NO175113B - Sealed tube joint and method for forming it - Google Patents

Description

Field of the invention

The present invention relates to tight pipe joints between bolt and box parts intended for tubular goods located down a hole and used for petroleum drilling operations. The invention also relates to a method for forming such sealed pipe joints.

According to the invention, the term "petro-:leum" shall include, but not necessarily be limited to, operations associated with the exploration, drilling and extraction of oil, gas, water and geothermal materials from the earth as well as

disposal of nuclear and/or toxic waste. In addition, the term "pipe" is used for all tubular goods that are located down a hole, regardless of whether these goods consist of pipes, a drill pipe, a casing or a production line etc.

The term "drilling" shall likewise include exploration for the extraction of materials from the earth as well as the formation of a deep hole through which the materials are extracted. However, it will be understood that a pipe with the same characteristics as those used in petroleum operations can also be used in the opposite sense, i.e. to bring materials into the earth. Such a method occurs when returning petroleum products for underground storage or transferring nuclear waste to disposal areas underground. According to the invention, the term "drilling" shall therefore also include preparation for such storage of petroleum with other products or deposition of nuclear or other waste below the earth's surface. The present invention relates to the connection between two pipe lengths. The ends of the two lengths of pipe to be connected together are usually referred to as a "bolt" and as a "box". In this context, a "bolt" can be an externally or internally threaded end of a pipe, and a "case" can likewise be an externally or internally threaded end of a pipe and a coupling which is connected to this with suitable threads for receiving a bolt. However, these designations must be interpreted sufficiently broadly to also cover connection mechanisms that are not threads. Furthermore, the term "assembly" and variations thereof shall mean assembly of two bolt and case parts, and the term "disassembly" and variations thereof shall mean disassembly of the bolt and case parts.

State of the art

The problems associated with petroleum drilling operations are many and extreme. The conditions encountered include extreme temperature conditions, not only between polar regions and equatorial regions, but also in terms of the products being extracted and the high temperature in deep formations. Pressures can be intense at depths below the earth as well as exposure to the inhospitable corrodibility caused by such toxic materials as sulfur dioxide and hydrogen sulphide. In particular, the stresses that tubular goods down in a hole are exposed to are to be feared if these are made up of a string of pipes that can have a length of several thousand feet.

Couplings or tubular connections for lengths of pipe are of the utmost importance to drilling operations and serve two primary functions. In the first case, they hold the weight of the pipe, and this can be a million kilos or more, and they serve to seal the pipe both against intrusions from outside the pipe as well as loss of the products that are extracted. The common type of pipe joints used for drilling operations are threaded joints, and the industry standards established by the American Petroleum Institute (API) are known as "API 8-round" and as "API buttress" threads.

Pipe joints with leaks have represented a significant problem for the petroleum industry, and the problem continues even though recent research and development efforts by joint manufacturers and operators have produced significant improvements in the technology. First-class joint constructions with various combinations of metal-to-metal seals with press-fit threads, new generation non-metallic sealing materials, high-alloy steels and computer/numerically controlled machining technology have been developed and are highly effective. Typical of such first-class joint stock-

instructions are those described in US patents no.

4,244,607 and US Reissue patent 30647. The spliced constructions described in these patents are typical of the technology of premium splices.

Some of these constructions include Teflon<®->o-rings or similar as sealing aids. In this case, sufficient material must be removed from the pipe end within the area of the joint to make room for the o-ring.

Such removal will necessarily weaken the joint and increase the stresses applied to the joint. Moreover, the o-ring material does not have sufficient plasticity to satisfactorily seal the spaces in the joint.

Nevertheless, failures continue to occur in part due to the increased sensitivity of a number of these structures to handling, driving and environmental factors. Single failures in production lines have cost millions of kroner, and they continue to occur as the industry continues to push the technological frontier forward. One of the most pronounced causes of joint failure is leakage. Apart from constructional problems, a number of new joints are easily damaged due to a number of different common rigging and handling methods.

In a further attempt to prevent joints from leaking, sealing materials have been developed and are widely used by industry. A wide variety of such sealing materials are available, such as Shell High Pressure Thread Compound manufactured by Shell Oil Corporation, EXXON 706 Thread Compound manufactured by EXXON Corporation and "Liquid-0-Ring" Thread Compounds manufactured by Oil Center Research, Inc., Lafayette, Louisiana.

These materials meet API standards and are designated as "API modified". The components for these sealing materials typically include an oil-based lubricant and sealing components which may include, for example, powdered graphite, lead powder, zinc dust or copper flakes. There is no chemical reaction between the sealing components and the lubricant. The agent is simply a mixture, and no curing step occurs during its manufacture or application. These sealing materials remain in liquid form and search for any cavities that occur between the adapted threads in the joint.

