como percloro etileno ou tricloroetileno. Um outro processo prevê a evaporação do oleo de estiramento e a aspiraçao dos vapores do oleo de esti ramento.In order to remove the stretch oil film, it is already known that degreasing agents, for example organic solvents such as ethylene perchlor or trichlorethylene, can be used. Another process provides for the evaporation of the drawing oil and the aspiration of the drawing oil vapors.

Um outro tipo de tratamento consiste em realizar o recozimento numa atmosfera redutora e em eliminar a película de carbono assim formada por meio de um jacto de limpeza. Para o efeito, in troduz-se no tubo um jacto de um meio auxiliar de limpeza ou com água sob pressão ou com ar comprimido.Another type of treatment is to carry out the annealing in a reducing atmosphere and to eliminate the carbon film thus formed by means of a cleaning jet. For this purpose, a jet of a cleaning aid is inserted into the tube, either with water under pressure or with compressed air.

A presente invenção tem eomo objectivo evitar a formação de películas de carbono e/ou de óxido quando se realiza a operação de soldadura com solda dura ou a dobragem pelo calor de tubos de cobre ou de ligas de cobre e, por consequência, melhorar a resistência â formação de fissuras destes tubos.The present invention aims to prevent the formation of carbon and / or oxide films when carrying out the welding operation with hard soldering or the heat bending of copper tubes or copper alloys and, consequently, to improve the resistance formation of cracks in these tubes.

Este objectivo é atingido, de acordo com a presente invenção, pelas caraeterístieas específicas referidas na parte de caracterização da reivindicação 1.This objective is achieved, according to the present invention, by the specific caraferístíeas referred to in the characterization part of claim 1.

Aperfeiçoamentos vantajosos são indicados nas reivindicações secundárias.Advantageous improvements are indicated in the secondary claims.

processo de acordo com a presente invenção diferencia-se dos processos até agora conhecidos empregados nos tubos de cobre essencialmente recozidos para amaciamento por uma combinação de fases de tratamento mecânicas e químicas. Com o processo de acor do com a presente invenção evita-se de maneira surpreendente a formação de películas prejudiciais, por exemplo películas que contem carbono ou películas de óxido, sobre a superfície interna de tubos de ferro endurecidos por estiramento. Estas películas que, de acordo com a teoria, actuam com eléctrodos bipolares, formam-se em geral às temperaturas usuais empregadas ao realizar a soldadura dura ou a dobragem a quente de tubos de cobre.The process according to the present invention differs from the previously known processes used in copper tubes essentially annealed for softening by a combination of mechanical and chemical treatment phases. With the process according to the present invention, the formation of harmful films, for example films containing carbon or oxide films, is surprisingly avoided on the inner surface of stretch-hardened iron tubes. These films, which, according to theory, act with bipolar electrodes, are generally formed at the usual temperatures used when performing hard welding or hot bending copper tubes.

Ensaios pormenorizados mostraram que é possível evitar pra ticamente de maneira completa a formação de películas prejudiciais se as superfícies internas dos tubos de cobre praticamente isentas de maneira completa de óleo de estiramento possuírem uma determinada rugosidade mínima depois de uma operação posterior de tratamento com jacto de modo que na superfície interna dos tu bos se obtenha uma certa estrutura superficial que possibilita apenas uma muito pequena aderência das películas obtidas com o tratamento térmico. Neste caso, não se podem formar elementos de corrosão estáveis que são a causa da formação de corrosão com fissuração. De acordo com uma forma de realização preferida, o tratamento com o material de jacto realiza-se de maneira que a superfície interna dos tubos possua um valor da rugosidade média compreendido entre 0,8 jum e 1,0 /un.Detailed tests have shown that it is possible to practically completely avoid the formation of harmful films if the internal surfaces of the copper tubes are practically completely free of stretching oil and have a certain minimum roughness after a subsequent jet treatment operation. that on the inner surface of the tubes a certain surface structure is obtained that allows only a very small adhesion of the films obtained with the heat treatment. In this case, stable corrosion elements cannot be formed which are the cause of the formation of cracked corrosion. According to a preferred embodiment, the treatment with the jet material is carried out in such a way that the inner surface of the tubes has an average roughness value between 0.8 µm and 1.0 µm.

Em seguida, ilustra-se mais completamente a presente inven ção por meio de exemplos de realização.In the following, the present invention is illustrated more fully by means of exemplary embodiments.

