UFC 3-240-13FN
25 May 2005
3-5
CHEMICAL REQUIREMENTS FOR BOILER LAYUP. Boiler layup also
requires special water treatment. Boilers that will be out of service for more than 4
calendar days require special water treatment to prevent internal corrosion. Boiler layup
can be either dry or wet. The advantages of wet layup are that it often provides better
corrosion protection and the boiler can be brought on-line much faster than when dry
layup procedures are used.
3-5.1
Operational Considerations. Operational considerations are important to
consider when determining the proper boiler status. The terms "lead" and "lag" are used
commonly for boilers that need to meet varying load demands. The lead boiler satisfies
the base steam load. The lag boiler meets any extra steam demand that might be
needed during hours of the evening or mornings or when (additional) process loads are
required. Lag status does not apply to a cold boiler that is not required for duty for a few
days. Such a boiler should be considered in layup condition and should be prepared
accordingly.
3-5.2
Common Problems that Occur During Layup. Common problems that
occur during layup are: oxygen pitting of tubes and condensate piping, sometimes to the
point of failure; general corrosion of tubes and condensate piping; and corrosion product
contaminating feedwater via the condensate system.
3-5.3
Dry Layup of Boilers. Boilers with manholes may be laid up in one of two
ways, depending on the length of storage and conditions in the boiler room: open dry
layup, or quicklime or silica gel layup.
3-5.3.1
Open Dry Layup Method. The open dry layup method is recommended
for short-term storage (30 to 150 days) where the boiler room is dry, has low humidity,
and is well ventilated. It is important to keep the boiler dry. The recommended
procedure consists of six basic steps:
1. Take the boiler out of service and drain it completely while still warm.
Make sure the water walls and gauge columns are not overlooked.
2. Lock and tag out boiler in accordance with written procedures.
3. Break the feedwater and steam connections to the boiler and blank off
connections if other boilers in the plant are operating.
4. The boiler may be opened and the inside washed of all loose scale and
sediment by flushing with high-pressure water.
5. Use a stiff brush to clean all internal surfaces that can be reached.
6. Leave boiler open to the atmosphere. Should a humid atmosphere exist,
the boiler must be closed up and the procedure specified in paragraph 3-
5.3.2 used.
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