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Can The Sign Of Wear And Tear On The Sealing Surface Help Analyze The Failure?
Apr 24, 2018

The signs of wear and tear on the sealing surface will help analyze the failure.

1. Widened wear: This indicates that the pump has experienced serious misalignment.

The reasons are: (1) bearing damage;

(2) Shaft vibration or shaft deformation;

(3) axis bending;

(4) pump cavitation vibration;

(5) Coupling is not centered;

(6) Severe deformation of the pipe;

(7) Sealed static ring tilt.

2. Narrowing of the wear scar: The wear scar is narrower than the minimum width of the two sealing surfaces. This indicates that the sealing overpressure, pressure or temperature causes the sealing surface to deform.

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3, no wear marks:

The sealing surface is not bonded. Check whether the compensation mechanism such as spring is slippery or obstructed.

4, the sealing surface without wear marks but bright spots.

Warp on the sealing surface will show bright spots without wear marks. The pressure is too high, the gland nut is not screwed or clamped, or the rough surface of the pump can create bright spots. When using two screw caps, their rigidity is not enough, and deformation is also a cause of bright spots.

The appearance of this symptom indicates that the seal may leak when driving.

5, the sealing surface has a trim:

This is due to the fact that the sealing surface is too open and breaks when closed. Flash evaporation (gasification) is the more common reason for the separation of the sealing surfaces, especially when there is condensate in the hot water system or in the fluid, the water expands into vapor from the liquid, and the sealing surfaces can be separated. (The cold medium vaporization will also cause the same)

Sealed metal parts, such as springs, fixing screws, transmission parts and metal sleeves, may become the root cause of seal failure. Corrosion of springs subjected to alternating stress is the most important issue because metal will rapidly corrode under stress. Stainless steel springs are vulnerable to stress corrosion of chlorides, and there are many chlorides in the world. Therefore, there are foreign departments. It is recommended not to use stainless steel springs. It is recommended to use springs with high corrosion resistance of Hastelloy. In addition, spring fatigue is another cause of failure due to improper assembly.

The fixing screws used for mechanical seals should not be made of hardened materials. The heat treatment will reduce the corrosion resistance of the metal, and the softer fixing screws without heat treatment can be fastened to the shaft.

Vibration, deflection, and misalignment can cause wear of the transmission. If the sealing surface sticks during start-up, the transmission member will bend or even be damaged, and the heat generated by friction will often aggravate corrosion.

The wear scar on the outer surface of the metal sleeve may be caused by solid particles entering the sleeve from the sealing side, which interferes with the sealing follow-up capability. It may also be skewed and caused by different reasons.

Metals need to change color during temperature rise. Stainless steel should pay attention to the following colors when used.

Light yellow - temperature is 700~800°F (about 370~432°C)

Brown color ---- temperature is 900~1000°F (about 486~540°C)

Blue - temperature is 1100°F (about 590°C)

Black—The temperature is 1200°F (about 648°C)