Although such sealing materials have given a reasonably good result in use, in terms of composition they are mainly a lubricant and only secondarily a sealant. The sealant components in the mixture seek out the voids in the threaded joint, but if a hole is large enough, the sealant will extrude, and the sealant will no longer

be effective for its intended purpose. It also often occurs in the inhospitable environments in which drilling operations take place that the liquid component in the sealing material is burned away under the extreme heat to which it is exposed; leaving voids and the metallic sealing components. These components typically have particle sizes in the range from 50 to 500 µm. This is not only undesirable during normal drilling operations, but becomes even more of a problem during pipe disassembly. Generally, the same pipe can be used for a number of new installations in the same well or in installations for subsequent wells. This is of course desirable because of the "very high price" of the pipeline. In the case where the lubricant is burned away, however, the particles left behind will have a sharp granular consistency, and during disassembly they will occasionally cause tearing to occur on This makes the cable more difficult to disassemble and greatly limits the renewed applicability of the cable.

Summary of the invention

It was with knowledge of the state of the art and the occurring problems that the initiative was taken to develop the present invention. The present invention thus relates to a pipe joint between bolt and box parts intended for use in petroleum drilling operations. According to a preferred embodiment, an anaerobic sealant is used in the form of a one-component material which is applied to one or both of the parts. The parts are then joined together, and the agent hardens into a solid form that binds the parts to each other and fills the space between them. The ingredients in the agent can be selectively varied to regulate the agent's lubricating ability, which also affects the build-up torque. Moreover, the concentration of the components in the sealant can be selectively varied to regulate the break-up torque for the joint to which the sealant is applied, and preferably the sealant should make the break-up torque significantly higher than the build-up torque. Excellent seals can be achieved using lower grade tubing, and the bolt and box parts can be built up using a lower assembly torque without reducing the sealing ability of the joint. The preferred agent also serves as rust and corrosion inhibitors for the joint.

The invention thus relates to a pipe joint which includes bolt and box parts with opposite surfaces and intended for use in petroleum drilling operations, and the pipe joint is characterized by the fact that a curable anaerobic sealant free of volatile solvent has been applied in an uncured state directly to the pipe joint when it was assembled, and then cured to prevent fluid leakage through the joint, the curable sealant being a liquid material in the uncured state and a solid material in the cured state.

Furthermore, the invention relates to a method for sealing a pipe joint which has a longitudinal axis and includes adjacent bolt and box parts with opposite surfaces and intended for use in petroleum drilling operations, and the method is characterized by the application of a curable anaerobic sealant which is free of volatile solvent on at least one of the opposing surfaces in the uncured state to prevent leakage after curing has taken place, that the two parts are connected to each other while the sealant remains in the uncured state, so that the sealant, after curing, adheres to the opposite surfaces to both the bolt and box parts and blocks the flow path in the longitudinal direction that occurs between the opposite surfaces, and that the sealant hardens to a solid state to thereby prevent fluid leakage through the joint.

The discussion below applies primarily

the preferred sealant. The curable sealant is, according to its preferred embodiment, an anaerobic resin with a high viscosity which can be combined with powder of PTFE (polytetrafluoroethylene) and/or polyethylene with particles with a diameter of approx. 10 |ira for lubrication. As the sealant has a consistency between a thick liquid (e.g. maple syrup) and a soft paste (e.g. toothpaste), the sealant will polymerize between tightly fitting metal surfaces so that a seal and resistance to solution with a low breaking strength is obtained. The sealant remains liquid for an unlimited time while it

is exposed to the air. However, when it is added to and used to build up joints, complex reactions occur in the sealant, and these cause it to polymerize in the absence of air to form a hard material with a high molecular weight and with adhesive and sealing properties. These reactions are further catalyzed by the presence of iron, copper, nickel or other metals.

The sealant has been specifically developed for use in sealing pipe joints for underground drilling for petroleum. Although such pipe joints have traditionally been of the threaded type, the use of the sealant need not be limited to threaded joints, but may just as well be used with similar results for a variety of other types of joints. It can be used on lightly oiled, cadmium and zinc plated, black oxide and phosphate and oil coated parts and still give satisfactory results. In order to

To achieve maximum benefits, the parts should be brushed clean, but they do not need to be cleaned with a solvent to remove an oil coating. This is because petroleum-based oils in their natural state have a sufficiently high iron content

causing the resin or monomer in the anaerobic sealant to polymerize.

Some of the advantages of the sealant include the fact that it can be applied to the fitted surfaces of bolt and case parts either using machines or by hand. For threaded joints, the sealant will seal between the threads to prevent spiral leakage paths. The sealant will effectively seal all voids, including micro-grooves,

and other areas, such as the metal-to-metal sealing areas that occur in premium connections. The sealant contains no lead (which is toxic to humans), it is non-stringy (and therefore easy to apply), and the sealant does not use flammable solvents (which would have been particularly risky on a petroleum drilling rig).

