INTERNAL ANTICORROSIVE AND ABRASIVE RESISTANT PROTECTION COATING FOR PIPES

Abstract

The present invention includes an inner anticorrosive and abrasive resistant coating (10) for metallic pipes (1) used for the transport of fluids. The coating includes: a layer of epoxy resin (2) having free hydroxyl groups, which are applied directly to the inside (1a) of the metallic pipe (1); a layer of thermoplastic adhesive (3) applied directly onto the layer of epoxy resin; and a layer of a plastic material (4) containing polyvinylidene fluoride or polyvinylidene difluoride (PVDF).

Claims

1. An inner coating (10) providing anticorrosive and abrasive resistant protection for metallic pipes (1) used for the transport of fluids, the coating includes: a layer of epoxy resin having free hydroxyl groups (2) applied directly onto the inner surface (1a) of the metallic pipe (1); a layer of thermoplastic adhesive (3) applied directly onto the layer of epoxy resin, the thermoplastic adhesive is anhydride modified polyolefin or acrylic acid modified polyolefin; and a layer of polyvinylidene fluoride or polyvinylidene difluoride (PVDF) as a thermoplastic material directly applied onto the adhesive layer.

2. The coating of claim 1, wherein the coating has a level of adherence higher than 15.3 Kg/25 mm at a temperature of 20 C.

3. The coating of claim 1, wherein it withstands sharp pressure drops at temperatures ranging from 30 C. below zero to 110 C.

4. An internally lined metallic pipe with an inner coating providing anticorrosion and abrasive resistant protection of the pipe, the coating includes: a layer of epoxy resin having free hydroxyl groups (2) applied directly onto the inner surface (1a) of the metallic pipe (1); a layer of thermoplastic adhesive (3) applied directly onto the layer of epoxy resin, the thermoplastic adhesive is anhydride modified polyolefin or acrylic acid modified polyolefin; and a layer of polyvinylidene fluoride or polyvinylidene difluoride (PVDF) as a thermoplastic material directly applied onto the adhesive layer.

5. A method to apply an anticorrosive and abrasive resistant inner coating to a pipe, the method comprising the steps of: burning the pipe to a temperature between 100 C. to 350 C.; cleaning an inner surface (1a) of the pipe by using abrasive blasting; heating an exterior surface of the pipe to a temperature of between 120 C. and 180 C.; applying while heating an epoxy resin layer (2) onto the inner surface (1a) of the pipe (1); applying a layer of thermoplastic adhesive (3) directly onto the epoxy resin layer (2) while continuing heating the exterior surface of the pipe; and pressing against the layer of thermoplastic adhesive, while continuing heating the exterior surface of the pipe, a layer (4) containing polyvinylidene fluoride or polyvinylidene difluoride (PVDF).

Description

BRIEF DESCRIPTION OF DRAWINGS

[0023] FIG. 1 illustrates a cross section of the metallic pipe (1), which includes the coating as described in the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0024] With the aim to make the present invention comprehensible so that it can be applied easily, a precise description of the preferred method for manufacturing will be presented in the following paragraphs. Said description includes a diagram illustrating the invention. Said description and diagram cannot be regarded in any way as limiting the invention. The components mentioned in the description can be selected among various equivalents, but without deviating from the principles of the invention set forth in the current documentation.

[0025] In the case described in the present documentation, it protects the metallic pipe with a three-layer coating, which includes an epoxy resin and a plastic material with an in-between layer made up of an adhesive, which allows said three layers to bond and fuse with each other and the metallic pipe.

[0026] Each of the component layers exhibits features that taken together afford a much superior protection compared to that of solutions in the prior art.

