Welding a copper boiler?

[awake]

A strange experience:
I experienced a weld - from a factory process, with speed controlled and jig held MIG torch, so gas, feeds and speeds, etc. all calibrated and set, and batch recorded.... but of thousands of welds joining structural end fittings to steel tubes, one single end casting had some "contamination" so the weld that looked as perfect as the rest had zero penetration into the casting. Sent to the Welding Institute for a report on "Why? and what went wrong?" they were completely bamboozled. This was not a pressure weld, but a tension member: When the load was applied as the structure was assembled, a ring of unwelded steel casting appeared as the end piece pulled-out of the tube. Micrograph sections showed perfect penetration and welding to the tube and a non-welded friction joint between the weld and the end casting. The report suggested the end casting may have been simply VERY cold, or had some insulating pollution (Oxide?) on the surface that prevented the arc from "hitting" real metal so the feed metal "spray" simply sat on the surface of the end casting. Further metallurgical lab studies had failed to find any contamination, so the Welding Institute report had "no conclusion" for the failure. - Had this been a pressure vessel shell, pipe-joint or whatever, the pressure test would have definitely exposed the faulty weld. The Company had stringent checks in place, so all welded and bolted joints were examined for movement as the structure was built and during loading up to completion. These checks had identified the failure part way through construction of the building. No other faults were found.
Conclusion. A visually externally perfect weld can have a total failure within. But if it "holds the load without failure", then it can be deemed OK. - Except the "Factor of Safety" may be compromised.
For Boilers in service, the equivalent loading "to ensure safety" is the periodic Hydraulic test at an excess well above the Safety valve release pressure. (ASME and UK regs require different pressures, but both have "Excess" pressure applied hydraulically).
I personally feel that there can be many boilers "in service" where joint integrity is "Imperfect", even by design, such that an over-pressure of the boiler could fail a joint at well below the "design expectation". The Safety valve must therefore be suitably respected and checked against the gauge at every steaming to be sure that boilers cannot experience adverse conditions. ALL Boiler operators MUST also be well trained and "compos mentis" when operating boilers to prevent operation outside the correct operating limits.
(compos mentis: = (law) Of sound mind, sane; thus criminally responsible for one's eventual wrongdoing).
K2

Jody at Welding Tips and Tricks recently released a video comparing MIG welds on hot rolled steel. For one he did not remove the mill scale, and for the other he did. The welds look more or less identical. Guess which one failed with barely an effort?

My sense is that the "visual test" is far more applicable/useful for TIG and SMAW than for MIG - but I'm no expert by any stretch, so perhaps someone else can correct or confirm ...

 

[Steamchick]

Thanks Andy. On the steel tube to steel casting welds where I experienced a failed weld, it was very comparable to the Mill scale plus COLD weld shown in the video. Which is what I remembered of the welding institute report. As welds and parts were batch welded (per shift) with a few samples taken for examination and testing through the shift, it was surprising we didn't identify any other bad welds of the thousands of welds passing through that shop and process. But that is statistical process control for you.... There is always one that "bites you where it hurts"!
Anyway, it demonstrates that the "good looking welds" can deceive!
In the case of a welded pressure vessel, the stress of pressurising the vessel during the hydraulic test should show any weak welds with almost no penetration, due to the pressure applying the stress that should break the weld. Any full penetration crack would show as a leak.
Dye penetrant testing is also a good guide as to the consistency of weld metal penetration and fusing with parent metal.
But only destructive testing tells the true story!
Thanks,
K2

 

[awake]

I have done a little experimenting with the cut and etch destructive testing. I got a new inexpensive import MIG welder and wanted to test out various settings.

For those that may not know the cut and etch test, you weld two pieces together (I typically do a T joint), then cut across it to get a cross section of the weld. That in itself is not enough to really see anything, but if you polish it and then etch it with acid, you can clearly see where the weld metal is vs. the original metal. I've seen a couple of different acids used in video (nitric? maybe hydrochloric?), but I decided to try with something simple: vinegar. Unlike the other acids that I've seen in videos, vinegar did not give immediate results, but I wasn't expecting that. I let the part soak in vinegar for a few minutes ... and sure enough, it worked - I could clearly see how much penetration (or not) that I got.

Note that this is a "point" test - it doesn't verify anything about the weld before or after this particular cross section. But it is a very useful procedure to see how your settings and technique are working.

 

[Steamchick]

Well done Andy. You make "micrographic analysis of weld sections" sound as simple as it really is. But you can do a test weld (to check and set the best voltage, current gas pressure, gaps, lead/lag of the arc per weld pool, etc. and section along the weld to check for porosity, penetration, consistency of the feed-rate of the weld (how steady you are?) , etc. I would suggest 3 cross sections (start, mid-weld and finish) and 2 longitudinal sections (mid-section and a section near the edge for undercutting or lack of penetration) could be a good judge of a welder and settings. - But I am not a welding engineer, so we need an expert opinion here.
Thanks,
K2

 

[awake]

I had thought about suggesting more than one cross section - definitely agree with start, middle, end. I have not seen a longitudinal section - I would be very interested in seeing that!

