Boiler Tubes Failure

[mjsamman]

thread794-252410
Tube Failures
If any water or steam carrying tube fails, the best shutdown method will be dictated by the size of
the failure, the ability to maintain a normal water level and the demand for the unit to remain in
service.
The following instructions are general since most of the conditions will require the judgment of the
operators.
WATERWALL TUBES
If a leak or tube failure does not involve a serious drain on the feedwater supply, the water level
should be maintained and the unit taken out of service in the normal manner:
a. Operate the soot blowers if conditions permit.
b. Switch the combustion control equipment to manual control and proceed to
reduce the firing rate and air flow in a normal manner.
c. When all fires are extinguished continue the air flow through the unit at a
reduced rate to purge all combustible gases, vapors, etc. Shut down the fans
when the unit is cooled sufficiently.
d. Feed water to the boiler by hand, maintaining a high level in the water gauge. To
speed cooling, boiler pressure can be reduced by opening the superheater outlet
drains. Open the drum vents when the drum pressure drops 6.9 to 20.7 kPa (1 to
3 psig); approximately 100°C to 104°C (212°F to 220°F) water temperature in
the downcomers.
e. Allow the boiler to cool at least to 93°C (200°F) (drum metal temperature); before
draining.
If there is a serious water loss and the water level cannot be maintained with the feedwater supply
available. use the following method:
a. Trip all fuel.
b. Shut down the last boiler circulating pump just before the water level drops out of
sight after the fuel is tripped.
c. Shut off the feedwater to the boiler.
d. Maintain only enough airflow to carry the escaping steam up the stack.
e. Leave the fans and air heaters in service until pressure is off the unit.
f. Once the unit is cool enough to enter, inspect the pressure parts for damage
caused by the loss of water level. After the necessary repairs have been made,
apply a hydrostatic test and obtain the approval of the proper authorities before
putting the unit back in service.

 

Please phrase your question in the form of a question

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[Steve Beck]

Hi, there is the few resaon why boiler tube is a failure.

1) The environmental conditions within the boiler can be highly aggressive and alter the microstructure of tubing.
2) Stresses caused by external loads, or induced by cold forming operations, uneven cooling or welding, may substantially lower the resistance of tubing to attack by certain corrosive media.

Fuel ash corrosion
Fuel ash corrosion is a high-temperature phenomenon in coal and oil-fired boilers

Carbide graphitization
The carbide phase of carbon and carbon-moly steels may be converted to graphite after long-time exposure to high temperature.

Dew Point corrosion
During periodic shutdowns of the boiler unit, tube failures can occur.

Oxidation
Steel tubing exposed to elevated temperatures for extended periods of time will oxidize; i.e., accumulate a protective coating of scale.

Stress corrosion cracking
Austenitic chromium-nickel steels that are highly stressed in tension may develop transcrystalline or intercrystalline cracks when simultaneously exposed to a specific aqueous corrosive medium.

 

[crshears]

I don't see a question, either...

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[SnTMan]

I seem to recall the OP replied his post was in relation to a closed thread, how else to reply to such? This reply seems to have disappeared without a trace. Unless I made the whole thing up...

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[crshears]

The way I've seen this done in the past looks something like this:

[1] Re: thread URL

[2] Question



CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[SnTMan]

Or 2) Reply

The problem with sloppy work is that the supply FAR EXCEEDS the demand