How to care
Pedro Lopez and Shannon
Nimchan, Dresser-Rand business, part
of Siemens, USA,
offer an insight into the
maintenance and operation of neglected valves.
T
rip, trip-throttle and swing
disc non-return valves
are critical to ensure
steam turbine safety. It is
understood across the industry that in less than
5 secs a runaway steam turbine can catastrophically
fail, which results in turbine blades and casing being
converted into shrapnel. A runaway steam turbine can
cost millions in loss of equipment, and can lead to injury or
even the loss of life.
Valves: ensuring safety
A paper written by William Nelson and Perry Monroe Jr. for
the Texas A&M Turbomachinery Symposium, illustrated an
acceleration curve for a typical turbo-generator (Figure 1). This
curve showed that in less than 2 secs the steam turbine could
exceed the maximum safe overshoot.
Investigation result show that the vast majority of trip-
throttle valve failures are caused by improper operation and/or
neglecting the recommended maintenance by the valve OEM.
The failure of trip, trip-throttle or swing disc non-return valves,
can lead to injury, death or millions of dollars of lost production
and damaged assets.
Each valve OEM may provide different recommendations
for maintenance, but typically operators should overhaul all
latch type and swing disc non-return valves every three years.
Similarly, all oil operated and electro-hydraulic valves should be
overhauled every five years.
There are a variety of causes that affect valve functionality
if maintenance is neglected, including environmental conditions,
steam contamination and oil contamination. Depending on the
region or location of the valve in the plant, the environmental
conditions can cause valves to deteriorate, appearing as if
they were sitting on the bottom of the ocean floor (Figure 2).
Without proper maintenance and operation, failure of the valve
could result in a catastrophic failure of the turbomachinery
it protects. Poor maintenance practices, incorrect testing
procedures and the use of non-OEM replacement parts and
service, can compromise the safety and reliability of the trip
throttle valve.
Carryover from the steam boiler can cause phosphate
deposits to cause the trip, trip-throttle or swing disc non-return
for your valves
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