3D printing 2

[pxp]

Did anybody tried to install a spare part which has been manufactured with 3D printing. If the answer is yes, how did you managed to certify the material for printing. I'm not speaking about SR item.

 

[MikeHalloran]

I can't think of an additive manufacture technology that I would want to see used for replacement of a 'real' part in a nuclear installation.

Granted, 3D Printing and such has come a long way in ~20 years, but I still think of it as mostly for 'dog and pony shows'.

Just my opinion.

Note that we have a 3D Printing forum:
3D Printers and Materials Forum
(663 members)
forum1536

Ask your question there. Better, browse it a bit, and judge for yourself if any of the subject technologies are ready for prime time, much less certification.



Mike Halloran
Pembroke Pines, FL, USA

 

[vpl]

Short answer: No, I've never tried, or heard of anyone trying.

But, if it's not a safety-related (SR) item, why would you need to qualify the material? You can use whatever you want, including stuff from the local hardware store. It doesn't affect the nuclear side of the house. That's the whole meaning of SR versus nonSR.

(Mike there's a lot in a nuclear plant that doesn't affect the nuclear part ... everything from routine plumbing and lights up to the turbine generator. I really wouldn't care if someone used a 3d printer to replace a part in the locker room.)

Patricia Lougheed

A FAQ for you to consider: FAQ731-376
Translation assistance: forum1529

 

[racookpe1978]

The 3D printing concept relies on various ways of depositing metal (usually powder) from an "inkjet style" ejector at precise locations in 3D space above, behind, and inside of the "part".

Then the sintering and forming of the piece starts to actually "forge" the powder into continuous grains. And, sometimes, traditional forging and machining follows to get finishes and surface in tolerance. So, even after 3D "assembly" for parts, you'd have to qualify the forming/forging follow-on processes for SR items. A traditional cast part needs qualification for voids, overflows, mold failures and internal flow blockages or bad grain structure. It's just that the nuke industry grew up with traditional casting and forging methods, so its QA "thought" and laws are old - but their intent is valid for 3D printed material.

You could even consider the coated powder fuel inside their coatings and the cooling paths inside the original Navy core plates as the original 3D assembly process.

 

[pxp]

When I put the question to forum I didn't describe the purpose. My company started a pilot project to discover whether we are able to replace obsolete items with items made by 3D printing. When we started a project we were not familiar with 3D printing technology and material. Now we discovered that we are able to print some complicated forms, but we have a problem with our internal processes. According to 10CFR50 App. B we need to follow the rules how to manufacture a SR item. In case of NSR items according to regulations we don’t need to this. On the other hand our internal rules are more restrict and control of configuration requires that you can replace items like for like. In case of 3D printing we don’t know if the printed material has the same properties as forging or casting material. Task of my group is to define inspection plan for 3D printed item (Nondestructive tests, destructive tests,…). The final result should give management confidence that 3D printed item (NSR) is the same quality as manufactured by classical methods. My question is what inspections should I propose for inspection plan beside:
• Certificate of material powder for 3D printing,
• NDE inspection (UT, RT, VT, PT)
• Destructive test in accordance with ASTM standards
• Print additional sample of item and cut it and inspect
Thank for any idea

Peter Lovrencic
NEK
Vrbina 12
8270 Krsko
Slovenia
Peter.lovrencic@nek.si

 

[racookpe1978]

Final geometry has to be the same (within tolerances) for any replacement item.
Surface NDE may, or may not, be the same: For example, a dye penetrant inspection might have been required for a forged and welded assembly because it was welded. The forging might have needed a mag particle exam because it was forged and the assembly needed to be checked for casting flaws. An assembly might have been xrayed because that was the only way (at that time) to assure some inspector that clearances or internal passageways were not blocked by mold residue or sand or grit from the molding process.

On the other hand, a 3D printed part may be questioned about gran structure and total strength BECAUSE it has been assembled in 3D and then sintered, but not rammed by a 35 ton press to squish the hot grain structure according to 1950's accepted metal-working practice. (That "Well, we always used to do it that way!" does NOT always mean "that way" was the best way or the only way or even the "needed-to-be-done" way. It DOES MEAN, however, "that way" has been written up and accepted - and it might be "the only way" as well. So you WILL have to justify differences from the old way.

Destructive testing of at least the first 3D product will almost certainly be "expected" even if it is not "written" because of the industry's and the regulator's proper and natural caution. BUT! A destructive test may not need final intrinsic exact machining of all surfaces and shapes. If the strength test does not stress parts of the unit that are intrinsically and elaborately machined, destructively test the "casting" of the 3D part. Do a leak check on the machined part.

Document what you proposed doing, get an independent opinion, perhaps of your other customers who may later buy your parts, and submit the package. Be conservative, but be real.

Expect closer scrutiny (as is proper!) when the new part has an ultimate strength close to requirements. For example, assume some actuator after all safety factors and "what if" scenrios and margins and estimates is required to survive (not fail) at 850 lbs on the actuator pin. You make a 3D part, sinter it, forge it (if required), heat treat heat, machine it, assemble it, and test it. If it fails at 1250 lbs on the actuator pin, people will accept the result. (The original part geometry was obviously overbuilt, over-designed.) But it is "passed" the destructive test at only 910 lbs force, you's probably should test a second part. The failure was very close to the required level. That -retest evaluation should be a part of your package as well. It shows you are addressing manufacturing variations and assembly variations in the 3D "assembly" and printing.

