Steam Trap Inspection and Testing Methods

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Steam Trap Inspection and Testing Methods

Steam trap is main element on all condensate piping as well as in steam plants. Inspection and testing of steam trap is vital role for normal operation of plant. This post provide some of the basic information about steam strap inspection and testing methods.

What is the general frequency of inspection of steam traps

The key to keeping your traps in good working order is periodic testing to determine if the trap is malfunctioning.

Frequency of inspection depends on condition of the line. To isolate the trap for inspection, close the inlet and outlet gate valves and open the sediment blow-off or the test valve to relieve the pressure. Inspection or repairs can be made while the trap is in the line or the trap can be removed from the line easily by loosening the unions.

Regarding frequency of inspections, process components of equipment, as well as drip mainstream traps should be checked twice a year.  Heating steam traps (in facilities that use steam for space heating) should be tested annually and instituting a reporting system to keep tabs on the location, type, size, capacity and condition of all traps in a steam system is imperative.

Why do we test steam trap?

The testing of steam traps is the only way to insure proper operation. Testing can be done by in-house personnel if you have the proper equipment and knowledge.

Most audits include a report which outlines the location, size, make, type, operating pressure, condition, and other details on every trap.

How can it be determined if a steam trap is operating properly? . . . Does it open? . . . Does it close?

The foremost method of reducing steam loss is to initiate and maintain a periodic steam trap inspection and repair process. A thorough inspection, tagging and repair process is typically the easiest method of assuring minimal amount of steam trap loss.

  • Steam trap inspection and testing can involve any of the following depending on the type of trap.
  • Review proper trap selection, sizing, and piping installation details
  • Use a test valve in the trap outlet tapping or piping to visually inspect what comes through
  • Listen to the trap using an ultrasonic device or stethoscope (a hissing   sound for steam and a gurgling sound for condensate)
  • Use instantaneous thermometers
  • Listen for opening and closing of bucket and disk traps with a stethoscope
  • Take advantage of manufacturers’ available Trap Monitoring Systems” and management software
  • Typical inspections for various applications range from every six months for steam main traps and process equipment traps to annually for heating system traps. It should also be noted that complete documentation of trap location, size, capacity, manufacturer, model number and application is essential to any steam trap maintenance program.

What are the different steam trap inspection methods?

The testing of steam traps is the only way to insure proper operation. Sound, temperature measurements and visual inspection have proven useful to maintenance personnel in checking for malfunctioning steam traps. Of the three, ultrasound is the most reliable.  Visual inspection requires an inspector to let a steam trap discharge to atmosphere. However, doing that changes the parameters of the closed system and, therefore, can be unreliable.

There are enough variables in the system – backpressure, for example – so that temperature is not the most reliable indicator either.  Portable infrared thermometers provide close estimations of pressures on valves, traps, and coil heaters.  These devices are also useful for spotting conditions such as heat loss, the need for insulation, overheating, overloads, and cooling failures.  Thus, an infrared thermometer is used along with ultrasound.

Sound Method (Acoustic)

Another way of checking steam traps is through sound analysis. The sound method is one of the most widely used methods when testing traps. Using a sound device, one can physically hear whether or not the steam trap is functioning properly. A properly functioning trap will cycle, and this can be heard. Sound measurement devices vary in sophistication from ultrasonic testing equipment to simple, hand-made steel welding rod or large screwdriver, mechanical stethoscopes, doctors stethoscope, etc.

The ideal listening device will allow users to listen to the sounds of steam trap operations while ignoring most ambient pipe sounds. This is where ultrasonic listening devices excel. Since they are sensitive to high frequency (short wave) signals, they tend to ignore most stray pipe signals. Also, they are very directional in their pick-up. For this reason, they will allow users to hear and see on meters the exact operations of steam traps.

Ultrasonic detectors usually have a stethoscope module, which contains an ultrasonic transducer attached to a metal rod that acts as a “wave guide”. The wave-guide is touched on the downstream side of a trap to determine trap condition such as mechanical movements or steam and condensate flow. Most ultrasonic detectors amplify the signals and translate them into the audible range where they are heard through headphones or seen as intensity increments on a meter. Some include frequency tuning to allow users to tune into desired trap sounds.

