1. Excessive system pressure. An emergency shutdown occurs, triggering gas venting or recirculation; the discharge check valve operates sluggishly or fails to seal tightly; or the check valve is located too far from the compressor outlet, resulting in a large volume of gas upstream of the valve. If the system load suddenly drops and the compressor cannot adjust in time—and the anti-surge system is not set to automatic—surging may occur.
2. Insufficient suction flow. External factors reduce the intake flow below the surge limit, and the rotational speed drives the compressor into the surge zone. Causes include: a clogged compressor inlet filter creating excessive resistance without a corresponding speed adjustment; a dirty filter element or icing in winter; or a reduction or cutoff of the inlet gas supply (e.g., insufficient feed gas or lack of a supplementary source). Failure to detect and rectify these situations promptly can lead to surging.
3. Damage or detachment of mechanical components. Improper installation, incorrect positioning, or detachment of components such as mechanical seals, balance piston seals, or O-rings can cause gas leakage between stages or sections, potentially triggering surges. Excessive filter resistance or a failed/damaged check valve can also cause surging.
4. Improper speed or pressure changes during operation. Speed and pressure are increased too rapidly, or pressure is not reduced before slowing down. Speed and pressure adjustments should be gradual and steady; depressurization measures—such as venting or recirculation—should be taken before reducing speed to prevent backflow as the rotational speed drops.
5. Changes in operating conditions. The operating point shifts into the surge zone. This can happen if speed, flow, or pressure are altered without consulting the performance curves, causing the operating point to enter the surge region.
6. Failure to engage the automatic anti-surge system. During normal operation, if the anti-surge system is not set to automatic, external changes—such as a drop in steam pressure, fluctuations in gas volume, a drop in turbine speed (where manual adjustment is too slow), or an interruption in gas supply—can lead to surging because the automatic anti-surge protection is inactive.
7. Changes in medium state. The occurrence of surging is closely related to the state of the gas medium. Since the state of the gas affects the flow rate—and consequently the surge flow rate—it naturally influences the occurrence of surge. Factors such as inlet temperature, inlet pressure, and gas composition (specifically molecular weight) all impact surge. At constant rotational speed and discharge pressure, an increase in gas inlet temperature makes surge more likely to occur; at a fixed rotational speed, a higher inlet pressure results in a higher surge flow rate; and at a constant inlet pressure and rotational speed, a significant decrease in gas molecular weight makes surge more likely.