Mechanical seal for kettle Leakage reason

Cause of mechanical seal leakage

Mechanical seal failures are mostly found after abnormal leakage, abnormal wear, abnormal torque and other phenomena. There are four reasons for mechanical seal failure: incorrect design and selection of mechanical seal; Poor mechanical seal quality; The accuracy of the machine using or installing mechanical seals cannot meet the requirements; Machine operation error.

Summary and analysis of causes of mechanical seal leakage

1. Periodic leakage

(1) The rotor axial string momentum and frequency are large, and the dynamic ring cannot be compensated in time;

(2) Periodic vibration of rotor with unstable operating pressure.

2. Frequent leakage

(1) One of the two ends of the east ring and the stationary ring is not perpendicular to the axis; Incorrect and uneven installation.

(2) The sealing ring is defective or the size is inconsistent;

(3) For some reason, the dynamic and static rings are deformed;

(4) The end face specific pressure is too small under the working pressure of the pump;

(5) The rotor shakes and vibrates excessively;

(6) The spring rotates reversely;

(7) There is dirt between the sealing surfaces, which will damage the friction surface after driving;

(8) The anti rotation pin is too long to hold against the stationary ring.

3. Large amount of leakage

(1) The stationary ring is damaged during installation;

(2) The deviation between sealing surface and axis is too large;

(3) The spring or moving ring is stuck so that the two ends cannot be stuck.

4. Sudden leakage

(1) Pump will open the end face to enter dirt;

(2) The static ring cannot be reset when the pump is empty;

(3) The pump diameter has been running for a long time, and the shaft sleeve surface is encrusted. After the sealing surface is worn, the moving ring can not be moved forward to compensate for the wear amount. The wearing surface enters the pressure liquid, pushing away force, pushing away a larger distance;

(4) When the wear amount of the friction pair exceeds the compression amount, the pressure liquid enters the friction end face and pushes it away;

(5) Local high heat of friction pair burns the seal ring;

(6) There are crystals or solid particles in the medium entering the friction surface, which makes the friction pair wear rapidly;

(7) Hard ring surface fracture quickly cuts soft ring;

(8) The pump vibrates violently, damaging the seals.

5. Leakage after shutdown

(1) The friction pair is coking, scaling or rusting, which hinders the axial sliding of the seal;

(2) The elastic element is broken before stopping.

Maintenance of mechanical seal

There are many kinds of mechanical seals with different models, but there are mainly five leakage points:

(l) Seal between shaft sleeve and shaft;

(2) Sealing between moving ring and shaft sleeve;

(3) Sealing between dynamic and static rings;

(4) Sealing between stationary ring and stationary ring seat;

(5) The seal between the seal end cover and the pump body.

Generally speaking, it is easy to find and solve the leakage between the shafts with extended shaft sleeves and between the seal end cover and the pump body, but it needs careful observation. Especially when the working medium is liquefied gas or high-pressure, toxic and harmful gas, it is relatively difficult. It is hard to distinguish and judge the remaining leakage intuitively, and the correct conclusion can be reached only by observing, analyzing and judging the leakage symptoms on the basis of long-term management and maintenance practice.

1、 Leakage cause analysis and judgment

1. Leakage during installation and static test. After the mechanical seal is installed and debugged, a static test is generally required to observe the leakage. If the leakage is small, most of them are dynamic or static ring seals; When the leakage is large, it indicates that there is a problem between the dynamic and static ring friction pairs. On the basis of preliminary observation of the leakage amount and judgment of the leakage position, manually turn the gear to observe. If there is no obvious change in the leakage amount, there is a problem with the static and dynamic ring seals; If there is obvious change in the leakage during turning, it can be concluded that there is a problem with the friction pairs of the dynamic and static rings; If the leakage medium is sprayed along the axial direction, the dynamic ring seal ring has most problems. If the leakage medium is sprayed around or leaked from the water cooling hole, the static ring seal ring is mostly invalid. In addition, leakage channels can also exist at the same time, but generally there are primary and secondary differences. As long as you observe carefully and know the structure well, you can make a correct judgment.

