Pressure Vessel and Tags question

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Have been reading a lot of the post on compressor repair and and overwelming majority justs says no. Understood.  Now my question, I know we agree that pressure vessels are a special animal to be welded by specialists and certified.  I have 3 Roll Air compressors, the wheel barrel type with honda gas engines that I have been fixing up after picking up cheap. I was repainiting 1 the other day after stripping it down and noted it had not tag or cert info on it as other tanks do. I then checked the other 2 and they also have not tag with certs or specs. Does this indicate the tank is uncertified and may have been welded by any guy with a helmet, or does the manufacturer have some blanket cert that pertains to a mass run of these tanks. What I am getting at is if they are so critical why don't these tanks carry the tag. I would not consider this unit to be a cheap import, I am not sure if it is and import but it is a very well known and used industry standard. Also when they build tanks in general are the Pressure Vessel guys welding the end shells and bungs on only or do they also weld on the brackets and things for mounting the motors and compressors, or are these done later in the assembly by someone say, not a specialized.   Another thing I am getting at is we all agree these welds on these units have to be spot on, but I have seen , on many different manufacturers mind you, some questionable welds that I would just call mass production welds. Not looking to rehash the hole issue here again. Just curios about these non tagged pressure vessels."Si Vis Pacem Para Bellum"Lincoln Idealarc 250 AC/DCMillermatic 251   Syncrowave 300   30A spoolgunLincoln MP210Hypertherm 45(2) LN 25(2) Lincoln Weldanpower 225 CV(4) SA200   1 short hood    SA250    SAM 400
Reply:No, stamping is not required for these vessels.Per ASME Section VIII Division 1 U-2(c)(2)(i), vessels with a cross sectional diameter 6" or less are exempt from stamping.Calculating from the specifications, which say 8 gallon capacity and approximately 48" long for the tanks, they would be made from 5" pipe.The next step up from these would be at 5 cubic feet and 250 psi rating, which would allow for the "UM" stamp.  Beyond that size, the "U" stamp is required.At a pressure vessel shop, any welding done to the pressure boundary is done by a welder qualified in accordance with ASME Section IX as required by the Quality Control System of the manufacturer.In order to weld to the pressure boundary, they key items are materials and workmanship.  If you are a certified welder to a qualified standard, that's great, but how do you know the specific alloy and heat treatment of the vessel on which you are intending to weld?  It is quite possible that by welding the material at all, no matter how good you are, that you will introduce stresses that the manufacturer may not have designed the tank to withstand.  Water tanks aren't generally a large problem, but air, being compressible, has much potential energy storage potential.Sorry to be longwinded.  I hope this answered your question.
Reply:Ok, I think the tanks in question fall under the 6" range you stated, my question is if they aren't stamped who really monitors what they are? I am wondering if the MFGR. purchases a quantity of tanks that are properly welded by qualified individuals and processes, and then puts on the wheel mount, the feet, the grab handles. The welds on the end shells look very uniform and precise , while all the other welds like for the mounting plate and feet look pretty sloppy, lends me to believe by another welder and another process, likely MIG. To me this throws the whole stress, and heat zone control thing out the window, This is where the large debate and general consensus of don't weld on these comes from, yet it appears as though brand new some of these smaller vessels don't have the same control that we demand here even though they are brand new and still operate at pressures up to or maybe exceeding 125 psi. Food for thought and playing Devil's avdocate for those that have welded these at home. Most poinant though is the question is it worth injury or worse for a $300 tank.   Not looking to get beat up here but these size units might slip through a crack in the cert. requirement and many , many are sold and in use without a lot of reported catostrophic failures that I am aware of.  Anybody here know more about the whole assemby process on these?Last edited by kolot; 08-28-2011 at 01:19 AM."Si Vis Pacem Para Bellum"Lincoln Idealarc 250 AC/DCMillermatic 251   Syncrowave 300   30A spoolgunLincoln MP210Hypertherm 45(2) LN 25(2) Lincoln Weldanpower 225 CV(4) SA200   1 short hood    SA250    SAM 400
Reply:I was at Home Depot the other day and took a look at them.  They are definitely under 6", so there is no monitoring.  The smaller you go in diameter, the stronger the pipe gets for a given thickness.  Since the burst pressure of pipe is generally quite high (6" Sch 40 has a theoretical burst pressure of about 4000 psi) you won't hit another code issue with the pressure tank until 3000 psi when Section VIII Division 3 *might* be applicable.The manufacturing process is as follows:-Plate is decoiled and flattened (or purchased as flat from supplier)-Shear shell to size-Roll and tack shell plate-Longitudinal seam is welded by a (robotic) seam welder using MIG-Ends are pressed-Ends and couplings are tacked-Ends and couplings are welded by another robotic MIG welderThe brackets are either added in this factory or the one assembling the tanks.  The brackets aren't generally difficult welds to make in comparison to the long seam and girth seams.
