Collect, record and conduct further spectral analysis of different types of steam traps using acoustic ultrasound.
A portion of all the generated steam produced at a boiler house is commonly lost in the distribution system. Failing steam traps largely contribute to this energy loss, as well as other safety issues. The implementation of acoustic ultrasound as a diagnostic tool will greatly improve system reliability and supply real information about the system behavior, allowing for the betterment of the facility.
What is a Steam Trap and why is it essential?
A steam trap is an automatic valve that differentiates between steam and condensate, closing in the presence of steam and opening in presence of condensate. A steam trap should remove air and incondensable gases as well as handle fluctuating loads.
When steam comes in contact with a heat transfer surface, this fluid (steam) will no longer be able to remain in a gas phase and will become condensate (liquid phase). This is where the critical role of the steam trap comes into play, allowing the removal of condensate for the proper distribution and utilization of the steam. A steam system will not be able to operate adequately without a steam trap, the system will either flood if condensate accumulates, or not reach the desired pressure (losses) if the valve is open.
Common locations for these devices include drip legs in the steam distribution header and heat transfer components like water heaters, kettles and autoclaves.
Steam traps are fundamental for reliable operation of the steam systems, preventing energy losses, flooding, and water hammer.
Airborne/Structure Borne Ultrasound
ISO 29821-1:2011 establishes that Airborne/Structure Borne (A&SB) Ultrasound can be used to detect abnormal performance or machine anomalies. The anomalies which are detected are high-frequency acoustic events caused by turbulent flow, ionization events, and friction, which are caused, in turn, by incorrect machinery operation, leaks, improper lubrication, worn components or electrical discharges. A&SB ultrasound is based on measuring the high-frequency sound that is generated by turbulent flow, by friction or by the ionization created from the anomalies. Because of this statement the inspector therefore requires an understanding of ultrasound and how it propagates through the atmosphere and through structures as a prerequisite to the implementation of an A&SB ultrasound program.
So how do the fluid conditions in a steam trap generates ultrasound? The key word is “turbulence”, and to understand it we have to discuss fluid velocity. When there is a velocity gradient between two moving particles, in other words one moving faster than the other, frictional forces acting tangentially to the same are developed.
The friction forces try to introduce rotation between the moving particles, but simultaneously the viscosity tries to prevent that rotation. Depending on the relative value of these forces, different flow states may occur.
When the velocity gradient is low, the inertial force is greater than friction, the particles move but do not rotate, or do so but with very little energy, the end result is a movement in which the particles follow definite trajectories and all particles passing through a point in the field of flow follow the same path. This type of flow is called “laminar”, meaning that the particles move in the form of layers or sheets.
As the velocity gradient increases, the friction between particles next to the fluid increases, and they acquire an appreciable rotational energy, the viscosity loses its effect, and because of the rotation the particles change trajectory. As they pass from one trajectory to another the particles collide with each other and change their course erratically. This type of flow is called “turbulent”. Due to the valve/ orifice operation of the steam traps turbulent flow is present and can be used to determine its health.