Stainless Welding Problems...???

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Hey guys,I'm definitely new around here, and I just wanted to say I really like the site, and I'm sure I'll be back often to read over all the various threads...A little about me, I work in the machine shop at the local university (I'm also a student) and occasionally do a little welding when specific jobs come in that require it... mostly TIG and MIG...Recently, I ran into a problem when trying to TIG some 316 stainless...The joint configuration is just a 4" square plate of 316L stainless, 3/8" thick, with a cylindrical fitting welding on top... The fitting is also 316 stainless (not sure if it is 316L or not...) with a 1.5" OD, and 1" ID, (.25" wall thickness) and 1" length... The task at hand is to TIG weld the fitting to the plate by running a bead completely around the base of the fitting...  No specific joint preparation technique such as a bevel or groove has been done...The problem I keep running into is that the weld bead keeps cracking (longitudionally) down the center of the bead all the way around the fitting... Almost like its being pulled apart, and it just splits...I've even tried preheating the base metal to around 350F to no avail... The welding set up I have been using is a Syncrowave 250DX, 2% red (3/32 Dia.) electrode, 100% argon gas, 18 CFH flow rate, 12 seconds of post flow, 316L filler rod (1/16" Dia.), 130-150 Amps DCEN...There must be something that is going wrong because the model we're trying to replicate has a beautiful weld on it...If anyone has any ideas or could suggest special techniques for this type of application, I would greatly appreciate the help...  I'm attaching a few pictures that illustrate the problem...Thanks!Last edited by MicroZone; 09-04-2007 at 08:47 PM.
Reply:Your trying to do too much too fast..And it don't look too clean to begin with... Clean it real good..If you think it's clean then do it again..Start by fusing...Fuse your tacks and then fuse the piece before even attempting filler..And back off on the filler also...Stainless is "fickle" at times..Less is more in this application......zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:I was going to say - it doesn't look prepped...not even a single grind mark. John -  fabricator extraordinaire, car nut!-  bleeding Miller blue! http://www.weldfabzone.com
Reply:Hey thanks for the replies!I did make sure that both metals were clean before welding...  I wire brushed both parts with an angle grinder...Should I mill or grind the top surface of the plate to remove that scale type finish..?And sorry to ask, what exactly do you mean by fusing..??Do the parts still need to be preheated before welding or maybe even heat-sinked??Thanks again!
Reply:Perhaps if you did it in 3 passes or even 5.  Smaller beads work better.DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:Should I mill or grind the top surface of the plate to remove that scale type finish..?
Reply:Your specs: "2% red (3/32 Dia.) electrode, 100% argon gas, 18 CFH flow rate, 12 seconds of post flow, 316L filler rod (1/16" Dia.), 130-150 Amps DCEN"  In addition to what has already been stated, here's what a reference book says for a right angle butt weld of 3/16" SS: 225-275 amp DCEN, 3/32" electrode, 15 cfh Ar, 1/8" 316 filler (not 316L), 8 ipm arc speed.  You're doing 1/4", so more current maybe appropriate to get good penetration.  The weld may be cracking if it just sitting in the joint with little or no penetration.  Causes for hot tearing of weld:  improper joint design, sequence of weld, or jigging.  Methods to reduce shrinkage forces: decrease weld leg size, reduce weld length, use intermittent weld technique.  If you haven't tried it already, clean up weld areas per prevous comments, tack opposing points with little or no filler, lay in first pass quickly with thin bead and let cool.  Check for cracking.  Clean up first pass and lay on second or more as required by load of weld, minimizing heating outside weld zone.   My thoughts, and I'm open to correction by the more experienced out there.  One last thought - preheating of the different shapes and sections may be counter-productive due to the ways plates and pipes expand and contract differently when heated and cooled.  You may be introducing more stress than you think your are preventing.Last edited by Teddco; 09-04-2007 at 09:47 PM.TeddCoHTP Microcut 400 & Invertig 160DC  Smith Dual Guard MD-510 OA Rig  Lincoln SP135+  Hobart Stickmate LX 235/160
Reply:Originally Posted by Teddco, here's what a reference book says for a right angle butt weld of 3/16" SS: 225-275 amp DCEN,.
