Testing Steam Traps

ROI 3-6 Months

A steam trap, in a simple definition, is an automatic valve which will vent non-condensables and condensate from a piece of steam consuming equipment and stop the loss of live steam as it enters the steam trap. Steam traps started to appear in use about 1900 and replaced the prior device which was typically a pinched piece of tubing or a cracked valve adjusted by a pipefitter. As you can imagine, this approach was neither efficient, effective, nor cost effective. Steam trap development started with float or bucket operated valves and then evolved into many other types.

Service, and therefore service life, on a steam trap can become demanding since it is the interface device which separates the steam side from the condensate return side of a steam system. Pressure and temperatures can be high, which when combined with condensate, flashes as it enters and discharges to the return system. All steam traps fail so the question is not “if” but “when”. Typically traps operating in the 100-150 psig range, if properly sized and selected, will last 5-7 years - results will vary. Imagine a facility with 100 steam traps which has been in operation for many years. If the average service life of all traps is say 5 years, then we can expect failures to be about 20% per year or 20 bad traps per year.  If the average life is 2 years, then 50% per year will fail and 10 years average life would forecast 10 failures per year.

Why then so much attention on a steam trap? A bit of math might help. Many traps operate 24/7 which works out to 720 hours in a 30 day month and 8,760 hours per year. If a failed trap blows $1.00 per hour of live steam, then it is costing you $720 per month and $8,760 per year.  If you have an installed base of 50 traps, the cost would be $438,000 which is more than enough to justify the manpower and equipment with a handsome return on investment.

A properly operating steam trap should be hot and quiet. By hot we mean the inlet trap temperature should be within 25-50 degrees of the expected temperature based on the steam pressure to the trap. As an example, if the inlet pressure to the trap is 100 psig with a saturation temperature of 338 degrees F (consult a steam table), the expected inlet temperature would be about 315-290 degrees F. The range is due to condensate cooling, the type of trap being tested and temperature measurement equipment used. The quiet is a measurement using a sound or vibration device to “listen” when the trap is open or closed. A trap showing continuous noise is blowing through and a trap failed closed will have no sound or vibration signature.

It helps to have some pressure/temperature points handy, so long ago I memorized the following which has been a big help over the years –

  • Steam at 0 psig is 212° F
  • Steam at 25 psig is 250° F
  • Steam at 50 psig is 298° F
  • Steam at 100 psig is 338° F
  • Steam at 150 psig is 366° F
  • Steam at 200 psig is 388° F

For steam table see –

http://www.engineeringtoolbox.com/saturated-steam-properties-d_273.html

Three primary techniques have evolved to test traps and each can be used with a degree of success depending on the equipment used and the experience of the testing inspector.

1. Visual Inspection

In a visual inspection the operator will check to determine if the discharge valve is functioning. This requires venting live steam to atmosphere and can pose safety issues. Because it opens the closed portion of the system it is not a 100% reliable test. Visual inspection is important because a trained operator can look for potential problems in engineering and design that can lead to trap failures.  

 

2. Thermal Inspection

Another method for routine testing of traps is with contact or non-contact temperature checks. Upstream and downstream temperature checks can reveal failed open traps. But variables such as back pressure in the system can make temperature checks less accurate. Thermal inspections are useful for identifying heat loss, overloads, and pressure build-ups. Relying on thermal inspections alone doesn't capture the entire picture.

                                   

3. Ultrasonic Inspection

Ultrasonic testing uses a noise or vibration instrument to “listen” to the steam trap for proper operation. Ultrasonic testing combined with temperature scanning equipment provides a very reliable test for steam traps.                                     

 

4. Thermal Imaging Inspection

Advances in thermal imaging equipment combined with low costs have made thermal imaging a practical option for testing steam traps. The thermal image will provide an inside look at the temperature profile for a steam trap which will allow a trained operator to check for proper operation or trap failure.

Steam trap testing can be done with low cost equipment or with more sophisticated equipment and programs. The essential take away is no matter what method you choose you can count on payback periods for replacing failed steam traps in 3-6 months-tops.

For more information on steam traps and systems see our EBooks at –

http://www.control-specialties.com/products/e-book-library.html