2. Leakage during test run. After the static test of the mechanical seal for the pump, the centrifugal force generated by high-speed rotation during operation will cause medium leakage. Therefore, the mechanical seal leakage during the test run is basically caused by the damage of the dynamic and static ring friction pairs after excluding the failure of the shaft to shaft and end cover seals. The main factors causing the failure of the friction pair seal are:

(l) During operation, large axial force is caused due to abnormal phenomena such as evacuation, cavitation, pressure holding, etc., which separates the contact surface of moving and stationary rings;

(2) When installing the mechanical seal, the compression amount is too large, resulting in serious wear and scratch on the end face of the friction pair;

(3) The dynamic ring seal ring is too tight, and the spring cannot adjust the axial floating amount of the dynamic ring;

(4) The static ring seal ring is too loose, and when the dynamic ring floats axially, the static ring disengages from the static ring seat;

(5) There is granular material in the working medium, and friction pairs are introduced during operation, and the sealing end faces of the moving and stationary rings are detected;

(6) Wrong design and type selection, low specific pressure of sealing face or large cold shrinkage of sealing material, etc. The above phenomena often occur in the test run, and sometimes can be eliminated by adjusting the stationary ring seat properly, but most of them need to be reassembled and replaced with seals.

3. Sudden leakage during normal operation. The sudden leakage of centrifugal pump during operation is seldom caused by normal wear or service life, while most are caused by large changes in working conditions or improper operation and maintenance.

(1) Evacuation, cavitation or pressure holding for a long time lead to seal damage;

(2) The actual output of the pump is too small, a large number of medium pumps circulate internally, and heat accumulates, causing medium gasification and sealing failure;

(3) The return flow is too large, causing the bottom of the container (tower, kettle, tank, pool) at the suction pipe side to rise and damage the seal;

(4) For long-term shutdown, there is no manual turning when restarting, and the sealing surface is torn by the friction pair due to adhesion;

(5) Corrosive, polymerizable and cementitious substances increase in the medium;

(6) Rapid change of ambient temperature;

(7) Frequent change or adjustment of working conditions;

(8) Sudden power failure or failure shutdown, etc. The sudden leakage of centrifugal pump during normal operation, if not found in time, will often lead to major accidents or losses, so attention must be paid and effective measures must be taken.

2、 Several Mistakes in the Maintenance of Mechanical Seals for Pumps

1. The greater the spring compression, the better the sealing effect. In fact, the spring compression is too large, which can lead to rapid wear and instant burning of the friction pair; Excessive compression makes the spring lose the ability to adjust the end face of the moving ring, leading to seal failure.

2. The tighter the dynamic ring seal diagram, the better. In fact, the moving ring seal ring is too tight and harmful. One is to intensify the wear between the seal ring and the shaft sleeve, causing premature leakage; The second is the resistance of axial adjustment and movement of the moving ring, which cannot be adjusted timely when the working conditions change frequently; Third, the spring is easily damaged due to excessive fatigue; The fourth is to deform the dynamic ring seal ring, which affects the sealing effect.

3. The tighter the stationary ring seal ring, the better. The static ring seal ring is basically in a static state, and the sealing effect will be better if it is relatively tight, but it is also harmful if it is too tight. First, it causes excessive deformation of the static ring seal and affects the sealing effect; Second, the stationary ring is mostly made of graphite, which is generally brittle and easy to be broken under excessive stress; Third, it is difficult to install and disassemble, and the stationary ring is easily damaged.

4. The tighter the impeller locknut, the better. In the leakage of mechanical seal, the leakage between shaft sleeve and shaft (leakage between shafts) is relatively common. It is generally believed that the leakage between shafts is the failure of the impeller locknut to lock. In fact, there are many factors that lead to the leakage between shafts, such as the failure and deviation of the inter shaft gasket, impurities in the inter shaft, large form and position errors at the fitting between the shaft and the shaft sleeve, damage to the contact surface, gaps between the components on the shaft, and too long screw lines on the shaft head. Excessive locking of the lock nut will only lead to premature failure of the inter axle gasket. On the contrary, lock the lock nut properly to keep the inter axle gasket always with certain compression elasticity. During operation, the lock nut will automatically lock in time to keep the inter axle gasket always in a good sealing state.

