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grover posted:I never quite understood why this is conventional wisdom; even a perfect weld can never match the optimum alloy, processing and annealing that gives a solid piece of metal its particular combination of strength and flexibility. Plus, the process of welding weakens the surrounding metal. A good weld will be strong, yes, but not necessarily stronger than an uncut piece. Welding filler is almost always specced to have a higher psi rating than the surrounding metal. You can always retreat metal after welding, which is what is done anyway if its that specialized. Or not welded in the first place.
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Feb 4, 2011 22:35
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DJ Commie posted:Welding filler is almost always specced to have a higher psi rating than the surrounding metal. You can always retreat metal after welding, which is what is done anyway if its that specialized. Or not welded in the first place.
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Feb 4, 2011 22:43
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grover posted:I never quite understood why this is conventional wisdom; even a perfect weld can never match the optimum alloy, processing and annealing that gives a solid piece of metal its particular combination of strength and flexibility. Plus, the process of welding weakens the surrounding metal. A good weld will be strong, yes, but not necessarily stronger than an uncut piece. This is pretty much it. When we inspect welds, yes we inspect the weld itself, but you also look just as hard around the weld joint. Because chances are it's going to fail at the edge of the weld, or within 3" of it. This is especially true if it's subject to bending stresses, and the weld isn't heat treated, or the toe isn't ground flush. There's a reason that welds to submarine hulls require ultrasonic or radiographic testing. The manuals we have for this poo poo are so specific it's ridiculous. I've seen very few welds posted on this site that would even make it past our visual tests for the most lax of weld classes.
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Feb 4, 2011 23:08
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Sockington posted:He's saying to simply remake the piece out of plate steel and weld that to the chassis rail (probably after welding a patch section there too). Oh yea, you're right but neither my uncle or I have access welder anyway so its easier to find the part somewhere.
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Feb 4, 2011 23:11
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grover posted:I know welding submarine hulls is a big deal because the welds weaken the hull, even if perfect. There are a lot of tricks you can use for strength in sheet steel that are quite simply impossible to work into welding rods or post-weld heat treatments. Welding is fatigue failure's best friend, so this doesn't surprise me very much. Under static loading, weld material may in fact be considerably stronger than the parent metal, but when you get into cyclic loading, all the flaws brought about by the process of welding and the cooling of the weld in the Heat Affected Zone (HAZ) will start propagating fatigue cracks, and eventually you have a catastrophic fatigue failure. Those same imperfections will often beef up the weld's yield strength, as they'll block the path for crystal planes in the metal to slip over one another, so it takes more energy to force the planes to slip and the metal to yield. This, in a roundabout way, is the reason carbon fiber is so drat strong. It's been a few years since I studied metallurgy and materials science, so feel free to correct me if I'm wrong.
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Feb 4, 2011 23:15
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iwentdoodie posted:There's a reason that welds to submarine hulls require ultrasonic or radiographic testing.
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Feb 4, 2011 23:17
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Poing posted:Did they make you watch that video with the audio from the Thresher too? Said they're not allowed to. Then showed the video to us during lunch.
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Feb 4, 2011 23:23
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Why, was it classified or something? I don't think there was anything in that video that required a clearance. (This is totally not OT because the Thresher was a horrible mechanical failure!)
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Feb 4, 2011 23:27
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Poing posted:Why, was it classified or something? I don't think there was anything in that video that required a clearance. They made us listen to it, too.
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Feb 5, 2011 00:08
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grover posted:Pretty sure it's been unclassified. I knew vaguely of the Thresher and Scorpion but the posts in this thread got me over to wikipedia to putz around. So apparently the only reason Ballard had the money to find the Titanic was because the Navy got a hold of him to find/map their submarine wrecks  I was crazy about Ballard's work when I was a kid so hearing about this now (har har, news is 2 years old) is kind of a mind gently caress.
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Feb 5, 2011 02:35
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What is this Thresher audio? I had a college teacher talk about going down to the Thresher and taking measurements to make sure the reactor wasn't leaking. Cool stuff.
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Feb 5, 2011 04:35
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I wasn't sure whether it would fit here, but I found it really interesting and thought it was in the spirit of the thread. What happens when you build zinc coated iron gas pipes next to steel gasoline pipes, underground, and in humid conditions?  http://en.wikipedia.org/wiki/1992_Guadalajara_explosions
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Feb 5, 2011 04:36
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SNiPER_Magnum posted:What is this Thresher audio? The sound of it imploding, from what I gather.