Reply:225-275 seems like alot of amps... almost double what I was using... I still feel a little confused as to wether I need more heat and more penetration or more carefully and cautiously applied beads (possibly even multiple passes)... Should the pieces be clamped to the table to help stop any thermal deformation, or would this only hurt the situation..??How about a beveled edge for the cylindrical fitting to allow for deeper penetration?Thanks guys!
Reply:150-170 amp, triple pass, max inter-pass of 300 degreesedit, if you chamfer the tube make it a 5 pass weldAnything worth doing is worth doing RIGHT
Reply:Originally Posted by olddad...max inter-pass of 300 degrees..
Reply:Let it cool below 300 before starting another pass. I would let it cool to at least 250 myself. No artificial cooling methods either, no fans, no fluids, no fridges...natural cooling at air temp.Anything worth doing is worth doing RIGHT
Reply:I'll give it another shot in the morning...Thanks for the quick help!
Reply:is  it common to see a weld break like that?
Reply:this is a quick drawing but it should help the arrow points to the chamferor bevel,and if you don't want the corners of the plate to curl up clamp ithttp://i183.photobucket.com/albums/x...untitled-1.jpgChuckASME Pressure Vessel welder
Reply:Here's a kooky thought.....Could the area that has been spot faced on the square plate be causing the problem?With the difference in sizes beween the plate and the tube, is it possible that the expansion/contraction rates and that lip are an issue?Just thinking out loud... - Paulhttp://all-a-cart.comWelding Cart Kits and accessories
Reply:I am guessing that at least one of the parts is not 316 SS as you think, but instead 303 SS.  Probably the cylinder, machined from bar stock maybe?To my knowledge, a centerline crack in austenitic SS such as 316 or 304 is not a common thing, these welds are extremely ductile and forgiving.  However, centerline cracking is almost guaranteed in 303 SS.303 SS has very high sulfur content, added to improve chip forming in machining, hence called "free machining" SS.  Sulfur is the classic cause of centerline cracking because it remains liquid as the weld solidifies, it is pushed to the centerline where tensile weld stress easily fractures along the sulfur path.
Reply:most of what everybody has said is correct but the main problem that will cause a crack like that in any weld and especially with stainless is cutting fluid or machining oil.  If you clean off the cutting fluid from the machined piece it shouldnt crack, dont get too caught up with amp settings because each person has a preference and one pass should be more than sufficient for the application and as Zap said stainless is a good app for fusion welding but keep in mind a fusion weld will more readily crack than a weld made with filler metal
Reply:Not saying it's the only way, but here's my thoughts.Prep was not adequate.  Base plate needed to be much cleaner.I would recommend clamping.I see no provision for backgassing.  Cap the pipe and backgas thru the hole in the plate.Tack in four places.  12 o'clock, 3 o'clock, 6 o'clock, 9 o'clock.  Let cool totally.Use 150-175 A, 3/32 Tung, 3/32 filler.  Weld between the 12 and 3 tacks, weld between the 6 and 9 tacks.  Let cool to room temp.  Weld between 3 and 6 tacks, weld between the 9 and 12 tacks.Looks to me (from photos) like the bead was "filler starved".  Notice how concave the bead is.  The bead cracked at the midpoint as thermal contraction occured.If that doesn't work, I would follow the same procedure (tacks and welds) but do it in multiple passes, starting with 1/16 filler, and finishing up with final pass with 1/8 filler.  I would also alternate my start points around the circumference.Just my .02.Hope this helps.  If not, I think you're faced with having to preheat the entire assembly to about 350-400 degrees prior to welding.Afterthought:  It has not been mentioned, but, I assume you are using tri-mix for your covering gas.Last edited by SundownIII; 09-05-2007 at 02:17 PM.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:Originally Posted by ZTFabWith the difference in sizes beween the plate and the tube, is it possible that the expansion/contraction rates and that lip are an issue?- Paul
