The project requires Killed Steel treatment on Pipe, Plate MTC.

Fully killed is the term to describe de-oxidized steel.

ASTM-A53-pipes-killed steel.jpg

After the steel is made, it is then poured into the continuous caster to make a long slab of steel. Think of a sausage maker – molten steel goes in at the top and rectangular slab comes out the bottom. This is called casting.

killed steel overview.jpg

During casting, small carbon monoxide bubbles can form between the steel grains if the oxygen is not removed. If you’ve ever painted a door and seen bubbles in the paint once you apply it you’ll recognize the similarities. To stop these bubbles appearing you paint slower, but in steel, you add certain elements to the steel as you define the metallurgy. For most steels to achieve this effect – de-oxidization – you add Silicon or Aluminium or both.

killed steel process.jpg

The impact is quite dramatic. A slab of steel is full of little steel grains. If you imagine a whole room full of golf balls you can also imagine the space between them. You don’t want the space, so one way of reducing it is to make the golf balls smaller. This is in effect what the Aluminium and Silicon do to the grains in a slab of steel.

So the term of Fine-grained steel is considered as “Killed” action on steel.

Refer to ASME SA 20, Para 8.2.2.1:

When aluminum is used as the grain refining element, the fine austenitic grain size requirement shall be deemed to be fulfilled if, on heat analysis, the aluminum content is not less than 0.020% total aluminum or, alternately, 0.015% acid-soluble aluminum.

Or Para S17.1 Material shall be vacuum carbon-deoxidized, in which case the silicon content at the time of vacuum deoxidizing shall be 0.12% maximum, and the content of deoxidizers such as aluminum, zirconium, and titanium should be kept low enough to allow deoxidation by carbon. The test report shall indicate that the steel was vacuum carbon-deoxidized. The minimum heat analysis and product analysis requirements for silicon do not apply to vacuum carbon-deoxidized steel.

If it isn’t killed then as the slab cools you can see little bubbles forming on the surface as the CO bubbles out.

killed steel example.jpg

The grains become smaller, reducing the spaces and it is then called fine-grained steel – improving the microstructure and thus, its strength. This is of great use for Structural and Pressure Vessels, indeed anywhere where you require improved strength.

Generally, if steel has Silicon content of more than 0.10% then it is considered to be killed – and ASME requirements for pressure vessels generally require any steel with a carbon content of more than 0.24% to be killed.

In the MTC, however, the statement of Killed-steel action is not needed to be provided as normal. The steel bar may be made by other Vendors, and the Rolling activities are carried out at other Vendors. Hence it is difficult to state that the Steel has been Killed or not due to the multi purchasing stage, meanwhile the PO order with the requirement of Steel plate that to be fully-killed at last moment.

There’s a solution that the statement from Vendor to be provided to the Buyer as below for your reference:

killed steel declairation.jpg

Hope this helps and have another amazing week.

Other Ref: EN10028-3 “Weldable Fine Grained Steels, Normalised”

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