RU2227240C1 - Method for sealing threaded pipe connections - Google Patents

Abstract

FIELD: pipe manufacturing industry. SUBSTANCE: method includes filling space between threaded portions with water- tightening material. As water-tightening material a composition of graphite with copolymer of tetrafluorinethylene and hexafluorinepropylene. Said water- tightening material is applied to threaded surface by powder spraying in electrostatic field. EFFECT: increased quality of threaded connections water-tightening, simplified technological process thereof. 3 cl

Description

The invention relates to the production of pipes and can be used to seal threaded joints of any pipes, including those used in the construction of oil, gas and gas condensate wells, as well as in the formation of pipe columns and pipelines.

Structural and technological clearances in threaded joints of casing pipes under the influence of excessive internal or external pressure lead to a violation of the tightness of the joints and their permeability to the medium. To reduce permeability, various fillers of structural and technological gaps are used. Fillers at the same time perform the function of lubricants to prevent seizing of rubbing surfaces when making screwed joints.

The most common fillers in the form of various greases on a fat or polymerizable basis.

Fat-based lubricants are a mixture of metal and graphite powders evenly distributed in a fat-based component of 30-40 wt.% (See inventions according to the patents of the Russian Federation No. 2136722 of 08.24.98, class C 10 M 129/02; No. 2032712 from 03/27/90, class C 10 M 169/04; No. 2032714 from 03/27/90, class C 10 M 173/00 and application for invention No. 95109583 dated 06/07/95, class F 16 J 15/00).

However, studies in laboratory and real conditions have shown that the use of grease based on fat does not guarantee the required tightness of the compounds. This is explained as follows. Lubricants should have a low viscosity at the time of screwing the threaded joints and a high viscosity when loading the compound with overpressure. With insufficient viscosity, the grease is washed out by the working medium at elevated temperatures and pressure, which leads to depressurization of the compound. The inconsistency of such requirements to the properties of the lubricant makes it difficult to develop high-quality grease-based sealants.

Greases based on polymerizable substrates satisfy the sealing requirements to a greater extent (see application for invention No. 93041784 of 08.20.93, class C 09 K 3/10). Such sealants typically consist of an epoxy compound, hardener and filler. The solid components used are graphite powder, lead powder, zinc dust and copper powder. Metallon is known as a filler; in the aforementioned sealant, finely dispersed fluoroplastic material (polytetrafluoroethylene) is used as a filler.

Threaded connections with such a lubricant are practically inseparable, which creates technological difficulties when unscrewing such connections during the prophylaxis process (heating to 300 ° C is necessary). The introduction of polytetrafluoroethylene into the sealant reduces friction when screwing threaded joints.

Common disadvantages of polymerizable lubricants include the need to prepare the thread surface (cleaning and degreasing), toxicity, the inability to automate, etc., which makes it difficult to work in the field.

There is also a method of sealing threaded joints by metallization - coating the surface of the product with metals and alloys to obtain physico-chemical and mechanical properties different from the original (metallized) material. As a coating, aluminum, copper, lead, zinc, chromium, silver, gold, bronze, brass, etc. are used (see, for example, invention patents No. 2049150 dated March 5, 94, class C 23 C 10/60 and No. 2162928 from 12.25.98, CL E 21 B 17/08, F 16 L 15/00). In modern practice, the galvanic method of applying metal to the thread of casing is widely used.

The metallization method is very expensive and does not exclude the use of greases on a fat or polymerizable basis.

The next known method of sealing threaded joints is the use of fluoroplastic sealing materials in the form of a tape that wraps the pipe threads before screwing the couplings onto it (see applications for inventions of the Russian Federation No. 93010518 of 03/01/93, class E 21 17/08 and No. 93041784 of 08.20.93, class C 09 K 3/10). In the first case, the tape is made of a capacitor film based on polytetrafluoroethylene. The sealing procedure consists in wrapping the male element over a threaded surface with tight turns on the thread profile.

The closest solution to the proposed can be considered a sealing method described in patent No. 2156911 from 12/21/98, class. F 16 L 13/007. According to this method, the sealing is carried out by applying gas-dynamic spraying to the final boundary zones of the threaded sections of the composite coating in the form of metal powders or their mixtures with ceramic materials accelerated by a supersonic gas stream. Before spraying, the corresponding surfaces are prepared by gas-dynamic powder bombardment with a higher hardness than the hardness of the treated surface.

