Patent Application
20240384385
The invention relates to the chemical and thermal treatment of metal products, in particular it relates to the technology of applying protective anti-corrosion coatings and can be used to apply zinc-based thermodiffusion coatings to parts of different shapes, e.g. oilfield grade steel pipes, couplings, fasteners, and other articles.
Various embodiments of the technology for application of thermodiffusion zinc-based coatings to steel products are known in the art, with the challenging problem being the ability to provide a uniform dense coating on articles of complex shape, for example, on the inner surface of the elongated pipes or tubes.
Russian Federation Patent RU2500833, MIC: C23C 10/36, published Dec. 10, 2013, discloses a method for applying an anticorrosion coating on metal products, including pipes, by their thermodiffusion zinc-plating. The method involves loading articles/workpieces/parts into a sealed container arranged in a muffle furnace; loading a saturating mixture containing zinc powder and an inert filler; mixing the mixture and articles; filling the container with an inert gas and heating to a temperature of 350-450° C. for a time sufficient to diffuse the zinc vapor onto the surface of the workpieces to form a protective layer of a predetermined amount. In this case, the workpieces are placed in the container in a regular manner using tooling with support surfaces, and the powder saturating mixture contains zinc crystals with a purity of 0.97-0.99% needle-shaped with an effective surface area coefficient of 10. The saturating mixture has a particle size distribution in the range of 3-7 μm, and its mass is 1-4% of the mass of the treated parts or 130-140% of the mass of the required coating on the surface of the treated parts.
The drawback of this method is the complexity of obtaining a uniform coating layer on the inner side of products such as long pipes.
From Russian Federation Patent No. RU2180018, IPC: C23C 10/28, C23C 30/00, published Feb. 27, 2002, it is known A Method of Manufacturing a Powder Mixture For Applying Thermodiffusion Zinc Coating, comprising activating the powder mixture with ammonium chloride while allowing the use of micron-sized zinc powder with spherical particles, flake-like shape or elongated oblong shape.
The use of a powder mixture of this composition does not provide a dense uniform coating of sufficient thickness for the anti-corrosion protection of oilfield steel pipes.
It is also known to provide a gas reaction medium in a sealed container for diffusion galvanizing by introducing an activator, which decomposes when heated to active gases, into the powder mixture. For example, from the description of the Russian Federation Patent Application No. RU2539888, IPC: C23C 10/36, published Jan. 27, 2015, there is known a method for Termodiffusion Galvanizing Of Steel Products, comprising providing a powder mixture composition for thermal diffusion zinc plating comprising a zinc powder, an inert filler and an activator, and processing the steel products in said composition by heating to a temperature of 420° C. The following is added to the composition of the powder mixture for thermodiffusion zinc related processing (mass %): 25-75% zinc powder and 75-25% inert filler, and 0.5-0.8% carbon tetrachloride from the mass content of zinc powder is added as an activator. In this method an increase in the saturation capacity of the powder mixture is achieved by replacing the previously used ammonium chloride with a more effective activator—tetramine methane. When heated, the activator decomposes into carbon and chlorine. The carbon then reacts with atmospheric oxygen and restores the oxides on the surface of the steel parts. The free chlorine atoms react with zinc, forming volatile zinc chlorides, which are then exchanged into exchange reactions, as a result of which zinc from the volatile compounds passes into the coating composition on the surface of the parts. This makes it possible to obtain coatings of a given thickness on hard-to-reach surfaces of parts.
The drawback of this method is the high chemical aggressiveness of free chlorine, which is released during thermal decomposition of tetrachloromethane and causes rapid wear of the equipment.
From the description of the Russian Federation useful model RU 27664, IPC F16L 15/08 published Feb. 10, 2003, it is known a tubing or drill string pipe, comprising a coupling and an adapter at the threaded ends, which is characterized in that on the threaded surfaces of the sleeve and the adapter a diffusion powder zinc coating with a thickness of 25+5-10 mu μm is provided.
