ply the two,” mostly through lack of
experience, James says.
Misapplication of standards extends
beyond this as well. Years ago, most valve
manufacturers used their own in-house
standards, and while later many of these
were merged under the International
Society of Automation (ISA) and other
bodies, there is still a certain amount of
proprietariness, says Jeff Parish, senior
product manager for global severe service
products, Flowserve. For example, one
manufacturer’s standards cannot be
applied for the sizing of the products of
another manufacturer, he explains, any
more than gasoline can be used in a diesel
truck. Smaller companies are the parties
valves.” And standards for multistage
valves promise to be even more difficult
to agree upon, he adds.
BIGGER AND BIGGER
One major trend in severe service valves
is that they’re getting bigger, especially in
the oil and gas area. “In a world where a
12-inch valve used to be a big valve, we
just bid a 36- by 42-inch angle valve,”
says Flowers. With heights at 25 feet or
more, you get a valve that is “just mas-
sive,” he says, and probably worth about
a million dollars. In the liquefied natural
gas (LNG) market, says Steinke, the
main compressor recycle valves of about
eight years ago that were on the propane
refineries, where reactor vessels are
starting to push the limits of how large
things can be made.
In refining applications, where the temperature limit
was once 1000° F, says Stephen James, “we’re seeing
stuff that’s up to 1600° F and higher.” This requires
changes in materials of construction for the pressure
boundary, which in turn affects trim materials and
temperature gradients.
that suffer the most from this reality, he
says. “Just because you have a standard,
and because you have a valve, doesn’t
mean you can apply the standard directly
to the valve,” he explained. To apply the
standard properly means additional testing, which may be more than a small
company can do.
And some areas just have no stan-
dards at all, or only proprietary ones,
James continues, “like multiphase flow
or non-Newtonian flow. There’s no stan-
dard equation on how to calculate flow
through a ketchup valve.”
Another issue with standards, adds
James, is they’re starting to become more
international. For example, NACE
MR0175 is now NACE MR0175/ISO
15156.
At the same time, not all standards
have kept up with what’s happening.
Look at ISA RP75.23, Considerations for
Evaluating Control Valve Cavitation, says
Steinke. “This attempt as a standard has
been in committee for 15+ years and is a
recommended practice rather than a
standard. This is because agreement on
how to rate and test valves in their capa-
bility to withstand cavitation cannot be
reached in committee on conventional
loops were designed with about a 14-inch
plug and about a 12-inch stroke operat-
ing at about two to three seconds. “Today
… those same valves have gone to 30-
inch plugs and 24-inch strokes, with the
same or faster response times,” Steinke
says.
HOTTER AND HOTTER
Along with the move to larger valves is a
trend towards subjecting them to higher
temperatures. Steinke cites combined
cycle power plants, “where 10 years ago
we were seeing units that were operating
at a maximum temperature of 1050º F
(566 º C) or 1025º F (552 C º), now
they’re stretching to 1100º F (593º C) or
more on your turbine bypass systems.”
And in refining applications, James says,
where the temperature limit was once
1000º F (538º C), “we’re seeing stuff
that’s up to 1600º F (871º C) and higher.” This requires changes in materials of
construction for the pressure boundary,
which in turn affects trim materials and
temperature gradients.
MORE SOUR STUFF
Another challenge for severe service
valve applications is that the valves face
tougher external and pressure challenges.
For example, “All the easy, low pressure, sweet gas in the world has kind of
gone away, so either it’s high pressure or
it’s sour, or it’s both,” says James.
This situation, says Flowers, is driving
the severe service market to a lot more
special alloy valves, which leaves industry
“to figure out how to make 36-inch super
duplex control valves.” The expense of
such requirements has led to another
trend, Flowers says, which is increased
use of cladding in large valves. Rather
than making solid duplex bodies, he says,
it’s becoming increasingly acceptable to
use carbon steel bodies and clad the
entire inside with Inconel. What’s made
this possible, he explains, is improved
robotic welding technology. “As long as
the body cavity is large enough to completely weld all the surfaces with a clad
