Leakage and maintenance of the check valve at the

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Leakage and maintenance of the check valve at the outlet of the high-pressure liquid ammonia pump

I. overview

the high-pressure liquid ammonia pump p101a/b is the key equipment of the urea plant. It is the hmp-5112 high-speed centrifugal pump introduced from the American Sundstrand company in the 1980s. Its working state is one open and one standby, the outlet design pressure is 27mpa, and the high-speed shaft speed is 20445r/min; Its outlet check valve is a single disc swing high-pressure self sealing check valve, which is mainly used to automatically close when p101a/b pump is reversed, prevent the pump impeller from reversing due to the backflow of high-pressure medium, and protect P101 pump. After more than ten years of operation, the two valves have serious internal leakage and the check valve at the outlet of p101a pump has external leakage. If the above two faults are not solved in time, they will seriously affect the safety production of the urea plant. Therefore, it is necessary to understand and repair them. Because the check valve at the outlet of the pump has internal and external leakage at the same time, the following is an example of this valve

II. Problems existing in the valve during maintenance

(1) due to the long-term working state of the valve core, the shaft hole of the valve core was ground into an ellipse, resulting in the sinking of the valve core, and the frequent opening seriously damaged the underside of the sealing surface of the valve seat, resulting in a serious leakage of 165 gigawatts of renewable energy installed worldwide in 2016

(2) due to manufacturing defects, medium corrosion and other reasons, the valve was manufactured with a sandwich structure. Cracks appeared in the outer sealing part of the bridge deck valve body of fiberspan brand, resulting in the leakage of liquid ammonia

III. maintenance scheme

as the valve is a welded valve, it cannot be repaired offline due to the limitation of maintenance time. Decide to use the method of on-site repair. Repair is carried out simultaneously for external leakage and internal leakage:

1 Repair plan for external leakage

(1) manually grind the cracks on the outer sealing surface of the valve body with a small electric mill, and conduct surface dye detection at the same time until the cracks are eliminated

(2) select A402 welding rod (chromium 26 nickel 21 stainless steel welding rod), and repair the grinding part of the outer sealing surface of the valve body by hot spot welding

(3) manually grind the welded joint with a small electric mill to make its height basically flush with the surface of the valve body

(4) make inner ring grinding ring

(5) grind the sealing surface manually with the manufactured grinding ring, and the inner diameter after grinding: 160.7mm

(6) make a sealing ring according to the inner diameter after grinding

2. Internal leakage repair scheme

(1) grind the sealing surface of the valve seat with a portable grinder. Ensure that it returns to circular shape in the presence of cemented carbide

(2) locate the center of the original valve core through the shaft hole with four clamps on the lathe, and ream the hole at the same time

(3) two machined rings (1gr18ni9ti) are embedded in the reaming. Ensure that it can be reasonably matched with the threading shaft and fixed by spot welding under the condition that the center is unchanged and the leaf spring is assembled in Jinan times

(4) turning threading shaft (1gr13)

(5) repair the valve head with cemented carbide d547 molybdenum electrode, and repair the sealing surface of the valve head according to the ground valve seat hole

(6) test with red lead after trial preparation to ensure its tightness

IV. conclusion

after the check valve at the outlet of high-pressure liquid ammonia pump P101 is overhauled according to the above scheme, the standard tension sample is stretched by the experimental machine at the speed specified in gb/t228 ⑵ 002 standard, and the leakage problem of the valve is well solved. After more than a year of operation, the use effect is good. This overhaul can be used as a reference for high-pressure check valves and other self sealing valves of the same type of factory

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