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What are common methods of destructive testing for pipe? A little background, I'm still a highschool student, and welding is my shop class. I've been practicing GTAW pipe (usually 4" sch 40). We have limited testing methods, visual and a large hyrdraulic press.
(4" sch 40, mild steel) Root, 2nd, and cover all got a visual "pass". Afterwords, I just pressed it down until there was approximated 1 3/8" space between the walls, and my instructor considered it a "pass". There was absolutely no visible cracks or deformation of the weld at that point. Only when pressed to make the walls 1/8" apart, did the cover pass begin to even show some small cracks.
So, would that be considered a valid testing method for this? I know that visually (sorry no digital camera for pics), all my passes passed (no pun intended), but would like to find a destructive method that can be done on our low budget.
EDIT: and what might be the criteria for a "pass" on said possible testing methods?
You might make a bending fixture for in the press. Hopefully someone will post pictures & bend radius dimensions as well as how to cut the specimines.
I had rough cut it with OFC to about 2 1/2" wide, because the original two pieces were not of equal length. Just wanted to make it roughly even and take some load off the press.
Here is the drawings of a standard guided bend jig. I built one to replace the old one when I was in welding school. It's a neat project, you learn some good skills building it, and you will have the prpoper equipment to do testing the same way you will be tested when you go to take your test on most jobs. I say most because 99% of jobs that subject to ASME code use this test for welder qualification, but like on pipeline jobs on your branch test they will most likely use a "Nick-Break" test, wich is a different type test. some jobs including some ASME jobs and pipeline and other types of codes require tensile pull tests or X-Ray testing, but anyway I'm getting off subject this jig can be either permanently attached to to a press like a bearing press with a hydraulic jack or made so the it can be installed and uninstalled so the press can be used for other uses. You can do guided bend test on the root side and face side on most pipe welder qualification you will cut 4 straps from you coupon and bend 2 face side up, and 2 root side up. You can also use this same jig for side bend type test which are also used for welder qualification on the job. A side bend test is did on this jig very similar to the root and face type bends except it's did with heavy wall pipe like XXS or sched. 160. I'll post the drawing for the jig, in the interest of you learning I'll let you look for the qualification specifications, how the straps should be cut and prepped for bending and what is acceptable for pass or fail. Honestly with a lil' research on the web It's not hard to find. If you just can't find it ask on here again and I'll help you. Here's you jig, happy bending.
Ok I can't figure out how to post it, sorry I'm a welder not a webmaster. But here is the link to it:
http://www.tpub.com/content/construction/14250/img/14250_170_2.jpg
You don't even need a press. A method we've used in the field many times is to just tack two pieces of pipe to a fab table, tack the end of your bend strap to one and bend the strap with a cheater around the other.
All you have to verify is that the pipe you bend around matches the proper radius required and that the distance of one pipe to the other allows the weld to be centered between bend tangents, or centered in the bend so that you get full fibre elongation in the weld.
This is about as economical as it gets. And all you need is 180deg at the proper radius.
@ UA: We have a setup very similar to that which is used for plate. Cut the plate into approx. 1 1/2" widths (orig. plates are 6"x3"x3/8") x 6" long. They are bent in that. Are you suggesting the pipe be perpendicular to the weld? So as to make it a slightly curved plate.
@ JS: I imagine this being like bending the pipe at an angle? Wouldn't that need to be calibrated by bending a section of base pipe (non welded) for comparison?
Do you guys normally TIG up or down hill? My instructor demonstrated it uphill, but it was very difficult for myself at this stage. He said it was fine to do it downhill, and this produced a much better weld (my work). Should also mention this is all 1G position.
Calibrated?
Yu're wrapping a bend strap around a piece of pipe. I'm not sure what needs to be calibrated. You have two pipes tacked to a table your strap and a piece of pipe preferably for a cheater bar for bending. Stick the pipe on the end of the strap and wrap the strap around the radius pipe.
Like this? Black rectangle would be the cheater. Blue circles pipes tacked to table. Red is your pipe, and the weld is highlighted.
Very close, yes.
You just need to make sure you have your weld entriely within the tangent of the bend so you get full 180 and outer fiber elongation on the weld all the way through the fusion line.
How many degrees would the piece need to be bent to be considered a "pass"? Also, what are the cutoff limits.
For example on the previously discussed hole-plunger method, our cutoff for a fail is the 3/8" plate bent around an approximate 1 1/2" radius, with cracks no wider than 3/32". Anything smaller and it's a pass. Most of the time no cracks are present at all when the welds are free from defects.
Nominally its 180deg. But some plunger type benders struggle with a full 180, especially if the strap was cut long. If the weld is within the tangent you have 180 on the welded portion of the strap.
Dare I correct you and say 90*?
Seems like it would be VERY hard, rather impossible, to bend a pipe section 180* without completely shearing the weld and base metal due to the nature of the shape? Unless of course you where [only] talking about a strap. In which case, the pipe section would have to be cut into straps. I had referenced back to plate welds to compare for a visual in my head.
Wouldn't doing so result in a skewed test because of the curvature of the strap itself? Due to the nature of pipe. Seems like the (pipe) strap would want to pop and shear at the edges if you put it convexly over the hole (bulged upwards to the plunger). And possibly be easier for the piece itself to bend if concaved over the hole.
EDIT: WOW! I just realized you stated to bend the STRAP over the pieces tacked to the table. That would be a poor man's hole-plunger setup. I thought you meant to bend the whole pipe section... my apologies.
EDIT2: spelling errors.
For what it is worth, mild steel will stretch about 20% before it tears, and the weld deposit [when everything is done properly] has even greater elongagation.
Atached is a picture of our bender.
But of couse it will cost money for the hydralic ram.
Pretty much what we have. Except we have (what I think) is a much more powerful ram. It's not a permanent setup like you have. Just a 12"x6"x4" steel block with a 2"x2" square cut into the center.
Use a 1 1/2" radius x 1 1/2" wide plunger. Probably not as "safe" as your setup, but have yet to have a problem.
As I said before, was just crushing the pipe, since both sides bent as expected, it was considered a pass for the qualification. I plan to do 6G on likely 4" sch 40 mild next week. I will cut that into straps and bend for a more precise measure of weld quality.
For a new, but related topic. One of the qualifications is "structural shape repair". Since we don't have any cracked structural shapes, my instructor said I can just cut a zigzag line in whatever shape. There is no specification for position or anything... I OFC'd a 12" zigzag into the web of a large channel piece. Ground a groove into it, did a 3G root with E6010, and 1G with some E7024 for a cover. Should I just cut these into straps for testing, also?
Fritz, you ask "Wouldn't doing so result in a skewed test because of the curvature of the strap itself? Due to the nature of pipe. Seems like the (pipe) strap would want to pop and shear at the edges if you put it convexly over the hole (bulged upwards to the plunger). And possibly be easier for the piece itself to bend if concaved over the hole."
Usually the test coupons are machined down to look like a piece of flatbar before they are bent. They are no longer curved.
Pipe straps are not machined or ground to make them "rectangular in cross section" prior to being subject to the guided bend test. The corners are radiused to prevent cracking at the corners and the face and root are ground flush before bending. However, if you are qualifying to NAVSEA TP248 using an open root joint, the root reinforcement is left as welded.
Only the reduced section tensile specimens are machined to provide a rectangular cross section it you are qualifying the WPS.
Al
Ah, I doubt an angle grinder would be precise enough to do this?
I don't have access to a mill or such.
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