How wide of a PT Beam can be X-Rayed?

[klecm]

Hi All - I'm having to retrofit an existing expansion joint - was hoping to add a series of steel corbels below for support. Trouble is, corbels would be attached to a pretty serious PT beam. I contacted an x-ray sub to scan the beam - they informed me that they are unable to perform the work as it is too wide (4'-0"). They can only scan up sections up to 30" deep. Is this typical? Apparently they apply the film on one side of the beam, and the machine on the other face and they can only be 30" apart max. This is my first time setting up x-ray personally so I'm not sure if I should try to find a sub with a more powerful machine. Thanks!

 

[Ingenuity]

For x-ray, depending on the isotope used, the depth of penetration may be limited. Also have safety issues with x-ray too.

But, most scanning these day uses GPR (sub-surface penetrating radar) and access to both side is NOT required. Scan the face of the PT beam and hopefully detect the tendons (and rebar) to the drilling depth you require.

The frequency of the GPR antenna will determine the depth and clarify of the signal.

However, not all GPR technicians are created equal - make sure the one you select that has relevant experience with such width/thickness.

 

[LittleWheels]

There is betatron radiography (using a cathode ray 'gun') and gammography (radioactive source), both X-ray methods but quite different processes. A fair few years ago, I did betatron radiography through 36" thick RC bridge decks in the UK but it took >20 minute exposure times, sensitive medical-grade film, the most powerful mobile betatron sources outside of the US military, lots of lead shielding and pretty large exclusion zones. Interpretation of the results was not a trivial exercise. No doubt techniques have improved massively since then.

Depending on sufficiently wide reinforcement spacing between the accessible surface and the tendons you want to know about, GPR is likely to be the better bet. As per Ingenuity, GPR results are very dependent on the person operating the equipment and interpreting the results.

 

[Ron]

Typically for that type of section a strong radioactive isotope is used. That's too thick for Iridium 192, the most common isotope for radiography. Cobalt 60 might do this one, but the exposure time would be relatively long. The generally accepted limitations of Ir192 and Cobalt60 are 12 and 36 inches respectively. I have successfully done 20 inch thick concrete sections with Ir192, but the exposure time was a couple of hours (Lift station restoration in Key West, FL...late 70's)