Use of a fluid, non-setting preparation for protecting underground objects against corrosion and method for sealing manhole covers

Abstract: The invention relates to the use of a preparation for insulation/sealing and coating purposes, comprising an apolar, non-setting fluid polymer having a glass transition temperature lower than -60 °C, wherein the polymer has a surface tension of less than 40 mN/m above the glass transition temperature. Preferably, the preparation contains one or more fillers having a different particle size and a different particle size distribution.

Description: The invention relates to the claim 1 and a method for sealing manhole covers. The invention relates in particular to the use of a preparation for insulating and sealing underground objects which are in contact with moisture or water, for example underground steel manhole covers, underground tanks, lines, pipes and cable sleeves. US Patent 4 094 911 discloses that linear poly(perfluoroalkylene oxide) with functional end groups, which has a glass transition temperature lower than -78 °C and a number-average molecular weight of 500 to 20 000, can be used as insulating material. European Patent Application 0 359 273 relates to polyurethanes comprising rubber-like polyoxyperfluoroalkylene blocks and rigid elements, which are derived from compounds having a low molecular weight and from (cyclo)aliphatic or aromatic diisocyanates. Said polyurethanes have a glass transition temperature lower than -80 °C. Said polymers can be used, for example, as insulating material and sealing means. GB A 2.106.307 discloses a mineral insulated electric cable having the filling of powdered insulated material, preferably powdered magnesium oxide, impregnated with a quantity of hydrophobic material, preferably liquid dimethylpolysiloxane, in particular Dow Corning Silicone Fluid No. 17. The hydrophobic material is preferably present in a proportion of 0.03 to 0.6 percent by weight in the insulating material, for example 0.11 percent by weight. EP A 024.882 discloses an electrical splice comprising a container for housing electrical wire splices, said container containing a fluid sealant having a specific gravity greater than 1. The fluid sealant is preferably a silicone fluid, preferably a methyl alkyl polysiloxane such as Dow Corning 230 fluid. US 4.962.151 discloses a composition of polymer and filler having improved extrusion properties. The polymer is preferably a polydiorganosiloxane having a degree of polymerisation of from about 200 to about 1000. The polyorganosiloxane has preferably hydroxyl end-groups. The chemical nature of the polymer is not thought to be important, as long as the polymer is essentially a linear polymer which does not chemically interact with the filler. Useful polymers are said to be polysiloxanes, polyurethanes, polysulfides, polyacrylics and polychloroprenes. EP A 244.738 discloses a sealant composition based on butyl rubber, polyisobutene, 30 to 55 percent by weight of kaolin and optionally soot. According to the example the butyl rubber contains unsaturated butyl rubber and cross-linked butyl rubber. The sealant composition is prepared by heating the butyl rubber and the polyisobutene (for example at a temperature of 100° to 200°C) and is mixed in soft form with the other components. The sealant composition is particularly suitable for use in cable sleeves, particularly cable sleeves for telecommunication cables. DE OS 2.100.478 relates to a device for the manufacturing of an insulated cable wherein a fluid or paste-like sealant is employed. The sealant is preferably a polyisobutene, more preferably a liquid polyisobutene, or a siloxane based resin. JP A 55016163 discloses a method for adhering a manhole or handhole cover in half-fixed state to a receiving frame, wherein to the surface of the manhole or handhole cover a primer is added and subsequently a hardenable type sealant which may be a silicone rubber containing sealant, said sealant comprising diorganopolysiloxane having hydroxy end-groups, ketoxysilane as the cross-linking agent, and water and air as hardening catalyst. Manhole covers are covers for manholes, which are openings in, for example, above- or below-ground steel or concrete storage chambers for liquids and gases, such as LPG tanks, boilers, cesspits and rainwater tanks. Said openings are of a size such that a person is able to pass through them. Manhole covers, underground tanks, lines and the like are made of metal and therefore show a tendency to corrode. This corrosion is undesirable since it weakens the metal. That is why attempts are made to counteract or to prevent this formation of corrosion. Various techniques and preparations are known for counteracting or preventing corrosion formation. For instance, lines and pipes of underground tanks, for example LPG tanks, are protected with the aid of so-called cathodic protection. This technique comprises the application of a low voltage to the tank or to the lines which are connected to the tank, as a result of which electrochemical reactions which lead to the formation of corrosion are not able to occur. However, this technique has a number of disadvantages. In addition to the continuous consumption of power, which is economically unattractive, there is a risk that the system will fail as a result of, for example, power disruptions. It is for this reason that preparations are preferably used to seal or insulate such lines and tanks, although the preparations according to the prior art frequently also give rise to problems. For sealing, for example, manhole covers, use is made not only of bitumen but also, for example, of preparations which contain synthetic, thermosetting resins, for example epoxy or polyurethane resins. These preparations have the disadvantage that a hard coating or seal is produced. This hard seal can easily split or tear under the influence of, for example, mechanical stresses. Another disadvantage of these preparations is that solvents are needed for their application. Following the application of the preparation, these solvents will evaporate, as a result of which a microporous seal or coating is produced, which is partially permeable to water. Water is therefore able to penetrate through this coating, with the result that corrosion formation occurs. The situation also arises that once the water has penetrated through the protective layer, the protective layer crumbles away as a result of the osmotic pressure (polar substances such as salts are not able to penetrate through the protective layer), with the consequence that the manhole cover is no longer adequately protected. Yet a further disadvantage of these preparations is that they are difficult to remove, which, for example, can be necessary in the case of repairs. It is therefore difficult to clean the surface of the manhole cover to be sealed, as a result of which the application of a fresh layer leads to mediocre sealing of the manhole cover. Bitumen-containing materials are also partially permeable to water and in general do not meet the requirements laid down by the KIWA (Keuringsinstituut voor Waterleidingartikelen; Dutch Inspection Institute for Water Supply Articles). Preparations which contain synthetic, thermosetting resins are also used for sealing cable sleeves. In these sleeves as well splitting and tearing can occur, for example as a result of mechanical stresses, for example road traffic, earth movements and the like, with the consequence that water is able to penetrate into the cable sleeve and that the cables contained therein are no longer adequately protected. Another problem which arises when sealing cable sleeves with preparations of this type is that once cable sleeves have been sealed said sleeves have to be replaced or additional cable sleeves have to be applied to make new branches. It is clear from the above that many problems can arise when the techniques and preparations according to the prior art are used. The present invention provides a solution to these problems by using a fluid material instead of setting materials. Said fluid materials have a better seating on the article to be sealed or to be insulated, as well as better deformability and very good adhesion, that is to say a good adhesive power to the surface. The preparation according to the invention is therefore also kneadable and simple to apply and to remove using a trowel. A clean surface is left behind on removal. The preparation according to the invention does not set and therefore remains soft and is also not permeable to water and is pore-tight. No additional adhesive means are required for the application of the preparation according to the invention to the surface to be sealed or to be protected. The invention therefore also relates to the use of a preparation as described in the preamble, characterised in that the polymer has a surface tension of less than 40 mN/m above the glass transition temperature. It is essential to use preparations which comprise apolar, non-setting, fluid polyisobutenes which have a glass transition temperature lower than -60 °C and a surface tension of less than 40 mN/m at 20 °C. According to the present invention, polyisobutene which has a viscosity of between 60 000 and 1 200 000 mm 2 /s at 20 °C is used. The preparation according to the invention is able to withstand many chemical substances. For instance, the preparation is able to withstand water-containing solutions of inorganic and organic substances such as salts, acids and bases, for example solutions of hydrochloric acid, sulphuric acid, phosphoric acid, chlorosulphonic acid, potassium hydroxide, sodium hydroxide, potassium bichromate, acetic acid, organic solvents, for example benzene, and corrosive gases, such as ammonia. The preparation according to the invention can also contain stabilising agents, for example agents against oxidation under the influence of heat, such as 2,6-di-t-butyl-4-methylphenol, and agents against the action of ultraviolet light. . The preparation according to the invention can contain one or more fillers. Said fillers can be of organic or inorganic nature. Examples of organic fillers are polyvinyl chloride, polyethene, polypropene, polyisoprene and