OA17209A - Process for producing a dry polyamide-imide film with high galling resistance on a threaded tubular component from an aqueous dispersion which is free of carcinogenic substances. - Google Patents

Abstract

The invention concerns a process for producing a dry film with a high galling resistance on a threaded element for drilling and/or operating a hydrocarbon well, characterized in that it comprises at least the following steps : - forming a stable dispersion comprising a polyamide-imide powder, a polar aprotic solvent with a boiling point of more than 180°C at 760 mm Hg, and water; applying the dispersion to one of the ends (1, 2) of said threaded element at a temperature in the range 20°C to 40°C; - drying the coated end.

Description

PROCESS FOR PRODUCING A DRY POLYAMIDE-IMIDE FILM WITH HIGH GALLING RESISTANCE ON A TH RE AD ED TUBULAR COMPONENT FROM AN AQUEOUS DISPERSION WHICH IS FREE OF CARCINOGENIC SUBSTANCES [001 ] The présent invention relates to a tubular element for drilling and/or operating hydrocarbon wells, and more prcciscly the threaded end of such an element. This end may be male or female in type and can be connected to a corresponding end of an analogous element in order to form a joint or a connection.

[002] The invention also relates to a threaded connection resulting from connecting two tubular éléments by makeup.

[003] The term “tubular element for drilling and operating hydrocarbon wells” means any element with a substantially tubular shapc that can be connected to another element of the same or different type, in particular in order to constitutc eîther a stem for excavating a hydrocarbon well or a work over riser, or, for example, a riser for operating such a well or a casing string or tubing string used in operating a well. The invention is also applicable to éléments used în a drill stem, such as drill pipes, heavy weight drill pipes, drill collais and portions of pipe and heavy weight pipe tool joints.

[004] Each tubular element comprises an end portion provided with a male threaded zone or a female threaded zone for making up with a corresponding end portion of an analogous element. Once connected in this manner, the éléments form what is known as a joint or a connection.

[005] Such threaded tubular components of a connection are joincd together under predefined toads in order to comply with the interférence fit and scal demands imposed by the service conditions. Further, it should be understood that the threaded tubular components may hâve to undergo scvcral makeup-breakout cycles, in particular in service.

* „4 [006] The conditions for using such threaded tubular components give rise to various types of loading, which make it necessary to use films on the sensitive portions of such components such as threaded zones, abutting zones or the sealing surfaces.

[007] Thus, makeup operations are general ly carricd out under high axial load, for example because of the weight of a tube several mètres in length to be made up via the threaded connection, possibly aggravated by a slight misalignment of the axis of the threaded éléments to be connectai. This gives rise to risks of galling at the threaded zones and/or at the metal/mctal sealing surfaces. The threaded zones as well as the metal/mctal sealing surfaces are routincly coated with fabricants.

[008] Furthermore, the threaded tubular components are often stored, then made up in an aggressive environment. This is the case, for example, in an offshore situation in the présence of saline mist or in an onshore situation in the presence of sand, dust and/or other pollutants. Thus, it is necessary to use films that counter corrosion on the surfaces that are intended to cooperate during makeup (in the case of the threaded zones) or corne into interfering contact (in the case of the metal/mctal sealing surfaces and the abutments).

[009] However, because of environmental régulations, it transpires that the use of greases complying with API (American Petroleum Institute) standard RP 5A3 does not constitutc a long-term solution because such greases are causcd to be extruded from the tubular components and released into the environment or into the well, causing plugs which require spécial cleaning operations.

[0010] In order to solve the problcms occurring with long-term corrosion résistance, galling résistance and environmental considérations, solid dry films (i.e. not pasty, unlike greases), fabricants and protectors hâve been devefopcd.

[0011 ] Sincc 1969, Whitford hâve proposed high performance XYLAN® coatings starting from a polyamide-imidc and fluoropolymer mixture for threaded Systems or threaded fasteners which require the friction in rapid makeup/breakout operations to be adapted.

Since 2002, in the context of threaded connections, Sumttomo Métal Industries hâve been studying coatings based on polyamide-imide resin to lubricate and ensure galling résistance during makeup, as described in documents EP 1 378 698 and EP 1 959 179.

[0012] Whitford and SMI principally proposed the production of dry films from a polyamide-amie acid prccursor dissolved in a polar solvent or in an ethanol/toluene mixture. The dry film generally contains a fitlcr in order to ensure fabrication as a function ofthe contact pressures in the thrcading. The proportion of filters is relatively high, with a pigment/binder weight rat» in the range 0.25 to 4, preferably greater than 3. The dry film is thus advantageously sacrificial and sufficiently wear résistant as a function of the selected solid fabricant (MoS₂, WS₂, PTFE).

[0013] The polar solvents, namely organic nitrogen-containing compounds, at iphatic ketones, ethers, or chlorinated aromatics, used to dissolve the polyamide-imide resin gcnerally hâve a négative impact on the attraction of polyamide-imide resins as a film, for example because those which hâve a low boiting point are flammabte, because long drying periods are required, often under reduced pressure for those with a high boiling point, or because of their toxicity if ingested through the skin, respiratory System or digestive System.

[0014] In addition, the polyamide-imide film is gcnerally formed aflcr drying at a température in the range 150-280°C. In this température range, the solvent or solvents nccessary for application and film formation are completely or partially evaporated.

[0015] In view ofthe régulations regarding the woridng environment (Directive

2004/37/EC from the Européen Parliament and Councit dated 29^ώ April 2004 regarding the protection of workers against risks linked to exposure to carcinogenic or mutagcnic agents in the workplace) and the classification of evaporated substances (Commission Directive 2009/2/EC dated 15^ώ January 2009, amending, for the proposes of its adaptation to technical progress, for the 31^e time, Council Directive 67/548/EEC on the approximation of dispositions relating to the classification, packaging and labelling of dangerous substances;

* - * (EC) Rule no 1272/2008 Européen Parliament and Council dated 16^ώ December 2008 rclating to the classification, labelltng and packaging of substances and mixtures), the risk to the user is particularly high [0016] Polar solvents (toluene, xylene), in particular polar aprotic solvents containing nitrogen, such as NMP, NJ4-dimethy!acetamide (DMAc), Ν,Ν-dimethylformamide (DMF), hcxamethylphosphoramidc (HMPA), etc, employcd when forming a polyamidc-imide film are substances which are classifïed as carcinogenic, mutagenic or reprotoxic (CMR) which are subject to prohibition or restricted use in many applications.

[0017] The limiting concentration thresholds for the most sensitive carcinogenic and mutagenic substances, classcd as 1A (can cause cancer), IB (may induce a genetic anomaly), are 0.1% or less in mixtures and 0.3% or less for reprotoxic substances. Other CMR substances of class 2, deemed to be of concem for fertility and human development, hâve to be in concentrations of 1% or less.

[0018] The classification of the polar aprotic solvents used and their known toxicity is given in the table below.

Substance name	CMR classification
Ν,Ν-dimcthyIacctami de	Reprotoxic cat. IB
N,N-d imethy lformami de	Reprotoxic cat. IB
Hexamethylphosphorami de	Carcinogenic and mutagenic cat IB
N-methylpyrrolidone	Reprotoxic cat. 1B
Toluene	Reprotoxic cat. 2

[0019] The new classification for CMR substances in classes IA, IB and 2 wil! be applicable to mixtures from June 2015, and so it would be appropriate to providc a novel alternative in order to prevent the risk of chemical exposure to CMR agents in application of the French Labour Code (article R4411-73 and articles R231-56 to R231-56-12). Starting from this point the présent invention proposes coating a thrcaded élément intended for drilling and/or operating a hydrocarbon well with a stable aqueous dispersion of a polyamidc-imide polymer containing no CMR substances, and no flammable substances, in order to obtain a dry film of polyamide-imîdc which is adhcsivc, protcctivc and fabricant with a coefficient of friction which is suitable for reducing the shear loads in the threaded portion and for increasing the clamping torque at the sealing surfaces.

