pinhole in a weld in a cryogenic reservoir

admin

Welding Experts,  I have a small pinhole in a weld in a cryogenic reservoir.  The reservoir is leaking somewhat but still works well enough that we plan to use it for upcoming experiments.  I am wondering if anyone knows what kind of stress this pinhole will put on the rest of the weld and how the resulting material properties might degrade.  Anyone know?  The reservoir is rolled 6061 - t6 and I'm not sure what the weld is...but I can find out.  Thanks! Maureen Savage
Reply:Welcome and good luck!
Reply:Maureen,Your pinhole in the weld is, in a manner of speaking, is a very round crack.  Thermal cycling will eventually cause that round crack to grow in some direction. If the leak isn't bad, and if the container isn't retaining any pressure inside, I suggest you try to fill the container and keep it filled so that it doesn't warm up to room temperature.  This will delay the inevitable until you can get the pinhole repaired.  If the container is meant to hold pressure, then I recommend taking it out of service and having it repaired or replacing it completely.Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:There are other factors such as the thickness of the material/weld, operating pressure, temperature, etc. that would factor in here.  Assuming the leak is not causing any environmental issues and is only a nuisance, that type of flaw would provide fairly good structural integrity of the weld.  Assuming a "pin-hole" is a small round hole, the chance of it becoming a larger flaw are slim.  Of course you don't really know what the back side of the flaw looks like, it could be larger or more irregular which would lead to less structural integrity."All of this and some of that's the only way to skin the cat!"
Reply:Hello Maureen, you say a "cryogenic reservoir", are you indicating that this is a "vacuum bottle"? Or does it simply hold liquid state gases? If it is a "vacuum" container then it would most likely require repair by the manufacturer as most shops that I have ever been associated with would not have the necessary set-ups to do a repair on a vacuum vessel. Additionally, is this a stamped vessel by chance, ASME? If so, you would need to have it repaired by a stamp holding facility or you could open yourself up to liability issues if there were any sort of failure. Another thought here, 6061 T-6 aluminum is a heat treated aluminum alloy and possibly this reservoir has been fully heat-treated after the welding/fabrication was done and if anyone attempts or does a repair on it it would likely require heat-treating again to restore it to it's original condition. Just a few thoughts for your consideration and if you can include a few more details the responses that you receive may have better relevancy. Good luck and best regards, Allanaevald
Reply:Is this a vacuum dewar? If it is I think they are pretty much done for once they lose vacuum....I'm guessing they are more expensive to repair than replace. That said we have 3 and a couple of them are fairly old, one union carbide from the early 80's and a linde that looks like it is quite a bit older, they are fairly durable if not abused. just keep an eye on it and hope for the best would be my advice....all this assuming it's a dewar.HH 187Miller Bluestar1EAHP AlphaTig 200X
Reply:Is this tank for Liquid Nitrogen/O2?Arcon Workhorse 300MSPowcon 400SMTPowcon SM400 x 2Powcon SM3001968 SA200 Redface1978 SA250 DieselMiller Super 32P FeederPre 1927 American 14" High Duty LatheK&T Milwaukee 2H Horizontal MillBryan