ASME Acceptance criteria

[Wondering1]

OK im new to this and im wondering if someone could explain to me in the most basic laymans terms the following ASME acceptance criteria.

If i was looking for what is a defect in 25mm thick pipe that is 12 inch.

ASME B31.12 Table 2 Flaw acceptance criteria
25mm ≤ t 64mm
Aspect Ratio - Surface Flaw - Subsurface Flaw
a/l a/t a/t
0.00 0.031 0.034
0.05 0.033 0.038
0.10 0.036 0.043
0.15 0.041 0.049
0.20 0.047 0.057
0.25 0.055 0.066
0.30 0.064 0.078
0.35 0.074 0.090
0.40 0.083 0.105
0.45 0.085 0.123
0.50 0.087 0.143

 

[stanweld]

You need to contact your phased array and TOFD Ultrasonic Testing experts.

 

[Wondering1]

They cost too much money, so i was hoping to find someone on here who deals with such codes.

 

[stanweld]

A number of companies that I know of in Texas will provide a half day introductory course for free. Longer courses 2-2.5 days are available to obtain a basic understanding of the UT methodology and acceptance criteria meaning.

 

[Wondering1]

Thanks but im a long way from Texas, thus my need for assistance online!

 

[metengr]

The aspect ratio a/l in Table 2 pertains to the ratio between measured flaw depth (a) or planar flaw depth (if subsurface - (a)) to flaw length (l). The ratio a/t pertains to the depth of the surface flaw/material thickness, and for subsurface flaw this would be the planar depth of the flaw/material thickness.

So, you scroll down the table to the ratio which is closest to that for the a/l aspect ratio. If your measured values exceed the a/t ratio for a surface or subsurface flaw, the flaw is rejectable.

 

[Wondering1]

Thanks for you help.

Just so i can fully get my head around this, is there any chance you can write down the equations needed so i can figure out what would be acceptable/rejectable for the dimensions of pipe i have given. (12 inch x 25mm)

Im a fractions kind of guy and maybe its the decimals that are throwing me.

Thanks

 

[weldtek]

I'm not familiar with B31.12, however, the table you've included is identical to that applicable to CC 2235-9 and ASME Sec VIII Div 2. The first thing you do is select an aspect ratio. ( a/l) 0.25 is common. For that a/l, a/t is shown as 0.055 and pertains to surface flaws. Note surface flaws do not necessarily break the surface but lie </= .5(a) from the surface.
So for surface flaws the formula for 'a' is t*.055
for 'l' the formula is a*4
This gives you 'a' - the height of the flaw and 'l' - the length of the flaw.

Subsurface flaws are calculated similarly.

 

[Wondering1]

Thank you very much for you help and time.

 

[Wondering1]

Back again, just to confirm im on the right track.

My imaginary defect is 1.5mm in height and 6mm in length, so its a 0.25 ratio?

a (depth of defect) = t x 0.055 = 1.375mm
l (length of defect)= a(1.375) x 4 = 5.5mm

Thus anything over these is a rejectable defect so my 1.5mm x 6mm is rejectable, but a 1mm x 4mm would be acceptable.

If this is correct my one question is where does the (4) come from that you multiplied with (a)?

 

[weldtek]

The multiplying factor of 4 comes from the .25 aspect ratio.