Cause Analysis of Thermal Damage to Seal of Boiler Feed Pump!

In the boiler and water pump installation, the mechanical seal of the mobile equipment accounts for about 80%-85% of the whole dynamic seal. In the machine pump failure, mechanical seal failure accounts for about half of the total maintenance workload. It can be seen that the mechanical seal in the maintenance of the pump position. Because the medium transported by the pump is very different and the process conditions are different, it is very important to understand these conditions for the selection and maintenance of machine seals.


The failure of the mechanical seals of the boiler feed pump, which is caused by overheating, is for thermal damage. The common thermal damage failures of Zui include end face thermal deformation, thermal cracking, blister scars, carbonization, elastic element loss, rubber parts aging, permanent deformation, cracking and so on. Many small heat spots and isolated discoloration areas are sometimes found on the seal face, which indicates that the sealing parts have local deformation and distortion under the influence of high pressure and heat. Sometimes, there are symmetrical discontinuous bright bands on the seal face, which is mainly due to irregular cooling, which leads to the local thermal deformation of the end face. Why does the seal of boiler feed pump cause thermal damage?


1. High leakage of mechanical seal in high temperature environment


In mechanical seals under high temperature, it is often found that pits and scars appear on the surface of graphite rings. This is because when the graphite ring of the impregnated resin exceeds its permissible temperature, the resin will be carbonized and decomposed into hard particles and precipitated volatiles, forming scars, thus greatly increasing friction and causing high leakage of surface damage.


The high temperature environment may reduce the elasticity of elastic elements, resulting in the insufficient sealing force of the sealing face and the serious leakage of the sealing face. The high temperature loss of metal bellows is a common and typical failure form of this kind of mechanical seals. The effective way to avoid this kind of failure is to select reasonable bellows material and conduct proper heat treatment.


2. High temperature is an important reason for the aging of rubber seals for mechanical seals.


High temperature is an important reason for aging, cracking and permanent deformation of rubber seals. Rubber aging is characterized by hardening of rubber, strength and elasticity, and cracking in severe cases, resulting in loss of sealing performance. Overheating also causes the rubber component to decompose, or even carbonize. In high temperature fluids, rubber rings continue to be sulfurized, and Zui eventually loses its elasticity and leaks. Permanent deformation of rubber seals is usually more serious than other materials. The sealing ring is in high temperature for a long time, and it will become the same shape as groove. When the temperature is kept constant, it can also act as a seal; but when the temperature is reduced, the sealing ring will shrink quickly, forming leakage channel and producing leakage. Therefore, attention should be paid to the usage temperature of all kinds of glue and should be avoided for a long time at the limit temperature.


3. Failure of mechanical seals of boiler feedwater pumps due to overheating.


The failure caused by overheating is thermal damage. The common thermal damage failure of Zui has end face thermal deformation, thermal cracking, blister scar, carbonization, elastic element loss, rubber parts aging, permanent deformation, cracking and so on. The thermal deformation of the sealing face of the boiler feed pump has local thermal deformation and overall thermal deformation. Many small heat spots and isolated discoloration areas are sometimes found on the seal face, which indicates that the seals have local deformation and distortion under the influence of high pressure and heat, and sometimes the symmetrical discontinuous bright bands on the seal face are found. This is mainly due to the irregular cooling, which leads to the local thermal deformation of the end face. Sometimes it is found that the inner face of the sealing face is very worn, and the larger the radius, the lighter the contact marks are until it is indistinguishable. There may be chip scraping and bouncing in the inner edge of the sealing ring. When the shaft rotates, the seal leaks continuously and the shaft does not leak when it is stationary. This is because when the seal is sealed, the outside is cooled fully, and the inner friction is serious, thus the inner heat deformation is greater than the lateral thermal deformation, and the inner contact type (the positive cone angle) end face caused by the thermal deformation is formed.


4. The thermal damage caused by the abrupt interruption of dry friction and cooling of the brittle material seal ring.


The seal ring of brittle materials, such as hard alloy, engineering ceramics, carbon graphite and other brittle materials, sometimes appears radial cracks, which causes the leakage of the seal surface to increase rapidly and wear the dual parts rapidly. This is mostly due to the heat loss caused by the rapid accumulation of the friction heat of the end face because of the dry friction of the seal surface and the sudden interruption of the cooling. The damage is invalidated.