The disadvantage of the known technical solution is that the diffusion powder zinc coating is applied only on the sleeve, and the long tubing pipe of the protective coating does not have the coating. Given that the zinc-based coating refers to the tread type, i.e. it protects the base metal from corrosion by its own dissolution, this means that when in contact with the steel surface, zinc forms a galvanic couple, wherein the sacrificial anode is a sacrificial anode. Therefore, the arrangement of the tubing string with alternation of pipes with a surface of different materials is undesirable. In the present case, there is an alternation of the steel and zinc-plated surface of the pipe, which inevitably leads to the fact that accelerated dissolution of zinc will start at the interface of dissimilar metals and a corrosion process will develop.
Russian Federation Patent RU2284368, IPC: C23C 10/52, F16L 58/08, discloses a method for creating a protective diffusion coating at the outer and inner surface of the pipe and its threaded sections, as well as a pump compressor pipe (tubing), produced by this method. The patent specification refers to oil assortment pipes, namely, tubing with a diameter of 60-114 mm and casing pipes with a diameter of 114-508 mm The method includes treating the threaded portions and adjacent surfaces of the tube by isothermal holding in a diffusion mixture comprising a metal powder and an inert filler powder, after which cooling is carried out in the air. This method uses a diffusion mixture containing a metal powder consisting of a mixture of zinc, copper and aluminum powders with grain size of 0, 1-0.5 mm, with the following content of components in the diffusion mixture (mass %): Zinc 25-40, copper 0.045-0.075, aluminum 0.175-0.225, inert filler-the rest. The isothermal holding is carried out for 1.0-3.0 hours at a temperature of 440±10° C. to obtain a protective coating with a thickness of 30-80 μm containing the following components (mass %): iron 6-15, zinc 84.1-93.4, copper 0.4-0.6, aluminum 0.2-0.3, wherein the coating has a microhardness defined by the reduced footprint of the tetrahedral pyramid in the range of 4500-5250 MPa.
The disadvantage of this method is the inability to obtain a dense uniform coating on the entire surface of the pipe. This is because the method includes processing only threaded sections and adjacent surfaces of the pipe, and not all of the pipe as a whole. The use of relatively large metal powders with a grain size of 0.1-0.5 mm can result in an uneven and porous coating, which also reduces corrosion resistance. Furthermore, the coating technique of this coating comprises holding for 1-3 hours at a temperature of 430-450° C. However, this temperature for carbon steels is critical in terms of austenite transition to austenite, which occurs already when the temperature exceeds 427° C. Thus, when applying the thermodiffusion coating in this way, it is possible to change the microstructure of the steel of the pipe being treated, which can lead to a loss of its strength, which increases the risk of accident when operating the oilfield grade pipes.
The prior art known to the inventors includes Russian Federation Patent No. RU2738218, IPC: C23C 26/00, published Sep. 12, 2020, which discloses a method for applying a zinc coating to metallic articles by thermodiffusion zinc plating, includes loading the workpieces into a sealed container. The saturating zinc-containing mixture is then loaded into the container, the container cavity is filled with an inert gas and heated. As a saturating zinc-containing mixture, a two-component zinc mixture is loaded, while the first component in the form of an acicular zinc powder with a size of 3-5 microns is loaded directly into the container, and the second component in the form of a spherical zinc powder with a size of 20-25 microns is loaded into a capsule with walls that are destroyed at a temperature of 400±20° C. with walls, the capsule is placed in a container simultaneously with the products being processed, after which the zinc flux-zinc chloride is loaded into the container, an inert process gas and an activating agent for intensifying the adhesion process are supplied. The galvanizing process is carried out in two steps, first by heating to a temperature of 350-380° C. to form a zinc inner layer on the articles by adhesion of the acicular zinc to the surface of the workpiece, and then after heating to a temperature of 400±20° C. and the destruction of the capsule material, said ball-shaped zinc powder is released to form an outer coating layer.
