JP2892450B2 - Circumferential welding method for ERW line pipe for reel barge installation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for circumferential welding of an ERW steel pipe line pipe excellent in laying a reel barge.

<Conventional technology> Conventionally, as a method of laying a submarine line pipe, as shown in FIG.
Girth welding or MAG (Metal Active Gas) welding is performed, and the connected pipe 2 is sent out to the sea floor 4
The most common method is to lay it. However, this method requires welding, inspection of a welded portion, coating, and the like on the barge 1, resulting in poor working efficiency due to a small working space, or poor working efficiency due to a large influence of weather. There was such a problem.

Therefore, as shown in FIG. 7 (a), circumferential welding, inspection, coating, and the like are performed on the land 5, and the completed long pipe 2 is wound up on the reel 3 of the barge 1 on the sea. As shown in FIG. 7 (b), a so-called reel barge method, in which a pipe 2 is rewound from a reel 3 and laid on a seabed 4 while being rewound, is being frequently used.

In this reel barge method, although it is possible to work very efficiently, when winding on the reel 3 or rewinding from the reel 3 for laying on the seabed, tensile and compressive stress is applied to a part of the pipe 2. As a result, as shown in FIG. 8, there is a problem that a crack 6 is likely to occur in a toe portion of a circumferential weld 7 of the base material 9 of the pipe 2.

On the other hand, seamless pipes have been widely used in terms of quality and strength of line pipes, but in recent years quality and strength have been improved, and attempts to use ERW steel pipes have been made in order to reduce costs. Was.

However, the ERW steel pipe is more difficult to prevent the toe portion from cracking at the circumferential weld than the seamless pipe.

The reason is that when manufacturing steel sheets for ERW steel pipes, the control drawing (hereinafter referred to as CR) method is adopted to obtain high strength and high toughness.
It is considered that the material is heated to _three or more points of Ac and the CR effect disappears, so that the heat affected zone is softened more than the base metal, and the toe portion cracks easily occur.

<Problems to be Solved by the Invention> Conventionally, as a method for improving the toughness of a welded portion, there is JP-B-60-31888 or JP-A-53-12751. The former specifies the carbon equivalent of the base metal component and performs heat treatment after welding, and the latter performs ultrasonic vibration to the material to be welded during welding. Although these are effective in improving the toughness of the weld, the former requires an additional heat treatment step. The latter requires a device for applying an ultrasonic wave and an appropriate adjustment of the frequency, and if the frequency is not appropriate, the application of the ultrasonic wave does not result in a higher toughness.

The present invention has been made in view of the above circumstances, and has been made in order to provide a circumferential welding method in which a welded portion is not cracked when a reel barge is laid.