[0027] The present invention includes an inner anticorrosive and abrasive resistant coating for metallic pipes used for the transport of fluids. The coating includes:

[0028] a layer of epoxy resin having free hydroxyl groups, which is applied directly to the inside of the metallic pipe;

[0029] a layer of thermoplastic adhesive applied directly onto the layer of epoxy resin, the thermoplastic adhesive is anhydride modified polyolefin or acrylic acid modified polyolefin; and

[0030] a layer of polyvinylidene fluoride or polyvinylidene difluoride (PVDF) as a thermoplastic material directly applied onto the adhesive layer.

Epoxy Resin

[0031] The epoxy resin used in the present invention may be any resin that contains free hydroxyl groups.

[0032] The epoxy resin having free hydroxyl groups adheres to the metallic surface because of the chemical bonds formed through electron sharing by groups on the substrate and the free hydroxyl groups of the epoxy resin, the curing is accompanied by polarity change.

[0033] It will be understood that the curing phenomenon of epoxy resin compositions involves chemical linking between polymer chains and that this linking (or cross-linking) mechanism is initiated almost immediately upon application of the epoxy resin upon a hot surface and continues as the epoxy resin composition melts, coalesces and gels.

[0034] Examples of preferred epoxy resins having free hydroxyl groups useful in the present invention are Epoxy, Phenolic Epoxy, Polyurethane Epoxy, and/or Novolac.

[0035] The thickness of the layer of epoxy resin is at least 30 microns, preferably between 30 and 250 microns.

Thermoplastic Adhesive

[0036] In the preferred method for manufacturing described in the present documentation, the adhesive (3) is of the thermoplastic type and it allows a chemical bond with the epoxy of the first layer (2), so as to obtain full adherence to the metal.

[0037] The thermoplastic adhesive used in the present invention may be Anhydride modified polyolefin or acrylic acid modified polyolefin, since the epoxy resins have free hydroxyl groups anhydride or acrylic acid adhesive that can react to form very strong bonds to the epoxy.

[0038] Epoxy resin combines very low permeability to oxygen with excellent adhesion to properly prepare metallic surfaces and excellent resistance to cathodic disbondment. However, it is permeable to moisture, and is easily damaged by mechanical impacts. It is therefore beneficial to cover the epoxy resin with a layer of a polymer that is highly resistant to moisture permeation and resistant to impact damage.

[0039] Polyolefin coatings are widely used to protect metal pipelines, especially oil and gas pipelines, from both corrosion and mechanical damage. Unfortunately, the actual thermoplastic internal coating or polyolefins liners are not bonded to epoxy resin. The present invention uses modified polyolefins that contain polar groups to bond to the epoxy resin layer.

[0040] It is to be understood that the term modified polyolefin, as used in the present invention, includes not only a polyolefin that is modified with an unsaturated carboxylic acid or an anhydride thereof, that is, a polyolefin copolymerized with the unsaturated carboxylic acid or the anhydride thereof, but also includes a blend of a polyolefin modified with the unsaturated carboxylic acid or anhydride thereof and an unmodified polyolefin.

[0041] The epoxy resin free hydroxyl-groups and the carboxylic acid dimer hydrogen bonding produces an epoxy resin-anhydride system. The gelation phase of reaction exhibits rapid initial hydroxyl-anhydride reactions.

[0042] The acid or anhydride modified polyolefins of the invention are, in most cases, acid or anhydride modified polyethylenes; polypropylenes, or combinations thereof. Most preferably the polyolefins of the invention are acid or anhydride modified polypropylenes, add or anhydride modified polypropylene derivatives, or mixtures of these. The acid or anhydride modified polyolefin component of the invention may also be mixtures of add or anhydride modified polyolefins with unmodified polyolefins. Preferably, if the emulsion comprises several polyolefins, most of the polyolefins have grafted thereto at least one acid or anhydride. The acids or anhydrides grafted on the polyolefins may be, in particular, ethylene-substituted carboxylic acids and/or polycarboxylic acids and/or acid anhydrides, such as, for example, maleic, acrylic, methacrylic, itaconic or citraconic acid (or anhydride). Most preferably the acid or anhydride modified polyolefins of the invention are maleic anhydride modified polypropylenes.

