Clarification SS316/316L 4

[pnrngv]

Hi,
In Client general Piping Class standard it is mentioned as SS 316/SS 316L. It is not specified as Dual Grade.

However, End user/Client deliverable (ISO, MTO and other documents) specified as SS 316L only.

Reviewer is insisting on the Dual Grade requirement.

Need some clarification on the interpretation. When specified as SS 316(Stroke)SS 316L, either of the grade or Dual grade can be selected based on the application.
Since the SS 316L is higher grade material and more corrosion resistant, the same can be accepted?

Please advice.

 

[EdStainless]

When I see them listed together I presume that the requirement is for dual certified.
That is far and away the most common requirement we see these days.

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P.E. Metallurgy

 

'Dual certified' in the context of 300 series stainless steels means 'permission' to use a alternate grade where it overlaps, so long as it meets all the requirements of the grade the designer wants (316L) . It's not something that makes any sense to make 'mandatory' in a tech spec.
Dual certification is just a means for stockists to reduce inventory (i.e., kill two birds with one stone).
For what it's worth I have long wanted to see the straight grades (304, 316) eliminated, since these steels are specified either for lower temperature corrosion resistance (L grades) or heat resistance (H grades).

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[EdStainless]

But it is a spec requirement, you must meet the chemistry of the "L" and the strength of the straight grade.
I do agree that the straight grades should go away.
We also should discuss the N exemption. You are allowed to and N deliberately, even enough to meet the "LN" spec and you still don't need to report it. This isn't all bad, you get higher strength and actually better pitting resistance also, ... but while the N does increase strength at low temps it does not work at higher temps (like C does).
In reality with 304 and 316 I have never seen an "L" heat not make straight grade mechanicals. These are very sold specs and are very conservative, and you combine that with a bit of N residual (usually less than the "N" requirement) and you easily get the strength.

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P.E. Metallurgy

 

[arunmrao]

With the introduction of converters of 5 ton capacity, foundries too are producing effortlessly the L grade by default. Truly the straight grades must be retired.

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[XL83NL]

Per default we always call out materials in our 304-series and 316-series pipe specs like that: 3XX(slash)3XXL. XX for 04 and 16.
With that we always require dual certified, so as to get the mechanical properties and advantages of the straight and the better weldability/metallurgical advantages of the L-grade.

Huub

 

[pnrngv]

Material test Certificates (MTC's) covers chemistry and strength of the Straight Grade. (Both Yield and Tensile), But the Grade marking and Letter Printed in the cert shows SS 316 L.
Still i would be a problem to accept the material by Client ?

 

[MagBen]

For some applications, the substitution of Type 304L for Type 304, or Type 316L for Type 316, may be undesirable because of design, fabrication, or service requirements. Spring applications, for example, often use high carbon version for a high hardening rate to boost tensile strength. Actually when carbon is increased to .06-.08%, we can call it either 302 or 304.

Ed made a point for higher strength level with addition of N. They are actually designed names as 304/316 LN, 304/316N with N at .10-.16%.

 

[EdStainless]

pnrngv,
What is the chem? If it is low C then it can meet 316L, but in most cases unless the producing mill certifies it as such it does not count. An end user could look at the MTR and say that since it is low C they will use it as 316L, but if one of my suppliers did that I would make them replace it.
Carbon is interesting. In SS it is a very strong austenite stabilizer. So even though 304H is stronger 304L it actually does not become as magnetic when heavily cold worked.

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P.E. Metallurgy

 

[pnrngv]

ED

Carbon content is <0.03 and it is in the range and as i mentioned before tested strength also meeting the straight carbon (SS316). Only the printed letter in MTC is in question.

 

[EdStainless]

If the MTR says 316L then you have to use it as 316L. Just because it is higher strength you cannot make the call to use the higher allowed stresses for the straight grade.
There is a lot of dual grade material out there that only meets the higher strengths because it is so grossly under-annealed.

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P.E. Metallurgy

 

[Deanlover]

In my opinion, this is dual grade.


I have a question.
As per ASME SA-312, TP316 seamless needs 11% nickel content,if client didnot specify 316/316L is a dual grade, can we select the 316L to substitute 316/316L?

