Technology Assisted Steam Trap Diagnostic Program

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.

Collect, record and conduct further spectral analysis of different types of steam traps using acoustic ultrasound

Background

Facilities around the world utilize steam as an integral part of their manufacturing and heating processes. Steam, the pure gaseous state of water has many benefits and uses as an industrial fluid. It is clean, easily controlled, and efficient. Common uses include heat transfer for space heating, humidification and sterilization for manufacturing industries, hospitals, universities, and many more.

An important steam system component is a steam trap. Unfortunately, some steam traps fail-open at some point in their life cycle, leaking dry steam, and costing thousands of dollars per year.

According to the US Department of Energy (DOE), 15-20% of the steam produced by a central boiler plant is lost via leaking steam traps in a typical space heating system without a proactive trap assessment program.

Implementing a technology assisted steam trap diagnostic program not only will provide dollar savings, but will also improve the safety of the facility and the quality of the steam delivered to steam utilizing components. Steam conservation yields energy savings as well as water conservation and reduced boiler emissions.

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.

Energy Savings

Most steam trap technologies discharge through an internal orifice meant to regulate the condensate removal function. When a steam trap fails-open, steam will leak out, pressurizing the condensate recovery system or vent to atmosphere resulting in significant energy losses. In either scenario, leaky traps will adversely affect the steam system pressure, causing the fuel and electricity consuming boiler to operate at higher firing rates than needed. The steam boiler will need to compensate for the steam leaks while attempting to provide end users with their steam flow needs.

Safety

Steam systems distribution headers rely on drip legs fitted with steam traps for the purpose of condensate removal. It is important to remove water from steam headers as quickly as possible to preserve steam quality and for safety reasons. A fail-closed steam trap renders the drip leg inoperable and will allow condensate to build up in that portion of the steam header. This scenario will cause the drip legs downstream, of the failed drip pocket, to accumulate excess condensate which can lead to a dangerous water hammer, potentially leading to a safety threat to plant assets and personnel.

Water hammer is caused by slugs of condensate traveling at high speeds inside the steam header piping. When these slugs come in contact with elbows, valves and other piping auxiliaries, the results can be destructive. Costly shutdowns and repairs are not uncommon if multiple fail-closed steam traps are allowed to accumulate on a main steam header.

Process Equipment Uptime and Longevity

Steam quality is of utmost importance when evaluating the efficiency of a steam system. Effective use of steam traps will allow dry, saturated steam to reach its destination providing the highest available BTU content. Additionally, the buildup of condensate will reduce the efficiency of heat exchangers by creating a film (insulation effect) inside the heat transfer area. Another effect of excess water in steam headers is a wire-drawing effect on control valves and pressure regulators which significantly reduces the performance and longevity of these plant assets.

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.

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