KR101607213B1 - Method of Manufacturing the pipe for Excellent High HAZ Toughness - Google Patents

Abstract

The present invention relates to an improved groove forming step of forming an inner groove improving groove and an outer groove improving groove in a pipe and processing the inner groove improving groove and the outer groove improving groove to have a difference of 20 ° to 40 °, To a pipe manufacturing method capable of manufacturing a pipe having excellent HAZ toughness including a welding step of performing merge arc welding.

Submerged arc welding, HAZ, ICCGHAZ, HAZ impact test

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a pipe having excellent HAZ toughness,

The present invention relates to a pipe manufacturing method, and more particularly, to a method of manufacturing a pipe having excellent HAZ toughness by submerged arc welding.

Steel pipes for transporting crude oil and gas generally follow the API (American Petroleum Institute) regulations. In the API specification, the physical properties required in the pipe weld are generally tensile strength, bending test, impact toughness, etc. In the case of the tensile strength of the welded part, the welded part is generally designed to have a higher strength than the base material, There is no major problem in obtaining the required strength unless selected.
Submerged Arc Welding (SAW), which has a relatively high heat input, is applied to weld steel pipes. This weld method has a considerably low weld defect ratio compared to other welding methods. low.
In addition, the impact toughness of the weld is divided into a weld metal impact test and a HAZ (Heat Affected Zone) impact test depending on the notch position, and the weld metal impact test is performed when the commercialized weld material is selected according to the regulations, Acquisition is possible. However, in the case of the HAZ impact test, as shown in FIG. 1, since the HAZ toughness test is performed by taking the specimen from the central portion of the pipe, a portion corresponding to the notch of the HAZ impact specimen is formed by a weak MA (Martensite -Austenite) organization, so that there is a problem that HAZ toughness is evaluated poorly.

It is an object of the present invention to provide a method of manufacturing a pipe having excellent HAZ toughness by submerged arc welding.

In order to achieve the above-mentioned object, the present invention provides a method of forming an inner surface improvement groove and an outer surface improvement groove in a pipe and improving the inner surface improvement angle of the inner surface improvement groove and the outer surface improvement angle of the outer surface improvement groove by 20 ° to 40 ° Groove forming step; And a welding step of performing submerged arc welding on the inner surface improving groove and the outer surface improving groove, wherein an area where an inner surface bead formed on the inner surface improving groove and an outer surface bead formed on the outer surface improving groove intersect is formed on the inner surface of the pipe The improvement angle and depth of the outer surface improving groove and the inner improving groove are adjusted so as to deviate from the central portion in the thickness direction and the depth of the groove having the greater improvement angle is further deeper than the outer surface improving groove and the inner improving groove, do.
At this time, the depth of the outer surface improving groove may be twice or more the depth of the inner surface improving groove.

