1. Water content in standard materials
During the experiment, if the flash point reference material used contains water, the water dispersed in the oil during the heating process will vaporize and form water vapor, sometimes forming bubbles that cover the liquid surface. It affects the normal vaporization of oil products, delays the flash time, and results in higher measurement results. Under normal circumstances, flash point reference materials are directly used after dehydration treatment and sealed packaging. However, due to the general specifications of flash point reference materials being (100-250) mL, and the required amount for measurement is about (50-70) mL, it is common to encounter situations where flash point reference materials are not used up after being unpacked for measurement. If they are not properly stored at this time. The high humidity in the surrounding environment may cause the sample to contain water. It is generally believed that when the moisture content of the sample is greater than 0.05%, it must be dehydrated before conducting the flash point test.
2. Setting of pre flashing value
Before measuring the flash point, a pre flash value needs to be set. If the pre flash value is set too low, the temperature at which ignition begins will advance. During each ignition, some oil and gas will be released and consumed, causing the temperature to reach the lower explosion limit to increase, resulting in a higher measurement result. If the pre flash value is set too high, a higher concentration of oil and gas will accumulate in some parts of the oil cup at the beginning of ignition, leading to early flash and lower measurement results.
3. Control of ignition
When igniting, the size of the spherical flame, the distance from the sample liquid surface, and the residence time should be in accordance with national standards. If the diameter of the spherical flame is too large, the distance from the liquid surface is too close, and the residence time is too long, it will lead to early ignition and lower measurement results. If electric ignition is used, it is necessary to pay attention to the brightness of the ignition wire. Currently, most electric ignition closed-end flash point instruments generally have a decrease in the brightness of the igniter after a period of use, and the temperature cannot meet the usage requirements. As a result, the measurement result of the flash point is too high. Therefore, when measuring the flash point meter, if it is using gas ignition method, it is necessary to always pay attention to the size of the flame, as the instability of the gas source often directly affects the fluctuation of the flame. If it is using electric ignition method, the brightness of the igniter should be observed. If the brightness is insufficient, the metal coil on the igniter should be polished first, or it is recommended to replace the ignition coil with all platinum.
4. Requirements for the operation of closed flash point measuring instruments
According to the standard requirements, the sample in the cup should be loaded to the circular line. Excessive or insufficient loading will change the height of the space above the liquid level, thereby affecting the mixed concentration of oil vapor and air, making the measurement results inaccurate. When pouring the sample, sometimes the part above the circular line will get stained. At this time, it should be carefully wiped and attention should be paid to the absence of bubbles on the liquid surface, otherwise it will greatly affect the measurement results of the flash point. When adding samples, the test cup is first placed smoothly on the instrument, and then the sample is carefully added to the scale. In actual operation, some personnel are accustomed to pouring the sample first, and then placing the test cup with the sample on the instrument. This may cause the liquid level to shake during movement, stick to the cup wall or edge, and cause inaccurate measurement results, which is more obvious for some samples with high viscosity.
5. Atmospheric pressure
The flash point of oil is related to external pressure, and the air pressure is low. Oil is prone to volatilization, resulting in a decrease in flash point. Conversely, the flash point increases. For example, GB/r261-2008 regulations. The reference pressure measured with a flash point of 101,3kPa is used. If there is any deviation, pressure correction is required. A correction formula is provided within the range of atmospheric pressure (980104,7) kPa. Therefore, for closed IZl flash point standards that are set according to this standard, it is necessary to ensure that the ambient atmospheric pressure is within the above range during the test. At the same time, for instruments without pressure correction, an empty box pressure gauge that has been verified and qualified should also be equipped. After correction, the measurement error should be calculated by comparing it with the standard value of the closed flash point standard material.
6. Test temperature
The test temperature of the closed flash point tester mainly refers to the ambient temperature during the test and the temperature of the instrument itself (closed cup, heater). When measuring lower flash point temperatures, such as when detecting diesel and kerosene, the high or low test temperature directly affects the evaporation rate of oil vapor, which in turn affects the measured flash point value. If the test temperature is higher, the measured flash point value is lower, and if the test temperature is higher, the measured flash point value is higher.