Products
Zhangjiagang city sinochem mechanical seal co., LTD
Address:Zhangjiagang cityof nahuy road industrial development zone
Tel:086-0512-58670570
Fax:086-0512-58185129
Contact Person:MR
Zip Code:215636
Website:www.zhjxmf.com
E-mail:webmaster@zhjxmf.com
Technical guidance
Mechanical seal failure analysis
There are many different kinds of pumps with mechanical seal and types, but the leakage point there are five main: (l) between the shaft sleeve and shaft seal; (2) between the collar and sleeves seal; (3) between dynamic and static ring sealing; (4) the static ring and static ring sealing between; (5) the sealing cover and seal between the pump body.
A, leakage reason analysis and judgment
1. Install the static leakage test. Mechanical seal after installation and debugging good, generally must carry on the static test, observe the leakage. Such as small leakage, are dynamic or static ring ring problems; Leakage is large, it shows that dynamic and static ring friction pair between the problem. In the preliminary observation, judgment, leak leakage, on the basis of observe manual turning again, if the leakage has no obvious change static/dynamic seal has a problem; Such as leakage has obvious change when turning can be concluded that is dynamic and static friction pair problems; The axial injection, such as medium leak, ring seal problems, leakage of medium around jet or leak from the water cooling hole, more for static ring seal failure. In addition, the leakage channels can also exist, but generally speaking, there are difference between primary and secondary, as long as observe carefully, be familiar with the structure, will be able to correct judgment.
2. The test run of leakage. Pumps with mechanical seal after static test, high speed rotating centrifugal force, when working could suppress leakage of medium. Therefore, when the mechanical seal leakage test run after exclusion between shaft and end cover seal failure, largely due to the dynamic and static friction ring caused by damage from vice. Cause friction pair of seal failure factors mainly include: (l) in the operation, because of time, cavitation, pressure-out anomalies, such as large axial force, caused by the dynamic and static ring contact surface; (for installing a mechanical seal, large amount of compression of the result in friction pair face serious wear and scratches; (3) ring sealing ring too loose or too tight, spring can't adjust the amount of the axial float ring; (4) static ring ring too loose, when axial floating ring, quiet ring from static ring; (5) has a granular material in the working medium, in friction pair during operation, testing dynamic and static ring seals; (6) the design selection, seal face specific pressure on the low side or sealing material cold sex is bigger. The above phenomenon often appears in the test run, and sometimes can be eliminated by appropriate adjustments such as the static ring for, but most need to tear open outfit, replace the seal.
Due to loss of lubrication film two seal face failure
A) because of the existence of end face seal load, the lack of liquid in a sealed cavity when start the pump and dry friction;
B) medium below the saturated vapor pressure, making the end liquid film flash, loss of lubrication;
C) as a medium for easy volatile products, in the mechanical seal cooling system scale or blocked, because of the friction stir and rotating components the saturated vapor pressure of liquid to generate heat and make the medium rise, also the condition of the medium pressure is lower than the saturated vapor pressure.
Mechanical seal failure due to corrosion
A) seal pastry erosion, and even penetrate.
B) due to the tungsten carbide rings and stainless steel welding, such as use of stainless steel intergranular corrosion caused by a;
C) welded metal bellows, spring, etc on the stress and corrosion medium under the joint action of prone to rupture.
Due to the high temperature effect of mechanical seal failure
A) cracking is a heat pump, such as oil pump, oil pump, atmospheric and vacuum bottom pump such as the failure of the most common phenomenon. In the sealing surface is due to dry friction, cooling water suddenly, mixed type protein Qian reimbursement of Jin 3 pavilions lamp that provoke ji cape pavilions squid over Jia Lu visit ping squid chi broken mantis salt exhausted? BR & b) carbonized is the use of carbon graphite - graphite ring when one of the leading causes of sealing failure. Due in use, if the graphite ring once more than the allowable temperature (generally - 105 ~ 250 ℃), its surface will precipitate resin, friction surface near resin carbonized will happen, when a binder, foam will soften, increase the sealing surface leakage and seal failure;
C) auxiliary seal (e.g., fluorine rubber, ethylene propylene rubber, rubber), after more than the allowable temperature will rapidly aging, crack and harden miss. Now the use of flexible graphite has good high temperature resistance, corrosion resistance, but its resilience. And brittle crack, easy to damage during installation.