 

[pnrngv]

To my understanding, for Dual Grade, Carbon content to meet SS 316 L (or any Chemical composition). And Grade strength to meet SS 316.

Grade strength to be calculated as per formula given in ASTM A -999 Clause 22.2.1 Eq. 3 and 22.2.2.
To be specified clearly in buying description.

 

[EdStainless]

You understand the definition correctly.
If you designed dual cert, ordered dual cert, and the MTR comes with dual cert you are fine.
You are usually not allowed to take material with an MTR that says "L" and decide for yourself that it is strong enough to use as dual cert. There are ways to do this and still be code compliant, but the paperwork has to be just so.

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P.E. Metallurgy

 

[WKTaylor]

XL83NL alluded to one critical factor I run-up against all the time... 'weldability'.

Any potential for welding should drive most projects to 321... but often uninformed engineers/welders often specify 304 or 316... which should never be welded [and probably never brazed] due to carbon/carbide growth in the HAZ/weld bead. CRES 304L and 316L offer moderately strong and metallurgically sound welds due to lower carbon and are alternates to... but not better-than 321.

Pet Peeve.
What I abhor as a service/depot engineer is systems assemblies mixed between 3xx series CRES... 302 or 304 for most straight/formed/parts... AND 316L or 321 for sheet/tube assemblies with welded joints/flanges/brackets/etc. This lulls engineers/mechanics into believing all associated CRES parts are weldable, IE for mods, repairs, etc. Results can be terrible [non-airworthy]!

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[EdStainless]

Wil, Mixed alloys are a common point of contention.
I have tested a lot of 304L/316L samples as welded (autogenous) and in gauges under 0.200" I find no sensitization. We are usually seeing 0.015-0.02% C so steel from other sources may have different results.
The higher N that we see in the US also helps.
321 can be filthy to weld. Often trying to shield it enough is a loosing battle. If you get a hold of some with higher Ti the welds look like crap. On the other hand most mills want to minimize the Ti so they run the C low, often less than 0.015% C, good corrosion resistance and low strength.

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P.E. Metallurgy

 

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[WKTaylor]

Ed... OK, I confess... I am really only familiar with tightly controlled aerospace/mil materials and processes... not industrial grades/work.

NOTE. My 'beef' with mixed metals [alloys and variations] is the unintended potential for mix-ups and long-term serviceability/repairs. To most welders and non-M&P engineers 3xx is the same as 3xxL. The road to hell is paved with good intentions and miss-steps and substitutions.

NOTE.
I was trained in welding [as a liaison/service engineer over ~7-years] by a master-aerospace welder who had immense/diverse welding background, amazing hands-on skills and a profound knowledge base. He rewarded my full attention with amazing revelations about the science and 'art' of welding every metal family/type/temper, mixed alloys where feasible... and ESPECIALLY when NOT [hell-no] to do something that is sketchy/un-sound... putting lives/equipment at risk. **
** On-the-other-hand he had no patience with the fool he had for a manager at the depot site... and was very outspoken and had a quirky independence. By the time he was fired, his welding reputation was so well established, he went across the Air Base and was instantly hired by LSI.

Story.
An old friend once explained people this way... Most well intentioned people claim to 'work by the book(s)'... but have no idea 'what book(s)[!?]'... much less where to actually find the page in 'what book(s)'". In many case the only book most have is dusty/old and is propping-open a door somewhere. Very troubling to my soul when the magnitude of this truism.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[EdStainless]

Wil, many of the AMS specs are very old and allow very wide ranges of chemistry. At least in the tubing business we tend to work to much tighter chem controls than the specs allow. Yes the biggest part of repair welding is often knowing what not to do.

IM, that is an old chart that everyone uses. For modern steels that are generally cleaner the times get longer with the lower C grades.

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P.E. Metallurgy

 

Ed,
If you have something more up to date I'd love to see it.

WKTaylor,
Maximum respect to your mentor, but what no welder can see are metallurgical changes happening as a result of the heat of welding, which may take years of service before the consequence is seen.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."