Wear of the dry gas seal surface

When a dry gas seal is operating properly, its end faces do not come into contact, so end face wear should not occur. When such a phenomenon occurs, it is considered that either the rotor series quantity is excessive, or there is a break in the supply of seal air or the operating pressure is outside the specified range.

Also, whether the sealing gas is clean.

The points mentioned above are all very good; this is an opportunity to discuss them. 1. Regarding the issue of excessive rotor shaft movement, taking the dry gas seal used in our units as an example, the seal in question is a John Crane T28AT model. According to its technical specifications, the allowable range for axial displacement of the seal is 3 mm – please refer to the diagram. The alarm threshold for shaft displacement in the unit is ±0.45 mm, while the shutdown threshold is ±0.475 mm. In other words, the unit will shut down even before the seal reaches its maximum displacement of 3 mm; thus, there is no risk of the seal being damaged due to excessive movement. If the displacement temporarily exceeds 3 mm, it is likely that the bearing components of the unit will also be damaged. This is my understanding; I’m not sure if it’s correct, or if there are any other special circumstances. I would appreciate it if experts could share their insights based on their experience. 2. The most likely cause is related to the quality of the gas. The natural gas we transport contains a significant amount of condensate. If the unit is started and stopped frequently, and remains shut down for an extended period after that, the natural gas will cool down, potentially leading to the formation of condensate at the seal location. It’s advisable to use heated seal gas to purge the seal thoroughly before restarting the unit. Additionally, it’s important to check whether the composition of the gas is corrosive to the springs in the seal, or whether any impurities might get trapped in those springs. 3. Generally speaking, the operating conditions are the factor most likely to cause damage to the sealing surfaces; in addition, operational procedures must be taken into account, such as introducing isolation gas first and then the lubricating oil system. 4. What is used as the isolation gas? If it is compressed air, it is possible that the air compressor system is not properly maintained, resulting in compressed air containing water and oil that ends up on the main sealing surfaces. 5. The sealing system should be drained regularly; generally, units are equipped with drainage facilities at the sealing points, so it is necessary to check the condition of this drainage. 6. The sealing gas pipelines usually have electric heating installed to prevent condensation from forming due to temperature drops, and it is important to verify that this heating is functioning properly. In short, there are many reasons that can cause damage to the sealing surfaces, but it is usually related to the quality of the materials used. We should start by looking for causes in this area. I also ask everyone to share information about their own situations on site so that we can discuss them together. After all, replacing a damaged sealing surface is very expensive, and it’s also a hassle and time-consuming process

For high-speed pumps? The installation dimensions are very important; additionally, is it a double-end dry gas seal or a tandem dry gas seal?

A dry gas seal is not a non-contact seal either; it is in contact during shutdown!