JP2002365202A - Method of predicting hydrogen embrittlement crack of bolt - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of predicting the damage due to the hydrogen embrittlement crack of a high-strength bolt or the like which is used when a structure such as a building, a bridge or the like by steel frames and reinforcing bars is built and to provide a method of deciding the time for executing effective measures against the damage of the bolt. SOLUTION: A dummy bolt whose quality is identical to that of the high- strength bolt or the like is coupled by a tightening force higher than that of the high-strength bolt, to a part near the coupling of the high-strength bolt or the like used when the structure such as the building, the bridge or the like by the steel frames and the reinforcing bars is built, the damage of the dummy bolt is detected, and the hydrogen embrittlement crack of the bolt is predicted. On the basis of the relationship between a load stress and the breakdown time in the hydrogen embrittlement crack, the breakdown time of the bolt is calculated, and the breakdown time of the bolt is predicted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bolt used for constructing a structure such as a bridge or a structure using a steel frame or a reinforcing bar, and more particularly to a method for predicting hydrogen embrittlement cracking of the bolt. Things.

[0002]

2. Description of the Related Art Bolts such as high-strength bolts (hereinafter simply referred to as "bolts") used in building structures such as steel structures and steel bars or structures such as bridges cause hydrogen embrittlement cracking. If a bolt is destroyed and left unattended, another failure may be induced and the function of the entire structure may be impaired. Here, hydrogen embrittlement cracking refers to a phenomenon in which a high-strength steel, which is the material of a bolt, is subjected to a static load continuously under an environment accompanied by hydrogen generation, and suddenly breaks after a certain period of time. Say. This hydrogen embrittlement cracking has the property that the higher the load applied to the bolt, the shorter the time to fracture (hereinafter, referred to as fracture time). Even under the same load condition, the fracture time is different depending on the environment and the material. So different
It is very difficult to predict the timing of the hydrogen embrittlement cracking. Therefore, inspections are normally performed periodically, and when a breakage of a bolt is found in the inspection, a measure for damage such as replacement of the bolt is promptly taken. Further, since the bolts may be replaced earlier than the service life under the use condition, the bolts are replaced more than necessary at present.

[0003]

With respect to the breakdown of bolts due to hydrogen embrittlement cracking of this type, since the mechanism of the failure has not been sufficiently elucidated, the actual machine designer of a structure or the like accurately detects the damage of the bolts. I could not predict. Also,
Since the bolt use condition exceeds the range of prediction, the bolt causes hydrogen embrittlement cracking, and a technology for non-destructively predicting the fracture has not been developed.

In addition, it is difficult to accurately predict the time at which a countermeasure for damage such as replacement of a bolt should be taken before the bolt for connecting the structure or the like causes hydrogen embrittlement cracking. The fact is that they are replaced earlier than their life under the conditions. Accordingly, the present situation is that excessive damage replacement costs such as bolt replacement are being spent.

[0005] The present invention has been proposed in view of such circumstances, and it is an object of the present invention to provide a method for predicting a fracture caused by hydrogen embrittlement cracking of a bolt in a structure having a bolt connection. And

[0006]

According to claim 1 of the present invention,
A dummy bolt having the same quality as that of the bolt and having been tightened with a tightening force higher than that of the bolt is connected to the vicinity of the bolt connection used in the structure or the like. Then, by detecting the hydrogen embrittlement crack of the dummy bolt, the hydrogen embrittlement crack of the bolt is predicted.
According to the present invention, it is possible to accurately predict whether hydrogen embrittlement cracking of the bolt may occur in the future, and it is possible to take measures before the bolt is broken.

The inventions of claims 2 and 3 show a specific method for detecting breakage of the dummy bolt in claim 1. According to the present invention, it is also possible to detect breakage of the dummy bolt 4 generated inside the bolt joint which cannot be visually detected, so that it is possible to improve the prediction accuracy of hydrogen embrittlement cracking of the bolt.

The invention of claim 4 detects the tightening force of the dummy bolt according to claim 1 and the life of the detected dummy bolt due to hydrogen embrittlement cracking. Is predicted. According to the present invention, the timing of hydrogen embrittlement cracking of a bolt can be quantitatively predicted with high accuracy.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a double logarithmic graph showing the relationship between the applied stress σ and the breaking time T. As shown in FIG. 1, the fastening force σ ₁ of the dummy bolt is set higher than the fastening force σ _{2 of the} bolt, and the fracture time T ₁ of the dummy bolt is set to be shorter than the fracture time T _{2 of the} bolt. This is intended to predict the hydrogen embrittlement cracking of the bolt by detecting breakage of the dummy bolt.

In general, hydrogen embrittlement cracking of a bolt has the property that the relationship between the applied stress σ and the fracture time T in hydrogen embrittlement cracking under the same environment and material conditions is expressed by the following equation. ing. σ ^m · T = const. (1) Here, m is a slope index in a diagram showing the relationship between applied stress and fracture time in hydrogen embrittlement cracking shown in FIG.

