Patent Application
20130320665
The present invention relates to a tubular component used for drilling and working hydrocarbon wells, and more precisely to the threaded end of such a component, said end being male or female in type and capable of being connected to a corresponding end of another component to form a connection.
The invention also relates to a process for producing a galling-resistant film on such a tubular component.
A component which is “used for drilling and working hydrocarbon wells” means any element which is substantially tubular in form intended to be connected to another element of the same type or otherwise to finally constitute either a string for drilling a hydrocarbon well or a riser intended for maintenance (also known as work-over risers) or for working, such as risers, or for a casing string or tubing string used in working wells. The invention is also applicable to components used in a drill string, such as drill pipes, heavy weight drill pipes, drill collars and the portions of pipe connections and heavy weight pipes known as tool joints.
Each tubular component comprises one end provided with a male threaded zone and/or one end provided with a female threaded zone each intended to be connected by screwing with the corresponding end of another component, the assembly defining a connection.
Threaded tubular components are connected under defined stresses in order to satisfy the requirements for tightening and sealing imposed by the service conditions, knowing that at the well, the threaded tubular components may be required to undergo several makeup-breakout cycles.
The conditions for use of such threaded tubular components give rise to different types of stresses which make it necessary to use coatings on the sensitive portions of such components such as the threaded zones, abutments or sealing surfaces.
Screwing operations are generally carried out under a high axial load, for example the weight of a tube several metres in length to be connected via the threaded connection, possibly localized by a slight misalignment of the axis of the threaded elements to be connected, which induces risks of galling at the threaded zones and at the metal/metal sealing surfaces. For this reason, it is necessary to coat the threaded zones, the abutment surfaces and the metal/metal sealing surfaces with lubricants.
Furthermore, the threaded tubular components are stored (sometimes for several years), then made up in a hostile environment. This is the case, for example, in an offshore situation with a salt spray and in an onshore situation when sand, dust or other pollutants are present. Thus, it is necessary to use coatings that counter corrosion, on the surfaces which have to cooperate by screwing (threaded zones) or by interfering contact (metal/metal sealing surfaces). It is also necessary to treat the surfaces against corrosion.
Environmentally, however, it appears that using screwing greases conforming to API (American Petroleum Institute) standard RP 5A3 does not constitute a long-term solution because such greases, which contain heavy metals, can be expelled from the tubular components and released into the environment or into the well, resulting in plugging which necessitates special cleaning operations. Furthermore, such greases do not provide sufficient protection against corrosion and have to be applied on site for each screwing operation.
In order to overcome the problems of requiring a long-term corrosion resistance and resistance to galling and to satisfy environmental prerogatives, the principal protagonists in the field of threaded connections have been actively developing solid dry coatings (i.e. not pasty and not tacky like greases) which are both lubricants and protect against corrosion, and which can be applied definitively, at the factory, to the tubular components.
In particular, coatings which are inert as regards the environment and which are resistant to wear are being developed.
The present invention is based on the discovery that using polyaryletherketones enables to obtain lubricating dry films which are highly resistant to wear, anti-galling, have high mechanical strength, with a low coefficient of friction and which are resistant to extreme hydrocarbon well working conditions. The solutions employed can also be adapted to various grades of metal for the connections for the tubular components cited above.
The use of such polyaryletherketones and their properties in the context of threaded tubular components as defined above have neither been described not suggested in the prior art.
More precisely, the invention concerns a threaded tubular component for drilling or working hydrocarbon wells, said tubular component having at one of its ends a threaded zone produced on its outer or inner peripheral surface depending on whether the threaded end is male or female in type, in which at least a portion of the end is coated with at least one lubricating dry film comprising at least 65% by weight of a polyaryletherketone.
Optional characteristics, which are complementary or substitutional, are defined below.
The polyaryletherketone is selected from a polyetheretherketone (PEEK), a polyetherketone (PEK) and mixtures thereof.
The lubricating dry film has a structure with a degree of crystallinity in the range 10% to 35%.
The lubricating dry film further comprises at least one class 4 solid lubricant in a proportion by weight in the range 10% to 35%.
The lubricating dry film comprises a perfluoroalkoxyethylene copolymer in a proportion by weight in the range 10% to 30%.
The lubricating dry film comprises a mechanical reinforcing agent selected from the list of the following pigments: carbon black, mica, wollastonite, nanometric aluminium oxide, nanometric titanium oxide, glass powders, nano-diamond, nanometric WS2 or WS2-fullerenes, in a proportion by weight in the range 1% to 15%.
The portion coated with lubricating dry film has previously undergone a surface preparation step selected from the group constituted by sanding, manganese phosphatation, electrolytic deposition of Cu or Cu—Sn—Zn alloys, and Fe and Zn alloys deposited by projection.
