Resources
September 21, 2018

STEAM TRAP STATION TESTING METHODS – TEMPERATURE AND HIGH FREQUENCY ULTRASOUND

Steam System Optimization

Testing Steam Trap Stations by Temperature and High Frequency Ultrasound

Kelly Paffel

Inveno Engineering LLC

Tampa, FL

www.invenoeng.com

My name is Kelly Paffel, I’m technical manager for Inveno Engineering, LLC, located in Tampa, Florida. Our firm is focused on steam and condensate systems. And today I want to talk about Steam Trap Station Testing Methods. The two methods I want to talk about is the temperature method and the high frequency ultrasound method.
One of the questions we ask is, why test steam trap stations? Number one is optimization. Proper end user performance. A steam trap blowing through a heat exchanger, or steam coil, or a reactor jacket will reduce the heat transfer efficiency by 11%. The other thing is that we want to ensure 100% steam quality going to the end users. So, without proper steam trap stations on our steam distribution system, we will not remove the condensate that can form in the steam line. Therefore, the condensate degrades our steam quality. The end user requires a hundred percent steam quality, and it’s up to us to maintain that steam quality.
The next is system reliability. Eliminate component failure. Failed steam traps in the open position or even the closed position can cause severe water hammer, and it does all the time. Which we can have major failures of steam or condensate lines in our system. The other thing is piping failures. Condensate that’s not removed from our steam distribution system because of steam trap station issues will have entrainment into the vapor and can erode elbows and cause erosion.
The next thing is reduce emissions. A steam trap blowing through will cost us tons of CO2, tons of NOX, and tons of SO2. For every one pound of steam that’s blowing through a steam trap, that’s one pound of more steam I have to produce at the boiler, which is lost.
Yes, finally, save energy. But the question is, which has higher energy loss, 250 psi of steam or 25 psi of steam? Most of the time, the answer is 25 psi of steam because the 25 psi low pressure systems discharge into a condensate tank that’s vented to atmosphere. The 250 psi steam systems should be going into cascade system. Therefore, the thermal energy is not lost, only the mechanical energy. So a plant must decide where to focus their attention.
Results from testing the steam trap station. Performance or lack of performance. Steam trap is isolated or not in operation. Priority number one, test result. It’s a major safety issue. Go out all the time on steam distribution systems, and they have their steam traps blocked out, isolated. These are critical steam traps. Steam traps are put there for a reason to removed condensate that will form in steam distribution system. If the steam trap is not in operation, condensate can accumulate and cause severe water hammer. So these are always priority number one.
Blowing steam or completely failed. Priority number two result. Yes, energy is an item, but more so, our condensate systems are not designed for steam traps blowing steam into the condensate return line. This steam going in there and trying to expand 1600 times will increase velocities in our condensate line above 4500 P per minute and cause again, severe water hammer. So these are priority number two. Priority number three is the leakage steam during operation. The other ones are, process is not in operation. Of course, we want all of them to have proper operation.
The question comes up, when or how often should the plant test the steam trap stations. Every three months till the failure rate during any steam trap station assessment is three percent or lower. Today, we should not have any steam trap survey or assessment to have a failure rate above three percent. After the failure rate is lower than three percent, every six months.
Next is prioritize testing your steam trap stations. Number one, largest potential for creating issues. So, if I have a reactor, I want proper drainage. That would consider to be a priority number one.
Methods for testing steam trap stations. Visual, temperature, ultrasound. People always ask me, “What’s the best method for testing steam traps?” Using all three. Visual’s very powerful. I walk in plants all the time and say, “That steam trap is bad.” People say, “You’re just looking at it, how do you know it’s bad?” “Because it’s upside down.” The other thing is I’ll be talking about is temperature and ultrasound is the other two methods.
Temperature measurement. The relationship between steam pressure and temperature. It’s very helpful understanding many different operating conditions of the steam components. Number one, I come in, I’m going to do a steam trap station assessment. I want to know if the process is in operation. Next thing I want to know is the steam trap station in operation? The other thing I need to know is what the operating steam pressure is, because that’s part of my calculations for energy loss, making sure I have the correct orifice in the steam trap for the correct pressure.
The other thing is the condensate system pressure. So, sizing a steam trap you need to know P1, steam pressure inlet, and two, condensate. P2 is condensate. So, temperature gives me a lot of information. Infrared temperature measuring is very quick and a versatile tool. Requires training and ensures success like any tool that you use in a steam or condensate system. Training is essential so people totally understand how to use the instrument to its fullest capability.
Diagnostic tools have positive features and negative. The thing is, is that we always want to know the positive of course, but we also need to know the negatives. One of the negatives with temperature, we’re taking a surface temperature. Corrosion, paint and insulation all have a negative effect of us taking that temperature measurement with non-contact measurement, which is infrared.
