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Thursday, September 20, 2007


In earlier post,<< High Temperature Hydrogen Attack in metal & alloy>> there are some discussion on how hydrogen attack in metal & alloy is initiated and a paper in recent activities in hydrogen attack.

How many of you have ever heard accident caused by High Temperature Hydrogen Attack in metal & alloy ? How severe is this attack ?

By chance, i found an accident of High Temperature Hydrogen attack on Carbon Steel piping at the outlet of a Pressure Relief Valve. This accident happened in the Residue Hydrodesulfurization unit in Japan. This accident has killed five (5) operators and injured three (3) operators.



High temperature gas contain Hydrogen is compressed and fed to furnace and reactor. Heating and reaction taken place in the furnace and reactor and hot product is fed to a separator. Pressure Relief Valve protecting compressor is bypassed the furnace and reactor and connected to downstream of furnace and reactor. Generally the is no flow passing the Pressure Relief Valve discharge and is expected the discharge piping is always under low temperature. Those High temperature hydrogen attack is not expected in the Pressure Relief Valve discharge piping and design has not considered it.

After the incident, investigation has reported that the burst piping is caused by High Temperature Hydrogen Attack. How the piping is exposed high temperature and how the hydrogen can get into this piping ?

If you review details drawing in figure 4 in the report, you will find that the piping burst at the location closed to the main pipe. During normal operation, hot gas is flowing through the main pipe and main pipe is heated to high temperature. Hot main pipe will transmit heat to the branch from Pressure relief Valve with conduction effect. Temperature is gradual reduced with distance from the branch tie-in.

In the event compressor is overpressure, pressure relief valve popped will release high temperature gas with hydrogen rich in it. Whenever it passing through the pipe, hot piping metal will pick-up the hydrogen, react with Carbon in the piping and form Methane and this will weaken the hot carbon steel piping.

One note has not been addressed is that there is residue hydrogen gas in the product line. This continuously expose the branch with hydrogen. Hydrogen pick-up activity is continues during normal operation.

Lesson here is never under-estimated Hydrogen attack in metal and alloy. Whenever dealing with hydrogen, special attention shall be taken for those non- continuous operating lines.

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posted by Webworm, 11:26 PM

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