FAILURE ANALYSIS AND COUNTERMEASURE OF MECHANICAL SEAL OF CENTRIFUGAL PUMP

Mechanical seals are devices that prevent fluid leakage by having at least one pair of end faces perpendicular to the rotating axis, which remain stuck together and slide relative to each other under the action of fluid pressure and elasticity of the compensating mechanism in conjunction with auxiliary seals. In this paper, the common failure modes of mechanical seals are briefly introduced, the failure causes are analyzed and some basic solutions are provided.

In industry, common seals are non contacting mechanical seals, spring seals, pump seals, gland packings, and elastomer bellows seals. Any seal has the possibility of failure.

Reasons for Leaks in Mechanical Seals

There are many reasons for continuous seal leakage, which are mainly manifested as end surface problems, such as uneven deformation of end surface, cracks on end surface, etc. Excessive specific pressure, friction heat, insufficient strength and uneven force of parts during installation may cause deformation of the end face.

Fault Phenomena

At the instant of pump start-up, smoke comes out from the mechanical seal at the non-driving end with oil leakage. When the pump stops, the pressure in the pump chamber rises instantaneously, and smoke comes out during coking.

Cause Analysis

When the pump is disassembled, you can see that a lot of coke accumulates on the inner wall of the moving and static rings. High temperatures often cause coking problems and small amounts of leakage can carbide on the side of the seal close to the atmosphere. There is friction between the driving part of the moving ring and the driving sleeve. There is metal powder on the surface of the moving ring, which shows that the operation time of the seal is short and the moving ring surface is seriously worn.

Solution

Crude oil has the characteristics of high viscosity, high freezing point, high impurity content and high sulfur content. In order to prevent the spring from being stuck by crystals and impurities in crude oil, it is recommended to use static mechanical seal. When adhesive wear or abrasive wear occurs, the harder the material is, the more wear-resistant it is. In order to reduce the wear rate and the seal failure caused by wear, the end face made of silicon carbide is selected, and the auxiliary seal ring is made of fluororubber, which has the advantages of high temperature resistance, oil resistance and chemical corrosion resistance.

Reasonable flushing lines must be designed, otherwise the moving and static rings of mechanical seals will lose floatability and the spring will fail due to crystallization and particle impurities. If the pipeline is not cleaned in time, particle impurities will worn the seal and lead to rapid destruction of the mechanical seal.

Clean the flushing lines regularly to keep them clear. Before starting the pump, exhaust the gas in the pump. When dealing with the problem of mechanical seal failure and pump leakage, comprehensive consideration must be given to many factors such as installation accuracy, working conditions and assembly accuracy of the pump to solve the problems pertinently.