Field Measurements 1

[SteelPE]

How do you determine the thickness of HSS squares and rounds in the field? Is there a way to estimate the thickness based upon field measurements, or is this something you would need an ultrasonic thickness gauge for?

Also, has anyone used an ultrasonic thickness guage for such measurements in the past? What kind of results should you expect with regards for accuracy and tolerances from the mill?

 

[gte447f]

I have used an ultrasonic thickness gauge once before to measure the thickness of some HHS columns in an existing building. It was great. It has been several years ago, but if memory serves, it seemed to give repeatable measurements on the same column within a few 1/100's of an inch. I don't recall doing any testing on known thicknesses to verify the accuracy, but I used the results for design checks for the HSS.

I wish I had one of these devices. The one I used was a loaner from another consultant on the project, and I had to return it to them after. Have you shopped around for one of these devices? Any suggestions for where to get one and how much $$$?

 

[gte447f]

I meant to add that I am not aware of any other way to reliably estimate the thickness based on outside dimensions of HSS. There is supposedly a rough correlation between wall thickness and corner radius (r=2t maybe off of memory? )for square and rectangular HSS, so you could maybe use a framing square to measure the corner radius and use that measurement to estimate wall thickness, but I wouldn't imagine that the correlation is reliable enough for design due to mill variation.

 

[jayrod12]

If you can accurately enough determine the radius of the corner you can approximate squares. The radius is 1.5 to 2 times the thickness.

 

[SteelPE]

Jayrod,

I was thinking about measuring the radius, but getting an accurate measurement for an item that can vary 1/16" would be very difficult.

I did purchase a ultrasonic thickness gauge..... I didn't spend a lot of money. I was sick of not knowing what the thicknesses of existing columns were. I bought a calibration block.... at is appears to be dead on to off a few thousands of an inch. I then went to measure some TS columns I have in my basement.... they are suppose to be 1/4" thick.... but I was getting readings of 0.28 to 0.3. So I am not sure how accurate it is going to be. Now, the steel columns came from an old fabricator I used to work with, and it is possible they just upsized the columns based upon what they had that was available. I measured through the primer and at a location where I sanded off the primer.... both within a few thousands of an inch difference.

I also measured the flanges of a W8x58 and W8x67 that I also have in my basement. I measured those through the primer.... and those were a little closer to what you would expect.

With rolling tolerances. I am just not sure what to expect for results from field measruements. I know the following:

Hss thickeness +/- 10%
TS thickness +/-10%

I also don't know if it's a good meter or not (probably not that good as it's from China).... but it did work on the calibration block (I haven't measured the block with my micrometer).

I guess it's about as good as I can get without cutting a coupon out of the column. I would just have to estimate the size based upon my measurements.

 

[Ron247]

The ultrasonics I have used were pretty close. Remember the mill tolerance combined with the machine accuracy has to be accounted for. I think really old tube and pipe had worse tolerance than more modern manufacturing

 

[CrabbyT]

If you have access to a 3D printer, you could try creating and printing a radius gauge.

 

[robyengIT]

what about a digital external small radius gauge ?

 

[SteelPE]

I’m not sure about radius gauges. Also, those will not help with round members.

 

[KootK]

Another, ever so slightly destructive option:

1) Measure the outside dimension of the HSS. Call this dimension A

2) Drill a small diameter hole in one face of the HSS. Perhaps not easy for thicker pieces.

3) Stick something in the hole until it hits the inside face of the opposite wall. Call this dimension B.

4) t = A - B

Do this at the bottom and call it a new weep hole.

HELP! I'd like your help with a thread that I was forced to move to the business issues section where it will surely be seen by next to nobody that matters to me:

http://www.eng-tips.com/viewthread.cfm?qid=456235

 

[BUGGAR]

My engine guy has a ultrasonic meter for measuring cylinder wall thickness. I think less than US$200. It has a scan feature that helps "smooth" instrument tolerances.

 

[EdStainless]

I have used Dakota UT tools in the past and liked them.
New they are mid-range price, from $1k-2K depending on features.
I am sure that you can find them our there used.
Look for suppliers of NDT equipment.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[Ron]

I use an ultrasonic thickness gage. The one I have was about $1500 I believe. Not sure I would rely on one that costs $200, though you can certainly calibrate it with a small piece of steel and a micrometer.


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[dold]

I'm not suggesting this as a solution for OP, but could one measure this based on the resonance of the tube? I.e., hit it with a hammer and listen/record/measure the sound it makes. I'd imagine the only way you could do this would be to build a library of sounds/frequencies for a full set of sections, then compare the waveforms. I suspect ultrasonic instruments work on a different principle? Certainly this would not be a reliable way of doing this... Would the stress in the member change the sound?

 

[Ron247]

Would length change the sound?

 

[dold]

Ron, I'd think so. I was thinking more of how the web would vibrate locally between the two flanges. Obviously this is a gross oversimplification. Like knocking on it with your knuckle and look at the radius you can get a 'feel' for the wall thickness. "This is closer to 3/16 than 3/8"

 

[MIStructE_IRE]

Why complicate it so much? Drill and measure.

 

[Tomfh]

Ultrasonic testers send ultrasonic pulse and listen for the echo. The pulse bounces off the inside face (the back wall). Longer delay = thicker piece.

 

[kingnero]

Where I come from, destructive testing is not allowed in inspection. Certainly not where the members are coated.

Radii of corners are not conclusive, big difference in cold vs. hot rolled members, and not useable on round HSS.

Cheap ultrasonic thickness testers work remarkably well. Even on coated or hot zinc dipped profiles. you don't need 1/1000" accuracy, just enough to get to to the catalog's closest profile. Carry some (home-cut/milled pieces of profiles) calibration pieces in most common thicknesses that you work with/expect, and call it a day.

Iy you need 1/1000" accuracy, shell out for a quality german or US piece of equipment.

 

[SteelPE]

kingnero,

That is basically what I was thinking about the process. I have a also purchased a calibration block with the ultrasonic meter. The meter isn't 100% accurate, but within +/-.005 inches of what it is suppose to be... which should be enough for structural steel (I have yet to put a mic on the calibration block).

Another aspect of this process is what to expect from real word results. We know they don't mill to +/-.005 inches. Also, on square or rectangular HSS's, you need to make sure you don't hit the seam weld (so you would need to measure on 2 faces and take the smaller of the two). Drilling a hold would be great, but again, you need to make sure you don't hit the seam weld.

A $1,000 meter would be nice, but I'm not sure if it would be anymore accurate than what I need..... and I am not even sure how useful it is going to be. We are talking about a piece of equipment I am going to use 2x/year.