Steel Pipe Restraint - Is It Necessary for This Application
Steel Pipe Restraint - Is It Necessary for This Application
(OP)
We are replacing a a very long 42" welded steel pipe header at a water treatment plant with the same. The header is in a gallery (not buried) and carries water from flocculation to sedimentation tanks - this is gravity flow with no bends (probably about 6' driving head). Because of the sequencing necessary to keep portions of the line in service, couplings are being shown to connect new segments to existing welded steel segments.
The contractor is asking for harnessing (tie-rod) details, and client is asking why is that necessary? It seems harnessing is always just an assumption to put it in to be safe, but there is no thrust to speak of, pipe flows less than half-full, and the cost could be come extensive considering the length of the header. Would harnessing really be necessary in this application?
The contractor is asking for harnessing (tie-rod) details, and client is asking why is that necessary? It seems harnessing is always just an assumption to put it in to be safe, but there is no thrust to speak of, pipe flows less than half-full, and the cost could be come extensive considering the length of the header. Would harnessing really be necessary in this application?





RE: Steel Pipe Restraint - Is It Necessary for This Application
RE: Steel Pipe Restraint - Is It Necessary for This Application
Stephen Argles
Land & Marine
www.landandmarine.com
RE: Steel Pipe Restraint - Is It Necessary for This Application
Steve
RE: Steel Pipe Restraint - Is It Necessary for This Application
Also, while not enough detail has been provided to know if same might be issues in your application, there are also other forces or movements that could conceivably be brought to bear on/in an unrestrained pipe joint of at least a "very long" exposed even low pressure length of piping, specifically hydrodynamic forces as a result of high flow velocities at bends or through branches, as well as periodic thermal expansion and contraction of piping length on either side of the joint(s).
Finally, I believe there have also been at least a few cases where gravity or normally very low pressure exposed piping happens to be/is inadvertently subjected to much more pressure or thrust than in normal service or assumed (this could happen e.g. if a section of piping were flanged or capped off and filled with a fire hose for testing, even if the "bleed" hole in test plumbing is left wide open, at that point in time when all the air is exhausted from the pipe section, the pipe section becomes full, and water hammers the convergence of the bleed aperture – the test gravity piping section, even when not fully closed off, might well then see much of the pressure of the fire line!) While it can certainly be argued that many low pressure lines can be safely filled without such effects, or this restraint is not a designer's responsibility, I guess anyone who happens to be standing in front of exposed piping provided with restraint (including perhaps/incidentally the designer or Owner) when the inadvertent pressure hits has whoever the provider was to thank when it doesn't let loose! As Mr. SteveWag eruditely notes, it doesn't take much pressure in big piping to develop sizeable loads.
Maybe for some experiential reasons such as these most exposed plant piping (unless provided with secure tie downs or external anchorages) is inherently restrained joint, in the fashion of flanged, grooved or shouldered, or welded etc., and for wherever utilized unrestrained connections such as mechanical joints, stuffing-box couplings like Smith-Blair or Dresser etc., flanged adaptors or flexible isolation couplings, and conventional expansion joints etc., are often provided with at least some modicum of supplementary tie-rodding or harnessed-type external or other restraints?