NO871463L - CORROSION PREVENTION MIXTURE. - Google Patents

Description

This invention relates to a corrosion-preventing preparation and its use in pipe connections.

Offshore production of oil and gas has become a very important business. This has given rise to several problems. One of these problems is related to the fact that pipelines, such as oil pipelines, risers, drill pipes, etc., are in constant contact with seawater. Seawater tends to be very corrosive. Especially in the places where parts of a pipeline are connected to each other (connections), the corrosion turns out to be quite serious. As a result of the corrosion, the pipeline's strength decreases very strongly, so that there is a risk of the pipeline breaking. To avoid this risk, expensive repair of the pipeline or replacement of the coupling is necessary within a relatively short time.

There is thus a great need for a good anti-corrosion agent for such connections. Conventional greases are not satisfactory, whether they contain a corrosion inhibitor or not. In conventional pipe couplings with screw threads, the grease is pressed out when the parts of the coupling are put together.

In more sophisticated switching systems, e.g. in the systems described in British Patent Nos. 1,573,945 and 2,064,041, it is difficult to apply a corrosion-preventing preparation between the coupling's trade and female.

By means of the present invention is overcome

the problems mentioned above. The invention relates to a corrosion-preventing preparation containing from 60 to 98% by weight

of a liquid hydrocarbon filler, from 1 to 30% by weight

of a corrosion inhibitor and from 1 to 10% by weight of a gelling agent which, over a certain period of time, gives the preparation a viscosity of at least 650 cSt, preferably 750 cSt, at 25°C,

as all weight percentages are based on the total amount of filler, corrosion inhibitor and gelling agent.

The corrosion-preventing preparation is produced by mixing the hydrocarbon filler, the gelling agent and corrosion inhibitors into a low-viscosity mixture that can be easily pumped 2) a corrosion inhibitor, which is available on the market under the trademark "Corexit 8466", and which consists of a 73% by weight solution of fatty acid -alkanol/alkylamine/salts in a mixture of an aromatic hydrocarbon and butoxyethanol, 3) a gelling agent, which consists of phosphate esters of ethanol, octanol and decanol in an aromatic solvent,

and which is available on the market under the trademark "J 2 92", and

4) a catalyst, which consists of sodium aluminate and sodium hydroxide, and which is available on the market under the trademark "J 2 92".

The following preparation resulted in gels having a viscosity of over 750cSt at 25°C, and which were stable after 9 months:

Example II

To demonstrate the excellent anti-corrosion properties, metal test pieces coated with a 50µm thick film of Preparation 2 of Example I, having a viscosity of 760cSt at 25°C, were kept immersed in aerated seawater for 6 months. They remained uncorroded. Based on impedance measurements carried out during the entire exposure time, it was determined that the corrosion rate for the metal test pieces was less than 0.004 mm per year. Uncoated test pieces showed a corrosion rate of 1-2

etc. per year.

to and/or applied to the desired surfaces. After a while, the gelling agent causes an increase in the viscosity of the preparation. Preferably, the desired viscosity is reached after from 60 to

600 minutes after mixing the ingredients.

The liquid filler must not be corrosive in itself. In order to make handling safe, it must also not be flammable. Therefore, the filler is preferably a hydrocarbon with an initial boiling point of at least 80°C.

It can be chosen from a wide range of hydrocarbons. Thus

specific alkanes or alkylarenes such as alkylbenzene, -toluene and -xylene are useful. From an economic point of view, the hydrocarbon filler is preferably a gas oil, which includes diesel oil and heavier fuel oils.

Many corrosion inhibitors can be used in the preparation according to the invention. It is appropriate that they are very effective, so that they can counteract the corrosive effect of seawater environments. The corrosion inhibitors are preferably selected from salts of fatty acids with alkanolamines and/or alkyl amines.

The gelling agent must be capable of providing the desired viscosity. If the viscosity were to become lower, there would be a risk that the preparation could be washed away from the surface it is supposed to protect. If desired, the amount of gelling agent can be adjusted so that a preparation with the desired viscosity is obtained. Very suitable gelling agents can be chosen from organic phosphates, especially from C^_^^-alkyl phosphates.

The preparation according to the invention contains the ingredients in the quantities indicated above. Preferably, the preparation contains from 65 to 85% by weight of the filler, from 5 to 25% by weight

of the corrosion inhibitor and from 1 to 5% by weight of the gelling agent. If desired, it can also contain a catalyst that affects the gel formation. Suitable catalysts include alkali metal aluminates, which may or may not be combined with hydroxides. The amount of these is suitably from 5 to 20% by weight, calculated on the gelling agent.

The invention also relates to the use of the corrosion-preventing preparation in a pipe connection which comprises a tubular tip part and a tubular socket part, the inner surface of which essentially corresponds to the outer surface of the tip part, each surface being provided with elevations and depressions that run in engagement with each other.