[0020] In particular, the présent invention concems a process for producing a diy film with a high galling résistance on a threaded élément for drilling and/or operating a hydrocarbon well, characterizcd in that it comprises at least the following steps:

• forming a stable dispersion comprising a polyamidc-imidc powder, a polar aprotic solvent with a boiling point of more than 180°C at 760 mm Hg, and water, • applying the dispersion to one of the ends (1,2) of said threaded elcment at a température in the range 20°C to 40°C;

• drying the coated end.

[0021] The dispersion may be produced with at least:

• a step in which the polyamide-imide powder is dissolved in the polar aprotic solvent with a boiling point of more than 180°C at 760 mm Hg, in order to obtain a polyamide-imide solution;

• a step in which the polymer solution is prccîpitated in an aqueous mixture at ambient température;

• a step in which the precipitated solution is disperscd by milling the polyamideimide partîcles.

[0022] The dispersion may also bc produced with at least:

• a step in which the polyamide-imide powder is dispersed by mcchanical agitation in a homogcncous mixture containing water and a polar aprotic solvent with a boiling point of more than 180°C at 760 mm Hg;

• a step in which the polyamide-imide dispersion is stabilized by means of a treatment with uhrasound or by milling.

[0023] The proportion of polyamîde-imidc may be 35% by weight or less.

[0024] The step for dissolving the polyamide-imide powdcr may be carricd out at a température of more than 50°C, preferably more than 80°C.

[0025] The précipitation step may be carried out at ambient température in an aqueous mixture containing distillcd water and at least one non-ionic surfactant, the aqueous mixture being free of polyoxyethylenated alkylphcnyl ethers.

[0026] The step for dispersion of the polyamide-imide powdcr by mechanical agitation may be carried out at a température in the range 60°C to 80°C in a homogcncous mixture containing distillcd water, the polar aprotic solvent and at least one non-ionic surfactant.

[0027] The non-ionic surfactant, selected from the group constituted by polyoxyethylenated acetylcnic diols and high molecular weight block copolymers containing groups with a high affinity for pigments, may hâve a hydrophilic-lipophilic balance of 13 or less, preferably 8 or less.

[0028] The stabilization by ultrasound treatment may be carricd out at a minimum frequcncy of 20 kHz and a minimum power of200 W.

[0029] The milling may be carried out using a bead mill, the milling yield being in the range 40% to 95%, preferably more than 90%.

[0030] The size of the polyamide-imide polymer particles in dispersion may be less than 70 pm, preferably less than 20 pm and primarily less than 10 pm.

[0031 ] The aqueous polyamide-imide dispersion may comprise a thixotropic agent which is thcrmally stable at températures of250°C or more selected from the group constituted by organically modified sheet silicates of the laponite, saponite, bentonite or smcctite type with a pH in 2% by weight suspension in the range 9 to 11.

[0032] The aqueous polyamide-imide dispersion may comprise in the range 0.05% to 0.4% by weight of a bactericidal and/or fangicidal agent for protection in storage and for

benzisothiazolinone, chloromethyl-isothiazolinone and methylisothiazolinone.

• 4 [0033] The aqueous polyamide-imide dispersion may comprise a spreading agent of the polyether modified dimethylpolysiloxane type to rcduce the surface tension.

[0034] The aqueous polyamide-imide dispersion may comprise an émulsion of hydrophobie components containîng silicone and/or parafïînic minerai oils.

[0035] The polyamide-imide (P AI) powder may be selected from aromatic polyamideimide powdcrs.

[0036] The selected aromatic polyamide-imide may bc obtained from a réaction between a trimellitic acid anhydride chloride and an aromatic diamine selected from compounds other than 4,4*-methyIenedianiiine.

[0037] The selected polyamide-imide may bc selected from the group formed by aromatic polyamide-imide polymers with a molecular mass in the range 10000 to 30000 g/mole, and a glass transition température in the range 220°C to 285°C.

[0038] The maximum particle size in the polyamide-imide powder may bc less than 150 pm, 95% of the particles having a size of less than 75 pm.

[0039] The mean volume granulomctry ofthe polyamide-imide particles may be in the range 30 to 40 pm.

[0040] The polar aprotîe solvent may bc selected from the group constitutcd by dimethylsulphoxide, sulpholane and γ-butyrolactone.

[0041 ] The polar aprotic solvent may bc dimethylsulphoxide.

[0042] The stable dispersion may further comprise solid lubricating particles selected from the list constituted by graphite, boron nîtrides, BiîSj, M0S2, WS2 and fluoropolymers.

[0043] The dry film may comprise at least one solid lubricant particle or a combination.

[0044] The proportion of solid lubricating particles with respect to the polyamide-imide is in the range 0.01 to 4.

i [0045] The stable dispersion may further comprise solid anti-abrasive particies selected from the list constituted by cristobalite, mica, colloïdal silica, paraphenyleneterephthalamide (aramid) and silicone resin.

[0046] The stable dispersion may comprise a or a combination of corrosion-inhibiting pigments having a synergistic effect.

[0047] The step for applying the dispersion by spraying onto the end (1,2) of the threaded élément may be preceded by a supplémentai step for preparing the surface selected from the list constituted by sand blasting, conversion treatments, electrolytic déposition and non-reactive treatments.

[0048] The step for applying the dispersion by spraying onto the end ( 1,2) of the threaded élément may be completcd by a supplémentai step for curing said aqueous dispersion applied to the threaded element at températures in the range 230°C to 325°C.

[0049] After curing, the thus-coated threaded element may be cooled to ambient température.

[0050] The thickness of the dry film may be greater than the roughness of the surface préparation and in the range 10 to 45 gm.

[0051 ] The dispersion may be applied to the wholc of the threaded zone of the threaded element.

[0052] The dispersion may be applied to the sealing surface of the threaded element.

[0053] Some characteristics and advantages of the invention are set out in more detail in the description below made with référencé to the accompanying drawings.

[0054] Figure 1 represents a polycarboxylic diimide monomer and an aromatic diamine comonomer, [0055] Figure 2 represents an imide unit on the left and an amie acid on the right;

[0056] Figure 3 represents a 1,3-polyamide-imide configuration on the left and a 1,4polyamîde-imide configuration on the right;

j >

[0057] Figure 4 represents the granulomctry of an aqueous dispersion of polyamide-imide obtained by a process in accordance with the invention;

[0058] Figure 5 represents the freezing point for a watcr-dimethylsulphoxide mixture as a fonction of the fraction of dimcthylsulphoxide;

[0059] Figure 6 is a diagrammatic view of a connection resulting from connecting two tubular components by makeup;

[0060] Figures 7,8,9,10 and 11 show test graphs.

[0061 ] First of alL, the process consiste of preparing an aqueous dispersion of a ready-to-usc polyamide-imide polymer. Said process then comprises at least one step for applying said dispersion as well as a curing step.

[0062] Amorphous polyamide-imide polymers (PAIs) hâve mechanical bending, impact résistance and résistance to brcaking properties which are superior to other heterocyclic polymers, namely polyimides (PI), polyetherimides (PEI), phenylenc polysulphide (PPS) or polyether etherketone (PEEK). It can also be used to improve extrusion or moulding operations (as well as ovcrmoulding), due in part to their having glass transition températures which are lower than the corresponding polyimides (Slade H Gardner “An investigation ofthe structure-propcrty relationships for high performance thermoplastic matrix, carbon fibre composites with a tailored polyimide interphase’’, 1998).

