Structural Steel at Elevated Temperatures 1

[gharli]

Hi All,

We're busy designing a structure using Grade 355JR structural steel (I think the equivalent in the US would be A572 grade 50).

The structure will be subjected to an elevated temperature of around 250 deg C (482 deg F).

Other than designing for reduced mechanical properties: yield of 80%(?), modulus of 75%(?) and thermal expansion/contraction - do you foresee any major issues with structural steel at these temperatures?

Insulating isn't an option and we'd prefer to stick to a steel that we're familiar designing with.

Thoughts/comments would be appreciated.

Thanks.

 

[JStephen]

If it helps any, A36 plate can be used up to 500 degrees F in API-650 tanks and somewhat higher in ASME pressure vessels, making allowances in the yield strength and modulus of elasticity as appropriate.
Increased corrosion in heated service might be something to check also.

 

[CANPRO]

How closely are you looking at the thermal expansion/contraction? And what is the nature of the structure and connections? Depending on the temperature at installation, you could end up with a temperature swing in excess of 250 deg C from install to service - I suspect that for typical steel connections, that would induce a considerable amount of load in the members due to restraint. Is the temperature going to be fairly consistent throughout the structure?

 

[MGZmechanical]

In EN 1993 there are some provisions of steel in case of fire. The mechanical properties are:
Yield = 70%
Elasticity modulus = 85%

Then you have to consider all the dilatations because they can induce huge actions.

Best regards,

 

[GC_Hopi]

AISC refers to "For application involving long-duration loading at elevated temperatures, the effects of creep must also be considered...see Brockenbrough and Merritt (2011)"
See attached

 

[JStephen]

Note that the creep data there are for 800 degrees, minimum, and I don't think would normally be considered at 482 degrees.

 

[drbrainsol]

For once, a topic I actually have some experience in! My 2 cents below.

The capacity of steel elements at elevated temperatures can be calculated using BS EN 1993-1-2:Structural fire design. The code includes a couple of methods for calculating the capacity and provides necessary reduction curves for yield strength, elasticity modulus etc. I would suggest you have a look through the code, determine the correct reduction parameters and calculate your resistances accordingly.

Main thing to watch out for is thermal expansion / contraction. Especially important if your temperature varies significantly over time as it could lead to deformations at the joints or even fatigue issues. Also note that while yield strength may not be impacted too much by the relatively modest 250C temperature, the elasticity modulus will reduce. Hence you may need to consider the reduced modulus in SLS calculations (if applicable).

All things considered, 250C is not a very high temperature for steel so you should be able to make it work.