Bryan Boilers Forced Draft Steam Boilers ユーザーズマニュアル

 

 

 

 

 

 

 

 

 

 

 

 

 

 
GENERAL 
Corrosion damage to boilers is often the result of 
improper lay-up during non-operating periods. 
Substantial damage can occur in only a few days 
in proper precautions are not taken. This damage 
is irreversible and will reduce boiler reliability, 
increase maintenance costs and eventually 
shorten the useful life of the boiler tubes. 
 
Idle boilers are vulnerable to attack when air 
contacts untreated wet metal surfaces. To prevent 
corrosion, the boiler metal must be protected by 
either keeping the surfaces completely dry or 
excluding air from the boiler. Air exclusion is 
accomplished either by keeping the boiler 
completely full of water (short term lay-up) or filling 
the boiler with nitrogen gas (long-term lay-up). 
The nitrogen gas prevents air infiltration and does 
not react with the metal. 
 
In addition to the corrosion damage that occurs, 
the metal particles that are released will form an 
insulating scale on the tubes when the boiler is 
returned to service. These corrosion products will 
accumulate on critical heat transfer areas of the 
boiler, increasing the potential for localized 
corrosion and over heating. 
 
PRE-OPERATIONAL CLEANING AND LAY-UP 
Proper lay-up techniques must be used on an idle 
boiler even if it has never been in operation. 
Before pre-operational lay-up, the boiler must be 
chemically cleaned as outlined in Section 3.2 of 
this manual. This is required, as noted in this 
section, to remove preservatives, oil and grease 
from the tube surfaces. Follow the short term or 
long term lay-up procedure as appropriate. 
 
TAKING BOILERS OFF LINE 
In operation, boiler water contains suspended 
solids which are held in suspension due to water 
circulation and the action of treatment chemicals. 
Unless care is exercised when draining the boiler, 
these suspended solids settle on the tube 
surfaces and will air dry to an adherent deposit, 
sometimes requiring chemical cleaning to remove. 
In addition, these deposits may be misleading 
regarding the effectiveness of the chemical 
treatment program. 
 
PRE-SHUTDOWN PRECAUTIONS 
For a period of three to seven days prior to 
shutdown, manual blowdown frequency should be 
increased. During this period, the lower 
conductivity limit should be below 3500 micro-
mohs per centimeter. The feed of internal 
treatment must be increased to maintain a specific 
residual concentration. Continuous blowdown 

(when used) should be kept to a minimum so the 
reduction of solids is achieved by the increased 
manual blowdown. 
 
WASHDOWN 
As the boiler cannot be washed immediately, the 
heat in the boiler may cause baking of residual 
sludge. The boiler should not be drained until 
cooled enough to prevent this. However, never 
leave the boiler filled with water for any extended 
period of time without taking measures to prevent 
corrosion. 
 
LAY-UP CONSIDERATIONS 
There are two basic methods of steam boiler lay-
up: Wet lay up or Dry lay-up. The choice of which 
method should be used depends on: 

 The possibility that the boiler may need to be 

placed in operation on short notice. 

 Disposal of lay-up solutions 
 Freezing potential 

 
Wet Lay-up is recommended for relatively short 
outages, such as seasonal lay-up. This method 
has the advantage of allowing the boiler to be 
brought on line with short notice. But it can pose 
problems if there is any likelihood of freezing. 
 
Dry Lay-up is recommended for longer periods of 
boiler shut-down or storage. But it is practical only 
if boiler can be drained hot (120 F to 170 F) or if 
external drying can be provided. 
 
WET LAY-UP OF STEAM BOILERS - SHORT 
TERM 
In the wet lay-up procedure, the boiler is to be 
filled with chemically treated water and sealed to 
prevent air in-leakage. Nitrogen gas under slight 
pressure can also be used to displace air and 
protect the boiler surfaces from corrosion. The 
following steps should be taken for wet lay-up of a 
boiler: 
 
1a. Procedure for operational boiler: 
At least thirty minutes before the boiler comes off 
line, add the following chemicals: 
Sodium Sulfite - 0.5 lbs. per 100 gallons water 
Polymeric Sludge Dispersant - 0.1 lbs. per 100 
gallons water 
Caustic Soda - 0.3 lbs. per 100 gallons water 
 
1b. Procedure for idle boiler: 
If the boiler has never been on line or has been 
out of service for cleaning - Select the highest 
quality water available to fill the boiler. Steam 
condensate, softened water, filtered fresh water, 
and boiler feedwater are generally acceptable for