[0063] The polyamide-imide polymer is preferably selected from aromatîc polyamideimides. Aromatîc polyamide-imides arc of particular interest in producing high temperature-rcsistan t films and fibres.

[0064] The aromatîc polyami de-imide polymer may be synthesized by a polycondensation reaction between a polycarboxylic dit mi de monomer and a diamine or diisocyanate comonomer in a polar solvent. Figure 1 represents an exemple with a dibasic carboxylic acid imide on the left and a diamine on the right.

> · * ίο [0065] Synthesis of the polymer may also involve polycondensationof a diamine and a trimellitic add anhydride chloride in a bipolar aprotic solvent. The reaction between the diamine and an anhydride produccs an intermediate product, polyamic acid, which has to be cyclized. Cyclization or imidization of this precursor polymer by a chemical or thermal pathway gives rise to the final polyamide-imide. As can be seen in Figure 2, the precursor obtained may hâve ahemating imide and amie acid units, and preferably an imide unit proportion of more than 90%. Figure 2 shows an imide unit on the left and an amie acid unit on the right in more detail.

[0066] As can be seen in Figure 3, depending on the diamine selected, the polymer may hâve a 1,3-polyamide-imide configuration, a 1,4-polyamide-imide configuration or a mixture. Figure 3 shows a 1,3-polyamidc-imidc configuration on the left and a 1,4polyamide-imidc configuration on the right in more detail.

[0067] For the puiposes of the invention, the selected aromatic polyamide-imide polymer is preferably obtained by a pathway which consiste ofreacting a trimellitic acid anhydride chloride and an aromatic diamine selected from compounds other than 4,4’methylcnedianilinc, which is dassified as a CMR substance.

[0068] The selected polyamide-imide polymer is preferably selected from the group formed by aromatic polyamide-imide polymers with a molecular mass in the range 10000 to 30000 g/mole, a glass transition température in the range 220°C to 285°C, a molar fractionof polyamide-amie acid of 0.1 or less or an acid index of20 mgKOH/g or less.

[0069] The thermal résistance of the polyamide-imide polymer incrcascs with its molecular mass and its degree of imidization, and so an aromatic polyamide-imide polymer with a high molecular mass will advantageously be selected in order to increase the performance of the film (Robertson G, Polymers 2004, vol 45, pp 1111-1117).

[0070] ln an advantageous embodiment, the Applicant proposes preparing an aqueous dispersion from a polyamidc-imide powder with a maximum particle size of less than 150 i

gm wherein 95% of the particles hâve a size of less than 75 gm. Preferably, the mean granulometry by volume is in the range 30 to 40 gm.

[0071] In a first variation and in a first step, the polyamide-imidc polymer is dissolved in a polar aprotic solvent boiling point of more than 180°C at 760 mm Hg for which the Hansen total solubility parametcrs, cxpressed as MPa^1/2, arc close to those ofthe polyamide-imidc polymer. The polymer solubility paramcters, extracted from the European Polymer Journal, volume 22, Issue 10,1986, pages 821-825, are approximately 3 MPa^1/2.

[0072] In order to ensurc good stability on dispersion, the différence between the solubility paramcters, Ssolvent and Spolymer, should preferably be less than a value of 4 where therc are strong spécifie solvent-polymer interactions, as shown by PAI dispersions in a watcr/NMP mixture, while the respective solubil ities of water and NMP are respectively 47.9 MPa^1/2 and 22.9 MPa^1/2.

[0073] The polar aprotic solvents are advantagcously selected from the group constituted by the following compounds: dimcthylsulphoxide, sulpholane and γ-butyrolactone, preferably dimethylsulphoxide (DMSO) which has a zero-danger classification. In fact, DMSO is known to be one ofthe least toxic compounds. Its uses and applications form a compound that is in common use in the pharmacy field (Parcell S, “Sulfur in human nutrition and applications in medicine”, Ahcm Med Rev 2002, vol 7, pp 22-44). DMSO has approximately 40 pharmacofogical properties which may be bénéficiai in the prévention, relief or régression of many diseases (Morton W, “DMSO, Naturc’s Hcalcr”, New York;

A very 1993).

[0074] Other solvents such as acetone, ethyl acetate, cyclohexanone, 1,3-dioxolanc, mcthylcthyl ketone, tetrahydrofuran or triethylamine, which are capable of complying with the solubility requirements, are clcarly prohibited in view of their being classifïed as highly flammable substances.

[0075] The polyamide-imide polymer is preferably dissolved in DMSO at a température of more than 50°C with mechanical agitation, preferably at more than 80°C, in order to facilitate dissolution and to avoid recrystallization phenomena at ambient storage température.

[0076] The proportion of polymer dissolved in the solvent is 35% by weight or less, advantagcously 30% or less in order to providc a kincmatic viscosity which is acceptable in view ofthe second step.

[0077] In a second step, the solution of polymer, maintained at a minimum température of 50°C, is stowly précipitated in an aqueous mixture at ambient température. The aqueous mixture contains distilled water and at least one non-ionic surfactant selected from the group constituted by polyoxyethylenated acctylenic diols. The non-iomc surfactant preferably has a hydrophilic-lipophilic balance of 13 or less, preferably 8 or less, in order to reduce the surface tension at equilibrium and the dynamie surface tension and to ensurc that the polymer-solvent system is wetted in the water. The aqueous mixture is free of polyoxyethylenated alkylphenyl ethers.

[0078] The aqueous mixture may also comprise a thixotropic agent which is thcrmally stable at températures of250°C or higher selected from the group constituted by organically modified sheet silicates ofthe laponite, saponite, bentonite or smectitc type with a pH in suspension at 2% by weight in the range 9 to 11.

[0079] The aqueous mixture may also comprise in the range 0.05% to 0.4% by weight of a bactericidal/fungicidal agent or a synergy to providc protection on storage and protection of the film selected from the group constituted by the following biocidally active substances: iodopropynyl-butyl-carbamate, benzisothiazolinonc, chloromcthyl-isothiazolinone and methylisothiazolinone.

[0080] The présent invention comprises a third step of fincly milling the suspendcd partie les to ensurc mechanical dis intégration of the associated particles (agglomérâtes and aggrcgates) into fincr particles and stabilization of the fîner partides produced during dispersion to prevent them from re-agglomerating (or flocculating). Fine milling using a bead mill is carried out at a minimum rate of600 rpm and at constant power. The bead mill is a vertical or horizontal System with a reirculatîon System. The diameter of the ccramic or metallic beads is 1 mm or less, preferably 0.4 mm or less. The milling yield is in the range 40% to 95%, preferably more than 90%.

[0081 ] The bead mill is preferably a horizontal System with a recirculation process and comprises a cooled, pressurized milling chamber in order to rcduce the milling time.

[0082] The partide size may be measured in the liquid phase using a CILAS 1064 laser granulometer. The size of the polyamide-imide polymer partides in dispersion is preferably less than 20 gm and primarily less than 10 gm. Figure 4 illustrâtes the granulometry ofan aqueous polyamide-imide dispersion obtained by said process.

[0083] The functional pigment fillers are added during milling or as a subséquent addition.