The portion coated with lubricating dry film has previously been coated with an undercoat of polyetheretherketone with a semi-crystalline structure and containing mica pigments.
The entire threaded zone is coated with lubricating dry film.
The threaded tubular component comprises a metal/metal sealing surface, said sealing surface being coated with lubricating dry film.
The invention also concerns a threaded tubular connection comprising a male threaded tubular component and a female threaded tubular component made up one into the other, in which at least one of said threaded tubular components is as defined above.
The invention also concerns a process for coating a threaded tubular component for drilling or working hydrocarbon wells, said tubular component having at one of its ends a threaded zone produced on its outer or inner peripheral surface depending on whether the threaded end is male or female in type, comprising the following steps:
Optional characteristics, which are complementary or substitutional, are defined below.
The mixture also comprises a coalescing agent with a rapid evaporation rate with a boiling point in the range 100° C. to 200° C. and in proportions in the range 2.5% to 10% by weight.
The mixture further comprises a non-ionic wetting and dispersing agent in proportions in the range 2.5% to 10% by weight.
The mixture also comprises at least one class 4 solid lubricant in proportions in the range 3% to 12% by weight.
The class 4 solid lubricant is a perfluoroalkoxyethylene copolymer in a proportion by weight in the range 3% to 12%.
The mixture also comprises a mechanical reinforcing agent selected from the list of the following pigments: carbon black, mica, wollastonite, nanometric aluminium oxide, nanometric titanium oxide, glass powders, nano-diamond, nanometric WS2 or WS2-fullerenes, in a proportion by weight in the range 0.5% to 5%.
The portion of the end is coated using a pneumatic spray system, the diameter of said system being in the range 0.7 to 18 mm and the air pressure being in the range 4 to 6 bars.
A surface preparation step selected from the group constituted by sanding, manganese phosphatation, electrolytic deposition of Cu or Cu—Sn—Zn alloys, and particles of Fe and Zn alloys deposited by projection is carried out before applying the mixture to the portion of the end.
A surface preparation step consisting of producing an undercoat of polyetheretherketone with a semi-crystalline structure and containing mica pigments is carried out before applying the mixture to the portion of the end.
The invention also concerns a process for coating a threaded tubular component for drilling or working hydrocarbon wells, said tubular component having at one of its ends a threaded zone produced on its outer or inner peripheral surface depending on whether the threaded end is male or female in type, which comprises the following steps:
Advantageously, a step for degreasing the portion to be coated is carried out before heating said portion.
The features and advantages of the invention will be described in more detail in the description which follows, made with reference to the accompanying drawings.
The threaded connection shown in
The Applicant has also foreseen other configurations wherein the abutment formed in the present case by the two contact surfaces 7 and 8 is replaced by self-locking tightening cooperation of the threaded zones 3, 4 (see U.S. Pat. No. 4,822,081, US RE 30 467 and US RE 34467).
As can be seen in
The polyaryletherketones used in the invention may be obtained from aqueous polyetheretherketone dispersions or from aqueous polyetherketone dispersions. These aqueous dispersions may comprise organic or inorganic mechanical reinforcing agents such as mica pigments of the muscovite and/or biotite type constituted by aluminium silicate and hydrated potassium or magnesium, amorphous aluminium oxides with a gamma crystalline structure and with a particle size in the range 20 to 300 nm, titanium dioxide pigments with a particle size in the range 10 to 100 nm, perfluoroalkoxyethylene copolymer resins (PFA), amorphous carbon black pigments, synthetic graphite powders with a diameter of less than 5 μm, nano-diamond powders obtained by detonation and with a particle size in the range 4 to 6 nm, C type glass with a fibre thickness in the range 1 to 1.3 μm with a diameter D90<50 μm, WS2 fullerene nano materials with a particle size in the range 80 to 220 nm, or WS2 tungsten bisulphide lamellar pigments with a particle size D50=55 nm.
Polyetheretherketones, the abbreviation for which is PEEK, and polyetherketones the abbreviation for which is PEK, are obtained by a nucleophilic substitution type synthesis pathway. Polyetherification results in rigid semi-crystalline polymers with high melting points. They fall into the category of the most high performance materials in the thermoplastic material range. They have a glass transition temperature of 143° C. and, because of their semi-crystalline nature, retain their excellent mechanical properties up to temperatures close to their melting point which is 343° C. Their quasi-linear and aromatic structure provides PEEK and PEK with excellent long-term thermal stability.
The molecular structure of polyetheretherketones is as follows:
The molecular structure of polyetherketones is as follows:
With a glass transition temperature of 157° C. and a melting point of 374° C., polyetherketones, PEKs, offer extended performance at high temperatures compared with polyetheretherketones, PEEKS, while having all the same advantages such as rigidity, solidity and chemical resistance.
