#27659 - 05/22/09 10:53 AM
Force and moment due to flow direction change!
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Member
Registered: 04/03/09
Posts: 13
Loc: Saskatoon Canada
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Hi,
I got forces and moments on the thrust blocks from restraints report generated by CAESAR II. My understanding is that all the forces and moments are induced by pipe and fluid weight,internal pressure,thermal expansion and other components.
I have a a question about it, does CAESAR II consider the force and moment induced by flow direction change? I have a thrust block at a 90 degree elbow. The flow direction change will generate force and moment and finally acting on the thrust block. it seems CAESAR doesn't consider it because CAESAR II doesn't need to input the pipe flow rate. but the flow rate is crucial to calculate the force and moment due to flow direction change.
Any advices will be appreciated greatly.
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#27662 - 05/22/09 11:53 PM
Re: Force and moment due to flow direction change!
[Re: Young2009]
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Member
Registered: 04/12/04
Posts: 493
Loc: London, UK
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Ask yourself a question: do you model the pressure thrust load in your system? Pressure forces will generate a longitudinal load of PXA due to end closures or change in directions. In absence of thrust blocks, this loading will be equilibrated only by longitudinal stress.If this thrust loading is not modelled , CAESAR II will only generate loading due to other sources.
CAESAR II will only generate and analyze for those loads which are specified . It will not make any guess about the physics of the problem.
Internal pressure effect is generally taken care of my checking the pipe stresses ( hoop and longitudinal) . The thrust effect is taken into consideration only when specified.Internal pressure also effects in strain, something which is known as Bourdon effect.You can activate/deactivate the same in CAESAR.
_________________________
anindya
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#27700 - 05/25/09 08:25 AM
Re: Force and moment due to flow direction change!
[Re: anindya stress]
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Member
Registered: 04/03/09
Posts: 13
Loc: Saskatoon Canada
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Ask yourself a question: do you model the pressure thrust load in your system? Pressure forces will generate a longitudinal load of PXA due to end closures or change in directions. In absence of thrust blocks, this loading will be equilibrated only by longitudinal stress.If this thrust loading is not modelled , CAESAR II will only generate loading due to other sources.
CAESAR II will only generate and analyze for those loads which are specified . It will not make any guess about the physics of the problem.
Internal pressure effect is generally taken care of my checking the pipe stresses ( hoop and longitudinal) . The thrust effect is taken into consideration only when specified.Internal pressure also effects in strain, something which is known as Bourdon effect.You can activate/deactivate the same in CAESAR.
In my project, there are several concrete thrust blocks for the pipelines and structure engineer wanted to know how big the forces and moments on those thrust blocks. I did CAESAR II calculation and got forces and moment from restraint report. From your reply, I understand that the forces and moments I got from CAESAR II weren't taken into consideration of flow direction change, isn't it?
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#27703 - 05/25/09 08:55 AM
Re: Force and moment due to flow direction change!
[Re: Young2009]
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Member
Registered: 04/12/04
Posts: 493
Loc: London, UK
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Thrust blocks are important when the mechanical or Adhesive joints ( I am try to paint a picture with a broad brush ie referring to both FRP as well as metallic pipes)are not capable enough to take care of pressure thrust.
To your specific question, you have not mentioned anything about your modelling detail whether you have included pressure thrust loading in your system. If you have modelled pressure thrust , CAESAR II has taken care of it, else NO.
Regards
_________________________
anindya
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#27706 - 05/25/09 01:24 PM
Re: Force and moment due to flow direction change!
[Re: anindya stress]
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Member
Registered: 04/03/09
Posts: 13
Loc: Saskatoon Canada
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Thrust blocks are important when the mechanical or Adhesive joints ( I am try to paint a picture with a broad brush ie referring to both FRP as well as metallic pipes)are not capable enough to take care of pressure thrust.
To your specific question, you have not mentioned anything about your modelling detail whether you have included pressure thrust loading in your system. If you have modelled pressure thrust , CAESAR II has taken care of it, else NO.
Regards Thank you, Anindya stress. I calculated the forces and moments on thrust blocks during sustained, operating and expansion load cases. my input included internal pressure and operating temperature. I am not sure how to include pressure thrust loading in my system and if it is needed for my calculation of forces and moments on the thrust blocks.