 

[Steamchick]

My garage is all topsy-turvy just now: in the process of installing a new bench and material store shelves. (All the junk fills the work-space!). So, I can't get at my stick welder to do a "bad" weld and section it for you. (I find it easy to do the "bad" welds... until I have practiced a bit!).
Sorry,
K2.

 

[Richard Hed]

My garage is all topsy-turvy just now: in the process of installing a new bench and material store shelves. (All the junk fills the work-space!). So, I can't get at my stick welder to do a "bad" weld and section it for you. (I find it easy to do the "bad" welds... until I have practiced a bit!).
Sorry,
K2.

Nowadaze, MIG and TIG welders for 5 year olds are so cheap you could get one of each of thoze or a cheapo that doez both. I find they are a lot of fun compared to stick. (Stik has it's place tho' if you are into welding battle ships in your bakyard.) Of course, you can't make really important welds with the kidz toyz.

 

[awake]

My garage is all topsy-turvy just now: in the process of installing a new bench and material store shelves. (All the junk fills the work-space!). So, I can't get at my stick welder to do a "bad" weld and section it for you. (I find it easy to do the "bad" welds... until I have practiced a bit!).
Sorry,
K2.

Oh, I wasn't actually hinting that you should do the longitudinal test; I was thinking more that I'll need to see if I can hunt up a video or two on YouTube to get an idea of this test.

Yes, my stick welding skills are at a low ebb. That is all that I ever did for many years; then I "graduated" to TIG, and that is what I mostly do. But as I said, I recently got a cheap MIG machine, which seems to perform surprisingly well thus far, so I am starting to learn MIG. But I don't feel as much confidence in the quality of the welds without doing some checks. With TIG and stick, I've heard it said that "if it looks good, it probably is good." I can testify that that isn't always the case, but it does seem much easier to lay down a beautiful bead with no penetration using MIG.

 

[Bentwings]

I like your test this type was don periodically in the weld shop also the dye penetrant was used extensively
I have done a little experimenting with the cut and etch destructive testing. I got a new inexpensive import MIG welder and wanted to test out various settings. Virtually al tubing or closed vessel welds wet don with back purge argon even the tank trucks a purge blanket or seal was used picture welding in s metal closet on its side with round sides both inside and outside purge system If you were phobic it was terrible wiring conditions there was a trained medical person inside with you but it was scary. Fortunately the pay was much easier to accept LOL SMALL VESSELS WERE HYDRAULICALLY TESTED ALL OF OUR Race somewhere I still have sample test welds CAR FRAMES WERE WELDED USING BACK PURGE and dye penetrant tested

For those that may not know the cut and etch test, you weld two pieces together (I typically do a T joint), then cut across it to get a cross section of the weld. That in itself is not enough to really see anything, but if you polish it and then etch it with acid, you can clearly see where the weld metal is vs. the original metal. I've seen a couple of different acids used in video (nitric? maybe hydrochloric?), but I decided to try with something simple: vinegar. Unlike the other acids that I've seen in videos, vinegar did not give immediate results, but I wasn't expecting that. I let the part soak in vinegar for a few minutes ... and sure enough, it worked - I could clearly see how much penetration (or not) that I got.

Note that this is a "point" test - it doesn't verify anything about the weld before or after this particular cross section. But it is a very useful procedure to see how your settings and technique are working.

 

[Bentwings]

I used to see the no pen mig welds a lot my comment was something like “ what do you feed your chickens?
Oh, I wasn't actually hinting that you should do the longitudinal test; I was thinking more that I'll need to see if I can hunt up a video or two on YouTube to get an idea of this test.

Yes, my stick welding skills are at a low ebb. That is all that I ever did for many years; then I "graduated" to TIG, and that is what I mostly do. But as I said, I recently got a cheap MIG machine, which seems to perform surprisingly well thus far, so I am starting to learn MIG. But I don't feel as much confidence in the quality of the welds without doing some checks. With TIG and stick, I've heard it said that "if it looks good, it probably is good." I can testify that that isn't always the case, but it does seem much easier to lay down a beautiful bead with no penetration using MIG.

 

[Steamchick]

Re #68: No problem Andy. I was tempted to do longitudinal seections for a good bit of fun! - till I thought "Finish re-organising the garage first" - which will mean it is a lot easier to do everything. Yesterday I was distracted by the fine weather encouraging me to build a brick and concrete step up into my new greenhouse... next is a potting bench and pot store, shelves, etc.
Too many jobs, too little time and energy
K2

 

[awake]

Too many jobs, too little time and energy

Amen!

