Corrosion protection for cast iron pipes and method for producing same

Abstract

The invention relates to corrosion-protected ductile cast iron pipes, a method for producing corrosion-protected ductile cast iron pipes, and the use of specific compositions for producing corrosion-protected ductile cast iron pipes. More particularly, the invention relates to corrosion protection for ductile cast iron pipes using latex-modified cement mortars based on calcium-aluminum cements.

Claims

1. A ductile cast iron pipe having a surface, at least a part of said surface comprising a coating of a latex-modified cement mortar, wherein said latex-modified cement mortar is a cement mortar comprising a calcium aluminate cement composition that comprises the following: at least 5% by mass of CaAl.sub.2O.sub.4 based on 100% by mass of dry calcium aluminate cement composition, at least 5% by mass of Ca.sub.3Al.sub.2O.sub.6 based on 100% by mass of dry calcium aluminate cement composition, and at least one inorganic filler.

2. The ductile cast iron pipe of claim 1, wherein said surface comprises an inner cylindrical surface, wherein said coating of a latex-modified cement mortar is at least on part of said inner cylindrical surface.

3. The ductile cast iron pipe of claim 1, wherein said surface comprises an outer cylindrical surface, wherein said coating of a latex-modified cement mortar is at least on part of said outer cylindrical surface.

4. The ductile cast iron pipe of claim 1, wherein said surface comprises an inner cylindrical surface and an outer cylindrical surface, wherein said coating of a latex-modified cement mortar is at least on part of said inner cylindrical surface and said outer cylindrical surface.

5. The ductile cast iron pipe of claim 1, wherein said latex-modified cement mortar further comprising one or more further aluminates.

6. The ductile cast iron pipe of claim 1, wherein said latex-modified cement mortar further comprising auxiliaries, secondary phases and amorphous components.

7. The ductile cast iron pipe of claim 1, wherein said latex-modified cement mortar comprises 5-35% by mass of CaAl.sub.2O.sub.4, based on 100% by mass of dry calcium aluminate cement composition.

8. The ductile cast iron pipe of claim 7, wherein said latex-modified cement mortar comprises 15-30% by mass of CaAl.sub.2O.sub.4, based on 100% by mass of dry calcium aluminate cement composition.

9. The ductile cast iron pipe of claim 1, wherein said latex-modified cement mortar comprises 5-35% by mass of Ca.sub.3Al.sub.2O.sub.6, based on 100% by mass of dry calcium aluminate cement composition.

10. The ductile cast iron pipe of claim 9, wherein said latex-modified cement mortar comprises 5-10% by mass of Ca.sub.3Al.sub.2O.sub.6, based on 100% by mass of dry calcium aluminate cement composition.

11. The ductile cast iron pipe of claim 1, wherein said latex-modified cement mortar comprises at least 20% by mass of said at least one inorganic filler, based on 100% by mass of dry calcium aluminate cement composition.

12. The ductile cast iron pipe of claim 1, wherein said latex-modified cement mortar comprises at least 40% by mass of said at least one inorganic filler, based on 100% by mass of dry calcium aluminate cement composition.

13. The ductile cast iron pipe of claim 1, wherein said latex-modified cement mortar comprises 60-70% by mass of said at least one inorganic filler, based on 100% by mass of dry calcium aluminate cement composition.

14. The ductile cast iron pipe of claim 1, wherein said coating has a thickness of not more than 2 mm.

15. The ductile cast iron pipe of claim 1, wherein said coating has a thickness of not more than 500 m.

16. The ductile cast iron pipe of claim 1, wherein said latex-modified cement mortar is a cement mortar which has been modified with at least one latex selected from among polyisoprene latexes and polychloroprene latexes.

17. The ductile cast iron pipe of claim 1, wherein said latex-modified cement mortar further comprises at least one melamine-formaldehyde resin.

18. The ductile cast iron pipe of claim 1, wherein said latex-modified cement mortar further comprises at least one silane bonding agent.

19. A method for producing a coated ductile cast iron pipe, said method comprising the steps of: providing a ductile cast iron pipe, said ductile cast iron pipe comprising a surface, and coating at least part of said surface of said ductile cast iron pipe with a latex-modified cement mortar, wherein said latex-modified cement mortar is a cement mortar comprising a calcium aluminate cement composition that comprises at least 5% by mass of CaAl.sub.2O.sub.4 based on 100% by mass of dry calcium aluminate cement composition, at least 5% by mass of Ca.sub.3Al.sub.2O.sub.6 based on 100% by mass of dry calcium aluminate cement composition, and at least one inorganic filler.

20. The method of claim 19, wherein said surface comprises an inner cylindrical surface, and wherein said coating of a latex-modified cement mortar is provided at least on part of said inner cylindrical surface.

21. The method of claim 19, wherein said surface comprises an outer cylindrical surface, and wherein said coating of a latex-modified cement mortar is provided at least on part of said outer cylindrical surface.