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#27736 - 05/26/09 02:02 PM
Re: Force and moment due to flow direction change!
[Re: Young2009]
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Member
Registered: 04/12/04
Posts: 493
Loc: London, UK
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The pressure thrust loading is simply PXA.You can vectorially add this load with the restraint load at thrust blocks from other load cases.You need not model this force in CAESAR II.Make sure that the loads from other cases are realistic as otherwise there will be too much of deviation w.r.t reality.
_________________________
anindya
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#27741 - 05/26/09 07:56 PM
Re: Force and moment due to flow direction change!
[Re: anindya stress]
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Member
Registered: 02/16/07
Posts: 508
Loc: Singapore
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There could be one more problem if there are two thrust block in a straight line for mechanical joint that do not take care of thrust load ( by longitudinal stress) ( slip type joint) Caesar report will reflect huge thermal axial load , again if we manually added pressure*area load it might be a problem.
One way we can manage it just to put stiffness at mechanical joint points with Cnode
Like for pipe in X direction 20 is mechanical joint
20 Z with Cnode 21
20 Y with Cnode 21
20 Rx with Cnode 21
20 Ry with Cnode 21
20 Rz with Cnode 21
20 X with Cnode 21 Stiffness Zero ( or low vendor supplied value)
Pressure thrust( P*A) have to claculate manually & add at all change in direction.
Regards
Habib
Edited by shr (05/27/09 07:32 AM)
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#27764 - 05/27/09 11:00 AM
Re: Force and moment due to flow direction change!
[Re: shr]
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Member
Registered: 04/03/09
Posts: 13
Loc: Saskatoon Canada
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There could be one more problem if there are two thrust block in a straight line for mechanical joint that do not take care of thrust load ( by longitudinal stress) ( slip type joint) Caesar report will reflect huge thermal axial load , again if we manually added pressure*area load it might be a problem.
One way we can manage it just to put stiffness at mechanical joint points with Cnode
Like for pipe in X direction 20 is mechanical joint
20 Z with Cnode 21
20 Y with Cnode 21
20 Rx with Cnode 21
20 Ry with Cnode 21
20 Rz with Cnode 21
20 X with Cnode 21 Stiffness Zero ( or low vendor supplied value)
Pressure thrust( P*A) have to claculate manually & add at all change in direction.
Regards
Habib
Thank you! All connections are welded joints.
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#27769 - 05/27/09 06:48 PM
Re: Force and moment due to flow direction change!
[Re: Young2009]
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Member
Registered: 02/16/07
Posts: 508
Loc: Singapore
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Hi Young2009
If you are using metallic piping with welded joint then why you need thrust block ?
Pipe material ( Longitudinal stress due to pressure) will itself take care of pressure thrust.
If you are using a untied expansion bellow you may require a thrust block.
Regards
Habib
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#27970 - 06/04/09 07:56 PM
Re: Force and moment due to flow direction change!
[Re: shr]
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Member
Registered: 01/14/09
Posts: 38
Loc: china shanghai
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Hi Young2009
because of the momentum change in the steady folw,Normally this force is constant,and is small enough that it can be easily absorbed through tension in the pipe wall,to be passed on to adjacent elbow which may have equal and opposite loads,therefore zeroing the net load on the system,therefore these type of the momentum loads are usually ignore by the stress analyst.if the fluid velocity or density change quicklly with time,this momentum load can lead to a dynamic load ,so which may not be cancelled!
regards
Edited by zzw (06/04/09 07:59 PM)
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#28819 - 07/22/09 09:18 PM
Re: Force and moment due to flow direction change!
[Re: shr]
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Member
Registered: 04/03/09
Posts: 13
Loc: Saskatoon Canada
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Hi Young2009
If you are using metallic piping with welded joint then why you need thrust block ?
Pipe material ( Longitudinal stress due to pressure) will itself take care of pressure thrust.
If you are using a untied expansion bellow you may require a thrust block.
Regards
Habib Hi, Habib, Sorry for the late response. In this projet, the pipeline is about 5 km and the thermal expansion and contraction are huge. My understanding is this is the only reason the client want a thrust block.
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