The invention further relates to a method for applying the corrosion-preventing preparation between a pipe coupling tip part and socket part, in which method the filler material, the gelling agent and the corrosion inhibitor are mixed together, the mixture is pumped under pressure through a port in the socket part to cause the socket part to expand and/or the tip part to contract, so that a space is formed between the parts, which is filled with the mixture, and the mixture between the parts is allowed to reach an increased viscosity of at least 650 cSt at 25°C. The fluid can be depressurized before or after the gelation of the mixture. The pressure relief is preferably carried out before gel formation has taken place.

The invention shall be illustrated with reference to the drawings, where fig. 1 partly shows an axial section, partly a side view, of a pipe coupling where a tip part and a socket part are in full engagement with each other, and fig. 2 shows in more detail a partial axial section of part of the pipe connection.

As shown in figures 1 and 2, the pipe connection comprises a tubular tip part 1, which is attached, e.g. by welding, to the end of a pipe 2, and a tubular socket part 3, which is attached, e.g. by welding, to the end of a pipe 4 to be connected to pipe 2. The tip part and the socket part can telescopically engage each other, and they usually have frusto-conical outer and inner peripheral surfaces 5 and 6, respectively, which overlap each other when the tip part is fully telescoping in the sleeve part, as shown in fig. 1. The parts 1 and 3 have radially projecting surfaces 7 and 8 at their free, outer end, and when they are completely assembled, one of the radially projecting surfaces 7, 8 respectively will abut against a radially projecting surface 9 or 10 of a shoulder arranged at the inner end of the frustoconical surface of the socket part or the tip part respectively for the transmission of axially directed forces, e.g. pile impact forces, between parts 1 and 3. As shown, the surface 8 of the socket part and the surface 10 of the tip part are in contact with each other.

The generally truncated cone-shaped peripheral surfaces 5, 6 comprise truncated cone-shaped end portions, 11, 12 respectively

and 13, 14, at the inner and outer ends of the frustoconical surfaces, and between these end portions the surfaces are provided with elevations and depressions 15 and 16 which can engage with each other.

A port 17 is arranged in the sleeve part 3, which port provides an opening into the part provided with the elevations and depressions. The port is intended for connection to a source of fluid under pressure.

To assemble the coupling, the sleeve part and the tip part are moved axially towards each other. Through port 17, a pressurized fluid is supplied to expand the socket part and/or compress the tip part, so that the parts can be moved further, so that they are brought completely together. The pressurized fluid, which is usually a hydraulic fluid, is replaced with a preparation according to the invention. The low-viscosity preparation,

which is obtained after mixing the components, is supplied under pressure through port 17, so that it is brought in between surfaces 5 and 6 and surfaces 8 and 10 of parts 1 and 3. The pressure is relieved,

and port 7 is closed with a plug. After a while, the preparation reaches the required viscosity. As a result of the high viscosity, the preparation will not leak out of the coupling, but will provide a long-lasting corrosion-preventing effect.

Example I

For the production of stable anti-corrosion preparations according to the invention, the following starting materials were used: 1) a hydrocarbon solvent, which is available on the market under the trade mark "Corexit 8811", and is based on a diesel oil and contains Cg-C^Q hydrocarbons,

Claims (8)

1. Corrosion-preventing preparation, characterized in that it contains from 60 to 98% by weight of a liquid hydrocarbon filler, from 1 to 30% by weight of a corrosion inhibitor and from 1 to 10% by weight of a gelling agent which, over a certain period of time, gives the preparation a viscosity of at least 650 cSt, preferably 750 cSt, at 25°C, all weight percentages being based on the total amount of filler, corrosion inhibitor and gelling agent. 2. Corrosion-preventing preparation according to claim 1, characterized in that the viscosity of at least 650 cSt at 25°C is reached 60-600 minutes after the mixing of the components. 3. Corrosion-preventing preparation according to claim 1 or 2, characterized in that the filler is a hydrocarbon with an initial boiling point of at least 80°C. 4. Corrosion-preventing preparation according to claim 3, characterized in that the filler is a gas oil. 5. Corrosion preventing preparation according to claims 1-4, characterized in that the corrosion inhibitor is selected from salts of fatty acids and alkanol and/or alkyl amines. 6. Corrosion-preventing preparation according to claims 1-5, characterized in that the gelling agent is selected from among organic phosphates. 7. Use of a corrosion-preventing preparation according to claims 1-6 in a pipe connection comprising a tubular tip part and a tubular socket part, the inner surface of which essentially corresponds to the outer surface of the tip part, each surface being provided with elevations and depressions that run in engagement with each other. 8. Method for applying a corrosion-preventing preparation according to claims 1-6, between a pipe connection tip part and socket part, characterized in that the filler material, the gelling agent and the corrosion inhibitor are mixed together, the mixture is pumped under pressure through a port in the socket part to cause the socket part to expand and/or the tip part to contract, so as to form a space between the parts, which is filled with the mixture , and the mixture between the parts is allowed to reach an increased viscosity of at least 650 cSt at 25°C.