Nope , "lager the flexibility factor the more 'flexible' the component".Intitutively , imagine an pulling an circular bend and making it straight.As you tend towards a straight pipe of the same length the radius increases.An straight pipe has an infinite radius and its flexibility factor is 1 .Remember all these times the length , diameter and thickness of the element under consideration is kept constant.
Duplicating the Flexiblity V/s Bend Radius problem L shape Configuration
I duplicated the L shaped configration .You will notice that the loads in CASE 1 for a long radius elbow is more than CASE 2 for Standard Elbows.Notice the flexibility factors.Hence higher flexibility factor means higher flexibility and lower loads.I am reproducing loads at a single point only.
Configuration
Y = 2000mm
X= 3000mm
Input Data
Pipe Size= 6"
Sch 40
Temp 120 deg C
Pressure None
Material API 5L Gr B
CASE 1 : Long Radius
Radius (2D) = 304.8 mm
In-plane Flexibility Factor =4.943
Out-Plane Flexibility Factor=4.943
In-Plane SIF = 1.87
Out-Plane SIF =1.558
Loads (Forces in lb and moments in lbf)
Fx=-577 Fy=-1703 Fz=0 Mx=0 My=0 Mz=2879
CASE II : Standard Radius
Radius (1.5D) = 228.6 mm
In-plane Flexibility Factor =6.59
Out-Plane Flexibility Factor=6.59
In-Plane SIF = 2.26
Out-Plane SIF =1.888
Loads (Forces in lb and moments in lbf)
Fx=-529 Fy=-1632 Fz=0 Mx=0 My=0 Mz=2698
Shivaprakash C Rao
Tessag Edeleanu
www.edeleanu.com.sg
-----Original Message-----
From: Mark upston [SMTP:mmwind@cnsp.com]
Sent: Friday, August 31, 2001 12:09 AM
To: PipingDesign@yahoogroups.com
Subject: RE: [PipingDesign] Stress analysis
Sorry you are mistaken a long radius bend is more flexible than a Short
radius
You are correct the Bend flexibility factor is inversely proportional to
Bend Radius
but the smaller the flexibility factor the more 'flexible' the component.
Model a simple stress model e.g L system with 2 anchors and observe the
loads
when changing the short to long radius bend.
Mark Upston
APPEGGA PE
-----Original Message-----
From: Shivaprakash [mailto:shivaprakashcrao@yahoo.com]
Sent: Wednesday, August 29, 2001 11:25 PM
To: 'PipingDesign@yahoogroups.com'
Subject: RE: [PipingDesign] Stress analysis
Hi vij ,
Caesar II does not take care of the nos of cycles.The Engineer has factor-in the increased cycles during the selection of the expansion joint.After selecting the appropriate model , feed the various stiffness values in the caesar model.An example is given in the link below.
http://www.pipingtech.com/products/expjtcat/expansion_joint-howto-sflex.htm
2. Which has more flexibility - Short radius elbow or a long radius elbow ? Please explain.
The flexibility of a Short Radius Elbow is more.Let us look at the defination of flexibility factor
Flexibiliy Factor is the ratio of the flexibility of bend to that of a
straight pipe having the same length and cross section.
The bend basically gets its flexibility bcos the cross section gets
flattened thus increasing its flexibility.This means that the
circumferential stresses is many times that predicted by ordinary bending
theory.This is taken care by increased the SIF values factored in in
calculating the stresses.
Now if we consider B31.3
Parameter h = ( (Wall thickness) *(Radius of Bend))/square of (mean radius
of pipe))
Flexibility Factor = 1.65/h
SIF in plane = 0.9 / (h) to power 2/3
SIF out of plane = 0.75 /(h) to power 2/3
From this it is evident
Flexibility is inversely proportional to Bend Radius ( Larger the Bend Radius lower the Flexibility)
Stress is inversely proportinal to Bend Radius to power 2/3 ( Larger the Bend Radius lower the Stresses)
Hence using a short elbow you will increase the flexibility reducing the terminal loads but at the cost of increased stresses.
3. How to check flange leakage in caesar ? Should we model valve and flange with connecting nodes taking care of gasket compressibility ?
There is a Flange Leakage/Stress Calculation program.It is an independent of the main stress analysis program.You have to feed the external bending and axial loads I think the CNODE concept is not used here.As regards the compressibility of the gasket is considered CAESAR II assumes the gasket to be fairly stiff. Some of the limitations of using this for flange leakage are as follows
a)Cannot be used for ring type joints.
b)Cannot be used for highly flexible gaskets.
Basically flange leakage depends on various factors.ASME checks for the line pressure using the "m" factor.Caesar II uses this as the basis and goes one step further by including the external loads in the final analysis.
You can also use the Equivalent Pressure method using the Rating table to do a casual check.
Shivaprakash C Rao
Tessag Edeleanu
www.edeleanu.com.sg
-----Original Message-----
From: vijay venkatraman [SMTP:v2jay@yahoo.com]
Sent: Wednesday, August 29, 2001 11:49 PM
To: PipingDesign@yahoogroups.com
Subject: [PipingDesign] Stress analysis
_________________________________________________________ Do You Yahoo!?Get your free @yahoo.com address at http://mail.yahoo.com
Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
<< File: ATT00006.html >>
This archive was generated by hypermail 2.1.8 : Mon Oct 27 2008 - 20:23:54 EDT