Chemical Engineering September 2010 - 42

Concept
Feature Report
Thermoplastic
pressure pipe
reached the state that jointing
of PVC-U, for instance, can be
done with a special solvent cement
that is even able to cope
with long-term and steady contact
to strong oxidizers, such as
concentrated sulfuric acid.
As soon as the dimensions of
fabrication tolerances of pipes
and fittings exceed a certain
limit, solvent-cement jointing
becomes no longer practically
feasible due to both the gaps
that need to be " bridged " and
the procedure of assembly (required
forces, application of
the cement and so on). In all
those cases the dual laminates
(based on welding and flanging)
are then widely accepted
as an alternative. Note that no
solvent-cement jointing is recommended
in the field of dual
laminates.
Double
containment
Dual
laminates
TABLE 1. THE VERSATILITY OF POLYMER-PIPING SYSTEMS
Characteristics
Jointing technology Typical
OD-range /
mm
(Butt-fusion) welding;
solvent cement jointing,
flanging
Solvent cement
jointing;
butt-fusion welding
Welding (butt fusion /
rod); flanging
16 - 2,000 Standard in the CPI
20 - 225
(Inner pipe)
Increased safety due to
pipe-in-pipe concept; outer
shell frequently made of
transparent PVC-U
16 - 2,000 Increased safety due to
pipe-in-pipe concept; significant
increase of the
range of applicability as the
thermoplastic inliner is only
used as the " chemical barrier " ;
all mechanical load
is handled by the external
FRP-layer
Tubes
Push-fit sockets, flaring,
screwing, customized
solutions
< 2 in.
Coiled tubing made, for
example, from full fluorinated
polymers used in
double containment piping
are of particular interest
for very demanding CPIapplications
(for instance,
electronic-grade chemical
media handling)
Ventilation
pipes
QA and standardization
Since the market introduction
of polymer-piping systems a
few decades ago, many national standards
(for instance, DIN in Germany
or ASTM in the U.S.) have been elaborated,
continuously developed and
stepwise accepted - also globally in
many cases. Nevertheless, standardization
of polymer-piping systems
is completed by international application
norms which are updated
regularly by international competent
working groups. For selected applications
(such as drinking water or gas
supply) additional approvals combined
with external third-party testing
supervised by a separate quality
assurance body (for example, the DIN
Certco in Germany) do effectively
increase the quality level of such approved
piping systems. As a rule, such
approvals are based on even stricter
national quality-assurance (QA) regulations
(such as various DIN Certco
guiding rules). For the global CPI it
is very important to consider that the
so- called German Institute for Building
technology (DIBT; Berlin; www.
dibt.de) provides a unique, worldwide
approval based on such QA guidelines.
This DIBT approval is the basis
for a very narrow-meshed testing program
and documentation of each lot of
Customized
piping
Socket jointing in
combination with solvent
cement joining
or (rod-)welding
Multiple and very
individual
< 800
Frequently the only economical
alternative to handle
corrosive exhaust fumes
Usually
< 250
piping products. In particular, while
setting a strong priority on the commitment
to a clearly defined material
formulation - to be disclosed to the
DIBT by a non-disclosure agreement
(NDA) and an integrated third-party
testing procedure - approved products
are also linked to a comprehensive
chemical-resistance list that will
also provide additional safety factors
(distinguishing between temperature
and media concentration) for appropriate
dimensioning of the piping system.
Thus, this DIBT-approval should
be considered as much more than just
a national German QA issue; it is
rather a very helpful specification tool
for end-userss making use of polymerbased
piping systems for conveyance
of hazardous chemical media.
In addition to its presence in the
standards of the American Welding
society (AWS), the jointing of such
systems is documented and updated
in comprehensive detail by the guidelines
issued by the German Welding
Society (DVS) [5]. Similar to the fabrication
standards of polymer-piping
system components, these guidelines
have been globally accepted over
many years, laid down in many end34
CHEMICAL ENGINEERING WWW.CHE.COM SEPTEMBER 2010
Pipes as semi-finished
products; mostly no systemconcept
required
user specifications and are continuously
being updated and completed.
Furthermore, the regular training
and education of polymer-welders is
based on these standards. Note that
a given DIBT pipe approval does directly
refer to the respective DVS
guidelines regarding planning, construction
and joining of the respective
piping products. Thereby, additional
support is given to keeping up
with quality.
In addition, many competent endusers
(typically bigger companies in
the CPI) rely on the use of a sensible
and in-house developed system
of standards, which are also part of
their respective process specifications.
Of course, these internal and
individual standards are also regularly
reviewed and updated based on
a steady growing experience gained
from practical long-term use of polymer
piping systems.
Versatile piping concept
There is no other class of material
showing a larger variety of piping concepts
available for CPI applications
than polymer pipes. Table 1 presents
a number of these.
http://www.dibt.de http://WWW.CHE.COM
Chemical Engineering September 2010

Table of Contents for the Digital Edition of Chemical Engineering September 2010
