KR20070049187A - Double wall pipe - Google Patents

Abstract

The present invention relates to an internal high pressure pipe (1) having an internal flow space for hazardous and / or combustible liquids, in particular fuel or working fluid to be injected, and an external protective pipe (2) for potential leak or spill liquid from the internal pipe. As an example, it is directed to a double wall pipe comprising an outer protective pipe 2 arranged coaxially around the inner pipe and having an outer flow space between the inner pipe and the outer pipe. The double wall pipe has a plurality of grooves 23 in which the protective pipe 2 is arranged substantially long on the inner surface 21, and the inner high pressure pipe 1 is tightly coupled to the inner side of the protective pipe 2. After bending of the double wall pipe 100, the double wall pipe 100 is integrated by surface pressure due to deformation of the bending process.

Description

Double wall pipe {DOUBLE WALL PIPE}

The present invention has an internal high pressure pipe having an internal flow space for hazardous and / or flammable liquids, in particular injection fuels or fluid oils, and an internal pipe having an outer flow space between the internal pipe and the external pipe for the possibility of leakage or spillage from the internal pipe. A double wall pipe provided with an outer protective pipe arranged coaxially around.

Industrial steel pipes that carry hazardous and / or flammable liquids such as fuels, fluid oils, acids, and the like, require external protection as a means to prevent spills. This type of spill protection is also required for main and secondary ship engines in accordance with the international convention for the safety of life at sea (SOLAS). Today's standard treaties stipulate the use of flexible hoses or simple-pipes covering high pressure transport pipes. We have studied two separate pipes or pipes and hoses to achieve this requirement.

Flexible hoses are usually fitted with composite holders. Such composite holders only have a defined lifetime due to the different vibrations between these two parts. For this reason, after an unspecified time, the protective hose is in contact with the high pressure pipe and subjected to mechanical damage. The solution of using ordinary steel pipes as protective tubes presents the same problem due to the undefined contact between parts due to pipe bending during the manufacturing process. In summary, the two parts thus far need to meet the requirements for double wall pipes in order to provide some effective spill protection for high pressure transport pipes.

Particularly in the field of large combustion engines used as main or auxiliary engines of power plants or ships to produce heat and / or electricity, fuel pipes of diesel engines inside other pipe sheaths with the possibility of leakage from the inside of the sheath. It is known to arrange. In the case of a leak, the leaking fuel can be carried along the inside of the shell away from near the engine. Such a device with a double wall pipe system is described in EP 1 150 006 A2.

US 6,286,556 B1 also describes high pressure fuel injection pipes for diesel engines with external protection pipes as a specific embodiment to prevent scattering and leakage of fuel out of the engine. Nevertheless, the protective pipe has an inner diameter slightly larger than the outer diameter of the injection pipe such that the two tubes are not connected to each other over the section. Vibration from the engine results in different vibrations of non-uniform components of the double wall fuel pipe.

In particular, in fuel injection pipes for two-stroke diesel engines, a significant amount of fuel is injected into the cylinder through the injector under high pressure. There is a need for high quality tubes that are susceptible to damage due to ambient and frictional induced heat up to 100 ° C. in and around the fuel pipe, with reciprocating loads from nearly atmospheric pressure to high injection pressures of 700 bar. Such undesirable vibrations, undesirable contact surfaces and other irregularities will damage both pipes.

Accordingly, the present invention seeks to improve the life of double wall pipe and reduce the manufacturing cost.

The invention consists of a double wall pipe according to claim 1. According to the invention, the protective pipe has several grooves arranged substantially axially through the inner surface, so that these grooves serve as external flow spaces for potential leak or spill liquids. In order to be able to fit a high pressure inner pipe inside the protective pipe, there is only a small gap between the two folding pipes. Thus, it is possible to push the inner pipe into the inside of the protective pipe. As a result, a double wall pipe having a preferred configuration for an engine or the like is formed by the cold bending process. The material deformation of the two folded pipes due to the bending process allows the two parts of the double wall pipe to be integrated into one part.