The continuous service temperature is 240° C. and the deformation under load temperature exceeds 300° C. for reinforced grades of PEEK and PEK compared with other polymers.
PEEK has high level mechanical properties and retains its properties up to 250° C. for tensile strength and up to 300° C. for bending strength. These mechanical characteristics are greatly improved by incorporating 10% to 30% of solid lubricants such as graphite, carbon black, fluorinated PTFE type polymers or perfluoroalkoxyethylene (PFA) type resins, or glass fibres.
PEKs supply up to three times the wear resistance of PEEKS at high temperatures and retain their mechanical and physical properties at temperatures of more than 30° C. above those for PEEK while accommodating higher loads without permanent deformation.
PEEKs and PEKs have chemical resistance, in particular against saturated salt solutions, gaseous hydrogen sulphide at 200° C. and also resistance to hydrolysis at 200° C. under 1.6 MPa with a temperature resistance comparable to fluorinated polymers. Table 1 clearly shows the superior mechanical properties of PEEK and PEK compared with fluorinated polymers (PTFE and PFA).
Various implementations are possible for PEKs and PEEKs, but involve a transformation by melting at a temperature in the range 370° C. to 420° C. Deposition may be carried out by electrostatic powder projection, by spraying aqueous dispersions and by thermal projection. In the molten state, PEEKs and PEKs are not sensitive to corrosion, but they may be polluted by the moulds formed from alloys containing copper or chromium (as in certain grades of martensitic stainless steels comprising 13% of chromium, for example) which will catalyse degradation and produce coatings less resistant to oxidation. Overall, after transformation by melting, PEKs and PEEKs adhere well to metal, especially if it is not well polished. The permitted roughness represents between 20% and 25% of the total desired thickness of the dry film The adhesion may be increased using an undercoat as an adhesion promoter or by using a surface treatment by mechanical abrasion (sanding or shot blasting), by mordanting in chromic acid or by plasma treatment with an oxidizing agent of the air, or O2 type or even a NH3 type reducing agent. At the same time, superficial oxidation of almost all metals tends to reduce the adhesion of the polymer. Heating the metal in an inert atmosphere or by induction proves to be necessary in order not to modify the surface energy of the support. Finally, the cooling must be sufficiently slow to result in good re-crystallization, and to conserve the intrinsic properties of the polymer, such as wear resistance and scratch resistance. Rapid cooling would produce an amorphous coating which could still be re-crystallized by annealing the parts at 200° C. for 30 minutes. The mechanical properties of the polymer may be increased by increasing the crystallinity by means of a controlled cooling process, for example with a cooling rate of 10° C./min from 400° C. to 250° C. followed by a constant temperature stage of 30 minutes to 1 hour at 250° C.
In a first stage, the Applicant investigated obtaining a polyaryletherketone coating from an aqueous suspension of polyetheretherketone sold by Victrex under the Vicote F800 series name which can contain at least one solid lubricant, preferably a fluorinated polymer of the perfluoroalkoxyethylene copolymer resin type to strengthen the wear resistance and/or at least one inorganic carbon black type solid compound to strengthen the abrasion resistance. The physic-chemical characteristics of the various aqueous phase Vicote F800 series suspensions are evaluated in Table 2.
The Applicant has also accurately determined the composition of aqueous suspensions of polyetheretherketone powder. In particular, it was established that the aqueous suspensions may preferably comprise in the range 25% to 35% by weight of a PEEK powder with a particle size D90 of 10 μm sold by Victrex under the trade name Vicote 704.
The aqueous suspensions may also comprise solid lubricant particles from at least one of classes 1, 2 and 4 and preferably in the range 3% to 12% by weight of a solid lubricant from class 4 in the form of a fluorinated powder of the perfluoroalkoxyethylene copolymer type sold by DYNEON under the trade name Hyflon® PFA with a mean particle size in the range 20 to 30 μm.
The term “solid lubricant” as used here means a solid and stable body which, on being interposed between two frictional surfaces, can reduce the coefficient of friction and reduce wear and damage to the surfaces. These bodies can be classified into different categories defined by their functional mechanism and their structure, namely:
The aqueous suspensions may comprise mechanical reinforcing agents, preferably in the range 0.5% to 1% by weight of carbon black pigments sold by Evonik under the trade name Printex with a BET specific surface area in the range 25 to 300 m2/g and a mean particle size in the range 1 to 5 μm.
The aqueous suspensions may comprise a coalescing agent, preferably with a rapid evaporation rate and a boiling point in the range 100° C. to 200° C., of the ethylene glycol mono-butyl ether type, in the range 2.5% to 10% by weight and more preferably in the range 2.5% to 5% by weight of the suspension in order to facilitate coalescence or formation of a film by external plastification of the polymer entities and to modify the surface tension of the suspension in order to facilitate spreading.