<Means for Solving the Problems> The present invention, when circumferential welding the line pipe, at least 5kg / mm from the welding material used the last layer up to the previous layer
^This is a method of circumferentially welding a line pipe of ERW steel pipe for reel barge laying, characterized by welding using a welding material with a strength of at least ² or less. An electric resistance welded steel pipe line for laying a reel barge as described in the preceding paragraph, wherein welding is performed by restricting the radius of curvature of the extra toe portion, 120 ° ≦ the extra toe angle, and 0.8 mm ≦ the extra height ≦ 1.8 mm. It is a method of circumferential welding of pipes, and the chemical composition of the ERW steel pipe is as follows: C: 0.03 to 0.20 wt%, Mn: 0.50 to 1.5 wt%, Si: 0.05 to 0.50 wt%, Al: 0.005 to 0.060 wt% Within the range, Nb, V, Ti satisfies Nb + V + Ti ≦ 0.040% by weight, the balance substantially consists of iron and unavoidable impurities, and the carbon equivalent Ceq given below is 0.20 to 0.3.
Circumferential welding method of ERW steel pipe line pipe for reel barge laying of 6 or less and welding crack susceptibility Pcm of 0.25 or less, Ceq = C + Mn / 6 + V / 5 Pcm = C + Si / 30 + Mn / 20 + V / 10 The chemical composition of the electric resistance welded tube is as follows: C: 0.03 to 0.20% by weight, Mn: 0.50 to 1.5% by weight, Si: 0.05 to 0.50% by weight, Al: 0.005 to 0.060% by weight, Nb, V, Ti satisfies Nb + V + Ti ≦ 0.040% by weight, further contains one or two of Mo: 0.30% by weight or less, B: 0.002% by weight or less, and the balance substantially consists of iron and inevitable impurities; And the carbon equivalent given below
Ceq is 0.20 or more and 0.36 or less, and weld crack susceptibility Pcm is 0.
Ceq = C + Mn / 6 + Mo / 5 + V / 5 Pcm = C + Si / 30 + Mn / 20 + Mo / 15 + V / 10 + 5B When the chemical composition of the tube is within the following range: C: 0.03 to 0.20% by weight, Mn: 0.50 to 1.5% by weight, Si: 0.05 to 0.50% by weight, Al: 0.005 to 0.060% by weight, Nb, V, Ti is Nb + V + Ti ≤0.040% by weight, and one or more selected from Ni: 0.50% by weight or less, Cu: 0.50% by weight or less, Ca: 0.005% by weight or less, and Cr: 0.3% by weight or less And the remainder is substantially composed of iron and inevitable impurities, and the carbon equivalent Ceq given below is 0.20 or more and 0.36 or less, and the welding crack susceptibility Pcm is 0.25 or less. Ceq = C + Mn / 6 + Cu / 15 + Ni / 15 + Cr / 5 + V / 5 Pcm = C + Si / 30 + Mn / 20 + Cu / 20 Ni / 60 + Cr / 20 + V / 10, and the chemical composition of the ERW pipe is as follows: C: 0.03 to 0.20 wt%, Mn: 0.50 to 1.5 wt%, Si: 0.05 to 0.50 wt%, Al: 0.005 to 0.060 wt% Within the range, Nb, V, Ti satisfies Nb + V + Ti ≦ 0.040% by weight. Ni: 0.50% by weight or less, Cu: 0.50% by weight or less, Ca: 0.005% by weight or less, Cr: 0.3% by weight or less Contains one or more selected from among them, further contains one or two of Mo: 0.30% by weight or less, B: 0.002% by weight or less, and the balance is substantially iron and unavoidable impurities And the carbon equivalent given below
Ceq is 0.20 or more and 0.36 or less, and weld crack susceptibility Pcm is 0.
Ceq = C + Mn / 6 + Cu / 15 + Ni / 15 + Cr / 5 + Mo / 5 + V / 5 Pcm = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15
+ V / 10 + 5B.

<Operation> The operation of the present invention will be described below.

The present inventors took out the test piece 10 from the circumferential weld portion of the ERW line pipe according to the API standard 1104 as shown in FIG. As a result of conducting a repetition test by a repeated bending test (strain amount 5%) and using the same, it was confirmed that a crack 6 as shown in the typical example shown in FIG. 8 was generated from the circumferential weld toe. Was. It became clear that the cracks tended to occur when the difference in hardness between the weld metal of the final layer and the base material was large.

Accordingly, as can be seen from the schematic diagram of the hardness distribution shown in FIG. 10, this type of crack is caused by a difference in hardness between the weld metal and the base material. This is considered to be caused by non-uniform plastic deformation in the material part. That is, it is considered that the plastic deformation of the base material portion is restricted by the weld metal having higher hardness than the base material portion. Further, as shown in FIG. 10, the reason that the hardness of the weld metal in the final layer is higher than that in the base material portion is that the final layer is not softened by welding heat in the next pass.

From the above examination results, in order to make the hardness of the weld metal of the final layer closer to the base metal part, a girth welding was performed using a welding material with a lower strength than the welding material used for the final layer up to the previous layer, and repeated bending tests Was carried out. FIG. 1 shows the test results. It can be seen that the use of a welding material having a strength lower by at least 5 kg / mm ² or more than that of the welding material using the sampled layer up to the previous layer significantly reduces the crack generation rate. .

