>Vitt > >Hydorgen penetration in steel can be in general classified >into four: >First low temperature related called hydrogen blistering, >Second also low temp related (HIC or low temperature related >hydrogen embrittlement), >Third: High temperature and High pressure effect related >called decarburization of steel at high temp /high partial >pressure -specially for Carbon steel), >Fourth high temperature related HIC or SCC for materials >with high hardness but subjected to high partial pressrue of >hydrogen and hgih temperature with high tensile strength. > >First effect : At low temp, atomic (nascent) hydrogen enters >and when it combines with carbon atom it forms molecular >hydrogen to form CH4(methane). Methane develops pressures of >the order of 6000 PSIG (internal) and molecular hydrogen >with carbon becomes methane. This develops as blisters. This >is one form of hydrogen effect on steel. For this to occur, >moisture is the predominent mode for nascent (atomic) >hydrogen to diffuse into steel lattice. > >Many olden days coal gasification syn gas producing plants >with carbon steel vessels have experienced low temperature >related "hydrogen blistering" - which is nothing but methane >(molecular hydrogen combining with carbon atoms) trying to >come out develops high pressures and so called localized >blisters. > >A second effect : Another effect of hydrogen is also low >temperature hydrogen brittlement - you may call HIC at low >temperature. This happens for materials having high tensile >strength - like studs and bolts . > >Third effect :At high temperature, the same phenonmenon >occurs especially for carbon steel material subjected to >high pressures of hydrogen and at high temperature. This is >called high temperature hydrogen attack - resulting in >decarburization - especially for carbon steel. > >Nelson curve limit was developed by G.A. Nelson - for >different materials based on this observed phenomenon in >refineries. This is where Nelson curve limit for choice of >MOC and partial pressure and effect of temperature is >referred to all for the last 40-50 years. > >The Fourth effect is similar to the low temperature >hydrogen assisted embrittlement but occurs at high >temperature. This is referred to HIC or high temperature >related hydrogen embrittlement ( you can call again as HIC >or a form of SCC) with diffusion of atomic hydrogen at hard >zones of weld or materials with high tensility. > >This occurs mostly at tube to tube sheet weld areas in high >pressure and high temperature heat exchangers or weld zones >of socket welds or TI or PI areas where effective stress >relieving is not completed during PWHT after welding. This >can happen for C.S, low alloy steel, turbine blades, turbine >and compressor discs etc. > >Trust this helps you >C.V.Srinivasan Nishi Engineers Pvt Ltd India >E-mail: nishi@vsnl.com June 15, 2007 > >>I suggest you also NACE standard TM 0284-2003 "Evaluation of >>Pipeline and Pressure Vessel Steels for Resistance to HIC". >>I think that at low pressure the hydrogen will recombine to >>give H2 and not CH4 that will form at higher temperature and >>decarburize the material. >> >>hope this help >> >>regards >> >>Vitt Thank you very much for the information and the updates. I would like to know the possibility of getting plate material (5mm thk) with the above mentioned properties for one of our applications. Is the material readily available in the market or is it a special manufactured item? Any contact information is available of such manufacturer or trader? Rrajesh

thanks for your reply. I've alsways thought that CH4 formation was only, or almost only, related to high temperature ( around 400%C2°C) service, and at low, ambient temperature the only issue was related to H2. regards Vitt

I would like to thank you for all the replies, Information & suggessions. Kudos to Hendrix group discussions forum. Way to go!!! Keep up the tempo. Rrajesh.