JPS5942053B2 - Manufacturing method of high tension line pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an AP material having a welded portion with excellent sulfide cracking resistance.
The present invention relates to a method for manufacturing high tensile strength steel line pipes of I standard X60 or higher.

In recent years, as demand for oil and natural gas increases, pipelines are being buried on a large scale.

At this time, crude oil or natural gas often contains hydrogen sulfide, carbon dioxide, etc., which creates harsh environmental conditions.

In particular, welded parts of high-strength steel line pipes are susceptible to sulfide cracking due to residual stress, residual strain, and increased hardness caused by welding.

If a line pipe with a welded part with increased susceptibility to sulfide cracking is used in the harsh sour environment described above, there is a risk that sulfide cracking will occur, leading to a serious line pipe failure accident. There is.

The purpose of the present invention is to provide, in an inexpensive manner, a high-tensile steel line pipe that meets API standard It is something.

That is, in the present invention, the pipe base material has a weight ratio of C: 0.0.
3-0.20, Si: 0.01-0.50
, Mn: 0.50-1.20, P: 0.03
0 or less, S: 0.002-0.020, Cu:
C: 0.20 to 0.50, with the remainder being substantially iron, or C: 0.03 to 0.20
, Si:0. O]~0.50. Mn: 0.50-1.
20, P: 0.030 or less, S: 0.002-0.
020, Cu: 0.20 to 0.50, further Cr: 0.50 or less, Ni: 0.30 or less,
Contains at least one of Nb: 0.1 or less, V: O, 1 or less, Mo: 0.30 or less, Ca: 0.0050 or less, and Nl: 0.1 or less, and the remainder is substantially iron. After rolling a steel piece having a compositional system, or after rolling, subjecting it to appropriate quenching, tempering or normalizing treatment, and forming the obtained steel plate into a predetermined shape, submerged arc welding method,
Or weld by electric resistance welding method and then weld the seam with 50mm
A welded part with excellent sulfide cracking resistance, which is maintained at a temperature between 0 and 1000°C for an appropriate time and then slowly cooled to reduce the maximum hardness of the seam to a Vickers hardness equivalent to 230 or less. This is a manufacturing method of high tensile steel line pipe.

Next, the reasons for limiting the above-mentioned components of the pipe base material in the present invention are as follows.

C: If the carbon content is less than 3%, the required strength cannot be obtained, while if it exceeds 0.20%, the weldability deteriorates.
．． 03 to 0.20%.

Si: Silicon is required as a deoxidizing agent in an amount of 0.01% or more;
If it exceeds 50%, brittleness increases, so 0.01 to 0.50
I was in charge.

Mn: Manganese is an element necessary for deoxidizing and imparting strength and toughness, but especially when manufactured from large steel ingots or continuous casting, if it exceeds 1.20%, it will cause martensite or bainite etc. due to micro segregation. If it is less than 0.50%, it is not possible to secure the necessary toughness, so 0.50 to 1.2
It was set to 0%.

P: Phosphorus is an element that increases the susceptibility to sulfide cracking, and in the case of the present invention, the assumed environment is extremely harsh, so it is desirable to reduce the P content as much as possible, so it was set to 0.030% or less. .

S: Sulfur is an element that forms sulfide-based inclusions and has a very significant effect on sulfide cracking, and as mentioned above, in the case of the present invention, the envisaged environment is extremely harsh, so 0.002
~0.020 ratio.

Cu: Copper is effective in reducing hydrogen absorption, but a sufficient effect cannot be expected if it is less than 0.50%, while the effect does not improve significantly if it is contained more than 0.50%, and the weldability is rather reduced. Since it may cause deterioration, the value was set at 0.20 to 0.50 fO.

Note that Cr≦0.50% with respect to the basic steel of the present invention.

Ni≦0.30%, Nb≦0.1 jealousy, ■≦0.1%, M
.

≦o, 3ofO1Ca≦o, o 050% and Al
≦0.1 may be contained alone or in combination in order to adjust the toughness or strength required for the pipe base material.

The reason for limiting each of the above components is as follows.

Cr is included to adjust the strength, but if it exceeds a coefficient of 0.50, it promotes the formation of a low-temperature transformation structure due to local segregation and deteriorates the hydrogen sulfide cracking resistance, as well as the toughness of the weld. , the upper limit was 0.50%.

Ni is included to adjust toughness, but if it exceeds a coefficient of 0.30, it not only tends to cause pitting (pitting corrosion) in a hydrogen sulfide environment, but also deteriorates the hydrogen sulfide cracking resistance of the weld. Therefore, the upper limit was set at 0.30%.

