Boiler Hot Lay up with tube deflection

[mpeck1982]

I have an O Type water tube boiler (1 steam/mud drum) that has been used for a Hot lay up while other boilers are producing superheated steam. What keeps this boiler warm is a lower drum heating coil. This keeps the boiler at the drum 220 deg F at 5psig. My question is when the boiler reaches that temp and pressure, should I open my superheater drain valves to drain the remaining condensate out of the superheater circuit? The temperature in the superheater circuit is 205 deg F. I will still have steam/condensate in the drums.

The reason I am asking is because the superheater tubes have experienced sagging tubes. I am thinking that the added weight of the water in the tubes have caused the sagging. Anyone an expert on tube deflection?

 

[metengr]

The sagging in the tubes is not caused by the weight of trapped condensate. The sagging is caused by thermal bowing or one side of the tube is receiving higher heat in comparison to the other side. Investigate this aspect.

 

[chicopee]

Excessive heat in the superheater tubes caused the sagging and is due to not enough heat absorption by the flowing steam in the superheater tubes. Another word the superheater tubes were overheated. Is the sagging permanently set?

 

[rmw]

A hot lay up boiler connotes to me a boiler ready at a moment's notice to come on line and take up the slack if, for example, another boiler should trip. Can it have happened that this boiler has been called on to come to full load in a rapid fashion without the SH loops having been properly drained?

To answer your question, yes, if your SH circuit is only 205F, it is condensing steam which would man that the SH tubes have water in them should the boiler suddenly be called upon to come on line. Is the SH loop drained at that time?

rmw

 

[mpeck1982]

Yes chicopee, the sagging is permenantly set. It was found during an annual outage. Everything was drained/isolated so the boiler was cold and open.

RMW, That is the boiler hot standby set up that is at the plant I am at. Yes the superheater circuit has condensate in the tubes before it goes online. Operations never drains their superheater circuit. Because of the tube deflection, it has creted non drainable surfaces along the horizontal section of the superheater. I think operations should drain the superheater circuit when its in a standby mode. The mud drum coil can still keep the boiler setting at 220 deg F at 5-psig. What are your thoughts?

 

[chicopee]

Well,if you decide to replace certain superheater tubes, there may be interference from other tubes so you may have to replace the entire bank of tubes. My guess is that the deformed tubes were overheated, probably to red hot, and then somehow cooler water was introduced setting the tubes to be permanently deformed.