Such double walled pipes behave like a single tube. Due to the integration (uniformity) of these pipes, the vibration does not cause any damage between the protective tube and the high pressure tube, since the double wall pipe according to the invention operates as a single body under loads of the kind mentioned above. Vibration can be easily eliminated by using the holder directly on the outer side of the protective pipe. As a result, the double wall pipe according to the invention has a significantly improved life.

The preferred clearance between the inner high pressure pipe and the protective pipe is smaller than 0.5 mm, preferably 0.2 mm. The tolerance of the internal high pressure pipe is approximately 0.06 mm. In protective pipes with the same tolerance as a 0.2 mm clearance between the two pipes, the high pressure pipe can be pushed into the protective pipe by hand. The necessary deformations are formed in the bending process and integration as one part is achieved by surface pressure. Bending is performed under cold forming conditions as required by the engine manufacturer.

The grooves are evenly arranged on the circumference of the inner surface of the protective pipe in order to have an approximately uniform surface pressure after the bending process. The stresses and strains caused by the bending process are thus distributed over the entire circumference of the outer surface of the sensitive high pressure pipe. Preferably, three to twelve, in particular six axially directed grooves are provided on the inner surface of the protective pipe.

According to an embodiment of the present invention, each groove has a width w = (π / 2n) · ID ₂ , where n is the number of grooves in the protective pipe and ID ₂ is the inner diameter of the protective pipe. Thus almost half of the inner surface of the protective pipe is in contact with the outer surface of the inner high pressure pipe.

Preferably the cross sectional area of the outer flow space is larger than the cross sectional area of the inner flow space to satisfy the SOLAS requirement.

According to an embodiment of the invention, the inner pipe has a greater hardness value than the protective pipe. Therefore, highly sensitive high pressure pipes are hardly affected during the bending process. More precisely, the material of the protective tube should be chosen in such a way that even when using extreme bending angles and / or radii, the protective pipe is not affected by mechanical damage such as any groove or surface damage.

In order to prevent stress inside the single double wall pipe due to thermal parameters, the material of the inner pipe has a coefficient of thermal expansion substantially the same as that of the protective pipe.

In a preferred embodiment, the inner high pressure pipe is a St 52.4 material containing a steel tube, in particular C, Si, Mn, P, S and / or Al and the outer pipe is a St 35 material which is a steel tube, in particular a finished NBK.

The present invention will now be described with reference to the accompanying drawings.

1 is a cross sectional view of a double wall pipe according to the invention,

FIG. 2 is a schematic three-dimensional view illustrating an example of a bent double wall fuel pipe for a diesel engine according to the present invention.

1 is a cross-sectional view of a double wall pipe 100 consisting of an inner pipe 1 and an outer protective pipe 2.

The internal high pressure pipe 1 is a seamless precision steel tube made of St 52.4 material. The finishing operation of the steel tube is preferably NBK. The steel tube contains small amounts of C, Si, Mn, P, S and / or Al.

In one embodiment of a large diesel engine, in particular used as a main or auxiliary marine engine, in particular a two-stroke diesel engine, the high pressure pipe 1 has the following size. Outer diameter ID ₁ = 20 mm, inner ID ₂ = 9 mm, thickness 5.5 mm. The high pressure fuel injection pipe must withstand a test pressure of 1,350 bar and a temperature of 120 ° C.

In order to meet the above requirements, a low roughness high precision steel tube with little defects on the inner surface is needed. Preferably, the inner surface 11 of the high pressure pipe 1 has a tolerance of ± 0.10 mm. In addition, the outer surface 12 of the high pressure pipe 1 has a tolerance of ± 0.06 to 0.08 mm.

The protective pipe 2 is arranged coaxially with the internal high pressure pipe 1. The inner diameter ID ₂ of the protective pipe 2 is thus only slightly larger than the outer diameter ID ₁ of the internal high pressure pipe 1. According to the above-described embodiment of the inner high pressure pipe _{1 with} the outer diameter ID ₁ of 20.00 mm, the inner diameter ID ₂ of the outer protective pipe ₂ is 20.20 mm.

