Dear all,
I was reading ASME VIII Div. 1, Appendix 13 (13-4 Design of vessels of non-circular cross section) and I came across this:
........"Design shall comply with the applicable requirements
of Subsection A except where otherwise provided for in
this Appendix.
(a) Wall thicknesses of parts of vessels described herein
shall be determined by the appropriate formulas or methods
given in Subsection A and in this Appendix. Since, in a
rectangular or obround vessel, the walls can have different
thicknesses, many of the formulas contained herein require
solution by assuming a thickness, or thicknesses, and solving
for stress which is then compared with the allowable
stress value.
(b) Design according to this Appendix is based on both
membrane and bending stresses. Membrane stresses due to
pressure and mechanical loads shall not exceed the design
stress S, the value contained in the allowable stress tables
(see UG-23). At the weld joint, these membrane stresses
shall not exceed an allowable design stress SE, where E
is a joint efficiency factor [see 13-5, 13-18, UW-12, and
UG-23(c)]. The joint efficiency factor E shall also be
applied to the allowable design stress for evaluation of the
calculated bending stress Sb at the location of the joint
only. See 13-1(d), 13-5 footnote 1, and 13-8(b).
Any combination of membrane plus bending tension or
compression stress induced by pressure and/ or mechanical
loads, shall not exceed the following limits:
(1) for plate section of rectangular cross section, 1.5
times the allowable design stress SE;
(2) for other cross sections (such as composite reinforced
bar or shapes and plate sections, etc.), the lesser of:
(a) 1.5 times the design stress SE; or
(b) two-thirds times the yield strength Sy of the
material at the design temperature (see 13-5 for Sy) except
that due to the relatively low yield strength of some materials
listed in Table UNF-23.3 or Table UHA-23, higher
stress values were established in Section II, Part D at
temperatures where the short-time tensile properties govern
to permit the use of these alloys where slightly greater......."
Please notice that SE has both been addressed as allowable design stress and design stress.
It got me confused. May I ask if the two terms are mutually interchangeable?
Thanks.
Design Stress and Allowable Design Stress
