Ndt

[fesm_ndt]

I thought as many people are rebuilding vehicles from nothing I would post some info on NDT (Non Destructive Testing) and welding.

 

NDT is basically what is used to look for cracks. PT (Penetrant Testing) is the most simple form of NDT where a dye is applied to the component and it is allowed to soak in. The excess surface dye is removed and a developer is applied to soak the dye back out.

 

The defect has to be open to the surface. Kits are readily available but of interest if you soak something in oil, clean it and apply chalk dust you get the same result (albeit not as sensitive).

 

Anyway, I hope this subject is of some use

[robin craig]

As an alternative to the spray can for crack detection a poor mans alternative is using dyed diesel fuel. Here ours is red, so if using soap stone dust that turns pink when there is a crack.

 

Robin

[fesm_ndt]

Yep. The history of PT was that supposedly they used to coat the rail wheels in the store with oil to stop them going rusty.

 

The dust would collect and later they would see lines in the dust.

 

Another NDT method from railyards was/is hammer testing:

 

- hit it with a hammer if it rings (it's ok) if it doesn't (it's not). Still used on aircraft composites and testing bolts to be tight.

 

- hit it with a hammer, if it falls off (it's not ok). Self explanatory but often overlooked e.g. I often get asked to perform all types of fancy NDT on certain components. On several occasions I have said to them hit it with a hammer and if it falls off it needs replacing.

[fesm_ndt]

Prompted by some points raised in another post, I thought I better follow up with more on NDT, crack finding

 

Magnetic Testing (MT) or Magnetic Particle Inspection (MPI) is the other most common form of NDT. Used for inspecting ferromagnetic materials

 

The principle is fairly simple:

 

 

- Magnetizing an area to be examined

- Applying ferromagnetic particles to the surface

- Particles form patterns on surface / discontinuities cause distortions in nominal magnetic field.

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Oddly enough I have to go to the UK in a few weeks so if anyone is interested in NDT, inspection, welding and welding defects I could organise a spiel in Cambridge at TWI

 

 

 

 

 

[pinzmeister]

Hi Mike. Will you be in the UK long enough for a trip up to Sheffield ? It would be good to meet up and compare notes, my P93 is allmost ready to fire up. cheers Nigel.

[cosrec]

HGV tests the man goes around with toffee hammer taping wheel nuts and chassis bolts test for tightness but they also some times tap brakedrums when brakes are of if they dont ring chances are they are cracked

[fesm_ndt]

HGV tests the man goes around with toffee hammer taping wheel nuts and chassis bolts test for tightness but they also some times tap brakedrums when brakes are of if they dont ring chances are they are cracked

 

thats funny....... they used to test train rims that way and there is a famous story about a senior inspector who they found out very late that he was tone deaf. But it is true if one bit rings and the other don't then it is a quick check, just judging it can be a fine line.

 

There are other methods, especially used on aircraft that use small tap hammers looking for disbonds and electronic testers looking at resonance frequencies.

[fesm_ndt]

Hi Mike. Will you be in the UK long enough for a trip up to Sheffield ? It would be good to meet up and compare notes, my P93 is allmost ready to fire up. cheers Nigel.

 

We got an office in Sheffield. Would be a good trip. I haven't got my schedule as yet but I know it is urgent I go to the UK as soon as possible as I just rejoined TWI as off Monday.