[0084] In a second variation, the Applicant proposes dispersing the polyamide-imide polymer in a first step with mechanical agitation (300 to 600 rpm) using a propeller mixer in a water/DMSO with proportions of water and DMSO varying between 60/40 and 20/80 depending on the quantity ofpolymer to be dispersed. The efïicicncy ofdispersion is given by the shear rate at constant peripheral speed as a fonction of volume and diameter of the propeller. The température of the mixture is advantageously more than 60°C in order to facilitate dispersion and less than 80°C in order to limit évaporation. The aqueous mixture may contain at least one non-ionic surfactant selected from the group constituted by polyoxycthylenated acctylcnic diols and high molccular weight block copolymers with groups having a high affinity for the pigments. In a second step, de-agglomcration of the particles and homogenization of the dispersion are ensured by milling or an ultrasound treatment (uhrasonication) either in an ultrasound bath with mechanical agitation, or using an ultrasound probe (HIELSCHER® UIP, SONITUBE®). The frcqucncy and the minimum power are respectively 20 kHz and 200 W. In the case in which the fimctional pigment fïllers arc added during mechanical dispersion, the stability ofthe dispersion is preferably ensured by fine milling, by recirculating the dispersion in a horizontal bead mill with a cooled and pressurizcd milling chambcr.

[0085] The fimctional pigment fïllers may also be added during milling or post addition.

[0086] The proportion of polyamide-imide in the final dispersion is preferably in the range

5% to 20%. Ifthe concentration is greater than 20% by weight, the viscosity is high, which renders application dîffïcult; if the concentration is Iess than 5% by weight, it bccomes more complicated to form a film of sufficient thickness.

[0087] The proportion of co-solvent with respect to the water in the dispersion is preferably in the range 40% to 80% in order to guarantee good stability on cold storage. Figure 5 illustrâtes the freezing point for a water-dimcthylsulphoxidc mixture as a function of the dimcthylsulphoxide fraction.

[0088] The aqueous dispersion may also comprise a modifïed polycther dimcthylpolysiloxanc type spreading agent in order to reduce the surface tension and to improve film formation.

[0089] Finally, the aqueous dispersion may comprise an anti-foaming agent such as an émulsion of hydrophobie components containing silicone and paraffïnic minerai oils in order to fâcilitate film formation, particularly for high concentrations by volume of pigments.

[0090] In conclusion, the aqueous dispersion prepared thereby contains a minimum of 7% by weight of a polyamide-imide polymer formulation.

[0091 ] The aqueous dispersion contains no concentrations of a carcinogenic, mutagenic or reprotoxic substance appearing on the CIRC (IARC), ACGIH, NTP and/or OSHA lists in a concentration of 0.1% or higher.

[0092] The aqueous dispersion has a ncutral pH in the range 7 to 7.5, a dynamic viscosity in the range 0.1 to 1 Pa.s at 20°C depending on the proportion of potymer and a stability on storage of at least two wccks at a température of-5°C or 40°C.

[0093] The po lyamide-imidc film may be obtained by pncumatic spraying or cold electrostatic spraying. The aqueous dispersion is sufficiently thixotropic to allow it to be applied to a vertical surface. The solvents are evaporated off during a drying phase at 80°C. The dry film is formed after a curing phase at températures in the range 230°C to 325°C depending on the polymer, preferably at a température which is at least 10°C higher than the glass transition température of said polymer. Cooling may be carried out at ambient température.

[0094] The DMSO co-solvent, moderately volatile and thermaily stable at 150°C, is completely evaporated off during the drying step, principally between 40°C and 80°C by elution with water. No décomposition product apart from CO2, anaiysed by ATG-IRTF, is detected during the curing step between 230°C and 325°C. The volatile organic compounds given off during the drying phase, principally DMSO and dimethyl sulphide (DMS), is readily recycled by re-condensation.

[0095] In order to reduce the shear load in the mctal-mctal contact, principally in the threaded portion, by means of a dry polyamide-imide film, additives or functional pigment fit lers are added to the aqueous dispersion, preferably during milling, to ensure protection of 20 the metallic surface against galling and to provide fabrication, inter alia.

[0096] Thus, the aqueous dispersion of PAI may also comprise solid lubricating particles selected from the list constitutcd by graphite, boron nitride, B12S3, MoS₂, WS₂ and fluoropolymcrs.

[0097] These solid fabricants may be classificd into various categories defined by their functional mechanism and their structure:

• class I : solid todies owing their lubricant properties to their crystalline structure, for example graphite or toron nitride, zinc oxide;

• class 2: solid bodies owing their lubricant properties on the one hand to their crystalline structure and on the other hand to a reactive chemical element in their composition, for example molybdenum disulphidc M0S2, graphite fluoride, tin sulphides or bismuth sulphides;

• class 3: solid bodies owing their lubricant properties to their chemical reactivity, for example certain chemical compounds of the thiosulphate type;

• class 4: solid bodies owing their lubricant properties to a plastic or viscoplastic behaviour under frictional load, for example polytetrafluoroethylene (PTFE) or polyamides.

[0098] The aqueous dispersion of PAI may comprise solid lubricant powdcrs, alone or in combination, in a proportion in the range 0.0] to 4 as a ratio by weight with respect to the polymer.

[0099] The aqueous PAI dispersion may cxclusively comprise a fluoropolymer powder (preferably polytetrafluoroethylene with a mean particlc size in the range 0.2 to 2 pm) in order to reduce the coefficient of friction and to rcduce wear and damage under low load.

[00100] The aqueous dispersion of PAI may exclusivcly comprise a solid class 2 lubricant powder (preferably a WS2 or a B12S3 in which the mean particle size is in the range 2 to 8 pm).

[00101 ] The aqueous PAI dispersion may comprise a combination of solid lubricant powdcrs for a syncrgistic effect, namcly principally a class I or 2 solid lubricant and a class 4 solid lubricant in order to adjust the coefficient of friction as a fonction of the clamping zone and to increasc the galling résistance. The proportion ofclass 1 or 2 solid fabricants with respect to the class 4 solid fabricant is in the range 1:1 to 10:1.

« *r [00102] Similarly, the aqueous PAI dispersion may further comprise solid anti-abrasive particles in the powder form selected from the list constituted by cristobalite, mica, colloïdal silica, para-phcnyleneterephthalamidc (aramid) and silicone rcsin.

[00103] Finally, the aqueous PAI dispersion may comprise one or a combination of corrosion inhibitor pigments with a syncrgistic effect.

[00104] Advantagcously, the dry polyamidc-imide films obtained in accordance with a process of the invention are of application in threaded connections as is shown ïn Figure 6. This type of connection comprises a first tubular component with an axis of révolution 10 provided with a male end portion 1 and a second tubular component with an axis of révolution 10 provided with a female end portion 2. The end portions 1 and 2 each hâve a terminal surface disposed pcrpcndicular to their respective axis of révolution 10 and arc rcspcctively provided with a threaded zone 3 and 4, which cooperatc with each other for mutual connection of the components by makeup. The thread type of the threaded zones 3 and 4 may be sclf-locking, trapézoïdal, or of another type. In addition, mctal/mctal sealing surfaces 5,6, intended to corne into sealed interfering contact against each other after connection of the two threaded components by makeup, arc rcspcctively provided on the male 1 and female 2 end portions, adjacent to the threaded zones 3,4. The male end portion 1 has a terminal surface 7 which, when the two components are made up into each other, will abut against a corresponding surface 8 provided on the female end portion 2. The connection also comprises two sealing surfaces 5 and 6 rcspectively disposed on the end portions 1 and 2 and intended to corne into sealed interfering contact when the connection is made up.

[00105] In a variation, the abutment between the terminal surface 7 and the corresponding surface 8 may be replaced by threaded zones 3,4 arrange to coopcrate by self-locking interférence of the type described, for example, in US 4 822 081, US RE 30 647 or US RE 34467.

