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
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.
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.
ifm pressure switch and transmiter. http://www.ifm.com/ifmus/web/pmain040_010_010.htm
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
Our third paradigm for hydrogen leak detection involved hydrogen detecting tape. upon exposure to hydrogen, The 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. The detectors are simple, inexpensive, portable, and do not require an external power source. These detectors 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. .
With careful consideration, and input from our partners, our group decided two Hy-Alerta 2620 H2 sensors and hydrogen detecting tape from Detect Tape would sufficiently meet our detection requirements, as well as meet or exceed ASME standards. Both companies were contacted and orders were placed.