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Friction and its EffectsinPiping Systems
CONTENTS
Introduction to Friction Friction in Piping Systems Why We need to Consider Friction Calculation of Friction Force in CAESAR Effects of Friction in Piping Systems Minimizing Friction Effects.
FrictionFriction is a force that opposes motion between two touching surfaces.
W = mg
N = - mg
FFS
F = Force Causing Motion Fs = Force of Static Friction N = Force Normal Holds Surfaces in ContactW = Weight of Object ( Mass x Gravity)
M1
Types of FrictionForce of Static Friction (Fs)
This value represents the relative force which resists the object to
move.
Force of Kinetic Friction (Fk)
This value represents the relative force which is resisting the object in motion
Types Of Friction
Static Friction that acts on something that is not moving No heat or wear is generated
Sliding Force resulting when pushing or pulling an object over a surface. Heat and wear can result
Rolling Contact is reduced because of rollers or wheels or ball bearings. Less heat and wear will result.
Frictional Forces Occur When Materials are in Contact
W
fsF
N
Surfaces in Contact
F = Force Causing Motion Fs = Force of Static Friction N = Force Normal Holds Surfaces in ContactW = Weight of Object ( Mass x Gravity)
M1
Friction is a Force That Resists Motion
W
F
N
Surfaces in Contact
The Pink Block M1 Will not Move Until the Force F Exceeds the Force of Static Friction fs.
fsM1
The Relative Force of Static Friction Between 2 Objects is Expressed as the Quotient of the Force (F) Required to Move the Object
W
fsF
N
Surfaces in Contact
M1
Divided by the Weight W of the Object
This is Called the Coefficient of Friction
W
fsF
Surfaces in Contact
sFW
= Force Required to Cause Motion
= Weight of Object
= Coefficient of Friction
W
Fs
Coefficient of Static Friction
N
M1
Typical values of Mu:
SURFACES FRICTION FACTOR
Steel to Steel 0.3
Stainless steel to PTFE 0.1
Roller bearing 0.01
Steel to Concrete 0.4
Friction in Piping Systems
Pipes carrying high temperature process fluids, hence they will expand, hence there will be a movement of pipe, these leads to rubbing of surfaces, hence friction comes in to act.
Why we need to consider the friction…? Support friction in a piping system can prevent the pipe from free
expansion thus creating a higher stress in the piping systems, such as branch connections and a higher loads on the connecting equipments and restraints.
CALCULATION OF FRICTION FORCE IN CAESAR
CAESAR USES RESTRAINT STIFFNESS METHOD
CAESAR INSERTS A NON-RIGID STIFFNESS AT THE NODE EXPERIENCING DISPLACEMENTS
FORCE AT THAT NODE = DISPLACEMENT * FRICTION STIFFNESS
MAXIMUM VALUE OF THE FORCE AT THE NODE IS THE FRICTION FORCE F= μ * NORMAL FORCE
ONCE MAXIMUM VALUE IS REACHED FORCE AT THE NODE STOPS INCREASING
IF THIS RESULTANT FORCE IS LESS THAN THE MAXIMUM FRICTION FORCE THE NODE IS ASSUMED TO BE NOT SLIDING EVEN THOUGH WE SEE DISPLACEMENTS IN THE OUTPUT REPORT
Effects of Friction in Piping Systems
RESTRAINT FORCES IN OPERATING CONDITION
WITHOUT FRICTION WITH FRICTION
NODE Fx (N) Fy (N) Fx (N) Fy (N)
10 0 -1226 -2391 -1226
20 0 -3371 1011 -3371
30 0 -3371 1011 -3371
40 0 -1226 368 -1226
Effects of Friction in Piping Systems
RESTRAINT FORCES IN OPERATING CONDITION
WITHOUT FRICTION WITH FRICTION
NODE Fx (N) Fy (N) Fx (N) Fy (N)
10 0 -1209 -363 -1209
20 0 -3476 -1043 -3476
30 0 -2949 -885 -2949
40 0 -3123 0 -3123
50 0 -2949 885 -2949
60 0 -3476 1043 -3476
70 0 -1209 363 -1209
Effects of Friction in Piping Systems
RESTRAINT FORCES IN OPERATING CONDITION
WITHOUT FRICTION WITH FRICTION
NODE Fx (N) Fy (N) Fx (N) Fy (N)
10 -9477 -1209 -15088 -1209
20 0 -3475 1043 -3475
30 0 -2953 886 -2953
40 0 -3106 932 -3106
50 0 -3011 903 -3011
60 0 -3243 973 -3243
70 0 -2757 827 -2757
95 0 -3136 0 -3136
120 0 -2757 -827 -2757
130 0 -3243 -973 -3243
140 0 -3011 -903 -3011
150 0 -3106 -932 -3106
160 0 -2953 -886 -2953
170 0 -3475 -1043 -3475
180 9477 -1209 15088 -1209
Effects of Friction in Piping Systems
OPERATING LOADS AT NODE 10
WITHOUT FRICTION
Fx(N) Fy(N) Fz(N) Mx(N-m) My(N-m) Mz(N-m)
-3120 -2884 -1988 783 2223 -2505
WITH FRICTION
Fx(N) Fy(N) Fz(N) Mx(N-m) My(N-m) Mz(N-m)
-6385 -1645 -109 -2611 1769 -7577
MINIMISING FRICTION EFFECT
USING SLIDING PLATES
USING RIGID STRUTS NEAR THE CRITICAL EQUIPMENTS
USING Tie rods
Thank u
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