CN109781551B

CN109781551B - Method for avoiding abnormal fracture of X90/X100 pipeline steel drop hammer sample

Info

Publication number: CN109781551B
Application number: CN201811526255.6A
Authority: CN
Inventors: 李鹤; 池强; 封辉; 陈宏达; 邵晓东; 章传国; 黄卫锋
Original assignee: China National Petroleum Corp; Pipeline Research Institute of CNPC
Current assignee: China National Petroleum Corp; Pipeline Research Institute of CNPC
Priority date: 2018-12-13
Filing date: 2018-12-13
Publication date: 2021-08-27
Anticipated expiration: 2038-12-13
Also published as: CN109781551A

Abstract

The invention discloses a method for avoiding an abnormal fracture of an X90/X100 pipeline steel drop hammer sample, which comprises the steps of processing a DWTT sample according to a universal standard, prefabricating cracks at the root of a notch of the DWTT sample, adding a back groove at the back of the DWTT sample to ensure that the fracture appearance of the DWTT sample of an X90/X100 steel pipe is a normal fracture, and carrying out a DWTT test. The DWTT test sample prepared by the method has the characteristics of brittleness before toughness, and can effectively eliminate abnormal fractures.

Description

Method for avoiding abnormal fracture of X90/X100 pipeline steel drop hammer sample

Technical Field

The invention belongs to the technical field of material toughness testing, and particularly relates to a method for avoiding abnormal fracture of an X90/X100 pipeline steel drop hammer sample.

Background

Natural gas is a clean energy source and is also a flammable and explosive dangerous medium, once a high-pressure natural gas pipeline is cracked for a long time, great disasters and losses are caused, and therefore the safety of the pipeline must be ensured. In order to improve the economy of pipeline transportation, the trend of natural gas pipelines is to move to high steel grade (high strength grade). From 2000, canada initiated full-scale blasting tests of X100 pipelines worldwide and established X100 test segments. From 2012, the middle oil establishes a significant special item of 'third generation large-output natural gas pipeline engineering key technology research' and develops the industrial application research of the X90/X100 pipeline.

The shearing area of the DWTT fracture of the steel pipe is a key technical index for judging whether the crack of the high-speed expanded crack in the high-steel-grade pipeline can be stopped or not. The method is found that over 90 percent of DWTT samples have abnormal fracture in the domestic small-batch trial production process of X90/X100 steel pipes. According to the specification of API 5L/ISO 3183, the normal DWTT fracture morphology should be brittle fracture initiation, followed by ductile propagation. When an abnormal fracture occurs, the crack initiates toughness at the root of the notch in the DWTT test piece, and the fracture mode is changed from toughness to brittleness in the subsequent fracture propagation. According to the specification of API RP 5L3, when the DWTT sample has abnormal brittle fracture, the sample is judged to be invalid, and a resampling test is needed. The existing research shows that the high-toughness large-wall-thickness steel pipe is suitable for generating abnormal fracture. For the X90/X100 steel pipe, due to the further improvement of the smelting process and the purity, even if the wall thickness is thin (below 21.4 mm) and the toughness is low (300J), a large amount of abnormal fractures still occur. Therefore, an improved DWTT test sample for an X90/X100 steel pipe needs to be designed to ensure that the fracture morphology is normal fracture when the DWTT test of the X90/X100 steel pipe is carried out.

Disclosure of Invention

The invention aims to solve the technical problem of providing a method for avoiding abnormal fracture of an X90/X100 pipeline steel drop hammer test sample aiming at the defects in the prior art, and eliminating the generation of the abnormal fracture in the DWTT test of an X90/X100 steel pipe.

The invention adopts the following technical scheme:

a method for avoiding an abnormal fracture of an X90/X100 pipeline steel drop hammer sample is characterized in that a DWTT sample is processed according to a general standard, then a crack is prefabricated at the root of a notch of the DWTT sample, a back groove is additionally arranged at the back of the DWTT sample, so that the fracture appearance of the DWTT sample of an X90/X100 steel pipe is guaranteed to be a normal fracture, and a DWTT test is carried out.

Specifically, the processing of the DWTT test sample specifically comprises the following steps: and cutting a standard DWTT sample, and pressing a notch on the standard DWTT sample by using a pressing hammer.

