Boiler Codes or Standards - Summary of requirements
ASME Boiler Code
Boilers must have one gauge glass. Above 400psi operation two gauge
glasses shall be provided. For boilers with safety valves set at or
above 900psi two independent remote level indicators may replace one
of the two gauge glasses. If both remote indicators are in reliable
operation the remaining gauge glass may be valved off but must be
maintained in serviceable condition. If gauge glasses are not visible
to the operator two dependable Indirect Indicators shall be provided.
The lowest visible level of the gauge shall be at least 2" above
the lowest permissible water level where there is no danger of overheating
any part of the boiler. Each water gauge glass shall be equipped with
a top and bottom shutoff valve of through flow construction to prevent
stoppage by deposits of sediment. Straight run globe valves shall
not be used. Connections from the boiler to the remote level indicator
shall be at least 0.75" pipe size including isolation valves.
For gage glasses connected to the boiler the steam and water connections
shall not be less than I" pipe size. There shall be no sag or
offset in the steam pipe and no part of the water connection shall
be above the point of connection to the gauge.
It is
recommended that each boiler have two independent low water cut-offs.
The permanent installation of cutout devices for low water cut-offs
should not be provided; temporary devices can be installed for testing.
British Standard BS759. Part 1. 1984
Boilers shall have two independent gauge glasses each capable of being
isolated from the boiler. One water level gauge is permitted for boilers
of less than 145kg/h evaporative capacity. For boilers with safety
valves set at or above 60bar in two independent manometric remote
level indicators may replace one of the gauge glasses. One gauge glass
with its isolating valves shall be connected directly to the boiler.
Remote level Indicators which have been approved by an "Inspection
Authority" may replace gauge glasses.
The lowest visible level of the gauge shall be at least 50mm above
the lowest permissible water level where there is no danger of overheating
any part of the boiler. Steam and water isolating valves if straight
pattern globe type shall be mounted with the spindle horizontal.
The bore of steam and water connections shall be not less than 25mm,
local to fittings not less than 20mm. The level gauges shall be mounted
as close as is practical to the boiler shell or drum.
Automatic
controls shall effectively shut off the fuel supply in the event of
low water level.
There is a reasonable degree of commonality between the above requirements
and this is generally reflected in other National Regulations. Accepted
or recognised standards must be used for the design, material selection,
welding and inspection of pressure containing components.
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