Chemical Engineering February 2012 - 6

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Letters
Solutions for high-purity piping code
You ran a most illuminating article based on the new ASME
code (July 2011, New Piping Code for High-Purity Processes,
pp. 49-53), and I have been examining the welding industry's
response to the new challenges. Recent years have
witnessed an exponentially increasing demand for improvements
in piping fabrication quality. The introduction of a
new ASME piping code [1] is a formal recognition of this
emerging requirement that has been stimulated mainly by
the bioprocessing sector, but also by industries such as pharmaceuticals,
semiconductors and food production.
An essential element in pipework is the production of
welded joints, and the stringent inspection procedures
imposed by ASME 33.1 apply as much to welded joints as
they do to all the other fabrication processes involved.
A previous paper [2] highlighted more general aspects
of the significance of the new code as it applies to the
manufacture of high quality pipework. Producers of welding
accessories designed specifically to meet the requirements
have been quick to meet the new challenges imposed
by ASME 33.1.
The problem. One of the fundamental requirements imposed
during the welding of pipes is to prevent oxidation
of the weld during the first pass. The welding torch provides
inert gas coverage of the top of the fusion zone, but
unless precautions are made there is no coverage of the
weld root. The problem has always been recognized, and
over the years a variety of solutions have evolved, some
eccentric, others practical but largely ineffective.
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6 CHEMICAL ENGINEERING WWW.CHE.COM FEBRUARY 2012
ing, the application to the pharmaceutical, semiconductor
and food production sectors demands particularly high
standards of cleanliness. Hygienic purity is the driving
force for joints destined for use in pharmaceutical and
food production. Elimination of particulate contamination
is the crucial requirement in semiconductor manufacture.
With some semiconductor manufacturers producing chips
with dimensions at the 32-nm level, and research going on
at the 15-nm level, it is easy to see why the design, fabrication
and maintenance practices required to ensure exacting
purity requirements of their process fluid-distribution systems
are of paramount importance.
In the food processing industries, statutory legislation
and a plethora of litigation suits have forced plant manufacturers
to introduce quality control levels previously
considered unnecessary. Contamination introduced during
fabrication is now unacceptable.
The solutions. The welding supply industry is leading the
way in responding to the new demands imposed by ASME
33.1. See the online version of this article (at www.che.com
under Web Extras) for references and specific solutions.
Michael J. Fletcher
Delta Consultants, U.K.
Postscripts, corrections
In the call for nominations for our Personal Achievement
Award, we mistakenly said part of the activity must have
taken place in 2007-2009. It should have said 2009-2011.
The online version has been corrected.
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Chemical Engineering February 2012

Table of Contents for the Digital Edition of Chemical Engineering February 2012
