JPS59153521A - Production of high squeezing type electric welded tube - Google Patents

Abstract

PURPOSE:To produce electric welded tubes having high crushing strength inexpensively after producing pipes by sizing with a high total drawing rate, then subjecting the pipes to heat-treatment at relatively low temp. and for a short time. CONSTITUTION:Residual compressive stress in the inside of pipes generated in stages prior to the sizing stage is reduced in the process for producing electric welded tubes by sizing with >=1.0% total drawing rate for the pipes. After the drawing stage of the pipe, the pipes are heated at 100-250 deg.C and held in this temp. range for 30sec-30min to increase the yield stress of the pipes. By this treatment, the crushing strength of the pipes is remarkably improved. Necessary total drawing rate described above is at least 1.0% for the production of high squeezing steel pipe, but >=ca. 3.5% total drawing rate is undesirable because of generation of roll marks. To perform the heat treatment at higher temp. than the upper limit of the treatment or for a longer holding time than described above are also undesirable because of causing increase of cost in spite of little margin of the yield strength.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing an electric resistance welded steel pipe having high crushing strength.

In recent years, gas and oil wells have tended to become deeper and deeper, and the demand for high collapse type oil country tubular goods has been increasing year by year. ERW steel pipes have higher dimensional accuracy than normless steel pipes, and have a fine-grained structure that gives them higher strength, making them suitable for highly crushed oil country tubular goods.

However, since each process of forming ERW steel pipes, determining the diameter of the pipe, sizing the pipe to make it perfectly round, and straightening the pipe to make it straight, compressive residual stress is generated on the inner surface of the pipe. cannot be avoided.

This residual stress acts to reduce the crushing strength of the electric resistance welded steel pipe. Therefore, it has been well known for some time that omitting the sizing and straightening steps results in lower residual stress and higher crushing pressure. However, this is technically impossible at present, and a sizing process and a straightening process are essential to ensure roundness and straightness.

Although it has been known that heat treatment can be used to reduce residual stress, there is also the problem that heat treatment lowers the yield stress of the pipe, thereby reducing its crushing strength.

Therefore, in order to obtain a highly crushed OCTG, it is necessary to use high-grade materials that can be quenched and tempered, and to perform these heat treatments 7, which significantly increases manufacturing costs.

This invention was made to solve the above-mentioned problems in manufacturing high-pressure crush type ERW steel pipes, and aims to provide a method for manufacturing ERW steel pipes with high crush strength at low cost. be.

In this invention, the tube has a total squeezing rate (the squeezing rate of all stand choirs)
Sizing at 1.0 or higher, pipe size 100 to 2 after pipe making
Heat to 50C and hold for 30 seconds to 30 minutes.

In sizing as above, is the total aperture rate? By setting it to 10% or more, which is more than twice that of the conventional one, it is possible to reduce the compressive residual stress on the inner surface of the tube that occurs in the process before sizing. In addition, the yield stress 2 of the pipe can be increased by the heat treatment after pipe forming. , these significantly improve the crushing strength of the tube. On the other hand, the above heat treatment is performed at a low temperature;
Moreover, since it is carried out in a short time, it can be carried out at low cost.

The present invention will be explained in detail below.

This invention, contrary to conventional wisdom, aims to reduce residual stress by increasing the sizing reduction ratio.

The work hardening generated by increasing the sizing drawing ratio is effectively utilized by strain aging through low-temperature, short-time heat treatment.

While the normal total sizing rate is about 02 to 0.6φ, in this invention the total sizing rate is only 1.0%.
That's all. Although it is not clear whether large drawing ratios reduce residual stress, such drawing ratios generate tensile stress on the inner surface of the pipe during sizing, which has the effect of reducing compressive residual stress, which has an adverse effect on crushing pressure. it is conceivable that.

FIG. 1 is an example of a graph showing the relationship between the total proofreading rate of sizing and the internal compressive residual stress immediately after sizing. In the figure,
The symbol A indicates the conventional method, and the symbol B indicates the range 2 of the total accuracy rate of the present invention. As is clear from the figure, the residual stress decreases as the total reduction ratio increases.

In this invention, as mentioned above, the entire school rate of Zizing is 1.0.
% or more. The lower limit of 10% was determined from the value of residual stress allowed to obtain the crushing strength 2 required for practical soil. Also, if 10% is replaced with residual stress, it will be 15
This residual stress corresponds to kf/mTL2, and this residual stress has a crushing pressure of 40
kf/cm2, and a reduction ratio of at least 10% is required for the production of high-pressure soaked steel pipes.If the reduction ratio exceeds 35%, problems such as roll defects are likely to occur. However, there is no limit in terms of residual stress.

Further, in the present invention, a low-temperature, short-time heat treatment 2 is performed after pipe formation. A large number of dislocations are generated in the material due to sizing with a high reduction ratio, and solid solution nitrogen and solid solution carbon are fixed to these dislocations by the above heat treatment. As a result, the Baussinger effect disappears and the yield strength significantly stops. Figure 2 shows the heat treatment according to the present invention (A) and the one without heat treatment (B).
Stress-strain diagram with? It shows. As is clear from the figure, yield strength can be improved by performing heat treatment 2 at a low temperature and for a short time.

The above heat treatment conditions naturally depend on the manufacturing method of the material, but the effect is even more remarkable if the temperature and time are varied depending on the overall sizing rate.

According to the results of experiments, it is desirable to hold the image in a temperature range of 100 to 250 C for 30 seconds to 30 minutes when the total aperture ratio is in the range of 10 to 35 coefficients. The heating temperature is 1. If the OOC is less than 30 seconds or the holding time is less than 30 seconds, there will be no effect of improving the yield strength, and if the heating temperature exceeds 250'C or the holding time exceeds 30 minutes, the increase in yield strength will be small.
The cost will be high.

Conventional heating, for example induction heating or gas heating furnaces, is used to heat the tubes. The temperature increase rate is approximately 10~], 000ty=. After maintaining the tube at a predetermined temperature, the tube is allowed to cool.

Here, an experimental example showing the effects of this invention will be given.

Table 1 shows the crushing pressure of two electrically welded steel pipes (as-rolled type) with a diameter of 51/27/ and a wall thickness of 0.3041t manufactured using various sizing and heat treatment conditions. A comparison is shown. Residual stress was measured using the Crampton method.

As is clear from Table 1, according to the method of the present invention, the crushing pressure of the electric resistance welded steel pipe is approximately 20% higher than that of the pipe not subjected to low-temperature, short-time heat treatment 7 (Comparative Example H).

The above heat treatment can be performed in-line following straightening, or off-line after cutting the tube to a required length.

[Brief explanation of drawings]

Figure 1 is a graph showing an example of the relationship between total sizing proofing rate and internal compressive residual stress, and Figure 2 is a graph showing the effect of the heat treatment of this invention? 1 is a stress-strain curve shown in FIG. Patent applicant representative Patent attorney Tomoyuki Yafuki (and 1 other person)

Claims (1)

[Claims] A method for producing a high-pressure crush type electric resistance welded steel pipe, which comprises sizing the pipe to a total reduction ratio of 10% or more, heating the pipe to 100 to 250C after pipe forming, and holding the pipe for 30 seconds to 30 minutes.