5. The new one is better than the old one. Relatively speaking, the effect of using the new mechanical seal is better than the old one, but the quality or material selection of the new mechanical seal is not appropriate, and the matching size error will affect the sealing effect; In polymerizable and permeable media, it is better not to replace the stationary ring if there is no excessive wear. Because the stationary ring is in a static state for a long time in the stationary ring seat, the polymer and impurities are deposited together, playing a better sealing role.

6. Dismantling is better than not. Once the mechanical seal leaks, it is urgent to disassemble and repair it. In fact, sometimes the seal is not damaged, and only needs to adjust the working condition or properly adjust the seal to eliminate the leakage. This can not only avoid waste, but also verify your fault judgment ability, accumulate maintenance experience and improve maintenance quality

Failure Analysis and Failure Analysis of Mechanical Seal

1。 Corrosion failure

There are many failures of mechanical seals caused by corrosion, and the common types of corrosion are as follows.

(1) Surface corrosion

Due to the erosion of corrosive media, mechanical seals will suffer from surface corrosion, and corrosion perforation can also occur in severe cases. Spring parts are more obvious. Stainless steel materials can reduce surface corrosion.

(2) Pitting corrosion

The spring sleeve often has large area pitting or regional pitting, some of which lead to perforation. Such local corrosion will not cause serious consequences for the use of the seal, but it should also be replaced during overhaul.

(3) Intergranular corrosion

The stainless steel ring seat of tungsten carbide ring is connected by copper welding. In use, the stainless steel seat is prone to intergranular corrosion. In order to overcome the influence of sensitization, the stainless steel should be subject to solution treatment.

(4) Stress corrosion cracking

Metal welded bellows, springs, etc., often break under the combined effect of stress and medium corrosion. The seal fails due to the sudden fracture of the spring, which is generally solved by increasing the spring wire diameter.

(5) Crevice corrosion

The gap corrosion occurs between the inner hole of the moving ring and the surface of the shaft sleeve, between the screw and the screw hole, and between the O-ring and the shaft sleeve due to the difference in the concentration of the medium inside and outside the gap. In addition, the gap corrosion also occurs between the ceramic insert ring and the metal ring seat. Generally, ceramic is sprayed on the surface of the shaft sleeve, and the surface of the insert ring is coated with adhesive to reduce the gap corrosion.

(6) Electrochemical corrosion

Heterogeneous metals often cause electrochemical corrosion in the medium, which loosens the inlay ring and affects the sealing. It is also generally overcome by coating adhesive at the inlay joint.

2。 Heat loss failure

(1) Hot cracking

If the sealing surface is in dry friction, cooling is interrupted suddenly, impurities enter the sealing surface, and are evacuated, radial cracks will appear on the ring surface, resulting in rapid wear of the dual ring, and the leakage of the sealing surface will increase rapidly. Hot cracking of tungsten carbide rings is common.

(2) Foaming and carbonization

If the graphite ring exceeds the allowable temperature during use, resin will precipitate on its surface, and the resin near the friction surface will be carbonized. When there is adhesive, it will foam and soften, increasing the leakage of the sealing surface and sealing failure.

(3) Aging, cracking, swelling

If the rubber continues to be used beyond the allowable temperature, it will rapidly age, crack, harden and lose its elasticity. In case of organic medium, it will swell and lose its elasticity, which will lead to seal failure.

In case of seal failure due to heat loss, the key is to reduce the friction heat as far as possible, improve the heat dissipation, and prevent the temperature at the sealing surface from changing dramatically.

3。 Wear failure

If the friction pair is made of materials with poor wear resistance, large friction coefficient, excessive end face specific pressure (including spring specific pressure), and the sealing surface enters solid particles, the sealing surface will wear too fast and cause sealing failure. The balanced mechanical seal is used to reduce the specific pressure of the end face and reduce the spring pressure properly during installation, which is beneficial to overcome the failure caused by wear. In addition, good friction pair materials can reduce wear. The materials are arranged as tungsten carbide carbon graphite, cemented carbide carbon graphite, ceramic (alumina) carbon graphite, sprayed ceramic carbon graphite, silicon oxide ceramic carbon graphite, high-speed steel carbon graphite, and hardfacing cemented carbide carbon graphite in the order of wear resistance.

