Weekly Topic

Turbocharger components experience accelerated wear and fatigue

The design operating conditions for anti-surge valves are divided into two categories: fully closed (normal stable operation) and fully open at a large degree (for surge protection during start-up and shutdown). An intermediate opening degree of 30%–70% falls within the harsh throttling range; maintaining an opening degree of 50% for an extended period can cause various irreversible damages. The main causes of these issues are high-pressure differential throttling, high-speed cavitation/erosion, and vibration fatigue. 1. Throttling due to a high pressure difference results in a surge in flow velocity: During normal operation of the unit, the pressure difference between the inlet and outlet is high; with the valve open at 50%, the flow cross-section is small, causing the flow rate of the medium (air/gas/steam) to increase sharply. This creates high-speed jets that directly impact the valve core, the sealing surfaces of the valve seat, and the inner walls of the valve body ； Consequence: Seal failure, with increasing internal leakage in the valve ； If it cannot be shut down at a later stage, the unit is unable to stabilize against surge, resulting in increased energy consumption. 2. Severe vibration and fatigue damage to the valve body and piping: (1) A 50% opening degree is the range in which throttling valves experience high levels of vibration; the fluid jet creates vortices and pressure fluctuations in the valve chamber and outlet pipes, which periodically impact the valve core and valve stem. 1) The valve core and valve stem undergo high-frequency reciprocating vibrations, which increases friction between the valve stem and the packing; as a result, the packing fails rapidly and leakage occurs ； 2) Alternating stresses at the valve stem threads and the connection point of the valve core lead to thread loosening and valve core fracture ； 3) The valve body, flanges, and connections suffer from vibration fatigue; the welds and flange gaskets crack, leading to medium leakage. (2) Resonance risk: Resonance occurs when the natural frequency of the valve approaches the frequency of fluid pulsations, causing the vibrations to amplify several times. In severe cases, the brackets and actuator bases may tear, and the supports of the connected return pipes may loosen or the pipes may deform. 3. Energy consumption increases significantly, the operational efficiency of the unit is poor; backflow occurs at 50% opening of the anti-surge valve, and a large amount of work done by the compressor is wasted due to medium circulation. 4. Overload and increased wear of the actuator: (1) The valve stem is continuously subjected to the thrust from unbalanced fluids, while the actuator diaphragm/cylinder are under uneven loads for extended periods; this leads to fatigue cracks in the diaphragm and air leakage in the cylinder seals ； (2) The actuator needs to continuously generate a signal to counteract the fluid thrust; components wear out quickly, control accuracy declines, and the valve is prone to drifting ； (3) Vibration and wear of the connecting rods and hinges lead to sticking, preventing the valve from opening fully quickly under emergency surge conditions; this poses a serious safety risk of unit surge and runaway. 5. Noise levels are above the specified limits, resulting in substandard occupational health conditions at the site.