Non-destructive strength tests 1

[Tuckabag]

Are there any non-destructive tests available for determining a materials yield strength and UTS?
I can't imagine there is, however I am not overly familiar with this type of testing.
We have a client who has a bunch of equipment that they have asked us to perform calculations on for determining compliance with AS1210-2010, however the equipment in question is pretty old and traceability for materials used is non-existent.
I would imagine that all forms of strength testing must be destructive in order to find the yield/UTS, obviously destructive tests on equipment rather than raw materials is not going to cut it.
Appreciate any feedback on if there are non-destructive test methods out there for this.
Thanks!

 

[GregLocock]

Vickers hardness machines are non destructive and may help with UTS.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[EdStainless]

There are a number of techniques that use micro indenters that are inserted and then moved. They leave very small amounts of damage.

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P.E. Metallurgy, Plymouth Tube

 

[dhengr]

Tuckabag:
Your first steps at analysis and calcs. don’t really need this info. Do a good analysis to start to see where the critical locations are, and what the stress are at those locations. Does inspecting these locations indicate any yielding or distress, due to the types of loads the system has already seen. This indicates a lower bound for Fy. You know it is steel or some such, and you are looking for stress and stress levels, which will finally be checked against Fy or Fult, on down the line. Once you know the max. stress locations, and the low stress locations, this might indicate some locations where you could safely take some samples of the various materials, for a regular testing program for Fy and Fult. This testing can give you tensile strengths and also chemistry which will allow a good testing lab to hone in on the mat’l. specs. from the correct era. What was the basic mat’l. spec. for each type of mat’l. from the era when the equip. was built, as a lower bound? I would still look a little deeper for detailed drawings and shop drawings of the equip. or structure: the plant maintenance dept. might have some; the original purchase file, if it still exists; who manufactured it, any name plates, part numbers, etc. The first time you ask this question everyone shrugs their shoulders, they don’t want the extra work of looking, and they wouldn’t know were to start looking, you might have to suggest places to look. They know the plans aren’t hanging on the wall in front of their desks. It always blows my mind that people will spend millions of dollars for something, and then they don’t keep some files with the important basic info. on the equip. Experience should teach that at some point they will want to modify the equip. or add new equip. loads to the structure, etc. Then, they can’t imagine that we can’t guess at this kind of info. and give them the answers they wish for.

 

[Tuckabag]

Thanks for the feedback so far.
To clarify a little further, the items in question are very small, portable pressure vessels up to 1,000cc maximum volume.
We know the base material of construction is 316SS, however we do not know the exact standard the raw stock was manufactured to, therefore yield/UTS is unknown.
The vessels are stamped with MAOP's and we have routinely proof tested these to 1.5x MAOP, so we know they are fit for service, however in order to register the design we must provide calculations to show that the vessel is indeed suitable for use up to the stated MAOP.

I did some quick research on the portable Vickers machines, my current understanding is that the portable units are generally used to verify that hardness is below XXX, but they are not normally used (nor accurate enough) to provide definitive hardness readings that can then be derived into strength. This is more the domain of a lab type Vickers device that would need a section of material to work with. Is that correct?

 

[metengr]

I would not recommend any hardness testing because you are dealing with austenitic stainless steel, versus carbon or low alloy steel. Instead, go back to the original code of construction and use the specified minimum mechanical property values for one of the 316 ss plate or pipe material. Select the most conservative minimum values or allowable stress values and go from there.

 

[Tuckabag]

Thanks Metengr.
Problem being we dont have an original code of construction, only very basic GA drawings.
The issue for us is ensuring that whatever material code we decide to use for the calcs does not exceed the actual yield/tensile.

 

[BrianE22]

Are there legs or anything else you could cut off to use as specimen for a tensile test?

 

[EdStainless]

The min strength for these grades hasn't changed in the specs for many decades.
If you used todays values for 316L do the numbers work?

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P.E. Metallurgy, Plymouth Tube

 

[metengr]

It seems as though you are trying to back-fit an existing PV, which was designed and fabricated with no stated construction code. Seems rather risky to me especially if you have pressure retaining welds. Have these been subject to RT or UT? Have you verified wall thickness with UT surveys? If one of these goes kaboom your organization's name will be on this thing.

 

[JStephen]

Be very cautious about what you do on something like that. A lot of the standards are set up to describe how something is to be made. If you have the finished product before you, you can test it to your heart's content, but still can't certify that the construction/fabrication process met that standard. On a typical vessel, this might come up on materials test results, on weld procedures, welder certifications, etc. You might be able to show that the product is safe, is adequate, etc., but still can't certify that it was built in a certain way.

