NDT Bridge surface

[Jamesliska]

Hi All

I have a problem where a trapezoidal channel has been welded to the underside of a bridge surface, the upper surface has a layer of tar that cannot be removed. We have been asked to carry out a NDT on the area where the surface meets the channel on the inside. See attached
Does anyone know of an ultrasonic method of testing this area, we have 150 metres to test.

Thanks in advance

James Maclennan

 

[unclesyd]

In the area marked for testing what are you looking for, cracking?

If it's cracking do you expect through cracks?

 

[Jamesliska]

it is cracking we are expecting, we would expect these cracks through the whole bridge surface but cannot remove the tar surface to check from the top.

 

[unclesyd]

I would get with an NDT company and have their UT level III or II look at the actual area to be tested. Your thickness of the plate to be tested is approaching being too thin. It might take some preparation of the plate outside the area of interest to be able to see the area of anticipated cracking.

 

[arunmrao]

Seeing is believing. Do not accept or assume the structure is healthy. Last year, I inspected a bridge on river Scioto in Columbus. There was a large hole over 3' in diameter. however,it was covered with tar/bitumen on the top surface. There were several cracks. A barge was stationed under the bridge and after thorough cleaning the defects were noticed.Vehicles were plying over the bridge at a slow speed. The rot had set in.

The contractor was awarded a minor contract for 15 days,but eventually turned out to be over 6 months and he was not compensated.

 

[Metalguy]

So why can't the tar be removed? Have you considered RT for this job?

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[rustbuster]

Shear wave UT, Low frequncy electromatic technique (LFET), and eddy current (surface scan method) will all work in my opinion. As unclesyd advised, contact a local NDE service provider.

 

[Ron]

Is the trapezoidal area large enough for a person to crawl through? If not, can it be pressurized? If you can pressurize the section, you can then soap test the edge interface to see if you have leaks. If you do, you likely have weld anomalies, cracks or discontinuous sections.

 

[Jamesliska]

The Tar is to be removed next year and the areas can be fully tested from the surface, what we are trying to do is plan our resources as we have a narrow time frame to carry out repairs when the tar is removed.
Unfortunately the trapezoidal section is not large enough for an inspector to crawl through, I will discuss rustbuster's suggestions with our NDT contractor.
Thanks for the heads up unclesyd, we will not commit ourselves to repair work without qualifying the quantities.