Stainless grade low temperature properties question 2

[robsalv]

I was having a chat with a colleague, who had a supplier come back to him saying that they couldn't supply all stainless components in 304L or 304/L and could supply some small bore 800# valves in 304H instead.

He is managing a low temperature service project (about -101degC). I alerted him to potential problems with lower corrosion resistance, possible sensitisation and possible embrittlement at the welds with the H grade - but at the service temperatures, corrosion is unlikely to occur.

It got me thinking, if you got around those issues, is there anything inherent about the H grade that makes it unsuitable for low temperature service. It presumably has the same austenitic structure and lack of ductile to brittle transition... however, our local code only mentions MDMT values for the L and plain grades.

Can anyone case light on this academic question?

Thanks in advance.



Rob


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[mcguire]

Unless the material is sensitized by, say welding, the extra carbon in the "H" alloy will only make the austenite more stable at low temperature, a positive factor. If senstization does occur, then lower ausstenite stabilty will ensue with the possibility of lower corrosion resistance and some transformation to martensite with loss of some dimensional tolerance.
Check the actual carbon level. Normal 304 is ususally about 0.06 to 0.07% carbon. 304H cannot be more than 0.010% or as low as 0.04%, so there may be no significant difference.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[unclesyd]

Adding to mcquire's post.
I don't have data for 304H but the data for 305. 0.12C shows it to be safisfactory at cryo temperatures.

 

[robsalv]

Thanks gents. That's elucidating! It's good to know that the H grade should have similar cryo properties - can't find that confirmed officially though.

304H cannot be more than 0.010% or as low as 0.04%, so there may be no significant difference.

...presume that was a typo? I think you meant 0.1%?


Ok... some confusion is creeping in... Plain 304 has max carbon 0.08%. H has max carbon 0.1%. Soooo(you know where I'm going to go with this...) given the possible C overlap, what makes an H an H???? I know there are minimum heat treatment and grain size requirements for H grades - are they really all that seperates a plain grade with the same C as a certified H grade???

Thanks for the advice regarding sensitization - clearly it's equally valid for the plain grade - presumably the best way to minimise the risk of it occuring is to have low carbons and/or stay below the critical temperature (or above it for as short a length as possible). I'd appreciate any further comments or suggested links/reading on this topic.



UncleSyd, 305 has a higher nickel content than 304 - presumably that would have a greater bearing on low temperature properties - but I think you make the point well that the the higher C content doesn't necessarily result in poor low temp properties. Thanks for that comment.

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"Life! No one get's out of it alive."
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[unclesyd]

One thing you will find is that Carbon content of SS has varied over time. It depends on the time the data was assimilated. I have been the whole route with 304L SS. We never order 304L unless we nail down the C.

 

[robsalv]

Unclesyd, I frankly don't understand that last post! LOL

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"Life! No one get's out of it alive."
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[EdStainless]

An H grade is one where C is deliberately added.
In the US there are only two grades of 304 melted, 304L and 304H. The H meets the chemistry and mechanicals for straight 304, but so does the L.

I have never seen low temp impacts on as welded samples of 304 with 0.10% C.

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Plymouth Tube

 

[unclesyd]

In regards to my last post. The values and limits of some stainless steels have been changed over the years. The carbon value has seen the most change. Taking 304L as an example, some listings in the 50's gave a max value of 0.035 and with the industry practice of rounding you could easily have an actual value of O.O38 or better. Causative factors were the inability to produce low carbon consistently and the analytical techniques weren't that good.

 

[robsalv]

I'm gathering that querying H grade low temperature properties is an unusual question and it isn't something which has a common understanding.

Fair enough.


I had no idea that stainless was made in either of two melts and then sorted into three grades based on chemistry.

That's interesting because I certainly recall valve material certs with H grade stamping but C=0.06%, so clearly something else must have differentiated H grade from plain in those instances. As best as I can tell, it's heat treatment and grain size... but I'd imagine that based on chemistry alone, the heat must have been dual certified at the foundry.

The H meets the chemistry and mechanicals for straight 304, but so does the L.

Is that right? The plain L grades are listed with lower SMYS's in the ASTM standards.

Appreciate your further comments.

Thanks.

Rob






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"Life! No one get's out of it alive."
"The trick is to grow up without growing old..."

 

[EdStainless]

The L and straight grades have no minimum C, so as long as the C is below 0.03% and the material meets the higher mechanicals for the straight grade then the material is in fact fully compliant with both grades.

A similar situation exists with H and straight grade. The minimum C for H is below the maximum for straight. So if the C is in that window (0.04 - 0.08) and the properties are high enough for the H grade then it meets both.
In order to be uniquely straight grade it would have to have a C in the range of 0.03-0.04.
The grain size is another issue. I don't recall, does ASTM require coarse grain for H, or is it only ASME?

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Plymouth Tube

 

[unclesyd]

Here is some impact data for annealed 304H

Temperature Charpy V-Notch Energy Absorbed
°F °C Foot - pounds Joules
75 23 150 200
-320 -196 85 115
-425 -254 85 115

http://www.sandmeyersteel.com/304H.html

Two things mentioned in the USS book (Low Temperature and Cryogenic Steels}, that degrade the impact properties of SS at cryo temperatures is sensitization and cold work. The question is will the higher carbon in 304H lend itself to a much lower impact values in the HAZ. The data from Sandmeyer only has the annealed values.

 

[robsalv]

Edstainless, well that ASTM versus ASME comment teased out an interesting extra!

I don't have access to the ASTM standards directly, but I have access to the ones referenced in ASMEII, and the ASMEII version for A213 has the following statement at the start:
"(Identical with ASTM Specification A 213/A 213M-99a except for the additional H Grade heat treatment requirements in 6.4, the editorial deletion of 11.5, and the editorial addition of Grade T92 to 6.1.3.)" (Bolding added for emphasis)

So if the grain size (No.7 or coarser) is an ASME requirement and not part of the ASTM standard then a melt with 0.06C is inherently dual certified because all the mechanical and composition requirements are the same.

Frankly, for high temperature services I'm starting to form the opinion that my organisation doesn't have to pay extra for H grades when there's virtually nothing seperating the plain from the H... unless of course C>0.08%


UncleSyd, I came across the same site but didn't interpret those figures as typical figures for 304H directly. Apart from the first paragraph, the information on the 304, 304L and 304H pages is identical.

Thanks for reinforcing the sensitisation and cold annealing effect on low temperature properties.

Cheers

Rob




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