Process for coating water pipelines.

Abstract: A two-part coating system comprises a first part comprising a blend of an aliphatic polyisocyanate with a non-reactive resin or a liquid epoxide resin and a second part comprising an aromatic polyamine, such that the two parts when mixed together and applied to a surface form a rapid-setting impervious coating. The coating system is suitable for application by spraying using equipment in which the two parts of the system are first combined at the point of spraying, at the spray head. In particular the system may be used to apply an impermeable lining to the internal surfaces of pipelines, for example by means of a centrifugal spinning head.

Description: THIS INVENTION relates to the development of a novel method for forming a protective coating for the protection of water pipelines where a fast setting composition with rapid protection properties is required. For many years, the oil, gas and water industries have specified and used a variety of materials for the internal and external protection of pipelines, tanks and associated steel equipment. These materials have included coal-tar enamels, petroleum tapes, fusion bonded epoxies, asphalt, liquid applied epoxies and many many more. More recently, coatings for the internal protection of pipelines in service have been used by the water industry in particular. These coatings have been used to reline pipelines which have been in service for a number of years and which require refurbishment work to be carried out due to salt deposition, corrosion or a combination of both. Refurbishment of water pipelines and indeed oil and gas lines can be carried out by the in situ formation of plastic linings or resin impregnated linings or by the application of a liquid applied coating such as an epoxy resin or a polyurethane resin formulation. European Patent Application No. EP 0 421 393 A2 discloses a resin composition, and method for manufacture of the same, which is suitable for the manufacture of shaped articles to be used in high temperature environments. The resin composition comprises an isocyanuratering-containing polyisocyanate, an epoxy compound and an aromatic polyamine. The isocyanuratering-containing polyisocyanate, that is to say organic polyisocyanate trimer, may be trimeric hexamethylene-1, 6-diisocyanate and the epoxy compound is preferably bisphenol A epoxy resin. The aromatic polyamine is preferably 3,3'-dichloro-4,4'- diaminodiphenylmethane. The shaped article can be manufactured using conventional methods for moulding a polyurethane resin, for example, by casting a multi-mixture of an isocyanuratering-containing polyisocyanate, an epoxy compound and an aromatic polyamine into a casting mould, causing it to cure in situ and releasing the cured resin product from said mould. A curing catalyst is preferably used, which may be formed from, for example, organometal salts such as dibutyltin dilaurate or stannous octoate. The application of a two-part liquid applied system involves the initial cleaning of the pipe using a mole or screw arrangement followed by water flushing and then the application of the liquid system itself using twin feed heated lines, a slave mixing assembly and finally, a centrifugal spinning head to apply the mixed product. Using variations on this method, liquid applied epoxy coatings have been successfully applied to hundreds of kilometres of pipeline and have produced a smooth internal surface suitable for long term contact with drinking water. The major disadvantage of such a resin system however lies in the fact that the coating has to be left for minimally 16 hours before the pipeline can be returned to service simply because the coating hardens very slowly at ambient temperatures of around 5°C. This is a major drawback when considering pipelines which serve the public and which are required to be back in use as quickly as possible. This delay in returning the pipeline to service has led to a demand for a coating which can be applied to the internal surface of pipelines and which will set rapidly thereby allowing the pipe to be returned to service within two to three hours with a minimum of disruption to the water supplies involved. It is an object of the present invention to provide a method involving a rapid setting coating which can be applied to internal water pipeline surfaces and which will allow the line to be returned to service within two to three hours of application. According to one aspect of the invention there is provided a method for applying a coating which comprises a liquid epoxide resin, an aliphatic polyisocyanate and a difunctional amine in any combination to produce a high performance, rapid-setting, lining system. In its preferred form, the