CN113804541B - Steel pipe sample for tensile test under high-pressure hydrogen environment and preparation method thereof - Google Patents

Abstract

The invention relates to a material mechanical property test technology, and aims to provide a steel tube sample for a tensile test in a high-pressure hydrogen environment and a preparation method thereof. The steel pipe sample comprises an upper sleeve, a lower sleeve and a pipe section to be tested, wherein the upper sleeve and the lower sleeve are respectively sleeved at two ends of the pipe section to be tested in a mode of firstly heating and then welding so as to realize fixed connection; external threads are arranged on the outer sides of the upper sleeve and the lower sleeve. The steel pipe sample consists of the upper sleeve, the lower sleeve and the pipe section to be measured, and has reasonable design, simple and convenient processing and mass production. The clamping mode in the tensile test is threaded connection, and clamping is convenient. The acting force of the clamp on the sample does not directly act on the pipe section to be tested, but indirectly generates a tensile force on the pipe section to be tested through the interaction with the external threads of the sleeve, so that the extrusion effect on the pipe wall is avoided, and the problem that the clamping part of the pipe wall is easy to generate hydrogen-induced fracture due to stress concentration in the traditional technology is solved.

Description

Steel pipe sample for tensile test under high-pressure hydrogen environment and preparation method thereof

technical field

The invention belongs to the field of testing mechanical properties of materials, and in particular relates to a steel pipe sample used for a tensile test in a high-pressure hydrogen environment and a preparation method thereof.

Background technique

Austenitic stainless steel pipes with a nominal outer diameter of less than 26mm are often used in hydrogen refueling stations or vehicle-mounted high-pressure hydrogen systems, but their materials (especially welding parts) may appear due to high-pressure hydrogen embrittlement under the combined action of high-pressure hydrogen and loads. The deterioration of the mechanical properties of the system seriously threatens the safety of the high-pressure hydrogen system. Carrying out in-situ tensile test under high-pressure hydrogen environment is an effective means to obtain the anti-hydrogen embrittlement performance of materials, which has been introduced into the relevant standards of high-pressure hydrogen systems at home and abroad. However, for austenitic stainless steel pipes used in high-pressure hydrogen It is too small to take samples from the pipe wall and therefore cannot be tested with standard tensile specimens. A feasible alternative method is to cut a full-scale pipe section and put it into a high-pressure hydrogen environment for tensile testing, but this method faces a key problem, that is, how to prepare the sample and clamp it.

The tensile test of the steel pipe requires that the steel pipe sample breaks within the gauge length section, and the steel pipe sample and the fixture cannot slip off during the stretching process. One solution is to use a jaw clamp to directly clamp the end of the pipe section to be tested, but since the clamping section and the gauge section of the pipe section to be tested have the same structural size, under the action of the jaw load, the sample is likely to Flattening or fracture occurs in the clamping section. Another solution is to strengthen the clamping end of the pipe section to be tested. At present, the method of ASTM E8 is mainly used: insert a sliding-fit cylindrical metal plug into both ends of the pipe section to be tested to make a tensile sample, and then use the jaws of the clamp to Clamp both ends of the sample to complete the sample clamping. This method uses the pressure of the jaws to generate friction between the tube wall and the plug to prevent the sample from being pulled out. Although it is feasible in theory, the requirements for the precision control of the clamping force are too high in practice. If the value is small, the sample will slip during the stretching process. If the clamping force is too large, it will easily cause damage to the clamping end of the sample. The damage effect will be amplified in the hydrogen environment, resulting in the fracture of the sample at the clamping section. . In addition, because the metal plug blocks both ends of the pipe section to be tested, hydrogen cannot enter the pipe section, which is inconsistent with the actual service conditions of the steel pipe, and the pipe section is only subjected to external pressure, which may cause instability and failure.

To sum up, the existing steel pipe sample structure and its clamping method have problems such as the risk of slippage, easy breakage at the clamping point, and low hydrogen pressure in the tube during the stretching process, which cannot meet the requirements of stretching in a high-pressure hydrogen environment. Test requirement, so propose content of the present invention.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide a steel pipe tensile test sample under high-pressure hydrogen environment and its preparation method.

