Stainless grade low temperature properties question
Stainless grade low temperature properties question
(OP)
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
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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"Life! No one get's out of it alive."
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RE: Stainless grade low temperature properties question
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/
RE: Stainless grade low temperature properties question
I don't have data for 304H but the data for 305. 0.12C shows it to be safisfactory at cryo temperatures.
RE: Stainless grade low temperature properties question
...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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RE: Stainless grade low temperature properties question
RE: Stainless grade low temperature properties question
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"Life! No one get's out of it alive."
"The trick is to grow up without growing old..."
RE: Stainless grade low temperature properties question
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
RE: Stainless grade low temperature properties question
RE: Stainless grade low temperature properties question
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.
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..."
RE: Stainless grade low temperature properties question
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
RE: Stainless grade low temperature properties question
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.
RE: Stainless grade low temperature properties question
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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"Life! No one get's out of it alive."
"The trick is to grow up without growing old..."