JPS6027732B2 - Manufacturing method for oil well steel pipes with excellent collapse strength - Google Patents

Description

[Detailed description of the invention] The present invention is a coraf.

The present invention relates to a method for manufacturing oil well steel pipes with excellent strength. In recent years, Yui wells have become increasingly deeper, with some wells even exceeding 10,000 meters deep.

The steel pipes used in these deep wells must have high tensile strength to suspend and support the entire weight of the wells, and the casing pipes used in deep wells in particular must have high collapse strength to withstand the large external pressures applied from the surroundings. ing.

Collapse strength refers to the strength against external pressure that is related to the roundness, uneven wall thickness, and yield stress of a steel pipe, and is expressed by the following formula.
P=-15590 1317250 (D/t)-1-11
05 mu 23 do1 950 y here P: Collapse strength (p
si) D: Outside diameter of the steel pipe (inch) t: Wall thickness of the steel pipe (inch) u: Roundness (%) G: Thickness unevenness (%) oy: Yield stress (psi) Especially recently, steel pipes with this Hycolabus strength have been developed. Demand is increasing, and even AP1 (American Petroleum Institute) has high standards.

Scaling is about to be standardized. Normally, high-tensile oil well steel pipes are subjected to some kind of heat treatment in order to obtain a predetermined strength, but quenching and tempering are generally mainstream.

However, quenching and tempering heat treatments deteriorate the roundness and bending of the tube due to thermal strain and transformation strain that occur during heating and cooling, and the tube cannot normally be shipped as a product.

As mentioned above, the external roundness of a steel pipe has a strong correlation with its collapse strength, and a steel pipe with poor roundness will have a reduced collapse strength and may also cause trouble when threading the pipe end. There is.

For this reason, after the conventional normal tempering, the roundness is improved by performing warm or lining processing. Due to the special nature of the application, prevention of screw breakage in joint threads, prevention of trouble during transportation, etc., it is necessary to limit bending to within about 1 yen per meter of steel pipe.

For this reason, warm or cold straightening is performed after quenching and tempering, but warm straightening causes a decrease in the graininess of the steel pipe.
In cold straightening, yield strength decreases due to residual stress during processing, and collapse strength also decreases at the same time.

In particular, for steel pipes that require high collapse strength,
In order to remove this residual stress, stress relief annealing (hereinafter referred to as SR)
However, there are cases where bending occurs again during SR, which causes confusion in the manufacturing process and poses a quality control problem as straightening and SR must be repeated. Furthermore, even if SR is performed, the residual stress generated in the steel pipe is not completely removed, so it is inevitable that the mechanical properties will be slightly lower than those without straightening. An object of the present invention is to solve the above-mentioned problems and provide an effective method for manufacturing a steel pipe with excellent collapse strength.

In other words, during quenching and tempering of steel pipes using induction heating, by compressing the pipes while maintaining a constant transport speed and maintaining the roundness of the pipe cross section, it is possible to produce oil well steel pipes with excellent collapse strength. It is to manufacture. The gist of the present invention is as follows.

That is, in a method for manufacturing steel pipes for oil wells in which the steel pipe is subjected to quenching and tempering heat treatment by induction heating, the steel pipe during the heat treatment is restrained by self-weight canceling type pinch rolls, and the heating temperature at the time of restraint and the rolling force of the self-weight canceling type pinch rolls are This is a method for manufacturing oil well steel pipes with excellent collapse strength, which is characterized by adjusting and maintaining the relationship within the ABCD region shown in FIG. 3 attached. Generally, in a conveying device that continuously conveys steel pipe materials, when heat treatment such as heating and cooling is performed during conveyance, the tube bends due to uneven heating temperature.To prevent this bending, the conveyance speed of the steel pipe material is kept constant. to hold.

For this purpose, means for restraining the long steel pipe material with restraint rolls is usually adopted. These methods will be explained with reference to FIG. That is, a plurality of conductive heating devices A are installed as heating devices for quenching in the conveyance line of steel pipes, a cooling device B is installed for quenching the same, and then a plurality of conductive heating devices are installed in the Gyobo process as well. Device C is installed. In this case, restraining rolls E for restraining the longest steel pipe material D are provided at a plurality of locations outside and in the center of the heating devices A and B, so that the longest steel pipe material D is conveyed while being maintained at a constant speed. The present invention first uses induction heating to heat the steel pipe to heat it to a high temperature in a short time, and also heats the steel pipe in the circumferential direction by selecting an appropriate heating frequency that takes into account the dimensions and heating temperature of the steel pipe. and minimize the temperature difference in the wall thickness direction.

If a steel pipe, which is a magnetic material, is passed through an electromagnetic induction coil at an unrestrained speed, it will be pulled in the direction of the coil due to the influence of electromagnetic force, so the conveyance speed will change and a temperature difference will occur in the longitudinal direction, causing bending. Cause.

Therefore, in order to obtain a stable heating temperature, it is necessary to restrain the steel pipe during transport and keep the feed rate constant, but the required restraint force is strong under strong pressure in low-temperature regions where electromagnetic force is strong and deformation resistance is large. Furthermore, in high temperature regions where electromagnetic force is weak and deformation resistance is small, it is necessary to adjust the rolling force to be small.