[00106] As shown in Figure 6, the end portion 1 or 2 of at least one of the tubular components is at least partially coated with a dry film 12 of polyamide-imide in accordance with a process of the invention.

[00107] This in particuiar requîtes that either a portion or the entirety ofthe threaded zones 3 and 4 is coated with the dry polyamide-imide film 12.

[00108] At the same time, the sealing surfaces 5 and 6 may either both be coated with a dry film 12 or indeed just one surface may be coated.

[00109] The dry film is preferably applied to a rough surface. A rough surface incrcases the contact surface and as a resuit incrcases adhesion and the fabricant rétention capacity, in particuiar in the limiting fabrication régime. The surface roughness may be produced by mechanically sand blasting the steel, or it may be produced by means of a surface préparation employing a chemical conversion, such as zinc or manganèse phosphatization. It is préférable to hâve a mean departure for the roughness, Ra, in the range 1 to 3.5 pm and a maximum ridge depth, or Rmax, in the range 10 to 25 pm. The thickness o f the formed film must be greater than or equal to the maximum depth of the ridges, or Rmax.

[00110] Altematively, the surface préparation may be an electrolytic deposit, preferably a CuSnZn temary alloy comprising a Wood’s nickel keying sub-layer. A higher Vickers hardness than steel and a low afïïnity ofthe deposit for steel provides for an adhesive anti-wcar coating on the steel itself in the event of failure of the dry film.

[00111] The term “dry film” means a solid film which is not tacky to the touch.

[00112] From an experimental viewpoint, the Applicant initially worked on obtaining a stable aqueous dispersion of polyamidc-îmidc polymer. The polyamide-imide polymers used are princîpally powdcrs sold by Solvay Advanced Polymers under the trade name TORLON® 4000T, which has a purity of more than 99.9%; the glass transition température was measured by TGA-SDTA as 265°C.

« '4 [00113] Secondly, the Applicant produced aqueous dispersions of polyamide-imide polymer with a composition comprising at least one additive selected from the list formed by solid lubricants or corrosion inhibitors. To stabilize the préparations, it was advantageous to add thickening agents, coalescence agents, stabilizers, dispersants and other anti-foaming agents, selected from those which are the most compatible and which respect the operating environment. For the compositions with additives, particular attention was paid to the critical pigment volume (CPV) in order to guarantee the impermeability of the film, and to limit the porosity, the risk of blistcring and of triggering the corrosion mechanism.

[00114] The dispersion is applied by means ofa pneumatic spraying system. The température of the mixture and the substrate must be similar, preferably in the range 20°C to 40°C.

[00115] The film was coalesced at the application température for a period of 5 minutes. Drying for 10 minutes in a température range in the range 60°C to 80°C followed by curing for 30 minutes in a température range in the range 230°C to 325°C, preferably in the range 275°C to 300°C, completely eliminated the residual water and formed the dry film.

[00116] The dry films were produced on carbon steel spécimens or low alioy steel spécimens with or without surface treatments. The separate treatments could be sand blasting, phosphatization, preferably with manganèse, or elcctrolytic CuSnZn type déposition comprising a sub-layer of Wood’s nickel. The thickncsscs ofthe study films were in the range 10to45 pm.

[00117] Ail of the dispersions tested had compositions which complied with the proportions listed in the table below.

<

Chemical nature	Composition (% by weight)
Water	30-70
DMSO	30-70
Polyamide-imide resin	5-20
Surfactant	0.5-2.5
Stabilizer/thickening agent	0-1
Film formation agents	0-1
Functional pigment fillers	0-20
Preservativcs	0-0.05

Table 1 [00118] 1 n the dispersion with référencé number 1,45 g of a polyamide-imide polymer powder (Torlon® 4000 TF) dissolved in 283 g of DMSO (ROTIPURAN® > 99.8% p.a, ACS, ISO) was introduced slowly with vigorous agitation into a mixture constitutcd by

283 g of distilled water, 6 g of a polyoxyethylenated acetylenic diol (Surfynol® 440 or

Dynol® 604), 3 g of an organically modified bentonite (Optigel® CK), 1.8 g of a polyether modifïcd polydimethylsiloxane (Byk® 348) and 1.8 g of anti-foaming agent (Byk® 037). The suspension of particles of precipitatcd polyamide-imide resin was then finely millcd in a vertical ceramic bead mill at a rate of600 rpm. After milling for 24 hours, the aqueous polyamide-imide dispersion obtained after rinsing with a watcr/DMSO mixture in the initial proportions had a yellow cotour, a dynamic viscosity of500 MPa.s (Brookficld R4,100 rpm, 20°C), a neutral pH of7 (10% dilution in water) and at least 90% of the particles had a size of less than 7.5 gm. Because ofits suitable thixotropy, the dispersion with référencé number I had excellent stability on storage in a température range in the range -5°C to +40°C. Under extreme storage conditions, the facility ofapplication remaîned unchanged over three months. However, after vérification of the dry extract, dilution with water was possible in the case of storage at +40°C in order to facilitate spray application and to préservé the initial properties.

[00119] The dry film obtained from the dispersion with referencc number 1 had a thickncss in the range 10 to 20 gm. It did not demonstrate any corrosion on carbon steel coated with a manganèse phosphatization after 1000 hours of exposurc to satine mist. It will be recalled that the neutral saline mist test is carricd out in a climatic chamber under the < <

following conditions: 35°C with a 50 g/L saline 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 recovcred at a mean rate of 1.5 mL/h.

[00120] Intact rust-free samples hâve to correspond to class ReO of ISO standard 9227 after exposure. The method provides a means for verifying that the comparative quality of a mctallic material with or without corrosion-protectivc coating is maintained.

[00121] In a second stage, the capacity of the film obtained from the dispersion with référencé number 1 to be separated from the contacting surfaces, the capacity to lubricate under shear compressive load, the dynamic adhesion and the friction or abrasion résistance force under increasing load were initially evaluated using the scratch test lt will be rccallcd that the scratch test can be used to evaluate the adhesive force or adhesion of a film to a surface or a surface préparation. It consists of shearing and deforming a film with a spherical bead under an increasing load and can be used to déterminé the coefficient of friction ofthe critical load corresponding to the onset of film detachmcnt.

[00122] The experimental conditions employed a tungsten caibide bead with a diameter of 5 mm and a metallic carbon steel or Z20C13 steel specimen with a roughness Ra of less than 1 micromètre, as well as the following parameters: an increasing load of 10 N to 310 N or 250 N to 750 N, a bead disp lacement rate of 2 mm/s, a period of 20 s and a track length of 40 mm. The increasing load ofl0Nto310Nis représentative ofthe contact pressure in the threaded portion. The increasing load of250 N to 750 N is représentative of the contact pressure at the sealîng surfaces.

[00123] In the dispersions with référencé numbers 2 to 5,67 g of a polyamide-imide polymer (Torlon® 4000 TF) dîssolved in 419 g of DMSO (ROTIPURAN® > 99.8% p.a, ACS, ISO) was introduced slowly with vigorous agitation into a mixture constitutcd by 374 g of distilled water, 18 g of a non-ionic wetting agent (Surfynol® 465), 4 g of a polyphosphate modified synthetic silicate (Laponite® RDS), 3 g of a polyether modified polydimethylsiloxane (Byk® 333) and 3 g ofanti-foaming agent (Byk® 037). The suspension of prccîpitated particies of polyamide-imide resin was then finely milled in a vertical ccramic bcad mill at a rate of600 rpm. Solid lubricating particies such as a suspension of polytetrafluoroethylene in water free of perfluorooctanoic acid and ethoxylated alkylphenol (Dyncon® TF5060GZ), a graphite, a bismuth trisulphide, a tungsten disulphide were introduced alone or in combination during milling. After milling for 24 hours, at least 90% of the particies in dispersion had a size of less than 12.5 gm irrespective of the proportion of additives.

