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Up Topic Welding Industry / Technical Discussions / Backing ring loss of head
- - By G.S.Crisi (****) Date 11-05-2013 18:30
Gentlemen,
Do any of you know how to calculate, figure out or at least estimate the loss of head produced by backing rings in piping?
Is there any chapter in a book, article in technical magazine, paper presented at a conference, rule of thumb formula?
Thanks for the answers.

Giovanni S. Crisi
São Paulo - Brazil
Parent - - By pipewelder_1999 (****) Date 11-19-2013 23:34
Hello Mr. Crisi,

I am not sure what you are referring to with "head". If you are referring to the pressure drop/flow restriction then I would imagine formulas exist for such but my ability to understand them is limited. I would think it is treated no differently than any other flow calculation across an orifice.

Here is a paper on flow induced corrosion http://www.ndt.net/article/ecndt2010/reports/1_12_03.pdf that may have some other references but other than that, I couldn't find anything.
Parent - - By G.S.Crisi (****) Date 11-19-2013 23:55
Yes, the term "loss of head" in liquids means actually loss of pressure. This is because liquids are uncompressible. Loss of head is an academic expression that you can find in any mechanical or chemical engineering book written in English. I'm quite used to it, that's why I wrote it on my posting. 
Gases, however, are compressible, so for gases loss of head means the increase of volume that the gas suffers for each psi of pressure drop in a piping. Mathematically, loss of head = V dP.

I thank you very much for your kindness in searching the article and deliver it to me. I took a quick look to it and will read it carefully during the next days.
Again, thank you very much.
Giovanni S. Crisi
Parent - By pipewelder_1999 (****) Date 11-20-2013 00:13
That is what I figured. In my very limited experience I always thought of "head" as a static pressure. And thus a change in orifice size would never affect it until there was flow. But my use of engineering terms is extreme likely to result in snickers from those properly educated.

Wish I could think of 4 years of welding experience I could trade for a degree but cannot think of any to give up. :)

I also searched through the McGraw Hill piping handbook and found many statements indicating flow restrictions resulting from backing rings but no references .

Have a great day.

Gerald
Parent - - By 46.00 (****) Date 11-20-2013 08:56
http://www.rkstat.com/Downloads/article-FlowCalculationsforValveSizing.pdf

http://www.pressure-drop.com/Online-Calculator/
Parent - By G.S.Crisi (****) Date 11-21-2013 18:47
Thank you very much, 46.00
Giovanni S. Crisi
Up Topic Welding Industry / Technical Discussions / Backing ring loss of head

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