ANALYSIS OF MECHANICAL SEAL FAILURE

Failure analysis is a very effective method to solve seal leakage and damage. This method is simple and easy, and it is easy to find the focus of the problem and solve it in a targeted manner. Among the failure examples of mechanical seals, the proportion caused by friction pairs and auxiliary seal rings has the highest proportion. The following are the most typical examples for your reference.

Uneven end

A flat crystal was used to detect the sealing surface under a sodium light lamp, which the flatness error was 2.7um. The local plane error of the sealing surface is caused by poor grinding and polishing. In this case, the leakage of the seal is serious.

Adhesive wear

Due to the overheating and overload of the seal, fragments of soft materials are attached to the surface of hard materials, and agglomerated particles are formed very frequently, and then collapse, resulting in strong wear.

Thermal deformation

There is a symmetrical discontinuous bright band on the sealing surface, which is caused by thermal deformation. Sometimes this state cannot be observed, only when the end face is coated with red powder, and it can be found by gently grinding with the flat surface. This situation is mainly due to irregular cooling, which causes thermal stress deformation of the sealing surface.

Hot crack

There are three types of fine cracks on the sealing surface: radial crack, radial crack with blisters or scars and surface cracks.

Ceramic or cemented carbide ring sealing surfaces are particularly prone to such damage. This crack, like the cutting blade scraping the sealing surface of the carbon graphite ring or other materials, will quickly disappear the soft ring boss of the grinding. The most common causes of thermal cracking are lack of proper lubrication and cooling measures, vaporization and evaporation of the liquid film on the sealing surface, and high PV values.

Deflection

It is characterized by uneven wear of the sealing surface, which causes the sealing surface to be convex or concave. Under the condition of varying pressure of the medium, the performance of the sealing is unstable. It can increase the friction torque of the sealing surface and generate a large amount of frictional heat. The reasons for the deflection of the end surface are that the working pressure exceeds the allowable value, or the hydraulic balance is not selected properly.

Rubber O-ring extrusion damage

O-type rubber ring becomes soft due to pressure and erosion of the medium, which is squeezed into a small gap. And the seal ring breaks or flakes due to stress concentration.

Rubber O-ring permanent deformation

The rubber O-ring becomes square due to high temperature, excessive compression, or overload.

Rubber O-ring aging

Rubber aging is shown to be hard, which is usually due to long storage period, exposure to sunlight, ozone or heat aging. Then it hardens and loses its elasticity.

Any type of mechanical seal has its advantages, but it inevitably has some limitations. We need to grasp its principle, consider from various aspects, comprehensively analyze the cause of the failure, and then analyze it separately for different equipment and different working conditions, and select the best matching plan to solve the on-site failure of the mechanical seal. Follow us to learn more.