REPORT ON C.G.
CALCULATION
HOW CAN C.G. DEFINED?
Plate that point in the plane of the area about any axis
through which the moment of area is zero, it considers
with the center of gravity of the area materialized as
infinitely thin homogeneous and uniform.
IMPORTANCE OF C.G. CALCULATION :
As per C.G. calculation, location of lifting and tailing
lug to be decided ehich in turn would decide a smooth
erection.
While transporting saddle is spaced equal distance from
C.G. so as to avoid tilting of equipment.
While shop manufacturing if C.G. is known, counter
weight can put for easy rotation of job.
Accurate C.G. calculation is required to load
components on a material on a machining set up (i.e.
milling, drilling & turning)
For carry out hydrotest of vertical vessel C.G. can be
required to put saddle support at adequate place.
In road transportation of vessel consignment to balance
load we required C.G.
During erection of equipment and do site joints of
cylindrical part C.G. required.
STEPS OF C.G. CALCULATION :
Fix (0,0) of job for reference X & Y values.
Find out weight of the all parts of the job (i.e. shall,
cone, D/E etc.)
Find out X & Y values for all components (i.e. shall,
cone, D/E etc.)
The same values of X and Y components shall be find
out by using following formulas
_ Wt * X _ Wt * Y
X = ---------------- Y = -------------------
Wt Wt
WHERE,
Wt = Sum of weight of all parts
X = C.G. point in vertical direction of all parts
Y = C.G. point in horizontal direction of all parts
X = sum of Wt * X co- ordinate of all parts.
Y = Sum of Wt * Y co ordinate of all parts.
DESIGN PROCEDURE AS PER ASME SECTION VIII
DIV 1
SHELL: -
CIRCUMFERENTIAL SHELL
PR
t = ----------------- + C.A.
SE 0.6P
LONGITUDINAL SHELL
PR
t = ----------------- + C.A.
2SE 0.4P
SPERICAL SHELL
PR
t = ----------------- + C.A.
2SE 0.2P
WHERE,
T = thickness
P = inter design pressure
R = out side radius
S = allowable stress value
THICKNESS OF FORMED HEADS
ELLIPSOIDAL HEAD
PD
t = ----------------- + C.A.
2SE 0.2P
TORISPHERICAL HEAD
0.0885PL
t = ----------------- + C.A.
SE 0.1P
HEMISPHERICAL HEAD
PL
t = ----------------- + C.A.
2SE 0.2P
CONICAL HEAD
PD
t = --------------------------- + C.A.
2 COS (SE 0.6P)
WHERE,
T = THICKNESS
P = INTERNAL DESIGN PRESSURE
D = INSIDE DIAMETER OF THE HEAD
S = MAXIMUM ALLOWABLE STRESS
E = LOWEST EFFICIENCY OF JOINT
L = INSIDE SPERICAL OR CROWN RADIUS
THICKNESS OF NOZZLE WALL
PRn
tn = --------------------------- + C.A.
SE 0.6P
WHERE,
P = INTERNAL DESIGN PRESSURE
Rn = INTERNAL RADIUS OF THE NOZZLE
S = ALLOWABLE STRESS OF MATERIAL
E = JOINT EFFICIENCY
Tn = THICKNESS OF NOZZLE PIPE
REINFORCEMENT CALCULATION :
A = DtrF + 2 tntrF (1- frl)
WHERE,
D = FINISHED DIAMETER OF CIRCULAR
F = CORROSION FACTOR
Frl = Sn/Sv
Tr = Required thickness
tn = Nozzle wall thickness
DESIGN PROCEDURE AS PER ASME SEC VIII DIV 2
1. CYLINDRICAL SHELLS
PR
t = ---------------- + C.A.
S 0.5P
2. SPHERICAL SHELLS
0.5PR
t = ---------------- + C.A.
S 0.25P
3. CONICAL SHELLS
PR
t = ---------------- + C.A.
S 0. 5P
WHERE,
T = THICKNESS
P = INTERNAL DESIGN PRESSURE
R = RADIUS
S = ALLOWABLE STRESS
HEADS:
4. HEMISPHERICAL HEADS
0.5PR
t = ---------------- + C.A.
S 0. 25P
For hemispherical heads the minimum required
thickness shall be as required for spherical shell.
5. TORISPHERICAL HEAD/ELLIPSOIDAL HEAD
D
t = ----(E^P/S 1) + C.A.
2
WHERE,
T = MINIMUM REQUIRED THICKNESS
P = INTERNAL DESIGN PRESSURE
D = INSIDE DIAMETER
S = ALLOWABLE STRESS
E = LOWEST EFFICENCITY
L = INSIDE SPHERICAL OR CROWN RADIUS
THICKNESS OF NOZZLE WALL :
tn = PRn / S 0.5P
WHERE,
tn = NOZZLE WALL THICKNESS
P = INTERNAL DESIGN PRESSURE
Rn = OUTSIDE RADIUS OF THE SHELL
S = ALLOWABLE STRESS VALUE
