JP3416842B2 - Butt-welded heat exchange tube with internal projection - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat exchange tube useful as a pyrolysis reaction tube for ethylene production, which is formed by butt welding a metal tube having a spiral projection on the inner surface of the tube.

[0002]

2. Description of the Related Art In a pyrolysis furnace for producing ethylene, a mixed gas containing hydrocarbons (naphtha, natural gas, etc.) is fed at high speed to a reaction tube in the furnace, and high temperature and pressure are applied by heat supplied from the outside of the tube. Under the conditions of (about 800 to 1100 ° C, 5 kg / cm ² or less), olefins such as ethylene can be obtained as a thermal decomposition reaction product. In order to efficiently carry out this thermal decomposition reaction and obtain a high ethylene yield, the raw material fluid in the pipe is quickly brought to a predetermined temperature so that the secondary reaction of olefin (dehydrogenative decomposition reaction of ethylene, etc.) is suppressed. It is necessary to raise the temperature by heating and achieve the reaction in a short time. In order to prevent the precipitation of free carbon from the reaction system (free carbon adheres to and deposits on the inner surface of the pipe and causes carburizing deterioration of the pipe material, etc.), rapid heating and heating can prevent the formation of a predetermined amount of heat in a short time. It is necessary to complete the reaction. As a reaction tube having high heat transfer performance to meet this demand, a reaction tube provided with a spiral projection on the inner surface of the tube has been proposed (Japanese Patent Laid-Open No. 8-82494). This makes it possible to heat the temperature of the internal fluid to the required reaction temperature in a short time to the central region of the cross section of the tube by forming a turbulent flow by using the spiral projection on the internal surface of the tube as a stirring element for the internal fluid. .

[0003]

The formation of the pipe joint in the piping configuration of the pyrolysis furnace is performed by applying butt welding and performing TIG welding or the like from the outer peripheral surface side.
Since the reaction tube is used under conditions of high temperature and pressure, it is necessary to sufficiently melt the weld metal to the inner surface of the tube in the welding process. However, in the butt welding of pipes with spiral protrusions on the inner surface of the pipe, the wall thickness of the pipe differs between the portion where the spiral protrusion is present and the portion where it is not, and the portion with the protrusion is only the height of the protrusion. The wall is thick. For this reason, in the portion where the protrusion is present, insufficient penetration easily occurs, and it is difficult to guarantee sound joint quality.

Further, it is not easy to butt the two pipes to be welded together so that the spiral projections of the two pipes are exactly aligned with each other. As shown in FIG. 6, two welded pipes (1
0) If the positions of the spiral protrusions (12 ・ 1) and (12 ・ 2) of (10) disagree with each other, a stagnation / vortex of the fluid in the pipe is generated in that portion, which is due to the free carbon in that portion. It causes adhesion and deposition (coking) to be promoted. An object of the present invention is to eliminate the problems associated with butt welding of heat exchange tubes having such a spiral projection on the inner surface of the tube.

[0005]

DISCLOSURE OF THE INVENTION The present invention is a heat exchange tube in which two metal tubes having spiral projections on the inner surface of the tubes are butted and welded so that the spiral loci of the spiral projections substantially match. In the welding part, there is no spiral protrusion, and the end of the spiral protrusion facing the welding part is 4 to 3 in the pipe axis direction with the welding part interposed therebetween.
The front surface of the end part is 0 mm apart and the inclination angle α: 80
It is characterized in that it has a slope of α ≦ α <90 °. If desired, the heat exchange tube of the present invention may have a radius of curvature R: t to 2.5 t (t is a spiral shape) as the inclined surface of the end front surface of the spiral projection sandwiching the welded portion, instead of the above inclined surface. A curved slope, which is the height of the protrusion, mm) is given.

[0006]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below with reference to the drawings illustrating an embodiment. FIG. 1 shows the inner surface of the heat exchange pipe in the vicinity of the butt welded portion of the heat exchange tube, and FIG. (10) is a tubular body, (1
Reference numeral 2) is a spiral projection formed on the inner surface (11) of the tube. There is no spiral protrusion (12) on the pipe inner surface (11) in the region along the welded portion (15) of the pipe body (10) (10), and the wall thickness of that portion is constant over the entire circumference (mother). Is equal to the wall thickness of the timber). Therefore, in the welding process,
Insufficient melting such as in the case where the spiral protrusion (12) crosses the welded portion is avoided, and a sound pipe joint sufficiently melted to the inner surface of the pipe can be formed over the entire circumference.

