Any used cheaper ultrasonic metal thickness testers?

[MoreWellie]

I am thinking of this style of thing

https://www.ebay.co.uk/itm/GM100-Di...338101?hash=item3f875387f5:g:g1UAAOSwNd9ZwLRW

are they any use on compressor tanks?

would it also be useful on chassis? double skinned bodywork?

 

[500e]

Have been reading a bit about these machines confusing, how do they tell if you are looking at metal with rust on the inside or a void between 2 plates,There are a lot of NDT units out there, looking for a simple explanation of the different types & their drawbacks & good points, so much to learn & little time .

 

[chriskelland]

Been looking for something like this. Need to measure wasting on steel boiler plate about 1/4 inch thick. I didn't realise prices had come down that much. Anyone used anything like that?

Chris.

 

[timgunn1962]

I've used one similar (around £100 on ebay a couple or 3 years ago) on waste gas pipework to check for corrosion (condensate at the bottom eating them away from the inside). I'd not want to consider it as definitive or precise, but it will certainly show up significant thinning.

I always took 3 measurements on the top to get a "normal" reading, then measure on the bottom. Top readings were generally consistent within 0.2mm and when the bottom readings were significantly lower and we changed pipes or borescoped them, they were clearly corroded.

I've used it on compressor receivers too, but we have timed autodrains and life the (reciprocating, 3 HP, 150L) compressors at 5 years, so I've never seen any reduction in measured thickness on them.

 

[500e]

Do you still have it ? if so will it measure voids say if 2 metal parts were glued together & there is a dis-bond or air gap in the bonding material, not really looking for a specific measurement + - just as a first line of testing

 

[MoreWellie]

I have bought one to try and will do a review as soon as I can

I can say that it won't measure voids or at least I don't think so. You basically set the unit to the velocity of the signal in the medium and it then looks for echoes at the point where the medium changes so if there is a gap then you get an echo from it

It only just arrived but I have already worked out you need a smooth surface to work against otherwise the air gaps interfere with the signal. In other words if the surface you are putting the probe against is rusty and pitted you need to grind it smooth first

 

[500e]

I have noticed some of the expensive units use jell as a contact agent just like baby scans
KY jell should do
Your looking to get an airtight seal between transducer & item, is the instruction book any good ?

 

[MoreWellie]

I am using some ultrasound gel as that was quite cheap and if you really want to save money then some forums have instructions on how to make it yourself

Without the gel I couldn't seem to get a reading but that was a very quick try as it only arrived yesterday

The instruction booklet also suggests machine oil for very smooth surfaces but I haven't tried that

The instructions had about half a dozen pages and seem to tell you what you need to know and most of it is pretty good but there are a few bits that have lost something in translation

 

[Shox Dr]

Any updates

 

[chriskelland]

Going to Bristol ME show today, will see what is about. My ME club has to get to grips with checking steel boilers for wastage. Large boilers like traction engines usually have traps so you can see inside but our small 7 1/4 gauge locos are too small to have them. Spent the last few weeks looking at specs and they seem to be mostly the same, apart from two types. Acoustic and magnetic coupled. I'll get back once I know more, could be a while though.

 

[MoreWellie]

Any updates

Unfortunately work gets in the way of playing with new toys.

The unit I have is labelled Benetech GM100 with the 5Mhz probe. It's stated measuring range is 1.2mm to 225mm and it seems reasonable at the lower end but the accuracy depends on knowing the velocity of the 5mhz signal in the substance being measured and they give different velocities for Iron/Steel, Steel 4330 (mild) and Steel 330. My tests were at 5,900 m/s which is the given Iron/Steel velocity

I tested on sheet steel which the vernier told me is 1.18mm and the display read 1.1mm (only 1 decimal place available). I tried a piece of cheap steel plate that came with a chinese press and the vernier said 23.44mm the display read 23.6mm

I have used it to test the compressor and found that the results were repeatable and showed minor variation between the bottom of the tank (3.6mm to 3.7mm) and up the sides (3.9mm) Both these readings are lower than expected as there is a manufacture plate on the tank which tells me that it was made out of 3/16 (4.76mm). I will see what I get when I remove some of the paint (at least 3 layers)

A new piece of galvanised steel read 2.3mm when the vernier said 2.11mm

All of the above were using the ultrasound gel and I haven't tried anything else yet

I really wanted to try some steel that was flat on the test side and rusty/blowing on the reverse but haven't found any yet. I'll update this when I do find some

 

[MoreWellie]

One thing I should mention is the instructions say to calibrate the unit using the metal button on the front. Mine has this and also came with a separate test piece which the vernier tells me is 3.99mm if I calibrate with the built in button the unit under reads slightly as in it tells me the separate test piece is 3.8mm

so basically use the separate test piece to calibrate and if you don't have one find a separate piece of 4.0mm steel to calibrate with