4。 Fault analysis caused by installation and operation

(1) Leakage occurs during water filling or static pressure test

Due to poor installation, mechanical seal may leak during water filling or static pressure test. Poor installation includes the following aspects.

a. The contact surface of moving and stationary rings is uneven, and there are bruises and damages during installation.

b. The dynamic and static seal rings have wrong dimensions, are damaged or are not pressed tightly.

c. Foreign matters are trapped on the surface of moving and stationary rings.

d. The moving and stationary V-ring seals are installed in the opposite direction, or the opposite side is installed.

e. The set screw is not tightened, and the spring seat moves backward.

f. The shaft sleeve leaks, the seal ring is not installed or not pressed tightly enough.

g. If the leakage directivity of the shaft is rotated by hand, there are the following reasons: the spring force is uneven, the single spring is not vertical, and the length of multiple springs is different or the number is small; The seal chamber end face is not vertical enough to the shaft.

h. The static ring is pressed unevenly.

(2) Periodic leakage caused by installation, operation, etc

During operation, if the axial displacement of the pump impeller exceeds the standard, the rotating shaft has periodic vibration and the process operation is unstable, and the pressure in the seal cavity often changes, the seal will leak periodically.

(3) Regular leakage

a. The deformation of the contact end face of the moving ring and the stationary ring will cause frequent leakage. If the end face specific pressure is too large, the friction heat will lead to the thermal deformation of starting and stationary rings; The structure of sealing parts is unreasonable, and the strength is not enough to cause deformation; Residual deformation due to material processing; Unequal force on parts during installation is the main reason for deformation of seal face.

b. The leakage at the joints of the moving and stationary rings inlaid or bonded causes frequent leakage of the pump. The residual deformation, improper use of materials, unqualified interference, and deterioration of the adhesive due to unreasonable inlay process will all cause leakage at the joints.

c. The friction pair is damaged or deformed and cannot run in to cause leakage.

d. Particle impurities are trapped in the friction pair.

e. The spring pressure is too small.

f. The seal ring is incorrectly selected, and the swelling is invalid.

g. The V-ring is installed reversely.

h. The non perpendicularity error of dynamic and static ring sealing faces is too large.

i。 After the seal ring is compressed, the drive pin and anti rotation pin will press against the parts.

j. The big spring rotates in the wrong direction.

k. Shaft vibration.

l. Scale formed between the moving and stationary rings and the shaft sleeve cannot compensate for wear displacement.

m. There is groove or pit corrosion at the shaft sleeve where the seal ring is installed.

n. The end face pressure is too large, and the moving ring surface cracks.

o. The static ring has poor floatability.

p. There is a problem with the auxiliary device.

4. Sudden leakage

The pump seal will leak suddenly due to the following reasons.

(1) The strong vibration and evacuation of the pump destroyed the friction pair.

(2) The spring is broken.

(3) The anti rotation pin falls off or the drive pin breaks and loses its function.

(4) The failure of the auxiliary device causes the sudden change of the cooling and heating of the moving and stationary rings, resulting in deformation or cracks on the sealing surface.

(5) Due to the temperature change, the medium around the friction pair condenses and crystallizes, affecting the sealing.

5. Leakage occurs when the pump is stopped for a period of time before spending

Solidification and crystallization of the medium near the friction pair, and scale on the friction pair; The loss of elasticity due to corrosion and blockage of the spring may cause leakage when the pump is restarted.

What are the faults of mechanical seal? How to handle

Faults of mechanical seal and handling methods are as follows:

1、 Performance of mechanical seal failure on parts:

1. Failure of sealing end face: wear, hot cracking, deformation, damage (especially non-metallic sealing end face).

2. Failure of spring: relaxation, fracture and corrosion.

3. Failure of auxiliary seal ring: assembly failure includes falling, cracking, bumping, crimping and twisting; Non assembly failures include deformation, hardening, cracking and deterioration.

Mechanical seal failure in operation is characterized by vibration, heating, wear, and finally in the form of medium leakage.

2、 Cause Analysis and Treatment of Mechanical Seal Vibration and Heating

1. The end faces of rotating and stationary rings are rough.

2. The clearance between the moving and stationary rings and the seal chamber is too small, and the collision is caused by the vibration. Treatment method: seal the inner diameter of the cavity or reduce the outer diameter of the rotating parts to ensure a clearance of at least 0.75 mm.

3. The sealing face has poor corrosion and temperature resistance, and the friction pair is improperly matched. Treatment method: change the material of moving and stationary rings to make them resistant to temperature and corrosion.

4. Insufficient cooling or particle impurities on the end face during installation. Treatment method: coolant pipe diameter or increase hydraulic pressure.

3、 Cause Analysis and Treatment of Mechanical Seal Leakage

1. Leakage during hydrostatic test

(1) The seal face is bruised, deformed and damaged during installation.

(2) When installing the sealing end face, it is not cleaned up and contains granular impurities.

(3) The gland (the stationary stationary ring assembly is a pressure plate) is not pressed tightly because the positioning screw on the sealing face is loose or not tightened.

(4) The accuracy of machines and equipment is not enough, so that the sealing surface is not fully fitted.

(5) The seal ring of the moving and stationary rings is not compressed or the compression amount is insufficient or damaged.

(6) The V-shaped seal ring of rotating and stationary rings is installed reversely.

(7) If the shaft sleeve leaks, the shaft sleeve seal ring is not compressed or the compression amount is insufficient or damaged during assembly. Treatment method: strengthen inspection and cleaning during assembly, and assemble in strict accordance with technical requirements.

2. Periodic or paroxysmal leakage

(1) The axial displacement of rotor assembly is too large. Treatment method: adjust the thrust bearing so that the shaft displacement is not greater than 0.25mm.

(2) Periodic vibration of rotor assembly. Treatment method: find out the cause and eliminate it.

(3) The pressure in the sealing chamber often varies greatly. Treatment method: stabilize the process conditions.

3. Regular leakage

(1) Frequent leakage caused by seal face defects.

a. The spring compression (mechanical seal compression) is too small.

b. The spring compression is too large, and the graphite moving ring cracks.

c. The seal face width is too small, and the sealing effect is poor. Treatment method: seal face width and corresponding spring force.

d. The floating performance of the compensation seal ring is too poor (the seal ring is too hard or hardened for a long time or the compression amount is too small, and the clearance of the compensation seal ring is too small). Treatment method: If the clearance of the compensation seal ring is too small, compensate the clearance of the seal ring.

e. Leakage at the joint of the inserted or bonded moving and stationary rings (poor embedding process, residual deformation; uneven materials; uneven and deformed adhesives).

f. Dynamic and static rings are damaged or cracked.

g. The sealing face is severely worn, and the compensation ability disappears.

Mechanical seal flushing scheme and characteristics

The purpose of flushing is to prevent the accumulation of impurities, prevent the formation of air bags, maintain and improve lubrication, etc. When the temperature of flushing fluid is low, it also has a cooling effect. The main flushing methods are as follows:

1、 Internal flushing

1。 Positive flushing

(1) Features: The sealed medium of the working host is introduced into the sealing chamber through the pipeline from the outlet end of the pump.

(2) Application: it is used to clean fluid, p1 is slightly greater than p, when the temperature is high or there are impurities, cooler, filter, etc. can be set on the pipeline

2。 Backwash

(1) Features: The sealed medium of the working host is introduced into the sealing chamber from the outlet end of the pump, and flows back to the pump inlet through the pipeline after flushing.

(2) Application: It is used to clean the fluid, and p enters<><>

3。 Full flush

(1) Features: The sealed medium of the working host is introduced into the sealing chamber through the pipeline from the outlet end of the pump, and then flows back to the pump inlet through the pipeline after flushing.

(2) Application: The cooling effect is better than the first two. It is used to clean the fluid, and p1 is close to p inlet and p outlet.