The aqueous suspensions may comprise a surfactant, and preferably a non-ionic wetting and dispersing agent of the sodium dioctylsulphosuccinate type (a compound of sulphuric acid and an aliphatic ester in a mixture of water and ethanol) in the range 2.5% to 10% by weight and preferably in the range 2.5% to 5% by weight of the suspension in order to improve wetting of the support and prevent the powders from settling out of the solution.
Regarding the process for depositing a dry film on the portion of the end 1, 2 of the threaded tubular component, the Applicant has established that the Vicote 704 polyetheretherketone powder grade may be applied by projection using an electrostatic gun using either a dry or wet procedure.
In a first variation, the portion of the end 1,2 is pre-heated to 400° C. before applying the PEEK powder. Next, the coated portion is maintained at a temperature in the range 360° C. to 420° C. for 2 minutes and preferably at the initial temperature of 400° C. to generate a good surface appearance. The operation may be repeated several times in order to produce the desired thickness. The powder must have been dehydrated for a minimum of 2 h at 180° C.
In a second variation, the portion of the end 1, 2 is coated by pneumatic spraying of a cold aqueous suspension of Vicote 704 powder which may or may not have been reinforced. For this process, it is preferable for the portion of the end 1, 2 to be perfectly clean and degreased using a solvent, preferably a polar aprotic solvent such as acetone.
Application may be carried out using a pneumatic gun spraying system with a gravity feed gun and cup, the portion of the end 1, 2 being at ambient temperature. The temperature of the mixture is preferably close to the ambient temperature, said ambient temperature preferably being in the range 20° C. to 30° C.
The diameter of the gun nozzle is preferably in the range 0.7 to 1.8 mm and the minimum air pressure of 4 bars is preferably in the range 4 to 6 bars.
The coated part is then left at ambient temperature for a period in the range 5 to 10 minutes.
The part is placed in an oven or furnace at a temperature of 120° C. for a period in the range 5 to 10 minutes. This drying operation may be carried out by induction, for example. Next, the part is placed in a furnace either at 400° C. or at a lower temperature, followed by raising it to 400° C. at a rate in the range 10° C. to 20° C./min.
Once the maximum temperature of the metal has been reached, the portion of the threaded end 1, 2 is left at this temperature for 5 to 15 minutes and preferably for at least 10 minutes in order to allow the dry film to fuse completely and form a homogeneous film.
The threaded end portion 1, 2 is then taken out of the furnace and allowed to cool to ambient temperature. The cooling rate is preferably slow, namely in the range VC/min to 200° C./min in order to obtain a semi-crystalline structure.
An alternative to electrostatic projection consists of applying a Vicote powder by dry thermal projection onto the portion of the threaded end 1, 2 using a heat gun. In this process, it is preferable for the portion of the end 1, 2 to be perfectly clean and degreased with a solvent, preferably a polar aprotic solvent such as acetone.
The part is pre-heated in an oven or furnace at 260° C. The Vicote powder is applied to the part using a heat gun with a vector gas allowing the fine particles of polyaryletherketone to be heated to the melting point, accelerated and transported to the substrate. The operation is followed by rapid cooling in air to ambient temperature. The operation may be repeated several times in order to obtain the desired thickness.
The thickness of the dry coating is in the range 20 to 70 μm, preferably in the range 30 to 50 μm.
The tests consist of evaluating a certain number of parameters, namely:
The Bridgman test enables to determine the tribological characteristics of dry film pigments during a screwing operation specific for “premium” connections. More precisely, the torque on shoulder resistance CSB, also known as the ToSR (torque on shoulder resistance), is simulated and determined. This torque arises during screwing operations specific for premium connections used in the oil industry and represented in
The curve in
In a first portion P1, the external threads of the male threaded element (or pin) of a first component of a threaded tubular connection as yet have no radial tightening with the internal threads of the corresponding female threaded element (or box) of a second component of the same threaded tubular connection.
In a second portion P2, the geometrical interference of the threads of the male and female threaded elements generates a radial tightening which increases as screwing continues (generating a small but increasing screwing torque).
In a third portion P3, a sealing surface at the external periphery of the end portion of the male threaded element interferes radially with a corresponding sealing surface of the female threaded element to produce a metal/metal seal.
In a fourth portion P4, the front end surface of the male threaded element is in axial abutment with the annular surface of a makeup abutment of the female threaded element. This fourth portion P4 corresponds to the terminal phase of makeup.
The makeup torque CAB which corresponds to the end of the third portion P3 and to the start of the fourth portion P4 is termed the shouldering torque.