The welding method in this case is usually performed by hand welding, but MIG
Welding or MAG welding may be used. Here, the welding material refers to a welding rod, and it is more preferable to use a cellulosic welding rod.

In addition, the strength of the welding material in the final layer is
From the viewpoint of joint strength, it is desirable to reduce the weight by 15 kg / mm ² or less.

 Next, the reasons for restricting the extra weld shape of the girth weld to 2mm ≤ extra toe radius of curvature, 120 ° ≤ extra toe angle, 0.8mm ≤ extra height ≤ 1.8mm are described.

As shown in FIG. 11, the crack 6 in the weld toe portion is generated as the extra height increases, the extra height H, the extra radius of the toe curvature radius r, and the extra extra toe angle α increase. In the case where the height of the overfilling is equal, the tendency of occurrence is large as the radius of curvature of the overfilling toe or the angle of the overfilling toe is small. If these three values are set in appropriate ranges, cracking is effective. It became clear that it could be prevented.

Therefore, this kind of crack is caused by the shape discontinuity in the joint part, and when tensile stress and compressive stress are applied during winding and unwinding, if stress concentration occurs at the toe part, that is, toe part, Conceivable. That is, it is considered that a sudden change in the geometrical shape at the welded portion complicates the flow of stress at the welded portion, causes a large stress concentration at the toe portion, and causes cracking.

From this examination result, in order to find out the requirements that need to be achieved in order to effectively achieve the object of the present invention, circumferential welding is performed with variously changed overfill shapes, and repeated bending tests are performed under the same conditions as the above conditions. The following requirements were newly found as a result of conducting a survey and investigating the occurrence of cracks in the toe.

The radius of curvature γ of the extra toe must be greater than 2 mm.

FIG. 2 shows the relationship between the radius of curvature γ of the extra toe and the crack occurrence rate at the toe. Fig. 2 shows the rate of occurrence of cracks in the toe portion with respect to the change in the radius of curvature γ of the extra toe under the conditions of the extra height H: 0.8 to 1.8 mm and the extra toe angle α: 120 to 150 °. It is the result of having investigated.

From FIG. 2, it is qualitatively recognized that the radius of curvature of the extra toe portion has a large effect on the incidence of cracking in the toe portion.
In addition, when quantitatively viewed in FIG. 2, it can be confirmed that the effect starts to appear when the radius of curvature of the extra toe is 1 mm or more, and the effect is satisfactory when the radius of curvature is 2 mm or more. With 10 mm or more, although the effect is slightly improved, it is necessary to increase the radius of curvature of the extra toe beyond the necessity, such as increasing the groove angle, so that the welding itself becomes unstable. Welding defects are likely to occur, and cracks at the weld are rather created. Therefore, in practice, the radius of curvature of the extra toe is 2 to 2.
10 mm is desirable.

The extra toe angle α is greater than 120 °.

FIG. 3 shows the relationship between the extra toe angle and the incidence of cracks in the toe. Fig. 3 shows the rate of occurrence of cracks in the toe with respect to the change in the angle of the toe toe under the condition that the height of the extra toe is H: 0.8 to 1.8 mm and the radius of curvature of the toe toe at the extra toe r: 2 to 10 mm. It is a result.

From FIG. 3, it is qualitatively recognized that the extra toe angle greatly affects the incidence of cracks in the toe. In addition, when quantitatively looking at FIG. 3, the extra toe angle is 100
It can be confirmed that the effect starts to be exhibited at an angle of 120 ° or more, and a satisfactory effect is achieved at an angle of 120 ° or more. If the angle is 150 ° or more, although a slight improvement in the effect is recognized, it is necessary to increase the groove angle similarly to the case of increasing the excess toe angle more than necessary. Becomes unstable and a welding defect is apt to occur, and rather, a crack is generated in a welded portion. Therefore, in practical use, it is desirable that the extra toe angle be 120 to 150 °.

