sch-10 304 turbo manifolds keep cracking.
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  1. #1

    sch-10 304 turbo manifolds keep cracking.

    I've been building turbo manifolds for a few years. They seem to keep coming back. I've tried a few things without much success. Normally the ones heated/stressed more are the ones to fail. The 4cyl's producing 400-600hp are usually a given... Just a matter of time.

    Currently I've been using sched-10 SS pipe. It's backpurged. I use a 3/32 tungsten (red). Normally I TIG it at about 80-100a. I have tried 1 pass and 2 passes. The joints are tightly fit with bevels - that's how the weld ells usually come. The filler rods are 308L and I've tried 1/16 as well as 3/32 - virtually no difference. I've cut apart a few test welds and the pen is usually very close to 100% with no sugar on the back.

    The welds usually come out a little oxydized for my taste - I'll try to get pics. I spent some time searching and my welds do look better than some posted by others. Just curious to know what I might be missing.

    -Michael

  2. #2
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    Re: sch-10 304 turbo manifolds keep cracking.

    Michael,

    I think the "close to 100% is the clue, here. When you're making a weld that is stressed, the stress tend to propogate from any discontinuity in the metal. A less than 100% weld in a stressed tube basically is a built in notch defect, and will concentrate the stress and apply it through the weld. Consider: take a piece of paper, hold it with your thumb and forefinger in two corners, and tug gently. Then put a very small tear in the paper, and tug again. Paper rips quite easily from the existing tear.

    Make sure you gap the tubes when you start to weld, to ensure you completely fuse in the root. A tight fit keeps you from getting a good burn on the root pass. Since you've got no sugar on the inside, sounds like your purge is good. 100% penetration will help, especially with the high HP stuff.
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    Re: sch-10 304 turbo manifolds keep cracking.

    80 to 100 amps is on the high side for .109 wall stainless IMO. Remember, you should be using less heat than you would for mild steel. If the welds are getting that greyish, oxidized appearance instead of the normal coloration, that's likely the problem. What grade stainless are you using?

    Also, where are they failing? I'm betting the crack is usually just outside the HAZ near the flanges. If so, you may want to look into small gusset plates from the flange to the tubing.

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    Re: sch-10 304 turbo manifolds keep cracking.

    Capnbondo shared this information:

    http://weldingweb.com/showthread.php?t=22270
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  5. #5
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    Re: sch-10 304 turbo manifolds keep cracking.

    As Supe said, more info (and ideally pics) on the mode of failure is needed to provide an autopsy. I'm guessing 304/304L but it'd be nice to know

    Of the cracked manifolds i see/get to fix, failure typically comprises either of the modes described by KBnit and Supe- sometimes both on the same manifold!

    Another thread where this subject is discussed... http://weldingweb.com/showthread.php?t=21809

    Personally i would steer well clear of gussetting something like this, allways seems to cause more problems than it fixs IMO, unless it's a support along the lines of the F1 example in the above link- known as 'turbo dampers' in Cosworth circles

    I did dig out the manifold i referred to in that thread, a (badly) gussetted example and will DPI it and post pics tomorrow as i've got a fairly quiet day lined up - well so far at least

  6. #6
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    Re: sch-10 304 turbo manifolds keep cracking.

    Hotrodder: I'm not big on manifold restraint myself. A recurring problem I did see was oversized turbos hanging at an angle, putting a great deal of stress right at the flange. A small, fairly non-restrictive gusset would alleviate a great deal of that stress. Yes, it is a bit of a tradeoff, but I've seen in DRASTICALLY reduce the number of cracked manifolds by using one.

    Then again, I did talk one customer into a set of inconel headers some time ago. One of my favorite jobs, loved it when they had deep pockets

  7. #7

    Re: sch-10 304 turbo manifolds keep cracking.

    Supe, no, they've never cracked at the flanges and those are usually the best "looking" welds. I've ordered a gas lens because I suspect it wasn't getting proper coverage. I read a few complete threads on the subject before posting. Some people in Capnbondo's thread suggested butting them, others like here have suggested leaving a gap.

    As per the title it's 304 welded with 308L rod. The cracks are usually on the border of the weld bead, not really on the edge of the HAZ. I've got a manifold coming back that has been re-welded 5-6 times so far and it just keeps cracking in different places. I'll try to snap some photos before I excavate the cracks and reweld again.