It is possible the 3D printing community has protocols for this conservatism, but probably not. Aero? More likely - they've been approaching 1.0 safety factors in rocketry since the V-2's first blew up on the launch pad.

 

[EdStainless]

In the aerospace world there is a lot of mechanical testing done on samples that are built in the same plane/orientation as critical sections of your part. The properties will vary with orientation.
As for NDT, if it is a fatigue critical part then CT is the only way to go. The CT will cost a lot more than the part.

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P.E. Metallurgy, Plymouth Tube

 

[harolddavy]

Agreed with EdStainless. In the case of aerospace manufacturing, mecanical testing is done on samples with help of FPI inspection mechanism in the process of 3d metal printing of the body parts. But in case for Nuclear testing CT is the way one sould go for. Although very expensive, but very effective and its worth it to use.

 

[EdStainless]

The other aspect is that you can't certify the properties. In most AM parts the properties (and grain structure) are orientation dependent, in the original material they are not. Do you know which orientation has the lowest strength? fatigue? toughness?
I have seen AM parts (scanning laser, Ebeam, and a few others) that were post HIPed and they still have very non-homogeneous properties.
Nothing that flys is built with less than 1.75, and a lot of the parts are 3.5.
If you can find parts that were built with SF of >10 and you want to reduce that to 6, then you might have some candidates. But building and testing three of four parts so that you can install one does not sound worth it.
One of the real problems is that none of the systems runs closed loop. That is to say that if the part building process has a variation in it (power, temp, pool size, powder feed...) does it correct, and does it record where that happened? Today those are both No.

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P.E. Metallurgy, Plymouth Tube

 

[vpl]

As a follow-on to this discussion, the NRC currently has open for comments a draft reg guide on commercially dedicated components (

https://www.regulations.gov/docket?D=NRC-2016-0133).

Although the original poster was asking about non-safety-related items, this document would eventually apply if an entity decided to dedicate those non-safety-related items for safety-related use. I don't have access to the EPRI documents which are being endorsed, so I don't know if 3D printing was discussed. I plan on making a comment to the NRC to ask if commercial dedication of items produced by 3D printing has been addressed. I'm sure the NRC would welcome additional comments.

Patricia Lougheed

A FAQ for you to consider: FAQ731-376
Translation assistance: forum1529

 

[racookpe1978]

The term CT was used above. Not DT (destructive testing?)

 

[pxp]

Our intention is to install printed impeller of non-safety related pump. Pump is part of Fire Protection system (jockey pump). In our order specification we put a request for CT inspection, RT, PT, VT and all sort of destructive testing. As I understand 3D printing process, is that printed material is not exactly the same as for instance SS 316. In our case we decide for reverse engineering. We had an old pump impeller and with 3D scanning and original drawings we will try to print a new one. Our partner in this pilot project will do all necessary NDT, Destructive tests and CT. In case of SR item I don't what the technical approach would be. Dedication for sure, but defining of critical characteristics is in this case more complicated. Does anybody has an idea?

 

[EdStainless]

Sorry, I meant CT, and in X-ray computed tomography. Because you have built the part in layers, at various angles, you need a true 3-d image of the internal defects. The power that it takes to CT a metal part is fairly high and the process is slow.

pxp, what material are they working in? They should plan on printing test coupons in the various orientations matching sections of the impeller for destructive testing.
So far I have not seen reported fatigue values for metal AM parts that reliably match those of castings.

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P.E. Metallurgy, Plymouth Tube

 

[pxp]

We are speaking about ASTM A 351 CF8M. Our partner is planning to print test coupons in different layers for destructive testing. The printing process is covered with QA program. It is not app. B, because we are not speaking about SR item.

 

[racookpe1978]

I believe you will find many tens of thousands of "parts" like impellers and housings that were made in the old foundries and pattern shops (by workers who apprenticed to masters who apprenticed to masters who started in the 1910's and 20's ... that cannot be made at anywhere today. Or poorly duplicated in China very slowly at best. (Environment restrictions, startup costs and energy and metals for foundries, wood pattern making, casting, forging, etc, etc, etc.)

But larger 3D modeling of complex parts IS going to be a growth industry as old cast parts wear out and corrode and get worn down. Turbines, pump impellers, engine and coolant castings. The forges and machine tool castings themselves that are no longer made.

So, keep to your goal. but yes, you are trying to break into the hardest part of the hardest, most strict industry with due cause to "feel" that it MUST BE conservative and not accept new technology - and the QA risks of small flaws in that technology.
"It ain't what you don't know that is the problem.
It ain't what you know you do not know that is the problem.
It's what you don't know you don't know that is the source of the problem."

 

[pxp]

I completely agree with you Racookpe1978. Our approach is very conservative. For Non safety Item there is no legal restriction to install it. It is only how much of risk you and management are willing to accept. For SR items is completely different story. In our case we are looking for the process, how to approve new technology through our QA Program. We are appreciating all comments and concerns.

 

[EdStainless]

Make sure that the coupons are not only in various layers but also different orientations (in plane with the vanes and normal to the vane plane). The properties will be different in every direction, and the defects will have a preferred orientation to them.
Are they planning to HIP these in order to get full density?

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P.E. Metallurgy, Plymouth Tube