The main advantages of the invention, in addition to the sealant's excellent sealing ability, are based on the sealant's lubricating ability, which improves the ability to build up and break up pipe joints, on the sealant's chemical stability and on the sealant's ability to regulate its cohesion and adhesion strength so that a desired predetermined value for break-up torque. As a result of some of these advantages, the sealant will extend the life of production strings and will enable the upgrade of less expensive pipelines for higher pressure applications.

A particularly important feature of the invention is due to

on the sealant's ability to make a difference

equal breaking torque for different parts of a pipe joint. Specifically, it is common practice to use lengths of pipe in the field that have a bolt at one end and a box at the opposite end. In this case, the box part of the joint is usually assembled in a factory, and then the pipe is shipped to the drilling site. As mentioned above, the components of the sealant can be regulated to thereby regulate the break-tor ion moment for the joint. In :henho_id hereto

can that of the resin or the monomer

concentration be constantly different when the sealant is applied to the mutually engaging surfaces of the case than when it is applied to the bolt, so that in a subsequent break-up the same end of each successive length of pipe will be a bolt and its opposite end will be a case. In this way, it becomes significantly easier to handle the pipe. Sealants according to the state of the art are usually not applied before build-up as the pipe moves down the well. With this embodiment of the invention, however, the sealant which has one concentration of the resin or monomer will preferably be applied at the factory at the time of assembly for the box part of the joint. The sealant with a different concentration of the resin or monomer will then be applied during the construction of the field.

Other and further distinctive features, purposes, advantages and beneficial effects of the invention will be apparent from the following description.

Detailed description of the preferred embodiments

The basic composition of the sealant

according to the invention is according to a generally known recipe which has been used for a number of other applications. Examples of US patents that have described the use of monomer compositions with anaerobic properties are US patents no. 3,625,875 and no. 3,969,552.

The monomers that are intended to be used for the sealant are polymerizable acrylate

esters. As used herein, "acrylate esters" shall include ot-substituted acrylate esters, such as methacrylate-, ethacrylate-

or the chloroacrylate esters. Monomers of these types, when mixed with a peroxy initiator, as described below, will form desirable adhesives and sealants of the anaerobic type.

Anaerobic adhesives and sealants are those which remain stable in the presence of air (oxygen) but which will polymerize to form hard, permanent resins when removed from the presence of air. This type of adhesive and sealant is particularly suitable for bonding metals and other non-porous or non-air-permeable materials because they effectively exclude atmospheric oxygen from contact with the adhesive or sealant, and the adhesive or sealant will therefore polymerize so that the surfaces are bonded to each other. Of particular utility as adhesive or sealant monomers are polymerizable di- and other polyacrylate esters because these, due to their ability to form cross-linked polymers, have more highly desirable adhesive or sealant properties. However, monoacrylate esters can be used, especially if the monoacrylate portion of the ester contains a hydroxyl or amino group, or another reactive substituent that serves as a site or center for potential cross-linking. Examples of monomers of this type are hydroxyethyl methacrylate, cyanoethyl acrylate, t-butylaminoethyl methacrylate, glycidyl methacrylate, cyclohexyl acrylate or furfuryl acrylate. The acrylate ester monomers are given anaerobic properties by combining these with a peroxy polymerization initiator, as discussed in more detail below.

One of the most preferred groups of polyacrylate esters which can be used in the adhesives or sealants described here are polyacrylate esters which have the following general formula:

wherein R?~ denotes a radical selected from the group consisting of hydrogen, lower alkyl of 1-4 carbon atoms, hydroxyalkyl of 1-4 carbon atoms, and R 2 is a radical selected from the group consisting of hydrogen, halogen and lower alkyl of from 1 to about. 4 carbon atoms, R<3 >is a radical selected from the group consisting of hydrogen, hydroxyl and

m is an integer equal to at least 1, e.g. from 1 to 15 or more, and preferably from 1 to approx. 8 inclusive, n is an integer equal to at least 1, e.g. 1 to 20 or more, and p is 0 or 1.

The polymerizable polyacrylate esters used according to the invention and corresponding to the above general formula are exemplified by, but not limited to, the following materials: di-, tri- or tetraethylene glycol dimeth acrylate, dipropylene glycol dimethacrylate, polyethylene glycol dimethacrylate, di-(pentamethylene glycol )-dimethacrylate, tetraethylene glycol diacrylate, tetraethylene glycol di(chloroacrylate), diglycerol diacrylate, diglycerol tetramethacrylate, tetramethylene dimethacrylate, ethylene dimethacrylate, neopentyl glycol diacrylate or trimethylolpropane triacrylate. The above monomers do not have to be present in a pure state, but can include commercial qualities in which inhibitors or stabilizers, such as polyvalent phenols, quinones, etc., are included. As used herein, the term "polymerizable polyacrylate ester monomer" includes not only the above monomers in their pure or impure state, but also such other materials as contain such monomers in amounts sufficient for the materials to acquire the polymerization characteristics of polyacrylate esters. The invention also aims to

obtain modified characteristics of the cured agent by using one or more monomers falling within the above formula, together with other unsaturated monomers, such as unsaturated hydrocarbons or unsaturated esters.

The preferred peroxy initiators for use together with the polymerizable acrylate or polyacrylate esters described above are the hydroxy polymerization initiators, and most preferably the organic hydroperoxides having the formula R 4 00H, in which R 4 is generally a hydrocarbon radical containing up to approx. 18 carbon atoms, preferably an alkyl, aryl or aralkyl radical containing from 1 to 12 carbon atoms. Typical examples of such hydroperoxides are cumene hydroperoxide, tert. butyl hydroperoxide, methyl ethyl ketone hydroperoxide or hydroperoxides formed by oxygenation of various hydrocarbons, such as methylbutene, cetane or cyclohexene. Other organic substances, such as ketones and esters, including the polyacrylate esters represented by the above general formula, can be oxygenated to form hydroperoxy initiators. However, other peroxy initiators, such as hydrogen peroxide or materials such as certain organic peroxides or peresters which hydrolyze or decompose to form hydroperoxides, can often be used. In addition, in US patent no. 3,658,624, peroxides with a half-life of less than 5 hours at 100° C are described as suitable in approximately related anaerobic systems.

The peroxy initiators that are used usually make up less than 20% by weight of the combination of monomer and initiator, as the initiators at concentrations above the specified begin to adversely affect the strength of the adhesive and sealing bonds that are formed. The peroxy initiator preferably comprises 0.1 - 10% by weight

of the combination.

Other materials can be added to the mixture of polymerizable acrylic ester monomer and peroxy initiator, such as quinone or polyvalent phenol stabilizers, tert. amine or imide accelerators or other functional materials, such as thickeners or colorants etc. These additives are used to achieve commercially desired properties, i.e. suitable viscosity and storage stability over a longer period of time (e.g. at least one month). The presence of these additives is particularly important when peroxy initiators are used which are not organic hydroperoxides. For a complete discussion of the anaerobic systems and the anaerobic curing agents, reference can be made to US patents No. 2,895,950, No. 3,041,332, No. 3,043,820, No. 3,046,262, No. 3,203,941, No. No. 3 218 305 and No. 3 300 547.

However, the above-mentioned monomer materials have been modified (e.g. by regulating the strength or lubricity, etc.) for the purposes to which the present invention relates, and more specifically as a sealing material for pipe joints, and more particularly between bolt and box parts intended for application for petroleum drilling operations. Monomers with anaerobic properties have in fact been completely unknown for the role described here, and they provide highly desirable results of a kind previously unknown.

As mentioned above, the liquid sealant is applied in relation to matched metallic surfaces. The sealant can be applied in any way, such as by brushing, using a mechanical applicator, using a tape applicator or with a sponge. As long as the parts coated in this way are kept exposed to air, the sealant will retain its liquid form. However, when the parts are joined, so that the internal interlocking surfaces are no longer exposed to air, the sealant will harden to a solid state. When this takes place, it forms a physical bond with the outer surface of a metal to which it has been applied. The presence of the metal to which the sealant has been applied can also initiate and thereby speed up the curing process. The sealant evenly fills micro-indentations formed in the metal, and this leads to the removal of leakage paths for gases and liquids. The sealant provides an absolute and positive seal that works equally well with "API 8-round", "SPI buttress" and "premium" joints. Although the industry has had good experience with "premium" joints, the present invention provides a sound support technique that is more practical and reliable than, for example, Teflon<®> quality o-rings which have been widely used. The sealant effectively provides a plastic seal all over

the area without the need to machine expensive depressions (which weaken the pipe) in contrast to what is necessary for the Teflon<®> seal.

Physical properties of the preferred sealant include the following:

Footnote: Thixotropy ratio refers to the gap-filling property of the sealant and its ability not to drip when applied. The above numbers indicate this ability of the sealant, and more precisely the more the thixotropy ratio is above 1.0, the less the sealant will drip.

Other desirable properties of the sealant in its uncured state include its ability to be easily dispensed, e.g. from a collapsible tube, its stability, i.e. its long possible storage time in a container before use, its low toxicity, i.e. its lack of lead or other heavy metals among its constituents, its non-flammability, i.e. its flash point above 100° C. Its lubricity is a measure of how much stress is applied to a joint for a given torque.

Lubricity

Tension at the following torques:

Fracture strength: as above, but after 4 hours at approx. 63° C Footnote: Unseen breakage means that the nut is free-spinning on the bolt. Other desirable properties of the sealant in its cured and curing state include: Its lubricity in the cured state, its resistance to heat: it has been tested at temperatures up to 166°C in heat cycling tests, its resistance to attack by chemicals (the is essentially chemically inert) and its heat strength - as it is a thermoset plastic material, the sealant has a high heat strength.