The makeup torque CP which corresponds to the end of the fourth portion P4 is termed the plastification torque. Beyond this plastification torque CP, it is assumed that the male makeup abutment (end portion of the male threaded element) and/or the female makeup abutment (zone located behind the annular abutment surface of the female threaded element) is (or are) subjected to plastic deformation, which may degrade performance as regards the tightness of the contact between the sealing surfaces by plastification of the sealing surfaces as well.
The difference between the values for the plastification torque CP and the shouldering torque CAB is termed the torque on shoulder resistance CSB (CSB=CP−CAB). A threaded tubular connection is subjected to an optimum tightening at the end of makeup, which is the guarantee for optimum mechanical strength of the threaded connection, for example as regards tensile forces, but also as regards accidental break-out in service, and for optimum sealing performances.
The designer of a threaded connection is thus obliged to define, for a given type of threaded connection, a value for the optimum makeup torque which, for all connections of this type of connection, must be lower than the plastification torque CP (in order to avoid plastification of the abutments and the resulting disadvantages) and be higher than the shouldering torque, CAB. Ending makeup with a torque which is less than CAB cannot guarantee correct relative positioning of the male and female elements and thus of an efficient interference fit between their sealing surfaces. Furthermore, there is a risk of break-out. The effective value of the shouldering torque CAB fluctuates greatly from one connection to another for the same type of connection as it depends on the diametral and axial machining tolerances of the male and female threads and sealing surface(s); the optimal makeup torque should be substantially higher than the shouldering torque CAB.
As a consequence, the higher the value of the torque on shoulder resistance CSB, the larger the margin for defining the optimized makeup torque, and the more the threaded connection will be resistant to operational stresses.
Friction tests were carried out using a Bridgman type machine. This type of machine has in particular been described in the article by D Kuhlmann-Wilsdorf et al, “Plastic flow between Bridgman anvils under high pressures”, J. Mater. Res., vol 6, no 12, December 1991. A diagrammatic and functional example of a Bridgman machine is illustrated in
This machine comprises: a disk DQ which can be driven in rotation at selected speeds; a first anvil EC1, preferably conical in type, permanently attached to a first face of the disk DQ; a second anvil EC2, preferably conical in type, permanently attached to a second face of the disk DQ, opposite its first face; first EP1 and second EP2 pressure elements, such as pistons, for example, which can exert the selected axial pressures P; a third anvil EC3, preferably cylindrical in type, which is permanently attached to one face of the first pressure element EP1; a fourth anvil EC4, preferably cylindrical in type, which is permanently attached to one face of the second pressure element EP2.
To test a lubricant composition, two pieces of a material identical to that constituting a threaded element are covered with said composition in order to form the first S1 and second S2 specimens. Next, the first specimen S1 is interposed between the free faces of the first EC1 and third EC3 anvils, and the second specimen S2 between the free faces of the second EC2 and fourth EC4 anvils. Next, the disk DQ is rotated at a selected speed while applying a selected axial pressure P (for example of the order of 1 GPa) with each of the first EP1 and second EP2 pressure elements, and the makeup torque to which each specimen S1, S2 is subjected is measured. The axial pressure, the rotation speed and the angle of rotation are selected in the Bridgman test in order to simulate the Hertz pressure and the relative speed of the abutment surfaces at the end of makeup. Using such a machine, it is possible to fix several different pairings of parameters (makeup torque, rotation speed) in order to impose predetermined makeup torques on specimens S1 and S2, and thus to check whether these specimens S1 and S2 closely follow a given makeup torque profile, and in particular whether they can reach a number of completed turns before galling which is at least equal to a threshold value selected with respect to the selected makeup torques.
In the present case, the selected contact pressure was 1 GPa and the rotation speed was 1 rpm. The test specimens were formed from stainless steel containing 13% Cr, machined then coated with different dry film formulations.
The Scratch test, shown diagrammatically in
The experimental conditions employ a spherical indenter formed from Inconel 718 with a diameter of 5 mm and a metal specimen formed from XC48 carbon steel which had been treated by zinc or manganese phosphatation or an electrolytic Cu—Sn—Zn deposit. The parameters were: a load increasing from 10 N to 310 N at a load increase rate of 15 N/s or a load increasing from 250 N to 750 N at a load increase rate of 25 N/s. The bead displacement rate was 2 mm/s for a period of 20 s (the track length was 40 mm). The measured coefficient of friction is considered to be low when it is in the range μ=0.05 for a load of 10 N and μ=0.09 for a load of 310 N. A μ of 0.07 was measured for a load of 310 N on a carbon steel surface. It should be noted that it is necessary to clearly set out the load and operating conditions for the test for each type of coating.
