CN114593971B - A Rolling Flattening Method of Steel Tube Lath-shaped Transverse Tensile Specimen - Google Patents

Abstract

The invention provides a rolling flattening method of a steel pipe plate strip-shaped transverse tensile sample, which solves the problem that the yield strength is reduced by the existing flattening method, reasonably controls the Banschinger effect by unifying and standardizing the rolling flattening method, ensures that the test result of the transverse yield strength of the steel pipe sample is stable, reliable and comparable, and comprises the following steps: cutting a lath-shaped transverse tensile sample with the arc length of about 2a +4t on the steel pipe, wherein 2a is more than or equal to 350mm, and t is the thickness of the sample; the upper press roll consists of 2 round rolls with axle center distance of l, and the lower support roll is a driving rotary round roll; placing the right end of the sample between the upper pressing roller and the lower supporting roller, and moving the upper pressing roller and the sample downwards until the lower surface of the sample is contacted with the lower supporting roller; pressing down the upper roller by (D-t)/2- ((D-t) ² /4‑l ² /4) ^1/2 +l ² /(6t(E/σ _t -1)) D is the steel pipe outside diameter; e is the modulus of elasticity; sigma _t The rated tensile strength of the material; rotating the lower supporting roll to enable the sample to move rightwards, and flattening the rest part of the sample; and moving the upper compression roller upwards, taking out the sample, and cutting off a certain length at two ends respectively to obtain the final sample.

Description

A Rolling Flattening Method of Steel Tube Lath-shaped Transverse Tensile Sample

technical field

The invention relates to the technical field of flattening and flattening methods for arc-shaped samples.

Background technique

Oil and gas transmission pipelines are energy arteries. Preventing plastic deformation of pipeline steel pipes during operation is the basic criterion for pipeline design. The principal stress of the pipeline is the hoop direction, and the hoop direction yield strength is the most important index for pipeline design. The hoop yield strength of steel pipe can be tested by rod, plate, ring expansion and hydrostatic pressure test. Rod-shaped, ring-shaped and hydrostatic pressure samples are limited due to the minimum diameter of the sample, high processing costs and high test costs; plate-shaped samples are the basic choice for testing.

In the processing of plate samples, it is necessary to flatten the curved steel plate first. Different flattening methods lead to different sizes of Banschinger effect, and the test results of different test institutions are quite different, which causes great troubles to the normal inspection and evaluation of steel pipes. .

Contents of the invention

The invention provides a method for rolling flattening of a strip-shaped transverse tensile sample of a steel pipe, which solves the problem that the current flattening method of a strip-shaped transverse tensile specimen of a steel pipe leads to a decrease in yield strength. , The standard rolling flattening method reasonably controls the Banschinger effect, so that the test results of the transverse yield strength of the steel pipe sample are stable, reliable and comparable, avoiding misjudgment of product quality and ensuring the safety and reliability of pipeline operation, which is of great significance.

The flattening process of the strip-shaped transverse tensile sample of the steel pipe in the present invention can be divided into 6 steps.

1) According to the requirements of relevant standards, the length of the sample is generally required to be 350mm, and the strip-shaped transverse tensile sample raw material is cut at a specific position on the steel pipe, with an arc length of about 350mm+4t and a width of 80mm, as shown in Figure 1. If it is flame cutting, the width should be appropriately enlarged to avoid the influence of heat input on the final sample.

2) Put one end of the strip-shaped sample 3 between the upper pressing roller 2 and the lower supporting roller 1, as shown in FIG. 2 . The upper pressing roller 2 is made up of 2 round rollers with a diameter of 140mm, which can move up and down. The lower support roller 1 is a circular roller with a diameter of not less than 400mm that actively rotates. Slowly move the upper pressure roller 2 downward until the upper and lower surfaces of the strip-shaped sample 3 are just in contact with the upper pressure roller 2 and the lower support roller 1, and one end of the upper surface of the sample 3 is in contact with the upper surface of the upper pressure roller close to the sample. The round roller at that end is tangent.

3) On this basis, press the upper pressing roller 2 downward, as shown in Figure 3, the amount of pressing down is (Dt)/2-((Dt) ² /4-l ² /4) ^1/2 +l ² /(6t(E/σ _t -1)) The center distance between the two round rollers in the upper pressure roller is l=160mm, see Figure 2; D is the outer diameter of the steel pipe, mm; t is the wall thickness, mm; E is the elasticity Modulus, MPa; σ _t is the rated tensile strength of the material, MPa. At this time, the position of sample 3 should be kept stable.

