AWS D1.1 Ultrasonic inspection - Attenuation Factor c 1

[UmbertoP]

Hi everybody,

can anyone clarify me the meaning of the “Attenuation Factor c”: according to AWS, it "...shall be attained by subtracting 1 in. [25 mm] from the sound-path distance and multiplying the remainder by 2. This factor shall be rounded out to the nearest dB value..."

But the sound path is in inches (or mm), so how do I pass from a distance (in or mm) to dB?

A few pages later, there is a table named "Scanning Levels", with the first column headed "Sound path in in. [mm]" and the second column named "Above Zero Reference, dB".
Does this have anything to do with the attenuation factor c and, if so, how is it used?

Thank you very much in advance for your help

Umberto

 

[JR97]

Umberto,

First, Attenuation Factor C. The calibration for D1.1 inspection is based on a single 1/16 diameter hole in the IIW block. The Attenuation Factor attempts to convert the single point calibration into a Distance Amplitude Correction (DAC) type calibration by adding a factor to compensate for the weakening of the sound as it passes through the part. The result of the equation is in dB. So you subtract 1 from the sound path, multiply the result by two and round to the nearest whole number which is in dB.

Second, Scanning Level. The scanning level is not related to attenuation factor. The calibration level (A) is the gain required to set the 1/16 inch calibration hole to 50-75% FSH. The scan gain is read from the table, based on the maximum scan path to be employed. This amount of dB are added to the calibration level to scan the weld. The scan level has no bearing on acceptance criteria. If an indication is detected, the gain is adjusted until the response from the indication is at the same % FSH as the calibration hole. This gain setting is value "B". You then subtract "B" and "C" (both in dBs) from "A" to obtain the indication rating (D). The acceptance of the indication is based on the indication rating "D".

Hope this helps.

JR97

 

[HgTX]

Not exactly what the poster was asking about, but since this item is under discussion I should point out that the factor of 2 only works for inches. I believe that this has been corrected to 0.08 for SI units in D1.1-2010.

Hg


Eng-Tips policies: faq731-376

 

[Duwe6]

in mm it is 0.8 x (Sound Path - 25.4) = 'C'