pedd formula sheet.pdf
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Transcript of pedd formula sheet.pdf
SHELLS
1) BASED ON INTERNAL PRESSURE
a) Cylindrical Shell
π‘ =ππ·π
2ππ½βπ=
ππ·π
2ππ½+π
Circumferential stress, ππ =ππ·
2π‘
Longitudinal stress, ππ =ππ·
4π‘
Where, p β internal pressure
D β Mean dia. of shell
Under Combined Loadings:
1) Circumferential/tangential stress:
ππ‘ = ππ·π+π‘
2π‘ (Tensile)
2) Longitudinal stress:
a) Due to the internal pressure-
π1 =ππ·π
4π‘ (Tensile)
b) Due to weight of vessel and
its contents-
π2 =π
ππ‘(π·π+π‘) (Compressive)
c) Wind load-
π3 = β+ π
π§ = β
+π/(ππ·π2π‘)
(Tensile/Compressive)
M = bending moment
ππ = π1 + π2 + π3
3) Stress due to offset piping and
wind:
ππ = 2π/(ππ‘π·π(π·π + π‘))
T = torque about vessel axis
Resultant stress β
ππ = (ππ‘2 β ππ‘ππ + ππ
2 + 3ππ 2)0.5
fc (permissible)
= 1
12β
πΈ
β3(1β π2)β
π‘
π·π/2
E = modulus of elasticity
Β΅ = Poissonβs ratio
b) Spherical shell
π‘ =ππ·π
4ππ½ β π=
ππ·π
4ππ½ + π
2) BASED ON EXTERNAL PRESSURE
Cylindrical Shell β
ππ =2.42πΈ (
π‘π·π
)2.5
(1 β π2)0.75 β {πΏ
π·πβ 0.45 (π‘/π·π)1/2}
ππππππ€ππππ =1
4β ππ
πΏ = π’ππ π π’ππππ‘ππ πππππ‘β
HEADS
1) INTERNAL PRESSURE:
I) CONICAL HEAD:
Circumferential stress: π =ππ·
2π‘ cos π
π‘β =ππ·
2ππ½ cos π+ πΆ. π΄
d = half apex angle of cone
II) TORRISPHERICAL HEAD:
π‘β =ππ ππ
2ππ½+ πΆ. π΄
Rc = crown radius
W = stress intensity factor =
1
4β (3 + β
π π
π π)
Rk = knuckle radius = 0.06 Rc
III) ELLIPTICAL HEAD:
π‘β =ππ·π
2ππ½
π· = πΌππ‘πππππ ππππππ‘ππ
π =1
6(2 + π2),
π =(πππππ ππ₯ππ )
πππππ ππ₯ππ
IV) HEMISPHERICAL HEAD:
π‘β =ππ·π
4ππ½ β π=
ππ·π
4ππ½ + π
2) EXTERNAL PRESSURE:
I) DOMED HEADS:
π‘β = ππ π{3(1 β π2)}1/4 βπ/2πΈ
+ πΆ. π΄
Where, d = 4 to 4.4
Rc = crown radius
E= youngβs modulus.
NOZZLES
AB = Max. horizontal distance = 2d
AD = Max. vertical distance = 6t or 3.5ts + 2.5tn
H1 = H2 = 2.5ts (by nozzle only)
Else, H1 = 2.5tn (by both ring pad and nozzle)
π΄ = ππ‘π ,
π΄π = π(π‘π β π‘π β² β πΆ. π΄) ,
π΄π = 2π»1(π‘π β π‘πβ² β πΆ. π΄),
π΄1 = 2π»2(π‘π β 2πΆ. π΄)
π΄β² = π΄π + π΄π + π΄1 =
πΆππππππ ππ‘πππ ππ£πππππππ
π΄ β π΄β² = π΄πππ ππππ’ππππ
FLANGES
BOLT LOAD
ππππ‘π= πππΊππ
Where Ya = gasket seating stress
b = bo if bo < 6.3
2.5βππ if bo >6.3
bo=(G0-Gi)/4
ππ,ππππππ‘ππ = π2ππΊππ +π
4πΊ2π
m = gasket factor
πΊ = (πΊπ + πΊπ)/2
π΄π,ππππππ‘πππ = ππ,ππππππ‘πππ
ππ,ππππππ‘πππ
π΄π,ππ‘π =ππ,ππ‘π
πππ‘π
Tensile stress,
π‘π = πΊβπ
ππ+ πΆ. π΄
π = 1/(0.3 + 1.5ππβπΊ
π»πΊ)
βπΊ = π΅ β πΊ
2
π» =π
4πΊ2π
f= permissible stress for flanges
Where,
Wm = total bolt load
B = Bolt circle diameter
G = diameter of gasket load
reaction
π = 0.51π2.09
Where,
Y = bolt area
X = nominal diameter
π΄π =2ππππΊπ
ππ
SPHERICAL SHELL
Subjected to external pressure-
ππ = 8πΈ
β3(1 β π2) (
π‘
π·)
2
D = outside diameter
Pallowable = 1/6*Pc
SHELL WITH EXTERNAL JACKET
π‘π = πβπ1π
π1+ πΆ. π΄
π‘π = πβπ2π
π2+ πΆ. π΄
Where,
k1 = 0.167
k2 = 0.12
SHELL WITH HALF COIL JACKET
πππΆ =πππ
2π‘π
πππ =πππ
4π‘π+2.5π‘π
πππΆ = ππ + πππ (total
circumferential stress)
= ππ·π
2π‘π +
πππ
4π‘π+2.5π‘π
Total longitudinal stress:
πππ = ππ + πππ + ππ
πππ = ππ·π
4π‘π +
πππ
2π‘π +
2Ξπππ2
3π‘π 2
P= internal pressure of shell
P=internal pressure of coil
Di= shell internal diameter
d= internal diameter of coil
FLAT PLATE HEAD
π‘ = πΆ β π·βπ
π
f = shear stress