Exemplo 1Example 1

Tubos de SF-Cu com 5 metros de comprimento, um diâmetro de 15 mm e uma espessura de parede igual a 1 mm, estirados a frio até às dimansões finais, foram mergulhados num bahho de dissolvente de tricloroetileno para a eliminação do óleo de estiramento numa primeira operação de tratamento. Numa segunda fase de tratamento, os tubos de cobre foram ligados ao local de uma instalação de tratamento com jacto e tratados durante 5 segundos com um jacto de corundo de granulometria 54 (correspondendo a um diâmetro médio das partículas compreendido entre 300 e 350 jmm).SF-Cu tubes 5 meters long, with a diameter of 15 mm and a wall thickness equal to 1 mm, cold drawn to the final dimensions, were immersed in a trichlorethylene solvent bath to remove the stretching oil in a first treatment operation. In a second treatment phase, the copper tubes were connected to the site of a jet treatment plant and treated for 5 seconds with a corundum jet of size 54 (corresponding to an average particle diameter between 300 and 350 µm).

A pressão do jacto de limpeza era igual a cerca de 0,55 MPa. Para se limpar a superfície interna dos tubos de partículas de corundo depois da passagem das últimas partículas pode, por exemplo, introduzir-se um rolhão de feltro que preenche a secção trans versai do tubo e, em seguida, fazer transportar o rolhão de feltro depois de eventualmente embebido com um agente de limpeza através do comprimento do tubo por intermédio de pressão. Muitas vezes, é suficiente uma simples sopragem com ar comprimido para remover as partículas de corundo aderentes à parede interna do tubo. 0 valor médio da rugosidade Ra foi determinado como sendo igual a 0,8 jum. 0 teor residual de carbono < 0,03 mg/dm inferior aos limites de detecção. Os ensaios de longa duração realizados com diferentes águasde redes de distribuição domésticas que provocam a corrosão não demonstraram a presença significativa de corrosão com fissuração. Igualmente depois da soldadura com solda dura e/ou da dobragem a quente não se detectaram ataques corrosivosThe cleaning jet pressure was about 0.55 MPa. To clean the inner surface of the corundum tubes after the last particles have passed, for example, a felt plug that fills the transverse section of the tube can be inserted and then the felt plug be transported afterwards eventually soaked with a cleaning agent across the length of the tube by means of pressure. Often, a simple blow with compressed air is sufficient to remove the corundum particles adhering to the inner wall of the tube. The average roughness value R a was determined to be 0.8 µm. The residual carbon content <0.03 mg / dm below the detection limits. The long-term tests carried out with different waters of domestic distribution networks that cause corrosion have not demonstrated the significant presence of cracked corrosion. Also after welding with hard soldering and / or hot bending, no corrosive attacks were detected

- 5 Exemplo 2- 5 Example 2

Correspondentemente às condições de realização do processo referidas no Exemplo 1, utilizaram-se tubos com as dimensões de 22 x 1 mm estirados até à dimensão final. Diferentemente desse processo, os tubos foram tratados com corundo durante 10 segundos. 0 valor da rugosidade média R_, depois do tratamento com £L jacto de corundo, foi de 1,0 jum. 0 teor residual de carbono e o teor residual de agente lubrificante era igualmente inferior ao limite de detecção.Corresponding to the conditions for carrying out the process referred to in Example 1, tubes with the dimensions of 22 x 1 mm drawn to the final dimension were used. Unlike this process, the tubes were treated with corundum for 10 seconds. The value of the average roughness R1, after treatment with a corundum jet, was 1.0 µm. The residual carbon content and residual lubricant content were also below the detection limit.

Exemplo 5Example 5

De acordo com uma outra alternativa das condições do processo anteriormente mencionadas, desengorduraram-se em primeiro lugar com tricloroetano tubos estirados até à dimensão final de 15 x 1 mm, secaram-se e depois mergulharam-se num banho de ácido nítrico durante um curto intervalo de tempo. As outras condições do processo para a limpeza com jacto corresponderam às do Exemplo 1. Ensaios de longa duração em estações de ensaio instaladas em zonas com águas favoráveis à formação de fissuras não demonstraram quaisquer indicações de ataque de corrosão com fissuras.According to another alternative to the process conditions mentioned above, tubes were first degreased with trichloroethane to the final dimension of 15 x 1 mm, dried and then immersed in a bath of nitric acid for a short time. of time. The other conditions of the process for jet cleaning corresponded to those of Example 1. Long-term tests in test stations installed in areas with water favorable to the formation of cracks did not show any indications of corrosion attack with cracks.

A superfície interna dos tubos tinha um aspecto metálico brilhan te. 0 caudal de água durante o tempo de duração da limpeza foi igual a cerca de 1,5 litros/minuto que, no tubo de ensaio, corres ponde a uma velocidade média de passagem de cerca de 0,2 m/s.The inner surface of the tubes had a shiny metallic appearance. The flow of water during the cleaning time was equal to about 1.5 liters / minute which, in the test tube, corresponds to an average passage speed of about 0.2 m / s.