The drawback of this technical solution is the need for each implementation of the method to produce a new special capsule with the walls breaking under heating to a temperature of 400±20° C. Thus, in order to reliably ensure the release of zinc powder from said capsule, it is necessary to heat the container in the furnace with an exposure at a temperature above 420° C., which can affect the change in the microstructure of the steel of the pipes being treated and reduce their strength.
The proposed technical solution is aimed at overcoming the drawbacks of the known prior art, as well as solving the problem of expanding an arsenal of technology, allowing the protective thermodiffusion zinc-based coatings to be applied to the long-length steel pipes usable in the oilfield industry, to completely cover their outer and inner surfaces as well as the threaded sections of the pipes.
The technical result achieved by the present invention is to reduce the duration of pipe exposure in the temperature range of thermal diffusion galvanizing when producing coatings of a given thickness with improved corrosion resistance properties, to improve uniformity and density of the coating on the entire surface of the pipe, as well as to reduce energy consumption and to increase productivity while ensuring the high strength of pipes processed by the method of the invention.
In order to resolve the above-noted problems, the method of the invention proposes applying the thermodiffusion zinc-based coating on steel pipes including: loading pipes into a container; loading a saturating mixture containing a two-component zinc powder, an activating agent and flux; hermetic closure of the container, its vacuum evacuation; filling of the container cavity with non-oxidizing gas; heating and holding at a predetermined temperature; subsequent cooling of the container and extraction of pipes. In the method, the first component of the two-component zinc powder having needle-shaped particles with a size of 3-8 microns is loaded into an internal cavity of the pipes, and the second component of the two-component zinc powder is loaded directly into the container; the exposure is carried out at a temperature of 300-425° C., wherein one or more tertiary amines are introduced as fluxes into the saturating mixture, and an activating agent is a filler comprising one or more components selected from the group consisting of silica, wollastonite, carbon black, aluminum oxide and copper alloys, with the following ratio of components (mass %):
According to the present invention, the method of applying the thermodiffusion zinc-based coating is carried out primarily for coating steel pipes or tubing having the linear or drilling steel pipes up to 8-12 m in length, wherein prior to loading into the container the outer and inner surfaces of the pipes are machined.
To obtain a uniform and quality coating layer, before loading into the container the pipes are assembled into the tooling having support surfaces to allow for regular placement of the pipes, wherein the pipes are placed into the container together with the tooling.
According to the present method, the flux composition may further comprise one or more components selected from the group comprising urea or derivatives thereof, piperazine or derivatives thereof, ammonium salts of fatty acids, chlorides, fluorides, bromides, iodides, sulfates and sulfates of fatty acids, as well as aluminum and lithium chlorides.
In the method of the invention a non-oxidizing gas is preferably a gas selected from the group consisting of argon, nitrogen or carbon dioxide, which. This gas, after the evacuation operation fills the container at a pressure within the range of 0.1-8 atm.
After the pipes are removed from the container, the thermodiffusion coating is passivated by applying a polymer layer. Passivation makes it possible to realize a synergistic effect of the protection in case of damage to the polymer layer. In the case of damage to the polymer layer, zinc from the iron-zinc intermetallic compound forms sparingly soluble substances preventing the development of under film corrosion at the iron-zinc intermetallide-polymer layer interface.
Further, the problem of formation of asphalt-resin-paraffin deposits (ARPD) on the inner surface is known to the oil pipes. Passivation of the inner surface of the pipes having a thermodiffusion zinc-based coating by applying a smooth polymer layer reduces the mass of the ARPD by 30-40%.
The passivation of the zinc-based diffusion coating may be performed on both the inner and outer surfaces of the zinc related processing of pipes or tubings. However, it is preferred to perform the passivation on the inner surfaces, which are exposed to the greatest impact of the corrosive environment. The passivation procedure is performed by applying a layer of the polymer composition upon the subsequent hot curing. Epoxy paints or epoxy-novolak phenolic two-component polymer compositions are used to apply the polymer layer.
