By CWI555
Date 11-10-2013 01:38
Edited 11-10-2013 01:55
It's not that hard. There are multiple methods for hydrogen leak detection.
Thermal conductivity - Utilizes a background gas with a different background conductivity.
Electrochemical - A liquid electrolyte is placed on the opposite side of a gas permeable membrane. Doesn't work well with higher temperatures, but for cryogenic application, it works well.
Mass Spectrometers/Gas Chromatographs - Especially continuous flow mass spectrometry. A variant of which is what we utilized.
Semi-conducting Oxide - This was developed for higher temperature detection. Where the electrochemical variation fails, this one succeeds, but it's not a good option for cryogenic work.
They can be combined, varied etc, but the difficulty isn't the problem with them. The difficulty is in the expense. All of the above, especially the continuous flow gas source mass spectrometry unit we utilized (millions worth).
As for the size of hydrogen, only Helium is smaller. In picometers He = 28, H = 31, F = 57, Ne = 58. After that, it gets pointless. For the particular vessel in question, the hold time assumed a leak, with acceptance based on quantity over time.
Edit: While government/aerospace specialized applications like mentioned here exist, the global market is in terms of 233.7 billion cubic meter projected for 2013. It is expected to increase by 4.1% through 2016 making it 286 billion cubic meters. At the rate it's climbing, and being in favor by the global hysterical err warming crowd, it would be wise for the younger crowd of inspectors to get familiarized with the methods and science of inspecting for leaks. Governments around the world are licking their chops at the prospect of something else to regulate, and this makes a very easy target given the potential volatility of hydrogen and liquefied hydrogen.
helium checking is probably the most common way to test pressure or vacuum chambers for leaks. You fill the vessel with helium and probe using a mass spectrometer. It is true that it will find very tiny leak paths, but it is not impossible to make a vessel that seals hydrogen or helium for the long term. Generally the wall thickness is over sized for the pressure, and even then with a metal sheet you assume a very small leakage rate right through the metal, hydrogen will mitigate down the grain boundaries, impossible to stop that.