22. The method of claim 19, wherein said surface comprises an inner cylindrical surface and an outer cylindrical surface, and wherein said coating of a latex-modified cement mortar is provided at least on part of said inner cylindrical sur-face and part of said outer cylindrical surface.

23. The method of claim 19, wherein said latex-modified cement mortar is applied by spray processes.

24. The method of claim 23, wherein said spray processes are airless spray processes.

25. The method of claim 19, wherein said latex-modified cement mortar is applied by casting processes.

26. The method of claim 25, wherein said casting processes are centrifugal casting processes.

27. The method of claim 19, wherein said latex-modified cement mortar is applied by extrusion processes.

28. The method of claim 19, wherein said coating step is followed by a step comprising wrapping of a nonwoven tape around at least part of said ductile cast iron pipe.

29. The method of claim 19, wherein said coating step is followed by a step comprising wrapping of a woven fabric tape around at least part of said ductile cast iron pipe.

30. The method of claim 29, wherein said woven fabric tape is a polymer woven fabric tape.

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(1) The cast iron pipe used for the purposes of the invention can be any cast iron pipe known to those skilled in the art. It can be in this case a pipe obtained directly after casting or a pipe which has been processed further, e.g. a pickled or sand-blasted pipe or a pipe which has been provided with an electrochemically active layer.

(2) The expression latex refers, for the purposes of the invention, to a colloidal suspension or dispersion of polymer particles in water. A latex usually contains about 50% by weight of approximately spherical polymer particles in a size range from 0.01 m to about 1 m. The polymers used in the latex can be either elastomeric polymers or thermoplastic polymers, with elastomeric polymers generally being preferred. The polymers used in the latex can be of either natural or synthetic origin. Examples of such polymers which are suitable for producing a latex for the purposes of the invention include but are not restricted to the following: polyacrylates, polymers and copolymers based on butadiene, for example styrene-butadiene or butadiene-acrylate copolymers, polymers and copolymers based on styrene, for example styrene-acrylate copolymers, polyisoprene rubbers and also polychloroprene rubbers. In some embodiments of the invention, preference can be given to the latex being a latex based on polyisoprene rubber or polychloroprene rubber.

(3) To produce the cement mortar used according to the invention, the dry cement used is mixed with the latex, with further additives optionally being added. The water present in the latex is usually sufficient to make up the cement mortar, but it is also possible for additional water to be added.

(4) For the purposes of the invention, the expression inorganic fillers refers to any particulate, inorganic material which is suitable as aggregate for cement mortar. This material is usually a finely particulate material having an average particle diameter of 500 m and less, preferably 100 m and less. However, it is also possible, for example, for the filler to be in the form of short fibers, e.g. in the form of glass fibers or carbon fibers (also referred to as whiskers). The inorganic filler can be a synthetic or natural material, e.g. a mineral filler. Examples of suitable fillers include but are not restricted to the following: quartzes; basalts; granites; feldspar; fillers based on aluminum, for example fillers based on aluminum oxides or aluminosilicates; clays or clay minerals such as kaolinite, chrysotile, illite, smectite, vermiculite, chlorite, montmorillonite, beidellite, nontronite, saponite or bentonite; fillers based on oxides of silicon, titanium or boron; and fillers based on the oxides and silicates of zirconium. In some embodiments, preference can be given to the inorganic filler being a filler based on silicon and in particular based on SiO.sub.2. Fillers based on SiO.sub.2 can be fillers based on amorphous SiO.sub.2, for example fillers based on kieselguhr or fillers based on crystalline SiO.sub.2, for example quartz.

(5) The cement mortar based on calcium aluminate cement can be a ready-mixed product or else be a specifically produced mixture. In some embodiments, the use of alumina cements as starting materials for the cement mortar based on calcium aluminate cement used for the purposes of the invention can be advantageous.

(6) In addition to the abovementioned constituents, the cement mortar used according to the invention can comprise further generally known auxiliaries and additives. Examples of these include but are not restricted to the following: antifoams, surfactants, e.g. surfactants for stabilizing the latex, bonding agents, reinforcing fibers or polymers and polymer particles.

(7) To apply the latex-modified cement mortar, it is possible use any method known in the technical field. Examples of such methods include the following: spray processes, casting processes, in particular centrifugal casting processes, and extrusion processes. The application of the cement mortar can optionally be followed by a step in which a nonwoven tape or a woven fabric tape, in particular a polymer woven fabric tape, is wrapped around at least part of the ductile cast iron pipe. In some embodiments, the cement mortar can preferably be applied by means of an extrusion process using a slit die. It can also be advantageous to apply the cement mortar by spray processes which are referred to as airless spray processes.

(8) For the purposes of the present invention, the expression comprise or comprising refers to an open listing and does not rule out constituents or steps other than the constituents or steps which are expressly mentioned.

(9) For the purposes of the present invention, the expression consist of or consisting of refers to a closed listing and rules out any constituents or steps other than the constituents or steps which are expressly mentioned.

(10) For the purposes of the present invention, the expression consist essentially of or consisting essentially of refers to a partly closed listing and refers to compositions which apart from the constituents mentioned comprise only such further constituents which do not materially alter the character of the composition or are present in amounts which do not materially alter the character of the composition.