As a result of implementing the present method, the pump-compressor pipes are obtained as a finished product. The outer and inner surfaces of such pipes are provided with a thermodiffusion zinc-based coating having a thickness of 20-140 microns (preferably 40-70 microns) with a microhardness in the range of 2500-3800 Mpa. The coating includes intermetallic compounds of iron and zinc of variable composition from FenZn to Fe4Zn, forming layers of gamma phase (γ-phase) and delta phase (δ-phase), providing corrosion resistance of the coating.
As a result of implementing of the method of the invention, a thermodiffusion zinc-based coating is produced having a predetermined thickness with improved corrosion resistance properties, uniformity and density of the coating Such coating can be obtained on the steel pump or compressor pipes and on other steel pipes for the oil industry on the entire outer and inner surfaces of the pipes. The length of such pipes is typically within the range of 8-12 m, with the inner diameter being no less than 45 mm and no more than 1000 mm. These parameters are typically determined by the capabilities of existing equipment.
To further improve corrosion resistance and durability in the severe operating conditions, the pipes are further provided with a passivating layer of the polymer coating, which is received as a result of hot curing of epoxy or epoxy-novolak phenolic two-component polymer compositions. The passivation layer is placed on top of, or in addition to the thermodiffusion zinc-based coating, preferably on the inner surfaces of the pipes.
The pump-compressor pipes for connecting to the column can be provided with threaded portions located at the ends of the pipe, wherein the thickness of the thermodiffusion zinc-based coating on the threaded surfaces of the threaded portions of the pipe is preferably 20-25 μm. The latter is determined by the requirements for the parts threaded connections.
The invention is illustrated by Examples 1-8 presented in Table 1 and
The method of the invention of applying a thermodiffusion zinc-based coating was carried out by providing the coating to the steel pipes having the length of 8.5 meters and the diameter of 60 mm. The batch of pipes in an amount of 50 pieces was initially subjected to mechanical (abrasive) processing at the outer and inner surfaces thereof. Then, into the inner cavity of each pipe the first component of the saturating mixture is loaded in the form of a zinc powder with needle-shaped particles 3-8 μm, mixed with a filler in the form of carbon black (carbon black) in an amount of 25 mass %. The pipes with the applied first saturating mixture component were assembled into tooling formed with the bearing surfaces. The pipes are fixed in a predetermined position to prevent direct contact with each other, as well as to prevent the movement of the pipes relative to each other when the container is moving. In the resulting assembly, the minimum distance between the tube surfaces to be treated was 3-5 mm. The pipes were loaded into the container together with the tooling.
A second saturating mixture component containing a zinc powder having spherical particles of 8-25 μm in size mixed with a filler in the form of carbon black in an amount of 25% wt. is then loaded directly into the container. As a flux, urotropine was introduced into the saturating mixture in an amount of no more than 1% wt. of the composition of the saturating mixture. Urotropine was a tertiary amine. After the flux was introduced, the container was closed, the lid was sealed, and the vacuum was established in the cavity of the container. Non-oxidizing shielding gas was then injected into the cavity of the container at a pressure of 4 atm. The gas was inert relative to the components of the saturating mixture. Nitrogen was selected as the non-oxidizing gas. The container was then placed into the oven and heated to a temperature of 380° C. The heated container was held in the oven at the temperature range of 380-400° C. for 3 hours.
The container was then removed from the oven, cooled and opened. The industrial vacuum cleaner was used to remove zinc-saturating mixture residues from the container, after which step the tubes were removed. The quality of the protective coating obtained on the outer and inner surfaces of the pipes was controlled. The resulting zinc-based coating consisted of iron-zinc intermetallic compounds forming a thin layer of gamma phase (γ phase) and a wider layer of dense delta phase (δ phase) with the thickness approximately 60 μm/microns and the microhardness of the coating surface of 3800 MPa, (HV400) with satisfactory continuity and density without any discontinuities or pores. The coating was formed having a uniform thickness along the entire length of the pipe at the outer and inner surfaces thereof. The resulting coating is shown in
To further increase the operational resistance on the inner surface of the pipe cavity, the first two turns of the thread and the chamfer of the pipe have been coated with a polymer layer passivating the thermodiffusion zinc-based coating. The passivation layer of the polymer coating is produced by the hot curing of the epoxy-novolak phenolic two-component polymer composition.
