UT instead of X-Ray 2

[roca]

Morning
Where in ASME VIII Div 1 and 2 does it state (if indeed it does) that you can replace X-Ray with UT - (Ultrasonic Testing)?
These days on thickish plate (say 60 mm and above) it is usual to apply UT and maybe even TOFD (Time of Flight Defraction) to check plates / welds.
This is normally written into the client or engineering companies Pressure Vessel specification.
Thanks

 

[johnnymist2003]

Hi,

try UW-11. I don't think that you are permitted by code to simply substitute UT for RT. I'm no ndt expert, but as far as I know. UT and RT are used to complement each other and will, in some cases, highlight different types of defects in the same welds (eg. UT may pick up lack of sidewall fusion which may not be detected by RT). Also, RT would provide a permanent record of defects, wheras UT may not. Added to this is the fact that you tend to rely on the skill of the UT technician to determine the acceptability / or not, of the UT results, whereas for RT you have specific guidelines in the code.

Hope this helps.

John

 

[bmoorthy]

UT can be done instead of RT only if RT is not possible.

For plates ove 3" thick you may use (Use Gamma ray instead of X ray)Cobalt Source for radiography. Iridium source has given satisfactory sensitivity even if thickness was 65mm.

UT may compliment but not exclude radiograrhy.

Ref UW 11, UW 51.

Further, the formula for thickness of the shell,Head etc(Internal Pressure) has joint effiency "e" and this is as per table UW 12. UW 12 refers to radiograpy not UT.

As regards detectatability of defects, UT is superior technique for detecting planer defects and RT is better in detecting voluminar defects.

 

[ctmfab]

See Code Case 2235 for UT in lieu of RT. This code case defines under what applications UT may be used in place of RT.

 

[deanc]

ctmfab is correct. CC2235-5 Talk to your AIA. Make sure the Jurisdiction will accept it.

 

[bmoorthy]

Can somebody please provide the extract of the code case 2235.

 

[gramya]

RT had been used since long as acceptable NDT for fabricated pressure vessels. UT was always used as complimentary technique to furthe investigate the defect sizes. The recent developments have brought UT at the forefront as the most reliable technique for defect evaluation. If you are aware about the fracture mechanics being used for defect acceptance and life assessment of the vessels, the analysis may not be possible at all unless you use UT testing to determine the full geometry of the defect.
Just think of a planar defect oriented parallel to the surface of the plate, like laminations. Will use of RT can identify the defect? How to determine the length and then the width of a planar defect? It may not be possible with RT. How to assess the depth of location of the defect in the wall thickness or the welds? RT will not give the clue. Hence the UT is now preferred by any inspector who is involve in assessing the life and certifying for the safety of the vessel.

Narendra K. Roy
Gramya Research Analysis Institute,
PO box 4016, Vadodara 390015, India
Website:

http://www.gramya.com

;

http://www.charismaglobal.com

 

[AsifUppal]

Hi,
I just want to share an information with johnnymist2003 as he mentioned the UT may not keep permanent record of defects. Modern UT thickness/ flaw detectors keep permanent record of the defect waveform by saving directly in the gauge or by saving in computer by a 2-way serial port. I have worked with one named PANAMETRICS 36DL+.
Secondly i have heard a phrase that,"EACH NDT TECHNIQUE SUPPLIMENTS OHTERS BUT CANNOT REPLACE."



Asif a uppal
Jr. Design Engineer
Sheikhupura,Pakistan.

 

[roca]

Thanks to all your replies. However I would like to know the situation in the US. What happens when you have a heavy wall vessel - say 8" thick (200 mm) or more? Do you use X-Ray? Would this be allowed?
RT provides reasonably definitive results for lower thicknesses. For higher thicknesses, RT films lose definition?
Depending on the power source (isothope) available, the range of acceptable definition increases as the power increases. However, in most countries, there is a limit to the power you can use. In Australia, you can only release sufficient power to X-ray up to 60 mm thick in 12 hours. In some countries, you can X-ray up to 150 mm. The limit adopted in Australia (and in most European countries) is 40-50 mm.
In Europe and Australia the strength of the X-Ray power source is obviously limited for safety reasons.
The Oz PV Code AS 1210 is more specific than ASME VIII.
Table 7.1 of AS 4037 (the NDT section of AS 1210) specifies the following:
a) t <= 10 mm, use RT Normal intensity.
b) 10 < t < 32 mm, use RT Normal intensity OR UT + MPI
c) 32 < t < 60 mm, use RT High intensity OR UT + MPI
d) t > 60 mm, use UT + MPI (Preferred) or RT High Intensity