Temperature measurement non-contact, oh important to understand the negative attributes to ensure an accurate temperature measurement in which I just talked about, clean surfaces, insulation, etc. Temperature measurement devices must be an integral part of your steam trap testing program. So, you must have all the tools when you go out to do a steam trap assessment.
Temperature measurement. Estimate the steam pressure by using a temperature testing device inlet to the process. So, up here at T1 up here, so we gain the knowledge of the steam going into the process. Also, gain knowledge of the condensate pressures present in the system, down in here and here in the system. Estimate the condensate line pressures, which I already talked about. So, temperature gives me a couple different, very critical pieces of information.
The next is example using the temperature method. When I’m using the temperature method here, I take a measurement up here. It’s 299 degrees Fahrenheit. The steam trap body down here should be closed to the inlet. Yes, there’s a slight pressure drop due to heat transfer, but we should be close. So, when I go up and testing the process, steam trap operation, I want to take an inlet to the process, 299. Then I want to test the steam test body, 293, 285. Yeah, steam trap is working good. This is true for 96% of the steam process application. There are some process applications where we have a tremendous amount of pressure drop through it and that would have an effect on the temperature at the steam trap. But 96% of the applications, we can use this method.
Low temperature measurement of the steam trap. When I come up to test the steam trap, one of the things I want to make sure is, if I’m up at 210 degrees. But if the steam trap body’s not but 210 degrees or higher, then the steam trap is not in operation. Then I need to proceed into root cause analysis. Understand if undersized steam trap, is there a fouled strainer, is there a high back pressure in a condensate line, etc. So, I come up, the steam trap has to be 210 degrees or higher before I proceed to the high proficiency ultrasonic test.
Surface temperature can be very useful in evaluating various potential conditions. Using it alone for testing steam trap stations will have a low accuracy for testing steam trap performance. People always ask me, “Can I test steam traps by using temperature?” It’s very, very, very difficult. Different statements are made, I’ve heard them throughout my career. That if a high temperature differential across the steam trap station, the steam trap is good operational condition. There is no or very low temperature differential, then the steam trap is blowing through. These statements are not correct, and I’ll kind of explain why I am saying that.
Here’s an example of a temperature measurement performance. So, here I have 299 degrees, here at the inlet to the steam trap, and at the outlet I have 214 degrees. So, I have a high temperature differential across the steam trap, and by this statement, a high differential temperature across the steam trap, the steam trap is good. In essence, the steam trap is blowing through. Why? Because down here the condensate line is running at zero psig. As the steam passes through the steam trap here, the steam has to get its temperature down to 212 degrees. Now, yes there’ll be a small percentage of super heat generated by the pressure drop across the steam trap, but condensate passing through there will zap the super heat out of the steam and bring it close to saturated conditions, or I put down 214 degrees. But the steam trap is blowing through.
The thing is that the dynamics of the system is always based down here on the condensate return line. So, another example here is 299 degrees going in here, and I have 284 at the outlet of the steam trap, and there’s no differential, which as the statement says, if there’s low differential across the steam trap, the steam trap is blowing through. Well, incorrect because the condensate line’s operating under pressure, so the steam coming through here, flash or blow through steam, is only going to come down to whatever pressure’s in this condensate line. So, the dynamics of the system really bases what we have for inlet and outlet pressures. So, it’s again, very difficult to analyze steam trap performance using temperature.
One more example, and this is a low pressure operating system. Let’s say low pressure down here. Let’s say 30 PSI or something like that. I’ve got 220 degrees, I have 212, and I’m going into an atmospheric system. So this low temperature differential, we don’t know if the steam trap’s blowing through or if it’s good. And that’s why we use high frequency ultrasound as our other test method. But again, never go out and do a steam trap station assessment without having temperature with you.
Temperature measurement procedures. Process inlet, we just talked about. Steam body temperature on a steam line drip legs trap must be 210 degrees or higher before proceeding into high frequency ultrasound test. Representative temperature, you want to scan six, ten inches up and down the pipe to get a reading, average reading of the temperature. Because again, it varies because of rust and paint, and process fluid dropping in on the piping. So, scan, just don’t take one spot. And the other thing is, is that temperature measurement, always make sure you understand target area. A low end infrared unit will have a very, very large target area and the higher cost units will have a much lower target area.
And the other thing is, is that testing with temperature must be part of your SOP and I’m big on SOPs, so your SOP for testing steam traps should be, I would say at least 50 pages in length. It must be detailed to ensure accurate testing of stream trap stations. If you don’t have an SOP, how do we know that people are testing the steam traps correctly? You know, it’s a big question. So I’m a big believer that everybody follow an SOP when they’re doing steam trap station assessment.
