Top 8 Reasons for Mechanical Seal Failure and How to Prevent Them

Mechanical seals are critical components of pumps, responsible for maintaining a fluid-tight seal between the rotating shaft and the stationary pump housing. However, these seals can fail due to various factors, leading to leakage, reduced pump efficiency, and costly downtime. In this article, we will discuss the top reasons for mechanical seal failure in pumps and how to prevent them.

1-Improper Seal Selection

Choosing the wrong mechanical seal can cause it to fail. Consider the following factors that can contribute to seal failure:

• Chemical compatibility: All seal components, such as the seal faces and O-rings, must be compatible not only with the process fluid being pumped, but also with non-process fluids used for cleaning, steam, acid, and caustic flushes, etc.

• Physical degradation: Using soft seal faces on abrasive liquids will not last. Shear-sensitive liquids, like chocolate, can break down and leave behind solids (such as cocoa powder) and force out liquids (like oil).

• Sedimentation: Some processes involve large fluctuations in temperature, viscosity, pressure, speed, etc. These constantly changing conditions increase the risk of sedimentation in or near the sealing gaps between the seal faces. Liquids that tend to solidify (crystallize) quickly can also form scales on the seal faces. As these deposits accumulate on the seal faces, the sealing gap opens further, causing leakage. Abrasive particles can also damage the seal faces.

• Temperature: Elastomers can swell with changes in temperature. Lapped hard faces are especially sensitive to temperature changes.

• Viscosity: Viscous products may restrict the free movement of the seal. Some liquids become more viscous with agitation (like cream turning into butter).

To avoid these failures, it's essential to select the right mechanical seal and ensure that it's compatible with the process fluid and operating conditions. Check chemical compatibility tables to ensure that the seal material is compatible with the pumped fluid. Frequent pump wear or early pump failure may indicate a chemical attack on the seals.

Mechanical seal failure (technoseal.gr)

2-Improper installation/ handling

Improper installation can cause damage to the mechanical seal. The seal is designed to move with the shaft, and some lateral and vertical movement is normal. However, if the seal is installed incorrectly, it can lead to excessive play and damaging forces that can cause the seal springs to snap or the faces to wear. It is important to follow proper installation procedures to avoid these issues.

To prevent human errors that may cause seal failures, it is important to follow proper start-up procedures and avoid installation mistakes such as hammering couplings onto the shaft. Handling seals made of brittle materials like Carbon or Silicon Carbide requires caution, as even minor mishandling can lead to chipping of the sensitive seal faces. Even small amounts of dirt, oil, or fingerprints can affect the alignment of the lapped faces. When a pump is taken offline, it should be thoroughly cleaned to prevent solidification of product on the seals, which can cause the seal faces to lock together and become damaged during startup. Proper handling of the seals and cleaning of the pump with CIP/COP can help prevent these issues.

3-Dry Running/ Lack of Lubrication:

One of the key factors in preventing mechanical seal failure is ensuring that the seal faces are properly lubricated. Without lubrication, heat can build up and cause the seals to fail. There are several scenarios in which lack of lubrication can occur, such as when a pump is running dry and there is no liquid present to lubricate the seal faces. Additionally, when a liquid is pumped at high temperatures or close to its vapor pressure, it may not provide sufficient lubrication. In double seal pumps, failure can occur if there is no buffer liquid or seal plan in place. To prevent these types of failures, it's important to implement proper mechanical seal flush plans and ensure that the flush media used is compatible with the liquid being pumped. By taking these steps, many instances of mechanical seal failure due to lack of lubrication can be avoided. 

4-Vibration/ Alignment

Vibration and misalignment can lead to various issues, such as seal failure due to the following reasons:

·      Pump and drive misalignment, bent or warped shafts, worn or loose bearings, or unbalanced rotating components can cause vibration.

·      Running the pump beyond its catalog limits can also cause vibration, leading to seal face chipping and seal opening.

·      Seal face opening can allow contaminants to penetrate between the faces, resulting in premature wear.

5-Cavitation

Cavitation occurs when a pump operates at the wrong parts of the performance curve, leading to accelerated part wear, including the seal. Operating the pump at the wrong parts of the performance curve can generate high amounts of vibration and noise, which can damage the seal faces. Ensure that the pump is operated within its performance curve to prevent cavitation and seal failure.

6-Excess Heat

High fluid temperatures can cause elastomers in mechanical seals to swell or melt, restricting their effectiveness and leading to leakage. This can be caused by prolonged recirculation of the fluid or by the process itself. To prevent excess heat, monitor the process temperature and ensure that the pump is operated within its temperature limits. Installing a temperature sensor or a thermal switch can help detect high temperatures and allow the operator to take corrective action before damage occurs.

7-Shaft Movement due to Bearing Wear:

If the shaft has too much lateral movement due to bearing wear, it can cause the seal to absorb these forces, leading to premature wear and failure. Regular inspection and maintenance of the shaft and bearings can help prevent excessive lateral movement and wear.

8-Worn Shaft or Wear

Certain elastomers can increase shaft wear, and if the shaft has worn down over time, the seal may not fit tightly, enabling fluid to leak. Inspect the shaft for wear and replace it if necessary, before installing a new mechanical seal.

Worn Shaft

In conclusion, mechanical seal failure is often a combination of a variety of the above factors. It can be prevented by understanding the causes and taking necessary precautions.

Regular inspection and maintenance of the pump and its components, monitoring fluid temperature, and ensuring proper installation and clearance can help prevent mechanical seal failure and keep your pump operating efficiently.

To gain a better understanding of how to diagnose mechanical seal failures, you may refer to the downloadable guides on self-diagnosing mechanical seal failures provided in the following link:

https://drive.google.com/file/d/1HPMGLTSA78qW20-mkclXHgH1pfdrLij9/view?usp=sharing

and

https://drive.google.com/file/d/1fl1lhMQ-YoLv_1MjLXlMfMnfWDk4IavI/view?usp=sharing

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