Current through Register Vol. 54, No. 38, September 21, 2024
(a) The maximum allowable working pressure on
the shell of an unfired pressure vessel is determined by the following:
(1) The strength of the weakest course
completed from the thickness of the plate.
(2) The tensile strength of the
plate.
(3) The efficiency of the
longitudinal joint.
(4) The inside
diameter of the course.
(5) The
safety factor allowed by the ASME Code.
(b) The equation for computing the maximum
allowable working pressure is:
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(1) TS equals
the ultimate strength of the shell plates in psi. If the tensile strength is
not known, 55,000 psi must be used for temperatures not exceeding 700°
F.
(2) T equals the maximum
thickness of shell plates of weakest course in inches.
(3) E equals the efficiency of longitudinal
joint depending upon construction.
(i) ANSI/NB
23, Appendix C, sections A-1 to A-9 must be used to calculate efficiency for a
riveted joint.
(ii) Fusion welded
joints must have the flowing E values:
(A)
Single lap weld is 40%.
(B) Double
lap weld is 60%.
(C) Single butt
weld is 60%.
(D) Double butt weld
is 75%.
(E) Forge weld is
70%.
(F) Brazed steel and brazed
copper is 80%.
(4) R equals the inside radius of the weakest
course of the shell in inches if the thickness of the shell does not exceed 10%
of the radius. The outer radius is used in the equation if the thickness is
over 10% of the radius.
(5) FS
equals the minimum safety factor allowed by this section. The minimum allowable
safety factors are as follows:
(i) For unfired
pressures vessels, except those of lap seam construction, the minimum safety
factor is five.
(ii) For unfired
pressure vessels with longitudinal lap joints the minimum safety factor is 5
1/2.
(iii) For unfired pressure
vessels with reinstalled or secondhand lap seamed construction the minimum
safety factor is six.
(iv) For
unfired pressure vessels with reinstalled or secondhand butt strap or welded
construction the minimum safety factor is 5 1/2.
(c) The ASME Code, section VIII, Division 1
is incorporated as the maximum allowable working pressure for cylindrical
unfired pressure vessels subjected to external or collapsing
pressure.
(d) The formulas in ASME
Code, section VIII, divisions 1 and 2 or ASME, section X are incorporated and
must be used to calculate the maximum allowable pressure for the head of an
existing unfired pressure vessel that was not constructed in accordance with
this chapter.
(e) The effect of
static head must be considered in checking an existing vessel's maximum
allowable working pressure.
This section cited in 34 Pa. Code §
3a.3 (relating to
scope).