Reply:OK, gonna pick a fight here, what the hey. So as I suspected these small tanks can be welded by say, other than a super certified vessel welder. And I probably will make the repair on mine of a tiny crack at the handle where it had been dropped. If you look at the posts here people will tell you if you weld that tank yourself the world is gonna come off it's axis and all sorts of woes. I will stack my ablility with what I see on these tanks, but I don't have to. My son caught wind of this,laughed, and flipped a cert down on my bench that I didn't know he had.Now I don't know how strict that section of the code is but it does refer to pipe and pressure vessel and is given by steam fitters and boilermakers. Pictures are enclosed name covered for obvious reasons. Now heres the funny part, He got this cert last year at a competition for the trade school he attends, this comp is a big deal and is held every year for seniors in pipe welding by a local contractor and the boilermakers union. First place is guaranteed  a job/ apprenticeship with the company. My son was a junior and had to argue to compete,  placed 3rd in the state. enough bragging, but with all the controversy here a kid with no field experience and limited overall experience is technically qualified to weld a pressure vessel, granted 1G but with all the nay sayers here I don't think it is quite as big a deal. I will guarantee my son doesn't know about heat affected zones and the stretch shrink factors and all the engineering but he did pass the testing both destructive and NDT. And if what the above post says is true, and the appearance of the tanks is exactly in line with the mfgr. process described, The press. vessel code is out the window for the same bomb that holds 135PSI as indicated on my guage.  OK I'm ready , beat me up. LOL      Now as the above post states the smaller the diameter the stronger the pipe, understood but the controversy here basically is if you touch that pipe with a welder you will weaken it to the point it will breach under pressure. If that was the case no one could weld them. I do understand you don't want a beginner undercutting the hell out of it or digging a crater in the end of the bead for a thin spot. Attached ImagesLast edited by kolot; 09-02-2011 at 11:37 PM."Si Vis Pacem Para Bellum"Lincoln Idealarc 250 AC/DCMillermatic 251   Syncrowave 300   30A spoolgunLincoln MP210Hypertherm 45(2) LN 25(2) Lincoln Weldanpower 225 CV(4) SA200   1 short hood    SA250    SAM 400
Reply:That weld cert and a dollar might get you a cup of coffee. It'd be good for a laugh or two on a jobsite.  No disrespect intended but that is a very generic cert.  As you said, earned by someone with no actual job knowledge or experience.The actual welding on the pressure boundaries are almost always done by robots.  All aspects pertaining to material, heat treat, filler metal, etc. have been figured and allowed for.  Testing has verified that the procedure is adequate for the production of sound welds on an ongoing basis.Feet, handles, mounting plates and other attachments are all done to certain standards as deemed by any applicable standards or laws.  The quality of the work must be sufficient to pass the requirements.The finished product must be of a high enough quality to be sold on the market and not pose a liability from defects.  If it does not have the required quality, accidents are usually the result with lawsuits coming in short order.What you are proposing is to weld a damaged area that now represents the pressure boundary.  Do you know what the material being welded is?  Is preheat or postheat required?  What about interpass temperature requirements?  Will you get a full pen weld? Or will you be relying on build up from a fillet to make a strong enough weld?  Can you at least dye check the welds?  Will extra weld in that area introduce unwanted stresses?There is a lot to consider when welding on a pressure vessel.  I've welded a lot of pressure vessels in the regular world and in the nukes (whole nother world).  You may be capable of making the repairs yourself.  May not be much of anything special about it.  But what if there is?  Or you don't make quite as good of a weld as you thought?  What if you, a friend or a family member are standing next to that vessel when the vessel ruptures?  It won't be pretty if it happens.  To paraphrase Clint Eastwood in Dirty Harry, "Do you feel lucky?  Well, do you?"Last edited by Bob the Welder; 09-03-2011 at 12:58 AM.Reason: Punctuation"The man of great wealth owes a peculiar obligation to the State, because he derives special advantages from the mere existence of government."  Teddy RooseveltAmerican by birth, Union by choice!  Boilermakers # 60America is a Union.