    -Michael

  8. #8
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    Re: sch-10 304 turbo manifolds keep cracking.

    the reason why the ones that were heated more fail on you is because 300 series stainless does not like too much heat or they will get heat embrittlement or carbide precipitation and will crack. Your amperage is way way too hot, 3/32 tungsten with 1/16 filler try from 40-70 amps.. 304 -> 308 /316 filler or 304L -> 308L / 316L filler

  9. #9

    Re: sch-10 304 turbo manifolds keep cracking.

    Some guys at a speed shop in my area run alot of 4 cyl turbos pushing over 400hp to the wheels. They use Sch 40 mild steel weld els for thier custom manifolds. He mentioned he had a similar problem to yours when he was using the Sch 10 stainless. He said the quality of the stainless steel in those chinese elbows is sub par, and they come apart too easy, and thats why he switched to the Sch 40 mild. Is it true, who knows?

    Now as far as the gusset is concerned, I do know that a buddy of mine ran a modified mild steel manifold on his 4 cyl turbo. It was originally set up for a right hand drive car in japan, but here in the states the steering components get in the way. He had the wastegate moved to clear the linkages, and a gusset was added for strentgh. After one day the tube had cracked at the weld along the exhaust manifold. After that he brougnt it to me and I rewelded the tube. The next day he was back, it had done the same thing. After some hard thinking, we surmized that the extreme heat on the tube required some room for expansion and movement of the tube. I cut out the old tube that held the wastegate as well as the gusset, and fabbed a new wastegate down tube out of thicker tubing. I left the gusset out of this design, and thankfully the thing didnt fail again. It took a major beating at the track, every other weekend for about a year, and was still solid when he sold the car. Who knows if its still going today.
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  10. #10
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    Re: sch-10 304 turbo manifolds keep cracking.

    I don't know if this pic will post but here is a case of one needing to be supported if there ever was one. This happened after 50 hours run time on this airboat.

    f171_12.JPG (37.0 KB)
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  11. #11

    Re: sch-10 304 turbo manifolds keep cracking.

    That one is holding quite a bit of weight. I think cast iron manifolds are best for turbo applications since they can support more weight. They might not perform like the tubular type, but reliability is better.
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  12. #12
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    Re: sch-10 304 turbo manifolds keep cracking.

    Quote Originally Posted by hackish View Post
    Supe, no, they've never cracked at the flanges and those are usually the best "looking" welds. I've ordered a gas lens because I suspect it wasn't getting proper coverage. I read a few complete threads on the subject before posting. Some people in Capnbondo's thread suggested butting them, others like here have suggested leaving a gap.

    As per the title it's 304 welded with 308L rod. The cracks are usually on the border of the weld bead, not really on the edge of the HAZ. I've got a manifold coming back that has been re-welded 5-6 times so far and it just keeps cracking in different places. I'll try to snap some photos before I excavate the cracks and reweld again.

    -Michael
    Doh! Had a bit of a senior moment there, 304 in the title didn't register

    Good pics would REALLY help. At the moment i'm thinking KB may well have nailed it. If there's any surface defects, even minor ones (thinking undercut, poorly tied in toes) then combined with LOF at the root...

    Don't know about elswhere but in the UK a lot of 304 etc carries the dual designation 304/304L. For the average guy buying 300 stainless the low carbon grades are what you get unless you specifically specify something else (say, 304H). Carbide precipitation isn't really an issue

    There's pros and cons to both ways of pipe fitting for this sort of work. A root gap lowers the amount of heat needed and helps with regard to getting complete fusion but makes the fabrication side a little more fiddly. A compromise would be to 'knife edge' the bevels during fitting and go without a root gap- best of both worlds for manifold work IMO

    Quote Originally Posted by Supe View Post
    Hotrodder: I'm not big on manifold restraint myself. A recurring problem I did see was oversized turbos hanging at an angle, putting a great deal of stress right at the flange. A small, fairly non-restrictive gusset would alleviate a great deal of that stress. Yes, it is a bit of a tradeoff, but I've seen in DRASTICALLY reduce the number of cracked manifolds by using one.

    Then again, I did talk one customer into a set of inconel headers some time ago. One of my favorite jobs, loved it when they had deep pockets
    Not been my experience but then you probably put more thought into the design than the mass produced ones i normally see. The manifold i'll DPI and post later shows how bad gussets can be!

  13. #13
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    Re: sch-10 304 turbo manifolds keep cracking.