 

[swarf]

Root and face bend tests are done for welder performance and procedure on butt welds on plate and pipe.
If an indication of larger 1/8" in any dimension shows (with the exception of the edges unless a definite weld fault from inclusions, cold lap, lack of fusion etc) the weld is acceptable.
Acceptable meaning for performance tests, the welder has proved he can deposit sound welds.
Acceptable meaning for procedure testing along with tensile, impact testing etc the weld meets the requirement of most structural and pressure vessel/piping codes (AWS, ASME)

 

[Bentwings]

I guess I havevtonqualifybyhe cheap welders test the China ones are pretty cheap. However if you ever have issue with one …….. it’s new unit as repair is pretty dismal Support is about the same I have a Lincoln 175 square wave . These were temporally discontinued then Lincoln suddenly re released then then added a slightly more powerful version it too has a very high resale value to day. I called Lincoln support once for some thingblong forgotten about they hooked me up with a real person in a matter of minutes who answered my question what ever it was I was impressed I’ve welded 1/2” aluminum many times . It’s a matter of experience and skill. I attended one series of classes purely to get a certification I already was able to do everything the class provided I did continue working in a small shop doing everything that came in the door I got into stainless and more exotic materials with increasing difficulty My “ little Lincoln “ just welded right along The shop got a top ofvthe line Miller with every option . Incredibly expensive piece . I explored al of the options but it became clear that I was already doing pulse And many alloys was it easier ? Well it took plenty of time to explore the options by using just standard settings and doing what I had been doing for a long time I was able to essentially do everything the big welder did. When somebody else came in they took forever to stop messing around then not getting quality welds much of what I did got dye pen or X-ray inspected other guys beat their heads against the wall trying to get things to work so it wasn’t the machine that made the quality welds. I do agree thatbifvyoubunderstandcwhatvyouvarectryingvtondobthevmonster may make it a bit easier But you really need to know the process or you will constantly fiddle with controls and still not getting the job done . A big job I worked at was performance based you had quotas to meet every day so that meant 100 % operation with no time for ducking around with the machine. So be carefull what you spend dollars on
MMIG and TIG welders for 5 year olds are so cheap you could get one of each of thoze or a cheapo that doez both. I find they are a lot of fun compared to stick. (Stik has it's place tho' if you are into welding battle ships in your bakyard.) Of course, you can't make really important welds with the kidz toyz.

 

[Bentwings]

Any one please?

I waded through most of this boiler stuff much of it I’m only interested in how it works and how the design was achieved . Did it psss regulations. I did check my local refs and for practical purposes if a fired unit was out doors they didn’t even want to look at it the comment was if it’s fired indoors but a commercial unit , don’t even try to build or make one it’s hard enough to just get nat gas plumbed in. So I looked back at my experience in industry. Aero space was the main area I was involved with active battery powered ordinance . EXTREMELY DANGEROUS STUFF as the battery is active and can’t be turned off . Military does no like dropping “ live” ordinanance anywhere except battle field targets . Landing on carrier with live ordnance almost takes admiralty clearance level . Anyhow much of the work was done on very high pressure vessels Al were hydraulically tested ther was slab thst had a big water tank “ fish tank” we called it. I was highly certified TIG and MIG. Welder so I got to weld lots of seams and fittings then test them . I’d some small copper tube that would be model boiler stuff copper welds vey nicely but needs after heat treat to bring back properties . As does stainless and high alloy steels. Amazing old RR. Steam engines lasted as long as they did . But copper was kinda unique even after heat treating some cylinder “ IE boilers would expand like balloons in the fish tank before rupturing at some pressure . Brazed and various soldered stuff simply failed at low pressures. I remember testing stuff and have scrapped my own boiler as poor design . Ever hear a senior engineer admit to poor design? Well you just did . I’m not boiler capable . My steamer run on compressed air or they don’t run . I’ve seen plenty of messed up compressed air tanks come apart and much prefer to vacate the area if shanagans are going on .



All I can say is follow the refs and be done with it

 

[Steamchick]

Understanding what you can do, and what you CANNOT do, is a significant step in Engineering anything. While not bound by ASME,
if such a body as the American Society of Mechanical Engineers says "do this" - I reckon they can... and if they say "Don't do this" I won't. - Learn from the best? (Just think about who they are? - Not government administrators, just ENGINEERS, with more experience than this whole website perhaps?).
So "Silver Soldered Copper Boilers up to 100psi" is a pretty simple rule for me. I don't need any more pressure than following their rules.
K2

 

[timo_gross]

deleted, just saw that is a 4 year old post.