If the owner is expecting to put nameplates on them certifying compliance with that standard, look in the standard and see what the requirements for installing a nameplate are. If the owner wants to certify them for some government agency, check and see what the requirements of that agency are.

 

[rb1957]

I think met makes good points ... verify the PV is what you think it is; welds particularly.

so now a pressure test isn't enough, and we're using FEM to validate the test (which validates the FEM ?).

I think Brian had a good idea too ... scavenge a test specimen from the PV. Could you remake a piece to use part of the PV as a test specimen.

I'd've thought hardness testing was reasonably accurate (conservative use the lowest in the range). Could you calibrate the testing by testing known coupons along with the PV specimens ?

another day in paradise, or is paradise one day closer ?

 

[dhengr]

Tuckabag:
I think you can find plenty of literature which suggests that hardness testing is a loose general indicator of Fult., for a number of material property reasons. But otherwise, it is a pretty poor indicator of the real (more accurate) Fult. What are the dimensions and thicknesses of the PVs, what working pressures, general construction, etc.? And, you regularly test them to (1.5)(MAOP). Do you have any out-of-service vessels which could be used to get some test samples from, or one you can sacrifice for the good of the effort? You should run a stress analysis on these vessels to determine the critical stress, locations and orientations, etc. Then strain gauge a few of these and test them to 1 and then to 1.5(MAOP) and see if you get reasonable and agreeable results. What stresses do you get and where are they w.r.t. typical Fy values? Run these tests with non-compressible fluids not a compressible gas, for obvious reasons. Having a good handle on the stresses in these vessels, you should be able to run this testing up to Fy, and you should see this on your gauge readouts, as a stop testing indicator. You are starting to have a value for the actual Fy, you probably don’t want to go beyond this point. I don’t know how you can get at Fult. without some tensile tests. In your reporting, be honest about your situation and what you can actually accomplish, without original design info. and mat’l. specs. etc., or actual mat’l. test samples, the wasting of a tank or two. Given the bad hand you’ve been dealt, putting a fair value of Fy, and testing to 1.5(MAOP) and getting stresses well below Fy, might be the best you can do, and report on. But, you don’t regularly operate at 1.5(MAOP) anyway, and you’ve got some years of good operating experience. So, admit it, explain the facts of the matter, and don’t assume any responsibility for things you can’t start to reasonably verify.

 

[racookpe1978]

QA me here.

Seems as if he were to hydrostatically test the PV's to 1.5 max allowed pressure, then they can be operated at 1.0 MAOP BECAUSE they passed the hydrostatic test. (Regardless of how strong the SS316 was when it was built the first time or the design basis the user is trying to verify now. ) If some design margin is now 2.15 assumed stress level or 2.05 or 2.25, that PV as a whole still passed the test at a greater pressure than it is expected to ever see in operation. Now, it is not good for any operating pressure over the MAOP, because it has not been up-rated.

 

[MintJulep]

Can't get there from here.

Sacrifice one to get the actual material properties and use those numbers.

How many tanks are you talking about?

I can't imagine a 1 liter tank costs more than US$ 1,000.

Is the cost of your time to do the calcs plus the cost of the lab work to get the material properties substantially less than buying new?

 

[rb1957]

I get it racook (I'm with you, the PV is shown good by test), but from the original post ...
"they have asked us to perform calculations on for determining compliance with AS1210-2010" ...
presumably not satisfied with successful testing ?

another day in paradise, or is paradise one day closer ?

 

[Tuckabag]

Appreciate all of the feedback, apologies for the delayed responses the time zone difference is killing me.

The reasoning behind the AS1210-2010 verification is that the customer requires OH&S design registration of these vessels to allow them to transport them full of hydrocarbons. We have chosen to verify against AS1210 as it is what we are familiar with and we use this standard when designing/registering our our cylinder/vessel designs.

There are no welds and we can quite easily determine wall thicknesses with the vessel disassembled.
I am happy to sacrifice 1x vessel for destructive testing, however with no material traceability there is no guarantee that they are all the same grade/strength material.

MintJulep hit the nail on the head, we are putting a case forward to the client re costs of testing/calcs/certification versus purchasing new units. At this stage the new vessels are looking like the winner.

The uncertainty of it all has me concerned, we aren't in the habit of putting our neck on the line based on assumptions (re material spec). Especially if those assumptions prove wrong and 800cc of hydrocarbons @ 3,000psi decides the exit the cylinder whilst an operator is using it.......