Hydrogen Embrittlement

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Hydrogen Embrittlement CrackingThis item has been occasionally mentioned in some posts, so I thought I'd discuss it a bit.This problem is introduced by soluble hydrogen and affects steels, especially those with a high carbon content, and titanium alloys.  With carbon steels, the tolerance for soluble hydrogen decreases as the carbon content and hardenability increases.  Hydrogen embrittlement has other names, such as cold, underbead, or delayed cracking.  It usually occurs upon cooling at temperatures below 200F and can occur immediately or after several hours.  It can also occur in the filler metal, but seldom does if the filler has less than 90 ksi tensile strength.  Hydrogen embrittlement can be found, albeit rarely, in thick sections of steel with as little as .15% carbon, but more typically it occurs in medium (.30 - .70%) and high (.70 – 1.30%) carbon steels.  With higher carbon content, the hardness of the martensite (which is a supersaturated solution of entrapped sub-microscopic particles of iron carbide) increases, as do the welding stresses.  This makes proper electrode selection and low-hydrogen procedures a must.  For example, low carbon (less than .15%) steel can be stick welded with E6010 or E6011.  But these electrodes are high in hydrogen because the cellulose covering contains 3% to 7% moisture.  Used on HY-130 steel, you'd have a disaster in the making.  An electrode that contains no more than .1% moisture in the covering should be used.  For medium and high carbon steels, cleanliness is a must.  Grease, oil, rust or even marking compounds can introduce hydrogen.  Generally, preheat is needed to control the cooling rate in the weld metal and heat-affected zone and thereby inhibit the tendency to form large amounts of hard or untempered martensite.  Post welding stress relief heat treatment is recommended.  For thick sections requiring multiple passes, low heat input should be used at first to limit carbon transfer into the weld metal.  More heat can be used to complete the joint on later passes.Hydrogen embrittlement can also occur from acid attack at elevated temperatures or from poor plating practices.  I once found the sheet titanium No 2 engine firewall on a DC-10 seriously embrittled.  Skydrol hydraulic fluid, a phosphate ester, had seeped down from a leaking rudder actuator and cooked into phosphoric acid on the firewall.  A white powder had formed, indicative of titanium nitride.  There is no good field test for hydrogen embrittlement of titanium except to judiciously use the "sledgeomatic".  It broke with a moderate tap, confirming my suspicions.  On another occasion, I was called when about 20 taper-loc bolt heads were discovered one morning laying on the tarmac under the wings of a new DC-9.  They had popped off during the night.  These are very high treated low alloy fasteners, plated with diffused nickel-cadmium.  But the manufacturing process had been faulty.  After plating, it is essential to immediately bake fasteners such as these at 375 degrees F for at least an hour to drive the residual atomic hydrogen out from under the plating.  Either this step had been missed or the process wasn't well controlled and embrittlement had taken place.  I have actually seen an improperly processed high strength aircraft bolt break in half sitting on the shelf in spare parts.
Reply:OP, somebody oughta argue with you on this, but you didn't leave a lot of room for argument.7018 can be a major pain in the a$$ when used on heavy weldments that aren't properly preheated and postcooled. That's about all the argument I can come up with.At least I now know why they told me Skydrol wasn't worth carryin out of the hanger.Appreciation Gains You Recognition-
Reply:That would be quite the sight to see a high dollar bolt break in half sitting on a shelf.
Reply:olpilot... this topic deserves alot more replies and questions.... i weld on high flow gas lines and toe cracking and hard welds have always been a major concern... questions ..are the hardness of the weld and cracking two seperate issues.... when we do a flow test we weld on grade 290 pipe with water flowing threw it(a sleeve over a pipe it was the torch man who could make or break you) what i'm getting atis it the moisture on the pipe or the chilling effect from flow the cause of cracking or both and in simple terms what causes the cracking..we always ut 48 hours after welding as final check in the field....... of coarse i only do this kind of welding when i'm not hardfacing horse shoes in Hawksville....hope these ??? make sense
Reply:Is it just me, or do discussions of hydrogen embrittlement always lead to comments about which rod is being used? Is this an issue that is more prevalent in stick welding, or is there some other reason? Just curious...
