Chemical Engineering January 2017 - 48

Inert
Argon
Flammable
Butane
Helium
Krypton
Neon
Nitrogen
Xenon
Cyclopropane
Deuterium
Ethane
Hydrogen
Methane
Propane
their game as well.
Not only does this require that
chemical processing systems have
the technology and ability to refine
chemical products down to
such high-purity levels, but it also
requires instrumentation with the
ability to detect, monitor and validate
at those levels. It also requires
process contact material of construction
(MOC) for such equipment
and instrumentation to handle
these chemicals without contributing
nano-sized particles to the fluid
stream. And finally, the fabrication
and handling of process contact
equipment and components has to
meet specific demands with regard
to welding, surface finish, mechanical
joint design, system cleaning
and system cleanability.
High-purity piping
Referring back to Mosby's definition
of " chemical purity, " we can make the
claim that purification, as it relates to
fluids, is the physical aspect of separating
a chemical substance from that
of any resident foreign substance
considered a contaminant or impurity.
Achieving and maintaining a high degree
of purity for any fluid, gas or liquid,
requires that all process contact
surfaces within the high-purity envelope,
or boundary limits, meet or exceed
a set of stringent requirements
pertaining to materials of construction
and fabrication of processing equipment,
filtration, instrumentation and
distribution systems.
Such specific criteria, as mentioned
previously, involves proper
material selection, unique welding
requirements, mechanical joint design,
product contact-surface finish,
piping and equipment installation parameters,
and a dogmatic approach
to quality management throughout
48
the entire process of equipment
manufacture through and including
installation and maintenance.
Processing equipment used in the
manufacture, handling, monitoring
and distribution of electronics chemicals
have to not only perform processing
functions at a painfully high
degree of accuracy, they have to do
so without being a source contributor
of impurities to the fluid stream.
These are impurities that can slough
off of poorly cleaned process contact
surfaces, or microscopic matter
that can form in a welding flaw and
periodically slough off contaminants.
It can also be a process contact
material that may not be sufficiently
compatible with the process fluid
and become susceptible to corrosion,
adding particulate matter to
the fluid stream.
These are all issues that confront
the
design, manufacture and operation
of equipment used to manufacture
electronics chemicals. The
manufacture or fabrication of such
equipment and piping systems is an
evolution guided by ever more stringent
requirements and verifying documentation
every step of the way.
A typical, simplified example of the
steps to required to fabricate highpurity
(H.P.) piping and equipment
systems is shown in Figure 1. Such a
process begins with the manufacture
and delivery of non-high purity (raw)
product components. The steps are
described in more detail as follows:
Step 1. Manufacture and delivery
of the basic raw material tubing, fittings
and other components needed
for finishing and preparing for use in
high-purity fluid services.
Step 2. The raw material products
are thoroughly examined upon receipt
to affirm that they meet the
required material specifications. The
Halocarbons
TABLE 3. EXAMPLES OF ELECTRONICS GASES
Hydride/inert
Hydrides
Carbon tetrachloride Ammonia
Hexafluoroethane
Perfluoropropane
Arsine
Germane
Phosphine
Silane
Arsine
(1-10%)
Germane
(1-10%)
Phosphine
(1-10%)
Corrosive
Boron
Chlorine
Dichlorosilane
Hydrogen bromide
Hydrogen fluoride
Silicon tetrachloride
Boron trichloride
Trichlorosilane
Other
Acetylene
Carbon dioxide
Carbon monoxide
Dimethyl ether
Nitric oxide
Nitrous oxide
Oxygen
Sulfur hexafluoride
components and material, having
been received with various mill surface
finishes, will then be cleaned
in preparation for having the inside
diameter (I.D.) surface or the outside
diameter (O.D.) surface of the
raw products mechanically polished
or
electropolished to meet specified
roughness average (Ra) surface
finishes. As the products complete
the final steps of the surface-finishing
process, they will transition into
a cleanroom environment. Such
cleanrooms will typically be environmentally
controlled to an ISO 4
or 5 classification (see Table 4 for
cleanroom
classifications).
Upon
further examination, ensuring that
the product meets all specifications
for chemical properties, mechanical
properties and surface finish, as
well as for weld-end fittings, end
preparation (prep) for autogenous
welding, the, now considered H.P.
product should have all openings
capped or covered, get individually
double bagged, then bagged again
as a lot-of-material. A lot is defined
by either the product finisher or the
user/buyer. Each individually bagged
item will contain its own material test
report (MTR), including a certificate
of conformance (C of C) pertaining to
the surface finishing process.
Step 3. The H.P. components and
material are then shipped to a fabricator
or manufacturer who will fabricate
and assemble the H.P. components
and material into their final
product form or assembly.
Step 4. The H.P. products will be
receipt-verified by the fabricator. This
may or may not entail un-bagging
samples for inspection. Otherwise,
all of the bagged material should
remain bagged until such time as it
is needed in fabrication. At the time
the material is needed for its part
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