Abstract: This paper briefly introduces the damage situation of the outlet check valve of the high-pressure liquid ammonia pump in urea plant and presents the solution. Keywords: liquid ammonia check valve leakage I. Overview P101A / B high-pressure liquid ammonia pump is the key equipment urea plant is the 20th century, 80's imported from the United States SUNDSTRAND HMP-5112-type high-speed centrifugal pump, the working status of a A preparation, the export design pressure of 27MPa, high-speed shaft speed of 20445R / min; the outlet check valve is a single valve swing type high pressure self-sealing check valve, the structure and basic parameters shown in Table 1, the main role in P101A / B automatically shut down when the pump to prevent high pressure medium backflow caused by pump impeller reversal, play the role of protection P101 pump. After more than 10 years of operation, two valves seriously leak, and P101A pump outlet check valve leakage, the two failure if not resolved in time, will seriously affect the safety of urea plant, so its disassembly repair, Because of the pump outlet check valve both inside and outside the drain, the following on the valve as an example to introduce. Second, the maintenance of the valve problems (1) the valve long-term due to the valve core is in working condition, so that the valve shaft wear hole into an oval, resulting in valve sinking, as shown in Figure 1, frequently open the valve seat seal Under the surface of serious damage, resulting in serious leakage, as shown in Figure 2. (2) The valve due to manufacturing defects and media corrosion and other reasons, the outer part of the valve body cracks appeared, leading to liquid ammonia leakage, as shown in Figure 3. Third, the maintenance program As the valve for the welding valve, subject to the inspection time, can not be offline repair. Decided to use on-site repair method to repair. Repair for leakage and leakage in two aspects at the same time: 1. Leakage repair program (1) with a small electric grinder manually seal the valve body seal surface cracks, while the surface coloring test until all the cracks and defects eliminated. (2) use A402 electrode (chrome 26 nickel 21 stainless steel electrode), with hot spot welding repair valve body sealing surface grinding Department. (3) Using a small electric mill manual grinding welding, so that the height of the valve body surface flush with the basic. (4) Production of inner ring grinding ring, shown in Figure 4. (5) with the grinding ring made by hand to seal the surface grinding, grinding the inner diameter: 160.7mm. (6) According to the inner diameter of the ring after the seal ring, as shown in Figure 5. 2. Internal leakage repair program (1) with a portable grinder seat sealing surface (see Figure 2). Make sure it returns to a circle in the presence of cemented carbide. (2) Find the original center of the shaft center hole through the four-card positioning on the lathe, meanwhile reaming the hole, as shown in Figure 6. (3) car system two rings (1Gr18Ni9Ti) set in the reaming. To ensure that the same in the center of the case, with a reasonable fit with the shaft, and spot welding fixed, as shown in Figure 7. (4) car through the shaft (1Gr13). (5) welded with tungsten carbide D547 molybdenum valve head, according to the valve seat after grinding repair valve head sealing surface. (6) After trial with Hongdan test to ensure its sealing. IV Conclusion In accordance with the above program on the high pressure liquid ammonia pump P101 outlet check valve for overhaul, a good solution to the valve leakage problem, after more than a year of operation, the use of good results, the maintenance of the same type of plant high pressure only Valve and other self-sealing valve has some reference.