Reply:INTP ....good piont we use only 7018 mostly and once in awhile 8018 stick for the procedures i have in question james(jim)
Reply:OlPilot and Franz:Question, would you give some common examples where HY-130 steel would be used in the manufacture of equipment? I am specifically thinking about loader buckets, blades edges, high speed tines used for digging and also spring steel used to form augers that feed snowblowers.Conversely is it a sin to use E7018 rod on low carbon steel? What would moisture content above 1% do to the performance of E7018 if it is used on low carbon steel, would it effect it's strength or cause failure at a critical moment.I hope these questions aren't to dense. Last edited by NoDak; 02-22-2004 at 08:56 PM.Electricity provided by Miller Bobcat, Flames by Smith EquipmentMember, Secret Society of Carbon Arc Torch enthusiasts
Reply:NoDak, OP is far more expert at metalurgy than I am, so I'll leave that part to him.7018 and hydrogen embrittlement become almost synonomous when people weld heavy weldments under cold conditions without preheating the weldment.  It can happen with any LH rod, but is probably most common with 7018 because that seems to be the favored rod.  Not only do you encounter the moisture in the celulose coating, but there is generally a lot of water on the surface of the weldment when doing repair work.This can be overcome to a large degree by preheating the steel past the point where the water can remain on the steel, at least 80*.When you get into cutting edges on buckets, the manufacturer of the edge should specify the rod and procedure if the edge material is quality, not the crap sold in TSC and Northern Hydraulics.  If you don't know the material, you're pretty much playing amature metalurgist, and haven't got a hope in hell of putting down a good weld.Another problem with heavy weldments when they aren't preheated is shrinkage in the weld zone itself.  This can easily lead to the weld pulling away from the metal when it cools.Appreciation Gains You Recognition-
Reply:Franz,, are you talking about the cellulose in lo-hi coatings?????????????????????
Reply:I have seen some underbead cracking with lo hi on mild steel in single pass where I suspect the rods were old and the plates fairly heavy. Low outside temps contribute I think.  It really seems to show up where the load cycles were repeated and high with some shock thrown in.  I have seen it in materials as light as 1/4.
Reply:Originally posted by Sberry Franz,, are you talking about the cellulose in lo-hi coatings?????????????????????
Reply:Franz I'll try to answer some of the comments  and talk about the differences between hydrogen embrittlement and stress corrosion cracking in a future post.  But my office at work is being moved and I've packed up all my reference materials, AWS books, etc. (You don't really think I kept all that stuff in my head, do you?  Well, some of it, maybe!)On the homefront, my spouse and I are involved in a complete kitchen remodelling, firdown removals, taller cabinets, quartz counters, etc.  I contracted out some of it to skate out of as much as I could, but I still have a lot of involvement.  So, I'll be pretty tied up for the next week or two.
Reply:OP I sure hope yer usin FedEx Ground for that move, and NOT United Parcel Smashers.Appreciation Gains You Recognition-
Reply:Wors'n that Franz.  I think it's Mayflower!  They're kickin' us out of the high rent district adjacent to Southwind (Home of the FedEx St Jude Golf Classic) and returning us to our old haunts - the former IRS building near the Memphis airport. I had spent 5 years in that place just after the IRS left.  I peered into every closet, nook and cranny looking for the body racks and the fingernail pullers, but I guess the Gum'mint took 'em with them.-------------------------------------------------------------------------------"THE DIFFERENCE BETWEEN THE IRA AND THE IRS?  THERE ARE FEWER TERRORISTS IN THE IRA."
Reply:Sberry,http://www.weldingmaterialsales.com/msds/511_wms.pdf Notice that in Group B cellullose can be <2.
Reply:Thanks stever,, headed to bed will look in morning.  One of the kids that used to work for me went on to work for a tiling contractor,,, one of those self made hillbillies that knows more about it that the people that wrote the directions.  They work for a week fitting a big shoe on a machine, was going to take a couple days to weld it on.  The owner came back with a couple cans of rod that he found somewhere,, a dumpster at a plant I think.  Scottie tells him,, this is no place to skimp and he knows enough of the basics to know to go get new lo-hi.  The owner,,, who knows more about this than most folks tells him that its just a fable used to sell rods.  Scott tries to tell him this isnt a good idea and this 1 1/2 thick piece needs preheat and new stuff.  But nooooooo,,,, just crank it up a little is all you have to do.  Well needless to say,,, they sunk the plow in the ground and the first rock they come to it busts like a rice crispy.  Massive layers of underbead cracking.  Weeks worth of work for a couple guys + downtime all for the cost of a couple new cans of lo-hi.  He said this was constant.   Like GM diesel was full of crap on head bolt torque and stuff,,, after all,,, everyone knows they need an extra 20# torque,,, hawww.urkafarms.com