While designing and operating a heat transfer fluid system an important maintenance aspect sometimes gets low priority – monitoring the conditions of the heat transfer fluid in service. Suitable corrective actions taken at the right time may not only extend the in-service life of the heat transfer fluid, but also reduce the risk of unwanted equipment failures or unexpected shutdowns. Insurance contracts or local regulations may also stipulate regular fluid monitoring. Finally, regular sampling histories allow for comparisons that can help detect problems before they occur or escalate. Therefore, including a fluid monitoring scheme using the appropriate equipment for safe and reliable sampling should be part of any design and operating manual for heat transfer systems.
Sample ports should be designed to enable safe collection of representative samples. The port should be connected to a line containing flowing liquid and should allow purging of the line before taking the sample. Cooling the sample to temperature below 60°C (140°F) may be necessary to prevent thermal burns, but also to prevent unwanted evaporation of potential moisture and low boiling components in the sample. After sampling, the bottle should be sealed promptly, and should be safe and appropriate to handle and ship. Some suppliers of heat transfer fluids may provide sample kits containing suitable bottles and instructions for sample taking and shipping.
A regular schedule for sampling the heat transfer fluid should be established right from the beginning. For a new system, the first sample, which will function as a baseline, should be taken within 24 hours of the plant start-up. A second sample should be collected after approximately six months of operation, and annually thereafter. Additional samples should be analysed after system cleaning, fluid changeout or major changes in operating conditions (e.g. different fluid used or higher operating temperatures). Also, in case of system operation issues, the heat transfer fluid should be analysed to determine whether the fluid properties have changed in a manner to contribute to these issues, or exclude the fluid from the list of potential root causes. What properties should be evaluated to determine the status of the in-service fluid?
Excess moisture in high temperature systems may lead to interruptions of the fluid flow due to its low boiling point and hence cause evaporating (or flashing) at pump inlet, creating cavitation. In cooling systems, the moisture could lower the efficiency of heat transfer due to the formation of ice crystals on chiller surfaces. Typical sources for moisture can be residues from system construction and testing, contamination with process water in-leakage or intake of humidity via expansion tanks open to atmosphere.....
Written by Matthias Schopf, Eastman, Germany.
Read the article online at: https://www.hydrocarbonengineering.com/special-reports/30082018/monitor-to-maintain/