The reason why petroleum product determination methods are divided into open cup method and closed cup method is mainly determined by the nature and use conditions of petroleum products.
Generally, the closed cup method is mostly used for light petroleum products with high evaporative properties, such as solvent oil, kerosene, etc. Since the measurement conditions are similar to the actual storage and use of light oil products, it can be used as a basis for fire safety indicators.
The open cup method is mostly used for lubricating oil and heavy petroleum products. Because in the open cup method, the steam formed by heating petroleum products continuously diffuses to the surrounding air, making the measured flash point higher. For most lubricating oils and heavy oils, especially when used in non-closed parts or under low temperature conditions, even a small amount of light blends will evaporate during use and will not cause fire or explosion Therefore, these products are measured by the open cup method.
In some lubricating oil specifications, there are two quality indicators: open and closed. The purpose is to check the width of the lubricating oil fraction and whether it contains light components. Some lubricating oils are used in airtight containers. During use, high temperatures are often caused by various reasons (such as overheating of equipment at high speeds or other reasons, current interruption, arcing, etc.). The lubricating oil may produce decomposition products, or from other reasons. The parts are infiltrated with lightweight components. After these components evaporate and mix with air in a closed container, there is a danger of fire and explosion. However, when the open cup method is used for measurement, the existence of such light components that are easy to evaporate may not be found, so it is stipulated that the closed cup method should be used for the measurement, such as solvent kerosene. This is entirely to adapt to the conditions of use, so that the measured flash point is similar to the actual situation in use.