For solving technical problem, solution of the present invention is:

Provide a steel pipe sample for tensile test under high-pressure hydrogen environment, the steel pipe sample includes an upper sleeve, a lower sleeve and a pipe section to be tested, each of the upper sleeve and the lower sleeve is thermally sleeved and then welded The sleeve is fixedly connected at both ends of the pipe section to be tested; external threads are provided on the outer sides of the upper sleeve and the lower sleeve.

As a preferred solution, the pipe section to be tested has welds or no welds; when there are welds, the welds are in the middle of the pipe section to be tested.

As a preferred solution, the two ends of the pipe section to be tested are provided with outer chamfers, and the two ends of the upper sleeve and the lower sleeve are provided with inner chamfers; at the outer ends of the upper sleeve and the lower sleeve, the outer The chamfer and the inner chamfer together form an annular groove as the welding position after shrink fit; at the inner end of the upper sleeve and the lower sleeve, the inner chamfer and the side wall of the pipe section to be tested jointly form an annular groove as a Welding position after shrink fit.

As a preferred solution, before the heat sleeve, the inner diameters of the upper sleeve and the lower sleeve are 0.02-0.03 mm smaller than the outer diameter of the pipe section to be tested.

The present invention further provides a method for preparing a steel pipe sample for a tensile test under a high-pressure hydrogen environment, comprising the following steps:

(1) Process external chamfers at both ends of the pipe section to be tested, and process internal chamfers at both ends of the upper sleeve and the lower sleeve;

(2) The upper sleeve and the lower sleeve are respectively inserted into the upper end and the lower end of the pipe section to be measured by adopting the heat-shrinking process;

(3) After cooling, perform welding at the annular groove formed by each chamfer, so that the welding material is filled in the groove;

(4) Carry out straight line correction on the steel pipe sample, and use the outer circle of the exposed surface of the pipe section to be tested as a parallel section to ensure that the deviation of the pipe outer diameter of the parallel section does not exceed ±0.02mm;

(5) Grinding the outer surface of the parallel section of the pipe section to be tested to make the surface roughness Ra≤0.4;

(6) Process threads on the outer surfaces of the upper sleeve and the lower sleeve.

As a preferred solution, the heating method of the shrink-fit process is flame heating, resistance furnace heating or induction heating, and the heating temperature is ≥800° C.; the welding is argon arc welding.

As a preferred solution, the length of the outer chamfer and the inner chamfer is ≥1mm, and the angle is 45°.

As a preferred solution, the control conditions during welding are: welding wire diameter≤2mm, welding current 50-80A, welding speed 1-5mm/s.

As a preferred solution, the materials of the upper sleeve, the lower sleeve and the pipe section to be tested are the same; the material of the welding wire matches the material of the pipe section to be tested.

As a preferred solution, the size of the pipe section to be tested conforms to the provisions of GB/T 228.1-2010; when the exposed surface of the pipe section to be tested is rounded, its diameter reduction is controlled to be ≤0.2mm.

Compared with prior art, the beneficial effect of the present invention is:

1. The steel pipe sample is composed of three parts: the upper and lower sleeves and the pipe section to be tested. The design is reasonable, the processing is simple, and it can be mass-produced.

2. The clamping method of the steel pipe sample during the tensile test is threaded connection, which is convenient for clamping.

3. The action force of the fixture on the sample does not directly act on the pipe section to be tested, but indirectly generates tension on the pipe section to be tested through the interaction with the external thread of the sleeve, thus avoiding the extrusion effect on the pipe wall and solving the traditional In the technology, there is a problem of stress concentration at the clamping part of the pipe wall and hydrogen-induced fracture is prone to occur.

4. The upper and lower sleeves are first inserted into the pipe section to be tested through thermal expansion and then welded, which increases the reliability of the connection and solves the problem that the pipe section to be tested may slip during the stretching process.

5. Both ends of the pipe section to be tested are open, so that hydrogen can enter the inside of the sample during the test, which balances the air pressure inside and outside the sample, and solves the problem of instability and failure of the sample under external pressure.