coating of the invention is a fast setting coating which can be applied to the internal surface of underground pipes and which will set in a matter of minutes to produce a lining which can be returned to service within two or three hours or less. The lining material is preferably applied by a centrifugal spinning head and is spun onto the internal pipe surface at a controlled film thickness. Ideally, the coating involved is not unduly affected by low temperatures or by surface moisture which is frequently present within underground pipelines. Furthermore, due to the rapid setting nature of the coating involved, the preferred system can be applied to metal, mineral or even plastic surfaces and will provide a smooth lining without the surface defects often associated with conventional liquid applied epoxy coatings. Due to the rapid setting nature of the preferred coating, the thickness of the applied film which can be achieved in one application may be from 250 microns to 5 mm or more. The coating preferably sets within seconds of being applied to the surface in question, so that sagging, which is normally associated with high film thicknesses, does not occur. The following Examples set out various formulations which were tried by the applicants, before the coating of the invention was arrived at, in attempt to find a fast setting coating which could be applied to underground and other pipelines in situ. In these Examples, as in the embodiments of the present invention to be described later, a two-part system was used to form the coating, that is to say a liquid resin and a liquid curing agent were supplied separately to a mixing site where the two components (resin and curing agent) were mixed, then sprayed onto the surface to be coated before the mixture set. Alternatively the two components could be mixed in the course of spraying. Table I below shows the results obtained with formulations which involved a conventional liquid epoxy such as DER 331 from Dow Chemical Company reacted with amine and polysulphide curing agents to produce a pipe lining. Curing Agent Thin Film Cure Time Suitability for Contact with Potable Water Aliphatic Polyamine 16 hours Yes Cycloaliphatic Polyamine 24 hours No Aromatic Polyamine 36 hours No Aliphatic Polyamine + 25 phr Polysulphide 12 hours No Cycloaliphatic Polyamine + 25 phr Polysulphide 16 hours No Aromatic Polyamine + 25 phr Polysulphide 24 hours No None of these systems could be considered suitable for use as a fast setting, in situ, coating due to a combination of high tainting properties and relatively slow curing characteristics at low temperatures. In view of these results, a second series of tests was conducted on resin systems based on polyurethane technology. In this series of tests, a number of proprietary polyurethane and poly(urethane-urea) systems were evaluated with respect to film cure, film integrity and effect on water quality. Table II details the results obtained. Resin System Thin Film Cure (5°C) Suitability for Contact with Potable Water Film Integrity in Presence of Water Aromatic Polyurethane (1) 60 mins Yes Severe foaming and blistering Aromatic Polyurethane (2) 15 mins Yes Severe foaming and blistering Aromatic Poly urethane-urea (1) 5 mins Yes Severe foaming and blistering Aromatic Poly urethane-urea (2) 2 mins Yes Severe foaming and blistering Several formulations in this series provided better results than the initial epoxy trials particularly with regard to speed of cure and suitability for contact with potable water. However all formulations evaluated exhibited varying degrees of sensitivity to high levels of surface moisture and a further series of tests was carried out to try and eliminate this water sensitivity. Table III details the results obtained. Urethane System Catalyst Thin Film Cure (5°C) Suitability for Contact with Potable Water Film Integrity in Presence of Water Aromatic Polyurethane (1) Tertiary Amine 120 mins Yes Severe Foaming and Blistering Organo Metallic 90 mins Yes Severe Foaming and Blistering Organo Metallic + Tertiary Amine 60 mins Yes Severe Foaming and Blistering Aromatic Polyurethane-urea Tertiary Amine 10 mins Yes Severe Foaming and Blistering Organometallic 8 mins Yes Severe Foaming and Blistering Organometallic + Tertiary Amine 5 mins Yes Severe Foaming and Blistering These results reinforced the view that whilst a pure polyurethane or urethane-urea would provide rapid cure characteristics and probably good water quality results, the systems involved were inheritedly sensitive to moisture regardless of the catalyst of the resin system used. With a view to overcoming this problem of moisture sensitivity, the inventors decided to try different systems comprising various polyamine combinations mixed