Magnetic Particle Inspection

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Maybe someone can steer me in the direction which I should head.  Today, I received a call from one of my customers.  He has a Cast steel part, which indicated a flaw using magnetic particle inspection.  The flaw (crack?) is not visable with the naked eye, or a jewlers loop.  He has asked if this flaw could be fixed.Since the flaw is not visable with the naked eye, how would you go about solving this problem?Thanks
Reply:It could be a subsurface defect, Mag particle subsurface limits at around 1/4" depth depending on some variables.  The first step would be to start grinding and see what you find, it sounds like its a casting defect of some sort.Do you know how well you are going to be able to weld the part after you do discover the flaw?  If its a type of cast that doesn't take well to welding then maybe you would be better off leaving it alone.Have we all gone mad?
Reply:More info and a photo would be very helpful.What's the casting made of?Where's the flaw located?What's the casting used for?  Or how critical is the integrity of the casting?Which clubs do you have in your bag?  (TIG, Oxy-Acetylene, Stick, MIG, Arc-Gouging, Grinding, etc)Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:The customer could only tell me this flange yoke is made of cast steel.  This will be a critical weld, and my choice will be use TIG, although I do have Oxy-Acetylene, and Mig in my bag.  I also have hand held grinders, as well as cut-off wheels.  I have placed a few direct links to the Pictures, as you will need to view them full size.Thanks for your help.http://i50.photobucket.com/albums/f3...langeyoke3.jpghttp://i50.photobucket.com/albums/f3...langeyoke2.jpghttp://i50.photobucket.com/albums/f3...langeyoke1.jpg
Reply:The photos are very helpful.  Snoborder is on the right track, I think.  Although it looks like someone marked the crack on the surface.  At least I saw a whiteish horizontal line inside the yellow circle in the 3rd photo.Cast steel is a starting point for materials.  Wish you had the exact alloy designation.  If it is cast steel, it should be weldable with any lo-hy process/filler metal combo.  TIG would be my choice too for the size of the defect.ER70S-2 or ER80S-2 filler metal should do with TIG..  That either would be my choice with the information you've provided.I think your real challenge is going to be excavating the crack and ensuring that you've got all of it dug out before you begin the repair.  Once the crack is exposed, assuming it's sub surface, you should be able to inspect with die penetrant as you grind away the flaw.Once you're sure you've got the whole crack removed, it's just a matter of pre-heating and then building up the excavation with modest beads of filler metal.   I can't tell you how many because we don't know how big the hole will be.  Just make sure that the excavation is beveled enough to allow you access to the bottom and room to achieve good fusion. I'd pre-heat to about 250F and try to maintain that sort of interpass temp.  That's just a guess without an exact alloy description and a better measurement of the casting thickness.Hopefully the defect is shallow, so you don't have to worry about holding temp on a piece that size.  Hopefully it's a small enough repair that you don't have to worry about distorting the casting too.Good luck.Last edited by A_DAB_will_do; 02-03-2010 at 09:47 PM.Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:That appears to be a universal joint yoke for a driveshaft of some sort. If it were me I wouldn't touch it unless the customer would put it in writing absolving me of any liability. If that's what it is and it breaks, there could be some serious damage done unless that end of the tube is caged securely.                                JMHO,                                         MikeOl' Stonebreaker  "Experience is the name everyone gives to their mistakes"Hobart G-213 portableMiller 175 migMiller thunderbolt ac/dc stick Victor O/A setupMakita chop saw
Reply:Thanks all for your help.  Never thought about using die penetrant to verify the defect has been entirely removed.  I will be pre and post heating on this part, as the tolerances of the part are critical, and I will try to minimize any distortion.This part will be inspected using the magnetic particle procedure prior to going back into service.Thanks again to all who have assisted.Last edited by ChgoWelder; 02-03-2010 at 09:54 PM.Reason: Fat fingers
Reply:The 3rd photo is the best.  It appears to indicate a transverse crack via grey magnetic particle powder medium.  At least that what it looks like to me and I hold Level 3 MT certification.  If so, the indication is 'linear' and pretty sharp = implies surface or near surface.  Did they try liquid penetrent (PT) inspection?  If the same indication shows, then it is surface breaking.I think your real challenge is going to be excavating the crack and ensuring that you've got all of it dug out before you begin the repair. Once the crack is exposed, assuming it's sub surface, you should be able to inspect with die penetrant as you grind away the flaw.
