JPS5939235B2 - Low hydrogen welding rod for on-site welding of steel pipes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a low hydrogen thread welding rod for on-site welding of steel pipes, which is particularly suitable for use in welding and connecting steel pipes at piping installation sites.

This type of welding operation is carried out from the top of the pipe body through both sides to the bottom, after the steel pipes to be welded are successively held against the ends of the pipes to form a pipeline.

The conditions that the welding rod used for such welding must meet are: 1. It must be able to weld with the same current in the downward direction along the circumference of the steel pipe.

2 At that time, the fluidity of the slag must be appropriate.

3 Also, the arc is strong and penetration is deep.

4 Especially in the route bus (first layer) 30 (V7l/
It is possible to weld at a high speed of min or more, and at this time, a deep bead is formed neatly.

Until now, welding rods that can satisfy these conditions have been limited to those using a high cellulose coating.

That is, conventionally, high cellulose thread rods have been mainly used in on-site welding of pipelines.

The main reasons for this are that it is possible to increase the welding speed of the route bus, which controls the pipeline laying speed, and that it is possible to perform downward welding around the entire circumference with the same current, which makes it easier to weld. No other line of rods can compete with high cellulose thread rods. However, since high cellulose thread rods contain approximately 30% organic matter in their coating, the amount of diffusible hydrogen in the weld metal reaches approximately 30g/1009, and because the amount of deoxidizing agent added is small, the amount of diffusible hydrogen in the weld metal is approximately 30%. The amount of nonmetallic inclusions is large. Therefore, when this type of welding rod is used for on-site welding of pipelines in cold regions such as Alaska, Canada, and Siberia, hydrogen is likely to be induced in the weld, and high temperature preheating is required to prevent this. However, this task is fraught with considerable difficulty.

In addition, high strength and high toughness are required for the steel pipes used in such pipelines and their welded parts, but the weld metal using high cellulose yarn welding rods has many nonmetallic inclusions, so the strength and toughness are low. Both have standard values (for example, yield point 49.
2kg/1 or more, absorbed energy [-40℃] is 4.2k
g・m or more) is not easy to meet. Therefore, the present invention has been devised so that the above-mentioned conditions can be satisfied with a low hydrogen yarn coating composition.

As has already been said, on-site welding of steel pipes requires a high welding speed in the route pass, and the wagon track shown by T in Figure 1 (approximately 1m77 deep!) often occurs in the welding area of this route pass. A sufficient penetration force is required to completely eliminate carbonates, organic substances, or crystalline water by welding the second layer, and this penetration force largely depends on the amount of gas generating agent in the coating. The latter two contribute to gas generation, but the latter two are not used for low-hydrogen yarn coating, so the penetration power mainly depends on the amount of carbonate added.

According to our first experiment, if the wagon track with a depth of about 1 mm that occurs in the root pass weld is eliminated by the second layer welding, the coating material composition should be 60% by weight.
It was found that CacO3, which occupies more than 100% of the total amount, is required.

On the other hand, CacO3 weighs 75? If the welding temperature is exceeded, the amount of oxidation of the metal S1 mixed as a deoxidizing agent in the coating material will increase, so there will be a strong tendency for molten metal to drip down, especially at welding positions where the welding position is vertical or upward, resulting in poor welding workability. Become. In this way, CacO3 weighs 60-75? limited to.
In addition, in order to increase the penetration power, it is effective to add graphite, especially graphite is 0.1 weight? Above, the penetration depth is increased in proportion to the blended amount.

But 0.7 weight? If it exceeds 0.15%, the amount of C in the weld metal under the commonly used steel core wire will exceed 0.15%, and there will be a risk of cracking. Therefore, the amount of graphite added is 0.
．． It is necessary to limit it to 7% or less. Note that it is effective to use graphite with a fine grain size as a method of lowering the yield in the molten metal. Here, in order to improve the welding workability of the welding part in the upward position, it is necessary to set the fluidity of the slag to an appropriate value, but even with this, the only way to effectively achieve this is by adjusting the blending ratio of CacO3 and CaF2.
It is to set F2/CacO3 to 0.1 to 0.2.

