Measures to prevent U-bolt fracture


1. Sega Horn   2. Improve standard section process […]

1. Sega Horn


2. Improve standard section processing technology


3. The quality of the bolt is determined by the length, specification, type, connection form and other conditions of the bolt.


4. The pre-tightening torque of the bolt makes the bolt subject to tensile stress and shear stress. The pre-tightening force is controlled to ensure that the flange connection system is tight and leak-proof, safe and reliable for long-term operation, and the gasket surface has sufficient sealing Specific pressure, especially under high temperature conditions, gaskets will age, creep and relax, flanges and bolts will undergo thermal deformation. Therefore, the sealing of high-temperature connection systems is much more difficult than normal temperature. At this time, the application and control of bolt pre-tightening force is more difficult. It is very important, too large or too small pre-tightening force will adversely affect the seal. If the pre-tightening force of the bolt is too large, the gasket will be crushed and lose its elasticity, and the bolt will even be broken; if the pre-tightening force of the bolt is too small, the residual compression stress on the gasket surface after compression will not reach the working seal. Specific pressure, resulting in leakage of the connection system. Therefore, how to control the bolt pre-tightening force is an important issue in production practice.


5. The tensile strength and yield strength of the bolt determine the strength of the bolt. The greater the strength, the longer the life expectancy.


6. Fatigue strength of bolts. It is related to the dangerous section area, the size of the stress on the bolt, the bolt stress amplitude, and the average stress of the bolt.

7. Bolt overload failure refers to the sudden and instantaneous fracture during service. This failure has no obvious signs in advance, so the damage is serious.


Overload failure characteristics:
High-strength bolts are widely used in hydropower plants. The threads on the bolts are actually the same as the notches, with a higher stress concentration factor. When it is matched with the nut, the stress concentration factor is further improved. For bolts that transfer load through the compression nut, the stress concentration is at the threaded thread close to the bearing surface of the nut. In addition, due to the structural characteristics of the bolt, the stress at the junction of the head and the rod is also concentrated. Therefore, the bolt's failure due to overload and breakage mostly occurs in these two parts.


8. Stress corrosion of high-strength bolts:

(1) Conditions for stress corrosion

There is tensile stress. The greater the tensile stress, the shorter the time required to break. The stress required to break is generally lower than the yield strength of the material. The tensile force that the bolt bears in service and the pre-tightening force during assembly are conditions that lead to stress corrosion.

(2) There is a corrosive medium that is sensitive to the material

When stress and corrosive media form a system, the material can suffer from stress corrosion cracking defects.

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