Next, I want to talk about steam trap ultrasonic comparison method. So one of the things using high frequency ultrasound, it’s always been a question, you know you’re going out testing the steam trap, where do I set the sensitivity? Well if I set the sensitivity a unit, then it’s not volume of sensitivity. If I set the sensitivity too high, all the steam traps are going to test fail. Why? Because I can pick up a leak on a one time standard ohm minus three with using high frequency ultrasound. Or I turn the sensitivity all the way down, it’s too low, then all the steam traps are going to test good. So, where do I set the sensitivity. There’s people say, “Oh, you set the sensitivity here for inverted buckets, you set it for swollen thermostatic.” Oh, that’s all questionable.
So, you must do what we call the comparison method because every steam trap is going to have some different dynamics to it, and the different dynamics, we must set up what we call baseline information. Now, the comparison method was developed by an engineer out of Minneapolis St. Paul many years ago. It proved tremendously successful when we applied it and on steam trap management programs and cross it with root cause analysis, we found accuracy levels up above 98.5% accuracy using the comparison method.
So, the comparison method, basically what we’re looking at is upstream, we call test point number one. Downstream, point number two, and point number three, downstream of the condensate discharge orifice in the steam trap. By sitting up these benchmarks and adjusting the sensitivity, what we’re doing is blocking out any competing ultrasound that might be occurring in the system. Therefore, we can go up and do an accurate test of the steam trap performance. So, if I didn’t have the benchmarks, I go up with one standard sensitivity setting, then I could be picking some background or competing ultrasound up and throw my readings off.
The method allows the steam trap station assessor to establish a base reading to filter out any competing ultrasound, which we just talked about. That can be generated upstream or even downstream. Without using a comparison method of testing, is very difficult to assess the steam trap performance because a technician will not know where to set the sensitivity setting. Again, there can be competing ultrasound in comparison method is just getting that competing ultrasound, baseline out of our actual reading or testing of the steam trap performance.
The ultrasonic unit must be a 25 kilohertz and unfortunately this says 40. We scratch that and it should be 25. At 25 kHz, we’ve found that, that gives us the highest clarity of a steam or condensate passing through the orifice of a steam trap. To activate a ultrasonic unit, pull the trigger. If the instrument is within the sensitivity range the decibel (dB) indicator will blink. The decibel reading should be set to about 20 db. So, we want to go out, make sure that we’re getting a reading up here, 20 dB or higher when we’re testing the steam traps.
The set up for testing, the kHz frequency indicator must be steady and not blink, and one of the things I always find when I’m training people who are testing steam traps, is they got to be aware if this is blinking, it’s in the mode to change the kilohertz. You’re not picking up any ultrasound. So you always have to be aware of that. So once the sensitivity mode is set for 25 kilohertz, it’s set. The sensitivity dial, which is located right here, turning it clockwise increases the sensitivity. Counter clockwise decreases the sensitivity and simultaneously, the level on the headphones.
The other thing, the instrument needs to be in range for accuracy. So it gives us indication, there’ll be a blinking arrow telling us to increase sensitivity, or they’ll know there will be an arrow telling us to decrease the sensitivity. So, it’s a very handy unit to have out in the field, because it gives us a lot of information. Again, too high will give us pointing arrow and you just reduce the sensitivity to get back within range.
Now when I go out and test steam traps with a high frequency ultrasound, there are two types of operation. On/off, continuous flow. And on/off, using a high frequency ultrasound is this. So if I was taking measurements here, using high frequency ultrasound, right here, you would see a distinct deflection because you’re picking up the ultrasound, and the dial coming back on. So, again, I’ll play this again. So deflect on the meter and then, deflects on the meeting. So, the thing is that, you want to open the steam trap when you’re testing it and see that operation on the dial or the back part of the ultrasonic indicator. So it gives me that dial so I can hear it discharge and then charge back up.
The other one is the continuous flow type steam trap. Now the continuous flow is always passing condensate, but there’ll be some cycling to it. There we go up here. And just watch that indicator here. You see the cycling. So when you’re testing this steam trap here, you’ll see some cycling on your indicator at the ultrasonic beam. That’s exactly what that tells us.
Now, high frequency testing, we want to say that we should be somewhere around six to ten inches here for our first reading, and that’s an estimated distance. We can come up and take more readings upstream if we want to. The same thing downstream, six to ten inches. But we can take more readings downstream. We want at least two base points for testing the steam traps.
Now, here’s an example of test results that we did. So up here on the first test point here, we have 32 db. Down here stream, we had 34 db. Right here at the discharge of the condensate orifice in the steam trap we had 34. So, if the ultrasonic sound is equal to or less than point one or point two, the steam trap is good. So equal or less, the steam trap is good. If it’s equal or less than our base point. So, this steam trap proved to be working good.
