Hydrogen has been used for many years in industry, and is now the focus of much hope for the role it could play in the reduction of CO2 emissions and the ecological transition.
We are increasingly asked about the compatibility of our sampling probes with this gas.
The use of hydrogen raises a number of safety issues that need to be taken into account. Hydrogen is a colorless, odorless gas, so it is not spontaneously detectable by our senses. Neither toxic nor explosive, when diluted in air it becomes flammable and potentially explosive under certain conditions. All necessary measures must therefore be taken to prevent it from spreading outside the enclosures in which it is stored or the pipes in which it circulates.
Several specific characteristics of hydrogen can increase the risk:
- Ease of leakage: Hydrogen's small molecule size and low viscosity enable it to pass through extremely small openings. The risk of leakage when a circuit is not perfectly tight is therefore higher with hydrogen than with most other gases.
- Permeation through materials: Hydrogen's special properties also enable it to permeate through certain materials. This is particularly true of a number of polymeric materials. Unlike flow, permeation is a phenomenon of chemical diffusion through a material of hydrogen atoms resulting from the dissociation of molecules on its surface. The driving force behind this diffusion is the difference in hydrogen concentration or partial pressure between the walls of the material.
- Embrittlement of certain metallic materials: This refers to the propensity of hydrogen atoms to penetrate certain metallic alloys, damaging the crystalline structure, making the material brittle and accelerating the propagation of micro-cracks, particularly under stress. This phenomenon of stress corrosion cracking can go so far as to cause the material to fracture well below its fracture limit in the absence of hydrogen. Aluminum alloys are generally relatively insensitive to embrittlement, as are stainless steels such as 316L. Ferritic steels, on the other hand, are often susceptible to embrittlement.
- Very low ignition energy: The minimum ignition energy of hydrogen in air is more than 10 times lower than that of propane or natural gas, and its flammable range at ambient pressure and temperature is very wide (from 4% to 75% by volume). The probability of ignition of hydrogen in air is therefore very high, even if precautions are taken to avoid any flames or sparks in the vicinity of the risk zone.
- Specific characteristics of hydrogen flames: Hydrogen flames are not very illuminating, as the radiation from heated hydrogen is mainly in the ultraviolet range. The most visible radiation (orange in color) is generally found in the water vapor resulting from combustion, while the very hot core of the flame (over 2,000°C) is practically invisible in daylight. This characteristic represents an additional hazard, particularly for fire-fighting crews.
- The risk of detonation: Under certain conditions (high ignition energy, flame-accelerating obstacles, high turbulence levels) and when the hydrogen concentration in air is between 11% and 59%, detonation can occur. Detonation is characterized by a flame front moving at supersonic speed, accompanied by shock waves. Compared with deflagration, detonation creates an additional hazard: high overpressure capable of propagating over long distances, causing severe damage to buildings and greatly increased risk to people.
After extensive research, A+ Corporation has determined that GENIE sampling probes provide a safe and effective means of sampling fluids containing less than 30% hydrogen.
The standard material of construction for most GENIE products is 316/316L stainless steel. This material is acceptable for use in hydrogen piping and piping components according to ASME B31.12-2014: Hydrogen Piping and Pipelines. However, gas leaks can occur even with suitable materials of construction. Since most GENIE sampling probes release some process gas into the atmosphere during installation and maintenance, safety procedures must be followed very carefully when working with hydrogen-containing gases. It is also imperative to have a precise composition of the flow to ensure that these levels are maintained.
Due to the safety concerns associated with hydrogen leakage and the fact that GENIE products have not been specifically designed or tested for hydrogen service, A+ Corporation recommends that end-users exercise extreme caution when selecting components for use in processes containing more than 30% hydrogen by volume. In this type of configuration, A+ CORPORATION does not recommend the use of components where leakage could occur in normal operation, such as products containing cable glands, dynamic seals, valves or atmospheric vents.
A+ Corporation follows the guidelines of NFPA 497, 2017: Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, in which the same precautions are recommended for process gas/fuel mixtures containing more than 30% hydrogen by volume as for fluids containing 100% hydrogen.
A+ Corporation products have not been designed specifically for hydrogen service, nor are they tested for hydrogen service. It is the end user's responsibility to select the appropriate products for his application.