rubber. Examples of inorganic fillers are inorganic minerals, salts and oxides, for example chalk, boron sulphate, aluminium oxide, silicon dioxide, ground quartz, glass, talc, slate, bentonite and the like. Preferably, a mixture of coarse and fine particles, in a specific mixing ratio, of one or more fillers is used. The rheological characteristics of the preparation according to the invention can be controlled by means of the amount of filler. According to the invention, it is therefore preferable that the fillers comprise one or more fractions, each fraction having a different particle size and a different particle size distribution. In particular, the fillers comprise at least one fraction having a particle size of 0.1 µm to 1500 µm. The fillers can be swellable or non-swellable, that is to say they increase substantially or slightly in volume as a result of the absorption of water. One example of a swellable filler is bentonite. The preparation according to the invention can therefore contain one or more polymers having a low molecular weight and/or a high molecular weight and one or more non-swellable and/or swellable fillers. The fillers can have a low or a high density. The density of the fillers can be between approximately 0.1 and 5 kg/dm 3 . Examples of a filler having a low density, for example between approximately 0.3 and 0.1 kg/dm 3 , are so-called "hollow spheres", which, for example, are produced from glass, polyvinylidene chloride or syndiotactic foams, and cork. Examples of fillers having a high density, for example a density of between 2 and 4 kg/dm 3 , are inorganic fillers such as talc and chalk. The preparation according to the invention can also contain one or more products which optionally have been obtained directly from petroleum. Examples of such products are bituminous products and paraffin-like products, for example petroleum gel and wax. The preparation according to the invention is very suitable for sealing manhole covers, which may or may not be underground. Materials which are used for sealing manhole covers must meet a number of conditions. For instance, the specific electric resistance must be high and, according to Netherlands Guideline NPR 6912, the current density of such materials must be less than 100 µA/m 2 , preferably less than 10 µA/m 2 . Therefore, according to the invention a preparation is preferably used which has an infinitely high electric resistance and a current density of less than 10 µA/m 2 , in particular of less than 1 µA/m 2 . When a preparation is used for the applications as described above, for example the sealing of manhole covers, the preparation must not be porous. If pores are present, these can fill with water in the course of time, as a result of which the sealing and insulating properties of the preparation become poorer, which is reflected in an increased current density. This effect will be more pronounced when the water contains an electrolyte, for example an inorganic salt, such as sodium chloride. It is therefore preferable that a material is used which is pore-tight, that is to say that the material contains relatively few to no pores. Therefore, according to the invention a preparation is preferably used which has a current density of less than 10 µA/m 2 when the preparation is in contact with a water-containing electrolyte which has a specific resistance of 100 Ω.m. Materials which are used to seal manhole covers must comply with the standard NEN 6910. For assessment of the pore density, these materials are spark-tested. According to the standard NEN 6910, the spark length must be at least 1.5 times the thickness of the layer of the material applied. Therefore, according to the invention a preparation is preferably used which has a pore density such that a spark having a length of 45 mm is not able to bridge a layer of the preparation which has a thickness of 30 mm, in particular of 16.5 mm. The preparation according to the invention is deformable, even long after it has been applied. Because the preparation is and remains deformable and it has a paste-like to rubber-like appearance, it is therefore capable of absorbing vibrations and shocks. Thus, in addition to the sealing effect, it also provides protection against mechanical effects, such as vibrations, with the result that damage to the article to be sealed will occur less rapidly. The preparation is not sensitive to low temperatures such as can occur during the winter months. In contrast to bitumen, the preparation does not change shape under the influence of temperature. Moreover, the preparation is not hazardous to the user, that is to say it is not toxic and does not release toxic substances and it is not irritating to the skin and the eyes. The preparation contains no substances which are harmful to the environment. The preparation adheres to every type of surface, for example surfaces comprising concrete, stone, glass, synthetic materials, such as plastics, and the like. These surfaces can be dry or damp. The preparation is preferably used at a temperature of no higher than 50 °C and no lower than -5 °C. The preparation