Petrochemical equipment is mainly reactive. High-pressure vessels, various cylinders, tanks, etc., the main features are contact with corrosive media such as acid, alkali, salt, etc., but also withstand the test of various harsh environments. Chemical equipment includes fasteners that operate in such internal and external environments. It is often required to work at high temperatures (such as hydrogenation reactor design temperatures up to 500 ° C) or low temperatures (such as liquid nitrogen process temperatures as low as -196 ° C), often accompanied by Other media (such as hydrogen, nitrogen, carbon monoxide and Strong corrosion of uric acid). Therefore, people in the industry attach great importance to high-pressure containers for chemical equipment and their sealing technology.
(1) The importance of sealing technology
United States, "Challenger" space shuttle explosion shortly after liftoff, causing the greatest tragedy in the history of this space mainly due to the left side of the rocket booster joints O-ring failure caused by leakage. It was this small seal that caused all seven astronauts to die, and the space shuttle worth $1.2 billion was vanished.
According to statistics, in the daily use and maintenance of machinery and equipment, almost 40%~50% of the workload of the pump is used for the maintenance of the shaft seal. Approximately 70% of the cost of repairing a centrifugal pump is used to handle seal failures. In the cause of failure of centrifugal compressors, lubrication and sealing failures account for 55% to 60%, and sealing systems account for 20% to 40% of unit prices. US seal technology workers believe that due to the development of sealing technology, only one steam turbine, saving energy costs of 300 million US dollars per year.
Therefore, preventing leakage of machinery and equipment is one of the key issues that must be solved for industrial production. In the past century, a new discipline has been formed to study the law of sealing, the design of seals and the use of scientific principles, called "sealing". In engineering, it has also developed into a special technology - sealing technology. .
(2) Performance requirements for steel for high temperature fasteners
1. Have a high enough yield limit
In order to ensure the sealing of the high temperature container, the tightening bolt and the nut must be given a certain preload. According to thermal power plant
The experience of the line generally requires a pre-tightening stress of 250 MPa to 350 MPa. In order to ensure that the bolt does not yield when pre-tightened, the room temperature yield strength of the fastener (bolt) steel is important.
2, to have higher relaxation stability
Relaxation stability is one of the important properties of fastener steel, and the bolt calculation uses the relaxation stability as the strength calculation index . The requirements for bolt materials for domestic power plant high-power ultra-high pressure units are 520 ° C, and the working period is 20000 h.
3, to have a high enough permanent plasticity
In order to avoid the brittle fracture of the bolt, the bolt steel is required to have a sufficiently high durability plasticity. It is generally considered that the permanent plasticity of the bolt steel after long-term operation at high temperature is less than 3% to 5% to slow the brittle fracture of the bolt steel.
3, with antioxidant properties
It has a certain oxidation resistance at the working temperature to prevent the bite between the bolt and the nut.
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