0.8mm ≤ extra height ≤ 1.8mm.

FIG. 4 shows the relationship between the extra height and the incidence of cracks in the toe. Fig. 4 shows the results of examining the rate of occurrence of cracks in the toe portion with respect to the change in the height of the extra embankment under the conditions of the radius of curvature of the extra embankment toe: 2 to 10 mm and the angle of the extra embankment toe: 120 to 150 °. It is.

From FIG. 4, it can be qualitatively recognized that the extra height greatly affects the incidence of cracks in the toe portion. Also, the fourth
When the figure is quantitatively observed, it can be confirmed that the effect starts to appear when the extra height is 2.6 mm or less and reaches a satisfactory effect when the height is 1.8 mm or less. If the thickness is less than 0.8 mm, although a slight improvement in the effect is recognized, there is an adverse effect on the joint strength, and the weld is likely to break. For this reason, it is desirable that the extra height be 0.8 to 1.8 mm.

The application of the strength of the weld metal and the extra shape of the welded portion has been described for the line pipe made of ERW steel pipe, but the invention is also applicable to a seamless or other line pipe.

The inventors have further found that softening of the weld heat-affected zone has an adverse effect on the occurrence of cracks in the circumferential weld toe, and the degree of softening does not cause any problem even when receiving heat during welding. By using the high-toughness ERW steel pipe shown in (1) above and using it together with the above-mentioned strength of the weld metal and the extra shape of the welded part, a welding method without cracks in the circumferential welded part was found.

(A) As a component of the ERW steel linepipe base metal, C: 0.03 to 0.20% by weight, Mn: 0.50 to 1.5% by weight, Si: 0.05 to 0.50% by weight, Al: 0.005 to 0.060% by weight And Nb + V + Ti ≦ 0.040% by weight with respect to Nb, V and Ti, the balance being steel substantially consisting of iron and unavoidable impurities, and carbon equivalent Ceq and weld cracking susceptibility Pcm
However, it is desirable to provide a high toughness ERW steel pipe line pipe excellent in laying a reel barge, characterized by satisfying 0.20 ≦ Ceq ≦ 0.36 Pcm ≦ 0.25.

In addition to the above steel components, (b) one or two selected from the group consisting of: Ni: 0.50% by weight or less, Cu: 0.50% by weight or less, Ca: 0.005% by weight or less, Cr: 0.3% by weight or less It is desirable to use a high toughness electric resistance welded steel pipe linepipe excellent in laying bar reels containing one or two of the following types and / or (c) Mo: 0.30% by weight or less, B: 0.002% by weight or less.

However, Ceq and Pcm are given by the following formulas. For alloying elements that are not contained, the element term is calculated as 0.

Ceq = C + Mn / 6 + Cu / 15 + Ni / 15 + Cr / 5 + Mo / 5 + V / 5 Pcm = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15
+ V / 10 + 5B The present inventors took out the test piece 10 from the circumferential weld of the ERW line pipe according to API standard 1104, and
Using a bending tester 11 as shown in the figure, a repeated bending test (strain amount 5%) was carried out and examined. As a result, it was confirmed that the cracks 6 were generated from the toe portion of the circumferential welded portion 7, and the cracks tended to be generated when the degree of softening of the heat affected zone was large. It has become clear that a smaller size can be effectively prevented.

Cracking of this kind is due to difference in hardness between the first 10 as can be seen from the schematic diagram of the distribution of hardness H _v shown in the graph of Figure, the weld heat affected zone 8 by welds 7 base material 9, Take-up,
This is considered to be caused by unevenness in plastic deformation between the heat affected zone 8 and the base material 9 during unwinding. That is, it is considered that the generation of cracks is caused by the deformation concentrated in the weld heat affected zone 8 having the softening zone, and the work hardening and embrittlement locally.

From the above examination results, in order to reduce the degree of softening of the weld heat affected zone, the degree of softening (ΔH _v ) was investigated for various component systems. I found that it can be kept small.

