UGh factor in RT

[bhart192]

Reading Asme V for RT technique, we have a vendor that has proposed a RT technique for isotope RT of heavy wall pipe ( 2.75 OD with .625 wall ), looking at ASME V for Ugh factor a source to film distance of 20" seems to fit the requirements for not exceeding the Ugh factor of .030 for materials gerater than 2" but less than 3" .Our client has a procedure thats states 28" source to film which we feel leads to excessive shot times . our set up is as follows F= Focal pt .136
d =source side of object to film 2.75
Do=source to object distance

Ugh= Fd/Do .136(.275)/17.25=.021

I understand the greater distance better shot but our set-up does meet the code . comments???????

 

[Duwe6]

Assuming that you can see the required Image Quality Indicator, of course it does. But it fails to meet your customer's spec. It is the customer's right to demand higher-quality RT 'shots', if they pay for it.

 

[JR97]

bhart192,

A 20" SFD does not meet the ASME Section V unsharpness limitation. The maximum Ug for your situation is 0.020 not 0.030. Per the note in T-274.2 the material thickness to use to determine the Ug limitation is the thickness on which the IQI is based. Paragraph T-276.2 defines the thickness as the nominal single wall thickness. For your situation that would be 0.625" which sets the Ug limitation at 0.020".

I caution you to read the referencing Code section (i.e. Section I, III, VIII). Some of those sections allow the Ug limitation of Section V to be violated provided, as Duwe6 states, you can see the required IQI. Not all of the referencing code sections have that allowance.

From an acceptable radiograph standpoint, you can probably produce an acceptable radiograph using a 20" SFD. The problem area will be complying with the paragraph T-282.2 density variation at the edges of the zone. You may need to reduce the width of each zon and take more than the required minimum number of shots to produce Code compliant radiographs.

JR97

 

[bhart192]

I hate notes , we're going with 24" SFD and 6 exps thanks to all

 

[Duwe6]

Thanks for sharing the resolution to your problem with us.