with proprietary aromatic polyisocyanates based on MDI. Table IV details the results obtained. Curing Agent Gel Time Thin Film Cure (5°C) Film Integrity in Presence of Water Aliphatic Polyamine Instantaneous Not Assessed Not Assessed Cycloaliphatic Polyamine Instantaneous Not Assessed Not Assessed Aromatic Polyamine 3 secs 1 min Foaming/Blistering Poly (Oxypropylene) Diamine 3 secs 1 min Foaming/Blistering Poly (Oxypropylene) Triamine 2 secs 30 secs Foaming/Blistering In the tests summarised in Table IV above, the polyurea systems resulting from the amine/isocyanate reaction were characterised by very rapid set times (typically <5 seconds) which would render them impractical as in situ applied lining systems. Furthermore, water sensitivity was still observed, albeit reduced when compared to pure urethane or urethane-based systems. The inventors accordingly decided to investigate the possibility of substituting alternative polyisocyanates in such systems. Table V below summarises the results of a further series of tests carried out to evaluate the effects of such alternative aliphatic polyisocyanates. Aliphatic Polyisocyanate Curing Agent Gel Time Film Cure (5°C) Film Integrity in Presence of Moisture Biuret of HMDI Aromatic Polyamine (1) 30 secs 2 mins Excellent Aromatic Polyamine (2) 45 secs 3 mins Excellent Aromatic Polyamine (3) 5 mins 15 mins Excellent Isocyanurate Trimer of HMDI Aromatic Polyamine (1) 30 secs 2 mins Excellent Aromatic Polyamine (2) 45 secs 3 mins Excellent Aromatic Polyamine (3) 5 mins 15 mins Excellent Modified Polyisocyanate Derived from HMDI Aromatic Polyamine (1) 40 secs 3 mins Excellent Aromatic Polyamine (2) 60 secs 5 mins Excellent Aromatic Polyamine (3) 17 mins 20 mins Excellent It can be seen from these results that combinations of aliphatic polyisocyanates with selected aromatic polyamines can yield polyurea systems which exhibit rapid film cure times at low temperatures, together with insensitivity towards moisture. However, it was noted that many of these systems exhibited high linear shrinkage when curing, which would be a major disadvantage when considering internal pipelining applications. The inventors conceived the idea of blending with the aliphatic polyisocyanate a non-reactive or less reactive resin, with a view to reducing shrinkage, and tried a variety of blends of routine and non-routine resins, in combination with an aliphatic polyisocyanate/aromatic polyamine system. Table VI below shows the results obtained for some of the systems tried which appeared to yield good results. Resin Modification Additional Level (Parts per 100 of (Polyisocanate) Linear Shrinkage (%) Non-Reactive Resin (1) 0 0.150 15 0.110 30 0.050 Non-Reactive Resin (2) 0 0.150 15 0.120 30 0.050 Liquid epoxide resin (Diglycidyl ether of Bisphenol A) 0 0.150 15 0.090 30 0.040 In the systems to which Table VI above relates, "Non-Reactive Resin (1)" was octyl benzyl phthalate and "Non-Reactive Resin (2)" was hydroxy modified aromatic hydrocarbon. It can be seen from these results that the linear shrinkage of an aliphatic polyisocyanate/aromatic polyamine system can be reduced significantly by the inclusion, in accordance with the present invention, of either non-reactive or lower reactivity resins, whilst still retaining rapid film cure. The inventors postulated that the resultant extended gel time and reduced heat of reaction could lead ultimately to more complete cure and a reduced effect on water quality. A series of tests were therefore undertaken in order to compare the effects of the systems to which Table VI above relates on water quality, when these systems were used for lining water pipelines. Table VII details the results obtained. Resin Modification Addition Level (Parts per 100 of Polyisocanate) Suitability for Contact with Potable Water 15 NO Non-Reactive Resin (1) 30 NO Non-Reactive Resin (2) 15 NO 30 NO Liquid Epoxide Resin (Diglycidyl Ether of Bisphenol A) 15 YES 30 YES In Table VII above, "Non-Reactive Resin (1)" and "Non-Reactive Resin (2)" were the same compounds as identically designated in relation to Table VI above. Whereas the last two entries in Table VII above utilised, as the liquid expoxide resin, diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol F may be utilised instead, or a combination of the two. These results show that the combination of an aliphatic polyisocyanate and an aromatic polyamine, modified by the inclusion of liquid epoxide resin, can yield a system with the necessary attributes for the in situ relining of drinking water pipelines. It can be seen that, by contrast, the inclusion of non-reactive resin modifiers has an unacceptable effect on water quality. With particular regard to the use for lining water pipelines, further work was