During the operation of the unit, the high-temperature pneumatic ball valve is mainly used on the residual oil pipeline between the heater outlet and the coke tower and the overhead oil and steam pipeline. The residual oil pipeline is the pipeline with the highest temperature in the whole coking unit and the most prone to coking. Its temperature is between 500~505 ℃, which is also the coking temperature of residual oil. Due to the characteristics of the internal structure of the high-temperature pneumatic ball valve, part of the residual oil will enter the cavity between the valve body and the ball body and the internal and external steam cavities of the bellows. Although there is steam injection at these two places, due to the location of steam injection (the steam injection location of the valve chamber is at the upper part of the valve) and the factors of steam injection volume (the steam temperature and its injection volume have an impact on the refining process), the residue is often deposited at the location far from the steam injection inlet, and then gradually forms hard coke. The residual oil coming in later will continue to accumulate and coke on the original coke block along the cavity wall. The coking in the valve body is mainly concentrated between the bottom of the ball and the valve body. The coking in this part will cause the ball position to be lifted by the coke block, causing local contact between the sealing surface of the ball and the sealing surface of the valve seat, resulting in internal leakage of the valve, and even more serious will cause the valve to fail to close. What is more serious is that a hard coke layer is formed outside the sphere, covering the whole sphere, and the valve action fails.

Discussion on Metal Bellows Contraction Joint
Metal bellows shrink joint is used for thermal compensation and increasing pipeline flexibility. It is used to absorb thermal expansion, cold contraction, system vibration, etc. in the pressure pipeline system or equipment by flexible deformation of thin wall corrugated pipes. At the same time, it can accept higher pressure. It is the most commonly used flexible key component in the pressure pipeline system or equipment, Therefore, in the design process of metal bellows contraction joints, attention should be paid to their similarities. Although the designers take the specifications and standards as the design basis, they often ignore some specific explanations in the standards or design conditions for some special working conditions. These omissions may reduce the acceptance ability of the contraction joints and affect their life, The bellows will be destroyed too early and thus the pressure pipeline system or equipment will be damaged, which will affect the safe consumption and operation of the pressure pipeline or design, and bring unnecessary losses to users