Mechanical seal failure caused by corrosion in high-temperature gear oil pump:
a) The sealing surface is corroded or even penetrated
b) Due to the welding between tungsten carbide rings and stainless steel seats, intergranular corrosion is prone to occur in stainless steel seats during use;
c) Welded metal bellows, springs, etc. are prone to rupture under the combined action of stress and medium corrosion
Mechanical seal failure caused by high temperature effect:
a) Hot cracking is the most common failure phenomenon of high-temperature gear oil pumps, such as slag oil pumps, refining oil pumps, and atmospheric and vacuum tower bottom pumps. Due to dry friction at the sealing surface, sudden interruption of cooling water, impurities entering the sealing surface, and evacuation, radial cracks can occur on the ring surface;
b) Graphite carbonization is one of the main reasons for seal failure when using carbon graphite rings. During use, if the graphite ring exceeds the allowable temperature (usually -105~250 ℃), resin will precipitate on its surface, and the resin near the friction surface will carbonize. When there is a binder, it will foam and soften, increasing the leakage of the sealing surface and causing seal failure;
c) Auxiliary seals (such as fluororubber, ethylene propylene rubber, and all rubber) will rapidly age, crack, harden, and lose elasticity after exceeding the allowable temperature. The flexible graphite currently used is resistant to high temperatures and corrosion, but its resilience is poor. It is also prone to brittleness and damage during installation
Sealing failure caused by wear on the sealing end face:
a) The materials used in friction pairs have poor wear resistance, high friction coefficient, and excessive end face pressure (including spring pressure), which can shorten the service life of mechanical seals. For commonly used materials, the order of wear resistance is: silicon carbide carbon graphite, hard alloy carbon graphite, ceramic ceramic carbon graphite, sprayed ceramic carbon graphite, silicon nitride ceramic carbon graphite, high-speed steel carbon graphite, and deposited hard alloy carbon graphite
b) For media containing solid particles, the entry of solid particles into the sealing surface is the main cause of seal failure. Solid particles entering the friction pair end face act as abrasives, causing severe wear and failure of the seal. The reasonable clearance of the sealing surface, the balance of the mechanical seal, and the flash evaporation of the liquid film on the sealing end face are the main reasons for the opening of the end face and the entry of solid particles
c) The balance degree β of mechanical seals also affects the wear of seals. Generally, a balance degree β of about 75% is most suitable. If β<75%, although the wear amount decreases, the leakage increases and the possibility of the sealing surface opening increases. For high load (high PV value) mechanical seals, due to the large frictional heat on the end face, β is generally recommended to be between 65% and 70%. For low boiling point hydrocarbon media, etc., due to the sensitivity of temperature to medium gasification, it is better to take β between 80% and 85% to reduce the influence of frictional heat