4) Gradually and slowly rotate the lower support roller 1 at a speed of about 5-10mm/s, so that the sample 3 gradually moves from the other end to one end, so that the remaining part of the sample 3 is also gradually flattened, as shown in Figure 4.

5) Lift the upper pressure roller 2 up enough to ensure that the sample 3 can be taken out. The sample taken out is shown in Figure 5, and both ends are still bent. At this time, only the straightness of the middle 350mm length should be checked. If the requirements are not met, the sample is placed between the upper pressure roller and the lower support roller, and the upper surface of the sample is in contact with the two round rollers in the upper pressure roller. Move the upper pressing roller and the sample downward until the lower surface of the sample touches the lower support roller, then press down the upper pressing roller slightly, and turn the lower support roller to gradually flatten the 350mm long part of the middle part of the sample.

6) Then cut off 2t lengths at both ends of the sample 3 shown in Figure 5, as shown in Figure 6, and then process the official final sample.

Using the rolling flattening method of the present invention, the overpressure radius/down pressure during the rolling flattening process is calculated, which ensures that the flatness of the sample can meet the requirements after one flattening, and avoids the flattening of the current existing method The overpressure parameter in the process is inaccurate, and repeated flattening and repeated flattening operations are required. At the same time, the method of the present invention ensures the amount of plastic deformation that occurs during the flattening process of steel pipe samples with the same pipe diameter and wall thickness, and The resulting deformation hardening, the Bauschinger effect, is the same, so that the experimentally tested yield strengths are stable, reliable and comparable.

Description of drawings

Figure 1 is a schematic diagram of a lath-shaped transverse tensile specimen cut from a steel pipe.

Fig. 2 is a schematic diagram when one end of the sample is placed between the upper pressing roller and the lower supporting roller.

Fig. 3 is a schematic diagram after pressing down by the upper pressing roller.

Figure 4 is a schematic diagram of the rotation of the lower support roller to flatten the sample.

Figure 5 is a schematic diagram of the flattened sample.

Fig. 6 is a schematic diagram of the sample after cutting off the bent sections at both ends.

detailed description

Example 1:

The transverse yield strength test is carried out on the Φ508×22mm X70 straight welded seam steel pipe, which is realized as follows.

1) According to the requirements of relevant standards, cut the strip-shaped transverse tensile sample 3 raw material at a position of 90° from the steel pipe to the weld seam, with an arc length of about 440 mm and a width of 100 mm, as shown in Figure 1. Because of flame cutting, the effect of edge heat input on the final specimen was considered.

2) Put the right end of the strip-shaped sample 3 between the upper pressing roller 2 and the lower supporting roller 1, as shown in FIG. 2 . The upper pressing roller 2 is made up of 2 round rollers with a diameter of 140mm, which can move up and down. The lower support roller 1 is a circular roller with a diameter of 400 mm that is actively rotating. Slowly move the upper pressure roller 2 downward until the upper and lower surfaces of the strip-shaped sample 3 are just in contact with the upper pressure roller 2 and the lower support roller 1, and the upper surface of the right end of the sample 3 is in contact with the round roller at the middle right end of the upper pressure roller. cut.

3) Then press the upper pressure roller 2 downwards, as shown in Figure 3,

Press down according to

D＝508, t＝22, l＝188, E＝210000MPa, σ _t ＝670MPa calculation:

The amount of pressing down is 19.77mm, and the position of sample 3 should be kept stable after pressing down.

4) Gradually and slowly rotate the lower support roller 1 at a speed of about 6mm/s, so that the sample 3 is gradually moved to the right, so that the remaining part of the sample 3 is also gradually flattened, as shown in Figure 4.

5) Lift the upper pressure roller 2 up enough, and take out the sample 3. The sample taken out is shown in Figure 5, and both ends are still bent. Check the middle 350mm length for straightness.

6) Then cut off 44mm lengths at both ends of the sample 3 shown in Figure 5, as shown in Figure 6, and then process the official final sample.