With this configuration, a pipe having excellent HAZ toughness can be manufactured in the HAZ impact test without any additional addition of components.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail.
It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.
Terms including ordinals, such as first, second, etc., may be used to describe various elements, but the elements are not limited to these terms.
The terms are used only for the purpose of distinguishing one component from another.
For example, without departing from the scope of the present invention, the second component may be referred to as a first component, and similarly, the first component may also be referred to as a second component.
It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, .
On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between.
The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise.
In the present application, the terms "comprises", "having", and the like are used to specify that a feature, a number, a step, an operation, an element, a component, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.
Also, the drawings in the present application should be understood as being enlarged or reduced for convenience of description.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the drawings, wherein like or corresponding elements are denoted by the same reference numerals, and redundant description thereof will be omitted.
2 is a cross-sectional view of a pipe weld according to an embodiment of the present invention.
2, a pipe welding method according to an embodiment of the present invention includes forming an inner surface improving groove 20 and an outer surface improving groove 10 in a welding portion of a pipe having a tensile strength of 700 MPa, (Hereinafter, the angle of the inner surface improving groove is defined as an inner surface improving angle and the angle of the outer surface improving grooves is defined as an outer surface improving angle)
The inner surface improvement angle 21 and the outer surface improvement angle 11 are variables that determine the area (welded area) where the welding wire melts during welding. Generally, a larger welding area requires a higher welding heat input.
If the angle of improvement exceeds 90 °, the welded area may excessively increase, requiring a higher welding heat input, and may cause a decrease in the mechanical properties of the welded portion after completion of welding.
On the other hand, when the angle of improvement is less than 50 °, the welded area can be reduced due to a narrow welding area, but the welded wire can not be deeply penetrated into the improved groove during welding. The possibility increases.
Therefore, the inner surface improvement angle 21 and the outer surface improvement angle 11 can be formed between 50 ° and 90 °, respectively.
At this time, the inner surface improvement angle 21 and the outer surface improvement angle 11 may be different from each other. More specifically, the outer surface improvement angle 11 and the inner surface improvement angle 21 may be different from each other by 20 ° to 40 °. Can be configured.
Further, the depth 12 of the outer surface improving groove may be different from the depth 12 of the inner surface improving groove. In more detail, the depth 12 of the outer surface improving groove may be two or more times deeper than the depth 22 of the inner surface improving groove.
The improvement angle and depth may be independently performed. For example, the outer surface improvement angle 11 and the inner surface improvement angle 21 are formed differently, but the depths may be formed to be the same, and the angles may be the same and the depths may be different. Such variations are freely changeable according to embodiments.
FIG. 3 is a conceptual view of submerged arc welding on pipes having different inner surface improvement angles and outer surface improvement angles, according to an embodiment of the present invention. FIG. And the arc welding is performed.
In the present invention, the welding heat quantity during submerged arc welding can be performed with a low heat input amount of 30 to 50 kJ / cm. It is general that the amount of heat input into the weld during submerged arc welding has a great influence on the heat affected zone (hereinafter referred to as 'HAZ').
That is, as the heat input amount increases, the phase transformation of the welded portion becomes worse, and the crystal growth coordination of the HAZ is accelerated at the welding, so that the amount of the heat of welding can be minimized in the present invention.
However, if the heat input is less than 30 kJ / cm, the mechanical properties of the welded part are good due to the low heat input. However, there is a high possibility of welding failure due to low heat input during welding, Since the HAZ due to heat input is softened to make the particles coarse, the object of the present invention can not be achieved and the tensile strength at the level of the raw base material can not be obtained. Therefore, in the present invention, the welding heat amount is maintained at a level of 30 to 50 kJ / .
At this time, when the thickness of the pipe exceeds 30 mm, it is impossible to weld with the heat input amount of 30 to 50 kJ / cm, and the HAZ toughness is drastically lowered due to high heat input at the time of external welding.
Since the submerged arc welding in the present invention is the same as that of the ordinary submerged arc welding, detailed description thereof will be omitted.
3, a metal (hereinafter, referred to as "outer bead") welded to the outer surface improving groove 10 is welded to a metal (hereinafter referred to as "inner surface bead") welded to the inner surface improving groove 20 And the ICCGHAZ (Inter Critical Coarse Grain HAZ) is generated at the intersection of the outer bead 14 and the inner bead 24.
At this time, the HAZ impact test piece (P) is taken for the HAZ impact test. Generally, the HAZ impact test piece (P) is collected near the center of the welded pipe.
The notch P1 is located at the center of the HAZ impact test piece P. Since the outer surface improvement angle 11 of the pipe manufactured according to the embodiment of the present invention is larger than the inner surface improvement angle 21, Is formed at a position different from the position of the notch P1.
Therefore, when the specimen is sampled and subjected to the impact test, it has an excellent HAZ toughness value because it does not include the ICCGHAZ portion composed of a weak MA (Martensite-Austenite) structure.
Such a configuration may have the same effect even if the inner surface improvement angle 21 is larger than the outer surface improvement angle 11. [
4, if the depth of the inner surface improving groove 20 is set to be deeper than the depth of the outer surface improving groove 10, the ICCGHAZ portion is not included in the HAZ impact test piece, so that the HAZ toughness value is further improved.
Similarly, even if the depth of the outer surface improving groove 10 is formed deeper than the depth of the inner surface improving groove 20, the same effect can be obtained.
Table 1 below is a table summarizing the values obtained by measuring the HAZ toughness in the welded state and the values obtained by measuring the HAZ toughness according to the comparative example, with a difference in the depth of improvement and the depth of the groove according to the embodiment of the present invention.
division Conduct No. Pipe Thickness (mm) Heat input
(Outer / inner) Outer improvement angle Internal Improvement Angle Outer surface improvement groove length Inner improvement groove (20) Length HAZ toughness
vE-20 < 0 > C (J)

