Decarbonisation Technology November 2025 Issue

Decarbonisation through innovation

Explore some of the latest available sustainable technologies

If the gas-phase sulphur is trapped in the bearing cavities and there is a drop in the temperature, the sulphur will solidify. This causes the bearing to shaft seizure, locking the disc in one position. When this situation occurs, the end user must apply a heat gun of some sort to unlock the valve. This procedure is not the best practice when operating a modern process facility. Most TOV manufacturers offer a welded-on steam jacket (see Figure 1 ) to use the steam’s latent heat to deliver heat to the bearing area. While this is good design practice, human error has negated this benefit when plant personnel simply turn off the steam to the jacket or unhook the connections to perform maintenance and fail to reconnect the steam to the fittings. In addition, every turnaround of a processing plant can be dangerous if media is still in the bearing cavity and that cavity does not have the right temperature. Other chemical applications, such as butadiene and styrene, have the same issues as described above, except that when these chemicals become trapped and dormant, it causes a phase change and popcorn, or polymerise, resulting in seizing of the bearings. Additional situations also contribute to fouling, such as simple pipe scale. Furthermore, during the start-up phase in new constructions, when the pipes have not been properly flushed, debris can migrate into the bearing cavities. Improper designs can also add to bearing failures once in service. If a certain design has not taken into account the thermal coefficients of both the bearing material and tolerances accompanied by the cross-sectional thickness, then the bearing could lock up during quick-changing thermal conditions. TOV manufacturers have been keenly aware of this potential problem, and in the early 1990s some manufacturers introduced the bearing protection ring, which has now become the industry standard (see Figure 2 ). However, this feature has proven not to be the solution. A single ring of die-form graphoil installed into

Zwick’s Sealed Bearing minimises emissions and protects the bearing cavity

Bearing failures are the highest root cause of failure in triple offset butterfly valves (TOV). This issue is directly attributed to the need to have metal bearings with very tight tolerances when accepting the shaft diameter. Properly designed TOVs are metal-to-metal torque-seated type valves. Therefore, very little shaft deflection can be tolerated to correctly torque the seal ring into the seat. Additionally, correctly designed TOVs should have the bearings located as close as possible to the centre line of the disc, which helps to deliver a rigid support of the shaft when torqueing into the seat. small. However, in the world of hundreds of petrochemical, power, and other applications, there are many potential problems with bearing failures. Many of these problematic situations are obvious, such as sulphur tail gas and acid gas services within refineries and gas processing plants. Sulphur in the gas state will have a phase change to a solid in temperatures below 115°C. In clean services, such as air or water, the chances of the bearings fouling are

Figure 1 TRI-CON valve with steam jacket