Reply:Playing devils avdocated here and will likely junk the tank and part out the components , but for my education define " Pressure Boundaries" would that be the seams of the components that form the tank, or would that be any portion of the assembly that would find itself under pressure. In post 4 and as you have said it seems these tanks are welded by robotics with all the variable of alloy, filler and alike figured in. But in #4 it states that the long seam and end shells are the most difficult welds with the handles and brackets fairly simple welds. And I think we have determined in this size tank no monotoring of the procedure is noted. My question at it's basic is this, are the people who weld the brackets and the handles and such any more qualified then the majority of us here.   In regards to the cert, yes it is generic, but it is given by the Boilermakers, which by your signature you are a member, and it is exacly the section, IX of ASME listed in the posts above.    Tank has a very small pin hole leak at the top, from a small fracture or crack, not a rust issue, If what we have discussed here is true and the what if's are taken into consideration, it would be just as dangerous to use it as is as it would be to weld it. In the end I will likely saw it in 2 and discard it as I don't want anyone hurt by it.  Thanks for the info/education"Si Vis Pacem Para Bellum"Lincoln Idealarc 250 AC/DCMillermatic 251   Syncrowave 300   30A spoolgunLincoln MP210Hypertherm 45(2) LN 25(2) Lincoln Weldanpower 225 CV(4) SA200   1 short hood    SA250    SAM 400
Reply:A pressure boundary is represented by an opening from the inside of the vessel to the outer shell.  Tanks of this sort are usually made of thin material.  There is a difference between welding a seam and welding an attachment to the shell.  But both have to be qualified.Anyone who welds on a pressure vessel must be qualified to do so.  If I test for a contractor (almost always 6G) and pass the test requirements I will be qualified by them to weld on a vessel that the test was given for.  If parameters change, material for example, I will have to test for that. Could be that the test I took was not for unlimited thickness.  Now the contractor wants me to weld on a 3" thick vessel.  I can weld to the maximum thickness that my cert allows, then another welder will do the same, followed by another until the weld is done.  Or I could take a test on a "monster coupon" that will allow me to weld the entire pass by myself by virtue of the "unlimited thickness" aspect of the test.And I think we have determined in this size tank no monotoring of the procedure is noted.
Reply:paid very little for the unit so I will keep the components and wait for another tank to come along that is in good shape.   So a pressure boundary would be the bungs that are welded in for the regulators or tank drains or any other fitting coming off the tank. What would a hydro test cost on a tank, is it comparable to when they test out of date gas cylinders? I have never had a gas cylinder tested as most of mine are exchanged when filled, but I here of guys who own the tanks having them done all the time. Can't be that much for a gas cylinder or they would replace them.   I did just do a 80 gallon compressor that I bought , cheap again, but the tank had been repaired at the bottom and it is fairly ugly. When I bought it it was holding air but because I didn't know who welded it and it is dated 1963 I replaced it with another tank dated 1995. Interesting is the difference in tanks, both are rated too 200 psi but the older tank is much heavier and the thickness  on the walls and shells listed is thicker than the newer tank by quite a bit. Some say this is due to newer stronger alloys, I am a fan of thicker.  anyway it will make a nice barbecue, something I hope to start soon and will post up.     reading the posts here and in other areas on the site makes you think twice about a used compressor, if Hydro is not that much it might be and option for peace of mind when buying and older used compressor."Si Vis Pacem Para Bellum"Lincoln Idealarc 250 AC/DCMillermatic 251   Syncrowave 300   30A spoolgunLincoln MP210Hypertherm 45(2) LN 25(2) Lincoln Weldanpower 225 CV(4) SA200   1 short hood    SA250    SAM 400