stock, rather than cast. “Castings are
frowned upon [in food service],” says
Lutkewitte, because they are more likely
to have pores, while “forgings are more
dense with no hidden cavities in them.”
In some areas, the requirements for
food valves are less stringent than for
those used in other industries, Andy
Butcher, product market manager, Spi-
rax Sarco, points out. One reason is that
the pressures involved tend to be lower,
and aside from the chemicals used for
clean-in-place (CIP) operations, they’re
not subjected to some of the highly cor-
rosive service of industries such as
chemicals. “On the utility side, where
we’re controlling, for example, steam
going to a heating vessel, they tend to be
general service control valves,” Butcher
says. With fairly low-pressure, low-tem-
perature steam going through them,
such valves will generally be made of
cast iron or carbon steel, he continues,
although some companies elect to spend
the extra money and use stainless.
Still, those CIP chemicals can be a
challenge, according to Wayne Labs,
senior technical editor of Food Engineering magazine, who wrote an Oct. 1,
2010 article entitled: “Tech Update:
Clean-in-Place Equipment.” CIP chemicals are becoming stronger, that article
says, and this has led some valve makers
to use AL-6XN, a corrosion-resistant,
iron-based, austenitic stainless alloy, in
place of 316. There also are claims that
AL-6XN is more resistant than 316 to
certain forms of rouging.
CLASSES OF ROUGING
While rouging tends to be more of a problem in high-purity pharmaceutical applications, it is also a potential danger in food processing. There are three classes of rouging on stainless steel. Class I involves materials carried from upstream (often from
pumps), and no valve material can prevent it completely. Class II, caused by a breakdown of the passivation of the metal surface, is affected by choice of material. Class
III appears in the presence of high-temperature steam, and can exist in a glossy
black (and generally harmless) or a powdery black form. The glossy form appears
more frequently on electropolished surfaces, while the powdery form appears more
on unpassivated mechanically polished surfaces.
Little information is available on the effect of changes in material. According to a
February 2004 article by Richard E. Aver in the newsletter of the Boston area chapter of the International Society for Pharmaceutical Engineering, Class I and II rouging could be stopped by a nitric-hydrofluoric acid pickle or nitric acid passivation, or
by an electropolish followed by a nitric acid passivation. As for Class III rouging, it
“cannot be removed by simple cleaning but must be removed chemically or by grinding,” followed by chemical passivation, according to Corrosion Doctors ( www.corro-sion-doctors.org/MatSelect/rouging.htm). “Once the system is back in service, it will
turn black once again, but hopefully not forming the powdery black film.”
REGULATORY TURMOIL
At first glance, it would seem that,
except for lead-content regulation, few
changes to regulations applying to
valves in food service applications have
occurred. In 2007, the pasteurized milk
ordinance (PM) changed the way mix-proof valves could be used in CIP applications, but the 3-A standards have
been around for many years. Still, taking a broader look, the picture looks less
clear.
Butcher explains that he sees some
confusion about exactly what applies to
the industry. “I think the food & bever-
age industry in general is pretty much in
turmoil with regulations and standards
for all of the processes in food and bev-
erage coming down from the FDA and
others,” says Butcher. He explains that
at a recent food safety summit he
attended in Washington, DC in early
2010, a general topic of discussion was
“exactly which regulations should be
enforced, how often the FDA should be
inspecting plants, and even when they’re
inspecting plants.” The industry in gen-
eral is not sure what standards are
applicable, he says.
CHANGES IN TECHNOLOGY
Some changes are taking place in the
way valves are used in the food industry—particularly in the area of automation and control. Lutkewitte cites the
increased use of remote setpoint control
for pressure regulators as an example.
“Instead of a hand crank to increase the
setpoint,” he says, “you put air pressure
on top of that valve.” This technique is
showing up more and more on CIP skids
and in other areas.