can be filled into cartridges or tubes or into larger containers such as buckets. The preparation can therefore be applied easily using a so-called mastic gun, a trowel, a spatula or a knife. The tools which are used can be cleaned easily using natural or synthetic soap and water. The preparation according to the invention is therefore suitable for sealing cable sleeves, underground lines and pipes and also tanks and manhole covers according to the standard NEN 2768. The preparation according to the invention is, in particular, suitable for sealing manhole covers. For this purpose, a layer of at most 30 mm of the preparation is applied around the manhole cover. The preparation according to the invention is also suitable for providing protection against mechanical effects from the outside, such as vibrations and shocks. In particular, the preparation according to the invention can be used to damp sound vibrations which have a frequency of 25 to 25 000 Hz. The preparation according to the invention can therefore advantageously be used for insulating, for example, machines, buildings, loudspeaker cabinets and the like. The preparation according to the invention is also suitable as an anti-corrosion agent for welded joints and connectors for both underground and above-ground pipelines and gas lines. The preparation can also advantageously be used to protect sensitive electronic apparatus, for example electronic measurement and control apparatus and electronic apparatus for sound recording and reproduction, against moisture, dust and gases, for example corrosive gases. The preparation according to the invention can also be used for the insulation of above-ground and/or underground components which are used in the electricity generating and consuming industries, for example low- and high-voltage cables and connectors, and for the protection thereof against moisture and gases, for example corrosive gases. The preparation according to the invention can furthermore be used in combination with specific types of tape or in combination with mats. The tape or the mats can be made of a butyl rubber, polysulphide, polyvinyl chloride, polyethene and the like. The width of the mat or tape can be 2 cm to 2 m. For an application of this type, an approximately 0.1 to approximately 2 cm layer of the preparation according to the invention is applied to the mat or tape. Mats or tapes of this type are, in particular, suitable for the provision of mechanical strength and/or for improving the chemical resistance of the article to which the mat or tape is applied. The mats described above can also be used in shipbuilding for covering very large surfaces. For an application of this type the mats can be up to 4 m wide. Such mats are, in particular, suitable for covering metal objects on the inside of ships. The preparation according to the invention can furthermore be used as such in shipbuilding and in the offshore industry, for example for protecting the legs of drilling platforms, and steel components and pipes located under seawater. The suitability of the preparation according to the invention for sealing, in particular, underground steel manhole covers has been determined in a number of tests. It has also been demonstrated in these tests that better and more durable sealing of manhole covers is obtained with the use of the preparation according to the invention than with the use of the materials according to the prior art. The following experiments were carried out on the preparation that had been applied two years previously to manhole covers in a petrol station. The preparation according to the invention also complies with the standard NEN 2768. Example I In order to determine the environment around the manhole cover that had been sealed using the preparation according to the invention, soil samples of the packing sand alongside the manhole cover were taken. The specific electric resistance of the packing sand in the dry state is about 1000 Ω.m and in the wet state about 500 Ω.m. This means that the packing sand complies with the CPR 8.1 guideline and is thus of high quality. The specific electric resistance of this packing sand has a preventive action against corrosion. The metal-electrolyte potential V in and the associated current density of a tank body which had not been dug free were determined (Experiment 1, Table 1). The metal-electrolyte potential is the voltage difference between a metal object (this is the tank in this experiment) in an electrolyte and a measurement electrode which is in contact with the electrolyte. The measurement electrode comprises a galvanic half-cell, consisting of a copper rod in a saturated solution of copper sulphate. The metal-electrolyte potential was measured as such and immediately after switching off the protective current. The protective current is a current supplied to the metal object by a galvanic sacrificial anode, which is made of a metal which is less noble than the metal from which the object is made, or by an external current source, and which neutralises the potential differences at the metal's surface. The measurement