Maintaining the health of the assets that make up a steam system brings benefits that are measured by cost reduction, improved product quality and decreased risk to safety. When employees undertake a project that delivers on goals like these, a fourth win is returned by default — improved reliability culture.
When steam system health is ignored, components degrade and efficiency erodes. Over time the system reaches a point where it is no longer able to deliver on its engineered purpose. The maintenance manager’s phone rings. Production needs a fix, and they need it fast. Now it is time to fight fires again.
Which scenario does an organization pursue? Should it pursue the reactive one or the calm, planned approach that sees problems before they emerge, reaps the benefits of cumulative cost savings, has impeccable safety records, and a culture of motivated and artistic employees eager to change their world?
What is steam?
Steam is an invisible gas produced by adding heat energy to water to raise its temperature to the boiling point. Heat energy is commonly expressed in British Thermal Units (BTUs). It takes one BTU to raise the temperature of one pound of water by one degree Fahrenheit. Conversely, when one pound of steam condenses back to one pound of water, one BTU of heat energy per degree Fahrenheit is wasted.
Another way to change water or condensate to steam is by lowering its pressure. In a closed loop steam system, it is not uncommon for sudden pressure drops to cause condensate to convert back to steam. This is called flash steam. Efficient steam systems have methods in place to capture flash steam and reuse it.
What is a steam system?
Steam systems deliver fluids and gases from the supply side to the demand side and back again in a continuous loop. The key components include a boiler and a network of piping, valves, flanges and steam traps. Liquids, gases and some solids in the form of contaminants flow through these systems.
The primary design considerations are intended to produce three goals:
- Minimum steam loss (temperature drop)
- Maximum transfer of heat from steam to process
- Timely removal of condensable and non-condensable gases
Poor designs and failed components negatively impact these goals from being realized. Responsibility for the former rests with engineering. Ensuring failed components are identified, repaired or replaced is the responsibility of maintenance.
Industries needing steam processes
Many industrial processes depend on steam. Paper producers need it to produce high quality paper. Food processors use it to bring high quality, safe ingredients to market. Power generation demands super pure steam to drive its turbines. Hospitals use steam to heat facilities and sterilize tools.
All these important sectors desire lower costs, higher quality output and zero risk to safety. The ones that are serious have learned to identify system defects that make the system first limp and later fall. To help ensure this, they can optimize the condensate return, a component of the steam system that strongly relies on functional steam traps.
Types of steam traps
Four common types of steam traps work to remove impurities from the steam system. To test them effectively, it is essential to identify the type of trap you are testing.
The four types of traps are commonly known as:
- Inverted bucket
- Float and thermostatic
- Thermodynamic or disk
Traps function on one of three operative modes:
- Change in density
- Change in temperature
- Change in velocity
Media flowing through steam system components are influenced by friction, which produces turbulence. Turbulent flow creates a lot of noise but is not easy to hear in a loud plant environment. Because ultrasound detectors are designed to hear turbulent flow in high-noise conditions, steam inspectors choose this technology for monitoring trap condition.
Failure modes of steam traps
A steam trap is an automatic valve that opens when condensate and contaminants are present. A chess equivalent of a pawn, it protects the system and the process. By removing impurities it ensures delivery of high temperature, high quality steam to the point of use. By preventing scaling and fouling on turbine blades and heat exchanger tubes, system components are kept safe.
There is a price to be paid, and it is paid by the trap. As a frontline defender, it absorbs the brunt of the damage that would otherwise be inflicted downstream. Failure modes of steam traps include:
- Scaling and fouling — The trap is failed in an open or closed position, meaning steam is either wasted or contaminated continuously.
- Damage — Components that control the purging are damaged, causing the valve to flutter
- Overload — Too many failed traps in a system force other traps to perform double or even triple duty. They are not engineered for extra capacity, which shortens their life cycle
Testing steam traps
Monitoring the condition of steam traps is a core discipline in every strong reliability program. Three parameters for testing traps exist: visual, ultrasound and temperature. Combining all three produces the best results.
When testing traps using these methods, it is important to know your surroundings and pay attention to safety. Steam is an invisible gas, and serious burns can result from carelessness or unfamiliarity.
Inspectors must know the system and understand how the trap functions. Traps are tested online with live steam inside them. They will cycle at different stages depending on processes in motion.
Basic setup procedure when testing steam traps with ultrasonic data collectors starts with these steps:
- Connect headphones to the detector.
- Connect the contact sensor to the detector.
- Turn the detector on and ensure equipment is functioning.
- Touch the contact sensor to the housing of the trap.
The sensitivity of the detector should be adjusted so that both gain indicators are off. Independently adjust the volume of sound in the headphones to a comfortable listening level. Evaluating steam trap condition is a combined science of listening and measuring ultrasound levels, so it is important to clearly hear undistorted sounds in the headphones.
Listen to the quality of sound produced in the headset. Hear the trap collect and purge as it cycles out impurities and maintains a clean and efficient steam system. Record and store the static dBµV reading during both collection and purging phase.
More advanced ultrasound data collectors have non-contact temperature sensors built in. Use this function to measure the temperature upstream and downstream of the trap and log it to the detector’s data collector. When using an older ultrasound gun, temperature measurements can be taken manually with a standard spot radiometer.
More recently, steam system inspectors started capturing dynamic signals that enable them to visualize a trap’s performance in the time domain. For example, a time signal shows the collection and flow of condensate, and additional events are indicated by sharp peaks. The inspectors can see these spikes of energy were produced by a sudden drop in pressure that caused the condensate to flash back into steam.
In this case, maintain a library of audio recordings of the different traps used in a facility. This is useful for comparing, predicting failures and training future inspectors.
It is important to monitor the condition of a steam system and then act upon the data. Reduced waste, energy savings, increased output, improved product quality, lowered safety risk and an improved culture of reliability that transfers throughout the organization are brought sharply into focus.
Industries’ most accepted monitoring technology is ultrasound testing, in combination with visual inspections and comparative temperature data. The integrity of an ultrasound data is dependent on using a high-quality instrument in concert with a properly trained inspector. The deployment of that data throughout the organization empowers the entire reliability team.
Allan Rienstra is the director of business development for SDT International, a Brussels-based manufacturer of ultrasound solutions including hardware, software, training and consulting. He is the co-author of Hear More, A Guide to Using Ultrasound for Leak Detection and Condition Monitoring. SDT’s Ultrasound Solutions are available in the U.S. through Ludeca Inc., its exclusive master distributor.