mictrik
Contributor
Nor should it they are entitled to their own rules. How ever I would not be surprised if their storage banks are comprised of even older cylinders. But again it's their rules.
Old steels denied fills due to store "policy"
- Thread starter Ana
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I applaud and respect you for doing so, the fact remains you shouldn't have to repeat to confirm. And in the real world VIs would NEVER be used to confirm an eddy current inspection. Pointless. (A testament to how poor the Visual Inspection equipment is)
In the real world the procedure [for any type of NDT test], should be written in such a way that fault (we call them discontinuity) indications are clearly and easily discernible. There should be easy distinction between the signal off a natural crack verses that of mechanical damage.
This is why [on real equipment] Timebase display is only used to find the clock position of the defect within the bore, and phase display is used to interpret the indication. A crack will have a different shape as well as being shown travelling in a different clock position - mechanical damage is normally +45 degrees from a crack in Aluminium
Visual plus did a good job of selling a piece of junk. Even I look at their example signal indications and say WTF. I'm sure they provide pretty but generally meaningless prints
Where as defecting indication on phase display would look like the picture below (Phase signal on the right with classic "reversed 6" indication and "W" signal on Timbase to left - this'll be from a rotor at +5000 rpm
Caveat - it's a perfect reference block indication although real life component have the same signal there is often a bit more noise on the signal
What is your recommendation for inspecting SLCs in suspect 6351 tanks?
SLC is nothing special (well the mechanism is) the result is just a tight fatigue crack in the bore of a hole. It's not difficult like say trying to find a 015" crack under a rivet head in the 3rd layer down.
If it were me, I'd be running a rotary Eddy Current test. Probe in, out and done, should take 10 seconds or less. It's only Aluminum, so either a 500 KHz or 1 MHz probe.
I haven't taught the theory since 2000, so I might be slightly rusty on the fine details (can't remember filter setting off the top of my head - but most bits of kit have default starter settings).
Rotary Eddy Current is fast and repeatable - we used to have an automated machine that would examine each drilled hole in a wing spar (because doing it manually would be very dull) a simple gated alarm on the signal and hey presto. I've walk down the flight line (on a cold windy night) doing bolt hole inspections on 767 wing pylons. No drama 1 min per pylon. If you got a fault indication then you'd identify location and depth for them to open the hole up and hopefully remove the defect before you re scanned.
The reason the Vis plus is useless is because it's cheap. It has poor signal processing, crappy filters and awful software code. Thats why its rotary probe runs at a few 100 RPM not 5000-6000. It's too small to be a door stop and not heavy enough to hurt if you throw it at someone. It's pointless.
Assuming a decent eddy current tester is out of reach (financially) I'd use a hand held probe. Place the tank on it's side and roll it along a bench 1 complete turn resting the probe on the threads. Move the probe in 0.020" and repeat
As long as you have a written procedure to follow (unless you have a Level II or III certified engineer) it's not hard. The equipment settings should allow an easy display or a signal showing the difference between cracks and mechanical damage, care needs to be taken in case there is small corrosion pits which can cause a different signal response or you can get a compound response (corrosion and crack or score)
It all depends on how many tanks you're inspecting as to your investment.
There's also no rational reason why you can't carry out an Eddy current check on all Ali tanks (non 6351) Ignore the BS about false positives - that's down to the vis plus being junk.
Ali is Ali in that apart from a few instances the alloys all have the same conductivity (Eddy current speaking) so the test settings and procedure would remain the same.
Ali cladding and having been subjected to excess heat will cause issues - but if you get a weird reading you reject because it's clearly not right
Steel on the other hand isn't you get huge variances between different alloys having differing magnetic influences along with heat treatments and different coatings such as Cad plate or galvanising all having influences.
With steel you have a test block that is of the same alloy, same heat treatments and same surface treatments as a baseline reference for setup
captain
Contributor
Take a steel tank to an good automotive machine shop and have them magnaflux it.
Because then you have to fully decontaminate all the oil based residues from the magnetic particle inspection, and if you had laps or folds in the threads you'd never be sure of getting it out.
I do so enjoy people who throw suggested methods about whilst having zero experience in their actual use.
A bit like design engineers of old suggesting Magnetic particle inspection of Aluminum components - that used to make me smile daily too.
I understand your point but... Are the oils or penetrants used different than other oils? Is there something that makes them more adhesive and harder to clean than other oily contaminates that might get in a tank so that a normal oxygen cleaning process wouldn't remove them? Not trying to be an ass, I'm genuinely curious and don't know. Thanks
mictrik
Contributor
I miss those golden guides. I still have a few but sadly not SCUBA.So, where is this Florida dive shop I should be getting my steel twin 38's with original hydro dates of 1941 and 1942, respectively, filled? Just because one if them was manufactured pre- Pearl Harbor doesn't make 'em unfillable.
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mictrik
Contributor
I find that most older cylinders like these go through long periods of inactivity. People get into SCUBA stop and have a cylinder in the closet for many years. So few are loaded with hydro stamps. Now cylinders for welding and other uses are more likely to have seen many hydros and it stands to reason more fill cycles.
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