carried out to optimise the additional level of liquid epoxide resin in terms of gel time, film cure and effect on water quality. The results are detailed in Table VIII. Liquid Epoxide Resin (Parts per 100 of Aliphatic Polyisocyanate) Gel Time Film Cure (5°C) Suitability for Contact with Potable Water 0 40 secs 2.5 mins Yes 10 50 secs 3 mins Yes 20 60 secs 4 mins Yes 30 75 secs 4.5 mins Yes 40 90 secs 5 mins Yes 50 120 secs 8 mins Yes The above results show that rapid curing systems offering suitability for contact with potable water can be produced over a wide range of levels of epoxide resin modification. However, from the point of view of in situ lining, gel times of 60 - 90 seconds allied to film cure times of 4 - 5 minutes have been established as being ideal, particularly where there may be a requirement to apply up to 5 - 10 mm thickness. Practical in situ lining trials through centrifugal spinning head equipment have confirmed the practicality of such a material, with excellent film forming properties observed in the presence of residual water. Subsequent independent testing of the applied lining in accordance with BS6920 has confirmed its suitability for contact with drinking water. The formulation, embodying the invention, employed in the last-noted trials was supplied as a two-part system, comprising Part A and Part B as set out below, the two parts being supplied along separate pipelines to apparatus in which the parts were mixed and simultaneously, or with minimal delay, sprayed onto the surface to be coated. The preferred formulation had the following composition:- FORMULATION DETAILS PART A parts by weight (pbw) Aliphatic Polyisocyanate 40 Liquid Epoxide Resin 15 Titanium Dioxide 5 Potassium Sodium Aluminosilicate 3 Silica Flour 35 Fumed Silica 2 100 PART B parts by weight (pbw) Aromatic Polyamine 50 Potassium Sodium Aluminosilicate 3 Silica Flour 45 Fumed Silica 2 100 The coating apparatus may comprise a centrifugal spinning head or a self-mixing spray gun assembly, or may comprise hot airless spray equipment. Further evaluation involved a practical lining trial with the material being applied through a remote centrifugal spinning head and also independent water analysis test to BS6920 to check the effect of the system on drinking water quality. The independent BS6920 tests confirmed the acceptable nature of the film and the in situ trials confirmed that the product could be applied by remote control through a spinning head assembly and an excellent film could be formed even under adverse underground conditions. Furthermore, these trials confirmed that not only would the applied coating provide a high quality lining but also, the system could impart some structural strength characteristics to the pipeline involved. The features disclosed in the foregoing description, in the following claims may, both separately and in any combination thereof, be material for realising the invention in diverse forms thereof.

Claims: A method of forming an internal coating on the interior of a water pipeline, the method comprising the steps of: (a) providing a first liquid part comprising a liquid aliphatic polyisocyanate, (b) providing a second liquid part comprising a liquid aromatic polyamine, (c) mixing together the first part and the second part to form a mixture, and (d) applying the mixture to a surface to be coated. A method according to Claim 1 wherein said first liquid part comprises a blend of (i) an aliphatic polyisocyanate and (ii) a liquid epoxide resin. A method according to Claim 2 wherein the liquid epoxide resin is diglycidyl ether of Bisphenol A. A method according to any of Claims 1 to 3 wherein said first liquid part comprises an aliphatic polyisocyanate derived from hexamethylene di-isocyanate. A method according to Claim 4 wherein the aliphatic polyisocyanate has an isocyanate content of 20-25%. A method according to any of Claims 1 to 5 wherein said aliphatic polyisocyanate comprises biuret of HMDI. A method according to any of Claims 1 to 5 wherein said aliphatic polyisocyanate comprises isocyanurate trimer of HMDI. A method according to any of Claims 1 to 5 wherein said aliphatic polyisocyanate comprises modified polyisocyanate derived from HMDI. The method of any of Claims 1 to 8 wherein the coating is applied by centrifugal spinning head to internal pipeline surfaces. The method according to any of Claims 1 to 8 wherein the coating is applied through hot airless spray equipment. The method according to any of Claims 1 to 8 wherein the coating is applied through a self mixing spray gun assembly.

Inventors: ROBINSON IAN, ROBINSON, IAN
Applicants: WOOD LTD E, E. WOOD LIMITED
Application year: 1999
Main classification: C08G59
IPC codes: C08G59, C23C30, F16L58, C09D175