1. Reasons for bolt breakage:
(1) Due to the material of the bolt, if the material we choose is better, then the quality of our bolts will be better. If the materials we choose are relatively poor, then our bolts will break to a certain extent.
(2) The strength of the bolt is not high enough. Since the pressure of the bolt is greater than the strength of the bolt, the bolt will be prone to breakage. Therefore, when using bolts, we should be able to understand how strong the bolt can withstand, so that we can choose bolts higher than this strength, and the possibility of bolt breakage is much reduced.
(3) If the manufacturing is unqualified, many bolts will be unqualified due to production, so there is no way to play the quality of the standard bolts, which will cause the bolts to break to a certain extent. We must pass the test after the bolts are produced, so that we can ensure that the bolts are qualified before they are sold. This is also the most basic guarantee for consumers.
(4) Due to the fatigue strength of the bolt. The most likely factor for bolt breakage is due to the fatigue strength of the bolt. We have no problem at the beginning of using the bolts, but there may be some looseness after the work of the objects. If the work is continued when it is loose, the fatigue strength of the bolts will increase, and when the bolts are reached, With the limits of the range, the bolts will break.
2. Measures to prevent bolt breakage:
(1) Saga horn
(2) Improve the bolt processing technology
(3) Improve the standard section processing technology
(4) The quality of the bolt is determined by the length, specification, type, and connection form of the bolt.
4. The pre-tightening torque of the bolt causes the bolt to be subjected to tensile stress and shear stress. The pre-tightening force is controlled to ensure that the flange connection system is tight and leak-free, safe and reliable for long-term operation, and the gasket surface must have sufficient Sealing specific pressure, especially under high temperature conditions, the gasket will be aging, creep and slack, and the flange and bolt will be thermally deformed. Therefore, the sealing of the high temperature connection system is much more difficult than the normal temperature. At this time, the preloading force of the bolt is applied and controlled. It is very important that excessive or too small preload will have an adverse effect on the seal. If the pre-tightening force of the bolt is too large, the sealing gasket will be crushed and lose its elasticity, and even the bolt will be broken. The too small pre-tightening force of the bolt will make the residual compressive stress on the surface of the gasket after the pressure not reach the working seal. Specific pressure, which causes the connection system to leak. Therefore, how to control the bolt preload is a problem that must be paid attention to in production.
5. The tensile strength and yield strength of the bolt determine the strength of the bolt. The greater the strength, the greater the life expectancy.
6, the fatigue strength of the bolt. It is related to the dangerous sectional area, the maximum and minimum stress on the bolt, the bolt stress amplitude, and the average bolt stress.
7. The overload failure of the bolt refers to the sudden and instantaneous breakage during the service. There is no obvious sign in advance of this failure, so the damage is serious.
Overload failure characteristics:
High-strength bolts are widely used in hydropower plants, and the threads on the bolts are actually the same as the notches, and the stress concentration factor is high. When it is fitted with a nut, the stress concentration factor is further increased. The bolt that transmits the load through the compression nut has the most concentrated stress at the first thread of the nut near the bearing surface. In addition, due to the structural characteristics of the bolt, the stress at the intersection of the head and the rod is also concentrated. Therefore, the overload of the bolt fails and the breakage thereof is generated at these two locations.
8. Stress corrosion of high strength bolts:
(1) Conditions under which stress corrosion occurs
There must be tensile stress present. The greater the tensile stress, the shorter the time required for the fracture. The stress required for fracture is generally lower than the yield strength of the material. The tensile force that the bolt is subjected to during service and the preload in the assembly are conditions that cause stress corrosion.
(2) There must be corrosive media sensitive to the material
When stress forms a system with corrosive media, the material can suffer from stress corrosion cracking defects.
Source: China Bolts Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)