Due to the wear of the seals of seal failure
A) materials poor wear resistance and friction coefficient of the friction pair, face specific pressure (including spring pressure) is too large, etc., will shorten the service life of mechanical seal. To the commonly used material, according to the abrasion resistance of the order as follows: silicon carbide, carbon graphite, tungsten carbide, carbon graphite, ceramic, graphite, carbon spraying ceramics, carbon, carbon graphite, graphite, silicon nitride ceramics high speed steel, carbon graphite and carbide surfacing, carbon graphite.
B) containing solid particles of the medium, the sealing surface into the solid particles is a major cause of lead to make the seal failure. Solid particles into the friction pair end surface grinding agent role, make the seal intense wear and failure occurs. Reasonable clearance on sealing surface, and the balance degree of mechanical seal, liquid membrane and seal face of flash is cause face open and make the solid particles into the main reasons.
C) the balance of the mechanical seal degree beta also affects seal wear. In general, beta = 75% optimum balance degree. Beta < 75%, the wear is reduced, but increased leakage and sealing surface open the possibility of increased. For high load (high PV value) of the mechanical seal, due to large friction heat, beta, it is advisable to take commonly 65% ~ 70%, the low boiling point hydrocarbon medium etc., due to the temperature of medium gasification and sensitive, in order to reduce the influence of friction heat, beta take 80% ~ 85% for good.
Because of the installation, operation or the device itself produced by the error caused by the mechanical seal leakage
A) caused by bad installation, mechanical seal leakage. In the following aspects:
1) the dynamic and static ring contact surface is rough, when installation, damage that touch an injury;
2) the dynamic and static ring sealing ring size is wrong, damaged or was not pressure;
3) there's a foreign body in dynamic and static ring surface;
4) the dynamic and static ring v-shaped sealing ring, way or install the edge;
5) collar leakage, the seal is not installed or clamping force is not enough;
6) spring force is not uniform, single spring not vertical, spring more different length;
7) sealed cavity end face and axis vertical degree is not enough;
8) had corrosion seal activity point on the shaft sleeve.
9) equipment in operation, the reason of mechanical seal leakage mainly include:
1) pump impeller shaft to the momentum over standard, axis of periodic vibration and unstable operation, seal chamber pressure change frequently, etc all can cause periodic leak sealing;
2) the friction pair cannot damage or deformation and running-in caused leakage;
3) improper seal material selection, swelling miss;
4) spring to wrong,
5) the equipment vibration during operation is too large;
6) is formed between dynamic and static ring and shaft sleeve scale make spring lost and can't compensate the wear of sealing surface;
7) sealing ring crack etc.
In c) pump stop after a period of time to restart when leakage occurs, this is mainly because the friction pair of medium near solidification and crystallization, friction pair on the scale, corrosion, blocking and miss spring.
D) pump shaft immunity is too big.
--
Some Suggestions on
The selection of high temperature heavy oil pump with mechanical seal
For petrochemical industry, the selection of high temperature heavy oil pump with mechanical seal has always been a big problem, such as catalytic cracking slurry oil pump, oil pump, atmospheric pressure, forerunning bottom bottom pump pump, decompression bottom pump, delayed coking feed pump radiation, etc.
High temperature heavy oil pump medium has the following common features:
High temperature: be in commonly 340 ~ 400 ℃;
Medium viscosity: general kinematic viscosity under temperature (12 ~ 180) x 10-6 m/s;
Medium grain: such as catalyst, coke, sand and other impurities.
Pumps with mechanical seal for high temperature heavy oil medium. Companies are now using welded metal bellows mechanical seal. Now use better DBM, XL - 609/604/606, YH - 609 - / - 604/606 type, etc. Corrugated pipe materials using AM350, INCONEL718, hartz B, C and other stainless steel; Corrosion resistance high temperature alloy, etc., some the double-deck wave plate, the bearing pressure from 2 mpa up to 5 mpa, which are effectively solve the problem of the miss of bellows.
