REQUIREMENTS PERTAINING TO METHODS
OF FABRICATION OF PRESSURE VESSELS
REQUIREMENTS FOR PRESSURE VESSELS FABRICATED BY
The rules in Part UW are applicable to pressure vessels
and vessel parts that are fabricated by welding and shall
be used in conjunction with the general requirements in
Subsection A, and with the specific requirements in Subsection
C that pertain to the class of material used.
UW-2 SERVICE RESTRICTIONS
aWhen vessels are to contain lethal42 substances,
either liquid or gaseous, all butt-welded joints shall be
fully radiographed in accordance with UW-51, except
for butt welds subject to the provisions of 2 and 3 below
and UW-11a4, and butt welds in stiffening rings
designed under the rules of UG-29. ERW pipe or tube is
not permitted to be used as a shell or nozzle in lethal service
applications. When fabricated of carbon or low alloy
steel, such vessels shall be postweld heat treated in accordance
with Tables UCS-56-1 through UCS-56-11, unless
otherwise exempted by Table UCS-56-1, General Note
b3. When a vessel is to contain fluids of such a nature
that a very small amount mixed or unmixed with air is
dangerous to life when inhaled, it shall be the responsibility
of the user and/or his designated agent to determine if
it is lethal. If determined as lethal, the user and/or his designated
agent [see U-2a] shall so advise the designer
and/or Manufacturer. It shall be the responsibility of
the Manufacturer to comply with the applicable Code provisions
see UCI-2 and UCD-2.
1 The joints of various categories see UW-3 shall
be as follows:
-a Except for welded tubes and pipes internal to
heat exchanger shells, all joints of Category A shall be
Type No. 1 of Table UW-12.
-b All Category B and C joints shall be Type No.
1 or No. 2 of Table UW-12.
-c Category C joints for lap joint stub ends shall
be as follows:
-1 The finished stub end shall be attached to
its adjacent shell with a Type No. 1 or Type No. 2 joint
of Table UW-12. The finished stub end can be made from
a forging or can be machined from plate material. [See
-2 The lap joint stub end shall be fabricated as
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+a The weld is made in two steps as shown
in Figure UW-13.5.
+b Before making weld No. 2, weld No. 1 is
examined by full radiography in accordance with
UW-51, regardless of size. The weld and fusion between
the weld buildup and neck is examined by ultrasonics in
accordance with Mandatory Appendix 12.
+c Weld No. 2 is examined by full radiography
in accordance with UW-51.
-3 The finished stub end may either conform
to ASME B16.9 dimensional requirements or be made to
a nonstandard size, provided all requirements of this Division
-d All joints of Category D shall be full penetration
welds extending through the entire thickness of the
vessel wall or nozzle wall.
2 Radiographic examination of the welded seam in
exchanger tubes and pipes, to a material specification permitted
by this Division, which are butt welded without
the addition of filler metal may be waived, provided the
tube or pipe is totally enclosed within a shell of a vessel
which meets the requirements of a.
3 If only one side of a heat exchanger contains a
lethal substance, the other side need not be built to the
rules for a vessel in lethal service if:
UW-1 UW-2 ASME BPVC.VIII.1-2023