Page 93 - Boiler_Operators_Handbook,_Second_Edition

78 Boiler Operator’s Handbook

Annual tests that should be performed by the boiler come off its seat to release the steam. If it doesn’t lift
operators include: Leak testing of fuel oil safety shut-off that means the valve isn’t operational and prevent-
valves, regulators, and vent valves. Calibration checks ing a steam explosion due to high pressure. How it’s
of gauges and thermometers. Removal and replacing of done is rather important because, and my ears should,
safety valves where the insurance inspector requires re- perhaps, be burning because some of you are saying to
building, normally on a five year per valve basis. yourselves “Hey, Ken, If we test the valve it’s going to
All the above assumes a bare bones boiler plant. leak.” I get that complaint from contractors all the time.
There is always additional equipment and systems that Well, if it’s done right it will not leak. Also, it won’t leak
need to be monitored and maintained on a regular basis provided there isn’t anything blocking its operation or
and service the facility and/or the boiler plant including that can clutter it up. Your round performed before lift
(but not limited to) domestic hot water heaters, air com- testing should include a close inspection of the safety
pressors, cooling towers, chillers, air handling units, etc. valve outlets, discharge piping, drip pans, and drains
Adding the monitoring, maintenance, and water condi- to ensure they’re all clear. A safety valve pops open and
tioning for those systems can easily consume another pops closed with no feathering or weeping because it’s
operator’s time for a normal day. either open or it’s shut and the transition is so fast that
there’s no way wire drawing can occur. Wire drawing is
a term used to describe the cutting of a valve seat, disc,
SAFETY TESTING or both by a small steam leak where the high velocity of
the leak erodes the metal.
Both the National Board of Boiler and Pressure According to ASME a safety valve should be lift
Vessel Inspectors and ASME have recommended that tested only when the pressure in the boiler is higher
safety valves be lift tested monthly on boilers operating than 75% of the valve setting. I’ve told many an operator
at pressures less than 400 psig and pop tested annually. it’s because the lifting lever will break if you try lifting
For higher pressures they recommend testing based on the valve without the steam pressure to assist it. That’s
operating experience. Since most of you are operating not necessarily a true statement but I use it to support
boilers at pressures lower than 400 you should be testing the contention that they should only lift test the valve
the safety valves. Whenever I bring this point up I see when the boiler pressure is as high as normal operation
the operator’s eyes begin focusing on the ceiling because will allow. Another consideration, one that may have
they don’t do it. Since those safety valves are the last line resulted in the contention by many that the valve will
of defense to prevent a boiler explosion checking them leak, is the load on the boiler. If there are only two safety
at a reasonable interval is very important. We’re only valves then lift testing when the load is higher than 50%
talking steam boilers here. Safety relief valves on hot is producing a temporary load greater than 100%. That
water boilers are another story and I’ll address them in means the steam and water separation in the drum will
maintenance. exceed what the manufacturer designed it for and it
As to the frequency, I’ve come to the conclusion could promote foaming and priming which could carry
that monthly lift testing isn’t such a good idea. That’s boiler water droplets into the safety valve at high veloc-
because plants will set a schedule for testing on, say the ity to produce damage from impingement and possibly
first of each month or the first Monday of each month produce deposits of boiler chemicals on the valve disc
and here’s what happens: The little old lady in tennis and seat that dry immediately as the steam becomes
shoes that lives nearby notes the schedule and is push- superheated; that’s how they can be made to leak. So, if
ing for local officials to be on hand to hear all that dread- you have two safety valves you shouldn’t lift test them
ful noise that’s upsetting and deafening her each month. unless the load on the boiler is less than 50%, with three
I suggest testing quarterly, every three months, and valves it’s 66%, four or more valves 75%.
at random hours on a random day because the longer Now, I want to say something about how to do a
period and randomness reduces complaints from the lift test. The problem is you have to lift that lever and
neighbors. And, since most of you aren’t testing regu- it’s on top of the boiler. It’s not convenient to get to and,
larly a quarterly schedule for lift testing ensures more to be perfectly honest, I don’t like to be near a valve that
frequent checks of the safeties than you were doing. automatically pops wide open. I’m always concerned
What exactly is lift testing? It’s raising the lever for the safety of the Operator and climbing up on the
on the safety valve to open it, thereby proving that the boiler, a ladder, or even an access platform, and lifting
mechanism will allow the disc in the safety valve to that lever doesn’t seem safe to me. Therefore, I strongly