The distance (pipe axis direction) D between the ends of the spiral protrusions (12.1) and (12.2) facing each other with the welded portion (15) interposed therebetween is
Must be at least 4 mm. That is, the ends of the spiral protrusions (12.1) and (12.2) are separated from the abutting surfaces by 2 mm or more in the tube axis direction. This is to avoid the above-mentioned insufficient melting and notch effect of the base part (12 ₁ ) on the front surface of the end of the spiral protrusion (12 ・ 1) (12 ・ 2) (concentration of thermal stress and crack generation due to welding work). This is to prevent the suppression. This distance D has an upper limit of 30 mm. This is because when the distance D is excessively increased, the effect (heat exchange property) of the spiral protrusion (12) is weakened.

Further, the spiral projections (12 ・ 1) (12 ・
2) The front surface of each end is an inclined surface as shown in Fig. 2.
(12A). The inclined surface (12A) is used to alleviate and alleviate the problems caused by the discontinuous spiral projections. That is, when the front surface of the end of the projection (12) is a vertical surface as shown in FIG. 4, the fluid flowing in the pipe (arrow A) is transferred to the front surface of the end of the spiral projection (12 ・ 2) on the downstream side. The stagnation (16) of the fluid is caused there by collision, and the stagnation (16) of the fluid is also generated at the end of the projection (12. 1) on the upstream side due to the step. In the ethylene production reaction tube, the deposition and deposition (coking) of free carbon from the reaction system is promoted in the portion where stagnation of the fluid occurs.

On the other hand, when the front surface of the end of the spiral protrusion (12.1) (12.2) is an inclined surface, the influence of the step is reduced and the fluid in the pipe flows along the inclined surface. This alleviates and eliminates the occurrence of stagnation. Also, the base (1
Since the angle formed with the inner surface of the pipe in 2 ₁ ) is an obtuse angle, the notch effect of the base portion (12 ₁ ) (concentration of thermal stress and crack generation during welding or during actual use of the actual machine) is also reduced. End of the spiral protrusion (12 ・ 1) (12 ・ 2) sloped surface (12A
The inclination angle α of) is 80 ° ≦ α <90 °. The inclination angle α is set to an angle smaller than 90 ° in order to obtain the effect of mitigating the blast against the fluid in the pipe, and 80 ° is set as the lower limit, and if it is smaller than that, the inclination angle α to the fluid in the pipe is decreased. This is because the stirring effect becomes poor.

FIG. 3 shows a spiral projection (12 ・ 1) (1
Another example of the inclined surface formed on the front surface of the end of 2.2) is shown. This inclined surface (12B) is a curved inclined surface. The inclination angle α gradually increases along the slope from the base (12 ₁ ) (inclination angle α = 0 ° at this position) in contact with the inner surface of the pipe,
It becomes maximum at the top (12 ₂ ) of the protrusion. The front surface of the end of the spiral protrusion (12) has such a curved inclined surface (12B).
In that case, the flow of the fluid in the pipe becomes smoother, and the stagnation reducing effect is enhanced. Also, the spiral protrusion on the downstream side
The flow along the slope of (12 ・ 2) has a large inclination angle with respect to the pipe axis direction at the projection top (12 ・ 2), and therefore, the fluid stirring effect can be obtained while effectively reducing and mitigating the stagnation. Moreover, the base (12 ₁ ) of the inclined surface (12B)
Has a tilt angle α = 0, so that the notch effect at the base portion is virtually absent.

The radius of curvature R of the curved slope (12B) is
R = t to 2.5t (t is the height of the protrusion 12). When R = t, the inclination angle (α _T ) at the top of the protrusion is α _T =
At 90 ° and R = 2.5t, α _T = 53 °. If the radius of curvature R is set to be t (protrusion height) or more, if it is smaller than that, the effect of alleviating and reducing the stagnation of the fluid in the pipe is insufficient, while the upper limit of 2.5t exceeds that. Then, the inclination angle α _{T of the} top of the protrusion becomes small, and the effect of stirring the fluid in the pipe becomes poor. Preferably R =
It is t-2t ((alpha) _T = 90-60 degree).