According to coal and coking and bellows inside and containing solid particles, etc., the solution about data have been related to specifications, such as the steam purging, friction pair with "hard in hard", flushing, etc., outside using these to a certain extent, played a good role, here no longer too much. The various methods and practical application submitted before but due to various factors effect is not ideal. In order to better improve the service life of mechanical seal, information consumption, according to various situation, suggested that the following measures should be combined using:
A) the metal corrugated pipe designed rotary type structure, rotating bellows mechanical seal has a self-cleaning centrifugal effect, it can reduce the bellows peripheral deposition and medial coking.
B) the friction pair group on the material, it is recommended to use "hard to hard" structure, generally using tungsten carbide tungsten carbide (including YG6 - YG6) of silicon carbide and tungsten carbide. Choose "hard to hard" structure, must pay attention to the following questions:
1) cooling system to guarantee, cooling water, in case the higher end, lubricating film flash and reduce the lubrication of the seals, aggravate wear;
2) during the installation process, mechanical seal to seal face pour some oil (oil or butter). In order to prevent the pump. The dry friction caused by seal face due to lack of lubrication;
3) by clean the outside of the irrigation is one of the more effective way to solve the solvent particles accumulate, but this method waste is bigger, and all kinds of medium, temperature, pressure of the pump (generally require flushing fluid pressure is higher than the lateral pressure of medium 0.07 ~ 0.12 MPa) and each are not identical, the flushing system structure is more complex, and washing facilities outside the investment and maintenance cost of consumption, can sometimes cause more harm than good, especially some small and medium-sized enterprises. So many companies abandoned in the sealing oil system, or there is no set up the system, aiming at these situations, it is recommended to use with isolation medium sealing structure, such as slurry pump, oil pump back, use double mechanical seal, between the two groups of seal face full of isolation medium (clean engine oil, etc.).
This structure can effectively extend the service life of mechanical seal, generally can reach more than 6000 ~ 8000 h. In addition, use this to consider the following two points:
(1) a set of near the impeller seal face material selection "hard to hard" structure (such as YG6 - YG6); And a set of seal face close to the mechanical seal gland can be made of leaching copper and antimony carbon - graphite of tungsten carbide and silicon carbide;
(2) to heat pump chosen isolation medium, to has the thermal decomposition temperature, high spontaneous combustion point, flash point (generally above 260 ℃), thermal oxidation stability, high temperature and evaporation losses small features.
The selection of liquid hydrocarbon pump with mechanical seal
Is a kind of low temperature liquid hydrocarbon medium liquefied gas, has a low boiling point, low viscosity, high vapor pressure. Applications under this working condition of mechanical seal, can cause a cold sealing material brittleness, atmospheric water vapor will freeze in the atmospheric side of the sealing device, friction pair end surface liquid film evaporation easily and so on. Especially when the media a slight leakage, leakage of liquid hydrocarbon in the atmosphere side vaporized immediately, take away a large amount of heat, mechanical seal temperature fell sharply, using general sealing material, such as rubber or ptfe generally brittle, lead to seal failure, leakage increase. Some enterprises to adopt double mechanical seal, one isolation chamber is set on the medium and the atmosphere end, during which pass to the sealing oil to mitigate the effects of low temperature. But this kind of complex structure and sealing liquid system. According to experience, the use of bellows mechanical seal is better, mainly displays in with metal bellows and flexible graphite instead of auxiliary seal ring, solves the sealing ring material cold short and miss and cushion problems, such as DBM, YH - 609/604/606, etc.
A) metal corrugated pipe material selection good low temperature resistance, good plasticity and toughness, -c, AM350, Carpenter20, etc.;
B) the friction pair material choose in two special cases:
1) the continuous operation of the equipment, if within the medium containing more solid particles, the use of hard "" hard (in actual YG6 - YG6) is better, general continuous operation life of more than 8000 h;
2) the intermittent operation equipment, friction pair chooses to special tungsten carbide and silicon carbide graphite.
C) due to the low temperature condition, the friction pair end surface vaporization of a great influence on mechanical seal performance, in addition to choose a suitable material, the reasonable choice face specific pressure (mainly is the amount of compression corrugated pipe, given in the general than the commonly used it is advisable to compress large amount of 15% ~ 30%), the mechanical seal components near the side 25 ℃ or so of the cooling water into the atmosphere, in order to improve friction pair lubricating environment.