[00124] The dry films were obtained following a curing period of 30 minutes at 300°C.

[00125] The tribological performances of the films obtained from the dispersions with référence numbers 2 to 5 were compared with other glide films or coatings obtained from aqueous polyamide-imide dispersions containing substances classified as CMR but also with a high performance thermoplastic film having a high wear résistance and obtained from an aqueous dispersion of polyether ether ketone as described in patent WO2011/076350.

[00126] The table below records the lubrication performances for the dispersions with reference numbers 2 to 5, each corresponding to a weight ratio between the additive, which is entirely or partially PTFE, and the polyamide-imide. This ratio by weight was in the range 0.25 to 3. The concentrations by volume, calculated using the bulk density, were less than 40% in order to provide suflîcient anti-corrosion protection after 336 hours of exposure to saline mist. The substrate was preferably a carbon steel with manganèse phosphatization. The thickncsses were in the range 20 to 30 gm.

Compositions	Fillers	Solids/PAI weight ratio	Mcan CoF (10-310N)	Mean CoF (250-750 N)
Reference 2	PTFE	0.25	0.085	-
Reference 3	PTFE	1	0.095	0.125
Reference 4	PTFE	3	0.11	-
Reference 5	BiîSj/PTFE	1	0.1	0.14

Table 2 [00127] The coefficient of friction, in the range 0.08 to 0.11, was significantly smallcr than the coefficient of friction of 0.13 of a glide coating with reference NTB3308 comprising / .

a combination of solid lubricating particles (M0S2, graphite, PTFE) and sold by Okitsumo Incorporated. Advantageously, a différence of 0.02 could be interpreted in the context of application to a 7” 32# L80 CS VAM TOP connection by a shouldering torque on makeup which is at least 2000 N.m Iower.

[00128] It was also established that în the case in which the wholc of the end portion 1 or 2 is coated with the dry film, the différence in the coefficient of friction as a fonction of the feed of 0.03 is advantageous in order to guarantee a low shouldering torque and a sufficient torque on shoulder résistance to ensure a seal of the connection, in contrast to an approach by the compétition aimed at coating only the threaded portion.

[00129] At the same time, the Applicant tested the galling résistance of the dispersion with reference number 5 by means of the pin-on-vee test. The pin-on-vee test was used in particular to evaluate, at high speeds, the anti-wear and extreme pressure properties of lubricating fluids in accordance with ASTM standard D 2670 and ASTM standard D 3233, but aiso to evaluate solid fabricants at low rates in accordance with ASTM method D 2625.

[00130] The pin-on-vee test is adapted to overcomc problems with connections:

• a semi-closcd contact geometry (to ensure that the third fabricant body is trapped);

• a pressure-rate interval (PV diagram) which suits that of the connection;

• the possibility of carrying out tests in one direction or in altcmating mode for make and break simulations.

[00131] The contact geometry o f the pin-on-vee test shown consists of a indenter P of carbon steel or alloyed stecl with or without manganèse phosphatization, mounted in rotation and compressed between two V blocks in the form of a V formed from carbon stecl or alloyed stecl treated by sand blasting or with an electrolytic CuSnZn deposit or by manganèse phosphatization and coatcd with the test film.

[00132] The test conditions employed an applied load of785 N corresponding to a mean pressure in the contact of 150 MPa, relatively close to that recorded during make up at the ‘•s start of shouldering at the threaded portion (100-300 MPa) and a prcssure-speed modulus (PV) = 11.2 MPa.m/s, close to that establishîng the wcar rule in the thrcaded portion at the load flanks where PV = 5 MPa.nVs.

[00133] The aim of this test was to simulate and evaluate the galling résistance for the various dry films without it being necessary to carry out the évaluation on connections. This test could be used to compare the performance of the various films with respect to real tests on the connection.

[00134] The galling criterion is defined by référence to ASTM standard D 2625-94 regarding the mcasurement of the loading capacity of a film of solid fabricant and corresponds to a sudden increase ta 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 of785 N. In general, galling is observed when the appiied load dccreascs, irrespecrive of the materials and the configuration.

[00135] The polyamide-imide film of the dispersion with référencé number 5 showed a degree of wcar before galling approximately 4 rimes lower than that of a polyether ether ketone film comprising 30% by weight of a pcrfluoroalkoxycthylcnc copolymer.

[00136] This test is illustrated in Figure 7, which represents the galling résistance of a block of XC48 carbon steel phosphatized then coated with the dispersion with référence number 5 (curvc A) and compared with that of a XC48 carbon steel block phosphatized then coated with a monolayer of polyether ether ketone (curvc B).

[00137] At the same rime, the Applicant established that a curing step, preferably at a température close to the glass transition température of the polymer, can be used to reduce the degree of wcar still further.

[00138] This test is illustrated in Figure 8, which represents the galling résistance of a XC48 carbon steel block phosphatized then coated with the dispersion with référence number 5 which has undergone curing at 300°C (curvc C) and compared with that of a XC48 carbon /,.

steel block phosphatized coatcd with the dispersion with référencé number 5 which has undergone curing at 275°C (curve D).

[00139] The Applicant has also established that the galling résistance is particularly improved by a sand blasting type surface treatment or by an electrolytic deposit of copper or a CuSnZn temary alloy. For sand blasting, it is préférable to hâve a mean roughness departure or Ra in the range 1 to 3.5 pm and a maximum ridge depth or Rmax in the range 10 to 25 pm. The thickncss of the film formed must be at least greater than the maximum depth of the ridges or Rmax.

[00140] At the same time, the Applicant developcd an alternative to the dissolution process which consisted of dircctly incorporating the powdered polyamide-imide polymer into a mixture constituted by distilled water and DMSO, with vigorous agitation, in a weight ratio in the range 60:40 to 20:80, preferably a weight ratio of30:70. After a minimum of 30 minutes agitation, the lubricating solids such as graphite and/or PTFE, had been incorporated. Agitation was maintaincd for 30 minutes. The dispersion was homogenized by an ultrasound treatment or by milling, then it was applied by spraying. The storage stability of this dispersion was determined to be satisfactory but Iimited (less than one month at 40°Ç), in contrast to that obtained by the process combining précipitation and fine milling.

[00141] The dispersion with référencé number 6 was produced by dispersing 115 g ofa polyamide-imide polymer (Torlon® 4000TF) slowly with agitation at 400 rpm in a mixture constituted by 455 g of DMSO (ROTIPURAN® > 99.8%, p.a. ACS, ISO), 226 g of distillcd water and 4 g ofan organically modîficd laponite (Laponite® RDS). The DMSO/watcr mixture was heated to between 60°C and 80°C to ensurc botter dispersibility of the polymer. After a minimum of 30 minutes, 170 of bismuth trisulphide then 30 g of polytétrafluoroéthylène (Xeon® F4) were incorporated into the above mixture with dispersion such that the weight ratio between the additives and the polyamide-imide rcsin / e» was 1.75 and the concentration by volume of additives was a maximum of 25%. After milling for 24 hours, at least 90% of the particles in dispersion had a size of less than 15 μτη.

