Thermal Shock

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Posted by Anthony Pritchard on May 13, 2000 at 14:28:53:

Regarding the qeustion of thermal shock and it's
effects: We have (3) 400 hp firetube boilers, one
of which we suspect has experienced a rather severe
thermal shock for the following reasons. Upon opening
the firsides for yearly cleaning and inspection (both
firesides and watersides inspection) we discovered
between 15 and 20 lbs of what appears to be scale and
rust that obvioulsly came from the tubes (curved
shaped debris). This boiler was operated for a number
of days without the Deaerater Tank. The boiler water
temperature is close to 345 deg. F, and normally with
the DA tank the inlet water to the boiler (boiler
feedwater) runs around 220 deg. F, however, without
the DA tank during these few days the inlet temp.
never rose above 150 deg. F, compound this with the
fact that the early morning load increases usually
result in a boiler load increase of anywhere from
30 to 60 percent resulting in the boiler taking a
'big drink' of relatively cold water.

Question one: Is it safe to assume, given the above
information (on a very carefully maintained boiler
that has yet to be inspected by a certified
inspector) that a thermal shock may have occured?

Question two: If a thermal shock did indeed occur,
what are the likely damages?

Question three: How seriously should the possibility
that a thermal shock did occur be taken?

The possibility of a thermal shock is presently being
brushed off as nothing to be concerned about.

Does anyone know of any web resources that deal with
this issue?

If you could reply to it would be
much appreciated.

Thanks in advance.


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