Corrosion of silicon carbide machine seals in pure water
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Hello everyone. Recently, our company has encountered a situation related to an application in which both the moving ring and the stationary ring are made of silicon carbide, the seal uses a single-spring rubber bellows, and the sealing ring for the stationary ring is a nitrile rubber O-ring. The application takes place in pure water with low conductivity. On the surface of the moving ring, powdery white spots first appear; after removing the powder, dot-like pits appear. Is it electrostatic corrosion?
@Wang Wei 2: Please ask Teacher Wang to answer: handshake
I need an answer; please, some expert can give an explanation
Hello, I took a look. Photos of the mechanical seal show surface damage to the silicon carbide layer beneath the white scale. It is likely that during long-term operation in a sealed environment with water as the medium, relative motion and friction generate high temperatures; water accumulates at the defects on the sealing surface, and when exposed to these high temperatures, the water evaporates, leaving scale attached to the surface. Since there is still a water film on the dynamic and static sealing surfaces, coupled with the presence of scale, this creates conditions for electrochemical corrosion. Such fantasies arise after long-term operation. This is my opinion; it’s not necessarily correct.
What is the medium temperature? Consider excessive end-face temperature, resulting in vaporization of the medium
The temperature of the medium shall not exceed 60°C; the medium itself is pure water, and it undergoes a continuous cycle of conductivity reduction using resin.
Moderator, we have encountered similar problems in our facilities: this issue occurs with bellows sealings in 12 or 32 plus 62 systems. The rings are made of silicon carbide paired with another silicon carbide component, and the reason for this phenomenon is unclear
Teacher Wang, thank you for your reply. I would like to ask you a few more questions: 1. The system is a closed-loop system; the temperature of the fluid never exceeds 60°C. The fluid used is pure water or distilled water that we drink, and it goes through resin treatment for deionization during the circulation process. Is the scale still that severe? 2. When both the rotating ring and the stationary ring are made of silicon carbide, this phenomenon occurs only on the rotating ring; is it not present on the stationary ring? 3. When the materials of the rotating ring and the stationary ring are changed to tungsten carbide, this phenomenon does not occur under the same medium and operating time (6 months). This phenomenon occurs only when the material of the mechanical seal is silicon carbide.
1. If water is in circulation within the system, scaling does not occur; however, between the dynamic and static seals, frictional movement generates high temperatures temporarily, and over time this leads to scaling when the water is exposed to such conditions. 2. Regarding the issue of this only being present on the moving ring, a detailed analysis based on the actual product is required. 3. This is related to the material of the stationary and rotating rings.
For MG series seals, has the working dimension of the seal been measured? Is it the same as that indicated on the seal sample? An excessive compression amount can also lead to high loads between the end faces, causing overheating of those end faces.