To prepare the epoxy-novolak phenolic polymer composition, a paint material from a Majorpack series of paint in red glossy or white glossy paint was used as a base. As the second component of the two-component polymer composition was used a hardener for the paint material of the Majorpack series of paint: red glossy or white glossy is used, with a ratio of the base to the hardener in the range from 4:1 to 10:1.
The implementation mode of the method of the invention according to Example 1 is shown in Table 1. In addition, Table 1 also presents details of Examples 2-7 of the method, which include the same sequence of steps as in Example 1. The modes of embodiments of Examples 2-7 are characterized by different temperature and exposure duration of the container with the products being treated in the furnace.
From the data shown in Table 1, it can be seen that for a reduction in the exposure duration of the pipes in the temperature range of the thermodiffusion zinc-based coating of 300-425° C. in the production of coatings of the predetermined thickness of 60 μm (with high quality properties), it was observed the effect of sharing a new flux-a tertiary amine and a filler selected from the group consisting of silica, wollastonite, carbon black, aluminum oxide, and copper alloys. Under these conditions, diffusion of the zinc vapor provided a uniform, tight coating of a predetermined thickness on both the inner and outer surfaces of the steel pipes, including the threaded portions. Note that in Example 2, the coating was applied to a batch of pipes of minimum diameter (the inner diameter of the pipes was 45 mm with a pipe length of up to 12 meters). Further, in Examples 3-7, additional tertiary amine flux was added urea, piperazine and others in an amount of 0.1-0.3% wt., which resulted in some slight increase in coating rate.
The intensification of the process of diffusion saturation of the surface of steel pipes in the present method of applying zinc-based coating by the gas thermodiffusion is achieved by replacing traditional activators with complexes of inorganic and organic substances, which at the operating temperatures decompose to activate zinc atoms and contribute to an increase in the saturation rate of the surface of the articles with a corrosion-resistant δ-phase.
Example 8 in Table 1 corresponds to the closes prior art known to the inventors, i.e. according to RU2738218. Comparison with this reference shows that the dwell time required to obtain a coating of a given thickness of 60 μm was reduced from 3.5 hours in the reference to 3 hours in the present method. This means that the dwell when applying the thermodiffusion zinc-based coating was reduced by 14%, which corresponds to an increase in the productivity of the present method and a reduction in energy costs. This is because the duration of operation of the electric heaters of the furnace required for heating the container and holding at a selected temperature was reduced.
Furthermore, the advantage of the coating technology of applying the thermodiffusion zinc-based coating according to the present method with respect to RU2738218 and other known analogs is the possibility of forming a thermodiffusion coating at lower temperatures (below 425° C.). As shown in Table 1, a preferred temperature range is lowered to effect soaking while applying the thermodiffusion zinc-based coating to the pipes, which improves the processing quality of steel pipes. This is because the lower temperature of the application of the thermodiffusion coating does not guarantee the weakening of the high carbon steels when the tubes are directed for application of the coating after the heat treatment. As is known, the heating and holding temperature at the level above 427° C. for carbon steels is critical. This is because it corresponds to the transition of perlite to austenite, which entails a change in the microstructure of the steel and a decrease in strength. Thus, the use of the present method ensures that the strength group of the oilfield grade steel pipe is maintained after application of the thermodiffusion zinc-based coating thereto.
The corrosion resistance test of the pipes prepared according to Example 1 shows an increase in their corrosion resistance in a medium containing hydrogen sulfide and carbon dioxide at a pressure of up to 2 atmospheres and a temperature of 80° C. Exposure under these conditions shows that the resistance of the coated tube was 1500 days without the corrosive damage.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022109894 | Apr 2022 | RU | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/RU2022/050327 | 10/13/2022 | WO |