Claims (9)

Reivindicações.Claims. 1.- Processo para a fabricação de tubos de cobre ou de ligas de cobre, intensamente estirados, resistentes à formação de fissuras, caracterizado pelo facto de, em primeiro lugar, se desengordurar os tubos e de, em seguida, se tratar adicionalmente a superfície interior dos tubos com um jacto de partículas solidas.1.- Process for the manufacture of copper tubes or copper alloys, intensely stretched, resistant to the formation of cracks, characterized by the fact that, firstly, the tubes are degreased and then the surface is additionally treated inside the tubes with a jet of solid particles. 2.- Processo de acordo com a reivindicação 1, caracterizado pelo facto de se mergulhar os tubos num banho de dissolvente orgânico para os desengordurar.2. The process according to claim 1, characterized in that the tubes are immersed in an organic solvent bath to degrease them. 3.- Processo de acordo com as reivindicações 1 ou 2, caracte rizado pelo facto de as partículas sólidas do jacto actuarem sobre a superfície interna dos tubos durante cerca de 3 a 30 segundos.3. A process according to claim 1 or 2, characterized in that the solid particles of the jet act on the inner surface of the tubes for about 3 to 30 seconds. 4. - Processo de acordo com a reivindicação 3, caracterizado pelo facto de o tratamento com o jacto de partículas ter lugar durante 5 a 10 segundos.4. Process according to claim 3, characterized in that the treatment with the jet of particles takes place for 5 to 10 seconds. 5. - Processo de acordo com uma qualquer das reivindicações 1 a 4, caracterizado pelo facto de a pressão com que o jacto actua sobre a superfície interna dos tubos ser igual a pelo menos 0,5 MPa.5. A process according to any one of claims 1 to 4, characterized in that the pressure with which the jet acts on the internal surface of the tubes is equal to at least 0.5 MPa. 6. - Processo de acordo com uma qualquer das reivindicações 1 a 5, caracterizado pelo facto de se tratar a superfície interna dos tubos com grãos de areia ou partículas de corundo que possuem um diâmetro médio das partículas compreendido entre cerca deProcess according to any one of claims 1 to 5, characterized in that the inner surface of the tubes is treated with grains of sand or corundum particles that have an average particle diameter between about 200 e 350 um.200 and 350 um. 7,- Processo de acordo com a reivindicação 1, caracterizado pelo facto de a superfície interna dos tubos ser decapada como alternativa ou adicionalmente ao tratamento de desengorduramento.7. A process according to claim 1, characterized in that the inner surface of the tubes is etched as an alternative or in addition to the degreasing treatment. 8.- Processo de acordo com uma qualquer das reivindicações 1 a 7, caracterizado pelo facto de a superfície interna dos tubos depois de tratados com o jacto possuírem uma rugosidade média compreendida entre 0,4 a 1,5 um.8. Process according to any one of claims 1 to 7, characterized in that the inner surface of the tubes after being treated with the jet have an average roughness between 0.4 to 1.5 µm. 9,- Processo de acordo com a reivindicação 1, caracterizadoProcess according to claim 1, characterized -8* pelo facto de o valor médio da rugosidade dos tubos tratados com jacto estar compreendida entre 0,8 a 1,0 pm.-8 * because the average roughness value of the jet-treated tubes is between 0.8 to 1.0 pm.
PT88473A 1987-09-10 1988-09-09 PROCESS FOR THE MANUFACTURE OF COPPER TUBES OR COPPER ALLOYS, INTENSELY STRETCHED, RESISTANT TO FISSURE FORMATION PT88473B (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE3730367A DE3730367C2 (en) 1987-09-10 1987-09-10 Process for the production of pitting-resistant hard drawn tubes made of copper or copper alloys

Publications (2)

Publication Number Publication Date
PT88473A PT88473A (en) 1988-10-01
PT88473B true PT88473B (en) 1992-11-30

Family

ID=6335681

Family Applications (1)

Application Number Title Priority Date Filing Date
PT88473A PT88473B (en) 1987-09-10 1988-09-09 PROCESS FOR THE MANUFACTURE OF COPPER TUBES OR COPPER ALLOYS, INTENSELY STRETCHED, RESISTANT TO FISSURE FORMATION

Country Status (11)

Country Link
EP (1) EP0306810B2 (en)
AT (1) ATE103225T1 (en)
DE (2) DE3730367C2 (en)
DK (2) DK493288D0 (en)
ES (1) ES2050684T5 (en)
FI (1) FI94496B (en)
GR (1) GR3033568T3 (en)
IE (1) IE63028B1 (en)
PL (1) PL163146B1 (en)
PT (1) PT88473B (en)
YU (1) YU46572B (en)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4417455C2 (en) 1994-05-19 1997-09-25 Wieland Werke Ag Use of a corrosion-resistant tube with inner oxide layers
FI107543B (en) 1998-07-30 2001-08-31 Outokumpu Oy A method for making a copper tube
FI20001467A (en) * 2000-06-20 2001-12-21 Outokumpu Oy Process for making internally coated copper or copper alloy tubes

