Steam Traps - The More You Know

What is a stream trap?

A steam trap is simply an automatic valve that permits condensate to pass while preventing steam from escaping a system. A steam trap also removes air and particulates that are not condensable from space normally occupied with steam. Did you know...

In a steam distribution system that has not been properly maintained for a period of 3 to 5 years, between 15% to 30% of the installed steam traps risk being defective, thus allowing live steam to escape into the condensate return system. In a system where there is a regularly scheduled maintenance program, the percentage of leaking traps decreases to below 5%. In a plant where the value of steam produced is $10.00 per thousand pounds, and where there is a trap that is stuck open with an orifice that is 1/8” in diameter on a 150 psig steam line, the estimated steam loss is 75.8 pounds per hour, that will ultimately result in an annual loss of $6640. Recommended inspection intervals

High pressure steam traps, more than 150 psig, ideally should be checked weekly, if not monthly. Medium pressure steam traps, from 30 to 150 psig, should be checked monthly or at least every 3 months. Low pressure steam traps, less than 30 psig, should be checked annually. Defective steam traps.

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The majority of steam traps remain stuck open when they are defective. When this condition exists, the boiler must produce excess steam in order to met the need. thus increasing the pressure of the condensate return system which can exceed the discharge capacity of the traps, which in turn can affect the quality and quantity of steam production. When a steam trap is stuck in the closed mode, condensate will take the place of steam, which reduces the temperature of the steam and increases the possibility of creating surges that could cause energy losses and equipment damage. Steam trap inspections

Inspection methods: Steam traps are tested to determine if they are functioning properly and not cold plugging or failing in an open position and allowing live steam to escape into the condensate return system. There are four basic ways to test steam traps: visual, ultrasonic (sound), thermal, and electronic.

Visual: While a defective steam trap does not generally show any visible signs of improper functioning, the inspector must open a valve downstream from the trap and look for signs of steam or condensate accumulation.

Ultrasonic: Ultrasonic leak detectors employ a transducer that detects ultrasonic frequencies (greater than 20kHz) and convert them to signals that are audible to the human ear. This permits an inspector to “hear” a steam trap while operating. Generally these transducers are so sensitive that they can detect leaks very early on in the process.

Thermal: When performing a thermal inspection of a steam trap, an operator measures the temperature at the inlet and at the outlet of the trap. A steam trap that starts leaking will allow steam to escape with condensate and will cause the temperature at the outlet to increase, and the temperature differential between inlet and outlet to decrease. (This technique can prove difficult to get accurate readings when the steam traps have common outlets.) An air locked steam trap (stuck in the closed position) will give you temperature readings lower than the temperature of steam. If the temperature at the inlet of the trap is lower, then a thermal detector can trace the line to the source of the problem.

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Thermal trends: An infrared gun with datalogging will allow an inspector to plot a trend of the purge cycle, which will indicate the proper functioning of the steam trap.

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