Example 2:

The transverse yield strength test of Φ609×18mmX65 straight welded seam steel pipes of shale gas wells is carried out as follows.

1) According to the requirements of relevant standards, cut the strip-shaped transverse tensile sample 3 raw material at a position of 90° from the steel pipe to the weld seam, with an arc length of about 440 mm and a width of 100 mm, as shown in Figure 1. Because of flame cutting, the effect of edge heat input on the final specimen was considered.

2) Put the right end of the strip-shaped sample 3 between the upper pressing roller 2 and the lower supporting roller 1, as shown in FIG. 2 . The upper pressing roller 2 is made up of 2 round rollers with a diameter of 140mm, which can move up and down. The lower support roller 1 is a circular roller with a diameter of 500 mm that is actively rotating. Slowly move the upper pressure roller 2 downward until the upper and lower surfaces of the strip-shaped sample 3 are just in contact with the upper pressure roller 2 and the lower support roller 1, and the upper surface of the right end of the sample 3 is in contact with the round roller at the middle right end of the upper pressure roller. cut.

3) Then press the upper pressure roller 2 downwards, as shown in Figure 3,

Press down according to

D＝609, t＝18, l＝201, E＝210000MPa, σ _t ＝572MPa calculation:

The amount of pressing down is 18.64 mm, and the position of sample 3 is kept stable after pressing down.

4) Gradually and slowly rotate the lower support roller 1 at a speed of about 7mm/s, so that the sample 3 is gradually moved to the right, so that the remaining part of the sample 3 is also gradually flattened, as shown in Figure 4.

5) Lift the upper pressure roller 2 up enough, and take out the sample 3. The sample taken out is shown in Figure 5, and both ends are still bent. Check the middle 350mm length for straightness.

6) Then cut off 36mm lengths at both ends of the sample 3 shown in Figure 5, as shown in Figure 6, and then process the official final sample.

Claims (4)

1. A rolling flattening method for a steel pipe plate strip-shaped transverse tensile sample is characterized by comprising the following steps:

1) Cutting a slab-shaped transverse tensile sample on the steel pipe, wherein the arc length 2a +4t of the sample is more than or equal to 350mm, the width of the sample is not less than 80mm, and t is the wall thickness of the steel pipe;

2) The upper press roll consists of 2 round rolls with the diameter of 140mm and can move up and down; the lower supporting roller is a circular roller which actively rotates and has the diameter not less than 400 mm; the upper press roll is positioned above the lower support roll, the axial center distance l of two round rolls in the upper press roll is 150-210mm, and the two round rolls are in bilateral symmetry with the axis of the lower support roll;

placing the right end of a sample between an upper press roller and a lower support roller, wherein the upper surface of the sample is contacted with two round rollers in the upper press roller, and the rightmost end of the upper surface of the sample is tangent to a right round roller in the upper press roller; moving the upper press roller and the sample downwards until the lower surface of the sample is contacted with the lower support roller;

3) Pressing down the upper roller by (D-t)/2- ((D-t) ² /4-l ² /4) ^1/2 +l ² /(6t(E/σ _t -1)) D is the outside diameter of the steel pipe, mm; e is the elastic modulus, MPa; sigma _t The material rated tensile strength is MPa;

4) Rotating the lower supporting roll at the speed of 5-10mm/s, and gradually moving the sample to the right to gradually flatten the rest part of the sample;

5) Moving the upper compression roller upwards, and taking out the sample;

6) The two ends of the sample are cut off for a length of not less than 2t respectively to obtain a final sample with a length of 350mm in the middle.

2. The roll flattening method of claim 1, wherein: and 5) checking the flatness of the middle 350mm of the sample, if the flatness does not meet the requirement, putting the sample between an upper compression roller and a lower support roller, contacting the upper surface of the sample with two round rollers in the upper compression roller, moving the upper compression roller and the sample downwards until the lower surface of the sample is contacted with the lower support roller, slightly pressing the upper compression roller downwards, and rotating the lower support roller to gradually flatten the middle 350mm part of the sample.

3. The roll flattening method of claim 1, wherein: the axial distance l between two round rollers in the upper pressing roller is 160-200mm.

4. The roll flattening method according to claim 1, wherein: and cutting the lath-shaped transverse tensile sample on the steel pipe by flame, wherein the width of the sample is 100mm.

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