Utilizing the above-mentioned properties, by a preliminary test,
Bolt load stress under the same environment and material conditions
And the slope index m indicating the relationship between
Load stress of dummy bolt σ₁Destruction time detected as
T₁, And bolt stress σ ₂And from the bolt break
Breaking time T₂Is calculated using the following equation (2), and
It was found that the failure time could be predicted. T₂= (Σ₁/ Σ₂)^m・ T₁… (2)

FIG. 2 is an enlarged front view showing a state where the present invention is applied to a steel girder of a bridge or the like in order to carry out the method for predicting hydrogen embrittlement cracking of a bolt according to the present invention, and FIG. It is sectional drawing of the steel girder connection part in 2.

In FIGS. 2 and 3, reference numeral 1 denotes a steel girder.
Are butted to each other, and they are connected by a connecting plate 2. The steel girder 1 and the connecting plate 2 are fastened by a number of bolts 3 as shown in FIG. Axial force acts on the connection bolt joint structure in the direction of the arrow. Reference numeral 4 denotes a dummy bolt. The dummy bolt 4 is disposed at a position where a stress equal to or greater than the stress acting on the bolt 3 is applied.
Fasten with a tightening force higher than the tightening force of the bolt 3.

As described above, the dummy bolts 4 are fastened between the bolts 3 so that the dummy bolts 4 can be used for periodic inspection of a structure or the like.
Is visually observed to confirm the state of hydrogen embrittlement cracking. The gradient index m of the load stress-failure time diagram shown in FIG. 1 is grasped in advance, and the load stress of the dummy bolt 4, the fracture time of the dummy bolt 4 due to hydrogen embrittlement cracking, and the load stress of the bolt 3 are determined. , The destruction time of the bolt 3 is calculated, and the destruction time of the bolt 3 is predicted.

The inclination index m used for estimating the time of failure of the bolt 3 is grasped by a preliminary test. Alternatively, two or more dummy bolts 4 may be fastened with different tightening forces, and the inclination index m may be determined from the load stress and the breaking time of the plurality of dummy bolts based on equation (1).
Figure out.

If the predicted destruction time is before the next periodic inspection, immediately replace the bolt 3 with a new bolt of the same type, or take measures such as changing the bolt shape and the bolt class and increasing the number of bolts.

If the predicted time of the breakdown of the bolt 3 is after the next periodic inspection, the bolt 3 is left as it is, and the inspection is carried out intensively at each periodic inspection. We will take measures. in this way,
By determining the time to implement the measures for the destruction of the bolt 3 in consideration of the predicted time of the failure of the bolt 3 and the time of the periodic inspection of the structure and the like, the bolt that is predicted to be damaged is used as long as possible. Therefore, it is possible to minimize the damage countermeasure cost required for replacing the bolt 3 and the like.

In the above embodiment, the dummy bolt 4
In the state observation, not only the visual resistance but also the electric resistance of the dummy bolt 4 is measured, and the resistance change due to the damage of the dummy bolt is detected, so that the presence or absence of the damage of the dummy bolt can be grasped. Alternatively, the breakage of the dummy bolt may be detected by embedding a strain gauge, measuring the strain of the dummy bolt, and detecting the release of the strain due to the breakage of the dummy bolt.

[0020]

As described above, according to the present invention,
By detecting breakage of dummy bolts, it is possible to easily predict hydrogen embrittlement cracking of bolts used in building structures such as steel frames and steel bars or structures such as bridges. It became possible to predict the time. In addition, by determining the most appropriate time to take measures for bolt damage from the predicted failure time and taking measures, the failure due to hydrogen embrittlement cracking of the bolt can be prevented at the minimum necessary cost for damage measures. Thus, it is possible to prevent the destruction that impairs the function of the entire structure starting from the destruction.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between applied stress and fracture time in hydrogen embrittlement cracking.

FIG. 2 is an enlarged front view of a main part showing an example of an embodiment for a steel girder such as a bridge in the method for predicting hydrogen embrittlement cracking of a bolt according to the present invention.

FIG. 3 is a sectional view of a steel girder connecting portion in FIG. 2;

[Explanation of symbols]

 L Load stress-break time diagram σ Load stress T Break time 1 Steel girder 2 Connecting plate 3 Bolt 4 Dummy bolt

Claims (4)

[Claims] 1. A dummy bolt is joined to a bolt joint used in a structure or the like with the same quality as the bolt and with a tightening force higher than the bolt, and hydrogen embrittlement cracking of the dummy bolt is detected. A method for predicting hydrogen embrittlement cracking of a bolt by using the method. 2. The method for predicting hydrogen embrittlement cracking of a bolt according to claim 1, wherein the hydrogen embrittlement cracking of the dummy bolt is detected by measuring the electric resistance of the dummy bolt. 3. The method for predicting hydrogen embrittlement cracking of a bolt according to claim 1, wherein hydrogen embrittlement cracking of the dummy bolt is detected by a strain gauge. Wherein when said dummy bolt has caused the hydrogen embrittlement cracks at breaking time _{T 1,} the breaking time _{T 2} by hydrogen embrittlement cracks of the bolt, the formula _{T 2 = (σ 1 / σ} 2) m · T ₁ (where σ ₁ is the applied stress of the dummy bolt, σ ₂ is the applied stress of the bolt, and m is the slope index indicating the relationship between the applied stress and the fracture time in hydrogen embrittlement cracking). 4. The method for predicting hydrogen embrittlement cracking of a bolt according to claim 1, wherein: