Maintaining Steam Traps
steam traps waste and adversely affect product quality. Therefore, a maintenance program
for steam traps is a good investment.
Gary W. Mohr, UE Systems,
Most plant and
facilities professionals with steam systems in their care have asked questions like the
following: What are the signs of a malfunctioning steam trap? How often should traps
be inspected? What inspection techniques are available? What testing instruments should we
use? How do we start a steam trap maintenance program? What kind of training
resources are required?
Steam trap basics
Basically all steam traps have the
same functions. They allow condensate and non-condensable gases to escape while
holding steam in a device where a thermal or heat transfer process occurs. A regulator
controls the input side of the process and the steam, after releasing energy to the
process, condenses and reverts back to its liquid state. The purpose of the steam
trap is to retain steam in the heating element and to release the non-condensable gases
and condensate. The principal design consideration is to balance the condensing rate
and the import rate of the control device on the input side with the exiting condensate.
Ultrasonic detectors translate
ultrasonic emissions into sounds the human ear can hear, allowing technicians to detect
failing steam traps before they fail completely.
Stephen Banyacski president of Nicholson
Steam traps (Walden, NY) emphasizes the need to choose the appropriate steam trap.
"Properly sized traps relieve the condensate, react quickly to changes in load, and
trap the steam while allowing air and other non-condensable gases to escape," he
Finding malfunctioning traps
As with any mechanical device, a
steam trap can malfunction. "If
the steam trap fails closed," the device that should be draining will flood and the heat transfer process
will stop, and whatever product is being produced ... will no longer be up to the required
quality standards. If the trap fails open, there will be a waste of energy, steam
will not be completely consumed or condensed in the exchanger and steam will blow
through." Banyacski notes that a plume of steam escaping from the condensate receiver
or from some part of the condensate return system signals such a condition.
He adds that it is difficult to
determine whether a steam trap has failed just partially open, indicating a slow leak and
a developing failure. "Such a ... failure could persist for quite
some time without any outward sign. Therefore, a maintenance person should make
periodic surveys of the installed base of steam traps. Banyacski emphasizes that
steam blowing through a trap indicates that the trap needs to be repaired or replaced.
Trap inspection methods
misapplied steam trap (too small, the wrong design) will malfunction.
Ultrasonics, infrared 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
There are enough variables in the system - back pressure, 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 be used along with
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%.
frequency of inspections, process components of equipment, as well as
drip main stream 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.
Creating a Maintenance program
A steam system
maintenance program should provide total system training and include a reference manual
written for plant personnel so they will have a reliable guide for the future.
Ideally, the program will also include videotapes to illustrate troubleshooting techniques
On-site workshops should also include a plant audit and that personnel be shown how to collect data
for their own predictive maintenance program. Correcting the problems and
energy losses documented during the initial audit will pay for the costs of The
consultants (instructors) within months.
For a maintenance management program to work it is
imperative to identify and document all components in both the steam system and the
condensate return system. Steam systems are often a maze of lines going in
every direction. Most have been modified over the years and maintenance personnel probably
have no idea how steam is distributed throughout the plant.
Therefore ... when
blueprints exist they should be studied to get a full understanding of the steam system,
the distribution of piping, and the placement of critical equipment such as valves and
traps. If there are no drawings, new ones should be
created. Blueprints should depict the
entire system, including boilers, main distribution lines, and the heat transfer system.
These plans need not be full isometric presentations. Flow diagrams are
sufficient for 90% of a facility's operation. In addition, locations of heat
exchangers, steam traps and valves should be included for future surveys.
All devices should be tagged with identifying numbers which are then recorded on
a plant map.
Finally, the most
important aspect of a preventive maintenance program is an information system that allows
analysis and extrapolation. Ideally, a software system should
accommodate steam traps, control valves, safety valves, check valves, and so forth.
This information should be stored for reporting and, more importantly, for analysis."
Why go through the hard work of setting up a
maintenance program for steam traps? A steam
trap maintenance management program can pay for itself in less than a year. And the
savings will multiply as the years pass.