The 13 most common ways to damage mechanical seals and preventive measures (2)

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This post was last edited by Junming Machinery on 2023-8-14 14:45 07 Pressure mechanical seal overpressure will cause gravity contact at the outer diameter of the dynamic and static ring sealing surfaces, and gradually decrease inward until there is almost no visible contact. High pressure can cause chipping (chips) on the outer diameter edge of the primary seal ring. Figure 9: Examples of Overpressure Damage How to Prevent or Repair Reduce seal chamber pressure as much as possible. To reduce distortion caused by high seal chamber pressures, changes in seal design or materials may be necessary. 08 Solid Particles Solid particles (abrasive) + wrong seal material = seal wear much faster than expected. The damage caused by solid particles to the sealing surface has the following signs:: 1) The sealing surface is severely worn 2) The worn groove has the appearance of a “gramophone record” 3) The sealing surface may have edges that are chipped or rounded Figure 10: Examples of Solids Damage How to Prevent or Repair Before application to services containing solids, the characteristics of the fluid, including solids content, solids size, and solids type, must be determined. Choose appropriate materials of construction, or seals specifically designed for applications containing solid particles. Next, look at flushing options. Modify the flushing arrangement so that the flushing fluid flushes on the sealing surface, increase the flushing speed, and increase the seal chamber pressure by installing a throat bushing. 09 Misalignment Misalignment is the most common cause of damage to mechanical seals. Misalignment can be caused by pipe strain, deflection during hard starts, shaft runout, and countless other conditions. Misalignment can put excessive stress on mechanical seal components, causing them to not function properly, wear prematurely, and eventually fail. Figure 11: Examples of Misalignment Damage How to Prevent or Repair Be sure to follow proper installation guidelines and use tools such as laser alignment to ensure accurate pump rotor alignment. However, the pump may become misaligned during operation, even if it was perfectly aligned during installation. Equipment displacement caused by thermal expansion and dynamic load changes can cause the pump to misalign. 10 Vibration Vibration can cause problems with almost any type of equipment, from pumps to fans. How to tell if vibration is the culprit of mechanical seal failure? Figure 12: Examples of Vibration Damage Just like misalignment, vibration can come from many sources: 1) Imbalance 2) Misalignment 3) Run away from BEP 4) Pump cavitation 5) Entrained air 6) Improper piping design How to prevent or repair Proper equipment installation is critical to solving vibration problems. The pump base should be properly installed and grouted to prevent soft foundation. The pump shaft should also be accurately aligned with the motor shaft such as by laser. OEM spare parts should be used. Vibration problems can occur when components exceed the dimensions and tolerances specified in the design. Finally, proper piping technology (according to ANSI/HI standards) can have a significant impact on minimizing vibration. 11Incorrect installation. Mechanical seals are easily damaged during installation. Here are some common installation errors that occur with mechanical seals: 1) The end face of the installed stuffing box is not perpendicular to the shaft 2) The coupling is installed on the shaft by hammering 3) Insufficient or improper lubrication used to install (slide) the mechanical seal onto the shaft 4) The installation steps described in the mechanical seal manual are not followed Figure 13: Examples of damage caused by not following all installation steps. How to prevent or repair mechanical seals. Care is required when handling and installing. Here are some tips during installation.: 1) Do not remove the packaging of the mechanical seal before it is officially installed. 2) Wash your hands before installation! Even tiny particles or oil on the skin may cause wear and leakage on the sealing mating surface during operation. 3) Do not touch the sealing mating surface with your hands. 4) Place a layer of clean wrapping paper on the workbench to prevent contamination of the mechanical seal. 5) Before installing the mechanical seal to the pump. Before installing a new seal on a worn pump, clean the sealing surface with a clean soft cloth and an approved solvent. 6) Use the manufacturer's recommended lubricant according to the installation instructions. 12. Before installing and/or replacing the mechanical seal, inspect and ensure that the pump (the parts that mate with the seal) are in good condition. A scratched shaft or bushing can damage the mechanical seal before it can operate. ； Scored shafts and bushings can damage O-rings when installing (sliding in) the mechanical seal. Bent pump shafts, old and out-of-spec bearings, and out-of-balance impellers can cause vibration, contact friction between dynamic and stationary parts inside the pump, bearing damage, etc., all of which can shorten the life of a mechanical seal. Figure 14: How to prevent or repair a severely scratched bushing All used parts should be thoroughly inspected before reuse to ensure they meet design dimensions and tolerance requirements. If the size of the used part exceeds the design requirements, it should be replaced with a new one. 13Operational Errors There is no doubt that accidents happen. Whether starting the pump improperly or running the pump with a valve closed, these incidents can have costly consequences. Improper starting of the pump can cause the motor to trip, the shaft to twist, or even abnormal movement of the mechanical seal. Dry starting the pump means running into all the problems seen in method #1 and eventually damaging the mechanical seal. Operating the system with the suction valve closed (dry running) or the outlet valve closed (deadhead) can cause premature seal failure. How to prevent or repair Ensure that all operating personnel are trained in the proper procedures for starting up the pump unit and operating the system. Summary To reduce seal failures, look at all stages of equipment application - how to select seals, installation practices, all the way through operation. Seal failures are often repeatable. If the seals functioned in the same manner, the same failure rates would be expected.