When this ratio is less than 0.1, the fluidity of the slag is low and the appearance of the heat is poor; on the other hand, when it exceeds 0.2, the fluidity of the slag is too large and welding is performed in a vertical position [clock position]. During welding (from 2 o'clock to 4 o'clock and from 10 o'clock to 8 o'clock), slag precedes welding, making workability worse. By the way, in general, there is a correlation between the welding speed of the root nozzle and the melting speed of the welding rod in circumferential welding using a low-hydrogen thread welding rod, as shown in Figure 2, and furthermore, the melting speed of the welding rod The relationship between current density and speed was investigated with regard to the presence or absence of iron powder blending and the effects of source polarity, and the results shown in Figure 3 were obtained.

In other words, for steel core wire diameter rods with wire diameters of 3.2, 4.0, and 5.0 m7IL, the amount of iron powder added is O and 15 weight? The comparison results show that there is almost no difference in the melting rate when AC power is used, whereas when DC positive polarity is used, the value is larger for iron powder mixture although it is relatively small; When using direct current with reverse polarity, the value is relatively much larger.Without the addition of iron powder, the melting rate is higher;
Moreover, it was found that the performance was superior to that of a high-cellulose thread rod. Therefore, a current of 130 A (DCR
Figure 4 shows the results of comparing the melting rates in P), when the amount of iron powder was 7% by weight. If you limit it to below, the melting rate is 350
．． It was confirmed that w1w/Min or more could be easily obtained and the root pass welding speed could achieve the target value of 30 (177!/[Tlln).In addition to the above, the low hydrogen yarn welding rod coating component The deoxidizing agents are mainly composed of Si and Mn, and also Al, Ti, etc. are used as the slag forming agents.
SiO2, Al2O3, TiO2, MnO and MgO
We investigated the amount of coating material composition using such materials, and we focused on the welding position in a vertical or upward position (from 2 o'clock on a clock) so that downward welding can be easily performed around the entire circumference of the steel pipe. It was confirmed that in order to prevent the slag from dripping at 6 o'clock and from 10 o'clock to 6 o'clock), it was necessary to set the weight ratio of the coating material to the core wire to 0.23 to 0.33. did.

If this weight ratio exceeds 0.33, workability will be hindered due to the advance of slag, while if it is less than 0.23, bead appearance will deteriorate due to insufficient amount of slag. Next, the present invention will be explained by examples.

In this example, the workability in circumferential welding of pipes was compared and the low-temperature toughness of weld metal was investigated using 13 types of welding rods shown in Table 1.

These results are summarized in Tables 2 and 3. Boiled 1 and 2 are low hydrogen thread rods for all position welding, Boiled 3 and 4 are low hydrogen thread rods exclusively for vertical downward welding. 5 to 10 are comparative examples, ? 11, 12, and 13 are low hydrogen thread rods according to the present invention. Welding has a 60° bevel,
Root face 1.6 dragon, root gear knob 1.6m71
The pipe joint part with L is 3.27nm1 in the root path.
The second and subsequent layers were coated with a coated rod using a steel core wire with a diameter of 4.0 mm under conditions of 130 to 190 A (DCRP).

Black 1 and 2 have coating weight/core weight of 0.40, CaF2/
With CacO3 of 0.36, the fluidity of the slag is good, and the workability in downward, vertical, and upward welding is quite good, but in downward welding as in this experiment, the slag precedes the weld line. It solidifies and becomes unweldable. RI)
．． 3 and 4 have coating weight/core weight of 0.38, CaF2/
When CacO3 is less than 0.1, the fluidity of the slag is particularly poor in the upward position, making welding impossible. In addition, in common with Nos. 1 to 4, the arc blowing is weak, so the penetration is shallow and no convex bead is formed, and the melting speed is slow, making high-speed welding impossible. Blacks 5 to 7 have slag fluidity suitable for downward welding, but black 5 has slightly weaker arc blowing, and slag 6 has a slower welding speed (Fi). In 7, the amount of C in the molten metal is 0.15? There is a drawback that high temperature cracks occur in the root pass when the temperature exceeds 1.

