FATT (fracture appearance transition temperature) 4

[vali1]

I have a problem with a turbine disk.(the material).The customer asked the FATT test for the disk material. In fact, my problem is about the minimal/maximal value accepted.If the disk works arround 50 Degrees Celsius, what is FATT value accepted, or the PERCENTAGE DEVIATION?
Any other information on this problem will be very good.

Thanks!

 

[ijzer]

Your customer should specify what the acceptance criteria is.
Usualy you make a S curve by testing at different temperatures to find out where your 50% point is.That point shall be equal or lower than the spec.

 

[vali1]

Hello ijzer!

Thank you for your prompt ansewer.
But the problem still remain because:

1.The customer has no ideea about the acceptance criteria.
2.I have to guarantee the disk will stay in opperation without problems.

The material of this piece is :
34 CrNiMo 6 according to EN 10083-1
or
36 CrNiMo 6 according to ISO 683-1:1987

Thanks again!

 

[unclesyd]

I concur with ijzer the normal criteria is a 50% shear/cleavage fracture. Make sure your client is aware of what he is asking and the added cost of providing same. Just getting this from a metal supplier is tough and test is much tougher

We used to call FATT "Fracture Arrest Transition Temperature".

We used the Navy explosive bulge test to plot the "S" curve to determine this temperature.

 

[metengr]

What type of turbine disk? Typically, if you use 50% flat fracture as your FATT acceptance criteria, the FATT value should be well below 50 deg C for the disk material. The last thing you want is to have any significant operating stresses that are applied to the disk material below the FATT - this could result in brittle fracture if you have any flaws or stress risers.

 

[vali1]

Hello Metengr!

It is a shrunk fit disk, from a Skoda Low Presure turbine shaft.But as I said, my problem is that I don't have any prescription (ISO, DIN, ASTM,etc)where I can read something precise. I mean a temperature value: It should be 10 or 15, or 5, degrees C below 50 Degrees C. If you have something related with this, an ISO, ASTM, anything, I will be very satisfied.

Thank you,

Vali

 

[metengr]

vali;
I can tell you that your FATT should be below 0 deg C (meaning at least -50 deg C below your operating temperature) for this LP turbine disc material. You need to account for stresses during startup of the machine - this is why I would recommend a much lower FATT to prevent lower toughness during unit start conditions.

I can tell you that in my turbine reference book "State-of-the-Art Weld Repair Technology for Rotating Components" from EPRI TR-107021-V1 for the various grades of LP turbine disk materials (A 470 Classes 1-3), the FATT (50%) is normally around 0 deg F (~-18 deg C).

 

[metengr]

Correction to above; ASTM A471 not A 470

 

[Carburize]

All the impact test type criteria, transition temperature for a specific absorbed energy, fracture appearance etc are all only comparative tests. The only real way to determine the fitness for purpose of a specific, design/application/material combination in terms of its ability to resist cracking is by performing appropriate fracture toughness tests

 

[vali1]

Hello Metengr!

Tanks again for your tips!
I came back to you again with another problem, and maybe you cen help me.

I would like to obtain the book you have mantioned before:
"State-of-the-Art Weld Repair Technology for Rotating Components"
And, if it is possible the ASTM A471, or an extract from it.
If you can halp me, tell me how do I have to proceed in order to obtein those things.

Thanks,

Vali

 

[yates]

Most of the FATT acceptance criteria for 34 CrNiMo 6 turbine wheels I have seen in my career have been centered on -40°C, with extremes specified at -60°C and -25°C. Most serious conditions for wheel stresses occur at cold during run-up, particularly when crossing through compressor surge zones, and especially when overnight shutdowns in winter have iced up your compressor dump valves !

 

[CoryPad]

You can get ASTM A 471 (and any other ASTM document) from ASTM International at:

http://www.astm.org

Just type A471 in the search window. It costs US$33.

You can order the EPRI document (and any other EPRI document) from EPRI at:

http://www.epri.com

Just type TR-107021-V1 in the Search window and you can view a summary. Beware of the cost: it is US$500.

Regards,

Cory

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