[0043] Examples of preferred acid or anhydride modified polyolefin dispersions useful in the present invention are maleic anhydride grafted polypropylene dispersions such as Hydrosize XM-10075, Hydrosize PP2-01, Hydrosize PPI-OI (all from Hydrosize Technologies, Inc., Raleigh, N.C.) and Michem Emulsion 91735 (available from Michelman, Inc., Cincinnati, Ohio).

[0044] The thickness of the layer of the adhesive is at least 50 microns, preferably between 50 and 300.

Polyvinylidene Fluoride or Polyvinylidene Difluoride (PVDF)

[0045] Onto the layer of thermoplastic adhesive (3) a layer of plastic material is applied. This makes up the inner protection, which is very effective against abrasion and corrosion caused by fluids transported through metallic pipes (1).

[0046] The plastic material is made of polyvinylidene fluoride or polyvinylidene difluoride (PVDF). PVDF is a semi-crystalline, high purity thermoplastic fluoropolymer having a chemical formula.

##STR00001##

[0047] and structural formula:

##STR00002##

[0048] The polyvinylidene fluoride or polyvinylidene difluoride (PVDF) is fused plastically with the adhesive of the layer of thermoplastic material (3) and the layer of epoxy resin (2) achieving complete adhesion to the metal.

[0049] Polyvinylidene fluoride (PVDF) withstands exposure to harsh thermal, chemical, or ultraviolet conditions. The insolubility and electrical properties result from the polarity of alternating CH2 and CF2 groups on the polymer chain. PVDF may be used at temperatures from 80 to 300 F.

[0050] PVDF has:

[0051] low weight;

[0052] low thermal conductivity;

[0053] high chemical corrosion resistance;

[0054] heat resistance;

[0055] mechanical strength and toughness;

[0056] high abrasion resistance;

[0057] resistant to most chemicals and solvents;

[0058] low permeability to most gases and liquids;

[0059] withstands exposure to harsh thermal and chemical conditions; and

[0060] unaffected by long-term exposure to ultraviolet radiation.

[0061] PVDF is not affected by long-term exposure to sunlight and other sources of ultraviolet radiation. It retains its properties in high vacuum and gamma radiation and is resistant to most acids and alkalis.

[0062] The preferred PVDF resins are those having a molecular weight in the range of about 10,000 to 70,000, most preferably about 30,000 to 50,000, a melting temperature of about 155 to 175 C., a melt flow index (according to ASTM D 3418) of about 3 to 30 g/10 min, most preferably about 5 to 10 g/10 min, and a melt viscosity (according to ASTM D 3835) of about 6,000 to 12,000 Poise (P) at 230 C., most preferably about 7,000 to 10,000 P. Coatings made from PVDF resins with molecular weights lower than about 10,000 have poorer mechanical properties. On the other hand, powders made from PVDF resins having a molecular weight greater than about 70,000 remain excessively viscous during the heat treatment.

[0063] Basically, the chains of the thermoplastic adhesive and the PVDF merge plastically when they reach the melting temperature producing a complete diffusion of the polymer chains, creating a fully united layer.

[0064] The thickness of the layer of the PVDF layer is between 1 mm to 8 mm.

[0065] The advantage of the above system lies in the fact that the epoxy coating provides good adhesion to the metallic surface, corrosion protection; high cathodic disbound resistance and excellent barrier to gases to the underlying metallic pipeline, and the PVDF layer provides excellent abrasion; impermeability to liquids, and impact resistance and acts as a complete barrier to the underlying pipe surface.

[0066] The PVDF layer, once it has cured, provides a tough, flexible and impermeable protective coating.

[0067] The epoxy resin layer (2) is applied onto the inner surface (1a) of the metallic pipe (1). Once the pipe has been burned (1) and later cleaned (abrasive blasting) with an abrasive material, so as to eliminate contaminants, the inside surface (1a) of the pipe (1) will be clean and ready for the epoxy resin (2) to be applied.