Traps that have failed completely open are easy to detect, but the object is to find failing traps before they fail completely.  Ultrasonic testing can do that.  In essence, using an ultrasonic instrument is like putting the inspector inside the steam trap and piping system allowing him to detect a leaking steam trap.   Ultrasonic detectors translate ultrasonic emissions into sounds the human ear can hear.

Technicians who use ultrasonic detectors on a daily basis can achieve accuracy that exceeds 98%.  The chart below shows the operating sounds of various types of traps.

Trap TypeSound – Operating ProperlySound – Failed
ThermodynamicOpening and snap-closing of discNormally fails open. Cycles in excess of 60 per minute
MechanicalCycle sound of the bucket as it opens and closesFails open – sound of steam whistling through the trap; failed closed – no sound
ThermostaticSound of periodic discharge if on medium to high load; possibly no sound if light load, throttled dischargeFailed closed – no sound

Temperature Method (Thermal)

Trap performance can be checked be making temperature measurements on the pipeline immediately upstream and downstream of the trap. A properly working trap will have a higher temperature on the steam side than on the condensate side.

Temperature varies with pressure (increase the pressure and you automatically increase the temperature) and steam charts are readily available for determining the temperature of steam at a given pressure. The pipe surface temperature will be about 90% to 95% of the steam temperature. If the pressure on both sides of the trap is known, then it is relatively easy to determine if a trap has failed using steam charts.

Several devices are available for measuring temperature. It includes pyrometry, a simple contact pyrometer, temperature sensitive crayon, heat bands (stick on temperature labels are wrapped around a trap, they change color as temperature increases), contact thermometer, non-contact infrared thermometer, heat sticks (which melt at various temperatures) and infrared viewer or camera can all be used to determine pipe temperature. Care must be taken to interpret the results of temperature measurement correctly. For example, if the pipe temperature is too low on the steam side of the trap for the known pressure then it may indicate another problem, such as a restriction in the line.

Portable infrared thermometers provide close estimations of pressures on valves, traps, and coil heaters. And these devices are also useful for spotting conditions such as heat loss, the need for insulation, overheating, overloads, and cooling failures. It is recommended that an infrared thermometer be used along with ultrasound.

Visual Method

The visual method involves visual observation of condensate discharging from the trap. Visual inspection depends on a release valve situated downstream of certain traps. An inspector opens these valves and looks to see if the trap is discharging condensate or steam.

It is perhaps the best way to check a trap’s performance. No special equipment is needed, but you should know the difference between flash steam and live steam.

Flash steam is the lazy vapor that forms when hot condensate is discharged from a steam trap to the atmosphere. The presence of flash steam is natural and does not imply waste steam or trap failure. Live steam, on the other hand, is a high temperature, high velocity discharge that causes chattering in certain trap types in excess of 60 times per minute.

This chattering noise is a good indication that the trap has failed. In many steam systems, there is a condensate collection tank, which returns the condensed water to the boiler. The tanks have pipes that vent a small amount of vapor, if flash steam is being vented then it is a good indication of failed traps.

How are steam trap tested?

The first step for systematic steam trap testing is to prepare a list of all steam traps in the plant by giving each trap a unique identification number. A trap map* is helpful for complex plants, because the maintenance worker can then locate the traps quickly. The list should also show the trap service (tracing, drip leg, etc.), pressure, and a code for the type of trap.

The second step is to make stainless steel marker traps for each trap in the list and attach them on the trap’s condensate side.

The third step is to have a separate set of colored ‘maintenance required’ tags.

Either a simple ultrasonic sound detector or a more sophisticated portable computerized steam trap tester could conduct the actual trap testing. The computerized steam trap tester would give accurate data on the status of traps (blowing, leaking, blocked, etc.) and quantify the steam loss. The data could be stored and downloaded in a personal computer for detailed analysis along the lines of the plant trap and manufacturer trap failure rates.

However, for smaller plants, an ultrasonic sound detector should suffice. Each type of trap gives a unique sound when there is leaking or blowing steam; which could easily be detected with some practice. For example, a ringing sound is made by a blowing bucket trap when the bucket hits the trap wall. A good disc trap cycles every 6 to 10 seconds and cycling faster than once per second indicates a leaking trap. A hot disc trap which does not cycle indicates that the trap has failed in an open position. The test reports need to be sent to the maintenance section so that they can carry out the necessary repairs.