It is, as shown in FIG. 5, the total amount of Nb, V and Ti.
It is to regulate the value of Ceq (carbon equivalent). FIG. 5 shows the relationship between the degree of softening (ΔH _v ) and Ceq when the amount of Nb + V + Ti is 0.040% by weight or less and more than 0.040% by weight. If Ceq is qualitatively increased, It can be seen that ΔH _v can be reduced. Quantitatively, Ceq
[Delta] H _v If more than 0.20 wt% can be the suppressed to 8 below. When ΔH _v is 8 or less, there is almost no crack from the circumferential weld toe according to the repeated bending test shown in FIG.

The reason that the limitation of the total amount of Nb, V and Ti is effective in suppressing softening is that these are elements that increase the strength of the base material, that is, increase the effect of CR by a simple substance or a combination thereof, and these elements This is considered to be because the effect of CR can be reduced by limiting. Furthermore, it is considered that the increase in Ceq is effective in suppressing softening because the effect of CR is basically reduced, and the degree of softening due to heat during circumferential welding is reduced, uniform deformation is performed, and bending ductility is reduced. It is thought to contribute to improvement.

The reason why Nb + V + Ti is restricted to 0.0040% by weight or less is that Nb + V + Ti needs to be 0.040% by weight or less in order to suppress the softening of the heat affected zone to a practically acceptable level. Therefore, it is preferable that the content be in the range of 0.040% by weight or less. When the range of Ceq is less than 0.20% by weight, the effect is not obtained. When it exceeds 0.36% by weight, the effect of increasing Ceq is not only saturated, but also the toughness is significantly deteriorated. Therefore, the content is preferably in the range of 0.20% by weight or more and 0.36% by weight or less.

Other reasons for limiting each component in steel suitable for use in the present invention will be described.

In order to obtain the required strength, C must be contained in an amount of 0.03% by weight or more. However, if it exceeds 0.20% by weight, susceptibility to weld cracking increases, so it is preferable that C be in the range of 0.03 to 0.20% by weight.

Si must be added as a deoxidizing agent and in an amount of 0.05% by weight or more for the purpose of securing strength. However, if it exceeds 0.50% by weight,
As the deterioration of low-temperature toughness and the susceptibility to weld cracking increase,
It is preferably in the range of 05 to 0.50% by weight.

Mn must be added in an amount of 0.50% by weight or more in order to secure strength. However, if it exceeds 1.5% by weight, the susceptibility to weld cracking increases and the bending ductility required when laying a line pipe is deteriorated. Preferably, it is in the range of 1.5% by weight.

Al is a strong deoxidizing element, but below 0.005% by weight has no effect, while above 0.060% by weight the effect not only reaches almost saturation but also increases nonmetallic inclusions. Therefore, the content is preferably in the range of 0.005 to 0.060% by weight.

Ni is effective in improving the strength and HIC resistance, and also significantly improving the toughness of the base metal and the heat affected zone. However, if it exceeds 0.50% by weight, the generation of scale flaws becomes remarkable, and the surface properties of the steel sheet are reduced. Therefore, the content was limited to 0.50% by weight or less.

Cu forms a stable film on the steel surface in an environment with a high pH, improves corrosion resistance, and is effective in improving HIC resistance. However, if the added amount of Cu exceeds 0.50% by weight, hot workability is impaired. Therefore, it is preferable to set the amount to 0.50% by weight or less.

Ca spheroidizes the shape of sulfide-based inclusions and suppresses sulfide-based inclusions from becoming the starting point of HIC.
Although it is an effective element for ensuring the water resistance, the addition of Ca exceeding 0.005% by weight may increase the size of large inclusions and reduce the HIC resistance and hydrogen blister resistance. It is preferred that

Cr has the effect of improving the corrosion resistance of steel to reduce hydrogen intrusion into the steel and also preventing the deterioration of SSC resistance due to the addition of Ni. However, if it exceeds 0.30% by weight, particularly the toughness of the welded portion is deteriorated. Therefore, the range is set to 0.30% by weight or less.

