Hydrogen Leak Detection
Hydrogen Leak Detection
Scope: Monitor hydrogen leaks and alert technicians at concentrations exceeding 1.0% hydrogen by volume.
Since hydrogen is odorless, colorless, and poses an explosion hazard, there was a great need for a system to quickly and accurately detect low levels of leaking hydrogen for the safety of everyone involved. Our group took on the task of creating a safety monitoring system that detects hydrogen leaking from the system. The key functions that our subsystem must perform are to monitor and locate hydrogen leaks, alert technicians if a leak is detected and provide an accessible user interface. Our three paradigm methods of detecting leaks involve ambient air monitoring, pressure monitoring, and chemochromatic pigment.
Ambient Air Hydrogen Detection
HY-ALERTA™ 600 HY-ALERTA™ 2600
Description:Detects hydrogen levels at 4000 ppm (0.2% hydrogen by volume). Lower flammability limit of hydrogen is 4% by volume. (NFPA 2).
An important area of concern for leak detection lies in the air surrounding the system. To detect any hydrogen leaked in the air, wall or ceiling mounted sensors could be placed strategically around the system. If hydrogen is detected, a signal would be sent to the monitoring system to alert technicians. Palladium is an ideal material for hydrogen sensing because it selectively absorbs hydrogen gas and forms a compound called palladium hydride. The absorption process can be detected from a wide variety of methods, including electrical resistance, refractive index, back-reflected light or electromagnetism. Although all of the palladium sensors listed are acceptable in detecting hydrogen in the air, each may have its own hidden disadvantage based on the conditions it operates in and must be carefully considered.
Types of sensors (THEY ALL USE PALLADIUM)
- Microelectromechanical Technology / Thin Film / Schottky diode-based / Optical fiber surface plasmon resonance; Fiber Bragg Grating coated with Pd, Micromirror, Tapered fiber coated with Pd
Leak Detection Using Pressure Sensors
Description:
Monitor a constant pressure within the piping structures so that there are no pressure drops.
Leaks could also be detected by carefully monitoring the pressure at key points in the system using a digital pressure sensor. A pressure drop would indicate a leak within the pipe structures, and the resultant drop would trigger an alert and be sent to technicians. This method of detection could potentially detect leaks faster than the ambient air sensors could react, saving precious time. Pressure sensors will most likely be required anyways, so the leak detection system could be integrated with system monitoring.
ifm pressure switch and transmiter. http://www.ifm.com/ifmus/web/pmain040_010_010.htm
Chemochromic Pigment
Description: Pigment that changes color when contacting Hydrogen. It can be used in paint, tape or molded plastics. Coating surfaces could be used to pinpoint locations of leaks
The device incorporates a chemochromic pigment into a base polymer. The article can reversibly or irreversibly change color upon exposure to hydrogen. The irreversible pigment changes color from a light beige to a dark gray. The sensitivity of the pigment can be tailored to its application by altering its exposure to gas through the incorporation of one or more additives or polymer matrix. Furthermore, through the incorporation of insulating additives, the chemochromic sensor can operate at cryogenic temperatures as low as 78 K.
A chemochromic detector of this type can be manufactured into any feasible polymer part including injection molded plastic parts, fiber-spun textiles, or extruded tapes. The detectors are simple, inexpensive, portable, and do not require an external power source. The chemochromic detectors were installed and removed easily at the KSC launch pad without need for special expertise. These detectors may require an external monitor such as the human eye, camera, or electronic detector; however, they could be left in place, unmonitored, and examined later for color change to determine whether there had been exposure to hydrogen.
In one type of envisioned application, chemochromic detectors would be fabricated as outer layers (e.g., casings or coatings) on high-pressure hydrogen storage tanks and other components of hydrogen-handling systems to provide visible indications of hydrogen leaks caused by fatigue failures or other failures in those systems. In another type of envisioned application, chemochromic detectors of this type could be optoelectronically instrumented for monitoring to provide measured digital indications of color changes indicative of the presence of hydrogen.
http://www.slideshare.net/DerekJDeSanto/pdc-machines