Page 97 - Boiler_Operators_Handbook,_Second_Edition

82 Boiler Operator’s Handbook

concentrate under a little growth on the inside of the pipe spection. I’m reminded of when my service technicians
and emit the acids and alkalis that attack locally. made repeated visits to a plant in an attempt to locate
Normally the solution for idle cold water piping an intermittent gas leak. They eventually discovered the
is simply opening a vent or drain valve to refresh the rubber disc of a bleed valve had been cut by the sharp
water in the idle piping once a week. Microbes can’t seat of the valve and occasionally buckled to block the
survive in water above 140°F and don’t do well in wa- valve partially open while the boiler was operating.
ter much warmer than 120°F. Water lines that are in the Fuel oil tanks that aren’t in use should be full ex-
upper levels or a boiler room shouldn’t have a problem cept for one that may be filling. That way you minimize
with microbial growth because of the heat but would the exposure of the metal in the tanks to air and its cor-
suffer from oxygen pitting if you regularly added oxy- rosive properties. You also limit the contact of air with
gen rich water to them. the oil. Full, of course, doesn’t mean up to the brim; you
Oxygen is another problem in water piping, not as always need some freeboard (space between the liquid
persistent as in boilers but the cold city water usually level and the top) to allow for expansion. I thought I had
warms up in idle pipes in the boiler plant and raising the matter of expansion down and filled fuel oil tanks
the temperature of the water reduces its ability to absorb up to the very top once. The oil was normally delivered
oxygen so some of it is released to produce the damage hot (good old bunker C) so it would shrink into the
we know as oxygen pitting. (See deaerator operation for tank. I discovered later that the particular shipment I re-
more on oxygen problems). If the piping is to be idle for ceived was colder than normal so it expanded instead of
long periods of time it should be drained and kept dry. shrinking and I got to spend a day cleaning up the fuel
That way, both microbes and water borne oxygen can’t spill I created. See fuel oil in the section on consumables
do damage to it. A dry line will develop a very thin coat for more on the wise use of fuel oil storage.
of rust that will protect it. Propane and fuel oil storage facilities have a bad
If you can’t keep the pipe dry then adding chemi- habit of becoming garbage dumps. In the fall leaves
cals to the water or filling the piping with nitrogen to accumulate in the diked areas around the oil tanks and
inert it are options. A nitrogen inerting system consist- on the ground around the supports of propane tanks.
ing of a regulator and safety valve on a portable cylinder That’s fuel for a fire from an inadvertent spark or ciga-
should maintain the inert status for several months. You rette that could produce a disastrous fire and possibly
only need to maintain a few inches of water column as an explosion. Water can accumulate in diked areas or
pressure in that idle piping. Nitrogen can find some simply form ponds that stand on metal pipes, supports
pretty small places to leak through and maintaining and tanks to promote their corrosion. Every day shift
high pressures will result in wasting a lot of nitrogen. should visit the fuel storage locations for the express
Vent and bleed lines for gas pressure regulators, purpose of identifying hazards and eliminating them.
gas pressure limit switches, and the bleed of double Raking leaves and mopping water may not be in the job
block and bleed shut-off valve systems are basically description but you are responsible for those facilities
idle piping. The vent lines from a regulator or pressure and should take any action necessary to protect them.
switch is there to provide a direct connection for atmo- A very important piece of equipment that’s idle
spheric pressure on the diaphragm of the control valve most of the time is an emergency generator. Many plants
plus convey fuel gas to a safe location in the event the test them on a regular schedule but they deserve atten-
diaphragm leaks. The bleed line is used intermittently tion between tests to detect any problems that might
to dump the gas trapped between the two safety shut- arise. There are probably many items and systems in
off valves. Those lines should always be treated as gas your plant that weren’t included in this discussion
lines even though they may contain air most of the time. but deserve your attention when they’re idle because
The condition of the terminations of gas system vents they’re critically necessary when you need them. You
and bleeds, normally a screened fitting, should also be have to identify them and make certain your SOPs in-
checked on a regular basis to ensure they aren’t blocked. clude procedures to check on them.
An ear to the line can detect a good sized gas leak.
They should also be checked by stretching a rag over their
outlet (or a union just inside the building when the outlet SUPERHEATING
is inaccessible) and soaking it with soapy water. Bubbles
indicate a leak. They should be checked whenever there’s The recent deregulation of electricity has resulted
reason to believe they could be leaking or on annual in- in more superheated steam boilers to permit plants to