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- since 1996 -
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Technical Discussions
Azhar Jamil
Azhar Jamil
01:42 May-16-2006
MPI of Steam Turbines

Dear all,

I hope you are fine and doing well. Below are two queries for you

1) Magnetic particle inspections of Steam Turbine:
For MPI of Steam Turbine Rotors and Diaphragms we are using the water based fluorescent magnetic ink and after inspection leave the inspection surfaces as it is, I want to know are there any chances of the after effect of the water based inks on the inspected components or not. If yes what is the best way to avoid it?

2) STEAM TURBINE JOURNAL BEARINGS
As a result of Dye-penetrant insepction, I found cracking on the white metal surface of the bearing. (white metal thickness is approximately 6mm), I want to know the depth of the crack in the white metal, if you can guide me please reply.

Thanks & Regards
Azhar Jamil




    
 
 Reply 
 
P V SASTRY
R & D, NDT tecniques metallurgy
TAKEN VRS FROM THE POSITION OF SR. DEPUTY GENERAL MANAGER BHEL CORPORATE R&D, India, Joined Jan 2003, 195

P V SASTRY

R & D, NDT tecniques metallurgy
TAKEN VRS FROM THE POSITION OF SR. DEPUTY GENERAL MANAGER BHEL CORPORATE R&D,
India,
Joined Jan 2003
195
09:12 May-17-2006
Re: MPI of Steam Turbines
Dear Mr. Azhar Jamil

If you have to use water based fluorescent ink for some specific reasons, it is advisable to use the standard mix that is supplied by the manufactureers which contains the required anti corrosive agents. If you are using your own mix you have to add the anti corrosive agent.

However It is very much advisable to use kerosene based flourescent ink as it gives higher sensitivity under field conditions. Frequently the turbine parts, other than those which have been thoroughly sand blasted, are contaminated with some oil and prevent proper wetting of the surface by water based inks. Light oil contamination is taken care by repeated spraying of the kerosene based ink. Heavy oil/grease contamination if present requires removal with a cleanere etc. Even after this cleaneing it is difficult to test with water based inks. Conditions are nearer to theory if you are testing a medium sized part in side the laboratory from those you encoundter on the shop floor trying to test the almost inaccessible roots of the turbine blades etc. There are many other small advantages of using kerosene based flourescent inks and you must switch over to it unless you have specific reason for using water based inks.


Coming to the second part of your question it is rare to get cracks in the white metal. You normally get porosity, metal burn out due to oil starvation, deep scouring marks etc. If you have got that rare crack on the white metal face, normally the depth can be assessd from the spread of the penetrant indication and the speed with which it is forming. In 6 mm depth you will not be be erring much. If the spread is much more than can be attributed to the 6mm depth, please understand that it must be coming from the interface.

Though we have never tried for this application, you may try crack depth meter for assessing the depth.

You are most welcome to write to me if you have any further clarifications.

Good luck

P V SASTRY

----------- Start Original Message -----------
: Dear all,
: I hope you are fine and doing well. Below are two queries for you
: 1) Magnetic particle inspections of Steam Turbine:
: For MPI of Steam Turbine Rotors and Diaphragms we are using the water based fluorescent magnetic ink and after inspection leave the inspection surfaces as it is, I want to know are there any chances of the after effect of the water based inks on the inspected components or not. If yes what is the best way to avoid it?
: 2) STEAM TURBINE JOURNAL BEARINGS
: As a result of Dye-penetrant insepction, I found cracking on the white metal surface of the bearing. (white metal thickness is approximately 6mm), I want to know the depth of the crack in the white metal, if you can guide me please reply.
: Thanks & Regards
: Azhar Jamil
:
:
------------ End Original Message ------------




    
 
