radiography of 2" welds

[rmx8004]

Can anyone tell me the correct way to shoot a 2" pipe weld using an ir-192 source to Asme V. Does the IQI need to be source side, and thus the standoff distance need to be very long, or can the IQI be film side, the standoff shorter, and only the nearest wall to the film interpretated.

 

[ndeguy]

rmx8004

ASME V Art 2 T-271.2.(b) "For materials and for welds in components 3 1?2 in. (89 mm) or less in nominal outside diameter, a technique may be used in which the radiation passes through two walls and the weld (material) in both walls is viewed for acceptance on the same radiograph..." , this may be either elliptical (2 shots @ 90 deg) or super-imposed (3 shots @ 120 deg).

"For double-wall viewing, only a source-side IQI shall be used. Care should be exercised to ensure that the required geometric unsharpness is not exceeded. If the geometric unsharpness requirement cannot be met, then single-wall viewing shall be used."

This is generally recognised as being the most efficient way of radiography of a small diameter pipe butt weld. However, single-wall viewing is not precluded by the Code as long as it can be demonstrated that complete coverage of the joint at the correct film density is achieved. Number of required exposures is dependent on the wall thickness/OD ratio. Film-side IQI placement has to be identified with an adjacent lead letter "F".

Minimum required stand-off distance for DWDI is calculated from pipe OD x focal spot or source size divided by Code maximum allowable unsharpness for the wall thickness.

Hope this helps




Nigel Armstrong
Lloyds Register
Independent Verification Body Surveyor

 

[rmx8004]

Thanks for the reply NDEguy.

For the single wall viewing of 2" welds, am I right in thinking that these can be shot from a standoff distance, and the single wall (closest to the film) be interpreted, whether it is shot elliptical or superimposed(top part of the superimposed weld ignored). To get the coverage for this way would a minimum of 3 shots@120 deg, for either elliptical or superimposed?

The reason for asking this is that the contractor is using an iridium source with a 4.5mm diagonal source size, and would have to shoot the 2" pipe from approx 2 meters away, to see the relevant wire on a 2" Sch 80 pipe with IQI source side. Am I right in thinking the IQI thickness for DWDI shots is based on the single wall thickness, or for DWDI shots is it based on 2 x the wall thickness?

 

[ndeguy]

rmx8004

I cant see your problem as 2" OD Sch 80 ellipticals or superimposeds to meet Code requirements are as common as muck. The essential wire for 5mm wall is #5 SS. So where does the 2m SOD figure come from - have the contractors made test shots?


IQI selection and wire-visibility requirements for ASME are always based on single wall thickness plus maximum allowable reinforcement.



Nigel Armstrong
Lloyds Register
Independent Verification Body Surveyor

 

[rmx8004]

They shot a 2" 80 weld with the IQI SS from 400mm on MX125 film, and no wires were visible. Shooting it from 400mm with the IQI film side, the wire#5 was visible.

wire no 5 is 0.2mm
F is 4.5mm
d is 60mm (for a 2" pipe)

D = (4.5x60)/0.2 = 1350mm

This is what i get would be the standoff needed to just see the wire if it was Source side.

My question is is it OK to shoot 2" from 400mm with the IQI film side, and only interpret what would be the image on the film side, even though another image is superimposed on it.

Or should it be shot from the longer SFD, making the exposure time very long.

I just want to know to see if my interpretation of the code is right or wrong as during my time I have seen 2" shot from a short sfd (approx 300mm) with the IQI film side.

What kind of setup do you normally have for shooting 2"?

 

[ndeguy]

rmx8004

The Iridium radiation source is not a good choice for such thin materials. The contractors should be utilising Selenium for this material thickness, see AME V Art 2 T-272. Switching will show a marked sensitivitiy. If Iridium is the only available radiation source, then the technique will need to be improved.

The calculation you are using is the SOD required for a maximum geometric unsharpness value of 0.2 , e.g. from a defect on the source side weld cap - the only connection with the required exposure so that wire #5 is clearly visible is that changing the SOD will invoke the inverse square law.

Single-wall interpretation and film side IQI are permitted by the Code, provided you can meet Code requirements for density, coverage and sensitivity.






Nigel Armstrong
Lloyds Register
Independent Verification Body Surveyor