Furthermore, the cutting edge angle of the pressing hammer is 45 degrees, and the size of the gap is 5 mm.

Specifically, the pre-crack is specifically as follows:

applying load on the back of the gap through the pressing hammer head by using universal testing machine equipment, prefabricating an initial crack, and continuously loading after the pressing hammer head is loaded to the maximum load; and when the load is reduced by 1.25% + -0.25% of the maximum load, stopping the loading, and obtaining the prefabricated crack.

Further, the sample bending is eliminated by the back pressure after the forward loading is finished.

Specifically, the length of the prefabricated crack is 3-5 mm.

Specifically, the back groove added on the back of the DWTT sample is as follows:

a back groove is formed in the middle of the back of the DWTT test sample in a linear cutting mode, and a hard alloy sample is filled in the back groove.

Furthermore, the width of the back groove is 5mm +/-1 mm, and the length of the back groove is 20mm +/-1 mm.

Further, the hard alloy is a quenched X100 material.

Specifically, in the DWTT test, the hammering energy of the drop weight tester is 100000J or more.

Compared with the prior art, the invention has at least the following beneficial effects:

according to the method for avoiding the abnormal fracture of the X90/X100 pipeline steel drop hammer test sample, the abnormal fracture is a fracture characteristic which shows toughness when a DWTT test sample cracks and then is converted into brittleness, and the abnormal fracture is defined as an invalid test sample according to the existing standard specification. Causing ductile initiation by a method of prefabricating cracks at the initiation portion; the method of adding a back groove on the back of the sample avoids the brittle crack arrest; the minimum impact energy is 100000J to increase the crack growth rate. The occurrence of abnormal fractures is avoided.

Further, compared with the traditional notch pressing method, after the crack is prefabricated, the crack is more brittle and easy to crack because the crack tip is very sharp and the stress is more concentrated and the energy consumption for cracking is less.

Furthermore, the length of the prefabricated crack is 3-5 mm, the length of the crack is too small, and the brittle fracture initiation effect is not obvious. The excessive length of the crack can cause the effective fracture area of the sample to be reduced. .

Furthermore, when the test sample without the back groove is hit by the hammer head of the drop hammer testing machine, the back of the test sample is greatly deformed. On the one hand, the extreme deformation of the back absorbs and consumes a large amount of impact energy, resulting in insufficient energy for crack initiation and propagation, causing the initiated portion to exhibit ductile fracture characteristics, resulting in abnormal fracture. On the other hand, the extreme deformation of the back causes work hardening of the back, which when the crack propagates to the back of the specimen, exhibits brittle characteristics, causing abnormal fracture.

Further, the quenched X100 material is extremely strong and has poor ductility. Therefore, when the hammer head of the drop hammer testing machine strikes, the deformation is extremely small, the hammer head striking energy can be completely transmitted to the middle part of the sample, and the back of the sample is prevented from generating a brittle zone.

Furthermore, the hammering energy of the drop hammer testing machine is more than 100000J, and the large hammering energy can improve the crack propagation speed and cause brittle fracture.

In conclusion, the DWTT test sample prepared by the method has the characteristics of brittleness before toughness, and can effectively eliminate abnormal fractures.

The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.

Drawings

FIG. 1 is a schematic view of a DWTT sample of the present invention, wherein (a) is a schematic view of the sample and (b) is an enlarged view of the notch;

FIG. 2 is a schematic view of an initial crack preparation loading mode;

FIG. 3 is a pre-crack loading curve;

FIG. 4 is a preformed initial crack;

FIG. 5 is a schematic view of a back groove;

FIG. 6 is a fracture morphology diagram of a DWTT sample;

fig. 7 is a conventional DWTT specimen.

Wherein: DWTT samples; 2. a notch; 3. pressing a hammer head; 4. a quilt cover; 5. and (6) prefabricating cracks.

Detailed Description

The invention provides a method for avoiding an abnormal fracture of an X90/X100 pipeline steel drop weight sample, which comprises the steps of firstly processing a common DWTT sample according to a universal standard, then prefabricating an initial crack at the root of a sample gap, and adding a back groove at the back of the sample to improve the hammering energy in a DWTT test, so as to ensure that the fracture appearance of the DWTT sample of an X90/X100 steel pipe is a normal fracture.

