CALIBRATION BLOCKS FOR U.T - FORGED vs. CAST

[ibf]

Hello:

According to ASTM A 609, reference blocks shall be made from cast steels that give an acoustic response similar to the castings being examined.
I have a supplier (overseas)that cannot pour heavy test-blocks for a 40"- facewidth gear; however, it has a forged bar which can easily fulfill the requirements (including chemical analysis).
Not being a U.T expert I ask:

1. Is it acceptable to use the forged bar as opposed to a heavy cast test-block ?

2. Assuming that a forged bar has a traditional tendency of being of a better quality than a casting (same alloy and same heat treat), would I be violating the ASTM STD by drilling the flat bottom holes on a forging ?

3. Would the calibration results obtained on a forged bar be deceiving due to its different manufacturing form ?

Thank you .

 

[CoryPad]

Which specific alloy is involved? Acoustic response is a function of elastic constants and density, so you need to consider the variables that can change these - e.g. second phases (dissolved, precipitated, eutectic, etc.) and crystal structure (ferrite, martensite, etc.).

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[ibf]

Alloy is carbon steel - ASTM A 27 GRADE 70-40 for the casting and ASTM A 291 CLASS 2 for the forging. Same heat-treatment cycle (NORMALIZED AND TEMPERED). Microstructure: Pearlitic (predominantly).

 

[metengr]

ibf;
Typically, when manufacturing UT calibration standards you want to simulate fabrication conditions as close to the fabrication condition of the actual component that will be subjected to ultrasonic examination. Grain size and pattern will affect attenuation for angle beam, more so than L-wave for UT. This will result in either over or under compensating establishment of DAC (distance amplitude correction) curves for the pre-drilled holes in the test block during calibration.

My question to you is how important is the UT exam? In other words, are you bound contractually to use ASTM A 609 for your specific application? Depending on the experience level of the UT operator you can do what you propose, if agreed upon between both parties or you know the exact type of defects or flaws that can occur in these components.

I want to caution you that the gain setting established by the forged test block will not be the same as for the cast component. This means that when you begin UT of the casting, you might start seeing noise caused by attenuation that may or may not affect your interpretation of results. If you are uncomfortable or believe the component is critical for an application, I would have the calibration blocks made from castings in accordance with the requirements of A 609.

One other option - have you considered radiographic testing (RT) or x-ray as a back-up in the event you can't obtain the necessary test blocks?

 

[EdStainless]

Differences in attenuation and the signle/noise ratio will be the major issues. Even good casting tend to be noisy. The thought of using x-ray as a back up NDT is a good idea

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[ibf]

Thanks metengr.

Our spec applies for A609 3 mm f.b.h because the area in question is the rim segment of a gear ( for us that zone is "Holy Ground").

I thank you all for the technical inputs.

ibf.

 

[Carburize]

Ivo,
I think you will need to find a way to cast the test block in order to calibrate the UT set before use on the gear. You will find a 3-mm FBH much more easily through a forged part than through the casting.
Is it possible that one of your other vendors has a cast test block that you could hire?