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Tangential Radiography of 16" pipe 1

mariolucas75

mariolucas75

Civil/Environmental
Sep 21, 2010
105
What are pros and cons using Selenium for tangential radiography of NPS 16 " pipes typical thickness 9-12 mm range to find an internal or external corrosion () ?
Since selenium has a lower penetration ability ~ 25mm and the beam may travel along the chord inside the thickness which may have a length more 25 mm ... may it mean that beam will not make its way through onto the film ?


Thank you so much.
 
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what's wrong with a UT probe?

Never heard of using radiography to determine corrosion before.

but you're prob better looking in the corrosion or QA forum.
 
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It has a corrosion deposit large enough 150 mm wide spot on pipe 30mm high
 
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The typical application of tangential radiography is for external corrosion, particularly CUI. You aren't looking for penetration of the steel, only the insulation around the pipe. This gives you a tangential view of the pipe surface, from which you can see CUI damage due to the expansive characteristics of iron oxide compared to steel. It is typical to perform several tangential views, say 3,6, and 9 o'clock, on the pipe to characterize the corroded area.

I've not heard of tangential radiography for internal corrosion.
 
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This article here seems to compare a few sources:

https://www.ndt.net/article/apcndt2006/papers/12.pdf

If you are specifically looking for general internal corrosion/erosion patterns where the order of magnitude is important, then you'd be better off asking a radiographic testing contractor.

I never used Selenium for radiography in the field, but the results for IR-192 is a standard one. So it really depends on what level of detail you need to get.
 
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RT has been used to find out internal pits in water wall tubes of boilers.
So, why not here?
Tangential shots with Se could be okay but why cost save on RT (compared to more number of shots with Ir)?
 
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The penetrated thickness is around 115 mm. For Se75, ISO 20769-1 recommends a maximum penetrated thickness of 55 mm for a basic technique, and 40 mm for an enhanced technique. Digital techniques may extend the recommended penetrated thickness. As to whether such techniques could give the necessary image quality, that would be down to experimentation.

 
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SJones said:
The penetrated thickness is around 115 mm. For Se75, ISO 20769-1 recommends a maximum penetrated thickness of 55 mm for a basic technique, and 40 mm for an enhanced technique. Digital techniques may extend the recommended penetrated thickness. As to whether such techniques could give the necessary image quality, that would be down to experimentation.

Click to expand...
Steve - where does the 115 mm penetrated thickness come from ?
OP has stated WT as 9-12 mm so penetrated thickness would be 18-24 mm (DWSI) ???
Or am I missing something here ?
 
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Dhurjati Sen said:
RT has been used to find out internal pits in water wall tubes of boilers.
So, why not here?
Tangential shots with Se could be okay but why cost save on RT (compared to more number of shots with Ir)?
Click to expand...
We did this many years ago.
Took a sample ( exact thickness and diameter) boiler tube and machined multiple slots at increasing depths on the internal surface.
Radiographed that tube as a reference graph.
After radiography of suspect tubes the density of any internal corrosion was compared with the densities of the reference graph to give an approximate depth of corrosion.
Obviously only approximate but it gave the engineers a pretty good idea of what was fine and what needed more in depth examination.
 
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@DekDee - the technique under discussion is tangential. The 115 mm comes from the formula in ISO 20769-1, i.e along the pipe wall, as opposed to straight through.
 
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