It was previously indicated that the sealant can contain PTFE and/or polyethylene additives in the form of a powder to achieve lubrication. Each of these additives can be used in an amount of 0 - 20% by weight. PTFE increases the lubricity slowly, while polyethylene increases the lubricity quickly per added unit quantity.

In liquid form, the sealant lubricates as well as or better than existing API thread compounds. Furthermore, because the sealant does not contain solvents, it cannot "burn out" or lose volume under the influence of temperature or with time, which is the case with known thread compounds. Because there is essentially no loss of volume when the sealant cures, this prevents leak paths from being developed. In its hardened solid state, when the pipes are disassembled, the sealant is pulverized into powder form with lubricating properties, and it continues to be as effective as a lubricant as it was previously in its liquid or uncured state. This is because the molecules of the sealant penetrate into and remain in the micro-degrees that occur on threads and other surfaces in the joint, and reduce the tearing effect caused by these.

The threads obtained are essentially clean and require little preparation for renewed use. The sealant according to the invention thus serves as a lubricant both during build-up and break-up operations, while providing an effective seal.

Another major advantage is that the sealant makes it possible to seal with lower build-up torques than currently used in connection with non-hardening sealants, as the hardening sealant will plug larger distances over the entire joint.

With known sealants, high torque is required to prevent leakage, even with "premium" compounds. It will be understood that at a lower torque, less deformation of the pipe occurs and thus an expected longer lifespan for the threaded connection. This will make it possible to use "API' 8-round" threading and "API buttress" threading in practically all cases, thereby eliminating the need for the expensive "premium" connections. This is of importance if it is taken into account that a currently occurring price range for "API 8-round" compounds is between 10 dollars and 20 dollars per connection, while the price range for "premium" connections is between 200 and 500 dollars per coupling. In some special cases, the "premium" connections can cost even more than 500 dollars per coupling.

Another advantage of a lower torque requirement is that less tension is applied to the pipe connections, and this ensures that the pipe will remain more resistant to the corrosive effects of such highly toxic substances as hydrogen sulphide and sulfur dioxide, which are common in petroleum well environments. Such toxic substances are known to corrode stressed areas in joints faster than non-stressed or less stressed areas.

Another significant advantage of the invention lies in the ability to regulate the strength of the sealant by regulating the percentage content of its constituents. Translated into the terminology used in the oil extraction industry, this means that the break-up torque can be regulated. More specifically, the greater the percentage of resin or monomer, the higher the breaking torque must be when the sealant is applied to a pipe joint, and vice versa. The strength can also be increased by increasing the amount of mineral filler, although this is not to the same extent as by varying the resin. Typical mineral fillers are titanium dioxide, which is used as a whitening agent, and mica, which is used as a reinforcing filler.

A further advantage of the invention is the sealant's ability to ensure a significantly higher break-up torque than build-up torque in such joints where a low build-up torque is desirable. It is achieved by regulating the concentration of the constituents in the sealant.

According to the preferred embodiment, the component is

which is regulated, the polymerizable acrylate ester monomer. This ensures that one end will not break up unintentionally due to low build-up torque.

The above-mentioned advantage of regulating the break-up torque by regulating the concentration of the resin or monomer in the sealant leads to a further advantage of the invention. More specifically, from a material handling point of view, it is desirable to know which end of a reusable pipe that is removed from a well will be a bolt and which end will be a box, so that the pipe can be stacked evenly in anticipation of further use. This purpose can be achieved by applying a sealant with a concentration of monomer to the case when it is assembled (most likely at the factory), then applying a sealant with a different concentration of monomer to the bolt at the drilling location. The concentration of the monomer will be known in each case, so that the torque to break up each part of the joint will also be known. If the concentration of the monomer is kept constant in each case, as the pipe is pulled out of the well for subsequent use, it will end up the same. each successive length of pipe will be a bolt and the opposite end will be a box. There was therefore until now no way to

know whether one end of the pipe would be a box or a bolt when broken. This led to difficulties for subsequent operations, and this will be eliminated by means of the present invention.

In addition to regulating the percentage of the resin or monomer in the sealant to regulate the breaking torque, it is possible by making further adjustments to the composition. :ensure that the prevailing strength is less than the breaking strength. The prevailing force is defined as the torque used to unscrew a bolt from a case after the bolt has been rotated through an optional angular arc, for example 180°. If the prevailing force is not kept at a value that is less than the breaking strength, the torque can increase with continued unscrewing of the bolt from the case, with the result that the dismantling of the bolt and the case will be very difficult.

In current practice, relatively high torques are used for screwing together,* and a somewhat lower torque than the screwing torque is required for finishing. The latter situation is not desirable, but is a characteristic feature of a joint for which known sealants have been used. The higher torques are necessary to ensure sealing in the joints. The following is an extract from Trial Summary 4 below according to this description. It clearly shows how the connection was built up to lower torques when the sealant was used, without this affecting its sealing ability.

