**Abstract:** The propylene outflow pump in an ethylene plant is a GSB-type high-speed pump that frequently experiences mechanical seal failures. By analyzing the specific pressure on the mechanical seal faces and evaluating the material and design of the moving ring, the root causes of the leakage were identified. A comprehensive reform was then implemented, leading to significant improvements in performance and reliability.
**Keywords:** high-speed pump, mechanical seal, leakage analysis, seal reform
The propylene supply pump (E-GA301A/B) in the ethylene unit plays a crucial role in providing raw material for the downstream polypropylene unit. Any failure in this pump can lead to a complete shutdown of both the ethylene and polypropylene plants. Since its commissioning in April 2001, the pump has experienced multiple issues with lubricating oil, sealing liquid, and propylene leakage. Despite repeated maintenance and replacement of mechanical seals, the problem persisted, causing significant losses in propylene, increased maintenance costs, and risks to stable production. Through detailed analysis and targeted improvements, the issue was effectively resolved.
**First, Basic Situation:**
The E-GA301 pump is a vertical high-speed GSB pump manufactured by the 11th Institute of the Aerospace Industry. It consists of a motor, gear box, pump, forced lubrication system, and a sealing liquid circulation system. The gear box increases the speed from 2950 rpm at the input shaft to 10275 rpm at the output shaft. The input shaft uses a lip seal, while the output shaft employs a mechanical seal (model 60C). The lower mechanical seal is lubricated and cooled via the forced lubrication system.
The pump features two sets of mechanical seals in series: the upper seal (model 60B) and the lower seal (model 60A). The space between them is filled with sealing oil, which is circulated through a dedicated system to lubricate and cool the seals. Each mechanical seal includes components such as the rotating ring, stationary ring, push ring, spring, spring seat, auxiliary seal, and retaining ring. The stationary ring is made of graphite (M106K), while the rotating rings vary in material—YG6 carbide for 60A and 60C, and a stainless steel base with a 1.5mm carbide layer for 60B.
**Second, Mechanical Seal Leakage Analysis:**
There is a cavity between the speed-increasing device and the pump body where lubricating and sealing oils tend to accumulate. This leads to oil leakage into the oil cup through the drain hole. Initially, oil was added every 3–5 days, but after 1–2 months, the mechanical seal began to deteriorate, resulting in sealing oil leakage and darkened oil in the cup and tank. Propylene started entering the sealing chamber, increasing vibration and eventually causing a large-scale leak, triggering a high-pressure alarm and pump shutdown.
Upon disassembly, it was found that the 60B seal had damaged surfaces, with black graphite powder adhered to the rotating ring. The 60A seal showed more severe wear, while 60C had only minor marks.
**Third, Reform Program:**
**1. Reform of 60A Static Ring and Auxiliary Seal:**
The original static ring was impregnated resin graphite, which performed well under light hydrocarbon conditions. However, during operation, wear particles could accumulate in the auxiliary seal, especially in the PTFE wedge ring, leading to indentation or interference with the compensation ring. To address this, a high-strength, heat-resistant, and friction-friendly impregnated graphite ring was selected. The auxiliary seal was replaced with a Viton O-ring and a rectangular Teflon washer. The washer was designed to fit tightly around the seal body, preventing solid particles from entering the sealing surface. Additionally, the O-ring was mounted with an axial floating structure, allowing direct spring force application to the compensation ring. This improved the seal’s reliability and cushioning effect during abnormal operations.
**2. Reform of 60B Rotating Ring:**
Although the specific pressure on the 60B seal face was low, the high rotational speed and zero pressure differential on both sides led to excessive wear. Therefore, the moving ring was redesigned with a new material and structure, without changing the end face pressure. After the reform, the pump operated smoothly since November 2001, with over two years of continuous, trouble-free operation and no leaks. The economic benefits of the reform were also significant.
**Fourth, Conclusion:**
By addressing the root causes of mechanical seal leakage in the high-speed pump, a comprehensive reform of all three seals was carried out. This significantly extended the maintenance cycle, eliminated safety hazards, and solved the leakage problem effectively. The approach provides a useful reference for similar equipment facing leakage challenges under comparable operating conditions.
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