Now proper operation here, when this steam trap discharges, here, this reading here is 34 db. Discharge as you can see is, discharge reading will go up, and then come back down. So this reading is high and it’s in discharge mode, just waiting for the steam to finish discharging and then come back to your base point readings. If it doesn’t come back it’s leaking or blowing. But cycling steam traps, you might catch it when it’s in its cycling mode, so we have to compensate for that.
Now here’s a steam trap that’s completely failed, and you say, “How do you know it’s completely failed?” Upstream reading of 25 dB, downstream reading of 32 dB, and here we have 64 db. So, has to be equal of less than these two readings, and it’s not, it’s much higher. So, this steam trap is blowing through. So by just logging in the dB ratings upstream and downstream, you can check the accuracy of your field assessors. So, when we’re doing steam trap station management programs, the sheets come back in and we look at the dB rating readings versus their test results on their sheets, so it’s a really good cross check.
Now, the continuous flow type steam traps are float and thermostatic. And we have one additional point that we have to take and that’s the air vent. So, I’m upstream and downstream, and a condensate discharge orifice, but also I have to test the air vent. Because there’s two orifices or two passages that steam can flow through a float and thermostatic steam trap. So, on float and thermostatic, we have four test points that we must take. Our two benchmarks or base points, upstream/downstream, but then we want to test the condensate outlet and the air vent. Now, just a comment in this here, the air vent has to be equal or less than T3, the condensate discharge. If it’s higher, the air vent has failed. So we want T4 to be equal or less than T3.
So, in here, we’re going to go through the test results here. Proper operation test point four, right here has to be equal or less point three, which I just talked about. Test point three, when test four is higher than test point three, the air venting mechanism here has failed. So, right here, this here is higher than T3, the air vent has failed. So, we need to check those two points when we’re using … this is only on float and thermostatic steam traps. Now, here’s a test results here. Oh excuse me, a little live here on my computer.
Steam trap leaking steam during operations. So, I want to see leaking steam. We say, if the dB at point three equals 35, we want it to be five or ten percent higher than test point two. We consider that to be leaking steam. So, if we are here, we’re five to ten percent higher, then we consider it to be leaking steam. Higher than ten percent, we consider it to be blow through steam. So if I was testing the steam trap here, my upstream here would be, go back here, up here would be 25, down here would be 32, and my discharge orifice right here would be 35, and we’d consider that to be leaking steam. As a visual indication, as you can see the leaking steam.
And last is competing ultrasound. We run into this all the time, and I get the review reports done by the steam trap companies or the steam trap assessment companies, and they say mechanical sound and I always question it. For one reason is that we take upstream here and downstream here and here, and test for it and we hear a clicking sound, is that traveled down the pipe here. If there’s a check valve sitting down here, a lot of times it’s the check valve causing the mechanical sound. People use a swing type check valve and they’re prone to have high failures. So, by going upstream and downstream, high frequency ultrasound’s very directional and you will pick it up.
Listening to a steam trap, and the other thing with high frequency ultrasound, listening to a steam trap you should be aware of some distinct sounds while testing steam traps. Condensate will crackle, and with condensate flowing through the steam trap orifice, flash occurs in the condensate orifice of the steam trap, kind of mixes and gets you a cracking sound. Steam passing through the orifice is totally a whistling sound, which is a true characteristic of steam passing through the steam trap orifice.
So one of the key things is always listen to a steam trap and tell people do it for two years. After that, you can watch the meter and take your dB ratings, but you can associate the meter readings with the sounds that are occurring into the steam trap. I always watch people and look at their meters, I can tell them exactly what they’re hearing in the steam trap.
The thing is, is that there are a lot of things that go into steam trap testing. One of the things we do have is a SOP that we’re more than willing to share with people so they can go up and do steam trap testing very successful. So, you can email me or Graham here at our email addresses and we’re more than happy to share information regarding that. The other thing is that, if there are any questions on steam or condensate, you can always contact us. This is our focus in life. We do steam system assessments, troubleshooting. We do steam balancing, steam performance, and also a key factor is we do training, to ensure any system that we put in will have great operational life and reliable.
Long term impact things we do is we do upgrades, process changes, and improve reliability and safety. The only comment I have to you is steam traps operating in pressures under 250 psi should last you at least 10 years, and I would say 15. So, anyway, this is my presentation and if you have any questions, please email me and I’ll be more than happy to discuss anything with you, or if you have questions, email me. I’m more than happy to answer your questions. Have a great day.