When the known sealing materials are used, the finishing torque is typically lower than the tightening torque. As a result of the invention, however, the finishing torque can be made greater than the screwing-in torque by regulating the properties, more specifically the percentage of resin or monomer in the cured polymer. In the above test, for example, the connection broke up at a torque that is somewhat less than the screwing torque when the build-up was done with API compound. When the sealant was used and the connection built up to 2,880 cm-kg, the finishing torque was 16,128 cm-kg.

A further significant advantage of the invention is the chemical stability of the sealant. More specifically, its composition is such that it is inert to chemicals normally encountered in petroleum drilling operations. In addition, the sealant is non-toxic if used correctly, and it will not pollute the environment in contrast to what known sealants do that contain heavy metals, such as lead or nickel etc. Extensive tests have not produced any adverse effects when exposed to chemicals found in the oil industry. the extraction area, including hydrogen sulphide and sulfur dioxide.

Another significant feature of the invention is the self-cleaning ability of the sealant. More specifically, the solid polymer material will be pulverized during finishing and leave a fine coating on the threads. This fine coating does not adversely affect a subsequent screwing together, but has proven effective in preventing oxidation to an extent that is better than with most known corrosion-resistant protective coatings.

Extensive trials have been carried out with regard to the sealant, and the following shows some of the more significant trials that have been carried out up to today using both the anaerobic sealant

and previously known means for a variety of different applications.

Trial summary 1

In this group of experiments, they used joints

standard "VAM" single metal to metal sealing joints with saw threads. "VAM" is a trademark of Vallourec, Paris, France, one of the leading manufacturers of "premium" compounds. Leaks were caused on the test sides of the connections by means of grooves which had been filed into the seals. The connections were then tested to ensure that they leaked easily when screwed together with API (American Petroleum Institute) modified "premium" threads and were then tested as follows:

(a) 7.3 cm tube. Pressure: 703 kg/cm 2nitrogen. Heat cycling: from ambient temperature to 160° C. Tensile: 90716 kg 2 (b) 8.26 cm sleeve. Pressure: 703 kg/cm hydrostatic (c) 19.37 cm sleeve. Pressure: 633 kg/cm <2>nitroene.

Heat cycling: from ambient temperature to 14 9° C.

In all cases, the couplings were sealed when the anaerobic sealant was applied to the corroded side of the coupling. The finishing torques averaged approx. 150% of the tightening torques. There was no sign of demolition.

Trial summary 2

Tube size: 19.37 cm

Coupling types: "VAM" premium couplings with metal-to-metal seals and serrated threads.

Two stub pipes and two end plugs were mounted with respectively three connections arranged between the stub pipes and the end plugs. One of the end plugs was unable to hold a pressure above 281 kg/cm 2 and prevented testing of the entire assembly. This connection was further weakened by shards that were felt into the seal to cause it to leak. The

anaerobic sealant was then applied

on the threaded area, and the coupling was again screwed together,

and the entire assembly was exposed to heat and pressure cycling for several days. The coupling maintained the pressure through the threads during the entire test period, while leaks occurred in several of the healthy couplings in the assembly. The maximum pressure was 633 kg/cm<2 >nitrogen, and the temperature was cycled from ambient temperature to approx. 149°C.

Trial summary 3

In this test, 7.3 cm 8-round pipe was used and was made to compare the anaerobic sealant with an API modified high pressure thread compound

produced by Shell Oil Corporation.

The test included two threaded bolts and one single coupling. One bolt contained a machined groove to simulate a field defect. The groove was cut to the root of the thread over the entire length of the thread. The slot was cut to a width of 1.524 mm at the nose of the bolt and tapered to a width of 0.51 mm at the end of the thread.

The sample was screwed together to a torque

of 2650 cm-kg using a light application of API modified pipe paste manufactured by Shell Oil Corporation. The sample was pressure tested with nitrogen gas, and a leak was noted immediately at the grooved end. It was disassembled and additional API modified paste was applied to the threaded end to simulate field conditions. The sample was re-bolted to a torque of 2189 cm-kg using the same amount of turns used for the original bolt-on. Internal gas pressure was then applied and with an overpressure of 246 kg/cm 2 it was noted that paste was extruded at the machined slot. A leak developed and the internal pressure dropped to zero kg/cm 2 overpressure.

The sample was disassembled, cleaned and inspected. The anaerobic sealant was applied to the grooved end, while the API modified paste was applied to the other bolt end. The sample was screwed together to 195 8 cm-kg and allowed to cure at ambient temperature (approx. 35 C) for 5 hours. An internal gas pressure of 527 kg/cm 2 was applied and maintained for 2 hours. No leakage could be observed.

