2 replies to this topic

[E-Tantoy]

Good day to all!

I have a question regarding carbon steel. What is the difference (in terms of composition) of LTCS (low temperature carbon steel) from CS and the galvanized CS? Someone told me that the composition of the three is just the same and that LTCS is only considered LTCS after the impact test is done, is it correct (cause i am not quite convinced and i've been having difficulty in looking for references regarding this topic )? And how about galvanized CS?

Thank you very much in advance!

[daryon]

Good day to all!

I have a question regarding carbon steel. What is the difference (in terms of composition) of LTCS (low temperature carbon steel) from CS and the galvanized CS? Someone told me that the composition of the three is just the same and that LTCS is only considered LTCS after the impact test is done, is it correct (cause i am not quite convinced and i've been having difficulty in looking for references regarding this topic )? And how about galvanized CS?

Thank you very much in advance!

Hi Ethan of Manila,

There is no difference in composition between CS and LTCS. What i refer to as LTCS is just normalised CS and all that means is it has undergone a different heat treatment process. Heat treatment of CS changes the mechanical properties of the steel and results in LTCS being stronger than CS.

Carbon steel materials used to be assumed acceptable down to minimum temperatures of minus 29 °C or minus 48 °C when normalised without impact testing. However ASME VIII Div 1 now advises that carbon steel materials with thicker wall thickness may fail in a brittle manner, at low temperatures and provides the chart (ASME VIII Div 1 Chart USC-66 / ASME B31.3 FIG. 323.2.2A) of minimum design temperature vs material thickness for CS without impact testing.

If impact testing of material is required the cost of the material and therefore the vessel or piping will increase. ASME Chart USC-66 should be consulted to ascertain below what minimum design temperature impact is required for given wall thickness. Alternatively for piping, Figure 323.2.2A from ASME B31.3 should be consulted. For wall thickness above 10 mm minimum design temperature of carbon steel is reduced.

Galavanised CS is CS that is coated with a protective layer of Zinc. The composition of the CS is the same. The Zinc layer is more resistant to corrosion, and if corrosion does take hold the zinc layer will be prefferentially corroded instead of the CS beneath. Galvanised CS piping is often used for seawater service, but it's tricky to weld as the zinc layer can often be damaged. This sometimes leads to flange connections between galvanised CS pipe spools which adds to weight and cost.

hope this answers your question
daryon of UK

[vittorio6]

LTCS are carbon steel (for example ASTM A 333 gr 6) that has a fine grain structure in order to be suitable to operate at low temperature.
http://www.astm.org/Standards/A333.htm

Galvanized Carbon Steel are carbon steel with a thin layer of Zinc that increase the corrosion resistance in some enviroments (atmospheric exposure).
http://www.galvanize...ip-galvanizing/

Vic

corrosion prevention