(1) The maximum allowable
working pressure of standard boilers shall be determined by the applicable
sections of the codes under which they were constructed and stamped. The
maximum allowable working pressure on the shell of a nonstandard boiler or drum
shell shall be determined by the strength of the weakest section of the structure
computed in accordance with formulas provided by the national board of boiler and
pressure vessel inspectors or any other nationally recognized engineering
authority.
(2) Each power boiler having not more than five hundred square feet of
water-heating surface shall have at least one approved safety valve. Each boiler
having more than five hundred square feet of water-heating surface shall have two
or more approved safety valves.
(3) The safety valve capacity of each power boiler shall be that which will
discharge all the steam that can be generated by the boiler without allowing the
pressure to rise more than six percent above the highest pressure any valve is set,
and in no case to more than six percent above the maximum allowable working
pressure.
(4) Power boilers equipped with one safety valve shall have the safety valve
set at or below the maximum allowable working pressure. If additional valves are
used, the highest pressure setting on additional valves shall not exceed the
maximum allowable working pressure by more than three percent.
(5) When two or more power boilers operating at different pressures and
safety valve settings are interconnected, the lower pressure boilers or
interconnected piping shall be equipped with safety valves of sufficient capacity to
prevent overpressure, considering the generating capacity of the boiler with the
lowest allowable pressure.
(6) All power boilers shall have a water-feed supply which will permit the
boilers being fed at any time while under pressure.
(7) Power boilers that are fired with solid fuel not in suspension and having
more than five hundred square feet of water-heating surface shall have at least two
means of feeding water. Each source of feeding shall be capable of supplying water
to the boiler at a pressure of six percent higher than the highest setting of any
safety valve on the boiler, and one such source of feeding shall be steam-operated.
(8) Power boilers fired by gaseous, liquid, or solid fuel in suspension and
having less than five hundred square feet of water-heating surface may be
equipped with a single source of feeding water if:
(a) Means are provided for immediate shutoff of heat release;
(b) The boiler furnace and fuel system do not retain sufficient stored heat to
cause damage to the boiler if the water-feed supply is interrupted.
(9) Power boilers that have a water-heating surface of not more than one
hundred square feet shall not have water-feed piping and connection to the boiler
smaller than one-half inch pipe size. For boilers having a water-heating surface of
more than one hundred square feet, the water-feed piping and connection to the
boiler shall not be less than three-fourths inch pipe size. The feed water shall be
introduced into a boiler in such a manner that the water will not be discharged
directly against surface-exposed gases of high temperature or to direct radiation
from the fire or near any riveted joints of the furnace sheets or shell. The water-feed pipe shall be provided with a check valve near the boiler and a valve or cock
between the check valve and the boiler. When two or more boilers are fed from a
common source, there shall be a regulating valve on the branch to each boiler
between the check valve and the source of supply. In all cases where returns are
fed back to the boiler by gravity, a check valve and stop valve shall be on each
return line, the stop valve placed between the boiler and the check valve, and both
shall be located as close to the boiler as practicable.
(10) Fire-actuated plugs, if used, shall conform to the requirements of the
A.S.M.E. boiler and pressure vessel code for power boilers.
(11) No outlet connections, except for damper regulator, feed-water
regulator, low-water fuel cutout, drains, or steam gauges, shall be placed on the
piping that connects the water column or gauge glass to the boiler. The water
column shall be provided with a drain valve of at least three-fourths of an inch pipe
size.
(12) Each power boiler, except forced flow steam generators designed to
operate without a fixed water level, shall have at least one water-gauge glass;
except that boilers operated at pressures over four hundred PSI shall be provided
with two water-gauge glasses which may be connected to a single water column or
connected directly to the drum, in which case they shall conform to A.S.M.E.
requirements. The gauge-glass connections and pipe connections shall not be less
than one-half inch pipe size. Each water-gauge glass will be fitted with a drain cock
or valve. When the boiler operating pressure exceeds one hundred PSI, the glass
will be fitted with a globe or gate-valved drain.
(13) The lowest visible part of the water-gauge glass shall be at least two
inches above the lowest permissible water level, which level shall be that at which
there will be no danger of overheating any part of the boiler when in operation at
that level. This subsection (13) does not apply to forced flow steam generators
which are designed to operate without a fixed water level.
(14) Each power boiler shall have a steam gauge, with dial range not less
than one and one-half times the maximum allowable working pressure, connected
to the steam space or to the steam connection to the water column. The steam
gauge shall be connected to a siphon or equivalent device of sufficient capacity to
keep the gauge tube filled with water and so arranged that the gauge cannot be
shut off from the boiler except by a cock placed near the gauge and provided with a
tee or lever handle arranged to be parallel to the pipe in which it is located when
the cock is open.
(15) Each power boiler shall be provided with a one-fourth inch nipple and
globe valve connected to a steam space for the exclusive purpose of attaching a
test gauge when the boiler is in service so the accuracy of the gauge may be
ascertained.
(16) Steam-gauge connections shall be suitable for the maximum allowable
working pressure and steam temperature; if the temperature exceeds four hundred
degrees Fahrenheit, brass or copper pipe or tubing shall not be used.
(17) When a steam-gauge connection longer than eight feet becomes
necessary, a shutoff valve may be used near the boiler if the valve is of the outside-screw-and-yoke type and is locked open when the boiler is in operation. The line
shall be of ample size with provisions for free blowing.
(18) Each steam-discharge outlet, except a safety valve, shall be fitted with a
stop valve located as close as practicable to the boiler. When such outlets are over
two-inch pipe size, the valve used on the connection shall be the outside-screw-and-yoke rising spindle type to indicate, at a distance, the position of its spindle,
whether it is closed or open. The wheel may be carried either on the yoke or
attached to the spindle.
(19) When power boilers provided with manholes are connected to a common
steam main, the steam connection from each boiler shall be fitted with two stop
valves having ample free-blow drain between them. The discharge of this drain
shall be visible to the operator while manipulating the valves and shall be piped
clear of the boiler setting. The stop valve shall consist preferably of one automatic
nonreturn valve set next to the boiler and a second valve of the outside-screw-and-yoke type; or two valves of the outside-screw-and-yoke type may be used.
(20) Each power boiler shall have a blow-off pipe fitted with a valve or cock.
All fittings and pipe shall conform to the applicable section of the A.S.M.E. boiler
and pressure vessel code.
(21) Provisions shall be made for the expansion and contraction of steam
mains connected to power boilers by providing substantial anchorage at suitable
points so undue strain shall not be transmitted to the boiler. Steam reservoirs shall
be used on steam mains when heavy pulsations of the steam currents cause
vibration of the boiler shell plates.
(22) All power boilers heated with gas, oil, or mechanical firing, except
stoker- or hand-fired coal-burning units which are constantly attended, shall be
provided with an automatic low-water fuel cutout and with an automatic fuel-regulating control, controlled by boiler pressure.
(23) All cases not specifically covered by this article shall be treated as new
installations or may be referred to the director for instructions concerning the
requirements.