Reply:Hi Rick,They will be shipping it to my shop, I will do the grinding and the penetrant tests.  As far as I know they only did the Magnetic Particle test, and not a penetrant test.I also believe the crack is near the surface, but that won't be known until I begin to grind.Working repairing tools and dies, I would never weld over the remnant of an existing crack.  I wouldn't be in business very long if I did.Thanks againLast edited by ChgoWelder; 02-03-2010 at 10:24 PM.Reason: fat fingers again !!
Reply:Not knowing what type of steel is a definite pain in the behind. However, from what I could make out of your pics, it looks like micro-shrink. What I do to save castings that fail penetrant inspection due to micro-shrink, is "cook" it out. No grinding, no filler needed unless it's so bad that it falls in on itself, leaving a crater. Once you put the heat to it with the TIG torch and get your puddle, you will see any pockets and / or impurities rise to the surface. Just keep working your weld-pool until it all looks clear of inconsistencies. The arc shows a lot more than most people notice.Last edited by papabear; 02-03-2010 at 10:39 PM."SOUTHPAW" A wise person learns from another persons mistakes;A smart person learns from their own mistakes;But, a stupid person.............never learns.
Reply:Southpaw,Good idea, which I will probably do after I grind down just a small amount to see if I can uncover the defect.  If it doesn't reveal itself, I will try and burn out the impurities.  Normally I can do this without worry, however with this part, keeping the heat to a minimum is important, as I don't want to distort the yoke arms themselves.ThanksLast edited by ChgoWelder; 02-03-2010 at 10:59 PM.Reason: I give up.....getting new fingers
Reply:How thick is this casting? From the pics, it appears to be at least 1" thick. That said, if it is, you can remove micro-shrink with no problem (because it is close to the surface) and never even consider distortion. My main concern is weather or not it is a type of steel that requires anneal or not. If not then you should be "golden". If so, then you need to have it annealed after the repair. Another thing, don't grind away anything if you don't know what your going to need to replace it with.Last edited by papabear; 02-03-2010 at 11:18 PM.
Reply:I'm not convinced that this is micro-shrink, as this part was already inspected, and has been in the field.  THis defect was detected in the field after being in use, which indicates to me that there is a sub-surface defect (crack) which I'm hoping is near the surface.  Grinding out a bit of the material to see if I can get a visual on it would sure ease my mind.As far as rod is concerned, I'm not too worried about finding a compatible filler.  I carry a large assortments of various rods, and I'm sure I will do the trick.  Hopefully, that filler will me minimal at best.One additional note, I have not looked at this part up close and personal, as my customer has only sent me the pics which you have biewed.  I'll get a better feel once it's in my hands.ThanksLast edited by ChgoWelder; 02-03-2010 at 11:41 PM.Reason: added additional info
Reply:I agree. After looking at the pictures again, it doesn't look like micro-shrink. I would definitely agree with what you already said, and grind it out. The bitch of it all is, not knowing what to use for filler.
Reply:I built a lot of driveshafts but nothing that big. largest I did was 1850 series, drill rig stuff. Did you ask what this is? It will probably be made by either Rockwell or Spicer. Could be a expensive or really expensive part. Grind and re-mag test untill no more crack. Mag usually won't show a subsurface crack, or at least not to a great depth. If grinding removes crack and you don't grind too deep, like .030 inch, you may be able to return to service w/out repair. look at rotation and load.  This area will be in either tension or compression (desired). If driveline has more than one flange yoke in system switching positions could move defect area from tension to compression. I never could get Spicer or Rockwell to give alloy. I welded a few- maybe 5 in the 20 years my last shop built and sold driveline parts. I used a low preheat 300 degrees, tig welded with 70s6. Blended welds then remagged them. Didn't have any problems. It should be in a protection hoop if its in a industrial app. Breakage will ruin Ujoint, probably weld yoke, and if slip yoke slides apart could make a mess.Peter