KR20110077220A - Method of manufacturing the pipe for excellent high haz toughness - Google Patents

Abstract

PURPOSE: A method of manufacturing a pipe is provided to improve HAZ toughness without additional element. CONSTITUTION: A method of manufacturing a pipe having superior HAZ toughness comprises next steps. An inner enhancement groove and outer enhancement groove are formed on a pipe. The inner and outer bevel angles(11,21) of the inner enhancement groove and outer enhancement groove are processed to have the angle difference of 20°~ 40°. The outer bevel angle is processed to be bigger than the inner bevel angle in an enhancement groove forming step. The inner enhancement groove and outer enhancement groove are submerged-arc welded.

Description

Method of Manufacturing the pipe for Excellent High HAZ Toughness}

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

In general, steel pipes for oil and gas transportation follow API (American Petroleum Institute) regulations. In the API standard, physical properties required for pipe welds generally include tensile strength, flexural test, and impact toughness.In the case of double welded tensile strength, welds are generally designed to increase the strength of the base metal, so excessive heat input during welding is required. Unless chosen, there is no big problem in achieving the required strength.

Submerged Arc Welding (SAW), which has a relatively high heat input, is used for welding steel pipes, and this welding method has considerably lower defect ratios than other welding methods. low.

Also, the impact toughness of the welded part is divided into the welded metal part impact test and the HAZ (Heat Affected Zone) impact test according to the notch position. The welded metal part impact test has excellent impact toughness when the commercialized welding material is selected according to the regulations. Can be obtained. However, in the case of the HAZ impact test, as shown in FIG. 1, the specimen is taken from the center portion of the pipe and subjected to the HAZ toughness test. Therefore, a portion corresponding to the notch of the HAZ impact specimen is produced in an ICCGHAZ (Inter Critical Coarse grain HAZ). -Austenite) There is a problem that the HAZ toughness is poorly evaluated to correspond to the tissue.

An object of the present invention is to provide a method for producing a pipe having excellent HAZ toughness by submerged arc welding, which is devised to solve the above problems.

In order to achieve the above object, the present invention provides an improved groove forming step of forming an inner surface improvement groove and an outer surface improvement groove in a pipe and processing the angle of the inner surface improvement groove and the outer surface improvement groove to have a difference of 20 ° to 40 °. And a welding step of submerged arc welding the inner improvement angle and the outer improvement angle.

At this time, the depth of the outer surface improvement groove may be constructed to be more than twice the depth of the inner surface improvement groove.

By the above configuration, it is possible to produce a pipe having excellent HAZ toughness in the HAZ impact test without additional addition of components.

As the invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description.

 However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

Terms including ordinal numbers such as first and second may be used to describe various components, but the components are not limited by the 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 the first component, and similarly, the first component may also be referred to as the second component.

When a component is referred to as being "connected" or "connected" to another component, it may be directly connected or connected to that other component, but it may be understood that other components may be present in between. Should be.

On the other hand, when a component is said to be "directly connected" or "directly connected" to another component, it should be understood that there is no other component in between.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

In this application, the terms "comprises" or "having" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, one or more other It is to be understood that the present invention does not exclude the possibility of the presence or the addition of features, numbers, steps, operations, components, parts, or a combination thereof.

In addition, it is to be understood that the accompanying drawings in this application are shown 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. Like reference numerals designate like elements throughout, and duplicate descriptions thereof will be omitted.

2 is a cross-sectional view of a pipe welded part according to an exemplary embodiment of the present invention.

In the pipe welding method according to the embodiment of the present invention, as shown in FIG. 2, an inner surface improvement groove 20 and an outer surface improvement groove 10 are formed in a weld joint of a pipe having a tensile strength of 700 MPa. ) And the outer surface improvement groove 10 will each have a predetermined angle. (Hereinafter, the angle of the inner surface improvement groove is defined as the 'interior improvement angle', the angle of the outer surface improvement angle groove is defined as the 'outterior improvement angle')

The inner surface improvement angle 21 and the outer surface improvement angle 11 are variables that determine the area (welding area) in which the welding wire melts during welding. Generally, the larger the welding area, the higher the welding heat input amount.

If the improvement angle exceeds 90 °, the weld area may be excessively increased, which may cause a problem that a higher welding heat input amount is required and may cause mechanical properties deterioration after welding is completed.

On the other hand, when the improvement angle is less than 50 °, the welding area is narrow, which can reduce the heat input of the welding. However, when welding, the welding wire does not go deep into the improvement groove. The chances are high.

Therefore, the inner improvement angle 21 and the outer improvement angle 11 may be formed between 50 ° and 90 °, respectively.

In this case, the inner improvement angle 21 and the outer improvement angle 11 may be configured to be different, and more specifically, the outer improvement angle 11 and the inner improvement angle 21 are 20 ° to 40 ° different from each other. Can be configured.

In addition, the depth 12 of the outer improvement groove may be configured to be different from the depth 12 of the inner improvement groove. Looking at this in more detail, the depth 12 of the outer surface improvement groove may be formed more than twice as deep as the depth 22 of the inner surface improvement groove.

The angle of improvement and the depth can be implemented independently. For example, the outer surface improvement angle 11 and the inner surface improvement angle 21 may be formed differently, but the depths may be formed the same, and the angles may be the same and only the depth may be formed differently. Such modifications can be freely changed in accordance with embodiments.

3 is a conceptual view in which the submerged arc welding is performed on a pipe having different inner and outer angle improvements according to an embodiment of the present invention, and FIG. 4 is a submerged pipe having different depths of the inner and outer grooves. This is a conceptual diagram of de arc welding.