    Manifold is off an S13 Nissan, apparently less than 9 months use with a standard size turbo...
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    This is the reason it was brought to me...
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    Pretty clear from this pic that after welding another pulsed autogenous pass was made to get 'the look' . Looks to have been 'well cooked' in places


    The gussets were a pain with regards to DPI but this is what we have after around 10 mins contact time
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    Re: sch-10 304 turbo manifolds keep cracking.

    Close up time...

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  15. #15
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    Re: sch-10 304 turbo manifolds keep cracking.

    Maybe I am just to new to this stuff, but wouldn't 308, or 316 be better suited for this?

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    Re: sch-10 304 turbo manifolds keep cracking.

    1-So much for making things look 'so pretty', with autogenous/fusion welds. Those NDT pics say volumes as to 'why' one needs to use filler, nice fairing, no undercut.....especially in stainless.
    Those really are great pics!

    2-I just had a Mazda, aftermarket, ss turbo collector in a week ago, for some supposedly 'minor' touchup welding. Well, this thing was cracking, upon cool down--outside fresh bead. Then got to looking some more (didn't bother with penetrant inspection) and it had all manner of tight cracking in various places. This part had seen a good amount of service, in use. The stainless was totally degraded. It was 304 SS. The collector was junk.

    Reason I'm mentioning the above, is yes--in high output, high heat applications---304 definitely has a limited life cycle, even with competent fabrication. Aircraft exhaust manifolds, which are like
    18-20 gauge, ss--use 347--for better heat resistance--and significantly higher cost factor.

    Maybe the lowbuck approach is to use heavier guage 304--not the S. 10 304, for increased service life
    Blackbird

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    Re: sch-10 304 turbo manifolds keep cracking.

    Quote Originally Posted by dave powelson View Post
    1-So much for making things look 'so pretty', with autogenous/fusion welds. Those NDT pics say volumes as to 'why' one needs to use filler, nice fairing, no undercut.....especially in stainless.
    Those really are great pics!

    2-I just had a Mazda, aftermarket, ss turbo collector in a week ago, for some supposedly 'minor' touchup welding. Well, this thing was cracking, upon cool down--outside fresh bead. Then got to looking some more (didn't bother with penetrant inspection) and it had all manner of tight cracking in various places. This part had seen a good amount of service, in use. The stainless was totally degraded. It was 304 SS. The collector was junk.

    Reason I'm mentioning the above, is yes--in high output, high heat applications---304 definitely has a limited life cycle, even with competent fabrication. Aircraft exhaust manifolds, which are like
    18-20 gauge, ss--use 347--for better heat resistance--and significantly higher cost factor.

    Maybe the lowbuck approach is to use heavier guage 304--not the S. 10 304, for increased service life


    Great post Dave!

    347 all the way. 304 will crack next to the weld when heat cycled, always! Nothing can be don to stop it. Adding more filler just moves the crack away from the joint that much more.


    Think about the what we are doing here, a dynamically loaded, high heat cycled, to more than 1000F and doing it several times a second, internally pressurized.

    My suggestion is to reduce the loads you can, lighten the hung weight. Add bracing back to the block bolted at both ends, to lessen the cyclic vibration. Use material better suited for the application such as 347, titanium some of the inconels(sp)


    I made one for a VW boosting to 24psi been racing for 9 years now (500 racing hours). self supported no added braces. Made from sch 40 steel pipe 90's and 1/2" plate for the flanges [look under the intake its wrapped in header wrap. The steel conducts a more even heat to the turbo so on spool up we have less lag. Price is weight return for the weight reliability.



    All just MHO take it or not I don't care.
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  18. #18

    Re: sch-10 304 turbo manifolds keep cracking.

    D'oh forgot my camera again today.

    Hotrodder what is that red stuff you're using to find the cracks? That looks like a chinese manifold - I see and replace a lot of them around my shop. I'm not sure what they put in their stainless but it's really shiny and polishes well but they always crack. It's advertised as 304 when you buy it from the chinese supplier but it sure doesn't weld like 304 and it's a brittle as hell. I've cracked it before by just heating and tapping on a section to shrink it.

    I've never had trouble with short logs like the one posted on the VW. It's usually the more complex ones.

    On another point does anyone know where to get 321 or 347 weld ells in 1.5 and 1.25 sc-10 size?

    -Michael

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    Re: sch-10 304 turbo manifolds keep cracking.