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Feb 5, 2011 04:45
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Poing posted:Why, was it classified or something? I don't think there was anything in that video that required a clearance. No, it's nothing to do with clearances. One of the Chiefs just said that they had too many people complain, and apparently one student went through who had a family member onboard. So they no longer show it in class. They show a video TALKING about it, but that's it.
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Feb 5, 2011 09:12
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https://www.youtube.com/watch?v=kCsSVLZ6wCI I don't recall this being posted here yet, but it's one of the more extreme engine failures i've seen, when the whole block tries to escape the vehicle.
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Feb 5, 2011 14:55
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Manny posted:https://www.youtube.com/watch?v=kCsSVLZ6wCI If it wasn't that one, there was a similar vid posted a long time ago. Same deal, tractor pull, engine decided to commit suicide by jumping from a moving vehicle. Still fuckin awesome though.
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Feb 5, 2011 15:03
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SNiPER_Magnum posted:What is this Thresher audio? quote:Everything was fine until 0913. At this time the USS Thresher sent this message. "We are experiencing minor difficulties, we have a positive up angle, and are attempting to blow. Will keep you informed". At 0916 & 0917 respectively, the USS Skylark received two garbled messages followed shortly by SONAR detection of a high energy, low frequency disturbance. This disturbance was the crushing of the USS Thresher as it had fallen below crush depth. One hundred twenty nine men had perished, including crew members, PNSY Officer Observers, PNSY civilian workers and contractor technicians.
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Feb 5, 2011 15:32
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grover posted:It's the sonar recording the hull crushing as USS Thresher sank.
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Feb 5, 2011 16:09
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Rev. Dr. Moses P. Lester posted:That's just to scare-straight the welders, right? Cause it wasn't failure of welds that sank the Thresher, was it? Was the emergency surfacing equipment or something... Some photos of the mechanical failures that resulted:   
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Feb 5, 2011 16:32
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grover posted:It's the sonar recording the hull crushing as USS Thresher sank.
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Feb 5, 2011 17:00
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anonumos posted:I want to point out that 1 atmosphere of pressure is not hard to deal with. The space station is rather flimsy compared to a submarine. The space program isn't run at 1atm. It's run at something like 8psi. (15kfeet iirc) Less when there are space walks involved. It looks like I was beaten to those numbers, but I am pretty certain they don't run the ISS or the shuttle at sea level. And the structures we're talking about are stressed in tension, not in compression. In tension you don't need to worry about buckle strength. in tension things straighten themselves out and pull to the best shape to resist the pressure. In compression the slightest ding, dent, or defect concentrates the stress and you get that sickening crush you saw on that rail car. With the cray failure, I'm wishing I had pictures of the APC CRACS at my old job that were designed in such a way that if the evaporators weren't perfectly clean water would drop off of them directly into the control box.
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Feb 5, 2011 17:57
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Clutch failure; The friction materials teleported out of the disk.  I've heard about the USS Thresher sinking back when I was in school, but I've never heard the actual radio logs. Google is not bringing up anything.
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Feb 5, 2011 19:57
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Poing posted:You can hear compartments imploding, one after another as the hull sank lower and lower. In context it's very creepy when you think about the people on board. Is this audio available anywhere for the public?
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Feb 5, 2011 22:40
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Nerobro posted:The space program isn't run at 1atm. Yeah, it is. Right off of the handy sidebar at Wikipedia's page for the ISS: quote:Atmospheric pressure 101.3 kPa (29.91 inHg, 1 atm) NASA backed the hell off of low-pressure pure oxygen after Apollo due to the Apollo 1 fire. Here's Boeing's page on the Joint Airlock to back up that claim (The page cited by wikipedia doesn't exist anymore, apparently). Boeing posted:The Equipment Lock campout is similar to any other campout in name only. The name stems from the requirement that the one or two astronauts who will be emerging from the ISS sleep in the Equipment Lock the night before. While they sleep, atmospheric pressure is reduced from 14.7 psi (the normal, sea-level pressure that is maintained in the ISS) to 10.2 psi. This purges nitrogen from their bodies and thus prevents decompression sickness (the "bends" that SCUBA divers sometimes experience) when they adjust to the 4.3 psi pressure inside their spacesuits.
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Feb 6, 2011 01:02
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I don't see what the apollo 1 fire has to do with this at all. They were running a ground test at +something psi on top of 14.7psi at sea level. So they were in a super concentrated pure o2 atmosphere. I stand corrected on the shuttle/iss "day to day" pressures.