In the present invention, the welding heat input during the submerged arc welding is possible to perform welding with a low heat input of 30 ~ 50kJ / cm. In the case of submerged arc welding, the welding heat input into the weld zone generally affects the heat affected zone (HAZ).

That is, as the heat input amount increases, the phase transformation of the weld portion increases, and the grain coarsening of the HAZ is accelerated during welding. In the present invention, the heat input amount of the weld can be lowered as much as possible.

Although the welding heat input is advantageously low, the mechanical properties of the weld are good due to low heat input at less than 30 kJ / cm, but it is more likely to cause welding defects due to low heat input during welding. On the other hand, excessive heat input at 50 kJ / cm The HAZ is softened by the heat input and the particles are coarse to achieve the object of the present invention, and since the tensile strength at the level of the base material cannot be obtained, in the present invention, the welding heat input is maintained at a level of 30 to 50 kJ / cm to be welded. Can be.

In this case, when the thickness of the pipe exceeds 30mm, welding is impossible with the heat input amount of 30 to 50 kJ / cm, and HAZ toughness is sharply lowered due to high heat input during external welding.

Since the submerged arc welding in the present invention is the same as the general submerged arc welding, detailed description thereof will be omitted.

Referring to FIG. 3, the metal welded to the outer surface improvement groove 10 (hereinafter, referred to as 'outer bead') is welded to the inner surface improvement groove 20 (hereinafter, referred to as 'inside bead'). It can be seen that ICCGHAZ (Inter Critical Coarse grain HAZ) occurs at the intersection of the outer beads 14 and the inner beads 24 compared to the deeper welds.

At this time, the HAZ impact test piece (P) is taken for the HAZ impact test. In general, the HAZ impact test piece (P) is collected near the center of the pipe at the welding site.

The notch P1 is positioned at the center portion of the HAZ impact test piece P. The pipe manufactured according to the embodiment of the present invention has an outer improvement angle 11 formed larger than an inner improvement angle 21, so that the ICCGHAZ portion It is formed at a point different from the position of this notch P1.

Therefore, when the specimen is subjected to an impact test, the ICCGHAZ part composed of a weak MA (Martensite-Austenite) tissue is not included, and thus has excellent HAZ toughness.

Such a configuration can bring about the same effect even when the inner improvement angle 21 is configured to be larger than the outer improvement angle 11.

In addition, if the depth of the inner surface improved groove 20 is formed deeper than the depth of the outer surface improved groove 10 as shown in FIG. 4, since the ICCGHAZ part is not included in the HAZ impact test piece, the HAZ toughness value is more excellent.

Similarly, even if the depth of the outer surface improvement groove 10 is formed deeper than the depth of the inner surface improvement groove 20 has the same effect.

Table 1 below is a table summarizing the measured values of the HAZ toughness in the welded state with a difference in the angle of improvement and the depth of the groove according to the embodiment of the present invention and the values of the measured HAZ toughness by the comparative example.

division Conduct number Pipe thickness (mm) Heat input
(Outside / inside) Exterior improvement angle Internal improvement angle Exterior improvement groove length Internal improvement groove (20) length HAZ Toughness
vE-20 ° 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

When referring to Table 1, it can be seen that all of the examples have a higher value of the HAZ toughness than the comparative example. It can be seen that the HAZ toughness was measured at least two times higher than that of Comparative Example 4 having no difference in improvement angle.

In addition, when the depth of the outer surface improved grooves as in Example 4 is formed more than twice the depth of the inner groove improved depth HAZ toughness value can be seen that the depth is improved by about 65% compared to the same Comparative Example 1.

Preferred embodiments of the present invention described above are disclosed for purposes of illustration, and those skilled in the art having various ordinary knowledge of the present invention may make various modifications, changes, and additions within the spirit and scope of the present invention. And additions should be considered to be within the scope of the following claims.

1 is a side view of a conventional submerged arc welded dip;

2 is a cross-sectional view of a pipe welding part according to an embodiment of the present invention;

3 is a conceptual view in which submerged arc welding is performed on pipes having different inner and outer angle improvements according to an embodiment of the present invention;

4 is a conceptual view of a submerged arc welding to a pipe having a different depth of the inner surface improvement groove and a depth of the outer surface improvement groove.

DESCRIPTION OF THE RELATED ART [0002]

Exterior improvementHome: 10 Exterior improvement angle: 11

Exterior improvement groove depth: 12 Interior improvement groove: 20

Internal improvement angle: 21 Internal improvement groove depth: 22

Claims (6)

An improvement groove forming step of forming an inner improvement groove and an outer improvement groove in the pipe and processing the inner improvement angle of the inner improvement groove and the outer improvement angle of the outer improvement groove to have a difference of 20 ° to 40 °; And And a welding step of performing submerged arc welding on the inner surface improvement groove and the outer surface improvement groove. The method of claim 1, The improvement groove forming step is a pipe manufacturing method for forming an outer surface improvement angle larger than the inner surface improvement angle. The method of claim 1, The improvement groove forming step is a pipe manufacturing method different from the depth of the outer surface improvement groove depth and the inner surface improvement groove. The method of claim 3, The depth of the outer surface improvement groove pipe manufacturing method of more than twice the depth of the inner surface improvement groove. The method of claim 1, The pipe has a tensile strength of 700MPa or more pipe manufacturing method. The method of claim 1, The pipe has a thickness of less than 30mm pipe manufacturing method.

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