Carbon steel embrittlement 1

[291432]

In Italy, last year the authorities applied a new law for embrittlement of steel due to low temperatures. In this law it is assumed that you must apply a safety system to avoid that the temperature in carbon steel equipment is lower than design temperature (i.e.: a temperature transmitter which controls a on/off valve).
In most cases, the design temperature for carbon steel is assumed -10°C (I think not mainly for real reasons, but as a "standard" value).
This would mean that if the gases coming from liquefation of criogenic liquids are passing trough these equipments after the vaporization during winter, the equipment would always be stoppped due to low temperatures.
What I'm asking is: what is approximately the minimum temperature I can reach with simple carbon steel, without having problems due to low temperatures?
Thank you
LB

 

[metengr]

294132;
For plain carbon steel material, I have seen a typical value of 0 deg C, where you see a transition from ductile to brittle fracture behavior (50% flat fracture). This is a conservative value.

As the carbon content decreases and depending on the phosphorus and sulfur contents of the steel, the ductile to brittle transition temperature will shift to lower temperature with a more distinct transition behavior.

 

[YLWEA]

The transition temperature can be quite different for different types of mild steel pipe, fittings, and other components. I agree that many times 0 dec C or lower is not difficult to obtain. However, we have also seen many test reports that show transition temperatures in the range of 20 deg C or more, particularly for relatively thick (about 12 mm or more) seamless. In some cases you might have to sort through several test reports to find heats that meet your requirements for toughness, and then require that the purchased materials only be taken from those specific heats that are acceptable, but often you can find what you need without having to specify different grades.

 

[GRoberts]

Carbon steels such as A352 Gr. LCC, A350 Gr. LF2 Class 1 and A333 Gr. 1 are designed to be used at temperatures as low as -45C.

 

[Carburize]

There used to be a British Standard BS 5500 - I don't know the number of the current European equivalent - which gave a method for determining the toughness requirements for low temperature service for pressure vessels.

 

[stanweld]

294132,
The EN Codes may be modestly different, but FIG. 323.2.2A of ASME B31.1 provides minimum design temperatures for variously manufactured carbon steels vs thickness where impact testing of the base material is not required. Similar curves are provided in ASME Section VIII, Div. 1.

Minimum design metal temperatures normally describe the minimum temperature of the steel at pressure and not the ambient atmospheric temperature.

 

[291432]

Thank you for all the informations.
Have you any data for A312 type?

 

[stanweld]

Oops! B31.1 should read B31.3. ASTM A-312 austenitic stainless steel pipe requires impact testing when the design temperature is less than -325 F per B31.3 and ASME Section VIII.

 

[Salvatio]

It is good to have such a law enforced. The transition temperature sometimes could be difficult to determine, as it may depand on the content of sulphur and phosphorus. If i'm not mistaken, the temperature will too change with respect to the carbon content (would it?).
If they have these kind of laws around (or even the knowledge or technology) some years back, maybe Titanic wouldn't sink (lol).

 

[davefitz]

You may wish to use a 2 out of 3 thermocouple reading prior to initiating a trip of the process. In particular, if you retain the -10C std limit and a single thermocouple junction fails, it would read ambient temperature ( which can be below -10 C in wintertime) as opposed to reading actual process metal temp.