Mo and B are both added to enhance the strength. But Mo
Is not economical because the effect is saturated even if it is added in excess of 0.30% by weight, and the toughness deteriorates if B exceeds 0.002% by weight. Therefore, Mo is reduced to 0.30% by weight or less and B is reduced to 0.002% by weight or less, respectively. Preferably, it is limited.

Pcm is an index of susceptibility to weld cracking.
If it exceeds 0.25, the susceptibility to weld cracking will increase significantly and the bending ductility of the circumferential weld will deteriorate. Therefore, the range is set to 0.25 or less.

<Example> (Example 1) An example of the present invention will be described.

Using a line pipe made of ERW steel pipe with an outer diameter of 273.1 mm and a wall thickness of 12.7 mm and having the composition shown in Table 1, the combination of welding rods was changed twice, and each time, using the conditions shown in Table 2, by covering arc welding. Circumferential welding of 6 layers and 6 passes was performed. Furthermore, API standard 1
12.7mm thick and 25.4m wide including circumferential weld according to 104
A test piece (n = 100) with a length of 230 mm and a length of m
%, And after bending 10 times in total, the presence or absence of crack generation near the weld was examined. Note that the tensile strength of the welding rod in Table 2 was measured in accordance with JIS Z 3111 prior to the repeated bending test.
It was determined by performing a tensile test on the deposited metal with the welding rod used in accordance with the above. Table 2 also shows the results of the crack occurrence rate by the repeated bending test.

In Table 2, when a welding material having a strength lower by at least 5 kg / mm ² or more than the welding material using the final layer as the front layer according to the present invention, almost no cracking was observed. On the other hand, in the comparative example, the crack occurrence rate is high. In particular, in the comparative example 1 and the example 2, the crack occurrence rate is increased only by changing the strength of the welding material in the final layer even though the base material component is the same B. It can be seen that it has decreased to 1/77. That is,
At least 5 kg / mm ² than the welding material used for the last layer as the front layer
Welding using a low-strength welding material improved the bending ductility of the welded portion and proved to be extremely effective for circumferential welding of ERW steel line pipes for reel barge laying.

In addition, a layer means a layer of a weld metal consisting of one or more passes, and a pass means a single welding operation performed along a weld joint. And split into single-pass and multi-pass.

(Example 2) Using a line pipe made of ERW steel pipe having an outer diameter of 273.1 mm and a wall thickness of 12.7 mm, circumferential welding was performed by coated arc welding under the conditions shown in Table 3, and the circumferential welding was performed according to API standard 1104. Collect a test piece of thickness 12.7 mm, width 25.4 mm, length 230 mm including the part,
After repeated bending tests with a strain amount of 5% and bending a total of 10 times, the presence or absence of cracks near the weld was investigated. further,
A tensile test was performed using test pieces of the same size, and the state of breakage was investigated. The results of these two tests are shown in Table 4.

In Table 4, according to the present invention, No. 7 to 10 in which the extra height, extra toe angle, and extra toe angle were set in appropriate ranges based on the present invention, almost no cracking was observed. Couldn't. On the other hand, in the comparative example, No.1 and No.2 have excessive heights, and No.3 has no excess height, extra toe angle and extra toe curvature radius. No. 4 deviates from the scope of the present invention, No. 4 has a small radius of curvature of the extra filling toe, and No. 5 shows that the extra height and the radius of curvature of the extra filling toe are within the range of the present invention. Although it is included, the extra toe angle is small,
The incidence of cracks in the toe was remarkable. In addition, No. 6 is when the extra height is less than 0.8 mm, and breaks occur at portions other than the base material portion, but in Examples No. 11 and No. 12, the extra height is 0.8 mm. When it was larger, the fracture of the base material was confirmed in all cases.

That is, by limiting to the extra fill height, the extra fill toe angle and the extra fill toe curvature radius according to the present invention, the bending ductility of the welded portion is improved and the ERW steel pipe line pipe for laying a reel barge is improved. It was proved to be extremely effective for girth welding.

