Minimum temperature range for common low carbon steels 1

[kdkimball]

Can anyone steer me in the right direction for determining what would be minimum recommended temperature range for common low carbon steel?

For instance, what would be the recommended minimum temperature that one should use ASTM A500-Grade B tubing in?

I am somewhat familiar with the Charpy Impact tests etc. for determining impact toughness, and we have needed to use this for projects with low temperature requirements. But I am having difficuly determining to what temperature range our product (without special material requirements)would be using our normal common materials.

Any help would be appreciated.

 

[metengr]

The ductile to brittle transition temperature can vary considerably for low carbon steels, and is dependent on grain size, heat treatment and alloy content. The fracture appearance transition temperature for 50% flat fracture (FATT @ 50%) is a good reference point for comparing materials.

From what I have seen, the FATT (@50% flat fracture) for low carbon steels can range from 20 deg F down to -20 deg F. To be conservative in design, I would recommend 20 deg F due to variability in material composition and grain size.

You can purchase fine grained, low carbon steels for use in low temperature service that could take you to about -50 deg F .

 

[kdkimball]

How or what are these "fine grained" low carbon steels classified as? Are they available in structural shapes such as rectangular tubing, i-beam, channel etc...?

 

[metengr]

You have several options for purchasing fine-grained carbon steel;

ASTM A 36 - "Structural Steel", which covers carbon steel shapes, plates and bars. Order with the following supplemental requirements to assure improved notch toughness; S2 silicon killed, fine-grain practice and S5 Charpy impact test.

For plates only, a specification like ASTM A 516 - "Pressure Vessel Plates, Carbon Steel, for moderate and lower temperature Service". Order with supplementary requirement S5 Charpy impact test.

ASTM A 573 - "Structural Carbon Steel Plates of Improved Toughness". These steels are made to a fine-grain practice.

 

[VeryPicky]

kdkimball

The standard carbon steel materials are usually divided into two groups wrt impact properties:
1. low temp steels
2. not so low temp steels

The ASTM requires for low temp steels better control of impurities, the steels are kileed, etc. And at the end of the day they are impact tested.
The "not so low temp steels" might not have all the bells and whistles specified but to make their life easier and probably it is cheaper in a long run, some of the mills make them to the same specification as low temp steels. The only difference is the "not so low temp steels" are not impact tested. This is true for piping, the structural steel might be different.
You may be able to use any carbon steel material provided the impact properties are confirmed by the test. Obviously what metengr says is true: the fine grain steels offer the best impact properties. I don't know how low the MDMT is going to be in your application.
Talk to your suppliers, they should be able to tell you what material they can guarantee and prove its properties. It might be worth your while to investigate this avenue.

 

[BillPSU]

I've manufactured ROPS, rollover protective structures, in the past. Generally we used materials which were tested to assure the low temperature capabilities but because we used relatively small amounts of the material the service center where we purchased the material picked materials from their inventory and tested. A special run of material was not used. The service center picked the material based on the pratices used in the manufacture of the product.

 

[VeryPicky]

The problem with ASTM A500 is that according to the Note 1 of the Scope "products manufactured to that specification may not be suitable for those applications such as dynamically loaded elements in welded structures, etc., where low-temperature notch-toughness properties may be important".

To make the long story short: they are not certified for low temperature service. And there is no say how low is "low" because the Specification does not give the figure. You could possibly compare that material to one of those listed in ASME IIA to assess the impact properties from UCS-66 but there is always a risk of not comparing "apples with apples".
If you want to use ASTM A500 Gr. B in your low temp. application you need to impact test the materials/components anyway.

Putting Human Factor Back in Engineering

 

[stanweld]

Curves for minimum design metal temperatures with & without inpact testing for various steel grades are found in ASME Section VIII and B31.3. Tables of materials fit for specific minimum temperature use for a large number of materials without impact testing are also provided in API 620 and 650.