Code Updates for Water Columns
There are certain code requirements for water columns that are not required on power boilers by ASME regulations but that, when specified, must be designed and manufactured to comply with the code.
A water column is used on a steam boiler to reduce the turbulence and fluctuation of the water level so the gauge glass can provide a steady, accurate water level reading. Water columns are made from either cast iron (maximum 250 psig) or fabricated steel (maximum 3,000 psig). Stainless steel is prohibited for the construction of water columns.
Water level indication devices in water columns include float alarm type, electrode (conductivity probe) alarm type, or no alarm. The latter is to be used for the sole purpose of supporting one or two water gauge glasses.
According to the National Board, a water column, if used, must be connected to the boiler using a cross or equivalent pipe fitting at each right-angle connection to allow visual inspection and cleaning of the connecting pipes. Sludge or sediment of any kind in the water column or connecting pipes can cause false water level indications (Figure 4).
4. Old reliable. The flat glass water gauge remains the mainstay of boiler drum water level measurement. Courtesy: Clark-Reliance
The ASME code requires a 1-inch minimum connection size from the boiler to the water column and a ¾ -inch minimum connection size from the boiler to a remote level indicator. Gauge glasses that are required by code may be connected directly to the shell or drum of the boiler or to an intervening water column. When two gauge glasses are required, both may be connected to a single water column.
Section 1 of the code has standards for the highest and lowest permissible water level in water column connections. The lower edge of the steam connection between a water column and level indicator device shall not be below the highest visible water level in the gauge glass.
Conversely, the upper edge of the water connection between a water column and level indicator device shall not be above the lowest visible water level in the gauge glass. These parameters are established to prevent any accidental overheating of the boiler, leading to unwanted downtime and possible worker injury.
Water columns are considered to be a standard pressure part, as defined in the ASME boiler code; therefore, a code stamp for manufacturing is not required. Code-recognized materials and applicable welding procedures are a must. Since 1991, the use of gauge cocks (also called try cocks) have not been required.
There are certain codes that apply to condensate removal from heat-recovery steam generators. Drain pots, which detect and remove unvaporized spray water, will include automatic detection of water and automatic operation of the drain pot valves using a sensor device that triggers operation of the drain valve.
Other Common Code Violations
Some steam boiler operators have unintentionally violated the code as a result of lack of oversight and failing to follow proper maintenance procedures, as outlined by the original equipment manufacturer. Other violations include:
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Isolated and inoperable water gauges.
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Missing water gauges.
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Missing illumination from ported gauges.
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Inadequate display of remote level indicators in control room, combined with isolated gauges.
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Contaminated water gauges preventing proper level reading.
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Multiple-section flat glass gauges without overlap.
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Poor maintenance practices that lessen the service life of the instruments.
To achieve optimum safety for boiler operation and plant personnel, any individual responsible for the selection, specification, and replacement of level instrumentation must understand the applicable code requirements. It is always wise for managers to consult with the plant’s insurance carrier to verify if they require additional instrumentation beyond the code minimum requirements.
— Contributed by James W. Kolbus, a product manager for Clark-Reliance Corp.
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