[0068] Before applying the epoxy resin (2), the metallic pipe (1) will be burned. In the burn-off step, the temperature must be controlled so as not to alter the metallographic conditions of the metallic pipe (1). For this reason, the burn-off temperature must not exceed 350 C. This temperature will easily eliminate oils, grease, and fuel residues that might be covering inside of the metallic pipe (1). On the other hand, the applied temperature must not be lower than 100 C., since below that level the desired burn-off will not be achieved.

[0069] The abrasive blasting step seeks to prepare the inner surface of the metallic pipe (1) by complementing the burn-off described in the previous step and, thus, improving the adherence of the epoxy resin (2). In the preferred method for manufacturing described, the abrasive blasting is done with non-contaminating material, preferably using O.sub.2Al.sub.3 grit.

[0070] Then comes a heating step, whereby the pipe (1) is heated at a temperature of between 120 C. and 180 C., since this temperature improves the curing of the epoxy resin (2), which is applied at a later step before it completes its polymerization. In the preferred method for manufacturing in the present documentation, in the step where the metallic pipe is heated, the heat is applied onto the exterior surface of said metallic pipe (1).

[0071] The next step involves applying a layer of epoxy resin on the inner surface (1a) of the metallic pipe (1). The epoxy resin can be applied in liquid, granular, or powder form.

[0072] Then a layer of thermoplastic adhesive (3) is applied directly onto the layer of the epoxy resin (2), while raising the temperature of the metallic pipe, thus, achieving a chemical bond between said epoxy resin layer (2) and the thermoplastic adhesive layer (3). This makes the adhesive (3) come into close contact with the epoxy resin (2). Hence, in the step where the temperature is raised, said epoxy resin (2) will be cured. The polymerization of the epoxy resin (2) and the fusion of the adhesive (3), which result from the step where the temperature is raised to ensure a very strong chemical coupling, due to union of the carboxyl groups and the epoxy groups. As in the previous heating step, in the step where the temperature is raised, the metallic pipe (1) is heated from the outside, so that in both cases the temperature reaches the inner surface (1a) of said metallic pipe (1) by conduction.

[0073] The temperature at which the metallic pipe (1) is heated in the heating step depends on the thickness and diameter of the metallic pipe (1). Of course, it is closely related to the composition and the temperature of the product that will be transported.

[0074] In the preferred method described in the present documentation, the temperature at which the metallic pipe is heated ranges between 180 C. and 350 C.

[0075] The layer (4) containing PVDF is pressed against the layer of thermoplastic adhesive by injecting a fluid (gaseous or liquid) at high pressure into the pipe, while the metallic pipe (1) is heated from the outside, thus, achieving the fusion between said adhesive and said plastic.

[0076] To determine the level of adherence to the metal, the inventors have conducted several trials following the CSA Standard Z 245.21-06 (Canadian Standard Association), Peel Adhesion (hanging mass) for System B1: >15.3 Kg/25 mm, 20 C.

[0077] The level of adherence obtained is higher than 15.3 Kg/25 mm at a temperature of 50 C.

[0078] Through the tests conducted, it is determined that the set of three layers on the inner surface of the metallic pipe (1) can withstand sharp pressure drops at temperatures ranging from 30 C. to 110 C., in accordance to the prescribed values in the autoclave trial defined in the NACE TM0185 specification.

[0079] In compliance with the specification, it is subjected, during 20 days, to pressures of up to 273 atm and temperatures of up to 110 C. The fluids used in the trial were kerosene, toluene, and formation water with 12% ClNa and gaseous phase CO.sub.2.

[0080] Above, this document describes one possible method to produce the invention and the way the invention works. Additionally, this documentation is supplemented with a summary of the invention contained in the claims that are added below.