 Reply 
 
Simon Amallraja
Simon Amallraja
09:18 May-17-2006
Re: MPI of Steam Turbines
----------- Start Original Message -----------
: Dear Mr. Azhar Jamil
: If you have to use water based fluorescent ink for some specific reasons, it is advisable to use the standard mix that is supplied by the manufactureers which contains the required anti corrosive agents. If you are using your own mix you have to add the anti corrosive agent.
: However It is very much advisable to use kerosene based flourescent ink as it gives higher sensitivity under field conditions. Frequently the turbine parts, other than those which have been thoroughly sand blasted, are contaminated with some oil and prevent proper wetting of the surface by water based inks. Light oil contamination is taken care by repeated spraying of the kerosene based ink. Heavy oil/grease contamination if present requires removal with a cleanere etc. Even after this cleaneing it is difficult to test with water based inks. Conditions are nearer to theory if you are testing a medium sized part in side the laboratory from those you encoundter on the shop floor trying to test the almost inaccessible roots of the turbine blades etc. There are many other small advantages of using kerosene based flourescent inks and you must switch over to it unless you have specific reason for using water based inks.
:
: Coming to the second part of your question it is rare to get cracks in the white metal. You normally get porosity, metal burn out due to oil starvation, deep scouring marks etc. If you have got that rare crack on the white metal face, normally the depth can be assessd from the spread of the penetrant indication and the speed with which it is forming. In 6 mm depth you will not be be erring much. If the spread is much more than can be attributed to the 6mm depth, please understand that it must be coming from the interface.
: Though we have never tried for this application, you may try crack depth meter for assessing the depth.
: You are most welcome to write to me if you have any further clarifications.
:
: Good luck
: P V SASTRY
: : Dear all,
: : I hope you are fine and doing well. Below are two queries for you
: : 1) Magnetic particle inspections of Steam Turbine:
: : For MPI of Steam Turbine Rotors and Diaphragms we are using the water based fluorescent magnetic ink and after inspection leave the inspection surfaces as it is, I want to know are there any chances of the after effect of the water based inks on the inspected components or not. If yes what is the best way to avoid it?
: : 2) STEAM TURBINE JOURNAL BEARINGS
: : As a result of Dye-penetrant insepction, I found cracking on the white metal surface of the bearing. (white metal thickness is approximately 6mm), I want to know the depth of the crack in the white metal, if you can guide me please reply.
: : Thanks & Regards
: : Azhar Jamil
: :
: :
------------ End Original Message ------------

You can use ACPD ( Alternate Current Potential Drop) units to measure the depth of the crack. If you are in India, contact me, and I will give you more detail and offer to you for supply.

D.Simon Amallraja.
Mahindra Intertrade Ltd. Secunderabad.


    
 
 Reply 
 
Azhar Jamil
Azhar Jamil
02:12 May-18-2006
Re: MPI of Steam Turbines: Some more information
Dear Mr. Sastry,

First of all I am very thankful for your detailed reply. Below is some information for further discussion on the topic.

1) Steam Turbine Rotor and Diaphragms:

Surface Condition:
100% grit blasting (by Aluminium Oxide) of the inspection surfaces carried out prior to inspection.

Quantity (Inspection volume):
HP - IP Rotor: 9 HP Stages and & IP Stages
LP Rotor:5 Stages double flow (It means that total 10 stages of LP Turbine rotor)

HP Diaphragms: 9 stages (Top & bottom halves)
IP Diaphragms: 7 Stages (Top & bottom halves)
LP Diaphragms: 10 Stages(Top & bottom halves)

I totally agree with you that kerosine based ink is more sensitive than the water based ink. The main reason of using the water based fluorescent ink is the volume of inspection...so the use of kerosine based inks make it little bit expensive....

As you have mentioned about the anti corrosive agent, we are using the Magnaflux products I think they have included the anti corrosive agent in their products.

Considering above information what you suggest.


2) Journal Bearings

The white metal bearings I am talking about have journal diameters of 430mm, 480mm and 535mm.
There is no confusion between cracking and the interface. We found cracking on the white metal surface (reason may be so many about which I am not sure). At the moment we are assessing it from the spread of the penetrant indication and the speed which you have mentioned.


Dear Mr. Simon Aallraja
I am also very thankful for your interest, I am in Pakistan infact.


Thanks & Regards
Azhar Jamil.



    
 
 Reply 
 

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