Steam traps: Testing with ultrasound

High energy prices and global competition dictate a need to reduce energy waste and improve system efficiencies whenever possible. Steam, as well as being one of the costliest utilities in plants, is an essential component to product quality in many processing industries. 

A major contributor to waste and inefficiency is leaks: both to atmosphere and through valves and steam traps. Improvements to the steam system may include insulating steam and condensate return lines, stopping any steam leaks, and maintaining steam traps. Experts have said that as much as 20% of steam generated at the central boiler is lost to leaking or failed steam traps.  

Ultrasound technology is used by maintenance and reliability professionals around the world and is considered to be the most versatile of any predictive maintenance technology. Typical applications include compressed air and gas leak detection, bearing inspection, motors, gearboxes, electrical inspection of energised electrical equipment, valves, and hydraulic applications. The technology can also be used for steam trap inspections.  

Testing with ultrasound

Before beginning your inspection, walk the area to identify and tag every steam trap. The tag should include a number, and information about the trap should be noted such as the manufacturer, type of steam trap, orifice size inside the trap, and the purpose of the steam trap. 

Before testing with ultrasound, it is recommended to take temperature readings with a simple spot radiometer. Not only will the temperature let the inspector know if steam is coming to the trap or not, but the temperature can be used to estimate steam pressure. If the temperature of the steam trap is cold, the inspector should check to make sure that the valves are open or if the trap has been taken out of service. If the steam trap temperature is warm/hot, then the inspector can note the inlet and outlet temperatures and proceed to test with ultrasound.  

When it comes to testing the steam traps with ultrasound, the most important item that the inspector will need to know is what type of trap is being inspected. This will determine what the steam trap should sound like once contact has been made between the steam trap and the ultrasound instrument. Steam traps will have one of the following sound characteristics: On/Off or Continuous Flow.

It is recommended that you listen to a number of traps prior to starting the inspection to determine a 'normal' sound characteristic for how the steam trap is operating under the operating conditions of your particular steam system.  

Physical contact between the steam trap and the ultrasound instrument is necessary in order to be able to 'hear' how the steam trap is performing. If using an ultrasound instrument that has frequency tuning, adjust the frequency to the recommending frequency setting of 25kHz. 

Regardless of the type of trap, the placement of the contact probe will always be at the discharge orifice of the trap, since turbulence is created on the outlet side of the steam trap when the steam trap releases condensate.

Once contact has been made, adjust the sensitivity/volume on the instrument until the sound of the trap can be heard.  

When inspecting steam traps with ultrasound, it is important to exercise patience. Make contact at the discharge orifice of the trap and wait for it to cycle. If the temperatures have been checked, and the trap has not cycled for approximately one minute, move on to the next steam trap. If the steam trap has not cycled within one minute, it may be difficult to know when the trap may cycle again, but if the temperatures are ok and there’s no indication of a plugged condition, proceed to the next steam trap to be tested.