Trouble with math problem

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I'm studying for the UA star exam. There is a question that asks for length of the outer wall of a 14" long radius 90°. A formula is provided (1.57 x radius of 90) but using it, I can't come up with the given answer. The book says I should be coming up with 43 and 15/16". I personally haven't dealt with much large diameter pipe, and although  I've tried laying it out on the floor, I must me missing something because its been no help. I can say that if you multiply 14x π you come up with 43.9... So pretty close but alas, I'm still perplexed as I'm not even sure if this will work on say a 20" 90.Any help is appreciated. I'm sure I'm making this harder than it has to be but I'm hard headed and this is starting to put a whooping on me. If this were "real life" I'd simply pull a string or tailors tape across the back of said 90, mark and measure, but I want to get to the root of the issue. Thanks for any thing you might have to offer.
Reply:ct1811You have posted too much data - and too little info.There are countless standards in the English speaking Craft World . . . Please clarify: what Continental Plate, does the UA Star Exam eminate. The shortest answer to your quandary - is to post a copy of the question directly from the 'test book / verbatim' - without [your] interpretation.When you: understand/discover - the concept of pipe/radiuses/bending;the numbers fall into place . . .Opus'
Reply:if you came up with 43.9 you have to convert .9 to inches or get an equivalence table and you will find that 15/16 = 0.9375, so you basically got it right. Just have to get current on changing decimals to fractions.
Reply:I understand that .9 is pretty much 15/16. The point is I got my answer just by throwing numbers around after THEIR formula wouldn't produce a usable answer. The UA star exam is for the US I'm in nc specifically. I can't post question ver batim right now, I'll try and get it up before the day is over with.
Reply:

Originally Posted by ct1811

I'm studying for the UA star exam. There is a question that asks for length of the outer wall of a 14" long radius 90°. A formula is provided (1.57 x radius of 90) but using it, I can't come up with the given answer. The book says I should be coming up with 43 and 15/16". I personally haven't dealt with much large diameter pipe, and although  I've tried laying it out on the floor, I must me missing something because its been no help. I can say that if you multiply 14x π you come up with 43.9... So pretty close but alas, I'm still perplexed as I'm not even sure if this will work on say a 20" 90.
Reply:I did that same calculation and came to that numbers, but he said that the book shows it should give 43, so either the book is wrong or he is not giving the whole exercise numbers correctly. I would wait until he prints the whole problem.
Reply:are you failing to give us the pipe diameter?    I would assume 14" is the centreline length, and that we would need diameter to calculate outer wall length....?
Reply:When I was taking exams in college, we would challenge the professor for asking a B.S. question that was poorly phrased without all the necessary data.  No Mercy!  Is this a pipe with 28" outside diameter?  What is a "radius of 90"? Does not compute."USMCPOP" First-born son: KIA  Iraq 1/26/05Syncrowave 250 w/ Coolmate 3Dialarc 250, Idealarc 250SP-175 +Firepower TIG 160S (gave the TA 161 STL to the son)Lincwelder AC180C (1952)Victor & Smith O/A torchesMiller spot welder
Reply:I'm thinking it's for a 14" diameter 14" inside radius elbow. If you take the 14" radius and add another 14" for pipe diameter the radius is now 28", when multiplied by 1.57 becomes 43.96"
Reply:I dont have access to the question right now, left my paperwork at the training center last night. The question was pretty straight foward with only 2 sentances. "Arc length can be found using the formula 1.57xradius. What is the outside arc length of a 14" long radius 90." I did discuss with classmates that the answer given could well be wrong, its definately not uncommon. The pipe diameter is 14". Because the question calls out a long radius 90, Its not as simple as figuring for a 14" circle as Minnesota Dave suggested although I wish it was. The chart I have for long radius 90s only goes to 12", but take outs for these 90s is typically figured as 1.5x diameter of pipe. 14" pipe in my case is 14" o.d. exactly. So, a 14" lr 90 takes out 21" ( end to center).  I've played with the idea that if I were to multiply 21x1.414, I would get a radius of 29 and 11/16". Multiply that as directed (by 1.57) and I come up with 46 and 5/8". This is definatly not an answer given. I've also figured that if I use the exact center of my 90 to lay out a circle, I will have a circle with a radius of 7". I used the formula pi*dia.*(90/360) to find my arc length, figuring The 90 actually starts its arc where the legs of a triangle extend from center of 90 to outer wall of pipe, if that makes sense. My answer from said formula is 11" (10.99). I then added  42" (21 for each side of 90 and come up with 53". Again, I'm lost here. Thank you for your patience. If it would help anyone, I can provide a picture of my lay out to clear things up.I should mention that both 11" and 53" were not given as answers.Last edited by ct1811; 04-01-2016 at 05:04 PM.Reason: Clarity
Reply:Sharon needles I never did figure for a short radius 90. I haven't checked your math on paper but it sounds right. I can say with 100 percent certainty that the question calls out a LONG RADIUS 90. But typos are a fairly common thing. Your input is greatly appreciated. I guess the biggest lesson learned for me is just like on the job, I should never take someone else's details as gosspel. Thanks
Reply:

Originally Posted by ct1811

Sharon needles I never did figure for a short radius 90. I haven't checked your math on paper but it sounds right. I can say with 100 percent certainty that the question calls out a LONG RADIUS 90. But typos are a fairly common thing. Your input is greatly appreciated. I guess the biggest lesson learned for me is just like on the job, I should never take someone else's details as gosspel. Thanks
Reply:I think I found your answer. You will have to use the drawing I will give you to understand it.http://www.piping-designer.com/Datas...eld,_ANSI,_WCSIf you look at the question, what you need to find is the radius to get it solved. Now take a look at the graphic and chart I provided you in the link. Now look at measure C for a # 14 90 degree long radius tube. You will see that the distance to the centerline is 21, but you want to find the arc of the outside curvature so you have to add the extra 7 inches. Since the diameter of the whole tube is 14 inches , and they are giving you the measure from zero to the center is 21 , you have to add the distance from the centerline to the outside curvature(half of the diameter of the tube which is 7 inches). Now that will make it 21+7 =28. Now use your formula to get 1.57 x 28=43.96. Now change that .96 to inches and you have your 43 15/16 ".  It is so much easier when you can see the diagram. Now that you now your exact radious to use , you can also use any other formula for arc and circunference. In you use now diameter to get the circunference it would be 2XDXPi and you will get a circunference of 175.9296. Divided by  4 to get what each 90 arc would be will get you 43.98, which is pretty close too. I hope this helps. I think that beside any mathematical skill, what they are really testing you is in being able to find the correct information to apply in the tube charts. See how each chart give you specific instructions of how the center radius of each tube is found out. This info would be different for a short radius 90, so basically they just want to know if you know how to get the info from the chart.Last edited by QCTechInsp; 04-02-2016 at 12:52 AM.
Reply:That is the problem with the tests today they breed and create poor engineering, poor practice. A real expert would not put his name on a answer to such a vague question. Although OCTechInsp is spot on, because he has been down this road. He knows the inside radius is equal to the diameter of the pipe more than likely in this case. The question is wrong, it assumes you are going to assume what they want to know, what you think they want you to know. But OCTechInsp, is guessing it is pipe, and he assuming that it is the inside of the pipe wall they want the length of. The outside of the pipe and the outer most part of the pipe fitting will be longer. Usually it is pipe you are dealing with, and the only reason for wanting to know the outer wall length would be to determine the friction created by the length of pipe inside the pipe. So if it were tube you would not know the length of the wall exposed to the substance being transported. Silly question.  The problem is that when they put all the information needed to answer a question with 100 percent confidence, almost anyone can answer it or figure it out. The truth is that you should not be playing detective to answer a question, read a blue print, or take orders. You should not assume that you know what the person asking the question wishes to know just because you did something similar the day before. That is how projects are destroyed. The scenario usually goes like, the plan is wrong, instead of anyone just saying that, people try to make sense of an incorrect plan, and then the project is ruined. Most of the time they do not measure the property, or the building properly, or they try to fit more building or material into the space they have and make errors on the plans. They leave out wall thicknesses or plumbing wall depths. Because of the almighty dollar and space. Reality is secondary to their needs. I have bent custom radius pipe it was called large radius bends. I have ordered custom radius bends. So the question would have to state, "Using a chart (to some standard), determine the radius of a standard long radius or large sweep 90 degree elbow."  I used to deal with stuff like this, and one persons long radius is not another persons long radius or extra long radius or large sweep. Poor engineering practice. Sincerely, William McCormickIf I wasn't so.....crazy, I wouldn't try to act normal, and you would be afraid.
Reply:That, in my opinion would have been a trick question. Given that all piping 12" and up are actual pipe size and all long radius 90's are 1.5 x pipe size. The fact that you would have had the material and if you are taking the UA STAR test you have at least 5 years experience this should have almost been a no brainer. Always keep in mind that measurement "c" equals 1.5 x pipe size then to get the outside curve it requires adding half the pipe size.