Both Nb and V are included to adjust the strength, but
If any content exceeds 0.1%, the steel becomes brittle and the toughness of the welded part in particular deteriorates, so the upper limit was set at 0.1%.

Mo is included to adjust strength and toughness, but its effect is saturated at 0.30% and is not economical, so the upper limit was set at 0.30%.

Ca is an element that spheroidizes nonmetallic inclusions in steel and improves hydrogen sulfide cracking resistance and toughness.Ca is mainly included to adjust toughness, but if it exceeds 0.0050%, it can cause nonmetallic inclusions to become spheroidal. The upper limit was set at 0.0050 because it causes agglomeration in clusters and deteriorates hydrogen sulfide cracking resistance and toughness.

Al is added as a deoxidizing agent, and is an effective element to refine grains and adjust toughness, but if it exceeds 0.1, it will embrittle the steel and cause deterioration of toughness. The upper limit was Section 1.

The heating temperature for the seam heat treatment in the method of the present invention must be at least 500°C, or the desired effect will not be obtained, while if it exceeds 1000°C, the quality of the steel will deteriorate, which is undesirable.

Therefore, it is important to heat-treat at a heating temperature between 500 and 1000°C to make the maximum hardness of the seam part equivalent to Vickers hardness 230 or less. Complete prevention of cracking is only possible with steel types such as .

The invention will now be further explained with reference to examples.

Example-1 Tables 1 and 2 show the chemical composition and welding method of the pipe base material used in the experiment.

Sulfide crack test pieces were taken from these pipes and machined into the specified shapes.

In the sulfide cracking test, a stress of 1.5 times the yield point of the base material is applied in a test solution with a pH value of 3.0 to 3.5, which is a 0.5 acetic acid aqueous solution saturated with hydrogen sulfide. The test was carried out using the four-point bending constant strain method at a test temperature of 25° C. and a test time of 330 hours.

This test was conducted three times at a predetermined stress level for each type of steel.

The test results are summarized in Table 3. In this example, the seam heat treatment was performed by holding the seam at 950°C for 1 hour and then slowly cooling it.

When the steel of the present invention was used as the base material and the maximum hardness of the welded part was reduced to v230 or less by heat-treating the seam part, there were no defects.

On the other hand, defects occur when a material other than the steel of the present invention is used as the base material, or when the seam portion is not heat-treated and the hardness becomes Hv>230.

Example 2 Table 4 shows test results regarding the influence of heating temperature in seam heat treatment for the present invention steel Mark H shown in Tables 1 and 2 of Example 1.

Note that the sulfide cracking test was the same as in Example-1.

As is clear from Table 4, less than 500°C or 1000°C
It can be seen that when the seam portion is heat treated at a temperature exceeding ℃, the sulfide cracking resistance is inferior.

As is clear from these examples, if the steel specified in the present invention is used as the pipe base material and the maximum hardness of the welded part is reduced to HV230 or less by heat-treating the seam, it can withstand extremely harsh environmental conditions. However, it is clear that welded parts have excellent resistance to sulfide cracking.

Claims (1)

[Claims] IC: 0.03 to 0.20%, Si: 0.01
-0.50 ratio, Mn: 0.50-1.20%, P:
0.030% or less, s: o, o 02-0.020
%, Cu: 0.20 to 0.50%, and the remainder is substantially iron, or after rolling, appropriate quenching, tempering or normalizing treatment is performed. After forming the obtained steel plate into a predetermined shape, welding is performed by submerged arc welding or electric resistance welding, and then the seam is kept at a temperature between 500 and 1000°C for an appropriate period of time, followed by slow cooling. A method for manufacturing a hypertonic Karaline pipe of API standard X60 or higher having a welded part with excellent sulfide cracking resistance, characterized in that the maximum hardness of the seam part is equal to or less than 230 Vickers hardness. 2C: 0.03-0.20, Si: 0.01-0.5
0 ratio, Mn: 0.50-1.20%, P: 0.03
0% or less, s: o, o O2~0.02 o%, C
Contains u: 0.20 to 0.50%, and further contains Cr: 0
．． 50% or less, Ni: 0.30 or less, Nb: 0.1 or less, V: 0.1 or less, Mo: 0.30'lo
Hereinafter, a steel slab containing at least one of Ca: 0.0050% or less and Al: 20.1% or less, with the remainder being substantially iron, is rolled, or after rolling, a suitable After quenching, tempering, or normalizing, the resulting steel plate is formed into a predetermined shape, welded using submerged arc welding or electric resistance welding, and then the seam is heated between 500 and 1000°C. High tensile strength of API standard Method of manufacturing line pipes.