The cross hatch test consists of evaluating the resistance of a mono- or multi-layer coating to being separated from a substrate when the coating is cross-hatched by making incisions until said substrate in accordance with a classification into six categories. Excellent adhesion of the coating to the substrate must correspond to class 0 of ISO standard 2409 (2007): perfectly smooth edges to the incisions, none of the cross hatch squares detached. In order to take the environment into account, the cross hatch test is carried out after being placed in a moist medium (35° C. and 90% RH). No change in appearance, no blistering no corrosion, no cracking, no scaling corresponding to the classifications in ISO standard 4628, and no loss of adhesion are characteristics of good moisture resistance.
The corrosion tests consist of a neutral salt spray test carried out in a climatic chamber under the following conditions: 35° C. with a 50 g/L salt solution with a density in the range 1.029 to 1.036 at 25° C., with a pH in the range 6.5 to 7.2 at 25° C. and recovered at a mean rate of 1.5 mL/h.
Specimens that were intact without rusting then had to correspond to the ReO class of ISO standard 9227 after exposure. The method provides a means of verifying that the comparative quality of a metallic material with or without a corrosion protective coating (metallic or organic coating on metallic material) is maintained.
The water resistance tests consist of subjecting the specimens to an accelerated corrosion test in accordance with DIN standard 50017 carried out in a climatic chamber. This test, comprising one cycle per day, consists of depositing water vapour by condensation under the following conditions: 35° C., 90% relative humidity (RH) for 8 hours, then allowing the specimen to dry. After 7 cycles, a check is made to see whether the substrate protected by the coating has corroded.
Excellent resistance must correspond to the classifications in ISO standard 4628: no corrosion, no blistering, no cracking, nor scaling of a chromium or carbon steel plate treated or not treated by phosphatation with zinc (8 to 20 g/m2 deposit of phosphate) or manganese or treated by an electrolytic deposit of a ternary Cu—Sn—Zn alloy with an intermediate layer of Ni.
The water immersion test is much more severe than the water resistance test of DIN standard 50017. It consists of testing the water resistance of the coatings. It is derived from ASTM standard D870-09 relating to industrial and automobile paints.
Immersion in water may cause coatings to degrade. Knowledge regarding the manner in which a coating resists immersion in water is useful for predicting its service life. Rupture or failure in a water immersion test may be caused by a number of factors, in particular a deficiency in the coating itself, contamination of the substrate, or insufficient surface preparation. Thus, the test is useful for evaluating the coatings alone or complete coating systems.
The test consists of half immersing a specimen in demineralized water for a period of 168 hours at 40° C. in an oven. Adhesion, blistering, rust, or blowholes are observed visually to indicate the sensitivity of the coating to water.
The high pressure wear resistance (also termed the Falex test) uses a rotating indenter compressed between two V-shaped blocks as described in
The test conditions are as follows:
The aim of this test is to simulate and evaluate endurance in terms of galling resistance for the various films without the need to carry out the evaluation on connections. This test means that the performance of the various coatings can be compared with actual tests on the connection. The galling criterion is defined using ASTM standard D 2625-94 relating to the measurement of the loading capacity of the solid lubricant film and corresponds to a sharp increase of the torque compared with the initial state of the order of 1130 N·mm or of the coefficient of friction of the order of 0.15 for a load of 785 N. In general, galling is observed when the applied load decreases irrespective of the materials and configuration.
The Applicant has evaluated the performance, especially tribo-rheological performance, of various films obtained with aqueous suspensions of polyetheretherketone in order to compare them, inter alia, with those observed with a thermoset film of the fluoroethane type or a viscoplastic film with a waxy thermoplastic matrix.
The fluoroethane film consists of an aqueous dispersion of fluoroethylenevinylether cured using an aliphatic polyisocyanate hardener.
The waxy thermoplastic matrix comprises at least one polyethylene wax and mainly an overbased calcium sulphonate in which friction modifying pigments are dispersed, as described in patent WO 2008/139058.
In a first stage, the Applicant evaluated the adhesion, the coefficient of friction, the anti-corrosion protection and the water immersion characteristics of aqueous suspensions of polyetheretherketone on various substrates that had received a particular surface preparation treatment:
Tables 3, 4 and 5 summarize the adhesion results obtained respectively for aqueous suspensions of Vicote F804, Vicote F805 and Vicote F807Blk on specimens that have received different surface preparations by means of the Scratch test and by means of the cross hatch test in accordance with ISO standard 2409.
It will be recalled herein that the Scratch test characterizes the adhesive force of a high performance material, preferably thermoset or thermoplastic, as a function of an increasing applied load. The critical load, determining rupture at the interface and thus the adhesive force of the material, is higher when the material is resistant and adhesive. A minimum critical load of 310 N corresponds to a minimum adhesion for pressures which may reach 1.1 GPa below which an increase in the quantity of wear product occurs in the contact and thus galling resistance is insufficient.