2、 External flushing

Features: clean fluid compatible with the sealed medium in the external system is introduced to the seal chamber for flushing.

Application: The pressure of external flushing solution shall be 0.05 - 0.1 MPa higher than that of the sealed medium, which is applicable to the occasions where the medium is high temperature or solid particles.

The flow of flushing fluid shall ensure that it can take away heat, and also meet the flushing needs, so as not to produce erosion on seals. Therefore, it is necessary to control the pressure of the seal chamber and the flow rate of flushing. Generally, the flow rate of cleaning flushing fluid should be less than 5m/s; The slurry liquid containing particles must be less than 3m/s. In order to reach the above flow rate, the difference between the flushing fluid and the pressure of the sealing chamber should be<>

The orifice where the flushing fluid enters and discharges from the sealing chamber shall be set near the sealing end face and near the moving ring side. In order to prevent the graphite ring from being washed or deformed due to temperature difference due to uneven cooling, as well as the accumulation and coking of impurities, tangential introduction or multi-point flushing can be adopted.

If necessary, the flushing fluid can be hot water or steam.

Corrosion and Protection Methods of Mechanical Seals

Mechanical seals have more chances of failure, with a large proportion. The common damage forms can be divided into corrosion damage, thermal damage and mechanical damage. Due to the special structure of mechanical seals and different working environments, their corrosion forms are also diversified.

1. Metal ring corrosion

(1) Uniform surface corrosion

If the surface of the metal ring contacts the corrosive medium, but the metal itself is not corrosion resistant, surface corrosion will occur, and the phenomenon is leakage, early wear, damage, noise, etc. There are two forms of uniform corrosion on the metal surface: film forming and film free. Metal corrosion without film is very dangerous. The corrosion process is carried out at a certain speed, which is mainly caused by wrong material selection. The passive film of film-forming corrosion usually has the characteristics of protection, but the passive film on the surface of the materials used for metal sealing rings, such as stainless steel, cobalt, chromium alloy, etc., is damaged in the end face friction, and it is difficult to generate a new film under anoxic conditions, which aggravates the galvanic corrosion.

(2) Stress corrosion cracking

Under the action of corrosion and tensile stress at the same time, the metal first produces cracks in the weak area, and then develops in depth to produce cracks, which is called stress corrosion cracking. Seal rings such as hardfacing carbide, cast iron, tungsten carbide and titanium carbide are selected, which are prone to stress corrosion cracking. The seal ring cracks are generally radial divergent, which can be one or more. These cracks communicate with the whole sealing end face, accelerate the wear of the end face, and increase the leakage.

According to the concept of fracture mechanics, the stress field intensity factor K1=y of the original crack inside the material σ 1a (y-coefficient). At the beginning, due to stress σ 1 Less than critical stress σ c. A is less than the critical crack ac, so K1 is caused by the corrosion propagation of the original crack a during corrosion. When a=ac and K1=K1c after a period of time, fracture occurs. Only when the original crack a is small enough, so that K1 ＜ K1c (stress corrosion cracking), the material will not occur stress corrosion cracking. ① The existence of stress. If residual stress, rotating centrifugal force and frictional thermal stress cause metal ring stress during surfacing or processing σ 1 is greater than σ 2c, stress damage is difficult to avoid. ② Material Science. The higher the strength and hardness index of the metal seal ring material, the lower the K1c, and the longer the pores, slag inclusions, and cracks in the material, the more prone to stress corrosion cracking. Generally, K1 (stress corrosion cracking)=(1/2-1/5) K1c, and the ratio of K1 (stress corrosion cracking)/K1c decreases with the increase of material strength level. ③ Wear. The brighter the component surface, the lower the susceptibility to stress corrosion cracking. The end face wear will destroy the passive film on the metal surface, reduce the smoothness, and promote the occurrence of stress corrosion cracking. ④ Media. Stress corrosion cracking only occurs in some specific "material environment" systems. For example, "austenitic stainless steel - cl", "carbon steel - NO3". ⑤ Temperature. The higher the temperature, the faster the hydrogen diffusion, and the faster the stress corrosion cracking. The end face of the seal ring is severely rubbed. If the specific pressure of the end face is too high, the surface finish is low, the cooling is not enough, and the surface lubrication is poor, the friction heat will accelerate the stress corrosion cracking.

