07:54 Jan-24-2009 aldo Engineering MRF, Pakistan, Joined Jan 2009 14
offset central conductor
I am a mechanical engineer ad i am a new member in this forum. My job is specialist in NDT and i work in aerospace and aeronautic sector. I have one question on circular central conductor. In astm E1444 (par. 220.127.116.11) is specified that "the distance along the part circumference (interior) that may be effectly examined shall be taken as approximately four times the diameter of the central conductor up to 360 degrees. The entire circumference shall be examined by rotating the part on the conductor, allowing for approximately a 10% magnetic filed overlap". Is there a mathematics formula that calculate the number exactly of rotation including in this formula also the 10% magnetic field overlap?
Tanks and best regards
Please try to keep this simple. The more people try to come up with mathematical formula and other things the more they get everyone confuse, because it gets to a point where people don't understand anymore.
Para 18.104.22.168 is fairly simple to understnad and apply. For one, it says that the maximum surface area to be inspected is 4 times the diameter of the bar. If the bar is 1 inch, it makes it 4 inches max. Than it says that you have to have a 10% overlap minimum. Again, if the circumference of your part is 12 inches, that would make it at least 4 shots (4 inches per shot, plus overlap). Don't forget, you also need to inspect the surface under your conductor as well.
What is important here to reach and be undersood by the people who will be using it.
Welcome to the forum, Aldo. Whilst I agree with Michel's response, i feel you have nothing to apolgise for. Remember "The only stupid question is the unasked question".
Plus its another reason to have a range of different diameter central conductors available, a high fill factor conductor can accomplish the task in the minimum number of shots. For Michel's example of a 12 inch circumference test item (approx 4inch diameter), a 2 inch central conductor would take just 2 shots for complete coverage and still leave enough space for viewing.
Don't think that it was a stupid question. All we have to remember is who is it intended for. I remember years ago having a question on a PT exam where I was asked what is the formula to measure surface tension of penetrant. Although important for manufacturer's of Penetrant Testing materials, from a technician's point of view no so much. As a technician, I believe in this situation, that the manufacturer has done is work to provide me with the products that will comply with the code I'm working to. In the NDT business, we all have a specific job to do. For some like me its to do the job according to code and to train futur tech in the same way. For other people likes engineers and others who have various degrees and Master's or Doctorate in some form of NDT it's to make NDT evolve and find new solutions to old problems. I know I've probably over simplify, but in a nutshell that's pretty well it. And it is true forum like this one, that we can educate and learn from one another.
I have been following the question and the answers with interest. They have made interesting and valuable points. But to get back to the question, I think if you go back to the Physics text books (the electricity part), you will find the calculations. Right now I don't have the books with me (I have retired from service) but I am sure you can go to the college library and do some search. And remember, ASTM and other standards take a conservative approach with a margin of safety. So, the theoretical results are modulated for practical use. Since the specification is the result of broad agreement in a committee where specialists from various disciplines are present, you can take the recommendations at the face value without going back to the drawing board. But if you are finding discepancies between the ASTM and other specifications (like BS or DIN, ISO etc.), then you need to do research and refer back to the ASTM committee.
NDT Guru and member of BIS Committee on NDT (till recently)
tanks for you replay and excuse me for late answer. If possibe can you suggest me some Phisic test books or link where i can find the calculations? On my Phisic text books i don't never found
I would like to suggest that the issue of what constitues 4D is somewhat irrelevant. This is one of the "rules of thumb" that we as an industry are gravitating away from. I believe you left out the most important part of the quote from E-1444 paragraph 22.214.171.124, "The distance along the part circumference (interior) that may be effectively examined shall be taken as approximately four times the diameter of the central conductor up to 360 degrees provided the presence of suitable fields is verified." Adequate flux density must be verifed via QQIs or a Hall Effect gaussmeter. We're working on the 2010 version of E1444 now and will be strengthening this sentence to emphasize this important point. Thanks!
ASTM E07.03 Magnetic Particle/Penetrant Subcommittee Chairman
Try this formula for calculating number of shots as per ASTM 1444 for 10% overlap.
(Outer Dia of part X Pi)/ (3.6 X Dia of conductor). round up for next higher number. This will give you theoratical value for number of shots. You have to evaluate according to your part configuration that this number fits according to your part configuration, so accordingly you can increase the number of shots.