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Blue Blush Build Up On Steam Valve Spindles
- Thread starter Cookie
- Start date
Come back with the material of construction of the spindle and the steam conditions. A little more information on where the blush is forming will also help.
Some steels, mainly the PH steel develop a pronounced blue blush while others will tend to get blush from oxidation or bluing.
Some steels, mainly the PH steel develop a pronounced blue blush while others will tend to get blush from oxidation or bluing.
- Thread starter
- #4
We are having the chemical composition verified. These are inlet steam valve spindles on a GE reheat steam trubine. 1450psi@1000F. The spindle material is Nitralloy B5E1A
This site had started cycling their turbine unit six years ago. They are now finding a very abnormal amount if build up on the valve spindles and inside the bushings.
This site had started cycling their turbine unit six years ago. They are now finding a very abnormal amount if build up on the valve spindles and inside the bushings.
By inlet valve spindles, I assume you mean the throttlng valves that modulate and govern the turbine speed, as opposed to the stop valves, or the intercept valves that basically do not move very often.
In the case of the control valves, in a unit that does not cycle much, the valves run open, or mostly open all the time, so they rarely close. Valves in this service build up the "blue" oxide. when the valve is cycled, the oxide is "peeled" off or scraped off by the valve sliding through the seals.
Stop valves and reheat valves have to be exercised perodically to remove this scale, and make sure that if they are called on to activate in a trip, that the oxide build up is not such that the valves would fail to function.
Now that your control valves are being called on to cycle often, the oxide is scraped off, and sometimes to the detirment of the seals or packing or bushings, and then a new layer or coating of oxide builds up, only to be scraped off the next time the valves cycle.
The oxide layer is self protecting. That is to say, that the layer of oxide prevents futher oxidation of the valve spindle. When this layer is scraped off, the base metal is exposed, and a new layer of oxide is formed, only to be scraped off, ad infinitum.
I hope this explaination sheds some light on the situation I believe you described.
rmw
In the case of the control valves, in a unit that does not cycle much, the valves run open, or mostly open all the time, so they rarely close. Valves in this service build up the "blue" oxide. when the valve is cycled, the oxide is "peeled" off or scraped off by the valve sliding through the seals.
Stop valves and reheat valves have to be exercised perodically to remove this scale, and make sure that if they are called on to activate in a trip, that the oxide build up is not such that the valves would fail to function.
Now that your control valves are being called on to cycle often, the oxide is scraped off, and sometimes to the detirment of the seals or packing or bushings, and then a new layer or coating of oxide builds up, only to be scraped off the next time the valves cycle.
The oxide layer is self protecting. That is to say, that the layer of oxide prevents futher oxidation of the valve spindle. When this layer is scraped off, the base metal is exposed, and a new layer of oxide is formed, only to be scraped off, ad infinitum.
I hope this explaination sheds some light on the situation I believe you described.
rmw
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