9% nickel steel - elevated temperture strength properties 1

[Suilven]

I am looking for elevated temperature properties (UTS) of 9% nickel steel (BS EN 10028-4 X8Ni9 HT 680)

Ideally I would like to know what reduction factor to use for 300, 400, 500 and 600°C for use in vessel rupture calculation under fire conditions.

 

[metengr]

Suilven;
Do you have access to ASME Boiler and Pressure Vessel Code, Section II, Part D? If so, 9% Ni steel is listed with allowable stress values as a function of service temperature. No need to reinvent the wheel.

 

[Suilven]

I do not have a copy, but may be able to get access at library - however does it cover such high tempertures for 9% Ni steel?

 

[TVP]

Yes.

 

[Suilven]

Have checked - library only has Part I and Parts VIII so still looking for help please. "Googling" indicates data is available for low temperature (up to ~100°) but not for high temperatures.

 

[metengr]

No, I just looked up the allowable stress and this material is limited to 250 deg F continuous exposure. Most likely, above this temperature, the mechanical properties become unpredictable, which is the reason why the Code committee probably limited continuous exposure use to 250 deg F.

Why are you considering such high temperatures for this material? If it for short duration, you can assume an artificially low knock down factor of say 10% of the room temperature tensile strength properties and go from there.

I do have some literature on this grade of steel, I’ll see what I can find.

 

[Suilven]

Thanks "metengr". We are doing a fire safety study on an existing vessel that is manufactured from this material and need to determine of it is likely to rupture under fire conditions.

 

[metengr]

Suilven;
From the literature I have reviewed, the reason this material is limited for continuous exposure at or below 250 deg F is because this is a high strength, nickel-ferrite alloy steel specifically developed for maximum toughness at low temperature service. The heat treatment required for this application is a quench and temper.

When you exceed the tempering temperature of the material, the mechanical properties will be altered resulting in much lower tensile and yield strength properties.

You can try to keep searching for elevated temperature tensile properties for this grade of steel, but based on what I have seen, the knock down factor of 90% (10% of ambient temperature tensile properties) is probably as good as any value with conservatism. My rationale for selecting 90% is based on past tensile data I have seen for typical carbon and low alloy steels that are exposed to service temperatures where the material is fully austenitic, similar to what I would expect for this alloy.

 

[Suilven]

Thanks, I suspected this was the case - we will need to evaluate the requirements for passive fire protection closely.