Robster1us
Mechanical
- Dec 31, 2009
- 27
I am a Mechanical Engineering PE in the state of Florida with mostly Industrial Ammonia Refrigeration experience. I have recently had the opportunity to branch out into some other aspects of the pressure piping design world, specifically process piping, and started looking around at various sources of information. I have B31.3 2006 and initially began my search based on the required flexibility analysis.
From other threads on the site, as well as some other sites on the Web, it became clear that simply having a pipe stress analysis package like Bently was a matter of "garbage in, garbage out", and unless one really understands what's going on, it's best to leave this to the professionals (meaning actual pipe stress engineers, not any old yahoo with a Bently or CAESAR II license).
However, you have to start somewhere, so I purchased copies of Rip Weaver's "Piper's Pocket Handbook" and both volumes of "Process Piping Design". They introduced me to my first pass/fail method of culling through piping arrangements for those that definitely have adequate flexibility and those that may need some analysis, an important thing when you could save thousands by honing in on only the items that need analysis.
That's it for the long preamble. My question is this: both books I mentioned have essentially the same exact text on flexibility and minimum leg lengths for the "L" method and its analogs. The chapters also mention guidelines for reaction forces/limits for various equipment types. I am having trouble interpreting these two portions of the text. It would seem to me that piping flexibility is a separate issue from reaction forces at equipment and/or anchor points. My interpretation of the "L" method in the books is that, should you come up with an answer within the criteria, the PIPING is adequately flexible and stresses are pretty-much garanteed gelow allowable from a thermal expansion point of view. However, what does this have to do, if anything, with acceptable reaction forces at anchor points and equipment connections? The text doesn't seem to address how to find reactions, and I must be missing something, but I don't know what it is. Can someone with more experience and familiarity with Mr. Weaver's work please shed some light on this? Am I even approaching this method correclty, i.e. can you provide a better expanation of what "adequate flexibility" means with respect to pipe stress added by the pipe flexing?
Incidentally, as a side question, when he talks about anchoring pipe, what type of support would this be? Is it permitted to weld the pipe itself to a support (I guess if the pipe is not penetrated, it might be OK, at least in Normal Fluid service in B31.3)?
Sorry for the long question, I wanted to give sufficient background for a targeted answer(s). For those who are curious, yes I do realize that the Refrigeration Piping Code, B31.5, requires adequate flexibility as well, but I myself have never performed one of these analyses, and they are uncommon in that industry unless dealing with especially low temperatures or suitability of certain, non-impact-tested materials for lower-temperature service.
From other threads on the site, as well as some other sites on the Web, it became clear that simply having a pipe stress analysis package like Bently was a matter of "garbage in, garbage out", and unless one really understands what's going on, it's best to leave this to the professionals (meaning actual pipe stress engineers, not any old yahoo with a Bently or CAESAR II license).
However, you have to start somewhere, so I purchased copies of Rip Weaver's "Piper's Pocket Handbook" and both volumes of "Process Piping Design". They introduced me to my first pass/fail method of culling through piping arrangements for those that definitely have adequate flexibility and those that may need some analysis, an important thing when you could save thousands by honing in on only the items that need analysis.
That's it for the long preamble. My question is this: both books I mentioned have essentially the same exact text on flexibility and minimum leg lengths for the "L" method and its analogs. The chapters also mention guidelines for reaction forces/limits for various equipment types. I am having trouble interpreting these two portions of the text. It would seem to me that piping flexibility is a separate issue from reaction forces at equipment and/or anchor points. My interpretation of the "L" method in the books is that, should you come up with an answer within the criteria, the PIPING is adequately flexible and stresses are pretty-much garanteed gelow allowable from a thermal expansion point of view. However, what does this have to do, if anything, with acceptable reaction forces at anchor points and equipment connections? The text doesn't seem to address how to find reactions, and I must be missing something, but I don't know what it is. Can someone with more experience and familiarity with Mr. Weaver's work please shed some light on this? Am I even approaching this method correclty, i.e. can you provide a better expanation of what "adequate flexibility" means with respect to pipe stress added by the pipe flexing?
Incidentally, as a side question, when he talks about anchoring pipe, what type of support would this be? Is it permitted to weld the pipe itself to a support (I guess if the pipe is not penetrated, it might be OK, at least in Normal Fluid service in B31.3)?
Sorry for the long question, I wanted to give sufficient background for a targeted answer(s). For those who are curious, yes I do realize that the Refrigeration Piping Code, B31.5, requires adequate flexibility as well, but I myself have never performed one of these analyses, and they are uncommon in that industry unless dealing with especially low temperatures or suitability of certain, non-impact-tested materials for lower-temperature service.