(Example 3) Pipe made of ERW steel pipe having the composition shown in Table 5 (outer diameter 273.1 m)
m, and a wall thickness of 12.7 mm), a circumference welding was performed in six layers and six passes using a cellulosic welding rod by covered arc welding.

In the welding of the present invention, as in Example 1, a cellulosic E7010 welding rod (tensile strength 55.2 kg / m
The m ^2), the final layer was used welding rod cellulosic E6010 (tensile strength 50.2kg / mm ^2).

In addition, as in the second embodiment, the shape of the extra bank is the radius of curvature γ of the extra bank toe, 4.6 mm, the angle of the extra bank toe α = 132 °, and the height of the extra bank 1.11.
mm.

Test pieces having the same dimensions as in Example 1 were taken, and after the same repeated bending test as in Example 1 was performed a total of 10 times, the presence or absence of cracking near the weld was examined. Table 5 shows the results.

In Table 5, component systems No. 8 to No. 1 based on the present invention are shown.
For 6, no cracks were found. On the other hand, Comparative Examples No. 1 to No. 7 use the same welding material as the welding material used up to the previous layer with the strength of the final layer according to the respective base metal strength, and are shown below. The crack generation rate is high as a whole due to its composition. Comparative Example No. 1 is a case where the C content of the base material and the upper limit of the welding crack susceptibility equation (Pcm) are out of the upper limit, and the crack occurrence rate is high. In Comparative Example No. 2, although the value of the weld cracking susceptibility (Pcm) was as small as 0.099, the value of the carbon equivalent (Ceq) fell below the lower limit, and the crack occurrence rate was 34% due to the occurrence of the softened portion of the weld heat affected zone. I have. Comparative Example No.3
And No. 4 have high incidence rates because Ceq and Pcm respectively exceed the upper limit values. Comparative Examples No.5, No.6, No
7 is Nb + V, although Pcm and Ceq satisfy the specified values.
Since the content of + Ti exceeds the specified value, the rate of occurrence of cracks is high.

<Effect of the Invention> According to the method of the present invention, in the circumferential welding of the electric resistance welded steel pipe line pipe for laying the reel barge, the occurrence of cracks at the toe portion at the extra welded toe portion of the welded portion was significantly reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a characteristic diagram of the results of a repeated bending test, and FIG.
FIG. 3 is a characteristic diagram showing the relationship between the radius of curvature of the extra toe portion and the incidence of cracks in the toe, FIG. 3 is a characteristic diagram showing the relationship between the angle of the extra toe and the incidence of cracks in the toe, FIG. 4 is a characteristic diagram showing the relationship between the extra height and the incidence of cracks in the toe, FIG. 5 is a graph showing the relationship between the degree of softening (ΔH _v ) and Ceq, and FIG.
Fig. 7 is an explanatory view of a general method of constructing a submarine line pipe, Fig. 7 (a) is an explanatory view of winding a pipe prepared on land on a barge reef at sea, and Fig. 7 (b) is a purpose. FIG. 8 is a sectional view of a welded portion showing a typical crack seen in a circumferential welding toe portion, and FIG. 9 is a repeated bending test method. FIG. 10 is a schematic diagram showing hardness distribution in CR material,
FIG. 11 is an explanatory view of the extra height, the extra toe radius of curvature and the extra toe angle. 1 ... barge, 2 ... pipe, 3 ... reel, 4 ... seabed, 5 ... land, 6 ... cracking, 7 ... weld, 8 ... heat affected zone, 9 ... base metal, 10 ... Test specimen, 11 ... Bending tester.