For the cross hatch test in accordance with ISO standard 2409, which provides a measurement of the adhesion after damage by Scratching the material to the interface, a mark of 0 corresponds to excellent adhesion while a mark of 5 defines very poor adhesion.
The films tested had insufficient adhesive forces irrespective of the surface preparation carried out on carbon steels with zinc phosphatation, except for carbon steels with manganese phosphatation. In addition, the polyetheretherketone film had little compatibility with a zinc phosphatation type surface treatment.
In order to explain these results, the Applicant also evaluated the incidence of roughness obtained without phosphatation. Since the adhesion mechanism for a polyetheretherketone film is principally physical by mechanical keying, the roughness of the substrate is a determining factor.
At the same time, it is recommended to sand the substrate by projection in order to obtain a roughness Ra (Ra being the arithmetic mean with respect to the mean line for the amplitude of the roughness) of 20% or 25% of the thickness of the desired final film in order to ensure good adhesion of the film i.e. a roughness Ra in the range 4 μm to 6 μm minimum. The roughness was determined using a rugosimeter in accordance with ISO standard 1997.
Table 6 illustrates that a relatively high roughness obtained by manganese phosphatation offers a better degree of adhesion. It also shows that very slightly polar surface preparations, such as the electrolytic deposition of ternary Cu—Sn—Zn, do not facilitate adhesion.
In view of these first results, the Applicant elected, to determine the corrosion resistance, only substrates with naturally low resistance to corrosion, thereby excluding martensitic stainless steel containing 13% chromium for which the critical adhesion load for polyetheretherketone films was more than 180 N.
The thicknesses of films produced by cold pneumatic spraying were in the range 20 to 45 μm. The degree of rusting in the range Re0 and Re9 was determined in accordance with ISO standard 4528-3. The degree of blistering and detachment in the range 2S2 (low concentration of blistering and of small dimensions) and 5S5 (generalized blistering and of large dimensions) was determined in accordance with ISO standard 4628-2. The results are summarized in Tables 7 and 8.
The corrosion resistance of surface preparations coated with the monolayer polyetheretherketone film was broadly insufficient except for the Cu—Sn—Zn electrolytic deposit, despite the low adhesion or strong loss of cohesion of the film under stress. The results also show that the Vicote F807Blk polyetheretherketone film comprising an inorganic carbon black type compound has relatively better corrosion resistance compared with Vicote F805 irrespective of the surface preparation. The absolute best result was obtained with the electrolytic deposit with only 5 spots of corrosion after 1000 hours. It was observed that adding an electrically conductive carbon black reinforcing agent reinforced the mechanism for protection against corrosion by acting as a sacrificial anode.
Finally, the Applicant evaluated the mean coefficients of friction of a film subjected to abrasive wear by means of a Scratch test over a wide load range between 10 N and 750 N. The results are summarized in Table 9.
The coefficients of friction of the polyetheretherketone films were less than 0.135 irrespective of the surface preparation and reached 0.075 for a mean contact pressure of 500 MPa for a polyetheretherketone comprising a fluorinated polymer of the perfluoroalkoxyethylene type.
The first results show that monolayer polyetheretherketone films are sufficiently lubricating with an anti-corrosion performance which depends not only on the composition of the film but also on the adhesion of the substrate.
In a second stage, the Applicant then developed a means for improving the adhesion and the anti-corrosion performance. The Applicant wanted to replace sanding when this was not possible due to the geometry of the parts to be coated. Above all, the Applicant investigated not modifying the composition of the commercial films studied. In fact, adding adhesion promoters or corrosion inhibiting pigments in proportions of more than 10% increases the PCV (pigment concentration by volume) beyond the PCV for which there is just enough binder to coat the powdered substances (pigments and fillers) and as a result the porosity and loss of cohesion of the film obtained from commercially available aqueous suspensions.
Other alternatives using Vicote 704 polyetheretherketone powder may also be foreseen.
The Applicant investigated increasing the adhesion with an undercoat of the adhesion promoter type. Direct adhesion between materials is rare. Since direct adhesion is principally but not uniquely linked to Van der Waals interactions, it only occurs with very smooth materials which are extremely clean (mica or silicon, for example), which are brought into intimate contact, i.e. to within distances on the atomic scale (nanometric). Thus, this is often impossible to carry out if the surfaces are rough, but in contrast is entirely suitable for films with low roughness.
Thus, the Applicant principally investigated a film compatible with the process for obtaining a polyetheretherketone film by melting at 400° C.
The undercoat may be a projected deposit of alloys of iron and zinc, sold under the trade name Dacroforge Z by Dacral to replace zinc phosphatation, but the process for obtaining it by mechanical projection equivalent to sanding/shot blasting limits it use in hollow bodies which have small diameters and are short in height.