in the absence of the protective current provides the true potential of the metal object V out , which is lower than the metal-electrolyte potential in the presence of a protective current. This reduction is caused by the current which flows through the electric circuit. The metal-electrolyte potential was also determined after the risers of the tank had been dug free (Experiment 2) and after the manhole cover had been dug free (Experiment 3). Experiment V in (mV) V out (mV) I (µA) 1 1520 820 45.0 2 1520 820 40.0 3 1520 820 40.0 These experiments show that the specific electric resistance of the preparation is infinitely high. Example II The current density of the preparation was also determined in the above experiment. It was found that in a high-ohm environment the current density was approximately 0 µA/m 2 . Example III The pore density of the preparation was determined with the aid of DC sparking equipment in accordance with the standard NEN 6910. The specification for a bitumen coating on the manhole cover is that no arc-over may occur when the spark length is 1.5 times the thickness of the layer applied (this approximately corresponds to a voltage of 4.5 kV per mm layer thickness). It was found that with a spark length of 45 mm no arc-over occurred with layer thicknesses of 30 mm and did not occur even with layer thicknesses of 16.5 mm. Example IV The pore density of the preparation was also determined in another experiment. The manhole cover from Example I was steeped with an electrolyte-containing solution which had a specific electric resistance of 100 Ω.m. That is to say the cavity dug out, in which the manhole cover is located, is filled with the electrolyte-containing water. The metal-electrolyte potential was then determined in the presence and the absence of the protective current, in accordance with the method of Example I, it being found that V in was 1520 mV, V out 800 mV and I 50 µA. This means that even in a damp and aggressive environment the specific electric resistance of the preparation is infinitely high. Example V In this experiment the adhesion of the preparation to metal was tested. A V-shaped cut was made in the preparation which had been applied to a manhole cover without an additional adhesive and the preparation was removed using a trowel. Traces of the preparation were visible on the metal, which demonstrates that the adhesion was satisfactory. It was also found that the metal surface was not corroded and that no accumulation of water had occurred beneath the preparation. Example VI The specific resistance of the preparation was also determined in the following experiment. The preparation was placed in a so-called CIGRE cell and the cell was then heated to 100 °C. A direct voltage of 500 V was then applied over the cell and the specific resistance was determined after 5 minutes. The specific resistance was found to be 19*10 12 Ω.m.

Claims: Use of a fluid, non-setting preparation having a paste-like to rubber-like appearance for protecting underground objects that are made of metal and that are in contact with moisture or water against corrosion, the preparation comprising an apolar, non-setting fluid polymer having a glass transition temperature lower than -60°C and a surface tension of less than 40 mN/m above the glass transition temperature, wherein the polymer is a polyisobutene having a viscosity of between 60.000 to 1.200.000 mm 2 /s at 20°C. Use according to Claim 1, wherein the preparation contains one or more fillers chosen from inorganic and organic fillers. Use according to Claim 2, wherein the fillers comprise one or more fractions, wherein each fraction has a different particle size and a different particle size distribution. Use according to Claim 2 or 3, wherein the fillers comprise at least one fraction having a particle size of 0.1 µm to 1500 µm. Method for sealing manhole covers which are located below ground level, wherein a layer having a thickness of less than 30 mm of a preparation as defined in any one of claims 1 - 3 is applied. Method according to Claim 5, wherein the preparation is used at a temperature of -10° to 50°C. Use according to any one of Claims 2 to 3, wherein the fillers are swellable fillers. Use according to any one of Claims 1 to 4 as an anti-corrosion agent for connectors for underground pipelines and gaslines, for flanges, crane books, welded joints, T-joints and thermit weldings in divisible shafts below the ground level. Use according to any one of Claims 1 to 4 for sealing objects wherein the preparation is used at a temperature of -30° to 150°C. Use according to any one of Claims 1 to 4 for sealing underground lines and pipes, tanks and manhole covers according to NEN 2768. Use according to any one of Claims 1 to 4, wherein the fluid, non-setting preparation is used in combination with a tape or a mat.

Inventors: NOOREN FRANCISCUS PETRUS, NOOREN, FRANCISCUS PETRUS
Applicants: FRANS NOOREN AFDICHTINGSSYSTEM, FRANS NOOREN AFDICHTINGSSYSTEMEN B.V.
Application year: 1996
Main classification: C09K3
IPC codes: C09D5, F16J12, E02D29, H02G15, C08L101, C08K3, C09K3, C08K5, H02G9