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Sample with DWTT (drop weight tear test) abnormal fracture preventing function and method for manufacturing sample

A fracture and standard sample technology, applied in the field of samples to avoid abnormal fractures of DWTT and their preparation, can solve the problems of easy occurrence of abnormal fractures, difficulty in crack initiation, and work hardening on the hammer side, so as to eliminate the occurrence of abnormal fractures and reduce the The effect of repeated experiments, simple preparation method

Active Publication Date: 2015-11-25
BC P INC CHINA NAT PETROLEUM CORP +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, these materials are prone to abnormal fracture when the standard DWTT specimen is used for the drop weight tear test, that is, ductile fracture under the specimen notch and then transformed into cleavage fracture. This situation is stipulated in APIRP5L3 as invalid specimen , a re-sampling test is required, but the re-test still cannot avoid the occurrence of abnormal fractures, and it is a great waste of time and cost
Although through a lot of research, there are literatures and related standards that put forward the judgment of the shear area percentage of abnormal fracture, but the appearance of abnormal fracture is quite complex, and the evaluation of the effectiveness of abnormal fracture is highly technical, and the evaluation method of abnormal fracture adopted Lack of theoretical support, to some extent still controversial
At the same time, the abnormal fracture of large wall thickness, strong and tough pipeline steel DWTT test is very different from the normal fracture shape, and the correlation with the physical blasting test fracture is also greatly reduced
The existing research results show that the main reason for the abnormal fracture of DWTT is that the material has high strength, good ductility and plasticity, and large thickness, which makes it difficult to open the crack of the sample when the hammer is hammered, and severe work hardening and cracking occur on the hammered side. phenomenon of increased thickness
Therefore, in order to avoid the abnormal fracture of large wall thickness and strong toughness pipeline steel DWTT test, it is necessary to select and design a new DWTT sample to overcome the phenomenon of difficulty in opening cracks and severe work hardening on the hammer side

Method used

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  • Sample with DWTT (drop weight tear test) abnormal fracture preventing function and method for manufacturing sample
  • Sample with DWTT (drop weight tear test) abnormal fracture preventing function and method for manufacturing sample
  • Sample with DWTT (drop weight tear test) abnormal fracture preventing function and method for manufacturing sample

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preparation example Construction

[0026] The invention also discloses a sample preparation method for avoiding abnormal fracture of DWTT, which includes the following steps:

[0027] The first step is to make a standard drop weight sample. First, use sawing and milling methods to process the sample blank, and press a V-shaped notch 3 with a depth of 5±0.5mm and an angle of 45°±2° on one side of the sample blank.

[0028] In the second step, the I-shaped incision 4 is processed. At the root of the V-shaped notch 3, an I-shaped notch 4 is cut by wire EDM.

[0029] In the third step, the L-shaped incision 2 is processed. On the opposite side of the V-shaped notch 3 (hammer side), an L-shaped notch 2 is cut by wire EDM. Among them, the diameter of the molybdenum wire used in the L-shaped incision 2 and the I-shaped incision 4 must be less than or equal to 0.15mm.

Embodiment

[0031] Take the DWTT sample of 33.0mmX80 pipeline steel as an example.

[0032] See figure 1 An example of the present invention provides a sample to avoid abnormal fracture of DWTT. The sample is prefabricated with an L-shaped notch 2 in the middle of the hammer side of the standard sample 1 and an I-shaped notch 4 at the root of the V-shaped notch 3.

[0033] The preparation method is prepared according to the following steps:

[0034] Step 1. Make a standard drop weight sample. First, use the method of sawing and milling to process the sample blank, and press the V-shaped notch 3 with a depth of 5±0.5mm and an angle of 45°±2° at the center line of one side of the sample blank.

[0035] Step two, I-shaped incision 4 processing. At the root of the V-shaped notch 3, an I-shaped notch 4 is cut by wire EDM. The depth of the I-notch in the width direction of the sample is 5±0.2 mm.

[0036] Step three, L-shaped incision 2 processing. On the opposite side of the V-shaped notch 3 (hammer...

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Abstract

The invention discloses a sample with a DWTT (drop weight tear test) abnormal fracture preventing function and a method for manufacturing the sample, and belongs to the field of material toughness tests. An L-shaped notch is prefabricated in the middle of a hammering side of a standard sample, and an I-shaped notch is prefabricated in a V-shaped notch root of the standard sample, so that the DWTT sample can be formed. The L-shaped notch and the I-shaped notch are manufactured by the aid of wire-cut electrical discharge machining processes, the depth of the L-shaped notch in the width direction of the sample is 10+ / -0.2mm, and the length of the L-shaped notch along the length of the sample is 20+ / -0.5mm; the depth of the I-shaped notch in the width direction of the sample is 5+ / -0.2mm. The diameters of molybdenum wires for carrying out wire-cut electrical discharge machining on the L-shaped notch and the I-shaped notch need to be smaller than or equal to 0.15mm. The sample and the method have the advantages that crack is easy to start when the DWTT sample is hammered by a heavy hammer, work-hardening of the hammering side can be reduced, DWTT abnormal fracture can be effectively reduced or prevented, test results are similar to actual explosion fracture, and the test cost can be saved.

Description

Technical field [0001] The invention belongs to the technical field of material toughness testing, and relates to a sample for avoiding abnormal fracture of DWTT and a preparation method thereof. Background technique [0002] For oil and gas pipelines, material toughness is one of its mechanical properties. The main methods used in toughness testing are: impact test (CVN) of small specimens, J integral based on linear elastic KIC and elastoplastic fracture mechanics, crack tip opening displacement (CTOD) test, and drop hammer tearing of large specimens Crack test and full-scale physical blasting test. The Charpy impact test of small specimens is simple and easy to perform. It can test the impact energy and fracture toughness and brittle area of ​​metal materials. However, due to the small energy test range, small specimens are used in the test, and the tested toughness and brittle transition temperature cannot be changed. Equal to the actual ductile-brittle transition temperatu...

Claims

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Application Information

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IPC IPC(8): G01N1/28G01N3/02G01N3/34
Inventor 何小东梁明华
Owner BC P INC CHINA NAT PETROLEUM CORP
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