The samples were then exposed to a temperature of

113°C for 1 hour. An internal gas pressure of 387 kg/cm<2> overpressure was applied for 1 hour while maintaining the elevated temperature, and no leakage was observed. The sample was allowed to cool to ambient temperature while the internal gas pressure of 387 kg/cm 2 overpressure was maintained. No play stock was observed.

The sample was then disassembled, cleaned and inspected.

A torque of 6649 cm-kg was required to finish the bolt with the machined groove, and a torque of

6206 cm-kg was required to f<g>jen<g>e the API modified bolt end. The slotted bolt went through smoothly and without problems. No tearing was observed on any of the bolt ends.

Trial summary 4

Thread construction: 19.37 cm wedge

Attempt (a)

This experiment was initiated to investigate a Teflon<®->ring as a support gasket in a known leakage device. At a screw-in torque of 2880 cm-kg it leaked at 105 kg/cm 2 . At 40320 cm-kg it leaked at 562 kg/cm 2 . The anaerobic sealant was applied and the coupling was screwed together at 2880 cm-kg. It maintained a pressure of 562 kg/cm 2. The release torque was 1612 cm-kg.

Attempt (b)

This coupling was bolted to 4032 0 cm-kg with API-modified lubrication and subjected to a combined tensile and internal compression load of

2

266712 kg. It leaked at 703 kg/cm . The Anerobr sealant was applied, and under the same conditions the coupling held a pressure of 914 kg/cm 2 .

Try (c)

This coupling was bolted together with API lubrication to 46080 cm-kg. It leaked at a pressure of 352 kg/cm 2. In an attempt to test the behavior of the anaerobic agent under severe conditions, the box end of the coupling was completely filled with 7.3 kg of drilling mud and the joint was pushed into the mud. A seal was achieved up to a pressure of 914 kg/cm<2> without adverse effects due to the presence of the drilling mud.

Trial summary 5

(b) During the use according to the invention of a preferred anaerobic sealant:

When using API-modified pulp:

(c) When using preferred anaerobic sealant:

When using API-modified pulp:

(e) When using the agent according to the invention:

Trial summary 6

For these tests, the couplings used were VAM-PTS 7.3 cm N80 premium couplings. No tearing was visible in the coupling or on the bolt during the test. In order to understand the terminology used, it should be noted that the column (1) below represents the time of day, the column (2) represents the tensile load created due to the internally applied gas pressure (nitrogen), the column (3) represents the load applied by the tensile frame, the column (4) represents the combined load according to columns (2) and (3), column (5) represents hot cycling, and with respect to column (6) leaks were noted by estimating bubbles per minute which escaped from a leaking coupling and was fed into a jar of water through a small diameter pipe.

Results:

No leakage over the first 2 complete cycles Slight leakage over the 3rd cold cycle

The leak closed over the 3rd heat cycle

Results:

No leakage on the first cycle Leakage on cold cycles

Leakage reduced or stopped during heating cycle

Results: The seal held during the entire experiment

Fourth attempt API mass

API compound was applied to the test connections, and strong leakage occurred at low pressure.

Trial summary 7

A test was carried out downhole in a real well on 6 July 1986. This comprised a string of 19.4 cm wedge connection with a length of 366 m in the form of a casing at the bottom of a 3900 m deep well. The tube was able to be screwed together very easily without any problems. The pipe got stuck in the hole when the string was lowered, and this made it necessary to pull out the string. This led to the unusual opportunity to complete the pipe after it had been exposed to the conditions down the hole for over 1 week. The coupling was very easy to complete and a minimum of cleaning was required compared to normal conditions using API pipe linings. The average tightening torque was 23040 cm-kg, and the average finishing torque was 34560 cm-kg. There was no sign of demolition. The experiment can be summed up by saying that it was completely successful.

The well is located approx. 10 miles southwest of Lafayette, Louisiana.

Drilling Rig - "Glasscock 73"

Operator - Davis Oil

Coupling Manufacturer - Tubular Corporation of America, Houston,

Texas

Claims (15)