(11) When, for the purposes of the present invention, a composition is described using the expression comprise or comprising, this expressly includes compositions which consist of the constituents mentioned or consist essentially of the constituents mentioned.

(12) In one embodiment, the cement mortar comprises 5-35% by mass, preferably 15-30% by mass, of CaAl.sub.2O.sub.4.

(13) In one embodiment, the cement mortar comprises 5-35% by mass, preferably 5-10% by mass, of Ca.sub.3Al.sub.2O.sub.6.

(14) In one embodiment, the cement mortar comprises at least 20% by mass, preferably at least 40% by mass and in particular 60-70% by mass, of the at least one inorganic filler.

(15) It has been found that the use of calcium aluminates and fillers in the abovementioned ranges leads to coatings which adhere particularly well.

(16) In one embodiment of the invention, the latex-modified cement mortar is a cement mortar which has been modified with at least one latex selected from among polyisoprene latexes and polychloroprene latexes.

(17) It has been found that the use of polyisoprene latexes and polychloroprene latexes for modifying the cement mortar leads to a coating which adheres particularly stably. Even though the applicant does not wish to be tied thereto, it is assumed that the use of polyisoprene latexes and polychloroprene latexes gives the coating particular elasticity.

(18) In a further embodiment of the invention, the latex-modified cement mortar further comprises at least one melamine-formaldehyde resin.

(19) It has been found that the additional incorporation of melamine-formaldehyde resins further assists the stability of the coating obtained; without being tied thereto, the applicant assumes that the addition of melamine-formaldehyde resin increases the cracking resistance of the coating obtained.

(20) In a further embodiment of the invention, the latex-modified cement mortar further comprises at least one silane bonding agent.

(21) It has been found that the adhesion of the coating to the ductile cast iron pipes can be improved further by the use of silane bonding agents. Even though the applicant does not wish to be tied to any theory, the applicant assumes that the use of silane bonding agents leads to a type of copolymerization, with the silanes firstly being capable of bonding to the cement phases and iron oxide phases of the scale, and also being able to interact with the polymers. This leads to an increase in strength and to an increase in the adhesion.

(22) In a further embodiment of the invention, the coating has a thickness of not more than 2 mm, preferably not more than 500 m.

(23) It has been found that coatings having this thickness are advantageous both in respect of the further processing of the pipes and also in respect of a very small increase in weight, without the corrosion protection being impaired thereby.

(24) In a further embodiment of the invention, the latex-modified cement mortar is applied by a method selected from the group consisting of spray processes, in particular airless spray processes, casting processes, in particular centrifugal casting processes, and extrusion processes.

(25) It has been found that the abovementioned methods are particularly suitable for applying the cement mortar.

(26) In a further embodiment of the invention, the coating step is followed by a step comprising wrapping of a nonwoven tape or a woven fabric tape, in particular a polymer woven fabric tape, around at least part of the ductile cast iron pipe.

(27) It has been found that wrapping the coated cast iron pipe in a nonwoven tape or a woven fabric tape and in particular a polymer woven fabric tape enables the resistance of the coating to be improved further.

(28) It goes without saying that the abovementioned features and the features still to be explained below can be employed not only in the combination indicated in each case but also in other combinations or alone without going outside the scope of the present invention.

(29) The invention will be illustrated below with the aid of an example and explained in more detail in the following description.

Example 1

(30) A hydraulically setting mineral composition consisting of 60% by mass of quartz and about 35% of alumina cement (about 26% by mass of CaAl.sub.2O.sub.4 and 7% by mass of Ca.sub.3Al.sub.2O.sub.6 based on 100% by mass of the dry cement), where the remaining 5% are made up by secondary phases, is mixed with a sufficient amount of a polychloroprene latex (mass ratio of dry cement/latex dispersion=3:1) in order to give a processable mortar. The latex used comprises 40% by weight of polychloroprene and 20% by weight of melamine formaldehyde resin and is stabilized by addition of polyoxyethylene sorbitan trioleate and also further surfactants based on fatty acid polyglycol esters. The cement mortar thus obtained is applied by means of the airless process to an untreated ductile cast iron pipe and cured at room temperature over a period of 3 hours. This gives an about 500 m thick crack-free closed coating which meets the corrosion protection requirements for pipes laid underground.

(31) In tests on the adhesion of the coating to the ductile cast iron pipe in accordance with DIN EN 15189, it has been found that cracks occur within the coating itself before the coating is torn from the ductile cast iron pipe and only parts of the coating are torn off, with sufficient coating material remaining on the total coated surface of the cast iron pipe to ensure corrosion protection. This clearly demonstrates the superior adhesion of the layer according to the invention. Likewise, it has been found in studies on the impact resistance in accordance with DIN EN 15542 that the coating of the invention has, with an impact resistance of more than 175 Nm, a superior impact resistance. The latter is particularly advantageous when the pipes are bedded using a coarsely particulate bedding material.