In case of No. 8, the coating weight/core weight is 0.35, so when placed vertically or vertically, slag precedes the bead, resulting in poor bead appearance. In case of ▲9, the coating weight/core weight is 0.21, so the amount of slag is insufficient and the bead appearance is poor. Contrary to these? 11, 12, 13
The fluidity of the slag is suitable for downward welding, the bead appearance is good, the spraying of γ-k has a suitable strength, and the welding speed can achieve the target value of 30 cm\Min in the root pass. In addition, the toughness of weld metal is 6.0 at -40℃.
It showed a sufficiently high value of ~7.2k9·m. What about comparative examples? In No. 10, the arc has a strong oxidizing atmosphere, the deoxidizing agent is often consumed, and the molten metal drips down at the downward welding part, resulting in poor workability. As explained above, the low-hydrogen thread welding rod of the present invention has good circumferential welding workability, and a weld metal with high toughness and low hydrogen content can be obtained.

When the low hydrogen yarn welding rod according to the present invention is used for circumferential welding of pipes, the following advantages can be obtained.

First, when comparing the amount of diffusible hydrogen in the weld metal, it is about 3a/1009 or less for a high cellulose thread rod, compared to about 30m1/1009, so preheating can be omitted. The temperature can be lowered if necessary. Second, when comparing the amount of oxygen in the weld metal, it is approximately 0.06% in the case of high cellulose thread rods, while it is approximately 0.06% in the case of high cellulose thread rods.
03%, which improves the low-temperature toughness of the welded part.

Thirdly, adjust the welding speed to the appropriate current (DCRP for a 4mm diameter rod).
When compared within the range (used in 17O to 190A), the number of passes required to complete one joint is 30 to 349/Min, compared to 25 to 289/Min for high cellulose thread rods. Since it can be done less, it is also possible to reduce the number of personnel involved in on-site welding. Further, the following fields of application can be mentioned.

First, if alloying elements such as Ni, Cr, and MO are added,
Since a weld metal with a strength of 60, 70, 801<g/Md class can be obtained, it can also be applied to higher strength pipe circumferential welding.

Second, even if an AC power source is used, the melting speed is only inferior and the welding workability is not deteriorated. As described above, by using the low-hydrogen thread welding rod of the present invention, the target root pass welding speed of 30 m/Min can be achieved, and furthermore, the welding speed is high, so the number of passes required can be reduced. Since high strength and high toughness can be obtained relatively easily, and the amount of diffusible hydrogen in the weld metal is about 3 m1/1009 or less, it is also possible to lower the pre-harvesting temperature.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of root hub welding, Figure 2 is a graph showing the relationship between rod welding speed and root pass welding speed, and Figure 3 is a graph showing the influence of polarity and iron powder addition amount on rod welding speed. , FIG. 4 is a graph showing the influence of the amount of iron powder added on the melting rate of the bar.

Claims (1)

[Claims] 1 60-75% by weight of the total formulation as a coating component
CaCO_3 which accounts for 0.1 to 0.7% by weight of graphite and the blending ratio to the amount of CaCO_3 is 0.1 to 0.7% by weight.
0.2 of CaF_2, and the remainder consists of a slag forming agent and a deoxidizing agent commonly used in low hydrogen coating compositions, and an amount of iron powder limited to 7% by weight or less. Low hydrogen for on-site welding of steel pipes, characterized in that the steel core wire is coated with a coating material of 0.23 to 0.33, and the weight ratio of the coating material to the steel core wire is 0.23 to 0.33, and is used with direct current reverse polarity. system welding rod.