The shape of the spiral projections of the heat exchange tube of the present invention (the pitch of the spiral projections, the number of spiral threads, the projection width such as the projection height, etc.) depends on the application of the heat exchange tube and the usage of the actual machine. It is designed accordingly. When performing the butt welding of heat exchange tubes, as shown in FIG. 5, an appropriate groove (1
3) Machining (V-shaped, Y-shaped, U-shaped, etc.), and a predetermined distance D between the ends of the spiral protrusions (12 ・ 1) and (12 ・ 2) that sandwich the welded part. Is given, the ends of the spiral projections (12 ・ 1) (12 ・ 2) near the pipe ends are cut off and the pipe ends are butted. The two tubes are spiral protrusions (12 ・ 1) and (12 ・
It is not necessary to exactly match the spiral trajectories in 2), and there is no problem even if they differ by about 5 mm in the circumferential direction. As described above, there is a space D between the end of the spiral protrusion (12 ・ 1) and the end of (12 ・ 2).
And the front surface of each end is a constant inclined surface.

Butt welding includes TIG welding, MIG welding,
Covered arc welding or the like is applied, and the welding is performed while the tube is placed on a horizontal rotating roll and rotated about the tube axis. When a filler material (welding rod) is used, a filler material having the same composition as the base material pipe body or a composition modified according to the base material pipe material is used. In addition, in order to ensure the soundness of the weld, such as preventing cracks in the weld, appropriate preheating and post heat treatment depending on the pipe material type, wall thickness, etc. are also performed. It doesn't differ.

[0014]

EFFECTS OF THE INVENTION The heat exchange tube having the spiral projection of the present invention is difficult to perform welding due to the spiral projection on the inner surface of the tube,
No welding defects occur, and the welding quality is sound over the entire circumference of the butt weld. Further, the spiral projection on the inner surface of the pipe has a discontinuous form interrupted at the welded portion, but a defect due to this, for example, stagnation of the fluid in the pipe in the reaction tube for ethylene production (which is a factor that promotes coking ) Is also reduced and alleviated, and the pyrolysis operation in ethylene production can be efficiently performed.

[Brief description of drawings]

FIG. 1 is a view showing an inner surface of a pipe in the vicinity of a butt welded portion obtained by half-dividing a heat exchange pipe of the present invention in a pipe axis direction.

FIG. 2 is an explanatory cross-sectional view in the axial direction of the pipe showing a spiral projection end portion in the vicinity of a butt weld portion of the heat exchange pipe of the present invention.

FIG. 3 is a pipe axial direction cross-sectional explanatory view showing a spiral projection end portion in the vicinity of a butt weld portion of the heat exchange tube of the present invention.

FIG. 4 is a cross-sectional explanatory view of the butt welding of the heat exchange tube of the present invention.

FIG. 5 is an explanatory diagram of stagnation of a fluid in a heat exchange tube.

FIG. 6 is a view showing an inner surface of a pipe in the vicinity of butt welding, in which a heat exchange pipe is half-divided in the pipe axial direction.

[Explanation of symbols]

10: Tube (tube for heat exchange) 11: Inner surface of the tube 12, 12, 1, 12 ・ 2: Spiral projections 12A, 12B: End inclined surface of the spiral projection 12 ₁ : Base of front surface of end of spiral projection 12 ₂ : Top of spiral protrusion 13: Groove 15: Weld

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) F28F 1/40 B21D 53/06 B23K 9/028 F16L 13/02

Claims (3)

(57) [Claims] 1. A heat exchange pipe in which two metal pipes having spiral projections on the inner surface of the pipe are butted and welded so that the spiral loci of the spiral projections substantially coincide with each other. The end of the spiral protrusion facing the welded part without a protrusion is 4 to 30 mm apart in the pipe axis direction across the welded part, and the front face of the end has an inclination angle α: 80 ° ≦ α <90 °. A heat exchange pipe with butt-welded inner surface protrusions, which is characterized in that it has a slope. 2. A heat exchange pipe in which two metal pipes having spiral projections on the inner surface of the pipe are butted against each other so that the spiral loci of the spiral projections are substantially coincident with each other. The ends of the spiral protrusions, which have no protrusions and face the welded part, are 4 to 30 mm apart in the pipe axis direction across the welded part, and the front surface of the end part has a radius of curvature R: t to 2.5t (t Is a heat exchange tube with butt-welded inner surface protrusions, which has a curved slope with a height of a spiral protrusion (mm). 3. The heat exchange pipe with butt-welded inner surface protrusions according to claim 1, which is used as a reaction pipe for ethylene production.