In the tank car industry, flat gaskets play a central role as the main barrier between the valve and the tank car itself, stopping any leaks of gas or liquid. They also keep out any harmful substances and are key to moving hazardous materials safely and effectively. Each tank car needs a variety of flat gaskets in different sizes to suit different conditions. Flat gaskets are not a new invention, but they are essential in stopping non-accidental releases (NARs) which often occur from derailments and can damage the environment and be harmful to people.
Creating a Quality Product
When producing flat gaskets for flange applications in the chemical transportation industry, an expert parts supplier will oversee every step of the process from compound formulation, to cutting the gasket and everything in between. They will combine superior raw materials with quality control measures in the mixing and calendaring processes for outstanding and consistent product performance. Chemical transportation customers should talk to their components supplier to ensure they are using approved materials that meet exact production specifications and industry standards.
Give It Up for Graphite
Effective sealing of flanges in applications containing extreme heat, hazardous chemicals or when low creep properties are required, is extremely challenging. Conventional rubber-bonded gasket materials cannot seal effectively in high temperatures. Graphite gaskets, particularly those made using high purity, expanded graphite, offer the optimum solution for the most extreme environments. During the production process, pure, ground graphite powder flakes are expanded into flexible, soft graphite, which is then formed into foil. When combined with a metal layer, graphite flat gaskets can withstand large temperature ranges, retain performance with changing loads, adapt to flange unevenness and maintain low creep properties in high temperature applications.
When an oxidant, such as oxygen, is present in an application, graphite gaskets are subject to oxidation at higher temperatures. This leads to a loss of graphite mass, thereby decreasing the sealing performance of the gasket. However, innovative technology can be used to make graphite more resistant to oxidation, which improves the long-term sealing performance of the gaskets in high-temperature applications, eliminating the need for more frequent maintenance.
Passing the Test
Flat gasket manufacturers perform tests on their materials to ensure they meet and exceed industry standards like the International Organization for Standardization (ISO) and the German Institute for Standardization Registration Association (DIN). However, not all parts suppliers will test their materials against their competitors. Trelleborg Sealing Solutions performs numerous tests on gasket materials, ranging from chemical compatibility to analysis verifying the mechanical strength and sealing capability of the materials. These include:
- Two-part temperature testing: First, the gasket is compressed at room temperature between two surfaces to measure the adaptability of the gasket during installation. In the second part of the test, the temperature is increased at a specified speed, while the surface pressure from the first step is held constant so the system is not allowed to “relax” because of gasket compression. The test significantly exceeds real-life operating conditions where the load on the gasket would be lower, thereby proving gasket performance.
- Oxidation testing: To provide reliable sealing, graphite gaskets must be resistant to oxidation. Since graphite purity is not a sufficient indicator of oxidation resistance, it is necessary to test oxidation properties. For example, graphite foil used in Trelleborg’s FlatSealTM HMF30 series gaskets has undergone testing to ensure reliable, long-term performance in high-temperature applications.
- Quality testing: Tests are performed to verify seals meet the quality requirements defined in EN 14772. This standard specifies that weight loss of graphite, due to oxidation, must be under four percent per hour over four hours at 1238 °F/670 °C. Trelleborg’s advanced proprietary technology further enhances the oxidation resistance of the graphite foil, reducing mass loss to under three percent per hour.
- Fujifilm testing: Used to examine how different gasket designs perform when surface pressure is applied. The expanded metal insert optimizes the distribution of surface pressure increasing sealing performance.
When needed, customer-specific tests are conducted to ensure optimum gasket performance in the specific application
Simplifying Flange Maintenance
When it is time to remove and replace a flat gasket, proper flange cleaning can be a challenge, particularly with tongue-and-groove flange connections. Leakage problems, attributed to incomplete removal of old gasket residue, are not unusual. In applications with conventional graphite gaskets, cleaning processes are time consuming requiring manual removal of all gasket residue. A supplier’s proprietary technology can simplify cleaning processes and protect sealing surfaces, optimizing maintenance operations and minimizing the risk of damage to the flange.
Conclusion
When it comes to safety in the tank car industry, high-quality flat gaskets provide a necessary barrier to prevent leaks and damage. Utilizing the strength and resilience of graphite, particularly high-purity, expanded graphite, flat gaskets offer a low-maintenance solution in even the most extreme conditions. However, a seal’s performance is not just about the materials used but also about the rigorous testing conducted by the manufacturer. Shippers, repair shops, valve equipment manufacturers and fleet management companies should choose a reliable sealing partner that invests in proprietary technology to enhance flat gaskets’ performance and adherence to the highest safety standards.
Brett Hopkins is Technical Manager Chemical Transportation, Trelleborg Sealing Solutions
