longitudinal stress in unrestrained section.
longitudinal stress in unrestrained section.
(OP)
How longitudinal stress arise in an unrestrained section of the pipeline . Since the pipeline is free to move axially when it is unrestrained .
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS Come Join Us!Are you an
Engineering professional? Join Eng-Tips Forums!
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail. Posting GuidelinesJobs |
longitudinal stress in unrestrained section.
|
RE: longitudinal stress in unrestrained section.
- Steve Perry
http://www.linkedin.com/in/stevenhperry
This post is designed to provide accurate and authoritative information in regard to the subject matter covered. It is offered with the understanding that the author is not engaged in rendering engineering or other professional service. If you need help, get help, and PAY FOR IT.
RE: longitudinal stress in unrestrained section.
RE: longitudinal stress in unrestrained section.
End cap pressure, line pressure, is multiplied by cross-sectional area of flow to give an axial tension force in the pipe wall.
Now including bending, the bending compression in the top-most part of the pipe and tension in the bottom-most part of the pipe are algegraicaly added to the axial tension. Those axial forces are combined with the hoop stress, and shear stress and torsional stresses, if any, and radial stress (equal to internal pressure), to arrive at a maximum equivalent shear stress, which is checked against the allowable equivalent shear stress.
What would you be doing, if you knew that you could not fail?
RE: longitudinal stress in unrestrained section.
RE: longitudinal stress in unrestrained section.
What would you be doing, if you knew that you could not fail?
RE: longitudinal stress in unrestrained section.
But ideally there is the effect of this lateral component of circumferential stress should be added to pd/4t in unrestrained section..ryt ?
RE: longitudinal stress in unrestrained section.
RE: longitudinal stress in unrestrained section.
When UN-restrained, the Axial tension stress component due to Poisson effect, 0.3 * Shoop, is NOT present, as the pipe when UN-restrained is free to contract. End cap load is there however, stress = PD/4/t, since that is not the result of trying to stop a strain; it is the result of an actual direct load on the pipe, pressure acting on the end caps. If Free Contraction is allowed, there will not be any associated stress due to the Poisson effect, as you have applied no load to resist the strains and it will freely contract.
When the pipe is REstrained, with anchors at each end, meaning anchors at the joint between the end caps and pipe, end cap loads are dumped into the anchors and not transmitted past the anchors into the pipe, provided it is a full, 100% longitudinal restraing. The longitudinal stress in a REstrained pipe segment is only due to radial pressure (and makes a tension load of 0.3 * Shoop plus the thermal expansion stress.
What would you be doing, if you knew that you could not fail?
RE: longitudinal stress in unrestrained section.
What my understanding is end caps are used for future tie-ins and to close the pipe during construction.
RE: longitudinal stress in unrestrained section.
What's the pressure on the end cap. It equals, nearly, the compressor discharge pressure, say 1000 psig.
Put a reducer on the other end. Due to flow losses in the manifold, 1 psi, the pressure at the reducer is now 999 psig. From that reducer add a pipe 100 miles long. Do a free body analysis on the reducer and the 100 mile long straight unrestrained pipe. The unbalanced forces show that the opposite end cap force is carried into reducer and the 100 mile long pipe as an axial load of 999 psig x cross-sectional area of flow, - flow friction losses in the 100 miles, balanced by the remaining pressure at the end of the pipeline x the cross-sectional flow area.
If you restrain the 100 miles of pipe by filling the trench with soil, the soil restraint will extract the axial load due to the one end cap at the manifold from the 100 mile long pipe, due to soil friction on the pipe in around the first 300 meters of pipe length. Only flow loss differential pressures need be balanced by being taken up by the pipe wall and also distributed to the soil after that.
What would you be doing, if you knew that you could not fail?
RE: longitudinal stress in unrestrained section.
Hey here goes another question ,
In ASME B31.4 , they are taking lateral component of hoop stress as poisson's ratio times hoop stress.On the contrary, in ASME B31.8 ,they took 0.3 times hoop stress .
What is the reason behind this ?
RE: longitudinal stress in unrestrained section.
What would you be doing, if you knew that you could not fail?
RE: longitudinal stress in unrestrained section.
RE: longitudinal stress in unrestrained section.
What would you be doing, if you knew that you could not fail?
RE: longitudinal stress in unrestrained section.
What would you be doing, if you knew that you could not fail?
RE: longitudinal stress in unrestrained section.
I mean what is its function and what will it do ??
Is it just a stopper ?
RE: longitudinal stress in unrestrained section.
other fittings here too,
http:
What would you be doing, if you knew that you could not fail?
RE: longitudinal stress in unrestrained section.
In ASME B31.4 definition of unrestrained section goes likes this ,
It is free to displace laterally and to strain axially..
displacement happens means there is strain..ryt ?
so that means it is free to strain in all directions..ryt ?
RE: longitudinal stress in unrestrained section.
why any doubts about that?
What would you be doing, if you knew that you could not fail?