ple onboard tanks. The loading and
diverting valves feeding these tanks are
usually required to have block and bleed
capability to keep from cross contaminating their liquid cargoes.
Automation has become very common on modern ships, and this translates to the piping systems. Automated
valve packages are seen more and more
in the engineering rooms of modern vessels. These systems often interface with
sophisticated computer systems that are
used to control all of the common shipboard engineering functions.
VALVE MATERIALS
Because of oxidation, water is hard on
piping systems. Even marine valve materials for fresh water applications must be
chosen carefully. More and more, stainless-steel valves and piping systems are
being installed in fresh water marine
applications, replacing the previously
common carbon steel materials.
Salt water is a different case altogether. Bronze valves or iron valves with
bronze trim were the most common seawater service marine valves for a long
time, and a carbon steel piping system
will not last for any length of time in a
salt-water environment.
Seawater valves today are quite
often still bronze alloys, Cu/Ni or even
higher alloys such as Ni/Cr or titanium.
Aluminum bronze is still quite popular
because of its adequate seawater corrosion resistance combined with relatively
low cost. The most interesting material
choice today, however, is titanium. Titanium is a noble alloy with extremely
good corrosion resistance, especially in
seawater service. But titanium has other
advantages for the marine environment
including its high strength and more
importantly, light weight.
Although titanium piping systems
(and valves) are expensive, the Navy
has chosen the material for many of its
key piping systems because of its overall lower cost of ownership. The titanium valves are particularly long-lived
and require much less repair than other
valves. Some metallurgists predict that
titanium piping systems will even outlast the ships in which they are
installed. Although complete titanium
piping systems are relatively easy to
These valve-laden manifolds control the
distribution of fresh water on a modern
freighter. Every large ocean-going ship
contains several fluid control systems that are
necessary for successful operation.
fabricate and install, it is a tricky
process to attach a titanium valve to
non-titanium piping components
because of the possibility of galvanic
corrosion. Insulating bolt sleeves and
gaskets must be used to keep this type
of corrosion from occurring.
MARINE VALVE STANDARDS
AND SPECIFICATIONS
In addition to some American Society of
Mechanical Engineers (ASME) standards, piping systems for marine use are
governed by documents written by the
American Bureau of Shipping and the
United States Coast Guard.
Valves for use by the Navy must meet
even stricter standards. Most of these
valves are Navy-owned designs that are
built per quotation for each specific
ship-building project. Prospective bidders must meet the Navy’s stringent
quality requirements before they are
allowed to bid on a valve package.
Providing nuclear service valves for
the Navy requires additional quality
requirements and documentation. Still
tighter are the requirements for components in the Navy’s “SUBSAFE Program.” This program is designed for
“critical systems whose failure or lack
of operation will have catastrophic consequences.” The program was developed
after investigations into the loss of the
USS Thresher, a nuclear submarine that
went down with all hands aboard in
1963. The program, which is very successful and actively used today, is applicable to all critical valves that are used
in U.S. nuclear submarines.
MARINE VALVE
APPLICATIONS
From stem to stern, tankers of all sizes
are covered with valves. This valving
includes a variety of block valves, with
many rising and rotating stem, double
block and bleed types. A special type of
tanker, the LNG ship, requires unique
product piping and valving systems.
LNG tankers contain large insulated
tanks similar to giant thermos bottles
but designed to carry cryogenic liquid
natural gas at -256° F and pressures
from 100 to 250 psi. The product valving on these ships has to be designed for
cryogenic temperatures, and on-off and
regulating valves must have extended
bonnets so the packing area does not
freeze, rendering the valve inoperable.
Chemical and oil barges are built to
carry both pressurized and non-pressur-ized loads. In addition to the usual product regulation and control valves, pressurized barges must have adequately
sized relief valves to keep the tanks
from over pressuring as they heat up.
The Navy shipbuilding program consumes thousands of valves yearly, with
needs depending upon which types of
ships are built. These projects could
require nuclear-grade pressure seal
valves, titanium butterfly valves, Ni/Cr
ball valves or even mundane bronze gate
and globe valves.
While it is true that the U.S. ship-building industry is not what it was 50
or even 25 years ago, there is still work
for the nation’s shipbuilders and applications where many marine valves are
needed. Shipyards on all three coasts
are active today in constructing barges,
work craft, smaller commercial ships,
oil industry vessels, and of course, all
U.S. Navy ships. In addition to new ship
construction, there is still a viable refur-bishment and repair industry that also
consumes a large quantity of marine
valves each year.
Although it seems to operate under
the radar, the marine valve industry
overall is strong and offers many opportunities for valve manufacturers and distributors alike. VM
GREG JOHNSON is a contributing editor to Valve
Magazine and president of United Valve
( www.unitedvalve.com), Houston, TX. Reach
him at greg1950@unitedvalve.com.
