Structural steel properties at elevated temperatures EN 1991-1-2 and EN 10028-2

[Staszkinson]

Hello,
I have got a question about yield strength of structural steel at elevated temperatures according to EN 1993-1-2 and EN 10028-2.

1/ According to EN 1993-1-2, reduction factors for yield strength are very striking. In a different publications we can find informations that at 50°C, yield strength and young modulus of structural steel decreases.

Here is the dependence between yield strength of P235GH steel(fy = 235 MPa at 20°C) according to EN 10028-2 vs. temperature:
50 °C - 227 MPa
100 °C - 214 MPa
150 °C - 198 MPa
200 °C - 182 MPa
...
400 °C - 133 MPa

It seems to be OK.

Now, look at the reduction factors for yield strength according to EN 1993-1-2:
100 °C - 1.0 * 235 MPa = 235 MPa
200 °C - 1.0 * 235 MPa = 235 MPa
300 °C - 1.0 * 235 MPa = 235 MPa
400 °C - 1.0 * 235 MPa = 235 MPa !!!
500 °C - 0.78 * 235 MPa = 183 MPa

I don't understand why there is so much difference.

2/ Do you have any good reduction factors or formulas for Young modulus of structural steel at elevated temperatures? I don't trust EN 1993-1-2 reduction factors at all.

3/

 

[DBreyer]

Hi,

I think you can't really compare the two codes.
EN 1993-1-2 is for structural fire design whereas EN 10028 gives design values for pressure vessel parts.
So the EN 1993 is a design for an emergency case (fire) where the construction has to withstand the elevated temperature for a relatively short time without failure (but not necessarily without deformation).
A pressure vessel may operate at elevated temperatures for quite a long time without deformation of the material!
This is clearly shown in Figure 3.1 of EN 1993 where you can see that the yield strength is not in the linear-elastic range any more. So there will be plastic deformation.
The proportional limit is much more temperature dependant and will give you lower allowed limits for your construction and is thus better comparable to the limits given in EN 10028.

Also your calculation from EN 1993 is a bit oversimplified. If you have a look at Figure 3.1 you can see that the value you have to use for the stress in the structure is dependant on the actual strain of the structure. The maximum strain for linear elastic behaviour reduces drastically with temperature and thus limits the region in which you can use the full yield strength for your calculations.

If you want to use construction steel (according to EN 1993) for pressure vessels, in the AD2000-W1 code you will find some values for elevated temperature strength of plate.

I hope this helps

Kind regards
Daniel

Daniel Breyer
Inspection Engineer

http://lnkd.in/dFcQA-w

 

[Staszkinson]

Hello,

Thank You very much for the answer.

First of all, the material I need to use is definitely 16Mo3. This is not typical structural steel.

Please take a look into EN 1993-1-2, 1.1.2 (8). You can find there information: "The methods given are applicable to any steel grade for which material properties at elevated temperatures are available, based on harmonized European standards".

According to this formulation I am going to use:

1/ yield strength of 16Mo3 from EN 10028-2,
2/ reduction factors for proportional limit from EN 1993-1-2
3/ reduction factors for Young Modulus from EN 1993-1-2.

In fact, in my FEM analysis all I want is to capture first yield stresses. Further behaviour of my structure (after yielding) is not important here because the design criterion is first occurence of equivalent plastic strains.

What do You think about it?

 

[DBreyer]

Most likely you will be on the safe side with your approach, although I assume a bit to conservative since 16Mo3 has better high temperature properties than carbon steel.
Please also note that your whole design concept has to be based on the Eurocode in order to use the given data correctly.
If you want to construct a pressure vessel please use an appropriate code.

Daniel Breyer
Inspection Engineer

http://lnkd.in/dFcQA-w

 

[Staszkinson]

You right. I got some test results for 16Mo3 at elevated temperatures and it has higher yield stress, especially at 20ºC. At this temperature the differences are the biggest. Anyway, I rather use code yield strength for 16Mo3 instead of real stress-strain data due to safety regulations.

Can You recommend any good code for flue gas ducts? This is the scope of my work.

 

[metengr]

http://cedb.asce.org/cgi/

http://WWWdisplay.cgi?97202

 

[Staszkinson]

Got this one! Thank you!