POWER May 2010 - 46

PLANT SAFETY
5. Good design practice. Typical purge
points should be designed into piping systems.
Courtesy: CEC Combustion Safety Inc.
workers, except those performing the gas
purge. Spectators should not be allowed.
■ Document all of the pressure testing results
(such as test pressures and how long
they were held).
What Codes and Rules Apply?
There are many codes that can have some application
to natural gas piping repairs. One such
code is OSHA 1910.147 for lockout/tagout
of hazardous energy sources. Much has been
written about these requirements, and most
workers make some attempt to comply with
them-at least for electrical devices. However,
the OSHA requirements also cover other plant
systems, such as natural gas and steam piping.
For instance, we often find a lock on electrical
disconnects, but seldom on a closed gas valve.
Even when workers attempt to isolate equipment
correctly, we find that they often do not
understand the issues surrounding lubricated
plug valves used in gas lines. Lubricated plug
valves, which represent 60% to 80% of natural
gas piping system manual shut-off valves,
have a small gap between the plug and the
valve body. If a sealant is not applied annually,
as required by code and the manufacturer, gas
will leak past the plug even when the valve is in
the closed position. We find that most facilities
do not have the knowledge or the equipment to
seal these and have never sealed them during
the life of the valve. Hence, closing or locking
out a valve in this condition does not necessarily
isolate the energy source. The more serious
issue is that if these are not regularly sealed,
the valve can become impossible to close. This
means you can have an emergency and lack the
ability to secure the gas supply.
The other code that applies to natural gas
piping is NFPA 54: The National Fuel Gas
Code (www.nfpa.org). The rules are rather
lengthy, and it does take time and effort to
fully understand the intent and requirements
of the code. Often we run across consulting
engineering firms and contractors that do not
understand the basic code requirements. This
lack of understanding often appears with a
plant design that lacks isolation points (that
is, blanks, blinds, and pancakes) and/or purge
points. There seems to be little thought given
to the NFPA requirements in the installation
of the gas pipe or to how the gas pipe will
be commissioned after installation or will be
inspected and serviced in the future.
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Start up and Commissioning
Owner's Engineer
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POWER | May 2010
Top 10 Gas Piping Hazards
During our years of inspecting and testing
fuel trains, we've repeatedly come across
many of the same gas piping issues and
hazards. Our top 10 most common hazards
involved in conducting natural gas piping
installation and repairs are provided below,
along with insights on how to avoid them.
Any time natural gas piping systems are designed
or worked on, these potential hazards
should be evaluated and addressed. Although
the process is not simple, it can be completed
safely if well-planned and properly implemented.
These tips and techniques should be
incorporated into your procedures for natural
gas piping purging and equipment start-up.
1. Purge Points. Purge points are pipe
nipples installed at strategic locations in the
piping system for the purpose of introducing
or removing nitrogen and natural gas at various
stages of the process (Figure 5). These are
generally 1-inch schedule 80 nipples (thicker
and stronger than common schedule 40 pipes)
with natural gas-rated ball valves on the ends.
It is important to select locations or orientations
that ensure that these are less susceptible
to damage from things like vehicle traffic (being
run into with a tow motor or scissors lift).
2. Isolation Points. Ensure that your fuel
trains are not exposed to excessive pressures
that can damage components during pressure
testing. Use line blinds to isolate components
that are pressure sensitive. Valves can accidentally
be left open or leak when in the
closed position. Blinds provide positive isolation
and eliminate the possibility of damaging
devices in a fuel train that are not rated
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POWER May 2010

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