Chemical Engineering May 2020 - 40

both the outside contractor and your
maintenance team will allow you to
follow trends in train performance.
The more that engineers learn
about the potential dangers of a
valve train, the greater peace of
mind they will enjoy knowing that the
one on their plant's floor has been
thoroughly inspected.
FIGURE 2. Valve trains serve the essential purpose of controlling the flow of pressurized gases into fuelfired
equipment
(UL) and the U.S. Environmental Protection
Agency (EPA).
A final word of caution: if you are
in a location that does not mandate
ASME CSD-1 (Controls & Safety Devices
for Automatically Fired Boilers)
or NFPA 85 compliance, the AHJ will
rarely address fuel-system issues.
Testing the interlock and gas train is
typically assumed to be a responsibility
of the owner. Therefore, an AHJ
saying your boiler or dryer " passed "
will bring no assurances that the
valve train is compliant.
Questions to ask
Owing to the presence of hazardous
vapors and gases, poorly designed
or inadequately maintained valve
trains have led to catastrophic explosions,
fires, asphyxia and burns,
not to mention property losses running
in the hundreds of millions of
dollars.
Thankfully, you can significantly
reduce the potential for
accidents by asking your plant or
safety manager five simple questions,
which are outlined in the
following sections.
1. Does the valve train receive an
annual inspection? The entire combustion
system must be inspected
at least annually, both internally and
externally, to assure compliance (Figure
3). NFPA 86 provides guidelines
to establish these measures, clearly
stating: " The user has the responsibility
for establishing a program of
40
inspection, testing and maintenance
with documentation, performed at
least annually. " This applies to both
new installations and modifications.
Annual testing is
typically
required
by insurance agencies, but facilities
may also need to adhere to other
(often overlapping) codes and standards
besides NFPA - for example
those set forth by ANSI, ASME, NEC
and the EPA. For instance, oil-fired
burners must comply with UL-296
Standard for Oil Burners, UL-726
Standard for Oil-Fired Boiler Assemblies,
or UL-2096 Standard for Commercial/Industrial
Gas
and/or OilBurning
Assemblies
with Emission
Reduction
Equipment.
Only a qualified
outside contractor
should
perform annual
inspections.
This company
will test, assess,
maintain and replace
necessary
components of
the gas train,
leaving you with
a system that is
code-compliant.
In addition, accurate
record
keeping by
2. How is the combustion system
being purged? Purging airflow ensures
that any flammable vapors or
gases that might have entered the
fuel-fired equipment during shutdown
are cleared. Two basic requirements
must be satisfied: purge
airflow and purge time. Purge airflow
can be tested by using a metering
device or by measuring a drop
in pressure. The second purge requirement
is testing the purge timer,
which is set to a calculated duration
to exhaust an accumulation of
hazardous gases from the chamber.
The time required for purging
is determined by the volume of the
equipment. Typically, this requires
four complete volume changes, but
may require as many as five to seven
cycles to displace the combustible
gases. If the timing cycle or purge
airflow gets interfered with during
purge testing, you must restart and
conduct a new full purge.
3. Are any components missing
from the train? As mentioned earlier,
valve trains are complex devices
FIGURE 3. An annual valve-train inspection should be comprehensive to ensure
that all components are operating efficiently and safely, and meet the
necessary industry standards
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