ASME VIII Div.1 - Hydrostatic Test Pressure for A240 304/304L 1

[wdavidchris]

Apologies is this has been asked before or is a silly question. For ASME VIII Div.1 for Hydrostatic Test, from UG99(b), it says the HT should be at MAWP X 1.3 X LSR. We have a tank with a specification of A240 304/304L material (dual-specification). The design / MAWP temperature for this vessel is 250 deg Celcius.
The S (from ASME II Part D) for A240 304 is 138 MPa and 89.9 MPa (at test & design temp 250); S for A240 304L is 115 MPA and 103 MPa (at test & design temp 250. So, the LSR for 304 grade is 1.54 (138/89.9), LSR for 304L grade is 1.12 (115/103).
So, my question, which LSR is supposed to be used for the Hydrotest; 1.54 or 1.12?
Choose the conservative 1.54 to be safe?

 

[IdanPV]

Which allowable stress did you used for the design?

 

[david339933]

See UCS-23. You have to pick one for design, you can't use both.

 

[IdanPV]

UHA-23 as it an High Alloy Steel.

The LSR is depending on the allowable stress you have chosen.
It is acceptable to use dual certified material, but you use only one allowable stress for your design.

 

[david339933]

Sorry, meant UG-23

 

[EdStainless]

9 times out of 10 the design will use 304 stresses and 304L chemistry.
Even though is this a poor practice since the material has 304 properties because of N2 in the alloy (not C) which does not contribute to higher temp properties (creep or SR).

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P.E. Metallurgy, consulting work welcomed

 

[wdavidchris]

@IdanPV @EdStainless @david339933 Thank you guys for the replies. I just realized how silly the question mostly is. It logically should be based on the grade used during the design / calculation.

However, this brings up another question. I'm not sure if it falls under the code or manufacturer's judgement.

How does the design / mechanical calculations remain valid in the case of the dual-specification. (I'm assuming here-) Dual certification (304/304L; 316/316L, A53/S106/API-5L) considers the Chemical Composition range and Mechanical Property range/minimum values (tensile, yield, elongation). It doesn't factor in the reduced strength at high temperatures. Like in the original question case of A240 304 vs 304L at 250 degC.
So, if the design was done to 304, and the material received is 304/304L, will there be a higher possibility that the material will fail during operations at the elevated temperatures (likewise, after the fact fail the strength calculations). What is the "S" for a A240 304/304L material at the elevated temp? This is my essential question.
Sorry if the above is very unclear. I'm terrible at explaining and I'm not sure if you question gets across.

 

[IdanPV]

Hi,

You wrote that S(304L, 250°C)=103MPa
and S(304, 250°C)=89.9MPa.

That means, you consider note G5 for 304 but not for 304L.
Considered G5 for both resulting in S(304L, 250°C)=76MPa.
Ignoring G5 resulting in S(304, 250°C)=122MPa.

Your LSR shall be:
LSR(304, G5)=138/89.9=1.54
LSR(304L, G5)=115/76=1.51

LSR(304)=138/122=1.13
LSR(304L)=115/103=1.12
In my opinion, the difference is negligible

 

[DekDee]

So, if the design was done to 304, and the material received is 304/304L, will there be a higher possibility that the material will fail during operations at the elevated temperatures (

- definitely not !
There are a lot of misconceptions with dual certification but it is pretty basic.
Ed Stainless can probably explain better than me but I will give it a go.
A mill will aim to produce a specific grade of material eg. 304 but after testing they find that the test results fall within the requirements of 304 but they also comply with the requirements for 304L - so the material can be dual certified.
The mill can then sell it to customers who require 304 and other customers who require 304L.
Hope that helps.

 

[EdStainless]

At 250C this isn't really an issue.
It is when people are at or near the creep limited temps/stresses that this gets messy.
What if you are above the 304L creep limit but below the 304 limit?

This is largely an artifact of these being very old grades and having minimum strengths set back when steelmaking was very different.
Back then properties varied much more, and they had to set the min low to assure that they would meet it.
Now that all SS is made via AOD it has much better chemistry control and it always contains some residual nitrogen.
The nitrogen is unique in that it does not need to be reported if it is not part of the spec.
And it is the one case where you can supply a single alloy to two different chemistries, 304N can be shipped as 304 or 304L provided things are right.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed