Thermal hot spots and corrosion damage are typical of damages occurring in pressure vessels and piping. Structural integrity of such components needs to be evaluated periodically to determine “fitness-for-service” (FFS) of the components. In the present paper, three alternative methods for level 2 FFS assessments (as described in API 579) are proposed. They are based on variational principles in plasticity, the $m$-alpha method, the idea of reference volume, and the concept of decay lengths in shells. Decay lengths in the axial and circumferential directions for cylindrical shells are derived based on elastic shell theories. They are used to specify the reference volume participating in plastic action and the extent of what can be called “local” damage. Interaction between longitudinal and circumferential effects is investigated. A linear interaction curve is shown to give good estimation of the “remaining strength factor” for damage of practical aspect ratios. The stretching and bulging effects due to the damage are also studied. The limit defining the threshold to dominance of stretching action is proposed by using an approximate equilibrium calculation based on yield-line analysis. The effectiveness of the proposed assessments is demonstrated through an example and verified by level 3 inelastic finite element analysis.

1.
American Petroleum Institute (API)
, 2000, “
Fitness-for-Service
,” API 579, Washington, DC.
2.
ASME
, 1984, “
Manual for Determining the Remaining Strength of Corroded Pipelines
,” American National Standards Institute (ANSI)/American Society of Mechanical Engineers (ASME), B31G.
3.
,
R.
, 2005, “
Integrity Assessment of Pressure Components With Local Hot Spots
,”
ASME J. Pressure Vessel Technol.
0094-9930,
127
, pp.
137
142
.
4.
Indermohan
,
H.
, and
,
R.
, 2005, “
Fitness-for-Service Methodology Based on Variational Principles in Plasticity
,”
ASME J. Pressure Vessel Technol.
0094-9930,
127
, pp.
92
97
.
5.
Ramkumar
,
B.
, and
,
R.
, 2005, “
Fitness for Service Assessment of Corroded Pipelines Based on Variational Principles in Plasticity
,”
Journal of Pipeline Integrity
,
2
, pp.
99
116
. 1475-4584
6.
,
R.
, and
Mangalaramanan
,
S. P.
, 1997, “
Lower Bound Limit Loads Using Variational Concepts: The mα
-Method,”
Int. J. Pressure Vessels Piping
0308-0161,
71
, pp.
93
106
.
7.
Tantichattanont
,
P.
,
,
S.
, and
,
R.
, “
Fitness-for-Service Assessment of Spherical Pressure Vessels with Hot Spots
,” 2007,
Int. J. Pressure Vessels Piping
0308-0161,
84
, p.
762
.
8.
Tantichattanont
,
P.
,
,
S.
, and
,
R.
, 2006, “
Integrity Assessment of Spherical Pressure Components with Local Corrosion and Hot Spots
,”
Proceedings of Pressure Vessels and Piping Division Conference PVP 2006
, Jul. 23–27.
9.
Kraus
,
H.
, 1967,
Thin Elastic Shells: An Introduction to the Theoretical Foundations and the Analysis of Their Static and Dynamic Behavior
,
Wiley
,
New York
.
10.
Donnell
,
L. H.
, 1933, “
Stability of Thin-Walled Tubes Under Torsion
,” NACA Report No. 479, pp.
95
116
.
11.
Hoff
,
N. J.
,
Kempner
,
J.
, and
Pohle
,
F. V.
, 1954, “
Line Load Applied Along Generators of Thin-Walled Circular Cylindrical Shells of Finite Length
,”
Q. Appl. Math.
0033-569X,
11
(
4
), pp.
211
245
.
12.
Johansen
,
K. W.
, 1962,
Yield-Line Theory
,
Cement and Concrete Association
,
London
.
13.
Bolar
,
A. A.
, and
,
S. M. R.
, 2005, “
Robust Estimation of Limit Loads of Plates
,”
33rd Annual General Conference of the Canadian Society of Civil Engineering
, Toronto, ON, Canada. Jun. 2–4.
14.
Tee
,
G. J.
, 2005, “
Surface Area and Capacity of Ellipsoids in n Dimensions
,”
New Zealand Journal of Mathematics
,
34
, pp.
165
198
. 1171-6096
15.
Bednar
,
H. H.
, 1985,
Pressure Vessel Design Handbook
, 2nd ed.,
Van Nostrand Reinhold
,
New York
.
16.
ANSYS
, 2004,
University Research Version, 8.1
,
SASIP, Inc.
,
Cannonsburgh, PA
.