This method does not provide the proper degree of sealing, because metal powders or their mixtures with ceramic materials do not have ductility, fluidity under pressure and have a high coefficient of friction.

The objective of the proposed solution is to improve the quality of sealing of threaded joints, as well as simplifying the sealing process.

To solve the problem in a method of sealing threaded pipe joints, including filling the inter-threaded space with a sealing material, a composition of graphite and a tetrafluoroethylene (TFE) copolymer with hexafluoropropylene (HFP) is used as the sealing material, and the sealing material is applied to the threaded surface by powder spraying in an electrostatic field .

The sealing material has the following composition, parts by weight:

TFE copolymer with HFP 85 - 95

Graphite 5 - 15

The thickness of the sprayed layer is from 20 to 150 microns.

Using the proposed composition provides complete and durable sealing of threaded joints in the temperature range from -100 to + 250 ° C.

The pure copolymer of tetrafluoroethylene (TFE) with graphite powder (HFP) (100%) has high heat resistance and physical and mechanical properties (strength, elongation), but at low and elevated temperatures the copolymer cuts and shrinks from sharp edges during installation, exposing metal, does not have cold flow (ductility), has a high coefficient of friction (K _Tr ) and therefore does not guarantee reliable sealing.

The addition of soft plastic filler-graphite in an amount of 5-15% leads to the appearance of plasticity of the copolymer, i.e. ability to "flow" under the action of stresses arising in the threaded joints during installation, reduces K _Tr , which contributes to the effective filling of the inter-threaded space and ensure the tightness of the pipe connection.

With an increase in the filler content (more than 15%), a significant decrease in the physicomechanical properties of the composition (strength, elongation) is observed, as a result of which the material begins to crumble and is removed from the inter-threaded space during installation. In this case, reassembling the connection does not provide sufficient tightness of the connection.

Using the electrostatic method of powder spraying, it is possible to process threaded joints in a production environment and to deliver pipes to the field already prepared.

The proposed composition can be obtained as follows.

Filler (graphite or other) is introduced into the TFE-HFP copolymer powder sieved onto a 025 sieve (mesh size 250 × 250 μm) and mixed thoroughly on a Henschel type mixer with a speed of 2000-3000 rpm.

The TFE-HFP copolymer and fillers (graphite, boron nitride, α-modifications, talc) are produced on an industrial scale.

The prepared composition is loaded into the hopper of the deposition unit in an electrostatic field of the type UENP or any other type, in which the composition powder is charged and transported in a high voltage electrostatic field (U _slave = 15-100 kV, I _slave = 50-100 μA). Charged particles of the composition are deposited on a grounded part (the inner surface of the threaded connection) in a dense layer, after which the part is placed in an electric furnace, where at 300-350 ° C the powder composition melts to form a shiny coating (black or white, depending on the filler used), firmly connected to the metal, which ensures the reliability of the metal and sealing.

The surface of the parts before spraying is degreased in a solution of soda ash or other alkaline degreasing solutions of the type KM-1, KM-2.

The electrostatic powder spraying method in comparison with the gas-dynamic one has the following advantages: low energy consumption (100-500 W) in comparison with tens of kW for the gas-dynamic method; noiseless method (gas-dynamic method is based on the use of high sound and supersonic gas velocities); the gas-dynamic method is practically unsuitable for spraying polymers, because polymer powders have a low mass, and it is impossible to give them sufficiently high energies. This method is more suitable for spraying metal, ceramic powders, which is used in the prototype method.

In this form, the pipes are delivered to the installation site. Thus, in the field, it is not necessary to carry out any additional sealing operations, since they have already been done under production conditions on automated equipment.

When making screwed pipe joints, the sealing coating is preserved and can be reused.

Thus, a reliable tight connection is achieved. Pipes can be assembled in the field, at any temperature conditions. The proposed method significantly improves the quality of sealing and simplifies operations for its implementation.

The method can be used for threaded pipe joints, as well as pipe joints through couplings.

Claims (3)

1. A method of sealing threaded pipe joints, comprising filling the inter-threaded space with a sealing material, characterized in that the composition of the sealing material is a graphite and tetrafluoroethylene copolymer (TFE) with hexafluoropropylene (HFP), and the sealing material is applied to the threaded surface by electrostatic powder spraying field. 2. The method according to claim 1, characterized in that the sealing material has the following composition, parts by weight: TFE copolymer with HFP 90 - 95 Graphite 5 - 10 3. The method according to claim 1 or 2, characterized in that the thickness of the sprayed layer is from 20 to 150 microns.