Also, during cooling of the steel pipe, it is desirable to restrain it at least in the longitudinal direction in order to obtain a stable cooling rate without being affected by the contact pressure of cooling operation. The present inventors have discovered that the range of pinch roll rolling force for effectively restraining the steel pipe depends on the heating temperature.

Therefore, as shown in Fig. 2, we used a self-weight canceling type pinch roll as shown in Utility Application No. 102353/1986, and varied the rolling force, adjusted the heating temperature accordingly, and repeated many experiments. Measure roundness, uneven thickness, etc. and make a coruff.

As a result of calculating the steel pipe strength, if it is adjusted within the relational range between the pinch roll rolling force (k9) and the heating temperature (℃) shown by ABCD in Figure 3, the hot strain due to the weight of the steel pipe during heating and the electromagnetic force will be reduced. It has been found that it is possible to produce oil well steel pipes that prevent changes in conveying speed due to heat treatment, obtain uniform mechanical properties, and have excellent dimensions and shapes without the need for shaping or straightening after heat treatment, and therefore have excellent collapse strength. Embodiments of the present invention will be described with reference to the accompanying drawings.

In the present invention, self-weight canceling type pinch rolls E are used at a plurality of locations at both outer ends and in the center of the heat treatment apparatuses A, B, and C for restraining the steel pipe D as shown in FIG. This self-weight canceling type pinch roll B is the actual amount of 1974-1
02353, as shown in FIG. 2, the dead weight of the lifting frame 3 of the upper roll is canceled by the dead weight canceling cylinder provided at the upper part, so that the dead weight of the lifting frame 3 is not applied to the steel pipe 4.

A steel pipe conveying roller 5A mounted on a fixed frame 8 of the pinch roll B is driven by a drive motor 6.
At the top of the steel pipe 4, an opposing conveyance roller 5B is attached with its axis attached to the lower end of the lifting frame 3 so as to be movable up and down, and the steel pipe 4 is sandwiched between these two conveyance rollers 5A and 5B. transported. An elevating cylinder 2 is provided at the upper part of the elevating frame 3. The elevating cylinder 2 can move the conveying roller 5B up and down and adjust the rolling force against the steel pipe 4 as desired. The present inventors investigated the effects of the heating temperature during heat treatment and the rolling force of the pinch roll on the collapse strength using the self-weight canceling pinch roll, and found that the heating temperature for obtaining excellent collapse strength was There is an upper limit shown by the AB curve and a lower limit shown by the DC curve between the (℃) and the pinch roll rolling force (k9), and this is set to 100
If the heating temperature is limited to a suitable heating range of ~1,000 qo, and the heating temperature and pinch roll rolling force are adjusted within the range shown by ABCD in Figure 3, excellent roundness can be obtained, and uneven thickness, denting, etc. can be avoided. It has been discovered that it is possible to obtain a steel pipe for oil wells that is completely free of oil wells, and therefore has excellent collapse strength.

Figure 3 shows outer diameter 114.3 side to 406.4 skin ◇, wall thickness 5
．． 0 side ~ pine. It has been experimentally obtained using a number of donated materials that cover most of the commonly used oil well tubular sizes in the Qiu Cape range. Table 1 shows the sizes of oil well steel pipes used in these experiments. Table 1 The reason why the heating temperature was set in the range of 100 to 1000 qo is that if the heating temperature is less than 10030 qo, the effect of heating will be weak, and if the heating temperature exceeds 1000 q0, the crystal grains will become coarser, which is undesirable. .

The reason why the upper limit AB line is determined in this figure is that if the rolling force is applied beyond this line, the roundness will deteriorate or a dented eave will occur as shown in FIG.

The lower limit CD line is determined by the strength of the magnetic force, the weight of the tube, and the rolling force that prevents smooth lifting and lowering operations. That is, the conveying speed cannot be kept constant with the rolling force applied below the CD line. FIGS. 4 and 5 respectively show the roundness and bending of the steel pipe manufactured according to the present invention. This is 139
．． 7◇, 177.80, 244.50, and 9.70 spots were arbitrarily sampled and measured, and the roundness and bending were extremely excellent. Figure 6 shows the heating temperature (9
0000) and the relationship between the rolling force of the pinch roll and the circularity after heat treatment, and the influence of the circularity on the collab strength.

The test material is 244.5 side J x 11.9 kalpa, and in order to satisfy the minimum collapse strength of 508 imitation si of HC-95 grade, which API is currently considering standardizing, it must be perfectly round as shown in the figure. It is necessary to reduce the degree to 0.91% or less, and for that purpose, the rolling force must be 140k9 or less. Fig. 7 The ABCD range steel pipe is a casing steel pipe with an outer diameter of 244.5 side ◇ manufactured by the present invention and has a high collapse strength, and it can be seen that it has a collapse strength far superior to API's HC-95 grade. .

Here, for contrast, APITentative
HIGH COLLAPSE The minimum value (API standard) of the collapse strength to be cleared for HC-95 is shown.

Note that, conventionally, only products equivalent to APIC-95 could be manufactured.