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Feb 6, 2011 20:27
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Nerobro posted:I don't see what the apollo 1 fire has to do with this at all. They were running a ground test at +something psi on top of 14.7psi at sea level. So they were in a super concentrated pure o2 atmosphere. I think that's what he meant, just worded strangely; like being in atmosphere vs. stored in tanks for gas mixtures like they do today.
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Feb 6, 2011 21:44
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Nerobro posted:I don't see what the apollo 1 fire has to do with this at all. They were running a ground test at +something psi on top of 14.7psi at sea level. So they were in a super concentrated pure o2 atmosphere. Pure oxygen is just a bad idea at anything above 3 PSI (the partial pressure of oxygen in a normal atmosphere). NASA was using it because having pure oxygen at 5 PSI meant less weight on board than a standard atmosphere, and they were really doing everything they can on that front. Apollo 1 was exacerbated by running at ~20 PSI absolute pressure during the ground test, but ANY accident would have been worse running 100% O2 at the normal 5 PSI than it would with a standard atmosphere. Keep in mind that pure O2 at 5 PSI is still 67% more than the partial pressure of oxygen in a normal atmosphere.
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Feb 6, 2011 23:29
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There isn't a post pics of horrible structural failures thread here so I'm posting my barn collapse pics ( and subsequent destruction of my classic mini, antique land rover and dads half restored MG TD. Thanks winter      So AI which one should I start restoring first?? 
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Feb 8, 2011 23:50
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N183CS posted:So AI which one should I start restoring first?? The barn
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Feb 9, 2011 00:01
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At least we have plenty of firewood now.
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Feb 9, 2011 00:03
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N183CS posted:At least we have plenty of firewood now. So this tragedy actually makes plenty of room for that new 60x60 concrete pad w/ car hoists...
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Feb 9, 2011 00:07
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I share your pain. I've got a car that was in a collapsed barn. The barn collapsed because it seemed like the best option at the time, given it was on fire. Yeah, that paint's going to need more than a bit of compound  .
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Feb 9, 2011 00:11
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The barn actually belongs to our neighbor, we were just renting space in it. He thinks his homeowners insurance will cover the damage since it should cover everything inside as well.
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Feb 9, 2011 00:14
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That'll buff out.
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Feb 9, 2011 01:22
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N183CS posted:The barn actually belongs to our neighbor, we were just renting space in it. He thinks his homeowners insurance will cover the damage since it should cover everything inside as well. Good lord it would suck to be that guy if the insurance didn't cover it.
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Feb 9, 2011 02:05
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ApathyGifted posted:Keep in mind that pure O2 at 5 PSI is still 67% more than the partial pressure of oxygen in a normal atmosphere. I'm well aware. I did a lot of research on the subject a few years back. o2 is scary stuff. At "fairly normal" pressures it get toxic. Rebreathers running pure o2 aren't exactly useful at more than 20'. No use having a rebreather when you're not breathing anymore.
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Feb 9, 2011 02:09
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N183CS posted:The barn actually belongs to our neighbor, we were just renting space in it. He thinks his homeowners insurance will cover the damage since it should cover everything inside as well. Homeowners should cover it. Good luck man, that really sucks. 
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Feb 9, 2011 02:10
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Nerobro posted:I'm well aware. I did a lot of research on the subject a few years back. o2 is scary stuff. At "fairly normal" pressures it get toxic. Rebreathers running pure o2 aren't exactly useful at more than 20'. No use having a rebreather when you're not breathing anymore. There was a diving accident in the North Sea where the rack mixing the gas was misconfigured for just a few seconds sending a shot of about 50% oxygen into the diver's helmet. Given that he was working at 200-250 feet, the partial pressure was so beyond lethal, the symptoms shown on the body where not known to science before the accident.
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Feb 9, 2011 02:18
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Ola posted:There was a diving accident in the North Sea where the rack mixing the gas was misconfigured for just a few seconds sending a shot of about 50% oxygen into the diver's helmet. Given that he was working at 200-250 feet, the partial pressure was so beyond lethal, the symptoms shown on the body where not known to science before the accident. This is really morbid, but do you have a link? The post mortems on these types of things are really fascinating, like the one where they opened the pressure chamber door early and one guy got sucked bodily through a gap about an inch and a half wide.
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Feb 9, 2011 02:21
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I tried to find a link to the place I read it, it's not that long ago. http://www.offshorediver.com http://www.pioneerdivers.org/ These sites also have off-site links, gotta be there somewhere.
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Feb 9, 2011 02:41
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