    Hackish,

    It's 'dye penetrant inspection' (DPI), one of many different forms of NDT for surface flaws- wikipedia probably has an article on it. Any welding store should carry it, it's cheap (under £20 for the three aerosols needed- dye penetrent, cleaner and devolper), easy to use and a bitch to remove from clothing

    Basically you clean the area to be tested, spray a generous coating of penetrant (the red) and have a tea/beer etc while it does it's thing- getting drawn into flaws via capillary action. Contact time is 10 mins minimum, longer contact time = detection of finer flaws. Excess dye is then removed with a clean lint free cloth before more thorough solvent cleaning- saturate a cloth in the cleaner and go over the area to remove any remaining dye on the surface. Don't spray the area directly with cleaner as that can result in the removal of dye from flaws. When it's clean and dry the devolper is applied- in this case a dryish white powder which helps 'draw out' the dye and is a contrasting colour

    It'll work on any metal (almost any non porous surface really) but the 'etched zone' on aluminium will hold dye so needs removing first really

    Yes, this manifold is from the far east i believe but i can't really comment on the quality of the tubing of this one- i've repaired/modified identical/similar manifolds that worked/welded fine. I just cut and shut some intake piping made from the 'really shiney' far eastern stainless, welded like crap, very dirty so i do know where you're coming from.

    321/347, never found it as preformed mandrel bends in the UK, the only stockists typically specialise in aerospace (my local supplier hadn't even heard of 321 ) and only carry straight lengths

  20. #20
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    Re: sch-10 304 turbo manifolds keep cracking.

    Smokeshow,

    A gross simplification but 304, 316 even 321 all have the same upper temperature limits and they're all 'modifications' of the basic chromium nickel alloy- adding a little molybdenum to 304 improves corrosion resistance, particuarly in chloride environments. This is 316, sometimes refered to as 'marine grade'. 321/347 are 'stabilised' (contain titanium/niobium respectively). While the maximum service temp is not increased they don't 'degrade' at intermediate temperatures/fluctuating temperatures the way 304/316 can, hence Dave and Fat Bastard mentioning them

    Fat Bastard,

    I don't specialise in this sort of work (far easier ways to make a living) but to say 304 WILL fail is an over simplification IMO. Typically i use sanitary bends (so 16g) and have never had a failure- not had any customers running the same set up for 9 years though, they usually change things around in the search for more power/better torque spread before that much time has passed. The manifold i posted a few months ago was bought second hand and had a year or so use before i was asked to modify it- entire thing was made from 16g 304, as were my mods. I expect the 'turbo damper' is probably the key. Titanium would however be an expensive mistake for a turbo manifold

  21. #21
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    Re: sch-10 304 turbo manifolds keep cracking.

    Thanks!

    I was just checking. I was trying to find out why everyone tends to use 304 and not others.

  22. #22

    Re: sch-10 304 turbo manifolds keep cracking.

    These are closeups of the manifold on my car. It didn't turn out quite nice enough to give to a customer so I used it on my own.



    Overall photo. Pretty dirty and has been used now for 4 days. Not too much heat yet.



    The flange looks OK. Never really had a problem with welding flanges.



    As you can see some of the round stuff is a bit sloppy and of course with a big macro lense it looks even worse.


    Here is the collector - more of the ugly colour. I assume too much heat? A little undercutting too but haven't figured out how to fix that. Torch is too big for those areas.

    Here are some more of a collector I was working on:



    Feel free to make any suggestions.

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    Re: sch-10 304 turbo manifolds keep cracking.

    A little hot in spots. My advice is to get a gas lens setup. It's a LOT easier to get into those tight spots when you've got 3/4" - 1" of tungsten stickout.

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    Re: sch-10 304 turbo manifolds keep cracking.

    Quote Originally Posted by smokeshow View Post
    Thanks!

    I was just checking. I was trying to find out why everyone tends to use 304 and not others.
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  25. #25
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    Re: sch-10 304 turbo manifolds keep cracking.

    Quote Originally Posted by Supe View Post
    A little hot in spots. My advice is to get a gas lens setup. It's a LOT easier to get into those tight spots when you've got 3/4" - 1" of tungsten stickout.
    Amen! to the gas lenses.
    They're available in a bunch of configurations.

    Another trick---none other that Zap---has shown repeatedly, in his work posts,
    is heat bending the sharpened 2% thoriated tungsten, to aim the arc at the weld joint.

    Additionally, what I suspect the production shops do for tiggin' down into
    those narrow areas, is use custom, small torch configurations.....and there's
    lots of those to choose from.

    It would be educational to hear from somebody who does a neat, no-undercut,
    filler-added, narrow space weld in those headers--as to the torch/gas lens setup
    they use to accomplish this.
    Blackbird

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