Claims (6)

(57) [Claims] When the line pipe is circumferentially welded, the final layer is at least 5 kg / mm ² less than the welding material used up to the previous layer.
A circumferential welding method for an electric resistance welded steel pipe line pipe for laying a reel barge, wherein the welding is performed using a welding material having a low strength. 2. When the line pipe is circumferentially welded, the shape of the extra bank is set to 2 mm ≦ the radius of curvature of the extra toe, 120 ° ≦ the angle of the extra toe, 0.8 mm ≦ the extra height ≦ 1.8 mm. 2. The method according to claim 1, wherein the welding is performed by restricting the welding. The chemical composition of the electric resistance welded steel pipe is as follows: C: 0.03 to 0.20% by weight, Mn: 0.50 to 1.5% by weight, Si: 0.05 to 0.50% by weight, Al: 0.005 to 0.060% by weight; , V, Ti satisfy Nb + V + Ti ≦ 0.040% by weight, the balance substantially consists of iron and unavoidable impurities, and the carbon equivalent Ceq given below is 0.20 to 0.36.
3. The method of claim 1 or 2, wherein the weld crack susceptibility Pcm is 0.25 or less. Note Ceq = C + Mn / 6 + V / 5 Pcm = C + Si / 30 + Mn / 20 + V / 10 4. The chemical composition of the electric resistance welded steel pipe is as follows: C: 0.03 to 0.20% by weight, Mn: 0.50 to 1.5% by weight, Si: 0.05 to 0.50% by weight, Al: 0.005 to 0.060% by weight; , V, and Ti satisfy Nb + V + Ti ≦ 0.040% by weight, and further contain one or two of Mo: 0.30% by weight or less and B: 0.002% by weight or less, with the balance being substantially iron and inevitable impurities. And the carbon equivalent given below
Ceq is 0.20 or more and 0.36 or less, and weld crack susceptibility Pcm is 0.
3. The method for circumferentially welding a line pipe of an ERW steel pipe for laying a reel barge according to claim 1 or 2, which is 25 or less. Note Ceq = C + Mn / 6 + Mo / 5 + V / 5 Pcm = C + Si / 30 + Mn / 20 + Mo / 15 + V / 10 + 5B The chemical composition of the ERW pipe is as follows: C: 0.03 to 0.20% by weight, Mn: 0.50 to 1.5% by weight, Si: 0.05 to 0.50% by weight, Al: 0.005 to 0.060% by weight; , V, and Ti satisfy Nb + V + Ti ≦ 0.040% by weight, and are further selected from Ni: 0.50% by weight or less, Cu: 0.50% by weight or less, Ca: 0.005% by weight or less, Cr: 0.3% by weight or less 2. The composition according to claim 1, which comprises one or more kinds, the balance being substantially composed of iron and unavoidable impurities, and having a carbon equivalent Ceq given below of 0.20 or more and 0.36 or less, and a welding crack susceptibility Pcm of 0.25 or less. Or 2
A circumferential welding method for an ERW steel pipe line pipe for laying a reel barge as described above. Note Ceq = C + Mn / 6 + Cu / 15 + Ni / 15 + Cr / 5 + V / 5 Pcm = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + V / 10 6. The chemical composition of the electric resistance welded steel pipe is as follows: C: 0.03 to 0.20% by weight, Mn: 0.50 to 1.5% by weight, Si: 0.05 to 0.50% by weight, Al: 0.005 to 0.060% by weight; , V, and Ti satisfy Nb + V + Ti ≦ 0.040% by weight, and are further selected from Ni: 0.50% by weight or less, Cu: 0.50% by weight or less, Ca: 0.005% by weight or less, Cr: 0.3% by weight or less Contains one or more, and further contains one or two of Mo: 0.30% by weight or less, B: 0.002% by weight or less, and the balance substantially consists of iron and unavoidable impurities. Carbon equivalent given by
Ceq is 0.20 or more and 0.36 or less, and weld crack susceptibility Pcm is 0.
3. The method for circumferentially welding a line pipe of an ERW steel pipe for laying a reel barge according to claim 1 or 2, which is 25 or less. Note Ceq = C + Mn / 6 + Cu / 15 + Ni / 15 + Cr / 5 + Mo / 5 + V / 5 Pcm = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15
+ V / 10 + 5B