[b]Scale Removal from Turbine Casing Joints[/b] 1

[zizzuu]

Hi,
l am in the middle of a major 660MW turbogenerator overhaul and am up to cleaning the scale off the half joints of the casings and diaphragms. l assume the scale is a form of iron oxide, most probably magnetite. At present oil stones are used to wear the layer off, which is a very labour and time consuming process. l am interested in any chemical treatments that may be used to carry out, or at least assist, this back-breaking process. l know we have used ammoniated citric acid solutions to clear boiler tubes of magnetite and am now starting to wonder if this or a similar may help.

 

[smckennz]

Hi Zizzuu
we use power wire brushes. With care.

Cheers

Steve

 

[TBP]

Before trying any kind of chemical solution, verify exactly what you're trying to clean off. The only deposit I can think of that could occur in a 660 MW turbine would be silica.

 

[zizzuu]

Thanks smckennz, but how would silica be found here assuming the concentration in the condensate circuit is zero.

 

[unclesyd]

Have you tried any type blasting are you in a position to where you can do this.
We have blast cleaned our turbine casings and diaphragms using walnut shells, dry ice, sodium bicarbonate, and Ultra pressure water.

Our biggest problem was the Linseed oil the continue to use on the casings.

We found Silica even though the condensate has none as in your case. We did find some in the steam where it condensed on an embrittlement detector.

 

[rmw]

The oil stone process, if done by a skilled millwright does more than just remove the scale. It also allows the millwright to find and work out high spots which would not be detected with other methods suggested, and which could then be detrimental to good sealing upon reassembly.

I guess I am just from the old school. That is the way I learned to do it, and being a hands on type of engineer, got in there and did it with the best of the craft workers (when union rules permitted, or the steward was one of the millwrights whose work I was doing). I can't imagine putting the top half back on with some of the high spots I have personally worked out of a lower half casing.

My two cents only.

rmw