**Abstract:** This paper presents a detailed analysis of the leakage issues encountered in the outlet check valve of the high-pressure liquid ammonia pump (P101A/B) in a urea plant, along with the effective repair solutions implemented. The study highlights the challenges faced during maintenance and the practical steps taken to restore the valve’s functionality.
**Keywords:** Liquid ammonia check valve, leakage, repair, high-pressure pump, maintenance
**I. Introduction**
The high-pressure liquid ammonia pump P101A/B is a critical component in the urea production process. It is a high-speed centrifugal pump imported from SUNDSTRAND, USA, in the 1980s, designed for continuous operation under extreme conditions. With an outlet pressure of 27 MPa and a rotational speed of 20,445 RPM, this pump plays a vital role in maintaining the flow of liquid ammonia. The outlet check valve, a single-disc swing-type self-sealing valve, is essential for preventing reverse flow and protecting the impeller from damage when the pump stops. However, after over a decade of operation, two valves began to experience severe leakage, posing a significant risk to the safety and efficiency of the entire urea plant. This paper discusses the inspection, diagnosis, and successful repair of the faulty check valve.
**II. Maintenance Challenges**
Several issues were identified during the inspection of the outlet check valve:
1. **Wear and Deformation:** Due to prolonged operation, the valve core experienced excessive wear, leading to oval-shaped holes in the shaft. This caused misalignment and frequent opening, resulting in severe damage to the sealing surface and significant leakage, as shown in Figure 1 and Figure 2.
2. **Cracking and Corrosion:** Manufacturing defects combined with the corrosive nature of the liquid ammonia media led to cracks on the outer surface of the valve body. These cracks resulted in leaks, as illustrated in Figure 3, requiring immediate attention to prevent further damage.
**III. Overhaul Plan**
Given that the valve was a welded unit and could not be removed for offline repairs, an on-site repair approach was adopted. The overhaul focused on addressing both external and internal leakage issues.
**1. External Leak Repair**
- The damaged areas of the valve body were manually ground using a small electric grinder to remove all visible cracks and imperfections.
- A402 electrodes (chromium-nickel stainless steel) were used for hot spot welding to restore the sealing surface.
- After welding, the surface was carefully ground to ensure it was flush with the original level.
- A custom inner grinding ring was fabricated and used to precisely grind the inner diameter of the valve to 160.7 mm.
- A new sealing ring was then installed based on the measured dimensions, ensuring a tight fit.
**2. Internal Leak Repair**
- The seat sealing surface was re-machined using a portable grinder to restore its circular shape and hardness, incorporating cemented carbide for durability.
- The original center hole was reamed using a lathe, ensuring precise alignment of the valve components.
- Two rings made of 1Gr18Ni9Ti were installed and spot-welded in place to ensure proper fit and alignment.
- A new shaft made of 1Gr13 was machined and fitted into the system.
- The valve head was welded with tungsten carbide D547, and the sealing surface was re-machined to match the seat.
- A final leak test was conducted to confirm the effectiveness of the repair.
**IV. Conclusion**
Following the implementation of the proposed overhaul plan, the high-pressure liquid ammonia pump P101A/B was successfully restored to full operational capacity. After more than one year of continuous use, the repaired check valve has performed reliably without any signs of leakage. This case study provides valuable insights for the maintenance of similar high-pressure check valves in industrial settings, offering a practical solution for restoring functionality and enhancing safety. The methods described here can serve as a reference for other plants facing similar challenges with self-sealing valves.
Mini Loaders,Mini Pay Loader,Mini Wheel Loader,Mini Front End Loader
Shandong Yineng Heavy Industry Co.,Ltd , https://www.yinengloader.com