2. Non metallic ring corrosion

(1) The graphite ring is corroded by resin impregnated impermeable graphite ring. There are three reasons for its corrosion: first, when the end face is overheated and the temperature is>180 ℃, the impregnated resin will separate the graphite ring, which will reduce the wear resistance of the ring; Second, if the impregnated resin is not properly selected, chemical changes will occur in the medium, which will also reduce the wear resistance; Third, the impregnation depth of the resin is not enough. When the impregnation layer is removed, the wear resistance decreases. Therefore, it is necessary to select corrosion resistant impregnating resin, use high-pressure impregnation and increase the impregnation depth for the establishment of sealed cooling system.

(2) The oxidation of graphite ring In oxidizing medium, when the end face is dry rubbed or poorly cooled, the temperature of 350-400 ℃ can make the graphite ring react with oxygen, produce CO2 gas, and make the end face rough or even broken. The non-metallic ring will also break under the simultaneous action of chemical medium and stress.

(3) Corrosion of polytetrafluoroethylene (F4) sealing ring F4 filling such as glass fiber, graphite powder, metal powder, etc. to improve its temperature resistance and wear resistance. The corrosion of the filled F4 ring mainly refers to the selective corrosion, dissolution or deterioration of the filler. For example, in hydrofluoric acid, glass fiber molecules are thermally corroded, so what to fill depends on the specific situation.

3. Corrosion of auxiliary seal ring and its contact parts

(1) Corrosion of auxiliary seal ring

The corrosion resistance varies with the type of rubber. Due to the corrosion and aging of rubber, the surface of its failed rubber becomes rough and loses elasticity after corrosion, and is easy to break. The oil resistance of rubber varies with varieties. The oil resistant rubber is prone to swelling, friction, and poor floatability, leading to seal failure. Rubber and F4 have poor temperature resistance. Silicone rubber has good temperature resistance and can be used at 200 ℃.

(2) Corrosion of the contact part with the auxiliary seal ring

There is no large relative movement between the moving ring, shaft sleeve, stationary ring and stationary ring seat of the mechanical seal and the rubber or F4 auxiliary seal ring, where the liquid is relatively static, it is easy to form a dead angle, which causes special corrosion to the metal shaft sleeve, moving ring, stationary ring seat and seal body, mainly including crevice corrosion, friction corrosion and contact corrosion. The three kinds of corrosion exist at the same time and alternate, Therefore, the corrosion surface is wide and deep. Observe that the seal leakage is serious when the surface depth is 1-1.5 times the seal ring diameter and the corrosion is not less than 0.01mm.

4. Protection method

(1) Material selection

Different environments and different materials shall be selected. Both the consistency of material selection and the difference of environmental corrosion shall be taken into consideration; Different materials are selected due to different temperature, concentration and pressure; The corrosion of the same medium varies with its temperature, concentration and pressure. It is necessary to understand the corrosivity and select materials as appropriate; Different corrosion forms lead to different materials.

(2) Structural design

① Design to avoid contact with media. Internal, external, spacer and other mechanical seals are used, and the coating and protective sleeve can also isolate from the medium. ② End face design. The mosaic structure is adopted, and the end face is under compressive stress, which can avoid stress corrosion cracking. ③ Spring anti-corrosion design. It is a good method to prevent the spring from contacting with the medium structurally, such as spraying a protective layer on the outside, adding a protective sleeve, etc. The rotation is changed into a static structure. ④ Auxiliary sealing ring. As long as the gap is small enough, all materials may have crevice corrosion. The bellows has a wide contact surface with the shaft sleeve and the auxiliary seal ring is eliminated, which is a good seal.

(3) Maintenance and use

Set up sealing fluid and cooling system, replace sealing fluid and coolant frequently, and strengthen end face cooling. During maintenance and installation, it is strictly prohibited to knock the seals to prevent local phase change from providing conditions for corrosion. The seals shall be cleaned strictly before installation