The undercoat is preferably a filled polyaryletherketone. The solution comprising, inter alia, mica pigments of the muscovite or biotite type in proportions of 25% to 50% by weight in an organic polyetheretherketone binder is sold under the trade name Vicote F817 by the supplier Victrex.
The process for application and melting the undercoat is identical to that for the upper layer. In contrast, a rapid cooling rate is desired in order to obtain a less crystalline structure that is more insulating in order to retard the initiation of corrosion pits and to reduce the passive current density of the material.
The thickness of the undercoat may be in the range 30 to 40 μm.
The anti-corrosion and adhesion properties of the undercoat evaluated using two processes with different cooling kinetics are summarized in Tables 10 and 11 respectively.
The Vicote F817 undercoat was sufficiently protective and adhesive but not sufficiently lubricating. The lubricating properties were supplied by the upper polyaryletherketone layer.
The anti-corrosion, adhesion and double layer friction performances are summarized in Tables 12 and 13. The total thickness of the film comprising the undercoat and the upper layer (topcoat) was in the range 40 to 70 μm.
The coefficients of friction for a mean contact pressure of 500 MPa were sufficiently low, particularly for the Vicote F807 Blk film wherein μ=0.085 irrespective of the surface preparation, and are comparable to the coefficients of friction for a fluoroethane or epoxide thermoset film, and must allow a shouldering torque value of less than 70% of the optimum makeup torque to be obtained.
Overall, the coefficient of friction, the adhesion and the anti-corrosion protection of the polyetheretherketone film are considerably improved, preferably with a polyetheretherketone undercoat with mica pigment filler and more particularly an upper layer of polyetheretherketone comprising at least one fluorinated polymer that deforms plastically under stress and/or a carbon black type mechanical reinforcing pigment.
Finally, the Applicant evaluated the tribo-rheological behavior of the film by means of a Bridgman test in order to determine the value of the torque on shoulder resistance. The torque on shoulder resistance value obtained for Vicote F807 Blk was equal to 85% of the reference value for API RP 5A3 grease on XC48 carbon steel and Z20C13 stainless steel. However, the difficulty in preparing the specimens due to the process for producing the film and the small diameter of the specimens meant that this value cannot be considered to be an absolute reference. The crystalline structure and many potential Van der Waals type intermolecular interactions in the polyetheretherketone point to the strong cohesion of the material and a high shear strength, and thus probably to a substantially higher torque on shoulder resistance value.
At the same time, the Applicant evaluated the galling resistance of the film by means of a Falex test. The configuration of a test matched to a connection may comprise a pair of V shaped blocks, Vee blocks, with different surface preparations coated with PEEK film in a mono or double layer and an as machined XC48 carbon steel indenter or Z20C13 stainless steel indenter containing 13% chromium.
The test conditions using a load of 785 N correspond to a mean pressure in the contact of 150 MPa which is relatively close to that recorded during screwing at the start of shouldering at the threads and the bearing surface (100-300 MPa) and a pressure-velocity modulus (PV)=11.2 MPa·m/s which is close to that establishing the wear law in the threading at the load flanks with PV=5 MPa·m/s.
The Applicant studied Vicote F805 and F807Blk reinforced polyetheretherketones.
In order to determine the limits to the galling resistance of the film below, the Applicant evaluated the endurance and the coefficient of friction of the film using the Falex test for increasing loads in the range 1335 N to 4200 N. The sliding speed was 10 mm/s, as opposed to the 20 mm/s employed before. The results are shown in
The results show that galling does not occur for mean contact pressures of 350 MPa and confirm the very high wear resistance of the film for the present invention. The coefficient of friction also decreased as the pressure increased and was in the range 0.056 to 0.078.
In order to confirm the galling resistance and the coefficient of friction observed in the laboratory using the Falex and Scratch test on specimens, in particular of carbon steel with an electrolytic Cu—Sn—Zn deposit, the Applicant carried out makeups on 7″ 29#L80 VAM TOP HT connections, which are highly sensitive to galling. The makeup torque was 29900 N·m.
The female end 2 of carbon steel was treated by electrolytic deposit and the male end 1 was treated by zinc phosphatation and coated with a UV curable acrylic resin described in patent publication WO 2006/104251. The double layer PEEK film was applied to the treated coupling with a cooling rate of less than 5° C./min. Table 14 summarizes the makeup results.
The makeup results obtained confirm the remarkable anti-galling nature of polyetheretherketone film and in particular reinforced polyetheretherketone film.
Thus, the present invention proposes a lubricant film having very interesting galling resistance properties when it is applied to a carbon steel surface or steel surface comprising at least 13% chromium. It also allows the use of electrolytic deposits of the binary Cu—Sn or ternary Cu—Sn—Zn type to be dispensed with.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 04399 | Nov 2010 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP11/05524 | 11/2/2011 | WO | 00 | 7/30/2013 |
