Induction bend in muskeg area
Induction bend in muskeg area
(OP)
Hi all,
I read in a document that no induction bend will be used in muskeg area without providing more details on why. Can someone shed some light on this please? Thanks.
I read in a document that no induction bend will be used in muskeg area without providing more details on why. Can someone shed some light on this please? Thanks.





RE: Induction bend in muskeg area
That very likely would have been taken out of context and may or may not necessarily be true depending on the properties of other surrounding soil, wall thickness, pipe material used, service fluid, installation temperature, hot temperature, restraint locations, and other things.
If you are installing pipe into muskeg your virtual anchor lengths will be relatively long, and any bends in the system will be relied upon to absorb correspondingly higher thermal growth. It might well be that such bends, in muskeg, will see higher stress levels than they would see in better soil conditions.
To me (a generalist), this is really a stress / flexibility analysis issue. Others in this forum who have spent most of their careers in pipelines might be able to comment on the validity of the statement in general from a more informed perspective.
Regards,
SNORGY.
RE: Induction bend in muskeg area
A question properly stated is a problem half solved.
Always remember, free advice is worth exactly what you pay for it!
http://www.ap-dynamics.ab.ca/
RE: Induction bend in muskeg area
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus
RE: Induction bend in muskeg area
Regards,
SNORGY.
RE: Induction bend in muskeg area
ColonelSanders83: The document in question is a spec from a reputable engineering company but without more details. It was just like a blank statement.
Sam62
RE: Induction bend in muskeg area
Water surrounding the pipe (with no buoyancy control) would tend to float the pipe as well.
Other than those considerations, nothing comes to mind that would make induction bends any more unique than cold bends.
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus
RE: Induction bend in muskeg area
After some thought, it occurred to me that more gradual bends will end up with the soil's lateral bearing resistance spread out over a larger area (length), tending to displace less and flex less. Induction bends are made in a hot condition in order to achieve a tighter bend radius without unacceptable cross-sectional deformation and strain hardening. It could, therefore, be that the avoidance of "induction bends" was really intended to mean an avoidance of "small radius bends" (e.g., 10-D as opposed to 20-D), perhaps with a view towards minimizing the stresses on a component that might already be locally stressed due to wall thinning, strain hardened, or ovalized. As stated, however, it is misleading to specifically draw attention to "induction" bends because, given the choice for a given bend radius, I would prefer induction bending over cold bending.
As for buoyancy, I probably tend to see smaller diameter pipe than BigInch, so "sinking" in muskeg is usually more of a concern than "floating".
Regards,
SNORGY.
RE: Induction bend in muskeg area
Also in general, you should avoid any induction bend, simply due to the extra costs involved with the bend, transport and fitup complications. Out on a pipeline RoW you're usually going to have enough space to make a cold bend, so I don't really understand why you wouldn't have that near muskeg areas and would have to use a hot bend there. Its not like such an area is going to be filled with a lot of fixed obstacles you have to avoid with tight turn hot bends. I've only used them on offshore platforms when connecting the riser around a manway, stairs, locating an ESD valve and hooking up into a launcher on the lower deck piping. Sometimes a standard 5R won't fit up and you simply must have a special bend made. Out on the RoW, its hard to see why. If anybody has any outright guesses they would like to propose in order to try to get to the bottom of this muskeg issue (so to speak), I promise I won't laugh if you publish.
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus
RE: Induction bend in muskeg area
As a Canadian, I assume that most Americans (for example) do not see a lot of muskeg (well...they might call it "quicksand" down there) unless they are in Alaska. In such instance, virtually all of your comments with the associated connection to geographic remoteness apply.
In the CSA Z662 Code (I haven't read the B31.8 Code but I suspect that most of what's in Z662 probably came from it), there is some nebulous criteria for cold bending of 12"-D pipe that limits you to 1.5 degrees change in direction per diameter of pipe length. Right or wrong, a lot of folks apply this for all pipe sizes (I am not one of those folks), and are disillusioned with the conclusion that they need a 60-D minimum bend radius for cold bends. I think what is more common industry practice on both sides of the border is to limit outer fibre elongation to somewhare around 2% for cold bends, from which something around a 20-D cold bend is generally accepted. In the absence of something more definitive from CSA, right or wrong, there is sometimes also a propensity to apply ASME B31.3 criteria of 5% towards the outer fibre elongation permitted for impact-tested materials without post-bend heat treatment; that would limit one to about a 10-D bend.
Personally, I would not cold-bend to as tight as 10-D without subsequent inspection for ovality, wrinkling and strain hardening at the extrados, none of which I would be immediately satisfied with without such testing.
To me, what it comes down to is whether or not you can fit a 20-D bend in the ROW. If you can, it's completely unnecessary to call for induction bends in anything other than prefabricated risers.
Which is pretty much what you have been saying all along.
Regards,
SNORGY.
RE: Induction bend in muskeg area
Having worked for Northern Natural Gas on some large diameter lines touching Canada up in northern Minnesota area, I have stumbled into muskeg more than a few times, as well as some other slippery, slidey stuff on occasion.
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus