Download - RESIDUAL LIFE ASSESSMENT OF ELBOW WITH VOLUMETRIC SURFACE DEFECT UNDER CYCLIC INNER PRESSURE
RESIDUAL LIFE ASSESSMENT OF ELBOW WITH VOLUMETRIC SURFACE DEFECT
UNDER CYCLIC INNER PRESSURE
Yukhymets Petr Sergejevich
Paton Welding Institute (Kiev)
RESIDUAL LIFE ASSESSMENT
Defect and its modeling with half-ellipsoid
functioncurvitywhere
cb
hb
hb
cb
cb
cb
db
325
175,011
2313,048,012,12
12
)(
fKwhere
eeforKee
eeforee
e
ykaei
k
ykai
k
Stress concentation factor
Cyclic stress range
Fatigue curve
[N]
Nominal strains
ei
straight pipe (circular ring, h=const) elbow (circular ring, h=const)
Torus geometry
Elbows measuring results
Elbow №
Dmax, mm
Dmin, mm
Ovalityα*, %
Thickness range h, mm
I 109,7 108,0 ~1,6 5,7-6,4
II 109,1 108,1 ~0,9 5,4-6,8
III 109,6 108,2 ~1,3 5,8-6,7
IV 109,7 108,4 ~1,2 5,4-6,8
nD
DD
DD
DD minmax
minmax
minmax 100200
5.5
6
6.5
76.7
5.8
h2
U2 x( )
7
4
0 1 x
Th
icn
ess
, m
m
φ, rad
Elbow III thickness distributionextended zone
compressed zone
Torus damage modeling
Experimental and calculated strains
1.57 0 1.57 3.14 4.71 6.2820
40
60
80
100
120
140
160141.3
27.123
ek1
ek2
ek3
ek4
a
os 1( )
oc ( )
ov ( )
oo ( )
o1s ( )
upr ( )
6.283
2
3 3 3 3 1
σφ,
MP
a
φ, rad
Cross section model Cross section scheme
Circular ring,
h = const
Circular ring,
h = variable
Elliptical ring, h = const
Elliptical ring, h = variable
NNP NNP corrected
Experiment details
Nominal stress determination method
Δek х10-6
NNP 17,77
NNP corrected 13.12
Elliptical cross-section, h = const
12,07
Experiment 8,27
Strain rate on the defect surface (P=0.1 MPa)
Fatigue crack
Ni, cycle Stress concentration, ασ
ΔP, MPa
10 000 2,53 6
6 500 5,25 19
Load history
Fatigue damage estimation
Method Damage,
df
NNP 20,20
NNP corrected 4,60
Elliptical,
h = const
3,08
1 10 100 1 103
1 104
1 105
1 106
1 103
1 104
1 105
1 106
3.388 105
2.433 103
a1 N( )
10000001 N
σa,
MP
a
N, cycle
Fatigue curve (σt = 524 MPa, σy = 327 MPa, Ψ = 49%)