The inner surface 21 of the protective pipe 2 is provided with six grooves extending axially through the pipe. The protective pipe 2 has a cylindrical outer surface 22 having an outer diameter ID ₁ of 27.00 mm and a thickness of 3.4 mm. Due to the groove 23 having a 1.4 mm depth, the wall thickness of the protective pipe 2 is reduced to 2.00 mm in the area of the groove 23.

In order to complete the production of the fuel injection pipe, the double wall pipe 100 composed of the outer protection pipe 2 and the internal high pressure pipe 1 is cold bent in a configuration suitable for a diesel engine in which the fuel injection pipe sheath is installed. Will be processed. During this bending, the integrity of the pipe is achieved by the surface pressure due to the deformation of the two pipes 1, 2 formed in the bend B of the double wall pipe. An example of a bent injector pipe is shown in FIG. 2.

Due to the characteristic design of the protective pipe 2 with several axial grooves 23 on the inner surface 21 of the pipe, the protective pipe is a star tube because the protective pipe looks like a star in the cross-sectional view of FIG. 1. It is referred to. The groove of the star tube 2 is provided with an outer flow space for outflow protection for the potential outflow liquid. These liquids flow through the grooves 23 of the star tube 2 to the end of the pipe and can be connected to the alarm system according to the requirements of SOLAS.

Explanation of symbols on the main parts of the drawings

100: double wall pipe

1: internal high pressure pipe

11: inner surface

12: outer surface

2: protective pipe

21: inner surface

22: outer surface

23: home

B: bend

Claims (10)

Internal high pressure pipes (1) with internal flow spaces for hazardous and / or flammable liquids, in particular fuels or working fluids to be injected, and An outer protective pipe 2 for potential leak or spill liquid from the inner pipe, the outer protective pipe 2 being arranged coaxially around the inner pipe and having an outer flow space between the inner pipe and the outer pipe. A double wall pipe comprising: The protective pipe 2 has several grooves 23 arranged substantially long on the inner surface 21, The internal high pressure pipe 1 is tightly coupled to the inside of the protective pipe 2, After bending of the double wall pipe 100, the double wall pipe 100 is characterized in that it is integrated by the surface pressure due to deformation of the bending processing process, Double wall pipe. The method of claim 1, The gap between the internal high pressure pipe 1 and the protective pipe 2 is characterized in that less than 5.0 mm, in particular less than 0.2 mm, Double wall pipe. The method according to claim 1 or 2, The grooves 23 are characterized in that they are arranged at regular periphery on the inner surface 21 of the protective pipe 2, Double wall pipe. The method of claim 3, wherein Characterized in that three to twelve, in particular six axially directed grooves 23 are provided on the inner surface 21 of the protective pipe 2, Double wall pipe. The method according to claim 1, wherein Each groove 23 has a width w of approximately w = (π / 2n) ID ₂ , where n is the number of grooves 23 in the protection pipe and ID ₂ is the inner diameter of the protection pipe. Made, Double wall pipe. The method according to claim 1, wherein Wherein the cross sectional area of the outer flow space is greater than the cross sectional area of the inner flow space, Double wall pipe. The method according to any one of claims 1 to 6, The inner pipe 1 is characterized in that it has a greater hardness value than the protective pipe 2, Double wall pipe. The method according to any one of claims 1 to 7, The material of the inner pipe 1 is characterized in that it has a coefficient of thermal expansion substantially the same as that of the protective pipe 2, Double wall pipe. The method according to any one of claims 1 to 8, The internal high pressure pipe 1 is characterized in that it is a St 52.4 material containing a steel tube, in particular C, Si, Mn, P, S and / or Al, Double wall pipe. The method according to any one of claims 1 to 9, The outer pipe 2 is characterized in that it is a steel tube, in particular a finished NBK worked St 35 material, Double wall pipe.

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