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2308436A1 (en) * 1975-04-25 1976-11-19 Cit Alcatel Avoiding carbon deposits during annealing, from lubricants - in the bore of drawn copper tubes, by sweeping with nitrogen
LU81564A1 (en) * 1979-07-31 1981-03-24 Liege Usines Cuivre Zinc METHOD FOR MANUFACTURING TUBES, TUBES OBTAINED BY THIS PROCESS AND THEIR USE IN CONDENSERS AND HEAT EXCHANGERS
DE3018036A1 (en) * 1980-05-10 1981-11-12 Kabel- und Metallwerke Gutehoffnungshütte AG, 3000 Hannover METHOD OF TREATING COPPER PIPES
IT1160196B (en) * 1983-02-24 1987-03-04 Dalmine Spa HOT DEOXIDATION PROCESS OF SEMI-FINISHED METAL TUBES
DE3415376A1 (en) * 1984-04-25 1985-11-07 Uhlmann, Otto, 3167 Burgdorf Method and apparatus for degreasing tubes
US4579596A (en) * 1984-11-01 1986-04-01 Union Carbide Corporation In-situ removal of oily deposits from the interior surfaces of conduits

Also Published As

Publication number Publication date
YU171088A (en) 1990-04-30
DK495488A (en) 1989-03-11
PT88473A (en) 1988-10-01
ATE103225T1 (en) 1994-04-15
DE3730367A1 (en) 1989-03-23
PL163146B1 (en) 1994-02-28
DE3888605D1 (en) 1994-04-28
EP0306810B2 (en) 2000-03-29
ES2050684T5 (en) 2000-07-01
GR3033568T3 (en) 2000-09-29
DE3730367C2 (en) 1997-10-09
DK495488D0 (en) 1988-09-06
FI94496B (en) 1995-06-15
DK170250B1 (en) 1995-07-17
YU46572B (en) 1993-11-16
FI884071A (en) 1989-03-11
EP0306810A2 (en) 1989-03-15
IE63028B1 (en) 1995-03-22
ES2050684T3 (en) 1994-06-01
EP0306810B1 (en) 1994-03-23
PL274547A1 (en) 1989-05-02
IE882707L (en) 1989-03-10
EP0306810A3 (en) 1990-05-30
FI884071A0 (en) 1988-09-02
DK493288D0 (en) 1988-09-05

Similar Documents

Publication Publication Date Title
Rebak et al. Corrosion behavior of nickel alloys in wet hydrofluoric acid
JPH0321640B2 (en)
PT88473B (en) PROCESS FOR THE MANUFACTURE OF COPPER TUBES OR COPPER ALLOYS, INTENSELY STRETCHED, RESISTANT TO FISSURE FORMATION
US3468774A (en) Electrolytic descaling of titanium and its alloys
Copson et al. Stress corrosion cracking of monel in hydrofluoric acid
US2254980A (en) Method of cleaning tubes and the like
DK169750B1 (en) Internally oxidized pipe, method of making such pipe and use of such pipe
JPS6335787A (en) Washing bath and method for removing niobium-containing coating on substrate
CN113549928B (en) Aluminum alloy pipe cleaning agent and process method
US832288A (en) Method of treating metal pipe.
JP5072059B2 (en) Cleaning method for inner surface of copper tube or copper alloy tube
US3232594A (en) Corrosion resistant apparatus for conversion coating of metals
Covington Pitting corrosion of titanium tubes in hot concentrated brine solutions
CN111702411B (en) Anti-wax-deposition surface rolling processing method for stainless steel petroleum gathering pipeline
JP2005029828A (en) Pickling agent for stainless steel
US2676180A (en) Cleaning phthalic anhydride condensers and like apparatus
JPS58153788A (en) Method of deterging inside of ring-form metal pipe
CN109763123A (en) Improve the erosion-resisting method of aluminum alloy materials
KR20220157666A (en) Passivation solution and method for passivation at room temperature using thereof
JPH0610152A (en) Treatment of base of polypropylene lining
EP0195969A2 (en) Process for the removal of paints
PL38948B1 (en)
KR19990047688A (en) Low Pollution High Speed Pickling Method
PL160578B1 (en) Method of removing bituminous deposits from surfaces of heat exchangers
PL160104B1 (en) Method of removing deposits formed during operation on heat exchange surfaces of,in particular,turbine condenser tubes on steam side

Legal Events

Date Code Title Description
FG3A Patent granted, date of granting

Effective date: 19920507

MM4A Annulment/lapse due to non-payment of fees, searched and examined patent

Free format text: MAXIMUM VALIDITY LIMIT REACHED

Effective date: 20080909