UFC 4-390-01
23 July 2003
material properties and, in particular, the effect of material
thickness on fracture characteristics. The structural design
basis used by the applicant for the analysis of brittle fracture
should be verified by destructive testing of the pressure hull
and component models and structures, or, where possible, by
reference to existing information and service experience.
All plates, parts and components must demonstrate adequate
strength and toughness over the range of design operating
temperature. Toughness characteristics of ferrous materials
should be referenced to the Nil Ductility Transition Temperature
(NDTT).
B.3
DESIGN STRENGTH PARAMETERS OF INTERNALLY-LOADED PRESSURE
VESSELS
In general, the applicant should demonstrate the structural
integrity of the pressure vessel under loading conditions to be
representative of those expected in service. Therefore, the
designer must take into consideration the effects of temperature,
cyclical loading, creep, ductility, corrosion rates and
anisotropy. Examples of pertinent fabrication variables include
material reproducibility, fabrication flaws and defects, vessel
openings, intersections of different shells of revolution and
attendant reinforcement(s), residual fabrication stresses and
deviations from the nominal geometry.
B.3.1 Inelastic Stability (Yield). For stable pressure vessel
structures (i.e., stiffened or un-stiffened shells which permit
the level of load-induced membrane stresses to approach the
material yield point), the ratio of the pressure that would
produce yield to the design operating pressure should be
justified. In determining the pressure at which yield occurs,
all fabrication and design-induced restraint and geometric
variables should be considered and their effect(s) included.
This is because the strength of moderately stable vessels can be
detrimentally affected by such variables (i.e., yield can occur
at levels of membrane stress below calculated levels of yield
stress).
B.3.2 Stress Analysis. The applicant should perform a complete
stress analysis of the pressure vessel and demonstrate that all
stresses are within the design criteria and that the vessel's
fatigue life is adequate for its expected service life. For
Category 1 and 2 materials, the allowable stresses under internal
pressure should be justified to the SCA. The stress levels
defined in paragraph B.3.3 may be used as guidelines; however,
the applicant must demonstrate compliance with only B.3.3.c.,
maximum peak stress. The design requirements for Category 3
materials must be comprehensive, provide at least the same degree
of conservatism as the design requirements for Category 1 and 2
materials and should be approved by the SCA.
B.3.3 Verification of System Design Pressure. For Category 1
and 2 materials, model testing or use of existing model test data
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