The invention discloses a method for avoiding abnormal fracture of an X90/X100 pipeline steel drop hammer sample, which comprises the following steps:

s1 DWTT sample processing

According to the general technical conditions of the Q/SY GJX 101 gas transmission steel pipe, a standard DWTT sample 1 (305 mm in length, 76.2mm in width and original wall thickness of the steel pipe) is cut, and a special tool with a cutting edge angle of 45 degrees is used for pressing a hammer 3 to press a gap 2 of 5 mm. The dimensions of the processed DWTT test specimens are shown in fig. 1.

S2 preliminary crack preparation

An initial crack was preformed by pressing the hammer head 3 to apply a load on the back of the notch 2 using a universal tester apparatus, as shown in fig. 2. And after the pressing hammer head is loaded to the maximum load, continuing loading. At this time, the DWTT bearing capacity may be reduced due to crack initiation and propagation. When the load drops by 1.25% ± 0.25% maximum load, the loading is stopped, as shown in fig. 3. By this process, a pre-crack 5 of about 5mm length is obtained, as shown in FIG. 4. Since the DWTT sample 1 is bent during the loading process, the bend of the DWTT sample 1 needs to be eliminated by back pressure after the forward loading is finished.

S3 back groove processing

After the prefabricated crack 5 is finished, a back groove 4 is cut in the middle position of the back of the DWTT test sample 1 in a linear cutting mode, the width of the back groove 4 is 5mm +/-1 mm, and the length of the back groove 4 is 20mm +/-1 mm, as shown in figure 5. The back groove 4 was filled with a sample of the same size cemented carbide (as quenched X100 material). After the back groove is added, the deformation absorption energy of the DWTT test sample 1 is reduced, and the propagation speed of the prefabricated crack 5 is improved.

S4, DWTT test

DWTT test is carried out according to SY/T6476 'pipeline steel pipe drop hammer tear test method', the hammering energy of the drop hammer test machine is required to be more than 100000J, and according to the DWTT test carried out by the method, the fracture of the sample is normal fracture after the sample is hammered off.

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to fig. 6 and 7, when a large-scale test is performed on a small-scale trial-produced od121916.3 mm thick X90 steel tube, more than 95% of DWTT specimen fractures are abnormal fractures and are judged to be invalid specimens when a conventional DWTT specimen is adopted. After the improved DWTT test sample and the method are adopted, over 96% of the DWTT test sample fractures are normal fractures, and as shown in figure 6, the test sample is effective.

A comparison test of a conventional DWTT sample and the DWTT sample is carried out on a 100000J hammer testing machine in a pipe and research institute, the conventional DWTT sample has the characteristics of toughness before brittleness, and the DWTT sample has the characteristics of brittleness before brittleness, so that abnormal fractures can be effectively eliminated.

The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.

Claims

1. The utility model provides a method for avoiding X90/X100 pipeline steel drop hammer sample to appear abnormal fracture which characterized in that, processes the DWTT sample according to general standard, then at the breach root prefabricated crack of DWTT sample, adds the back groove at DWTT sample back to guarantee that X90/X100 steel pipe DWTT sample fracture appearance is normal fracture, carry out the DWTT test, when the DWTT is tested, the hammering energy of drop hammer testing machine is more than 100000J, add the back groove at DWTT sample back and specifically do:

a back groove is formed in the middle of the back of the DWTT test sample in a linear cutting mode and filled with a hard alloy sample, the width of the back groove is 5mm +/-1 mm, the length of the back groove is 20mm +/-1 mm, and the hard alloy is a quenching-state X100 material;

the specific steps for processing the DWTT test sample are as follows: cutting a standard DWTT sample, and pressing a notch on the standard DWTT sample by using a pressing hammer, wherein the cutting edge angle of the pressing hammer is 45 degrees, and the size of the notch is 5 mm;

the prefabricated cracks are specifically as follows:

applying load on the back of the gap through the pressing hammer head by using universal testing machine equipment, prefabricating an initial crack, and continuously loading after the pressing hammer head is loaded to the maximum load; and when the load is reduced by 1.25% +/-0.25% of the maximum load, stopping loading to obtain the prefabricated crack, and eliminating the bending of the sample through back pressure after the forward loading is finished, wherein the length of the prefabricated crack is 3-5 mm.