[00142] The différence in the coefficient of friction as a fonction of the load, 0.06, was more advantageous than for the dry film comprising a fluoropolymer alone or in combination but as a conséquence of higher friction, the abrasion résistance determined using the coefficient of friction and the galling résistance were beyond the values recorded for the dispersion with reference number 5.

[00143] The dispersion with référence number 7 was produced by dispersing 67 g of a polyamide-imide polymer (Torfon® 4000TF) slowly with agitation at 300 rpm in a mixture constituted by 419 g of distilled water, 374 g ofDMSO (ROTIPURAN® > 99.8%, p.a. ACS, ISO), 18 g of a non-ionic wetting agent (Surfynol® 440), 4 g of a polyphosphate modified synthetic silicate (Laponitc® RDS), 3g of a solution of a polycther modified polydimethylsiloxane (Byk® 333) and 3 g ofanti-foaming agent (Byk® 037). After one hour, the dispersion was subjected to an ultrasound generator for a minimum of 30 minutes for homogenization. After the ultrasound treatment, a suspension of polytetrafluoroethylene in water free of perfluorooctanoic acid and ethoxylated alkylphenol (Dyneon® TF5060GZ) was incorporated into the above dispersion with mechanical agitation such that the weight ratio between the additives and the polyamide-imide resin was 1 and that the concentration by volume of the additives was a maximum of 40%. After 30 minutes, the final dispersion was defloceulatcd using a rotor-stator disperser. The polyamide-imide particle size was in the range 60 to 70 μτη.

[00144] Using this simplified process, the abrasion résistance determined from the coefficient of friction and the galling résistance were scen to hâve improved substantiaily, independently of the mean polyamide-imide particle size.

[00145] This is îllustrated in Figure 9, which represents the galling résistance of a XC48 carbon steel phosphatized then coated with the dispersion with reference number 5 obtained by précipitation then milling (curvc E) and comparcd with that of a XC48 carbon steel block phosphatized then coated with the dispersion with référencé number 7 obtained by dispersion then homogenization (curvc F).

[00146] In the dispersions with référencé numbers 8 and 9,75 g of a polyamide-imide polymer (Torfon® 4000TF) was disperscd stowly with agitation at 300 rpm at a température of 70°C in a homogeneous aqueous mixture constituted by 419 g of distilled water, 374 g of DMSO (DMSO Evol ® > 99.7%, p.a.), 18 g of a non-ionic wetting agent (Surfynol® 440), 4 g of a polyphosphate modified synthetic silicate (Laponite® RDS), 3g of a solution of a polycther modified polydimethylsiloxane (Byk® 333) and 3 g of anti-foaming agent (Byk® 038). After one hour, the dispersion underwent horizontal milling under pressure using ccramic beads to homogenize it. After milling for 6 hours, at least 90% ofthe polyamideimide particles had a size of less than 20 pm, and a bismuth trisulphide then a suspension of polytetrafluoroethylene in water free ofperfluorooctanoic acid and cthoxylated alkylphcnol (Dyneon® TF5060GZ) were incorporated into the above dispersion with mechanical agitation so that the ratio by weight between the solids and the polyamide-imide resin was respectivcly 1 and 1.75 and the critical pigment volume was a maximum of40%. The weight rat» between the polytetrafluoroethylene and the bismuth trisulphide was 1.5 parts for 8.5 parts. The dispersions were applied by spraying and the film was formed over 30 minutes at 275°C. The thickness of the dry film was in the range 20 to 30 pm. In order to provide the higher galling résistance of a dry PA1 film comprising a combination of solid lubricating particles with a synergistic effect, it is advantageous to hâve a ratio between the solids and the polyamide-imide resin of more than 1.

[00147] This is illustrated in Figure 10, which represents the galling résistance of a XC48 carbon steel phosphatized then coated with the dispersion with référencé number 8 with a weight rat» between the solids and the polyamide-imide resin of 1 (curve G) and comparcd with that of a XC48 carbon steel block phosphatized then coated with the dispersion with reference number 9 with a weight rat» between the solids and the polyamide-imide resin of 1.75 (curveH).

[00148] The Applicant also compared the galling résistance of a dry film obtained in the présent invention with the compétition. In the dispersion with reference number 10,67 g of a polyamide-imide polymer (Torlon® 4000TF) was dispersed slowly with agitation at 300 rpm at a température of70°C in a homogeneous aqueous mixture constitutcd by 419 g of distilled water, 374 g of DMSO (DMSO Evo! ® > 99.7%, p.a.), 18g of a non-ionic wetting agent (Dispetbyk® 190), 4 g of a polyphosphate modified synthetic silicate (Laponitc® RDS), 3g of a polyether modified polydimethylsiloxane solution (Byk® 333) and 3 g of anti-foaming agent (Byk® 038). After one hour, the dispersion underwent recirculating horizontal millîng using ceramic beads. After milling for 1 hour, at least 90% ofthe polyamide-imide particlcs had a size of less than 45 pm and a suspension of polytetrafluoroethylene in water free of pcrfluorooctanoic acid and ethoxylated alkylphenol (Dyncon® TF5060GZ) was incorporated into the above dispersion with mechanical agitation so that the rat» by weight between the solids and the polyamide-imide resin was equal to 1 and the critical pigment volume was a maximum of 40%.

[00149] The comparison was carried out using a pin-on-vcc tribometer and the dispersion with reference number 10 was applied symmetrically onto a block of phosphatized XC48 carbon steel and onto a phosphatized XC48 carbon steel indenter. The thickness of the dry film was in the range 15 to 25 pm In the competing tribosystem, a dry film comprising a mixture of solid lubricating particles of MoS₂ and graphite in an inorganic polymer was applied to the sand blasted XC48 carbon steel indenter (with a surface roughness corresponding to a maximum depth of ridges or Rmax of 20 pm) coated with a zinc-rich epoxy primer and a dry film comprising a mixture of PTFE and other friction modifying pigments in a réactive epoxy resin was applied to the XC48 phosphatized carbon steel block.

» [00150] By applying the dry film of the présent invention to both surfaces in contact, the value of the coefficient of friction was constant over a longer period after establishing the tribofïlm and the galling résistance was substantially better than that of the compétition.

[00151] This is illustrated in Figure 11, which represents the galling résistance of a tribosystem with the dispersion with reference number 10 (curve J) comparcd with that of a competing tribosystem (curve I).

[00152] In conclusion, the Applicant has establishcd that applying polyamide-imide films starting from an aqueous dispersion of polyamidc-imide free of carcinogenic, mutagcnic and

hydrocarbon wetls has a number of advantages. The principal but non-exhaustive advantages are compliance with professional constraints limiting exposure to substances dassified as carcinogenic, mutagenic and reprotoxic, compliance with extreme température constraints in wclls which may reach a continuous 250°C, excellent film-forming properties, a réduction in the shear load and a highly satisfactory galling résistance, excellent adhesion to ali metallic supports and very good résistance to corrosive agents.

