24 July 2003
including Change 1, Jan 2004 and Change 2, March 2005
caused by defective or improperly installed or operated firing equipment must be
corrected before the boiler is returned to service.
The inspector will examine the supports and setting of suspended boilers, especially
where a boiler is near the setting walls or floor, to ensure ash or soot does not bind or
produce excessive strains on the boiler by restricting its movement when operating.
The National Board recommends that under normal operating conditions, safety valves
installed on power boilers operating at 400 psi or less be manually tested once a month
by the operator and pressure tested once a year. (Under certain operating conditions,
these recommendations may not apply.) Actual operating experience will determine
how frequently safety valves on power boilers operating at more than 400 psi should be
The inspector will check safety and safety relief valves on heating boilers for the correct
set pressure and adequate relieving capacity. Any leaking or deteriorated valve must
be repaired by the manufacturer or an authorized safety valve repair facility or be
replaced. Discharge pipes must be adequately supported, and valves must be properly
sealed unless they are nonadjustable.
A common unsafe condition found in both safety and safety relief valves is the failure to
open at the set pressure due to buildup of corrosive deposits between the disc and
The National Board recommends that under normal operating conditions, the safety or
safety relief valve on a steam or hot water heating boiler should be tested manually
once a week and pressure tested once a year. Again, under certain operating
conditions, these recommendations may not apply.
The inspector will next determine that where required, all pressure gauges have been
removed and tested and their readings compared to the readings of standard test
gauge or a dead weight tester. He will determine whether any steam pressure gauge is
exposed either to high temperature from an external source or to internal heat due to
lack of protection by a proper siphon or trap. He will also check that provision is made
for blowing out the pipe leading to the steam gauge.
If tubes have been replaced or re-rolled, the inspector will check for proper
workmanship. If tubes are readily accessible, they may have been over-rolled.
Conversely, if it is difficult to reach the tube ends, they may have been under-rolled.
If the inspector requires additional information regarding a leak in a boiler or the extent
of a possible defect, he may require that a hydrostatic test be performed. To determine
tightness, the hydrostatic test pressure need be no greater than the set pressure of the
safety valve having the lowest setting.
The hydrostatic test pressure may not exceed 1.5 times the maximum allowable
working pressure. The safety spring may not be compressed to prevent the valve from
opening. The safety valve or valves will be removed and each disc held down by
means of a gag or testing clamp. A plug device designed for this purpose may be used.
Water used in the hydrostatic test should be at least 70F but may not exceed 120F
during the inspection. If a test is conducted at 1.5 times the maximum allowable