During a recent energy assessment in Thailand, I had the opportunity to work with a steam trap expert at a petrochemical plant. What I saw there and the methodology and techniques used in the steam trap audit prompted me to write this column. I hope you can pick up some good ideas and best practices and implement them in your plants.
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Different kinds of steam traps exist and their working principles rely on pure fundamentals of physics and thermodynamics. Knowing the trap type and understanding how it operates is imperative in testing its operating performance. The U.S. Department of Energy Steam Best Practices program advocates annual testing of all steam traps. Steam trap manufacturers and service providers estimate that 10% of steam traps fail every year. Should we care about this? Absolutely. Steam trap failures are classified generally as open and blowing; partially leaking; failed closed; and cold and plugged. Significant problems associated with these failures include energy loss, reduced operating capacity of process units, water hammer, and system reliability issues. So, the bottom line is we can’t afford to have failed steam traps in our plants!
The three main testing methods for steam traps include visual, thermography and ultrasonic. Most times, you will need a combination of these to confirm steam trap operation because a single methodology may not provide conclusive results. For instance, visual has limited applicability because most condensate return systems are closed systems.
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I have used screwdrivers and stethoscopes to listen to steam traps but that’s really old school. Nowadays, ultrasonic methodology is considered state-of-the-art steam trap testing and for good reason. With enhanced technology and sensor advances in industry, ultrasonic testing of steam traps has become very cost-effective. On my energy assessment trip in Thailand, we used an ultrasonic tester along with a visual wave editor that not only provided me the capability to hear what was happening inside the steam trap but also a visual temporal signal of that audio file. In addition, we were able to estimate the flow through the traps. Doing all this in the field and going from one trap to another was an excellent experience for me and well worth it from a learning perspective as well as providing value to the energy assessment.
Training is absolutely essential before undertaking ultrasonic inspection of steam traps. This is because it’s important to differentiate the acoustics from the traps. Certain traps (thermostatic, float and thermostatic) can have a continuous mode of operation and you must know how liquid, vapor and two-phase flow sounds through the orifice. Other traps (inverted bucket, thermodynamic or disc) will always have an on/off operation; so you should be able to hear the exact transition from on to off. Steam trap manufacturers and their service provider partners are a very good resource for undertaking steam trap audits and can provide hands-on training and understanding of steam trap operations. I highly recommend you work with your vendor to implement an ultrasonic-testing-based inspection methodology for steam traps.
Like everything else around us, steam traps have become smarter and manufacturers have incorporated intelligent sensors for continuous steam-trap monitoring. This allows plant operators to know immediately a trap’s operating status. You often can justify smart steam traps at certain locations in critical processes. Never forget that implementation of a steam trap management program can offer important benefits beyond energy savings: the reliability of operations, safety, and avoiding unplanned costly shutdowns.
As we work to make our systems efficient, our steam traps also have evolved. For instance, I came across one interesting variation of a steam trap that had heat recovery built into it. Given the industry knowledge base and expertise, I am sure technology will continue to make more efficient and robust steam traps, and our testing methodologies will ensure proper operations for years to come. For now, let’s just go and listen to them!