Claims (26)

1. CLAIM S

   1. A process for producing a dry film with a high galling résistance on a threaded élément for drilling and/or operating a hydrocarbon well, characterized in that it comprises at least the following steps:

   • forming a stable dispersion comprising a polyamide-imide powdcr, a polar aprotic solvent with a boiling point of more than 180°C at 760 mm Hg, and water, • applying the dispersion to one of the ends (1,2) of said threaded clément at a température in the range 20°C to 40°C;

   • drying the coated end.
2. 2. A process for producing a dry film on a threaded clément according to claim 1, characterized in that the dispersion is produced with at least:

   • a step in which the polyamide-imide powder is dissolved in the polar aprotic solvent with a boiling point of more than 180°C at 760 mm Hg, in order to obtain a polyamide-imide solution;

   • a step in which the polymer solution is precipitated in an aqueous mixture at ambient température;

   • a step in which the precipitated solution is dispersed by milling the polyamideimide particles.
3. 3. A process for producing a dry film on a threaded element according to claim 1, characterized in that the dispersion is produced with at least:

   • a step in which the polyamide-imide powdcr is dispersed by mechanical agitation in a homogeneous mixture containing water and a polar aprotic solvent with a . boiling point of more than 180°C at 760 mm Hg;

   • a step in which the polyamide-imide dispersion is stabilized by means of a treatment with ultrasound or by milling.
4. 4. A process for producing a dry film on a threaded élément according to any one of the preceding claims, characterized in that the proportion of polyamide-imide is 35% by weight or less.
5. 5. A process for producing a dry film on a threaded element according to claim 2, characterized in that the step for dissolving the polyamide-imide powder is carried out at a température of more than 50°C, preferably more than 80°C.
6. 6. A process for producing a dry film on a threaded element according to claim 2 or claim 5, characterized in that the précipitation step is carried out at ambient température in an aqueous mixture containing distilled water and at least one non-ionic surfactant, the aqueous mixture being free of polyoxyethylenated alkylphenyl ethers.
7. 7. A process for producing a dry film on a threaded element according to claim 3, characterized in that the step for dispersion of the polyamide-imide powder by mechanical agitation is carried out at a température in the range 60°C to 80°C in a homogeneous mixture containing distilled water, the polar aprotic solvent and at least one non-ionic surfactant.
8. 8. A process for producing a dry film on a threaded element according to claim 7, characterized in that the non-ionic surfactant selected from the group constituted by containing groups with a high afïinity for pigments preferably has a hydrophilic-lipophilie balance of 13 or less, preferably 8 or less.
9. 9. A process for producing a dry film on a threaded élément according to claim 3 or claim 7, characterized in that the stabilization by ultrasound treatment is carried out at a minimum frequcncy of 20 kHz and a minimum power of200 W.
10. 10. A process for producing a dry film on a threaded element according to claim 2 or claim 3, characterized in that mîlling is carried out using a bcad mill, the milling yield being in the range 40% to 95%, preferably more than 90%.

    ·'**
11. 11. A process for producing a dry film on a threaded élément according to any one of the preceding claims, characterized in that the size of the polyamide-imide polymer particles in dispersion is less than 70 gm, preferably less than 20 gm and primarily less than 10 gm.

    5 12. A process for producing a dry film on a threaded élément according to any one of the preceding claims, characterized in that the aqueous polyamide-imide dispersion comprises a thixotropic agent which is thcrmally stable at températures of250°C or more selected from the group constituted by organically modified shect silicates of the laponite, saponite, bentonite or smectite type with a pH in 2% by weight suspension in the range 9 to 1 !.

    10 13. A process for producing a dry film on a threaded élément according to any one of the preceding claims, characterized in that the aqueous polyamide-imide dispersion comprises in the range 0.05% to 0.4% by weight of a bactcricidal and/or fungicidal agent for protection in storage and for protection of the film, selected from the group constituted by iodopropynyl-butyl-caibamate, bcnzisothiazolinone, chloromethyl-isothiazolinone and ! 5 methylisothiazolinone.

    ! 4. A process for producing a dry film on a threaded element according to any one of the preceding claims, characterized in that the aqueous polyamide-imide dispersion comprises a spreading agent of the polyether modified dimcthylpolysiloxane type to reduce the surface tension.

    20 15. A process for producing a dry film on a threaded element according to any one of the preceding claims, characterized in that the aqueous polyamide-imide dispersion comprises an émulsion of hydrophobie components containing silicone and/or paraffinic minerai oils.

    ! 6. A process for producing a dry film on a threaded element according to any one of the preceding claims, characterized in that the polyamide-imide (PA1) powder is selected from 25 aromatic polyamide-imide powders.

    17. A process for producing a dry fdm on a threaded élément according to claim 16, characterized in that the selected aromatic polyamide-imide is obtained from a reaction between a trimellitic acid anhydride chloride and an aromatic diamine selected from compounds other than 4,4 ‘-methylenedianiline.

    18. A process for producing a dry film on a threaded élément according to claim 16 or claim 17, characterized in that the selected polyamide-imide is selected from the group formed by aromatic polyamide-imide polymers with a molecular mass in the range 10000 to 30000 g/molc, and a glass transition température in the range 220°C to 285°C.

    19. A process for producing a dry film on a threaded élément according to any one of daims
12. 16 to 18, characterized in that the maximum particle size in the polyamidc-imîdc powder is less than 150 pm, 95% of the particles having a size of less than 75 pm.
13. 20. A process for producing a dry film on a threaded élément according to any one of daims 16 to 19, characterized in that the mcan volume granulometiy ofthe polyamide-imide particles is in the range 30 to 40 pm.
14. 21. A process for producing a dry film on a threaded element according to any one of the preceding daims, characterized in that the polar aprotic solvent is selected from the group constituted by dimethylsulphoxide, sulpholane and γ-butyrolactone.
15. 22. A process for producing a dry film on a threaded élément according to daim 21, characterized in that the polar aprotic solvent is dimethylsulphoxide.
16. 23. A process for producing a dry film on a threaded element according to any one of the preceding daims, characterized in that the stable dispersion further comprises solid lubricating particles selected from the list constituted by graphite, boron nitrides, B12S3, M0S2, WS2 and fluoropolymers.
17. 24. A process for producing a dry film on a threaded élément according to daim 23, characterized in that the dry film comprises at least one solid fabricant particle or a combination.

    '· 1*
18. 25. A process for producing a dry film on a threaded element according to claim 24, characterized in that the proportion of solid lubricating particles with respect to the polyamide-imide is in the range 0.01 to 4.
19. 26. A process for producing a dry film on a threaded element according to any one of the preceding claims, characterized in that the stable dispersion further comprises solid antiabrasive particles seiected from the list constituted by cristobalitc, mica, colloïdal silica, para-phenyleneterephthalamide (aramid) and silicone rcsin.
20. 27. A process for producing a dry film on a threaded element according to any one of the preceding claims, characterized in that the stable dispersion comprises a or a combination of corrosion-inhibiting pigments having a synergistic effect.
21. 28. A process for producing a dry film on a threaded element according to any one of the preceding claims, characterized in that the step for applying the dispersion by spraying onto the end (1,2) of the threaded element is preceded by a supplémentai step for preparing the surface seiected from the list constituted by sand blasting, conversion treatments, electrolytîc déposition and non-reactive treatments.
22. 29. A process for producing a dry film on a threaded element according to any one of the preceding claims, characterized in that the step for applying the dispersion by spraying onto the end ( 1,2) of the threaded élément is completed by a supplémentai step for curing said aqueous dispersion applied to the threaded element at températures in the range 230°C to325°C.
23. 30. A process for producing a dry film on a threaded element according to the preceding claim, characterized in that after curing, the thus-coated threaded element is cooled to ambient température.
24. 31. A process for producing a dry film on a threaded element according to the preceding claim, characterized in that thickness of the dry film is greater than the roughness of the surface préparation and in the range 10 to 45 pm.

    *4
25. 32.
26. 33.

    A process for producing a dry film on a thrcadcd clément according to any one of the preceding claims, characterized in that the dispersion is applied to the whole of the threaded zone (3,4) of the threaded element (1,2).

    A process for producing a dry film on a threaded element according to any one of the preceding claims, characterized in that the dispersion is applied to the sealing surface (5,6) of the threaded element (1,2).