Re: Thermal Shock

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Posted by Roger R Link on May 14, 2000 at 06:07:48:

In Reply to: Re: Thermal Shock posted by Vern on May 13, 2000 at 20:44:19:

: Question one: No. What you are talking about is a rather typical
: situation. Not enough temperature differential is involved to worry about.

: Question two: If an actual thermal shock did take place, I would suspect
: possible tube end leakage, in extreme cases possible tube sheet damage.

: Question three: Don't worry about it. Firetube boilers like yours are operated
: on a daily basis with ambient degree water being fed to them with no damage.

: : 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.

: : Tony

I agree with all that Vern has said and would like to add that the breaking away of the scale is actually a positive occurence as scale is being removed. Jist make sure that you chemically treat the feedwater to help dissolve the scale and increase blowdown accordingly. It seems that what ever you are doing on the chemical treatment side is working and it may be necessary to perform more frequent cleaning of the waterside to get rid of the scale.

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