Example


One 19.8 35/31 80 60 7 7 102 2 19.8 37/25 80 70 10 4 97 3 25 38/33 80 40 10 10 107 4 25 45/30 80 70 14 6 112 5 25 42/25 80 70 16 4 120 6 28 44/42 60 40 11 11 132
Comparative Example

One 19.8 37/35 80 70 7 7 73 2 19.8 36/32 80 62 8 7 61 3 25 38/34 80 66 10 10 60 4 28 49/42 60 60 15 9 57
In Table 6, it can be seen that the HAZ toughness of each of Examples has a higher value than that of Comparative Example. Particularly in the case of Example 6, when the inner improvement angle and the outer improvement angle are made to differ by 20 degrees, The HAZ toughness was measured to be higher than that of Comparative Example 4 in which the improvement angle was not more than 2 times.
In addition, when the depth of the outer surface improving groove is formed twice as deep as the inner surface improving groove depth as in Example 4, the HAZ toughness value is improved by about 65% as compared with Comparative Example 1 having the same depth.
The foregoing description of the preferred embodiments of the present invention has been presented for purposes of illustration and various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention, And additions should be considered as falling within the scope of the following claims.

1 is a side view of a conventional submerged arc welded dip,
FIG. 2 is a cross-sectional view of a pipe weld according to an embodiment of the present invention, FIG.
FIG. 3 is a conceptual view of submerged arc welding to pipes having different inner surface improvement angles and outer surface improvement angles, according to an embodiment of the present invention;
FIG. 4 is a conceptual view of submerged arc welding to pipes having different depths of the inner surface improving grooves and depths of the outer surface improving grooves. FIG.
DESCRIPTION OF THE RELATED ART [0002]
Outside improvement groove: 10 Outside improvement angle: 11
Outer surface improvement groove depth: 12 Inner improvement groove: 20
Inner improvement angle: 21 Inner improvement groove depth: 22

Claims (6)

Forming an inner surface improvement groove and an outer surface improvement groove in the pipe and processing the inner surface improvement angle of the inner surface improving groove and the outer surface improving groove such that the outer surface improving angle has a difference of 20 ° to 40 °; And And a welding step of submerged arc welding the inner surface improving groove and the outer surface improving groove, The improvement groove forming step may be performed such that an area where an inner surface bead formed on the inner surface improving groove and an outer surface bead formed on the outer surface improving groove deviate from a center portion in the thickness direction of the pipe, And depth, Wherein a depth of a groove having a larger angle of improvement among the outer surface improving groove and the inner improving groove is made deeper. The method according to claim 1, Wherein the improvement groove forming step is formed such that the outer surface improving angle is larger than the inner surface improving angle. The method according to claim 1, Wherein the inner surface improvement angle is larger than the outer surface improvement angle. The method according to claim 1, Wherein a depth of a groove having a larger angle of improvement among the outer surface improving groove and the inner improving groove is greater than twice the depth of the remaining groove. The method according to claim 1, In the welding step, Wherein the heat input amount of the submerged arc welding is 30 kJ / cm to 50 kJ / cm. The method according to claim 1, Wherein the pipe has a thickness of 30 mm or less.

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