The numerical values shown in FIG. 7 are shown in Table 2. Table 2 The reduction force and temperature in this case are shown in FIG.

In FIG. 3, the steel pipe rises and overflows as it progresses from the entry side due to conductive heating. Regarding the compressing force, the optimum compressing force corresponding to the temperature at that time is applied. Therefore, the rolling force and temperature are shown by one curve for each outer wall thickness. In addition, the roundness and bending of the steel pipe in the embodiment according to the present invention shown in FIGS. 4 to 7 are defined as follows.

Roundness is measured at eight arbitrary points in the circumferential direction of a steel pipe using a micrometer, and is defined as follows with respect to the outer circumference D of the steel pipe.

Roundness = Maximum outer diameter - Maximum 4.Outer diameter x IO. (%) The bending of a steel pipe based on the average outer diameter is defined as follows.

If the total length of the steel pipe is y, and the maximum perpendicular distance between the line connecting both ends of the steel pipe and an arbitrary point between them is x, then bending = x/end (sail/m).In carrying out the present invention, It is desirable to pay attention to the following points and conduct sufficient management.

In the present invention, hot shaping is not performed, so the raw tube is manufactured with a target outer diameter that takes into account the outer diameter expansion coefficient during heat treatment in the quenching and firing oven, and the heating temperature and pinch roll reduction force according to the present invention are and management.

'o} To help ensure uniform heating and uniform quenching during heat treatment, rotation is always applied to the steel pipe during heating and quenching. 1. In order to prevent temperature variations in the thickness direction, longitudinal direction, and both ends of the steel pipe due to induction heating, it is preferable to apply a low frequency power source when heating at AC2 or below, and heat the pipe with the ends joined. . 〇 In addition to managing according to the present invention to prevent fluctuations in conveyance speed due to magnetic force, competing water pressure, etc., it is necessary to adjust the rolling force of the pinch rolls depending on the ratio of the outer diameter/wall thickness of the steel pipe.

It is preferable that the points of contact between the steel pipe and the pinch rolls have the same cross section, avoid opposing positions, and maintain the upper and lower rolls at a constant angle as shown in FIG.

Normally, the angle of the conveying rollers 5A and 5B is preferably 30 to 45 degrees with respect to the longitudinal direction of the steel pipe. N It is preferable to install an inclined drain device in order to completely remove residual water entering the pipe.

(G) Even in the cooling bed after dawn, it is desirable to give the steel pipe as much rotation as possible, so it is preferable to make forward and reverse movements.

In exchange for the present invention and sufficient control based on the above-mentioned precautions, it is possible to manufacture oil well casing steel pipes with extremely excellent collapse strength without performing hot forming and straightening the bends between the sleeves or warm. did it.

As described above, the present invention makes it possible to omit the conventional forming and straightening processes, thereby simplifying the process and reducing equipment investment, and making it possible to manufacture oil well steel pipes with excellent collapse strength at low cost. became.

[Brief explanation of drawings]

Fig. 1 is a diagram showing a heat treatment line for steel pipes that is the object of the present invention, Fig. 2 is a front view of a self-weight canceling type pinch roll,
Fig. 3 is a diagram showing the relationship between pinch roll rolling force (k9) and heating temperature (00) according to the present invention, and Fig. 4 is a graph showing the roundness (%) and wall thickness t/outer D of the steel pipe manufactured according to the present invention. Fig. 5 is a distribution diagram of the number of steel pipes produced according to the present invention and the bending of the pipe (fence/m), Fig. 6 is a distribution diagram of the outer diameter /8''◇,
Rolling force (k9) at heating temperature 900qo, roundness (
%) and collapse strength (psi), Figure 7 shows the relationship between the outer diameter (Z/8"), L/D (length/outer diameter) = 4. Collapse strength (psi) and wall thickness of the group's key pipe (in). 1... Self-weight canceling cylinder, 2... Elevating cylinder, 3... Elevating frame, 4... Steel pipe, 5
(5A, 5B)... Conveyance roller, E...
・Pinch roll, D...Steel pipe. Figure 1 Figure 3 Figure 2 Figure 4 Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] 1. In a method for manufacturing oil well steel pipes in which a steel pipe is subjected to heat treatment of quenching and tempering by induction heating, the steel pipe during the heat treatment is restrained by self-weight cancel type pinch rolls, and the heating temperature at the time of the restraint and the pinch rolls are As shown in the attached Figure 3, the relationship between the rolling force and the steel pipe outer diameter 406.4 mmφ and wall thickness 22
．． At 0mm, point A (100℃, 763kg) and point B (1000℃, 124kg) are intermediate point E (500℃
, 273 kg), this is the upper limit, and the steel pipe outer diameter is 114.3 mmφ and wall thickness is 5.
．． At 0mm, point D (100℃, 208kg) and point C (1000℃, 45kg) are intermediate point F (500℃,
45kg) (consisting of straight lines DF and FC) D
Manufacturing a steel pipe for oil wells with excellent collapse strength, characterized in that C is adjusted and maintained within the ABCD region according to the outer diameter and wall thickness of the two steel pipes with this lower limit set as the lower limit. Method.