Description of drawings

Fig. 1 is the structural representation of the steel pipe sample prepared in embodiment 1 of the present invention;

Fig. 2 is the structural representation of the steel pipe sample prepared in embodiment 2 of the present invention;

Fig. 3 is a schematic diagram of the clamping method of the steel pipe sample prepared in Example 1 of the present invention.

The reference signs in the figure are: upper sleeve 1, (with weld in the middle) pipe section 2 to be tested, lower sleeve 3, (without weld) pipe section 4 to be tested, upper spherical joint support 5, lower Ball joint bearing 6.

Detailed ways

Specific embodiments of the present invention will be described below in conjunction with the accompanying drawings.

Example 1

As shown in FIG. 1 , a steel pipe sample for a steel pipe tensile test under a high-pressure hydrogen environment includes an upper sleeve 1 , a lower sleeve 3 and a pipe section 2 to be tested with a weld in the middle. In this embodiment, the steel pipe used as the pipe section 2 to be tested is a commercial-grade 316L hydrogen pipe with an outer diameter of 6.2 mm and a wall thickness of 2 mm. The length of the parallel section of the pipe section 2 to be tested (that is, the surface exposed section in the middle) is 39 mm, and the length of the gauge section is 30 mm.

In the steel pipe sample, the upper sleeve 1 and the lower sleeve 3 are respectively fitted on both ends of the pipe section 2 to be tested in a manner of thermal sleeve and then welding to realize fixed connection; With external thread. The weld seam is in the middle of the pipe section 2 to be tested. The two ends of the pipe section 2 to be tested are provided with external chamfers, and the two ends of the upper sleeve 1 and the lower sleeve 3 are provided with internal chamfers; at the outer ends of the upper sleeve 1 and the lower sleeve 3, the external chamfers and The inner chamfer together forms an annular groove as the welding position after the thermal sleeve; at the inner end of the upper sleeve 1 and the lower sleeve 3, the inner chamfer and the side wall of the pipe section 2 to be tested jointly form an annular groove as a thermal sleeve post welding position.

The specific preparation method of the steel pipe sample comprises the following steps:

(1) Process outer chamfers (1.5mm×45°) at both ends of the pipe section 2 to be tested with a weld in the middle, and process inner chamfers (2mm×45°) at both ends of the upper sleeve 1 and the lower sleeve 3 ); Due to the large length of the chamfer processed, it can effectively increase the filling amount of the welding material and expand the welding area.

(2) Flame heating the upper sleeve 1 and the lower sleeve 3 (heating temperature 800°C), until the diameter of the inner hole expands and is larger than the outer diameter of the pipe section 2 to be tested, and then respectively inserted into the upper and lower sleeves of the pipe section 2 to be tested. end; the diameter of the inner hole before the upper and lower sleeves is 6.18mm, and the outer diameter is 13mm. The heating method adopts flame heating, which has the advantages of simple operation, concentrated heat, and easy control.

(3) After cooling, weld the upper and lower sleeves with the pipe section 2 to be tested. The welding process used is argon arc welding, the welding wire grade is ER316L, the welding wire diameter is 2mm, the welding current is 54A, the welding speed is 1mm/s, and It is filled in the grooves at the chamfers of the upper and lower sleeves; the purpose of slower welding speed is to better fuse the welding consumables and the base metal, thereby making the connection between the upper and lower sleeves and the pipe section 2 to be tested more firm reliable.

(4) After the welding is completed, the straight line is corrected, and the outer circle of the 2 parallel sections of the pipe section to be tested is turned to a diameter of 6.10±0.02mm; the outer circle of the 2 parallel sections of the pipe section to be tested is turned to eliminate the inconsistency of the pipe diameter and the test results The amount of turning should be as little as possible, so as to ensure that the original performance of the pipe section 2 to be tested does not change much.

(5) Grinding the outer surface of the parallel section of the pipe section to be measured to make its surface roughness Ra=0.4;

(6) Threads are processed on the outer surfaces of the upper and lower sleeves, and the specification is M12×1.5mm.

