Scale in Turb

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prasoon s Active Contributor Join Date: Aug 2011 Posts: 18	Scale in Turb 09/05/2012 3:33 AM
	I have observed scale in middle stages of HP Turbine during overhauling work. But could not think of its reason. Can anybody suggest me any answer of such finding. especially why it was not there in front and rear stages.
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PWSlack Guru Join Date: Jan 2007 Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on. Posts: 32175 Good Answers: 839	#1 Re: scale in turb 09/05/2012 3:36 AM
	It indicates a shortfall in the feedwater treatment process upstream. Remember that silica is partially soluble in steam. __________________ "Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
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prasoon s Active Contributor Join Date: Aug 2011 Posts: 18	#2 In reply to #1 Re: scale in turb 09/05/2012 4:03 AM
	fine sir..! u mean certain silica% which may have been present in water has dissolved in steam . but question is Why it dissolved in middle stages only? not on initial stages when steam is superheated and why not in last stages when steam is less superheated?
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PWSlack Guru Join Date: Jan 2007 Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on. Posts: 32175 Good Answers: 839	#3 In reply to #2 Re: scale in turb 09/05/2012 4:23 AM
	It is difficult to say, as it cannot be seen from here. Perhaps the surfaces it has come into contact with are at a lower temperature? __________________ "Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
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Suranjan Chattopadhyay Associate Join Date: May 2010 Posts: 26 Good Answers: 1	#4 Re: Scale in Turb 09/05/2012 9:30 AM
	Yes, there is carryover of silica. Check your Drum water pH. It should be 9.5 to 9.8. Moreover there may be a chance of low performance of Mixed bed. But the question is why deposition found in middle stage. If the turb extraction are near to the affected zone then it may happen as steam pressure and temp decreases at extraction zones and if it become sufficient for the phenomenon then max silica will diposited and very less amount will remain for the rear stages. As pressure and temp in front stages are much higher so silica dipositation not found there. __________________ Suranjan Chattopadhyay
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prasoon s Active Contributor Join Date: Aug 2011 Posts: 18	#6 In reply to #4 Re: Scale in Turb 09/10/2012 12:44 AM
	Mr Suranjan I'd like to inform u that here the pH value of drum water is 9.5 and also that there is no extraction in the middle stage of HP turb.
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ajwinemaker Power-User Join Date: Dec 2008 Location: Australia Posts: 143 Good Answers: 24	#5 Re: Scale in Turb 09/05/2012 11:46 PM
	If it is a white scale, then likely it is Silica. And is result of poor performance of water treatment system (as others have said). Why the middle stage (and not further along)? I'm guessing (asI don't know your exact system), that the cause is liquid/solid Silica solubility gets very complex at 300-400 degC, and at high pressure. It could be where you are observiing the deposit you are passing through a region of low solubility (middle stages) then into region of higher solubility again (in the rear stage). But I would guess if you are using media bed (NRMB) filter to purify the water, then you need to change the media. If you are using 2pass RO + EDI - then the plant isn't working properly. Check the water analysis exiting the plant. Confirm the plant is operating correctly, problem should go away. Hope this helps, Anthony
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