Mechanical seal for kettle Installation, operation, maintenance and fault analysis of

Mechanical seals have been widely used in petrochemical and other industrial sectors due to their advantages such as good sealing performance and long service life. However, accidents often occur if mechanical seals are improperly installed, operated and maintained. At that time, mechanical seals were not as popular as packing seals. Because mechanical seals are more precise components, correct installation procedures should be followed, Strict operation specifications and reasonable maintenance system are powerful measures to ensure the performance and normal operation of mechanical seals

Mechanical seal installation

1、 Preparations and precautions before installation

1. Take out the mechanical seal to be installed from the packaging box and put it on a clean plane, protect the sealing surface, and sort out all labels and certificates for inspection;

2. Check the model, specification and material certificate of the mechanical seal, the number of parts, the matching of dynamic and static rings to see if they meet the requirements of the drawing, and whether there are identification marks of the manufacturer on the parts;

3. Check the surface quality of each part, especially the sealing end faces of the moving and stationary rings for bruises and scratches. If damaged, repair or replace them

4. Check the axial runout, radial runout, relevant perpendicularity, concentricity, surface roughness, fit size and requirements for pump coupling of the host machine with mechanical seal according to the technical requirements

1. Axial runout: It is required to be no more than 0.1mm, generally between 0.025 and 0.1mm. The axial runout is too large, which makes the specific pressure of the mechanical seal spring unstable, causing excessive wear or leakage of the seal end face. The seal is damaged due to the vibration of the shaft, which is more obvious in the graphite ring. 2. In addition, the excessive axial runout will also cause local corrosion at the contact between the mechanical seal and the shaft (or shaft sleeve) Erosion or wear. In this regard, polytetrafluoroethylene seal rings are more affected because they are less elastic than rubber seal rings. Therefore, the axial runout is changed from the original requirement of ± 0.5mm to not more than 0.1mm, which can reduce the harm caused by excessive axial runout. On the other hand, if the axial runout is too small, if it is less than 0.025mm, it will have a negative impact on the bearing

Start operation

1、 Preparation before startup

1. Comprehensively check whether the mechanical seal and auxiliary devices as well as pipelines, valves, instruments, etc. are installed completely. The pipelines must be cleaned to prevent blocking, which is particularly important for new installations. Because impurities often enter the seal from the pipeline, affecting the sealing performance, the whole system should be emptied to prevent the formation of air plugs at the height of the seal chamber, leading to dry friction operation

2. Static pressure test shall be conducted before startup, and the test pressure shall be the same as the working pressure; Check the mechanical seal itself and relevant sealing points and joints for leakage. If there is leakage, try to deal with it

3. Turn according to the rotation direction of the pump and deliver it for use after meeting the requirements

2、 Start operation

1. Before the main engine is started, the sealing chamber shall be kept full of liquid or sealed medium. If there is a separate auxiliary sealing system, it shall be started first, and the cooling water system shall also start to flow (it shall be stopped finally when the engine is stopped); For conveying solidified medium or medium with high viscosity, the sealing chamber shall be heated with steam to melt the medium. Before starting, the turning gear must be turned to prevent sudden start from causing soft ring rupture

2. Before normal use, carry out constant cutting operation to observe whether the temperature rise of the sealing part is normal. If there is light leakage, run in for a period of time to make the end face fit more evenly until the leakage gradually decreases to normal. If the leakage does not decrease after 1~3 hours of operation, stop the machine for inspection

3. Pressure rise and temperature rise operation: the mechanical seal that has passed the normal pressure operation test shall be operated in a timely manner with the same pressure rise and temperature rise as the operating conditions. The pressure rise and temperature rise can be carried out separately. The process of pressure rise shall be slow, and attention shall be paid to the possible changes in the pressure rise (or temperature rise) process, such as whether the machine parts are collided, whether the end face is detached, whether the friction heating is too fast, and whether the anti rotation pin is detached or damaged, Whether the pressure is stable (the pressure fluctuation is required to be no more than ± 0.1MPa) and whether there is leakage at the sealing ring and sealing face. If everything is normal, it can be put into production.

Causes and treatment measures of mechanical seal failure

1、 Causes of mechanical seal failure

Mechanical seal failure is mainly caused by the following aspects:

1. Failure caused by poor mechanical seal;

2. Faults caused by host problems;

3. Failure caused by improper selection and application of mechanical seal;

4. Faults caused by improper installation and operation and poor management;

5. Faults caused by poor auxiliary devices or insufficient understanding of auxiliary devices

Mechanical seal failures include: wear of end face, hot cracking of seal ring, deformation, corrosion, loss of elasticity or fracture of elastic spring, damage of auxiliary seal ring, etc