The final sample, the clamping method in the steel pipe tensile test under high-pressure hydrogen environment is shown in Figure 3, specifically:

The steel pipe sample is clamped by the tensile test fixture. The upper spherical hinge support 5 and the lower spherical hinge support 6 are set opposite to each other in the fixture. The internal threaded holes in the two supports are M12×1.5mm. The outer threads of the upper and lower sleeves are installed in the fixture for tensile testing. The size of the outer threads of the upper and lower sleeves matches the size of the inner threaded holes of the fixture. The outer diameter of the upper and lower sleeves before shrinking is at least 1mm larger than the nominal diameter of the fixture threaded hole.

There is a through hole in the center of the two spherical joint supports, which is used to connect the hydrogen environment inside and outside the test pipe section. After the two ends of the steel pipe sample are screwed into the upper and lower clamps respectively, the experimental chamber where the clamps are located is closed and filled with high-pressure hydrogen, and the tensile test in the high-pressure hydrogen environment is started.

Example 2

Compared with Example 1, the pipe section 2 to be tested with a weld in the middle is replaced with the pipe section 4 to be tested without a weld, and the outer surface roughness of the parallel section of the pipe section 4 to be tested is Ra=0.3. The heating method of the heat-shrinking process is changed to resistance furnace heating, and the heating temperature is 900°C. Other structural dimensions, operation steps and steel pipe sample clamping methods are the same as in Example 1.

Finally, it should be noted that what is listed above are only specific embodiments of the present invention. The present invention is not limited to the above embodiments, and many modifications are possible. Those skilled in the art can directly derive or associate all deformations from the content disclosed in the present invention, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in this document. within the scope of protection of the invention.

Claims (4)

1. a preparation method of steel pipe sample for tensile test under a high-pressure hydrogen environment, is characterized in that, comprises the following steps: (1) Process outer chamfers at both ends of the pipe section to be tested, and process inner chamfers at both ends of the upper sleeve and the lower sleeve; the length of the outer chamfer and inner chamfer is ≥1mm, and the angle is 45°; (2) The upper sleeve and the lower sleeve are respectively inserted into the upper end and lower end of the pipe section to be tested by using the heat sleeve process; the heating method of the heat sleeve process is flame heating, resistance furnace heating or induction heating, and the heating temperature is ≥800°C ; (3) After cooling, perform welding at the annular groove formed by each chamfer, so that the welding material is filled in the groove; the welding is argon arc welding; (4) Carry out straight line correction on the steel pipe sample, and use the outer circle of the exposed surface of the pipe section to be tested as a parallel section to ensure that the deviation of the pipe outer diameter of the parallel section does not exceed ±0.02mm; (5) Grinding the outer surface of the parallel section of the pipe section to be tested to make the surface roughness Ra≤0.4; (6) Processing threads on the outer surface of the upper sleeve and the lower sleeve; The prepared steel pipe sample includes an upper sleeve, a lower sleeve, and a pipe section to be tested, and the upper sleeve and the lower sleeve are respectively fitted on both ends of the pipe section to be tested by thermal sleeve and then welding to realize fixed connection; The outer sides of the upper sleeve and the lower sleeve are provided with external threads; the pipe section to be tested has welds or no welds; when there are welds, the welds are in the middle of the pipe section to be tested; the pipe section to be tested The two ends of the pipe section are provided with external chamfers, and the two ends of the upper sleeve and the lower sleeve are provided with internal chamfers; at the outer ends of the upper sleeve and the lower sleeve, the external chamfers and internal chamfers are jointly formed The annular groove is used as the welding position after the thermal sleeve; at the inner end of the upper sleeve and the lower sleeve, the inner chamfer and the side wall of the pipe section to be measured together form an annular groove as the welding position after the thermal sleeve; Before shrinking, the inner diameters of the upper sleeve and the lower sleeve are 0.02-0.03mm smaller than the outer diameter of the pipe section to be tested. 2. The method according to claim 1, characterized in that the control conditions during welding are: welding wire diameter≤2mm, welding current 50-80A, welding speed 1-5mm/s. 3. The method according to claim 1, wherein the materials of the upper sleeve, the lower sleeve and the pipe section to be tested are the same; the material of the welding wire matches the material of the pipe section to be tested. 4. The method according to claim 1, characterized in that, the size of the pipe section to be tested complies with the provisions of GB/T 228.1-2010; when the exposed surface of the pipe section to be tested is rounded, its diameter reduction is controlled ≤0.2mm.

Images