1. Pipe joint which includes bolt and box parts with opposing surfaces and intended for use in petroleum drilling operations, characterized in that a curable anaerobic sealant free of volatile solvent has been applied in an uncured state directly to the pipe joint when it was assembled, and then cured to prevent fluid leakage through the joint, the curable sealant being a liquid material in an uncured state and a solid material in the hardened state. 2. Pipe joint according to claim 1, characterized in that when the bolt and box parts are disassembled with the anaerobic sealant in a fully cured state, the sealant has been pulverized without causing tearing between the opposing surfaces. 3. Pipe joint according to claim 1 or 2, characterized in that the curable anaerobic sealant is partially composed of a polymerizable acrylate ester monomer, the concentration of the acrylate ester monomer being chosen so that the torque required to dismantle the pipe joint is not less than the torque that is necessary to install the pipe joint. 4. Pipe joint according to claim 3, characterized in that a torque is applied to the bolt and box parts which causes the joint to be under tension, and that the anaerobic sealant includes a lubricating component to thereby regulate the tension against the joint which results from the application of a specific torque on the bolt - and the box parts. 5. Pipe joint according to claim 4, characterized in that the lubricating component is at least one of powders of polytetrafluoroethylene and polyethylene. 6. Pipe joint according to claim 5, characterized in that it comprises a box part which includes a first bolt part with a threaded end and a threaded coupling part, the first bolt part and the coupling part having mutually engaging helical surfaces, and that the first bolt part and the coupling part are threadedly connected to each other; a cured anaerobic sealant having a first concentration of constituents and applied in the uncured state directly to the helical surfaces of the box portion to prevent leakage between the first bolt portion and the coupling portion along a helical flow path defined by the helical surfaces, wherein the first concentration of components lead to a first amount of torque necessary to disassemble the first bolt part from the coupling, a second bolt part with a threaded end, the second bolt part and the coupling part having mutually engaging helical surfaces, and the second bolt part and the box part are threadedly connected with each other, where the cured anaerobic sealant with a different concentration of ingredients is applied directly in the uncured state to the helical surfaces between the second bolt part and the coupling part to prevent leakage between them along a helical flow path defined by the helical surfaces, and as thedifferent concentration of constituents leads to a different amount of torque required to disassemble the other bolt part from the box part. 7. Pipe joint according to claim 6, characterized in that the anaerobic sealant is preferably partially composed of a polymerizable acrylate ester monomer, where the concentration of the acrylate ester monomer is chosen so that the torque required to dismantle the first bolt part and the coupling part is different from what is necessary to dismantle the other bolt part and the box part. 8. Procedure for sealing a pipe joint that has a longitudinal axis and includes adjacent bolt and box parts with opposite surfaces and intended for use in petroleum drilling operations § characterized in that a curable anaerobic sealant that is free of volatile solvent is applied to at least one of the opposing surfaces in a cured condition to prevent leakage after curing has taken place; that the two parts are connected to each other while the sealant remains in an uncured state, so that after curing the sealant sticks to the opposite surfaces of both the bolt and box parts and blocks the flow path in the longitudinal direction that occurs between the opposite surfaces, and that the sealant hardens to a solid state to thereby prevent fluid leakage through the joint. 9. Method according to claim 8 for sealing a pipe joint which includes bolt and box parts with threaded ends and with mutually engaging spiral-shaped surfaces, characterized in that the anaerobic curable sealant without volatile solvent in the uncured state is applied directly to at least one of the spiral-shaped surfaces, that the threaded ends are mounted so that the sealant blocks all possible leakage paths, including the spiral flow path that is delimited by the spiral surfaces, and that the hardenable sealant is hardened to thereby seal the pipe joint. 10. Method according to claim 8^ where the pipe joint includes first and second opposite threaded pipe ends and a threaded coupling for threaded engagement with the pipe ends, where the pipe ends and the coupling have helical surfaces which are mutually engageable in each other, characterized in that the anaerobic curable sealant free of volatile solvent is applied in an uncured state directly to at least the spiral-shaped surfaces of the pipe end, the concentration of constituents in the sealant being regulated to thereby determine the torque required to dismantle the pipe joint, and that the pipe ends and the coupling are assembled so that the sealant blocks all possible leakage paths including the spiral flow path that is delimited by the spiral surfaces, and the sealant hardens. 11. Method according to claim 9 or 10, characterized in that the anaerobic curable sealant is used which consists of a polymerizable acrylate ester monomer and other components and that the concentration of the acrylate ester monomer is regulated to thereby determine the torque that is necessary to dismantle the pipe joint . 12. Method according to claim 11, characterized in that the assembly of the threaded ends includes the step of applying a predetermined torque to the bolt and box parts, and that the regulation of the concentration of the acrylate ester monomer includes the step of selecting a predetermined concentration of the monomer, so that the torque required to dismantle the threaded ends is not less than that required to assemble the threaded ends. 13. Method according to claim characterized in that a torque is applied to the bolt and box parts which thereby causes a tension to be applied to the pipe joint, and that a sealant containing a lubricating component is used to thereby regulate the tension against the pipe joint which is due to the application of a particular amount of torque on the bolt and box parts. 14. Method according to claim 11, characterized in that a sealant is used with a lubricating component to thereby regulate the tension exerted on the pipe joint and which is due to the application of a special amount of torque on the respective pipe ends. 15. Method according to claim 11 or 14, characterized in that the step for applying the curable anaerobic sealant includes the steps that the sealant with a first concentration of the components is applied, so that a first amount of torque is obtained which is necessary to dismantle the first threaded touching end and the coupling, and that a sealant with a different concentration of ingredients is applied so that a different amount of torque is obtained which is necessary to dismantle the other threaded pipe end and the coupling.