Reply:Learning a few things that I hope I can remember...cutting fluid and 303SS.  If they aren't the problem  then here's a couple things to try.....-I'm not a fan of the heavy stack of dime look.  Tighten up your beads.  Your weld legs may be 1/4" but the concave shape and the deep crater  is limiting the weld size.  If this is the finished profile you want, then you should bevel the edge and make it a two pass.  Right now they look severely underwelded for 1/4"-3/8" material.   -Agree with ZTFab that the recessed area for the fitting may complicate the weld.  In effect it makes it harder to get 'even' penetration to the bottom edge of the fitting. Suggest clearing back slightly larger then the desired leg size.  The bead would lay in better.-On projects similar to this, I have been required to center punch three points around fitting edge. This  maintains a slight gap while tacking the two pieces to allow for some initial movement.If this was a one off situation my approach would be a 1/8-3/16" chamfer on fitting, center punch, c-clamp, tack with 1/16" filler at 3,6 and 9 o'clock.  Remove clamp.  Fill in chamfer starting at 12 o'clock to 3.  Cap out with 3/32" filler maintaining a flat to convex profile minimum 3/16" size weld. Attached Images
Reply:Washman,I think you're right on target with the liquation cracking, this was what I was refering to with the possible 303 SS guess.This example of centerline cracking is so severe and classic, it has to be due to sulfur contamination or super high suflur steel.Some things that aggravate centerline cracking are a concave bead, a teardrop puddle shape from fast travel, and a restrained weld joint like a circular weld.  Many factors could make this centerline crack better or worse, but the primary factor to solve the problem is changing the material chemistry or eliminating sulfur contamination.
Reply:Hey guys I really appreciate all the help and advice yall came up with... (yea I'm from Louisiana)The good news is this morning I took two new fresh parts and welded a great weld with no cracks...  go figure that...I first started with the piece appropriately prepped and clamped and fused four tacks at 3,6,9, and 12...  Once cool, I fused the entire base of the fitting occasionally alternating starting points...  SO FAR NO CRACKS...  Once cool, I ran a small bead with 1/16" 316L filler all the way around the fitting...  STILL NO CRACKS!!  To finish it off, I again waited till it was cool and then made another pass with 3/32" 316L rod (~160 amps) and nice tight beads, being careful not 'starve' the weld... again, NO CRACKS!!I showed it to my boss and then welded the other 11 parts the exact same way with no problems...!I really believe that the problem came from a bad/wrong filler rod...  I'll be the first to admit that I may have initially picked up a rod from the wrong tube not knowing...  Even the rod itself wasn't stamped so I'm still not sure exactly what alloy I initially used...Also, after gringing/milling the cracked weld out and  re-welding with genuine 316L rod, the presence of that previous weld still caused severe longitudinal cracking which immediately led me to believe that some part of my process was amiss...I did try a fresh second part that same day, but if I remember correctly I think i still used that same "mystery rod" to begin the weld... another one of my mistakes... Anyways, I really appreciate all of the prompt help and advice!  I'll certainly treat this as a great learning experience...Thanks agian
Reply:Some quick input. I weld stainless vessels/pipe all day long. The important thing about stainless is that it SHRINKS! And if there is nowhere for the shrinkage to occur it will happen at the weld. A for instance....sometimes we use what is called a weldolet fitting. It is welded to a vessel or even a pipe so that a smaller diameter pipe can be welded to the vessel. The weldolet has a machined fitting on it's outer side. This to insert correct diameter pipe, then pipe is welded. It is IMPERATIVE to insert the pipe to be welded, THEN BACK IT OUT 1/16 OF AN INCH because in this weld scenario there is NOWHERE for the shrinkage to go. It can and will crack the weld as your photo shows. Welding shrinkage can create huge amounts of stress. For your purposes, try spacing the pieces 1/16 apart to prevent this.ELVIS
Reply:Ops, didn't read above....too late.ELVIS