Strange number of RT exposures - pipe ASME V

[ElCidCampeador]

Hi,
I have a vessel with a nozzle+wn flange 1" Sp.9,09mm, material carbon steel. BW weld between flange and nozzle has to checked 100% RX acc. to ASME V.
Construction code is ASME VIII DIV.1.
NDT company for this joint used double wall double viewing technique, which means, acc. to ASME V par. T-271.2 (b)(2) at least 3 exposures.
But if look at the RT report, I find N°8 exposures! Ok, 3 it's minimum, but 8... why?
NDT company only answered me that it depends on the high thickness comparing to the small diameter of pipe...I hope they did not cheat me.

What do you think? Thanks

 

[DekDee]

It has nothing to do with the thickness of the nozzle related to diameter.
The only reason there would be more than 3 exposures was if there was insufficient access to achieve T271.2 (b)1 or 2.
Then T271.2 (b) 3 requires additional radiographs.
Without knowing the available access to the joint in question it is impossible to answer.
Is there 360 degree access around the joint ?
Regards,
Shane

 

[ElCidCampeador]

Is there 360 degree access around the joint ?

Access is complete.
1" pipe is welded 1 side to a WN flange and 1 side to a reduction tee 3x3x1". Other strange thing is that weld to reduction tee has 4 exposures, but with WN flange N°8...

 

[XL83NL]

Another strange thing is that a 3x3x1 tee is not a B16.9 tee as it isnt listed in B16.9.

 

[ElCidCampeador]

Another strange thing is that a 3x3x1 tee is not a B16.9 tee as it isnt listed in B16.9.

Let the problem of exposures be the strangest thing...for now

 

[DekDee]

If you are paying the NDT company per weld - they can take as many shots as they want, no cost to you.
If you are paying per shot you need them to justify why - and the answer given in your OP is not acceptable.
Regards,
Shane

 

[ElCidCampeador]

If you are paying per shot you need them to justify why - and the answer given in your OP is not acceptable.

I agree with you, but I also asked my AI and he said the same thing, it could depend on thickness...

 

[DekDee]

As an ex-radiographer that is what I am struggling with - thickness ?.
If you can achieve required density and required sensitivity from 1 x shot then you can perform an additional 2 x shots and be code compliant.
Why an additional 5 x shots are required ?
Cheers,
Shane

 

[ElCidCampeador]

These are the joints:

 

[JR97]

The thickness versus diameter affects the change in density on the radiograph from center to end. If there is a heavy wall, small diameter weld they were probably unable to hold the 2.0 - 4.0 density requirement across the whole length of zone requiring more, shorter zones. Kudoes to the NDE house for taking the time to check things instead of blindly shooting 3 shots and you get what you get.

 

[DekDee]

JR97
Your comment is correct but it still doesn't explain why 4 shots on one and 8 shots on another.
a 1"XXS is 33.4 mm OD
Subtract 2 x WT (9.09 mm) and you have approx 15 mm.
Whether it is DWDI or Superimposed you will still be looking at both walls so 30 mm is the viewing zone per shot.
4 x 30 mm = 120 mm
Circumference of a 1" pipe is 105 mm
Full coverage of the weld is achieved with 4 x shots

 

[ElCidCampeador]

Method used: Superimposed.