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Description / Abstract:
Overview
Part 1, paragraph 1.2 defines the scope of coverage for VIII-2.
The term scope refers to both the type of pressure equipment being
considered in the development of these rules, as well as the
geometric scope of the vessel that is stamped with the
Certification Mark and U2 Designator as meeting VIII-2.
In accordance with Part 1, paragraph 1.2.1.1, pressure vessels
are defined as containers for the containment of pressure, internal
or external. This pressure may be obtained from any external
source, or by the application of heat from a direct or indirect
source, as a result of a process, or any combination thereof.
The manner in which the scope of the standard is described
follows very closely to the introduction section of VIII-1. In the
following paragraphs, a discussion of requirements is provided only
where a significant difference exists between VIII-2 and the scope
definition from VIII-1, or where a major change was made from Old
VIII-2.
With regard to pressure vessels installed in non-stationary
applications, Part 1, paragraph 1.2.1.2.b now permits stamping with
the Certification Mark and U2 Designator of VIII-2 vessels
installed on motor vehicles and railway cars. This particular
application was prohibited in the Old VIII-2. Construction and
stamping with the Certification Mark and U2 Designator of VIII-2
vessels in non-stationary applications requires a prior written
agreement with the local jurisdictional authority covering
operation and maintenance control for a specific service. This
operation and maintenance control must be retained during the
useful life of the pressure vessel by the user in conformance with
the Users Design Specification.
Part 1, paragraph 1.2.1.2.e defines pressure vessels in which
steam is generated but which are not classified as Unfired Steam
Boilers that require construction in accordance with the rules of
Section I or VIII-1. A third category for a vessel that generates
steam that may be constructed to VIII-2 was added, paragraph
1.2.1.2.e.3: vessels in which steam is generated but not withdrawn
for external use.
One significant difference between VIII-2 and the Old VIII-2 is
special service vessels such as those in lethal service. In Old
VIII-2, paragraph AG-301.1(c), the user and/or his designated agent
had to define in the UDS if a vessel was intended for lethal
service. If lethal service was specified, then additional technical
requirements (e.g. enhanced NDE, restrictions on material, etc.)
were imposed on this vessel. In VIII-2, additional requirements are
not specified for lethal service or any other special service
condition. The rationale behind this change is that the user and/or
his designated agent are responsible to describe in the UDS (see
Part 2, paragraph 2.2.2), the intended operation of the vessel, and
if a vessel is intended for a service that is dangerous to life and
property, then the user should specify any additional requirements
to mitigate the risks. Just as it has been the rule in ASME that
it's standards would not define when a vessel is in lethal service,
what additional requirements would be appropriate for any given
vessel are best defined by the user, and not by the Committee.